CN113767671B - Method and apparatus for handover without interruption of data transmission and reception in next generation mobile communication system - Google Patents
Method and apparatus for handover without interruption of data transmission and reception in next generation mobile communication system Download PDFInfo
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Abstract
The present disclosure relates to a communication method and system for converging fifth generation (5G) communication systems supporting higher data rates than fourth generation (4G) systems and internet of things (IoT) technologies. The present disclosure may be applied to smart services based on 5G communication technology and IoT-related technology, such as smart home, smart building, smart city, smart car, networking car, healthcare, digital education, smart retail, security and security services. A method of a terminal in a wireless communication system according to the present disclosure includes receiving a message from a first base station through Radio Resource Control (RRC) signaling, the message including a handover command from the first base station to a second base station, identifying that the message includes information indicating a dual protocol stack handover, and receiving data from the first base station until a cell of the first base station is released in case the message includes information indicating a dual protocol stack handover.
Description
Technical Field
The present disclosure relates to a method and apparatus for efficient handover without interruption of data transmission or reception during handover in a next generation mobile communication system.
Background
In order to meet the increasing demand for wireless data services since the deployment of 4G communication systems, efforts have been made to develop an improved 5G or quasi 5G communication system. Therefore, a 5G or quasi 5G communication system is also referred to as a "super 4G network" or a "LTE-after-system". A 5G communication system is considered to be implemented at a higher frequency (mmWave) band (e.g., 60GHz band) in order to achieve a higher data rate. In order to reduce propagation loss of radio waves and increase transmission distance, beamforming, massive Multiple Input Multiple Output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, massive antenna techniques are discussed in 5G communication systems. In addition, in the 5G communication system, development of system network improvement based on advanced small cell, cloud Radio Access Network (RAN), ultra dense network, device-to-device (D2D) communication, wireless backhaul, mobile network, cooperative communication, coordinated multipoint (CoMP), reception-side interference cancellation, and the like is underway. In 5G systems, hybrid FSK with QAM modulation (FQAM) and Sliding Window Superposition Coding (SWSC) have been developed as Advanced Coding Modulation (ACM), as well as Filter Bank Multicarrier (FBMC), non-orthogonal multiple access (NOMA) and Sparse Code Multiple Access (SCMA) as advanced access techniques.
The internet, which is a human-centric connectivity network in which humans generate and consume information, is now evolving into the internet of things (IoT) in which distributed entities, such as objects, exchange and process information without human intervention. Internet of everything (IoE), which is a combination of IoT technology and big data processing technology through connection with cloud servers, has emerged. As IoT implementations require technical elements such as "sensing technology," "wired/wireless communication and network infrastructure," "service interface technology," and "security technology," sensor networks, machine-to-machine (M2M) communications, machine Type Communications (MTC), etc. have recently been investigated. Such IoT environments may provide intelligent internet technology services that create new value for human life by collecting and analyzing data generated between connected objects. IoT may be applied in a variety of fields including smart homes, smart buildings, smart cities, smart cars or networked cars, smart grids, healthcare, smart appliances, and advanced medical services through fusion and combination between existing Information Technology (IT) and various industrial applications.
Accordingly, various attempts have been made to apply 5G communication systems to IoT networks. For example, techniques such as sensor networks, machine Type Communications (MTC), and machine-to-machine (M2M) communications may be implemented through beamforming, MIMO, and array antennas. The application of cloud Radio Access Networks (RANs) as the big data processing technology described above may also be considered as an example of the fusion of 5G technology with IoT technology.
The above information is merely provided as background information to aid in the understanding of the disclosure. No determination has been made, nor has an assertion made, as to whether any of the above can be applied as prior art to the present disclosure.
Disclosure of Invention
[ Problem ]
In the next generation mobile communication system, a method for efficient handover is required to support a seamless data service with low transmission delay.
[ Solution to the problem ]
In order to solve the above-mentioned problems, the present disclosure provides a method of a terminal in a wireless communication system, which may include receiving a message from a first base station through Radio Resource Control (RRC) signaling, the message including a handover command from the first base station to a second base station, identifying whether the message includes information indicating a dual protocol stack handover, and receiving data from the first base station until a cell of the first base station is released, in case the message includes information indicating a dual protocol stack handover.
In addition, in order to solve the above-described problems, the present disclosure provides a method of a first base station in a wireless communication system, which may include transmitting a message to a terminal through Radio Resource Control (RRC) signaling, the message including a handover command to a second base station, and transmitting data to the terminal until a cell of the first base station is released, in case the message includes information indicating a dual protocol stack handover.
In addition, in order to solve the above-described problems, the present disclosure provides a terminal in a wireless communication system, which may include a transceiver, and a controller configured to receive a message from a first base station through Radio Resource Control (RRC) signaling via the transceiver, the message including a handover command from the first base station to a second base station, identify whether the message includes information indicating a dual protocol stack handover, and receive data from the first base station via the transceiver until a cell of the first base station is released, in case the message includes information indicating a dual protocol stack handover.
Further, in order to solve the above-mentioned problems, the present disclosure provides a first base station in a wireless communication system, which may include a transceiver, and a controller configured to transmit a message including a handover command to a second base station through Radio Resource Control (RRC) signaling to a terminal via the transceiver, and to transmit data to the terminal via the transceiver until a cell of the first base station is released, in case the message includes information indicating a dual protocol stack handover.
[ Advantageous effects of the invention ]
The present disclosure proposes various methods for efficient handover to prevent occurrence of data interruption time due to handover when performing handover in a next generation mobile communication system, thereby supporting seamless data service.
Before proceeding with the following detailed description, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms "comprises," "comprising," "includes," and "including," and derivatives thereof, mean inclusion, but not limited to, the term "or" being inclusive, meaning and/or, the phrases "associated with," and derivatives thereof, may mean inclusion, including within, with, interconnecting, containing, including within, connecting to, or with, connecting to, coupling to, or with, being communicable with, cooperating with, interleaving, juxtaposing, being proximate to, being bound to, or with, having an..attribute, etc., and the term "controller" means any device, system, or portion thereof that controls at least one operation, such device may be implemented in hardware, firmware, or software, or in some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely.
Furthermore, the various functions described below may be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms "application" and "program" refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase "computer readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer readable medium" includes any type of medium capable of being accessed by a computer, such as Read Only Memory (ROM), random Access Memory (RAM), a hard disk drive, a Compact Disc (CD), a Digital Video Disc (DVD), or any other type of memory. "non-transitory" computer-readable media exclude wired, wireless, optical, or other communication links that carry transitory electrical or other signals. Non-transitory computer readable media include media in which data may be permanently stored and media in which data may be stored and later rewritten, such as rewritable optical disks or erasable memory devices.
Definitions for certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases.
Drawings
For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
fig. 1 is a diagram showing a structure of an LTE system to which the present disclosure can be applied;
fig. 2 is a diagram showing a radio protocol structure of an LTE system to which the present disclosure can be applied;
Fig. 3 is a diagram showing a structure of a next-generation mobile communication system to which the present disclosure can be applied;
fig. 4 is a diagram showing a radio protocol structure of a next-generation mobile communication system to which the present disclosure can be applied;
fig. 5 is a diagram illustrating a procedure in which a terminal in the present disclosure switches from an RRC idle mode to an RRC connected mode and establishes a connection with a network;
Fig. 6 is a diagram illustrating a signaling procedure of performing a handover in a next generation mobile communication system;
fig. 7 is a diagram showing a first embodiment of an efficient switching method for minimizing data interruption time due to switching in the present disclosure;
Fig. 8 is a diagram showing second and third embodiments of an efficient switching method for minimizing data interruption time due to switching in the present disclosure;
fig. 9 is a diagram showing a fourth embodiment of an efficient switching method for minimizing data interruption time due to switching in the present disclosure;
Fig. 10 is a diagram showing a fifth embodiment of an efficient switching method for minimizing data interruption time due to switching in the present disclosure;
fig. 11 is a diagram illustrating a structure of a high-efficiency PDCP entity, which can be applied to an embodiment;
Fig. 12 is a diagram showing an operation of a terminal that can be applied to an embodiment set forth in the present disclosure;
fig. 13 shows the structure of a terminal to which the embodiment can be applied, and
Fig. 14 shows a block diagram of TRP in a wireless communication system to which the embodiment can be applied.
Detailed Description
The figures 1 through 14, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will appreciate that the principles of the present disclosure may be implemented in any suitably arranged system or apparatus.
Hereinafter, the operation principle of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description of the present disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear. The terms to be described below are terms defined in consideration of functions in the present disclosure, and may be different according to users, intention or habit of the users. Accordingly, the definition of terms should be determined based on the contents throughout the specification.
In the following description of the present disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.
In the following description, terms used to identify access nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, etc., are illustratively used for convenience. Accordingly, the present disclosure is not limited to the terms used below, and other terms regarding the subject matter having the equivalent technical meaning may be used.
In the following description, for ease of description, the present disclosure uses terminology and names defined in the third generation partnership project long term evolution (3 GPP LTE) standard. However, the present disclosure is not limited to these terms and names, and may be applied in the same manner to systems conforming to other standards. In this disclosure, for ease of description, the term "eNB" may be used interchangeably with the term "gNB". That is, a base station described as "enB" may be referred to as "gNB".
The present disclosure proposes a seamless handover method capable of minimizing a data interruption time due to handover or reducing the data interruption time to 0ms in a next generation mobile communication system.
In particular, the efficient switching methods presented in the present disclosure may have one or more of the following features.
If a handover command message (or RRC reconfiguration message) is received from the source base station to and from a terminal receiving data (uplink transmission or downlink data reception) through respective protocol entities (PHY entity, MAC entity, RLC entity, or PDCP entity) of the plurality of first bearers, the terminal may configure new protocol entities of the plurality of second bearers corresponding to the protocol entities of the plurality of first bearers (e.g., having the same bearer identifier) and may maintain data transmission and reception (uplink transmission or downlink data reception) with the source base station through the plurality of first bearers (without stopping the data transmission and reception), thereby performing transmission and reception of data (uplink transmission or downlink data reception).
-A protocol entity (PHY entity, MAC entity, RLC entity or PDCP entity) of the plurality of second bearers reconfigured after receiving the handover command message as described above may be configured to send and receive data to and from the target base station based on bearer configuration information or protocol entity information included in the handover command message.
The terminal may perform a procedure of random access to the target base station by the protocol entity (e.g. MAC entity) of the plurality of second bearers while transmitting and receiving data (uplink transmission or downlink data reception) to and from the source base station by the protocol entity of the plurality of first bearers. In this case, the random access procedure may include transmitting a preamble, receiving a random access response, or transmitting a message 3.
The terminal may complete the procedure of random access to the target base station through the protocol entities of the plurality of second bearers (e.g. MAC entities) while transmitting and receiving data to and from the source base station through the protocol entities of the plurality of first bearers, and may transmit a handover complete message to the target base station through the protocol entities of the plurality of second bearers.
The terminal may complete the procedure of random access to the target base station by means of the plurality of second bearer's protocol entities (e.g. MAC entities) while transmitting and receiving data to and from the source base station (uplink transmission and downlink data reception), may transmit a handover complete message to the target base station by means of the plurality of second bearer's protocol entities, and may perform (uplink or downlink) data transmission and reception.
When the procedure of random access to the target base station is completed { e.g. when a random access response is received, when a handover complete message (e.g. a "RRCReconfiguration" message) is sent to the target base station, or when data is initially sent to the target base station using PUCCH or PUSCH uplink transmission resources }, the terminal may stop sending data to and receiving data from the source base station through the protocol entities of the plurality of first bearers.
When receiving the handover command message, the terminal may continue to transmit and receive data to and from the source base station through the protocol entities of the plurality of first bearers (uplink transmission or downlink data reception), and may perform a procedure of randomly accessing the target base station through the protocol entities of the plurality of second bearers, and when receiving a random access response, when transmitting a handover complete message to the target base station, or initially transmitting data to the target base station using PUCCH or PUSCH uplink transmission resources, the terminal may stop transmitting uplink data to the source base station through the protocol entities of the plurality of first bearers, and may transmit uplink data to the target base station through only the protocol entities of the plurality of second bearers, and the terminal may continue to receive downlink data from the source base station through the protocol entities of the plurality of first bearers, and may continue to receive downlink data from the target base station through the protocol entities of the plurality of second bearers.
Hereinafter, the present disclosure proposes an efficient handover procedure without data interruption time based on the above-described features.
Fig. 1 is a diagram showing a structure of an LTE system to which the present disclosure can be applied.
Referring to fig. 1, a radio access network of an lte system may include evolved node bs (hereinafter, referred to as "ENBs", "node bs", or "base stations") 105, 110, 115, and 120, a Mobility Management Entity (MME) 125, and a serving gateway (S-GW) 130, as shown in fig. 1. A user equipment (hereinafter referred to as "UE" or "terminal") 135 accesses an external network through the ENBs 105 to 120 and the S-GW 130.
In fig. 1, the ENBs 105 to 120 may correspond to existing node bs of a UMTS system. The ENB may be connected to the UE 135 via a radio channel and may play a more complex role than an existing node B. In the LTE system, all user traffic including real-time services is serviced through a shared channel, such as voice over IP (VoIP) over internet protocol. Accordingly, means for collecting state information of the UE, such as a buffer state, an available transmission power state, and a channel state, and performing scheduling are used. The ENBs 105 to 120 function as such devices. One ENB generally controls a plurality of cells. For example, in order to achieve a data rate of 100Mbps, the LTE system uses orthogonal frequency division multiplexing (hereinafter referred to as "OFDM") in, for example, a 20MHz bandwidth as a radio access technology. In addition, an adaptive modulation and coding (hereinafter, referred to as "AMC") scheme is applied to determine a modulation scheme and a channel coding rate according to a channel state of a terminal. The S-GW 130 is a means for providing data bearers and generates or removes data bearers under control of the MME 125. The MME is a device that performs various control functions and mobility management functions of a terminal, and may be connected to a plurality of base stations.
Fig. 2 is a diagram showing a radio protocol structure of an LTE system to which the present disclosure can be applied.
Referring to fig. 2, the radio protocols of the lte system include a Packet Data Convergence Protocol (PDCP) 205 or 240, a Radio Link Control (RLC) 210 or 235, and a Medium Access Control (MAC) 215 or 230 in the terminal and the ENB, respectively. The Packet Data Convergence Protocol (PDCP) 205 or 240 performs operations such as IP header compression/decompression. The main functions of PDCP are summarized as follows.
Header compression and decompression (ROHC only)
-Transfer of user data
Sequential delivery of upper layer PDUs in PDCP re-establishment procedure for RLC AM
Sequence reordering { separate bearers in DC (support RLC AM only): PDCP PDU routing for transmission and PDCP PDU reordering for reception }
-Repeatedly detecting lower layer SDUs in PDCP re-establishment procedure for RLC AM
Retransmission of PDCP SDUs at handover for RLC AM and retransmission of PDCP PDUs in PDCP data recovery procedure for split bearers in DC
-Encryption and decryption
-Timer based SDU discard in uplink.
The Radio Link Control (RLC) 210 or 235 reconfigures PDCP PDUs (packet data units) to an appropriate size and performs ARQ operations and the like. The main functions of RLC are summarized as follows.
Data transfer function (transfer of upper layer PDU)
ARQ function { error correction by ARQ (for AM data transfer only) }
Concatenation, segmentation and reassembly of RLC SDUs (for UM and AM data transfer only)
Re-segmentation of RLC data PDU (for AM data transfer only)
Reordering of RLC data PDUs (for UM and AM data transfer only)
Duplicate detection (for UM and AM data transfers only)
Protocol error detection (for AM data transfer only)
RLC SDU discard (only for UM and AM data transfer)
RLC re-establishment
The MAC 215 or 230 is connected to a plurality of RLC entities configured in the terminal, multiplexes RLC PDUs into MAC PDUs, and demultiplexes RLC PDUs from the MAC PDUs. The main functions of the MAC are summarized as follows.
Mapping between logical channels and transport channels
Multiplexing/de-multiplexing MAC SDUs belonging to one or different logical channels as/from Transport Blocks (TBs) delivered to the physical layer on transport channels
Scheduling information reporting
HARQ functionality (error correction by HARQ)
Priority handling between logical channels of one UE
Priority handling between UEs by means of dynamic scheduling
MBMS service identity
Transport format selection
-Filling
The physical layers 220 and 225 channel-encode and modulate upper layer data and convert the upper layer data into OFDM symbols, which are then transmitted through a radio channel, or demodulate and channel-decode OFDM symbols received through a radio channel, which are then transmitted to an upper layer.
Fig. 3 is a diagram showing a structure of a next-generation mobile communication system to which the present disclosure can be applied.
Referring to fig. 3, a radio access network of a next-generation mobile communication system (hereinafter referred to as "NR" or "5G") may include a new radio node B (hereinafter referred to as "NR gNB" or "NR base station") 310 and a new radio core network (hereinafter referred to as "NR CN") 305. A new radio user equipment (hereinafter referred to as "NR UE" or "terminal") 315 accesses the external network through NR gNB 310 and NR CN 305.
In fig. 3, NR gNB 310 corresponds to an evolved node B (eNB) in an existing LTE system. NR gNB 310 is connected to NR UE 315 over radio channel 320 and may provide better service than existing node bs. In the next generation mobile communication system, all user traffic is serviced through a shared channel. Accordingly, means for collecting state information of the UE, such as a buffer state, an available transmission power state, and a channel state, and performing scheduling are used. NR NB 310 serves as such a device.
One NR gNB can control a plurality of cells. In order to achieve ultra-high data rates relative to existing LTE systems, next-generation mobile communication systems may have bandwidths equal to or greater than the maximum bandwidths of existing systems. In addition, the next generation mobile communication system may use Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology, and may employ a beamforming technology in addition thereto. In addition, an adaptive modulation and coding (hereinafter, referred to as "AMC") scheme may be applied to determine a modulation scheme and a channel coding rate according to a channel state of a terminal.
The NR CN 305 performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN is a device that performs various control functions and mobility management functions of a terminal, and may be connected to a plurality of base stations. In addition, the next generation mobile communication system may interwork with the existing LTE system, and the NR CN may be connected to the MME 325 through a network interface. The MME may be connected to an eNB 330 as an existing base station.
Fig. 4 is a diagram showing a radio protocol structure of a next-generation mobile communication system to which the present disclosure can be applied.
Referring to fig. 4, the radio protocol of the next generation mobile communication system includes NR SDAP 401 or 445, NR PDCP 405 or 440, NR RLC 410 or 435, and NR MAC 415 or 430 in the terminal and the NR base station, respectively.
The main functions of NR SDAP 401 or 445 may include some of the following functions.
-Transmission of user plane data
Mapping between QoS flows and DRBs for both downlink and uplink
Marking QoS flow IDs in both downlink and uplink packets
Mapping of reactive QoS flows to DRBs for UL SDAP PDUs
For the SDAP entity, the terminal may receive a configuration indicating whether to use a header of the SDAP entity or whether to use a function of the SDAP entity for each PDCP entity, for each bearer, or for each logical channel through an RRC message. In the case of configuring the SDAP header, the 1-bit NAS-reflective QoS configuration indicator and the 1-bit AS-reflective QoS configuration indicator of the SDAP header may instruct the terminal to update or reconfigure mapping information between QoS flows and data bearers in the uplink and downlink. The SDAP header may include QoS flow ID information indicating QoS. The QoS information may be used as data processing priority information, scheduling information, etc. for supporting an effective service.
The main functions of the NR PDCP 405 or 440 may include some of the following functions.
Header compression and decompression (ROHC only)
-Transfer of user data
Sequential delivery of upper layer PDUs
Unordered delivery of upper layer PDUs
Sequence reordering (reordering of PDCP PDUs for reception)
Duplicate detection of lower layer SDUs
Retransmission of PDCP SDUs
-Encryption and decryption
Timer based SDU discard in uplink
The above reordering function of the NR PDCP entity means a function of reordering PDCP PDUs received from a lower layer based on a PDCP Sequence Number (SN), may include a function of transmitting data to an upper layer in a reordered order, may include a function of transmitting data directly to the upper layer regardless of the order, may include a function of reordering sequences and recording lost PDCP PDUs, may include a function of transmitting a status report of the lost PDCP PDUs to a transmitting end, and may include a function of requesting retransmission of the lost PDCP PDUs.
The primary functions of NR RLC 410 or 435 may include some of the following functions.
Data transfer function (transfer of upper layer PDU)
Sequential delivery of upper layer PDUs
Unordered delivery of upper layer PDUs
ARQ function (error correction by ARQ)
Concatenation, segmentation and reassembly of RLC SDUs
Re-segmentation of RLC data PDUs
Reordering of RLC data PDUs
-Repeated detection
Protocol error detection
RLC SDU discard
RLC re-establishment
The above-described sequential delivery function of the NR RLC entity means a function of sequentially delivering RLC SDUs received from a lower layer to an upper layer, may include a function of reassembling and transmitting RLC SDUs in case that one original RLC SDU is divided into a plurality of RLC SDUs and received, may include a function of reordering received RLC PDUs based on RLC Sequence Numbers (SNs) or PDCP Sequence Numbers (SNs), may include a function of reordering sequences and recording missing RLC PDUs, may include a function of transmitting status reports of missing RLC PDUs to a transmitting end, may include a function of requesting retransmission of missing RLC PDUs, may include a function of sequentially transmitting RLC SDUs before only missing RLC SDUs to an upper layer in case that missing RLC SDUs exist, may include a function of sequentially transmitting all RLC SDUs received before a timer is started to an upper layer even if a predetermined timer expires, or may include a function of sequentially transmitting all RLC SDUs received until now to an upper layer even if a predetermined timer expires. In addition, RLC PDUs may be processed in the order received (in the order of arrival regardless of their sequence numbers or sequence numbers) and may be transmitted to the PDCP entity in an out-of-order delivery manner. In case of the segment, the segment stored in the buffer or to be received later may be received and reconfigured into one complete RLC PDU, and the RLC PDU may be processed and transmitted to the PDCP entity. The NR RLC layer may not include a concatenation function, and the concatenation function may be performed in the NR MAC layer or may be replaced with a multiplexing function of the NR MAC layer.
Unordered delivery of an NR RLC entity means a function of delivering RLC SDUs received from a lower layer directly to an upper layer regardless of the order, may include a function of reassembling and delivering RLC SDUs in case that one original RLC SDU is separated into a plurality of RLC SDUs and received, and may include a function of storing and ordering RLC SNs or PDCP SNs of received RLC PDUs, thereby recording lost RLC PDUs.
The NR MAC 415 or 430 may be connected to a plurality of NR RLC entities configured in a single terminal, and the main functions of the NR MAC may include some of the following functions.
Mapping between logical channels and transport channels
Multiplexing/demultiplexing of MAC SDUs
Scheduling information reporting
HARQ functionality (error correction by HARQ)
Priority handling between logical channels of one UE
Priority handling between UEs by means of dynamic scheduling
MBMS service identity
Transport format selection
-Filling
The NR PHY layers 420 and 425 may perform an operation of channel-coding and modulating upper layers into OFDM symbols and transmitting the OFDM symbols through a radio channel, or an operation of demodulating and channel-decoding OFDM symbols received through a radio channel and transmitting them to an upper layer.
Fig. 5 is a diagram illustrating a procedure in which a terminal in the present disclosure switches from an RRC idle mode to an RRC connected mode and establishes a connection with a network.
In fig. 5, if a terminal transmitting and receiving data in the RRC connected mode does not transmit and receive data for a predetermined reason or for an execution period, the base station may transmit an "RRCConnectionRelease" message to the terminal so that the terminal switches to the RRC idle mode (501).
Thereafter, if a terminal (hereinafter, referred to as "idle mode UE") that is not currently connected has data to transmit, the terminal performs an RRC connection establishment procedure with the base station. The terminal may establish reverse transmission synchronization with the base station through a random access procedure and may send an "RRCConnectionRequest" message to the base station (505). The message may contain an identifier of the terminal, a reason for establishing the connection (establishmentCause), etc. The base station may send a "RRCConnectionSetup" message to cause the terminal to establish an RRC connection (510).
The message includes configuration information of each service/bearer/RLC apparatus, each logical channel, or each bearer, information on whether or not each bearer/logical channel is to use ROHC, ROHC configuration information (e.g., information on ROHC version, initial information, etc.), information of "statusReportRequired" (information by which the base station instructs the terminal to report PDCP status), information of "drb-ContinueROHC", which is configuration information indicating that ROHC configuration information is maintained and used as it is, and may be included in PDCP entity configuration information (PDCP-config) for then transmission. In addition, the message may include RRC connection configuration information, etc. The RRC-connected bearers are also referred to as "Signaling Radio Bearers (SRBs)", and may be used to transmit and receive RRC messages as control messages between the terminal and the base station.
The terminal that has established the RRC connection sends a "RRCConnetionSetupComplete" message to the base station (515). The message may include a control message called a "service request" by which the terminal requests the MME for configuring a bearer for a predetermined service. The base station sends a message "service request" to the MME or AMF (520) included in the "RRCConnetionSetupComplete" message, and the MME or AMF determines whether to provide the service requested by the terminal.
As a result of the determination, if the terminal determines to provide the requested service, the MME or AMF may transmit an "initial context setup request" message to the base station (525). The message may include information such as quality of service (QoS) information to be applied when configuring a Data Radio Bearer (DRB) and security related information (e.g., may include at least one of a security key, a security algorithm, etc.) to be applied to the DRB.
In addition, if the base station fails to receive the capability information of the terminal from the MME or the AMF, the base station may transmit a UE capability information request message to the terminal to identify the capability information of the terminal (526). Upon receiving the UE capability information request message, the terminal may configure and generate and transmit the UE capability information message to the base station (527).
The UE capability information message may include the type of handover method supported by the terminal. An indicator for each handover method may be defined, the base station may identify UE capability information, and may transmit an indicator indicating a handover type to the terminal using a handover command message when indicating a handover.
The base station may exchange "SecurityModeCommand" messages (530) and "SecurityModeComplete" messages (535) with the terminal to establish security. When security is established, the base station sends a "RRCConnectionReconfiguration" message to the terminal (540).
The message includes configuration information of each service/bearer/RLC apparatus, each logical channel, or each bearer, information on whether or not each bearer/logical channel is to use ROHC, ROHC configuration information (e.g., information on ROHC version, initial information, etc.), information of "statusReportRequired" (information by which the base station instructs the terminal to report PDCP status), information of "drb-ContinueROHC", which is configuration information indicating that ROHC configuration information is maintained and used as it is, and may be included in PDCP entity configuration information (PDCP-config) for then transmission. In addition, the message contains RRC connection configuration information and the like. The RRC-connected bearer is also referred to as a "Signaling Radio Bearer (SRB)", and is used to transmit and receive RRC messages as control messages between the terminal and the base station.
In addition, the message includes configuration information on the DRB in which the user data is processed, and the terminal configures the DRB by applying the above information and transmits a 'RRCConnectionReconfigurationComplete' message to the base station (545). After completing the DRB configuration with respect to the terminal, the base station transmits an "initial context setup complete" message to the MME or AMF (550). Upon receipt of the message, the MME or AMF exchanges an "S1 bearer setup" message and an "S1 bearer setup response" message with the S-GW to configure the S1 bearer (555 and 560). The S1 bearer is a connection for transmitting data, which is established between the S-GW and the base station, and corresponds to the DRB in a one-to-one correspondence. When all the above processes are completed, the terminal transmits and receives data to and from the base station through the S-GW (565 and 570). The general data transmission procedure described above basically includes three steps, RRC connection establishment, security configuration, and DRB configuration. In addition, the base station may send a "RRCConnectionReconfigutation" message to the terminal to indicate the new configuration to the terminal, add another configuration, or modify the configuration for some reason (575).
In this disclosure, a bearer may include an SRB and a DRB, the SRB may represent a "signaling radio bearer", and the DRB may represent a "data radio bearer". The SRB is mainly used to transmit and receive RRC messages of the RRC entity, and the DRB is mainly used to transmit and receive user layer data. In addition, the UM DRB refers to a DRB using an RLC entity operating in Unacknowledged Mode (UM), and the AM DRB refers to a DRB using an RLC entity operating in Acknowledged Mode (AM).
Fig. 6 is a diagram illustrating a signaling procedure for performing handover in a next generation mobile communication system.
The terminal 601 in RRC connected mode may send a cell measurement report to the current source base station (source eNB) 602 periodically or upon satisfaction of a specific event (605).
The source base station may determine whether the terminal is to perform handover to a neighboring cell based on the measurement report. "handover" is a technique of switching a source base station serving a terminal in a connected mode to another base station (or another cell of the same base station). If the source base station determines a handover, the source base station may request a handover by sending a Handover (HO) request message to a new base station, i.e., a "target base station (target eNB)" 603 that will serve the terminal (610). If the target base station accepts the handover request, the target base station may send a "HO request acknowledgement" message to the source base station (615).
Upon receiving the message, the source base station may send a Handover (HO) command message to the terminal (620). The source base station may transmit a handover command message to the terminal using the RRC connection reconfiguration message.
Upon receipt of the message, the terminal may stop sending and receiving data to and from the source base station and may start a timer T304 (625). If the terminal fails to perform a handover to the target base station within a predetermined period of time, the timer T304 causes the terminal to return to its original configuration and switch to the RRC idle state. The source base station may transmit a Sequence Number (SN) status of uplink/downlink data to the target base station and, if downlink data is present, transmit the downlink data to the target base station (630 and 635).
The terminal may attempt to randomly access the target cell indicated by the source base station (640). Random access is intended to inform the target cell that the terminal is moving to handover and to match uplink synchronization. For random access, the terminal transmits a preamble corresponding to a preamble ID provided from the source base station or a randomly selected preamble ID to the target cell.
After transmitting the preamble, the terminal may monitor whether a Random Access Response (RAR) message is received from the target cell when a certain number of subframes pass. The monitored time period is referred to as a "random access response window (RAR window)".
If a Random Access Response (RAR) is received during a certain period of time (645), the terminal may transmit a Handover (HO) complete message to the target base station using an RRC reconfiguration complete message (655). That is, the terminal may include information indicating that handover is completed in the RRC reconfiguration complete message, and may transmit the message to the target base station.
Upon successful receipt of the random access response from the target base station as described above, the terminal may terminate the timer T304 (650). The target base station may request path modification from the MME/S-GW/AMF 604 to modify the path of the bearers configured for the source base station (660 and 665), and may send a request to the source base station to delete the UE context of the terminal (670). Accordingly, the terminal attempts to receive data from the target base station from the start time of the RAR window (675), and transmits an RRC reconfiguration complete message after receiving the RAR, thereby starting to transmit and receive data to and from the target base station.
The present disclosure proposes a seamless handover method capable of minimizing a data interruption time due to handover or reducing the data interruption time to 0ms in a next generation mobile communication system.
The terminal can configure a plurality of first bearers with respect to the source base station, perform transmission and reception of data (uplink transmission or downlink data reception) through respective protocol entities (PHY entity, MAC entity, RLC entity, or PDCP entity) of the bearers, and hereinafter, for convenience of description, examples of the terminal having one bearer will be shown and described in the drawings and description.
Fig. 7 is a diagram showing a first embodiment of an efficient switching method for minimizing data interruption time due to switching in the present disclosure. Although described herein as various embodiments, such as a first embodiment or a second embodiment, this description should not be construed as limiting. The various embodiments may be combined or separated into separate embodiments without departing from the scope of the present disclosure.
Referring to fig. 7, in step 701, even if the terminal 720 receives a handover command from the source base station 705 while transmitting and receiving data to and from the source base station, the terminal can continue to transmit and receive data to and from the source base station to minimize a data interruption time occurring during handover.
Accordingly, in step 702, when the terminal 720 performs a random access procedure, transmits a preamble, or transmits initial data to the target base station 710 indicated by the handover command message through uplink transmission resources (e.g., PUCCH or PUSCH transmission resources), the terminal 720 may stop transmitting data to and receiving data from the source base station (uplink data transmission and downlink data reception).
In addition, in step 703, the terminal 720 may complete a procedure of random access to the target base station, may transmit a handover complete message, and may start transmitting and receiving data to and from the target base station (uplink data transmission and downlink data reception)
Fig. 8 is a diagram showing second and third embodiments of an efficient switching method for minimizing data interruption time due to switching in the present disclosure.
Referring to fig. 8, in a second embodiment of the efficient handover method, in step 801, even if the terminal 820 receives a handover command from the source base station 805 while transmitting and receiving data to and from the source base station, the terminal can continue to transmit and receive data to and from the source base station through the protocol entity 822 of the first bearer to minimize a data interruption time occurring during handover.
In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 821 for the second bearer of the target base station may be preconfigured or established according to the configuration contained in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data interruption times from occurring for each bearer. In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer.
In step 802, even when the terminal 820 performs a random access procedure on the target base station 810 indicated by the handover command message through the protocol entity of the second bearer (e.g., before receiving a random access response after transmitting the preamble), the terminal can continue to transmit and receive data (uplink data transmission and downlink data reception) to and from the source base station through the protocol entity of the first bearer.
In addition, in step 803, the terminal 820 may complete the procedure of the random access target base station 810 through the protocol entity of the second bearer, and may transmit and receive data (downlink data reception and uplink data transmission).
In addition, if the first condition is satisfied, the terminal may stop transmitting data to and receiving data from the source base station 805 through the protocol entity 822 of the first bearer. In addition, the PDCP entity 821 of the second bearer can continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 822 of the first bearer. The first condition may include at least one of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 821 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
The source base station may determine, when performing the efficient handover proposed in the present disclosure, a time to stop transmitting downlink data to the terminal or a time to release the connection with the terminal based on a predetermined method. For example, the predetermined method may include at least one of when the predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target base station indicating that the terminal has successfully performed the handover to the target base station.
In addition, if downlink data is not received from the source base station for a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.
* Alternatively, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may then determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
Meanwhile, referring to fig. 8, in a third embodiment of the efficient handover method, in step 801, even though the terminal 820 receives a handover command from the source base station 805 while transmitting and receiving data to and from the source base station, in order to minimize a data interruption time occurring during handover, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 822 of the first bearer.
In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 821 for the second bearer of the target base station may be preconfigured or established according to the configuration contained in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data interruption times from occurring for each bearer.
In addition, the handover command message may include uplink transmission resources of the target base station and may then be transmitted to the terminal to omit a random access procedure of the terminal to the target base station through the protocol entity of the second bearer.
As another method, in case the handover command message indicates handover without a random access procedure, the terminal may synchronize with the target base station without a random access procedure and may receive uplink transmission resources from the target base station by monitoring the PDCCH. As described above, the data interruption time can be minimized by omitting the random access procedure.
In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer. In addition, in the case of RLC in AM, RLC retransmission may be continuously performed.
In the third embodiment, in step 802, the operation of the terminal 820 performing the random access procedure on the target base station 810 indicated by the handover command message through the protocol entity of the second bearer may be omitted. The terminal may configure a handover complete message, and may send the handover complete message to the target base station through the protocol entity of the second bearer using the transmission resource of the target base station indicated by the handover command message.
As another method, in case the handover command message indicates that there is no handover of the random access procedure but does not include uplink transmission resources to the target base station, the terminal may synchronize with the target base station without the random access procedure and may receive uplink transmission resources from the target base station by monitoring the PDCCH, thereby transmitting a handover complete message to the target base station. The terminal may continue to transmit and receive data (uplink data transmission and downlink data reception) to and from the source base station through the protocol entity of the first bearer.
In the third embodiment, the terminal 820 may transmit and receive data (downlink data reception and uplink data transmission) using the protocol entity of the second bearer in step 803.
In addition, if the first condition is satisfied, the terminal may stop transmitting data to and receiving data from the source base station 805 through the protocol entity 822 of the first bearer. In addition, the PDCP entity 821 of the second bearer can continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity 822 of the first bearer. The first condition may include at least one of the following conditions.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
The source base station may determine, when performing the efficient handover proposed in the present disclosure, a time to stop transmitting downlink data to the terminal or a time to release the connection with the terminal based on a predetermined method. For example, the predetermined method may include at least one of when the predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target indicating that the terminal has successfully performed the handover to the target base station.
In addition, if downlink data is not received from the source base station for a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* When the terminal transmits a predetermined preamble to a cell of a target base station and receives a Random Access Response (RAR) message, the terminal may determine that the random access procedure is successfully completed. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.
* Alternatively, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, when the terminal monitors the PDCCH thereafter and initially receives an uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal or initially receives an indication of the uplink transmission resource, the terminal may determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
Fig. 9 is a diagram showing a fourth embodiment of an efficient switching method for minimizing data interruption time due to switching in the present disclosure.
Referring to fig. 9, in step 901, even if the terminal 920 receives a handover command from the source base station 905 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 922 of the first bearer to minimize a data interruption time occurring during handover.
In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 921 for the second bearer of the target base station may be preconfigured or established according to the configuration contained in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data interruption times from occurring for each bearer.
In addition, in the fourth embodiment, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, a more detailed operation method of which will be described with reference to fig. 11.
In addition, in the case where the terminal is allowed to transmit uplink data to both the source base station and the target base station, there may be a problem of a reduced coverage due to insufficient transmission power of the terminal, or a problem of determining a base station to which to request transmission resources and transmit uplink data when transmitting uplink data (link selection problem). Therefore, in order to avoid the above-described problems, in the fourth embodiment, a terminal may transmit uplink data to a source base station and a target base station at different times through a Time Domain Multiplexing (TDM) scheme when transmitting the uplink data to the source base station or the target base station.
As another method, the base station may configure the threshold value through an RRC message, and in case the size of uplink data of the terminal is smaller than the threshold value, the terminal may transmit uplink data to the source base station (or the target base station), and in case the size of uplink data of the terminal is larger than the threshold value, the terminal may transmit uplink data to both the source base station and the target base station. The transmission of uplink data may be accompanied by a Buffer Status Report (BSR) procedure or a scheduling request procedure for reporting the size of data to be transmitted.
In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer. In addition, in case of RLC entity in AM, RLC retransmission may be continuously performed.
In step 902, the terminal 920 may continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer of the terminal even when the random access procedure is performed on the target base station 910 indicated by the handover command message through the protocol entity of the second bearer.
In step 903, the terminal 920 may complete the procedure of the random access target base station 910 through the protocol entity of the second bearer, may transmit and receive data (uplink data transmission and downlink data transmission), and may continue to transmit and receive data to and from the source base station through the protocol entity of the first bearer.
In step 904, if the first condition is met, the terminal 920 may stop sending data to and receiving data from the source base station 805 over the protocol entity 922 of the first bearer. In addition, the PDCP entity 921 of the second bearer may continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, and the like stored in the PDCP entity 922 of the first bearer. The first condition may include at least one of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 921 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
The source base station may determine, when performing the efficient handover proposed in the present disclosure, a time to stop transmitting downlink data to the terminal or a time to release the connection with the terminal based on a predetermined method. For example, the predetermined method may include at least one of when the predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target indicating that the terminal has successfully performed the handover to the target base station.
In addition, if downlink data is not received from the source base station for a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
Fig. 10 is a diagram showing a fifth embodiment of an efficient switching method for minimizing data interruption time due to switching in the present disclosure.
Referring to fig. 10, in the fifth embodiment, in step 1001, even if the terminal 1020 receives a handover command from the source base station 1005 while transmitting and receiving data to and from the source base station, the terminal can continue to transmit and receive data to and from the source base station through the protocol entity 1022 of the first bearer to minimize a data interruption time occurring during handover.
In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 1021 for the second bearer of the target base station may be preconfigured or established according to the configuration contained in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data interruption times from occurring for each bearer.
In addition, in the fifth embodiment, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, a more detailed operation method of which will be described with reference to fig. 11.
In addition, in the fifth embodiment, in the case where the terminal is allowed to transmit uplink data to both the source base station and the target base station, there may be a problem of a reduced coverage due to insufficient transmission power of the terminal, or a problem of determining a base station to which to request transmission resources and transmit uplink data when transmitting uplink data (link selection problem). Therefore, in order to avoid the above-described problem, in the fifth embodiment, the terminal may transmit uplink data to only one of the source base station or the target base station.
Accordingly, the terminal may request scheduling from only one of the source base station and the target base station, may report only a data size { e.g., a Buffer Status Report (BSR) } to be transmitted in the PDCP entity to one of the source base station and the target base station, may receive uplink transmission resources, and may then transmit uplink data to only one base station. In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer. In addition, in case of RLC entity in AM, RLC retransmission may be continuously performed.
In the fifth embodiment, in step 1002, even when the random access procedure is performed on the target base station 1010 indicated by the handover command message through the protocol entity of the second bearer, the terminal 1020 can continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer.
In the fifth embodiment, in step 1003, the terminal 1020 may stop transmitting data to and receiving data from the source base station through the protocol entity 1022 of the first bearer, may transmit uplink data to the target base station through the protocol entity 1021 of the second bearer, and may continue to receive downlink data from the source base station and the target base station through the protocol entities of the first bearer and the second bearer if the second condition is satisfied. In addition, the PDCP entity 1021 of the second bearer can continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, and the like stored in the PDCP entity 1022 of the first bearer.
The second condition may include at least one of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 1021 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station and switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station and switch uplink to the target base station
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the second condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the second condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the second condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
In case the terminal is able to continue to receive downlink data from the source base station and the target base station via the protocol entities of the first bearer and the second bearer, for AM bearers, RLC status reports other than data are allowed to continue to be sent to the source base station (or the target base station) via the protocol entities of the first bearer (or the second bearer) in the uplink in order to facilitate receiving downlink data from the source base station (or the target base station) or facilitating sending downlink data by the source base station (or the target base station). This is due to the fact that after the AM bearer transmits data to the transmitting terminal, if there is no RLC status report indicating successful delivery (that is, if the RLC status report is not received), the AM bearer cannot continue transmitting data thereafter.
In addition, in the fifth embodiment, in step 1003, even if the terminal 1020 stops transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer because the second condition is satisfied, and switches to starting transmitting uplink data to the target base station through the protocol entity 1021 of the second bearer, in order to facilitate reception of downlink data from the source base station (or the target base station) or transmission of downlink data by the source base station (or the target base station), the terminal may allow the protocol entity of the first bearer (or the second bearer) to continue transmitting HARQ ACK or HARQ NACK information or PDCP control data (e.g., PDCP status report or ROHC feedback information).
In addition, in the fifth embodiment, in step 1003, even if the terminal 1020 stops transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer because the second condition is satisfied and switches to start transmitting uplink data to the target base station through the protocol entity 1021 of the second bearer, the terminal can continue transmitting data due to HARQ retransmission of the MAC entity or continue transmitting data due to retransmission of the RLC entity in the AM to prevent data loss to the source base station.
In addition, in the fifth embodiment, in step 1003, if the terminal 1020 stops transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer because the second condition is satisfied and switches to starting transmitting uplink data to the target base station through the protocol entity 1021 of the second bearer, the source base station or the target base station may allocate transmission resources to the terminal by dividing the time so that the uplink transmission resources to the target base station and the uplink transmission resources to the source base station do not collide (or overlap) with each other. If the uplink transmission resource to the target base station overlaps with the uplink transmission resource to the source base station, the terminal may prioritize the uplink transmission resource of the source base station to maintain transmission of downlink data from the source base station, thereby performing data transmission to the source base station.
Alternatively, if the uplink transmission resource to the target base station overlaps with the uplink transmission resource to the source base station, the terminal may prioritize the uplink transmission resource of the target base station to maintain transmission of downlink data from the target base station, thereby performing data transmission to the target base station.
Specifically, in the case where handover corresponding to the fifth embodiment of the present disclosure is instructed upon receiving the handover command message, the terminal may perform a scheduling request through the first protocol entity until the second condition is satisfied, may transmit a buffer status report to the source base station, may receive uplink transmission resources, may transmit uplink data, and may receive downlink data from the source base station.
However, if the second condition is satisfied, the terminal may not transmit data to the source base station any more, may switch the uplink to perform a scheduling request through the second protocol entity, may transmit a buffer status report to the target base station, may receive uplink transmission resources, and may transmit uplink data to the target base station.
However, the terminal may continue to receive downlink data from the source base station and may continue to transmit HARQ ACK, HARQ NACK, RLC status report, or PDCP control data (e.g., PDCP status report or ROHC feedback information) corresponding to the downlink data. The terminal may also receive downlink data from the target base station if the second condition is satisfied.
In the fifth embodiment, in step 1004, if the first condition is met, the terminal 1020 may stop receiving downlink data from the source base station 1005 through the protocol entity 1022 of the first bearer. In addition, the PDCP entity 1021 of the second bearer can continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, and the like stored in the PDCP entity 1022 of the first bearer. The first condition may include at least one of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 1021 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
The source base station may determine, when performing the efficient handover proposed in the present disclosure, a time to stop transmitting downlink data to the terminal or a time to release the connection with the terminal based on a predetermined method. For example, the predetermined method may include at least one of when the predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target indicating that the terminal has successfully performed the handover to the target base station.
In addition, if downlink data is not received from the source base station for a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
Fig. 10 may illustrate steps in embodiment 5-2 of an efficient handoff method in the present disclosure for minimizing data interruption time due to handoff.
Referring to fig. 10, in the 5-2 th embodiment, in step 1001, even if the terminal 1020 receives a handover command from the source base station 1005 while transmitting and receiving data to and from the source base station, the terminal may continue to transmit and receive data to and from the source base station through the protocol entity 1022 of the first bearer to minimize a data interruption time occurring during handover.
In addition, a protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) 1021 for the second bearer of the target base station may be preconfigured or established according to the configuration contained in the received handover command message. The second bearer may be configured and established to have the same bearer identifier as the first bearer to prevent data interruption times from occurring for each bearer.
In addition, in embodiment 5-2, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity, a more detailed operation method of which will be described with reference to fig. 11.
In addition, in embodiment 5-2, in addition, in the case where the terminal is allowed to transmit uplink data to both the source base station and the target base station, there may be a problem of reduced coverage due to insufficient transmission power of the terminal, or a problem of determining a base station to which to request transmission resources and transmit uplink data when transmitting uplink data (link selection problem). Therefore, in order to avoid the above-described problem, in embodiment 5-2, the terminal may transmit uplink data to only one of the source base station and the target base station.
Accordingly, the terminal may request scheduling from only one of the source base station and the target base station, may report only a data size { e.g., a Buffer Status Report (BSR) } to be transmitted in the PDCP entity to one of the source base station and the target base station, may receive uplink transmission resources, and may then transmit uplink data to only one base station. In addition, even if the terminal receives the handover command message from the source base station, the terminal may continue to transmit and receive data due to HARQ retransmission to prevent data loss, and thus may not initialize the MAC entity of the first bearer.
In the 5-2 embodiment, in step 1002, even when the random access procedure is performed on the target base station 1010 indicated by the handover command message through the protocol entity of the second bearer, the terminal 1020 can continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer.
In the 5-2 embodiment, in step 1003, the terminal 1020 may stop transmitting uplink data to the source base station through the protocol entity 1022 of the first bearer, may transmit uplink data to the target base station through the protocol entity 1021 of the second bearer, and may continue to receive downlink data from the source base station and the target base station through the protocol entities of the first bearer and the second bearer if the second condition is satisfied. In this case, when the transmission of uplink data to the source base station through the protocol entity 1022 of the first bearer is stopped, the terminal may perform an RLC re-establishment procedure on a transmitting RLC entity among the protocol entities. In addition, the PDCP entity 1021 of the second bearer can continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, and the like stored in the PDCP entity 1022 of the first bearer. The second condition may include one of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 1021 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station and switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station and switch uplink to the target base station
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the second condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the second condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the second condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
In case the terminal is able to continue to receive downlink data from the source base station and the target base station via the protocol entities of the first bearer and the second bearer, for AM bearers, RLC status reports other than data are allowed to continue to be sent to the source base station (or the target base station) via the protocol entities of the first bearer (or the second bearer) in the uplink in order to facilitate receiving downlink data from the source base station (or the target base station) or facilitating sending downlink data by the source base station (or the target base station). This is due to the fact that after the AM bearer transmits data to the transmitting terminal, if there is no RLC status report indicating successful delivery (that is, if the RLC status report is not received), the AM bearer cannot continue transmitting data thereafter.
In addition, to facilitate reception of downlink data from the source base station (or target base station) or transmission of downlink data by the source base station (or target base station), the protocol entity over the first bearer (or second bearer) may be allowed to continue to transmit HARQ ACK or HARQ NACK information or PDCP control data (e.g., PDCP status report or ROHC feedback information).
Specifically, in the case where handover corresponding to the 5-2 th embodiment of the present disclosure is instructed upon receipt of the handover command message, the terminal may perform a scheduling request through the first protocol entity until the second condition is satisfied, may transmit a buffer status report to the source base station, may receive uplink transmission resources, may transmit uplink data, and may receive downlink data from the source base station.
However, if the second condition is satisfied, the terminal may not transmit data to the source base station any more, may switch the uplink to perform a scheduling request through the second protocol entity, may transmit a buffer status report to the target base station, may receive uplink transmission resources, and may transmit uplink data to the target base station.
However, the terminal may continue to receive downlink data from the source base station and may continue to transmit HARQ ACK, HARQ NACK, RLC status report, or PDCP control data (e.g., PDCP status report or ROHC feedback information) corresponding to the downlink data. The terminal may also receive downlink data from the target base station when the second condition is satisfied.
In the 5-2 embodiment, in step 1004, if the first condition is met, the terminal 1020 may stop receiving downlink data from the source base station 1005 through the protocol entity 1022 of the first bearer. In addition, the PDCP entity 1021 of the second bearer can continue performing seamless data transmission and reception to and from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, and the like stored in the PDCP entity 1022 of the first bearer. The first condition may include one of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 1021 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
The source base station may determine, when performing the efficient handover proposed in the present disclosure, a time to stop transmitting downlink data to the terminal or a time to release the connection with the terminal based on a predetermined method. For example, the predetermined method may include at least one of when the predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target indicating that the terminal has successfully performed the handover to the target base station.
In addition, if downlink data is not received from the source base station for a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
At the same time, indicators of the embodiments presented in this disclosure may be defined. Thus, when transmitting a handover command message to the terminal (620) in fig. 6, the base station may indicate to the terminal a handover procedure corresponding to a specific embodiment to be triggered through the handover command message (e.g., RRCReconfiguration message) as described above. In addition, the terminal may perform a handover procedure according to a handover method indicated by the handover command message, thereby performing handover to the target base station while minimizing a data interruption time.
As another approach, indicators for the embodiments presented in this disclosure may be defined for each bearer. Thus, the base station may more specifically indicate the embodiment and bearer of the application handover using the handover command message. For example, the embodiments may be applied only to an AM bearer driving an RLC entity under AM, or may be extended to an UM bearer driving an RLC entity under UM.
In addition, it is assumed that the embodiments presented in the present disclosure are applied to DRBs. However, if necessary (e.g., when the terminal maintains the SRB of the source base station and cannot perform handover to the target base station, thereby reporting a handover failure message or recovering through the SRB of the source base station), the embodiments presented in the present disclosure may be extended to be applied to SRBs.
In an embodiment, the MAC entity of the first bearer and the MAC entity of the second bearer may use separate Discontinuous Reception (DRX) periods to reduce battery consumption of the terminal when the terminal transmits and receives data to and from the source base station through the protocol entity of the first bearer, and when the terminal transmits and receives data to and from the target base station through the protocol entity of the second bearer. That is, the terminal may continue to apply the DRX period of the MAC entity that has been applied when transmitting and receiving data through the protocol entity of the first bearer even after receiving the handover command message, and may stop the DRX according to the first condition or the second condition in the present disclosure. In addition, the terminal may apply the DRX period to the MAC entity of the second bearer separately according to the indication of the target base station.
In addition, in the present disclosure, the operation of the terminal to stop uplink transmission to the source base station through the protocol entity of the first bearer and to stop downlink transmission from the source base station refers to an operation of the terminal to reestablish, initialize, or release the protocol entity (PHY entity, MAC entity, RLC entity, or PDCP entity) of the first bearer.
For convenience of description, the case where the terminal has the first bearer for the source base station or the second bearer for the target base station has been described in the above embodiments, and the embodiments can be easily extended and applied in the same manner to the case where the terminal has the plurality of first bearers for the source base station or the plurality of second bearers for the target base station.
In addition, the embodiments of the present disclosure can be easily extended and applied to a case where a plurality of bearers are configured for a plurality of target base stations in the same manner. For example, the terminal may configure the second bearer while performing the handover procedure to the first target base station, and if the handover is unsuccessful, the terminal may configure the second bearer while performing the handover procedure to the second target base station. As described above, the terminal may search for and determine a cell satisfying a predetermined condition (e.g., having a predetermined signal strength or stronger than a predetermined signal strength) among a plurality of target base stations, thereby performing a handover procedure.
Fig. 11 is a diagram illustrating a structure of a high-efficiency PDCP entity, which can be applied to an embodiment.
The present disclosure proposes a structure of a high-efficiency PDCP entity as shown in fig. 11. The structure of the PDCP entity shown in fig. 11 may be applied to the second, third, fourth, or fifth embodiments of the efficient handover method for minimizing data interruption time set forth in the present disclosure.
In fig. 11, a terminal 1120 may transmit and receive data to and from a source base station 1105 through a protocol entity of a first bearer, and may simultaneously transmit and receive data to and from a target base station 1110 through a protocol entity of a second bearer.
Although the PDCP entity of the first bearer and the PDCP entity of the second bearer are respectively configured in the terminal, the PDCP entity of the first bearer and the PDCP entity of the second bearer may logically operate as a single PDCP entity as shown in fig. 11. Specifically, a single PDCP entity may be implemented to have one upper layer PDCP entity 1123 and two lower layer PDCP entities 1121 and 1122 for a source base station and a target base station, respectively, according to the function of the PDCP entity.
The upper layer transmitting PDCP entity 1123 may be used to assign PDCP sequence numbers to data received from an upper layer entity. In addition, the upper layer transmitting PDCP entity 1123 may perform header compression. In addition, the lower layer transmitting PDCP entities 1121 and 1122 for the source and target base stations may apply an integrity protection procedure to PDCP headers and data (PDCP SDUs) in case of configuring the integrity protection using security keys set for the source and target base stations, respectively, and the lower layer transmitting PDCP entities 1121 and 1122 for the source and target base stations may apply a ciphering procedure to the PDCP headers and data and may transmit the PDCP headers and data to the transmitting RLC entity of the first bearer or the transmitting RLC entity of the second bearer.
In order to accelerate the data processing speed, the lower layer transmitting PDCP entities 1121 and 1122 may perform parallel processing of performing header compression, integrity protection, and/or ciphering processes in parallel, and may perform the integrity protection or ciphering processes using different security keys. In addition, in one transmitting PDCP entity logically, an integrity protection or ciphering process can be performed on different data using different security keys or security algorithms.
The upper layer receiving PDCP entity 1123 may perform a duplicate detection function on data received from the lower layer entity based on the PDCP sequence number. In addition, the upper layer receiving PDCP entity 1123 may sort received data in an ascending order of PDCP sequence numbers and sequentially transmit the data to an upper layer. In addition, the upper layer receiving PDCP entity 1123 may perform header decompression.
Further, in case that integrity protection is configured using separate security keys set for the source base station and the target base station, the lower layer receiving PDCP entities 1121 and 1122 for the respective one of the source base station and the target base station may apply an integrity verification procedure to PDCP headers and data (PDCP SDUs), the lower layer receiving PDCP entities 1121 and 1122 for the respective one of the source base station and the target base station may apply a decryption procedure to PDCP headers and data, and may transmit the PDCP headers and data to the upper layer receiving PDCP entity, thereby processing the data.
In order to reduce unnecessary integrity verification or decryption processes, the lower layer receiving PDCP entity may perform processes of discarding data outside a window and discarding duplicate data based on a PDCP sequence number, and may perform an integrity verification or decryption process only on valid data within the window.
In order to accelerate data processing speed, the lower layer transmitting PDCP entity may perform parallel processing of performing header compression, integrity protection, and ciphering processes based on the PDCP sequence number, and may perform an integrity protection verification or decryption process using different security keys. In addition, in one transmitting PDCP entity logically, an integrity protection or ciphering process can be performed on different data using different security keys or security algorithms. In addition, the lower layer receiving PDCP entity may perform an out-of-order decryption or integrity verification process on each piece of received data regardless of the order of PDCP sequence numbers.
The entities of the first bearer (or the first RLC entity) and the entities of the second bearer (or the second RLC entity) of the single PDCP entity are distinguished in such a way that uplink data and downlink data can be encrypted or decrypted by considering that they are connected to different MAC entities, by allowing them to have different logical channel identifiers, by considering that they are different RLC entities connected to different MAC entities, or based on that they use different ciphering keys, and can be compressed or decompressed using different compression protocol contexts.
When the fourth or fifth embodiment set forth in the present disclosure can be indicated to the terminal by a handover command message. At this time, if each bearer satisfies the following fourth condition, the terminal may convert, change or reset the PDCP entity for each bearer before receiving the handover command message to the efficient PDCP entity set forth in fig. 11, and may apply the efficient PDCP entity. The fourth condition may be one or more of the following conditions.
In case the terminal receives a handover command message from the source base station indicating to perform a handover using the fourth or fifth embodiment proposed in the present disclosure or indicating to apply the method of the efficient PDCP entity structure proposed in fig. 11
When the terminal performs a procedure of random access to the target base station through the entity 1021 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the fourth condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the fourth condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the fourth condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fourth condition is satisfied. As another method, the terminal may determine that the fourth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fourth condition is satisfied. As another method, the terminal may determine that the fourth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
In addition, when the fourth or fifth embodiment set forth in the present disclosure is indicated to the terminal through the handover command message, if each bearer satisfies the fourth condition, the terminal may convert, change, or reset the PDCP entity for each bearer before receiving the handover command message to the efficient PDCP entity set forth in fig. 11, and may apply the efficient PDCP entity.
Further, if the fifth condition is satisfied, the terminal may stop receiving downlink data from the source base station, and may reconvert, or reset the structure of the PDCP entity that has been converted, changed, or reset to the efficient PDCP entity set forth in fig. 11 to the PDCP entity for each bearer before receiving the handover command message. The fifth condition may be one or more of the following conditions.
When the terminal performs a procedure of random access to the target base station through the entity 1021 of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the fifth condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the fifth condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the fifth condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fifth condition is satisfied. As another method, the terminal may determine that the fifth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the fifth condition is satisfied. As another method, the terminal may determine that the fifth condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
As another method, if the fifth condition is satisfied, the terminal may stop receiving downlink data from the source base station, may release the RLC entity or the MAC entity as the first protocol entity for each bearer, and may apply the structure of the efficient PDCP entity set forth in fig. 11 to the respective bearers, thereby using the structure of the efficient PDCP entity.
Fig. 12 is a display diagram showing an operation of a terminal that can be applied to an embodiment set forth in the present disclosure.
Referring to fig. 12, the terminal may receive a handover command message (1205). The terminal may establish a protocol entity of a second bearer for the target base station indicated by the message (1210).
The terminal may then perform a procedure of random access to the target base station through the established protocol entity (1215). The terminal may continue to transmit and receive data (uplink data transmission and downlink data transmission) to and from the source base station through the protocol entity of the first bearer while performing the random access procedure (1220).
The terminal may identify whether a second condition is met (1225), and if the second condition is met, the terminal may stop sending uplink data to the source base station over the protocol entity of the first bearer and may send uplink data to the target base station over the protocol entity of the second bearer while continuing to receive downlink data from the source base station and the target base station over the protocol entity of the first bearer and the second bearer (1230). In addition, the PDCP entity of the second bearer may continue seamless data transmission to and seamless data reception from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity of the first bearer. The second condition may be one of the following conditions.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station and switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station and switch uplink to the target base station
In case the terminal receives a handover command message from the source base station indicating to perform a handover using the fourth or fifth embodiment proposed in the present disclosure or indicating to apply the method of the efficient PDCP entity structure proposed in fig. 11
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the second condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the second condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the second condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the second condition is satisfied. As another method, the terminal may determine that the second condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
If the second condition is not satisfied in the above step, the terminal may repeatedly check the second condition while continuing the existing procedure, that is, the procedure of transmitting and receiving data to and from the source base station and connecting to the target base station (1235).
Meanwhile, if the first condition is satisfied (1240), the terminal may stop receiving downlink data from the source base station through the protocol entity of the first bearer (1245). In addition, the PDCP entity of the second bearer may continue seamless data transmission to and seamless data reception from the target base station using information such as transmission/reception data, sequence number information, header compression and decompression context, etc., stored in the PDCP entity of the first bearer. The first condition may be one of the following conditions.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
The source base station may determine, when performing the efficient handover proposed in the present disclosure, a time to stop transmitting downlink data to the terminal or a time to release the connection with the terminal based on a predetermined method. For example, the predetermined method may include at least one of when the predetermined timer expires (the timer may be started after the handover indication) or when an indication is received from the target indicating that the terminal has successfully performed the handover to the target base station. In addition, if downlink data is not received from the source base station for a predetermined period of time, the terminal may determine that the connection with the source base station is released and may release the connection.
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the first condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the first condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the first condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the first condition is satisfied. As another method, the terminal may determine that the first condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
If the first condition is not satisfied in the above step, the terminal may repeatedly check the first condition while continuing the existing procedure (1250).
In the present disclosure, the PDCP entity operates to prevent the occurrence of data interruption time and data loss while performing the embodiments (first, second, third, fourth, fifth, or 5-2 th embodiments) of the handover procedure for minimizing the data interruption time set forth in the present disclosure. Accordingly, hereinafter, an embodiment of a PDCP entity procedure supporting the handover procedure proposed by the present disclosure to minimize a data interruption time is presented.
Indicators may be defined for various embodiments of the handoff process proposed in this disclosure for minimizing data interrupt time. Accordingly, when the base station transmits a handover command message to the terminal (620) in fig. 6, an embodiment of the PDCP entity procedure supporting a handover procedure for minimizing a data interruption time according to the present disclosure may indicate a handover procedure corresponding to a specific embodiment to be triggered to the terminal using the handover command message (e.g., RRCReconfiguration message). Accordingly, the terminal can perform a handover procedure according to the handover method indicated by the handover command message, thereby performing handover to the target base station while minimizing data interruption time.
In addition, an indicator of an embodiment of a PDCP entity procedure in a handover procedure for minimizing a data interruption time set forth in the present disclosure may be defined for each bearer or each PDCP entity. Accordingly, the base station may indicate the PDCP entity procedure corresponding to the specific embodiment to be triggered to the terminal using a handover command message (e.g., RRCReconfiguration message) so that the terminal may perform the indicated PDCP entity procedure.
Hereinafter, the present disclosure proposes a first embodiment supporting the PDCP entity procedure for minimizing the handover procedure for data interruption time proposed in the present disclosure.
In a first embodiment of the PDCP entity procedure set forth in the present disclosure, specific operations of transmitting and receiving PDCP entities are as follows. The first embodiment may be referred to as "PDCP re-establishment".
The transmitting PDCP entity may perform at least one of the following procedures if an upper layer entity (e.g., RRC entity) requests the first embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the first embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "RRCReconfiguration" message.
1. If there is no indicator that the UM DRB and the AM DRB continue to use the header compression protocol, the transmitting PDCP entity can initialize the header compression protocol and start the header compression protocol in a unidirectional (U) mode of an Initialization and Refresh (IR) state.
2. The transmitting PDCP entity sets window state variables (e.g., tx_next) of UM DRBs and SRBs to initial values.
3. As for SRBs, the transmitting PDCP entity discards all stored data (e.g., PDCP SDUs or PDCP PDUs) (since the data is generated for RRC messages sent to the source base station, they are discarded to avoid sending them to the target base station).
4. The transmitting PDCP entity applies the new security key and the new ciphering algorithm received from an upper layer entity (e.g., RRC entity).
5. The transmitting PDCP entity applies the new security key and the new integrity protection algorithm received from an upper layer entity (e.g., RRC entity).
6. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs) to which PDCP sequence numbers have been allocated (after discarding all existing stored PDCP PDUs) but which have not yet been transmitted to a lower layer entity as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the transmitting PDCP entity does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or ciphering procedure again, configures a PDCP header, and transmits it to a lower layer entity.
7. As for the AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment, starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not acknowledged its successful delivery (after discarding all existing stored PDCP PDUs), may perform an integrity procedure or ciphering procedure again, configure a PDCP header, and may transmit it to the lower layer entity, thereby performing retransmission or transmission. In other words, the transmitting PDCP entity performs retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
The receiving PDCP entity may perform the following procedure if an upper layer entity (e.g., RRC entity) requests the first embodiment of the PDCP entity procedure for a certain bearer or if the first embodiment of the PDCP entity procedure is indicated when the terminal receives a handover command message or an RRC reconfiguration message.
1. The receiving PDCP entity processes data (e.g., PDCP PDUs) received from a lower layer entity (e.g., RLC entity) due to re-establishment of the lower layer entity.
2. As for SRB, the receiving PDCP entity discards all stored data (e.g., PDCP SDUs or PDCP PDUs) (since the data is an RRC message received from the source base station, the receiving PDCP entity discards the date).
3. The receiving PDCP entity may stop and reset the timer if a reordering timer is running for SRBs and UM DRBs. In addition, the receiving PDCP entity may perform a header decompression procedure on all data (e.g., PDCP SDUs) stored for the UM DRB and transmit it to an upper layer entity.
4. If the indicator of the header decompression protocol is not continuously used for the AM DRB, the receiving PDCP entity performs a header decompression procedure on the stored data (e.g., PDCP SDU).
5. If there is no indicator for the UM DRB and the AM DRB to continue using the header decompression protocol, the receiving PDCP entity initializes the downlink header decompression protocol and starts the downlink header decompression protocol in a unidirectional (U) mode of a No Context (NC) state.
6. The receiving PDCP entity sets window variables (e.g., rx_next and rx_ DELIV) of UM DRBs and SRBs to initial values.
7. The receiving PDCP entity applies a new security key and a new ciphering/deciphering algorithm received from an upper layer entity (e.g., RRC entity).
8. The receiving PDCP entity applies a new security key and a new integrity protection/verification algorithm received from an upper layer entity (e.g., RRC entity).
Hereinafter, the present disclosure proposes a second embodiment supporting the PDCP entity procedure for minimizing the handover procedure for data interruption time proposed in the present disclosure.
In a second embodiment of the PDCP entity procedure set forth in the present disclosure, specific operations of transmitting and receiving PDCP entities are as follows. The second embodiment may be referred to as "PDCP data recovery".
The transmitting PDCP entity may perform at least one of the following procedures if an upper layer entity (e.g., RRC entity) requests the second embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the second embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "RRCReconfiguration" message.
1. If an upper layer entity (e.g., RRC entity) requests a PDCP data recovery procedure for an AM DRB, a transmitting PDCP entity may perform the following procedure.
A. The transmitting PDCP entity may perform selective retransmission of only all data, for example, RLC entity, of which successful transmission (RLC ACK) has not been confirmed yet by a lower layer entity, for example, RLC entity, among data, for example, PDCP PDUs, previously transmitted to the re-established AM RLC entity or the disconnected AM RLC entity, in ascending order of a count value (or PDCP sequence number). The transmission and retransmission may be performed on data previously stored in the buffer, or in the case where data has not been generated, the data may be generated first and then the transmission and retransmission may be performed on the generated data.
Hereinafter, the present disclosure proposes a third embodiment supporting the PDCP entity procedure for minimizing the handover procedure for data interruption time proposed in the present disclosure.
In a third embodiment of the PDCP entity procedure set forth in the present disclosure, specific operations of transmitting and receiving PDCP entities are as follows. The third embodiment may be referred to as "PDCP continuation" or another name. In addition, the third embodiment may be configured as embodiment 3-1 and embodiment 3-2.
The transmitting PDCP entity may perform one or more of the following procedures if an upper layer entity (e.g., RRC entity) requests the 3-1 rd embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the 3-1 rd embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "RRCReconfiguration" message.
As another method, if the handover command message includes an indicator indicating the fourth embodiment or the fifth embodiment proposed for handover in the present disclosure, the transmitting PDCP entity may perform one or more of the following several procedures in embodiment 3-1.
1. If there is no indicator for the UM DRB and the AM DRB to continue using the header compression protocol, the transmitting PDCP entity initializes the header compression protocol and starts the header compression protocol in a unidirectional (U) mode of an Initialization and Refresh (IR) state.
2. Since data transmission to the source base station and the target base station is continuously performed to minimize the data interruption time, the transmitting PDCP entity does not initialize a window variable (e.g., tx_next) for the UM DRB.
3. If a handover command message is received from the source base station, the terminal may set a window state variable (e.g., tx_next) of the SRB to an initial value since the terminal no longer transmits and receives RRC messages to and from the source base station. Alternatively, the terminal may release the SRB of the source base station. In addition, the terminal may also set a window state variable (e.g., tx_next) to an initial value for the SRB of the second bearer for the target base station.
As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message through the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing a transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set its window state variable (e.g., tx_next) to an initial value, thereby preventing a gap in PDCP sequence number from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted through the SRB of the source base station.
4. If a handover command message is received from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRB because it is no longer necessary to send and receive RRC messages to and from the source base station (since the data is a generated RRC message intended for the source base station, the terminal discards the data to avoid sending it to the target base station).
5. The transmitting PDCP entity may store and prepare new security keys and new ciphering algorithms received from an upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may continue to apply the old security key and ciphering algorithm, which were used before receiving the new security key and ciphering algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
6. The transmitting PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may continue to apply the security key and the integrity protection algorithm, which were used before receiving the new security key and the integrity protection algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
7. The transmitting PDCP entity may transmit a PDCP status report to the source base station when necessary, configured, or indicated, or at any time, thereby reporting a current transmission/reception status of data (e.g., successful or unsuccessful data reception).
8. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents of the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may apply a user data compression configuration to the target base station and may initialize the buffer.
If an upper layer entity (e.g., RRC entity) requests the 3-1 rd embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the 3-1 rd embodiment of the PDCP entity procedure when the terminal receives a handover command message or an RRC reconfiguration message, the receiving PDCP entity may perform one or more of the following procedures.
As another method, if the handover command message includes an indicator indicating the fourth embodiment or the fifth embodiment proposed for handover in the present disclosure, the receiving PDCP entity may perform one or more of the following several procedures in embodiment 3-1.
1. If a handover command message is received from the source base station, since the terminal no longer transmits and receives RRC messages to and from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRB (the data is discarded because it is an RRC message received from the source base station).
In addition, if the reordering timer is running, the terminal may stop the reordering timer. Alternatively, the terminal may release the SRB for the source base station. In addition, the terminal may set window variables (e.g., rx_next and rx_ DELIV) to initial values for the SRB of the second bearer for the target base station, and may stop the reordering timer if the reordering timer is running.
As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message through the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing a transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., rx_next) to an initial value, thereby preventing a gap in PDCP sequence number from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.
2. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, it is not necessary to separately process the stored data for the UM DRB.
3. If a reordering timer is running for the SRB and the UM DRB, the receiving PDCP entity stops and resets the timer, performs a header decompression procedure on all data (e.g., PDCP SDUs) stored for the UM DRB, and transmits it to an upper entity.
4. If the indicator of the header decompression protocol is not continuously used for the AM DRB, the receiving PDCP entity performs a header decompression procedure on the stored data (e.g., PDCP SDU).
5. If there is no indicator for the UM DRB and the AM DRB to continue using the header decompression protocol, the receiving PDCP entity initializes the downlink header decompression protocol and starts the downlink header decompression protocol in a unidirectional (U) mode of a No Context (NC) state.
6. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, the receiving PDCP entity does not set window state variables (e.g., rx_next and rx_ DELIV) to initial values for the UM DRB.
7. The receiving PDCP entity may store and prepare new security keys and new ciphering algorithms received from an upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the receiving PDCP entity may continue to apply a security key and ciphering algorithm, which were used before receiving the new security key and ciphering algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
8. The receiving PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the receiving DCP entity may continue to apply the security key and integrity protection algorithm used prior to receiving the new security key and integrity protection algorithm from the upper layer entity to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
9. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of the transmission data to and reception data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of the data for which successful delivery has been confirmed.
10. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents of the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may apply a user data compression configuration to the target base station and may initialize the buffer.
The transmitting PDCP entity of the terminal may perform the 3-2 rd embodiment if the upper layer entity (e.g., RRC entity) requests the 3-2 rd embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, and in particular, one or more of the following procedures.
1. The transmitting PDCP entity may apply the new security key and the new ciphering algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the source base station first bearer before receiving the new security key and ciphering algorithm from the upper layer entity.
As another method, the transmitting PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
2. The transmitting PDCP entity may apply the new security key and the integrity verification algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may release or discard the security key and the integrity verification algorithm applied to the PDCP entity of the source base station first bearer before receiving the new security key and the ciphering algorithm from the upper layer entity.
As another method, the transmitting PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
3. The transmitting PDCP entity may transmit a PDCP status report to the source base station or the target base station when necessary, configured, or indicated, or at any time, thereby reporting a current transmission/reception status of data (e.g., successful or unsuccessful data reception).
4. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs) to which PDCP sequence numbers have been allocated (after discarding all existing stored PDCP PDUs) but which have not yet been transmitted to a lower layer entity as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the terminal does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or ciphering procedure again, configures a PDCP header, and transmits it to a lower layer entity.
5. As for the AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data (or PDCP sequence number) in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before the third condition is met or before receiving RRC message) starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not confirmed its successful delivery (after discarding all existing stored PDCP PDUs). In addition, the transmitting PDCP entity may perform an integrity procedure or a ciphering procedure again, configure a PDCP header, and may transmit it to a lower layer entity, thereby performing retransmission or transmission. That is, the transmitting PDCP entity performs retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
As another method, when performing retransmission, the transmitting PDCP entity may perform retransmission only on data for which a lower layer entity (e.g., RLC entity) has not confirmed successful delivery. More specifically, as for the AM DRB, the transmitting PDCP entity (after discarding all stored PDCP PDUs to be transmitted to the source base station through the first protocol entity previously connected to the PDCP entity) may release a lower layer entity (e.g., RLC entity or MAC entity) that is the first protocol entity for transmitting data to the source base station. In addition, the transmitting PDCP entity may perform a new header or data compression process by applying a security key or header compression (or data compression) protocol context corresponding to the target base station in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before a third condition is satisfied or before an RRC message is received) from a lower layer entity (e.g., RLC entity) which is a first protocol entity for transmitting data to the source base station, may perform an integrity or ciphering process again, may configure a PDCP header, and may transmit it to a lower layer entity which is a second protocol entity for transmitting data to the target base station, thereby performing retransmission or transmission. That is, the transmitting PDCP entity may perform retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
As another method, when performing retransmission, the transmitting PDCP entity transmits only data, of which the lower layer entity (e.g., RLC entity) as a first protocol entity for transmitting data to the source base station has not confirmed its successful delivery, to the lower layer entity as a second protocol entity for transmitting data to the target base station, thereby performing selective retransmission. As another method, the transmission or retransmission operation may be performed after releasing a lower layer entity (e.g., RLC entity or MAC entity) which is a first protocol entity for transmitting data to the source base station.
6. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.
The receiving PDCP entity of the terminal may perform the 3-2 rd embodiment if the upper layer entity (e.g., RRC entity) requests the 3-2 rd embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, and in particular, one or more of the following procedures.
1. If data (e.g., PDCP PDUs) is received from a lower layer entity (e.g., RLC entity) due to re-establishment of the lower layer entity, the receiving PDCP entity processes the data.
2. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, it is not necessary to separately process the stored data for the UM DRB.
3. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, the receiving PDCP entity does not set window state variables (e.g., rx_next and rx_ DELIV) to initial values for the AM DRB or the UM DRB.
4. The receiving PDCP entity may apply the new security key and the new ciphering algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and ciphering algorithm from the upper layer entity.
As another method, the receiving PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
5. The receiving PDCP entity may apply the new security key and the new integrity verification algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and integrity verification algorithm from the upper layer entity.
As another method, the receiving PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
6. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of the transmission data to and reception data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of the data for which successful delivery has been confirmed.
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.
The third condition may be one of the following conditions.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal releases the connection with the source base station and releases the first protocol entity
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the third condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the third condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the third condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
If the third condition is not satisfied in the above step, the terminal may repeatedly check the third condition while continuing the existing procedure.
Hereinafter, the present disclosure proposes a fourth embodiment supporting the PDCP entity procedure for minimizing the handover procedure for data interruption time proposed in the present disclosure.
In a fourth embodiment of the PDCP entity procedure set forth in the present disclosure, specific operations of transmitting and receiving PDCP entities are as follows. The fourth embodiment may be referred to as "PDCP continuation" or another name. In addition, the fourth embodiment may be configured as the 4-1 th embodiment and the 4-2 th embodiment. In the fourth embodiment, since data continues to be transmitted and received, a procedure for initializing or handling a header compression protocol is not required.
The transmitting PDCP entity may perform one or more of the following procedures if an upper layer entity (e.g., RRC entity) requests the 4-1 th embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the 4-1 th embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "RRCReconfiguration" message.
As another method, if the handover command message contains an indicator to apply the fourth or fifth embodiment proposed in the present disclosure to handover, the transmitting PDCP entity may perform one or more of the following procedures in embodiment 4-1.
1. Since data transmission to the source base station and the target base station is continuously performed to minimize the data interruption time, the transmitting PDCP entity does not initialize a window variable (e.g., tx_next) for the UM DRB.
2. If a handover command message is received from the source base station, the terminal may set a window state variable (e.g., tx_next) to an initial value for the SRB or may release the SRB for the source base station since the terminal no longer transmits and receives RRC messages to and from the source base station. In addition, the terminal may set a window state variable (e.g., tx_next) to an initial value for the SRB of the second bearer for the target base station.
3. If a handover command message is received from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRB because it is no longer necessary to send and receive RRC messages to and from the source base station (since the data is a generated RRC message intended for the source base station, the terminal discards the data to avoid sending it to the target base station).
As another method, if the terminal cannot perform handover to the target base station, the transmitting PDCP entity may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message through the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing a transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., tx_next) to an initial value, thereby preventing a gap in PDCP sequence number from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.
4. The transmitting PDCP entity may store and prepare new security keys and new ciphering algorithms received from an upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may continue to apply a security key and ciphering algorithm, which were used before receiving the new security key and ciphering algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
5. The transmitting PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may continue to apply the security key and the integrity protection algorithm, which were used before receiving the new security key and the integrity protection algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
6. The transmitting PDCP entity may transmit a PDCP status report to the source base station when necessary, configured, or indicated, or at any time, thereby reporting a current transmission/reception status of data (e.g., successful or unsuccessful data reception).
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents of the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may apply a user data compression configuration to the target base station and may initialize the buffer.
The receiving PDCP entity may perform one or more of the following procedures if an upper layer entity (e.g., RRC entity) requests the 4-1 th embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the 4-1 th embodiment of the PDCP entity procedure when the terminal receives a handover command message or an RRC reconfiguration message.
As another method, if the handover command message contains an indicator indicating the fourth embodiment or the fifth embodiment proposed for handover in the present disclosure, the accepting PDCP entity may perform one or more of the following procedures in embodiment 4-1.
1. If a handover command message is received from the source base station, since the terminal no longer transmits and receives RRC messages to and from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRB (the data is discarded because it is an RRC message received from the source base station).
In addition, if the reordering timer is running, the terminal may stop the reordering timer. Alternatively, the terminal may release the SRB for the source base station. In addition, the terminal may set window variables (e.g., rx_next and rx_ DELIV) to initial values for the SRB of the second bearer for the target base station, and may stop the reordering timer if the reordering timer is running.
As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message to the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing a transmission delay due to the handover failure. As another method, the receiving PDCP entity may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., rx_next) to an initial value, thereby preventing a gap in PDCP sequence number from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.
2. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, it is not necessary to separately process the stored data for the UM DRB.
3. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, the receiving PDCP entity does not set window state variables (e.g., rx_next and rx_ DELIV) to initial values for the UM DRB.
4. The receiving PDCP entity may store and prepare new security keys and new ciphering algorithms received from an upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the receiving PDCP entity may continue to apply a security key and ciphering algorithm, which were used before receiving the new security key and ciphering algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
5. The receiving PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data. In addition, the receiving DCP entity may continue to apply the security key and integrity protection algorithm used prior to receiving the new security key and integrity protection algorithm from the upper layer entity to the PDCP entity with the first bearer of the Yu Yuanji station and to the data.
6. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of the transmission data to and reception data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of the data for which successful delivery has been confirmed.
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents of the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may apply a user data compression configuration to the target base station and may initialize the buffer.
The transmitting PDCP entity of the terminal may perform the 4-2 th embodiment if the upper layer entity (e.g., RRC entity) requests the 4-2 th embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, and in particular, one or more of the following procedures.
1. The transmitting PDCP entity may apply the new security key and the new ciphering algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the source base station first bearer before receiving the new security key and ciphering algorithm from the upper layer entity.
As another method, the transmitting PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
2. The transmitting PDCP entity may apply the new security key and the new integrity verification algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may release or discard the security key and the integrity verification algorithm applied to the PDCP entity of the source base station first bearer before receiving the new security key and the ciphering algorithm from the upper layer entity.
As another method, the transmitting PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
3. The transmitting PDCP entity may transmit a PDCP status report to the source base station or the target base station when necessary, configured, or indicated, or at any time, thereby reporting a current transmission/reception status of data (e.g., successful or unsuccessful data reception).
4. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs) to which PDCP sequence numbers have been allocated (after discarding all existing stored PDCP PDUs) but which have not yet been transmitted to a lower layer entity as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the transmitting PDCP entity does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or ciphering procedure again, configures a PDCP header, and transmits it to a lower layer entity.
5. As for the AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data (or PDCP sequence number) in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before the third condition is met or before receiving RRC message) starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not confirmed its successful delivery (after discarding all existing stored PDCP PDUs). In addition, the transmitting PDCP entity may perform an integrity procedure or a ciphering procedure again, configure a PDCP header, and may transmit it to a lower layer entity, thereby performing retransmission or transmission. That is, the transmitting PDCP entity may perform retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
As another method, when performing retransmission, the transmitting PDCP entity may perform retransmission only on data for which a lower layer entity (e.g., RLC entity) has not confirmed successful delivery. More specifically, as for the AM DRB, the transmitting PDCP entity (after discarding all stored PDCP PDUs to be transmitted to the source base station through the first protocol entity previously connected to the PDCP entity) may release a lower layer entity (e.g., RLC entity or MAC entity) that is the first protocol entity for transmitting data to the source base station. The transmitting PDCP entity may perform a new header or data compression procedure by applying a security key or header compression (or data compression) protocol context corresponding to the target base station in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before a third condition is met or before an RRC message is received) from a lower layer entity (e.g., RLC entity) which is a first protocol entity for transmitting data to the source base station, may perform an integrity or ciphering procedure again, may configure a PDCP header, and may transmit it to a lower layer entity which is a second protocol entity for transmitting data to the target base station, thereby performing retransmission or transmission. That is, the transmitting PDCP entity may perform retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
As another method, when performing retransmission, the transmitting PDCP entity transmits only data, of which the lower layer entity (e.g., RLC entity) as a first protocol entity for transmitting data to the source base station has not confirmed its successful delivery, to the lower layer entity as a second protocol entity for transmitting data to the target base station, thereby performing selective retransmission. As another method, the transmission or retransmission operation may be performed after releasing a lower layer entity (e.g., RLC entity) which is a first protocol entity for transmitting data to the source base station.
6. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.
The receiving PDCP entity of the terminal may perform the 4-2 th embodiment if the upper layer entity (e.g., RRC entity) requests the 4-2 th embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, and in particular, one or more of the following procedures.
1. If data (e.g., PDCP PDUs) is received from a lower layer entity (e.g., RLC entity) due to re-establishment of the lower layer entity, the receiving PDCP entity processes the data.
2. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, it is not necessary to separately process the stored data for the UM DRB.
3. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, the receiving PDCP entity does not set window state variables (e.g., rx_next and rx_ DELIV) to initial values for the AM DRB or the UM DRB.
4. The receiving PDCP entity may apply the new security key and the new ciphering algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and ciphering algorithm from the upper layer entity. As another method, the receiving PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink.
As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
5. The receiving PDCP entity may apply the new security key and the new integrity verification algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and integrity verification algorithm from the upper layer entity.
As another method, the receiving PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
6. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of transmission data to and reception data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of the data for which successful delivery has been confirmed.
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.
The third condition may be one of the following conditions.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal releases the connection with the source base station and releases the first protocol entity
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the third condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the third condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the third condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
If the third condition is not satisfied in the above step, the terminal may repeatedly check the third condition while continuing the existing procedure.
Hereinafter, the present disclosure proposes a fifth embodiment supporting the PDCP entity procedure for minimizing the handover procedure for data interruption time proposed in the present disclosure.
In a fifth embodiment of the PDCP entity procedure set forth in the present disclosure, specific operations of transmitting and receiving PDCP entities are as follows. The fifth embodiment may be referred to as "PDCP continuation" or another name. In addition, the fifth embodiment may be configured as the 5-1 th embodiment and the 5-2 th embodiment.
In a fifth embodiment of the PDCP entity procedure of the present disclosure, in the PDCP entity structure shown in fig. 11, each of the lower layer PDCP entities 1121 and 1122 can perform a header compression procedure on data to be transmitted based on different header compression protocol contexts (e.g., ROHC contexts), and can encrypt the procedure using different security keys.
Specifically, the first lower layer PDCP entity 1121 may apply a header compression procedure to data (e.g., PDCP SDUs) received from an upper layer based on a first header compression protocol context (e.g., ROHC context), and may encrypt the data using a first security key (a security key configured from a source base station or a target base station). In addition, the second lower layer PDCP entity 1122 may apply a header compression procedure to data (e.g., PDCP SDUs) received from an upper layer based on a second header compression protocol context (e.g., ROHC context), and may encrypt the data using a second security key (a security key configured from a source base station or a target base station). The two lower layer PDCP entities may perform a header compression procedure and a ciphering procedure in parallel, thereby reducing data processing time and data interruption time that may occur during handover.
In a fifth embodiment of the PDCP entity procedure of the present disclosure, referring to the PDCP entity structure shown in fig. 11, the lower layer PDCP entities 1121 and 1122 may perform a decryption process on data to be received using different security keys and may perform a header decompression process using different header compression protocol contexts (e.g., ROHC contexts).
Specifically, the first lower layer PDCP entity 1121 may apply a header decompression procedure to data (e.g., PDCP SDUs) received from the lower layer entity based on a first header compression protocol context (e.g., ROHC context), and may decrypt the data using a first security key (a security key configured from a source base station or a target base station). In addition, the second lower layer PDCP entity 1122 may apply a header decompression procedure to data (e.g., PDCP SDUs) received from the lower layer entity based on a second header compression protocol context (e.g., ROHC context), and may decrypt the data using a second security key (a security key configured from the source base station or the target base station). The two lower layer PDCP entities may perform a header decompression procedure and a decryption procedure in parallel, thereby reducing a data processing time and a data interruption time that may occur during handover.
In the above PDCP entity structure, if an upper layer entity (e.g., RRC entity) requests the 5-1 th embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the 5-1 th embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "RRCReconfiguration" message, the transmitting PDCP entity may perform one or more of the following procedures.
As another method, if the handover command message includes an indicator indicating the fourth embodiment or the fifth embodiment proposed for handover in the present disclosure, the transmitting PDCP entity may perform one or more of the following processes in embodiment 5-1.
1. Since data transmission to the source base station and the target base station is continuously performed to minimize the data interruption time, the transmitting PDCP entity does not initialize a window variable (e.g., tx_next) for the UM DRB.
2. If a handover command message is received from the source base station, the terminal may set a window state variable (e.g., tx_next) to an initial value for the SRB or may release the SRB for the source base station since the terminal no longer transmits and receives RRC messages to and from the source base station. In addition, the terminal may also set a window state variable (e.g., tx_next) to an initial value for the SRB of the second bearer for the target base station.
3. If a handover command message is received from the source base station, the terminal may discard all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRB because it is no longer necessary to send and receive RRC messages to and from the source base station (since the data is a generated RRC message intended for the source base station, the terminal discards the data to avoid sending it to the target base station).
As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message to the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing a transmission delay due to the handover failure. As another method, the terminal may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., tx_next) to an initial value, thereby preventing a gap in PDCP sequence number from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.
4. The transmitting PDCP entity may store and prepare the new security key and the new ciphering algorithm received from the upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity (e.g., second lower layer PDCP entity) for the second bearer of the target base station and then to the data. In addition, the transmitting PDCP entity may continue to apply a security key and ciphering algorithm, which were used before receiving the new security key and ciphering algorithm from the upper layer entity, to the PDCP entity (e.g., the first lower layer ODCO entity) with the first bearer of the Yu Yuanji station and then to the data.
5. The transmitting PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity (e.g., second lower layer PDCP entity) for the second bearer of the target base station and then to the data. In addition, the transmitting PDCP entity may continue to apply a security key and an integrity protection algorithm, which are used before receiving the new security key and the integrity protection algorithm from the upper layer entity, to the PDCP entity (e.g., the first lower layer PDCP entity) with the first bearer of the Yu Yuanji station and to the data.
6. The transmitting PDCP entity may transmit a PDCP status report to the source base station when necessary, configured, or indicated, or at any time, thereby reporting a current transmission/reception status of data (e.g., successful or unsuccessful data reception).
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents for the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may apply a user data compression configuration to the target base station and may initialize the buffer.
If an upper layer entity (e.g., RRC entity) requests the 5-1 th embodiment of the PDCP entity procedure for a certain bearer, or if an indicator indicates the 5-1 th embodiment of the PDCP entity procedure when the terminal receives a handover command message or a "RRCReconfiguration" message, the receiving PDCP entity may perform one or more of the following procedures.
As another method, if the handover command message includes an indicator indicating the fourth embodiment or the fifth embodiment proposed for handover in the present disclosure, the receiving PDCP entity may perform one or more of the following processes in embodiment 5-1.
1. If the handover command message does not continue to use an indicator of the header compression protocol for each bearer of the UM DRB and the AM DRB, the terminal may initialize the header compression protocol in a PDCP entity (e.g., a second lower layer PDCP entity) of the second bearer and may start the header compression protocol in a unidirectional (U) mode of an Initialization and Refresh (IR) state.
If the handover command message has an indicator to continue using the header compression protocol, the terminal may use the header compression protocol of the PDCP entity (e.g., the first lower layer PDCP entity) for the first bearer of the source base station to continue using the header compression protocol, or may perform a header decompression procedure. In addition, the terminal can continue to use the header compression protocol context without initializing the header compression protocol in the PDCP entity (e.g., the first lower layer PDCP entity) for the first bearer of the source base station.
2. If the handover command message is received from the source base station, since the terminal no longer transmits and receives RRC messages to and from the source base station, the receiving PDCP entity discards all data (e.g., PDCP SDUs or PDCP PDUs) stored for the SRB (the data is discarded because it is an RRC message received from the source base station). In addition, if the reordering timer is running, the terminal may stop the timer. Alternatively, the terminal may release the SRB for the source base station. In addition, the terminal may set window variables (e.g., rx_next and rx_ DELIV) to initial values for the SRB of the second bearer for the target base station, and may stop the reordering timer if the reordering timer is running.
As another method, if the terminal cannot perform handover to the target base station, the terminal may transmit a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration request message to the SRB of the source base station while maintaining the SRB connection with the source base station, thereby reducing a transmission delay due to the handover failure. As another method, the receiving PDCP entity may discard data (PDCP SDU or PDCP PDU) stored in the SRB while maintaining the SRB connection with the above source base station, and may set a window state variable (e.g., rx_next) to an initial value, thereby preventing a gap in PDCP sequence number from occurring later when a handover failure message, an RRC connection reestablishment message, or an RRC connection restoration message is transmitted to the SRB of the source base station.
3. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, it is not necessary to separately process the stored data for the UM DRB.
4. If a reordering timer is running for the SRB, the terminal may stop and reset the timer. As for the AM DRB, if there is no indicator for the PDCP entity { e.g., second (or first) lower layer PDCP entity } corresponding to the second (or first) bearer of the target (or source) base station to continue using the header decompression protocol, the receiving PDCP entity may perform a header decompression procedure on stored data (e.g., PDCP SDU) using an existing header compression protocol context. Thereafter, the receiving PDCP entity may initialize a header compression protocol context.
5. If there is no indicator for the UM DRB and the AM DRB to continue using the header decompression protocol, the receiving PDCP entity initializes the downlink header decompression protocol for the PDCP entity { e.g., the second (or first) lower layer PDCP entity } corresponding to the second (or first) bearer of the target (or source) base station and starts in a unidirectional (U) mode of a no-context (NC) state.
6. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, the receiving PDCP entity does not set window state variables (e.g., rx_next and rx_ DELIV) to initial values for the UM DRB.
7. The receiving PDCP entity may store and prepare the new security key and the new ciphering algorithm received from an upper layer entity (e.g., RRC entity) and may apply them to the PDCP entity for the second bearer of the target base station and to the data, or may perform deciphering. In addition, the receiving PDCP entity may continue to apply a security key and ciphering algorithm, which were used before receiving the new security key and ciphering algorithm from the upper layer entity, to the PDCP entity with the first bearer of the Yu Yuanji station and to the data, or may perform deciphering.
8. The receiving PDCP entity may store and prepare the new security key and the new integrity protection algorithm received from the upper layer entity (e.g., RRC entity), and may apply them to the PDCP entity for the second bearer of the target base station and to the data, or may perform integrity protection. In addition, the receiving DCP entity may continue to apply the security key and the integrity protection algorithm used before receiving the new security key and the integrity protection algorithm from the upper layer entity to the PDCP entity with the first bearer of the Yu Yuanji station and to the data, or may perform the integrity protection.
9. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status (e.g., successful or unsuccessful data reception) of the transmission data to and from the source or target base station and may reflect it on the data transmission or retransmission by the transmitting PDCP entity for the source or target base station. For example, the receiving PDCP entity may not perform transmission or retransmission of the data for which successful delivery has been confirmed.
10. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. As another method, the terminal may initialize the buffer if there is no indicator for continuing to use the buffer contents for the user data compression process. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may apply a user data compression configuration to the target base station and may initialize the buffer.
The transmitting PDCP entity of the terminal may perform the 5-2 th embodiment if the upper layer entity (e.g., RRC entity) requests the 5-2 th embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, and in particular, one or more of the following procedures.
1. If the handover command message does not continue to use an indicator of the header compression protocol for each bearer of the UM DRB and the AM DRB, the terminal may initialize the header compression protocol in a PDCP entity (e.g., a second lower layer PDCP entity) for a second bearer of the target base station and may start in a unidirectional (U) mode of an Initialization and Refresh (IR) state.
If the handover command message has an indicator to continue using the header compression protocol, the terminal may use the header compression protocol in the PDCP entity (e.g., the first lower layer PDCP entity) for the first bearer of the source base station to continue using the header compression protocol, or may perform a header decompression procedure.
2. The transmitting PDCP entity may apply the new security key and the new ciphering algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the source base station first bearer before receiving the new security key and ciphering algorithm from the upper layer entity.
As another method, the transmitting PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
3. The transmitting PDCP entity may apply the new security key and the new integrity verification algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, the transmitting PDCP entity may release or discard the security key and the integrity verification algorithm applied to the PDCP entity of the source base station first bearer before receiving the new security key and the ciphering algorithm from the upper layer entity.
As another method, the transmitting PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the transmitting PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
4. The transmitting PDCP entity may transmit a PDCP status report to the source base station or the target base station when necessary, configured, or indicated, or at any time, thereby reporting a current transmission/reception status of data (e.g., successful or unsuccessful data reception).
5. As for the UM DRB, the transmitting PDCP entity regards data (e.g., PDCP SDUs) to which PDCP sequence numbers have been allocated (after discarding all existing stored PDCP PDUs) but which have not yet been transmitted to a lower layer entity as data received from an upper layer (e.g., an SDAP entity or a TCP/IP entity), and transmits the data in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment. In addition, the terminal does not restart the data discard timer. Specifically, the transmitting PDCP entity performs a new header compression procedure on data (PDCP SDU), performs an integrity procedure or ciphering procedure again, configures a PDCP header, and transmits it to a lower layer entity.
6. As for the AM DRB, the transmitting PDCP entity may perform a new header compression procedure on data (or PDCP sequence number) in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before the third condition is met or before receiving RRC message) starting from the first data (e.g., PDCP SDU) for which the lower layer entity (e.g., RLC entity) has not confirmed its successful delivery (after discarding all existing stored PDCP PDUs). In addition, the transmitting PDCP entity may perform an integrity procedure or a ciphering procedure again, configure a PDCP header, and may transmit it to a lower layer entity, thereby performing retransmission or transmission. That is, the transmitting PDCP entity may perform retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
As another method, when performing retransmission, the transmitting PDCP entity may perform retransmission only on data for which a lower layer entity (e.g., RLC entity) has not confirmed successful delivery. Alternatively, the transmitting PDCP entity may perform selective retransmission based on the PDCP status report. More specifically, as for the AM DRB, the transmitting PDCP entity (after discarding all stored PDCP PDUs to be transmitted to the source base station through the first protocol entity previously connected to the PDCP entity) may release a lower layer entity (e.g., RLC entity or MAC entity) that is the first protocol entity for transmitting data to the source base station. The transmitting PDCP entity may perform a new header or data compression procedure by applying a security key or header compression (or data compression) protocol context corresponding to the target base station in ascending order of a count value (or PDCP sequence number) allocated before PDCP re-establishment (or before a third condition is met or before an RRC message is received) from a lower layer entity (e.g., RLC entity) which is a first protocol entity has not confirmed that it successfully transmits first data (e.g., PDCP SDU), may perform an integrity or ciphering procedure again, may configure a PDCP header, and may transmit it to a lower layer entity which is a second protocol entity for transmitting data to the target base station, thereby performing retransmission or transmission. That is, the transmitting PDCP entity may perform retransmission by accumulating data from the first data for which successful delivery has not been confirmed yet.
As another method, when performing retransmission, the transmitting PDCP entity transmits only data, of which the lower layer entity (e.g., RLC entity) as a first protocol entity for transmitting data to the source base station has not confirmed its successful delivery, to the lower layer entity as a second protocol entity for transmitting data to the target base station, thereby performing selective retransmission. As another method, the transmission or retransmission operation may be performed after releasing a lower layer entity (e.g., RLC entity or MAC entity) which is a first protocol entity for transmitting data to the source base station.
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.
The receiving PDCP entity of the terminal may perform the 5-2 th embodiment if the upper layer entity (e.g., RRC entity) requests the 5-2 th embodiment of the PDCP entity procedure for a certain bearer, or if a third condition is satisfied, and in particular, one or more of the following procedures.
1. If data (e.g., PDCP PDUs) is received from a lower layer entity (e.g., RLC entity) due to re-establishment of the lower layer entity, the receiving PDCP entity processes the data.
2. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, it is not necessary to separately process the stored data for the UM DRB.
3. Since data continues to be received from the source base station or the target base station without interrupting transmission and reception of the data, the receiving PDCP entity does not set window state variables (e.g., rx_next and rx_ DELIV) to initial values for the AM DRB or the UM DRB.
4. The receiving PDCP entity may apply the new security key and the new ciphering algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and ciphering algorithm from the upper layer entity.
As another method, the receiving PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
5. The receiving PDCP entity may apply the new security key and the new integrity verification algorithm received and stored from an upper layer entity (e.g., RRC entity) to the PDCP entity for the second bearer of the target base station and to the data. In addition, if downlink data is no longer received from the source base station, the receiving PDCP entity may release or discard the security key and ciphering algorithm applied to the PDCP entity of the first bearer of the source base station before receiving the new security key and integrity verification algorithm from the upper layer entity.
As another method, the receiving PDCP entity may release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station in the uplink, and may hold the security key and ciphering algorithm and apply them to data received in the downlink. As another method, the receiving PDCP entity may discard or release the security key and ciphering algorithm of the PDCP entity applied to the first bearer of the source base station upon completely releasing the connection (e.g., downlink data reception) with the source base station, and may continue to apply it to data received from or transmitted to the source base station until the connection with the source base station is completely released.
6. Upon receiving the PDCP status report, the receiving PDCP entity may read the current status of transmission data to and reception data from the source or target base station (e.g., successful or unsuccessful data reception) and may reflect it on transmission or retransmission of the data. For example, the receiving PDCP entity may not perform transmission or retransmission of the data for which successful delivery has been confirmed.
7. If a user data compression procedure (e.g., uplink data compression) is indicated to the terminal, the terminal may initialize a buffer for the user data compression procedure for the source base station or the target base station. As another method, if dictionary information is predefined, the buffer may be initialized using dictionary information. In addition, the terminal may release the user compression configuration for the source base station and may release the buffer.
The third condition may be one of the following conditions.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer and receives a random access response
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and sends a handover complete message to the target base station
-When the terminal completes the procedure of random access to the target base station through the entity of the second bearer and initially transmits data using PUCCH or PUSCH uplink transmission resources
-When the base station configures a separate timer for the terminal by means of RRC message and the timer expires
* The timer may be started when the terminal receives a handover command message from the source base station, when the terminal starts random access to the target base station (when a preamble is transmitted), when the terminal receives a random access response from the target base station, when the terminal transmits a handover complete message to the target base station, or when the terminal initially transmits data using PUCCH or PUSCH uplink transmission resources.
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, and configures and transmits a handover complete message to the target base station and when successful transmission of the handover complete message is identified by the MAC entity (HARQ ACK) or RLC entity (RLC ACK)
-When the terminal performs a procedure of random access to the target base station through the entity of the second bearer, receives the random access response, configures and sends a handover complete message to the target base station, and receives uplink transmission resources initially allocated by the target base station or receives an initial indication of the uplink transmission resources
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to switch uplink to the target base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the target base station to release the connection with the source base station
-When the terminal receives an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } from the source base station to release the connection with the source base station
-When the terminal releases the connection with the source base station and releases the first protocol entity
-When the terminal fails to receive downlink data from the source base station within a predetermined period of time
-When the terminal successfully completes the procedure of random access to the target base station through the entity of the second bearer and receives the first uplink transmission resources allocated by the target base station or an indication of the first uplink transmission resources
* For example, more specifically, if the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Free Random Access (CFRA) { for example, if a predetermined preamble or UE cell identifier (e.g., C-RNTI) } is allocated
* The terminal may determine that the random access procedure is successfully completed when the terminal transmits a predetermined preamble to a cell of the target base station and receives a Random Access Response (RAR) message. Accordingly, when the terminal receives the first uplink transmission resource allocated, included or indicated in the random access response message, the terminal may determine that the third condition is satisfied.
* If the terminal is instructed to perform random access to the target base station by receiving a handover command message from the source base station, and if the instructed random access is Contention Based Random Access (CBRA) { e.g., if a predetermined preamble or UE cell identifier (e.g., C-RNTI) is not allocated)
* When the terminal transmits a preamble (e.g., any preamble) to a cell of the target base station, receives a Random Access Response (RAR) message, transmits a message 3 (e.g., a handover complete message) using uplink transmission resources allocated, included or indicated in the random access response message, and receives a MAC CE (contention resolution MAC CE) indicating that contention has been resolved from the target base station, the terminal may determine that the procedure of the random access target base station is successfully completed. Accordingly, thereafter, when the terminal monitors the PDCCH and initially receives an uplink transmission resource or an indication of the uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal, the terminal may determine that the third condition is satisfied. As another method, if the size of the uplink transmission resource allocated by the random access response message is sufficient for the terminal to further transmit uplink data together with the message 3, the terminal may determine that the initial uplink transmission resource has been received, thereby determining that the third condition is satisfied.
In case the handover command message received by the terminal indicates a handover method (RACH-free handover) that does not require a random access procedure
* If the handover command message includes uplink transmission resources to the target base station
* When the terminal transmits message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource of the target base station and receives the UE identity confirmation MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
* In case the handover command message does not include uplink transmission resources for the target base station
* When the terminal receives an uplink transmission resource through a PDCCH corresponding to a C-RNTI of the terminal by monitoring a PDCCH of a target base station (or cell), or when the terminal transmits a message 3 (e.g., a handover complete message or a "RRCReconfigurationComplete" message) using the uplink transmission resource and receives a UE identity acknowledgement MAC CE from the base station, the terminal may determine that the random access procedure is successfully completed, thereby determining that the third condition is satisfied. As another method, the terminal may determine that the third condition is satisfied when the terminal receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of the terminal by monitoring the PDCCH after the random access procedure is successfully completed.
If the third condition is not satisfied in the above step, the terminal may repeatedly check the third condition while continuing the existing procedure.
The embodiment of the PDCP entity procedure set forth in the present disclosure can be extended and applied to a structure in which an upper layer PDCP entity performs a header compression procedure on data transmitted in the PDCP entity structure shown in fig. 11 using a common header compression protocol context (e.g., ROHC context), and in which respective lower layer PDCP entities 1121 and 1122 perform a ciphering procedure on the data using different security keys.
In addition, the embodiment of the PDCP entity procedure set forth in the present disclosure can be extended and applied to a structure in which respective lower layer PDCP entities 1121 and 1122 perform a decryption procedure on data received in the PDCP entity structure shown in fig. 11 using different security keys, and in which an upper layer PDCP entity performs a header decompression procedure on the data using a common header compression protocol context (e.g., ROHC context).
According to a specific embodiment of the PDCP entity set forth in the present disclosure, the following different procedures may be performed depending on the handover type indicated by the handover command message received by the terminal.
-If the handover type indicated in the handover command message received by the terminal from the source base station is a first handover (e.g. normal handover procedure)
* The terminal may perform the first embodiment (e.g., PDCP re-establishment) of the PDCP entity proposed in the present disclosure.
If the type of handover indicated in the handover command message received by the terminal from the source base station is a second handover (e.g. the handover method of the fourth or fifth embodiment presented in this disclosure)
* The terminal may perform the third, fourth, or fifth embodiment of the PDCP entity (e.g., PDCP entity continuation) proposed in the present disclosure.
In addition, in a case where the source base station in the present disclosure instructs the terminal to perform handover using the embodiment set forth in the present disclosure, the source base station may start forwarding data to the target base station when the following fifth condition is satisfied. The fifth condition may mean that one or more of the following conditions are satisfied.
When the terminal receives an indication from the target base station that the handover has been successfully completed
-When a handover command message is sent to the terminal
-When a handover command message is sent to the terminal and successful delivery of the handover command message (HARQ ACK, NACK, RLC ACK or NACK) is acknowledged
-When the source base station receives from the terminal an indication { e.g. RRC message (e.g. "RRCReconfiguration" message), MAC CE, RLC control PDU or PDCP control PDU } to release the connection with the source base station
-When a predetermined timer is driven after sending a handover command message to the terminal and then the timer expires
-When an acknowledgement (HARQ ACK, NACK, RLC ACK or NACK) of successful transmission of downlink data is not received from the terminal within a predetermined time
Fig. 13 shows a structure of a terminal to which the embodiment can be applied.
Referring to fig. 13, the terminal includes a Radio Frequency (RF) processor 1310, a baseband processor 1320, a storage unit 1330, and a controller 1340.
The RF processor 1310 performs functions of transmitting and receiving signals through a wireless channel, such as frequency band conversion and amplification of signals. That is, the RF processor 1310 up-converts the baseband signal supplied from the baseband processor 1320 into an RF band signal, thereby transmitting the RF band signal through the antenna, and down-converts the RF band signal received through the antenna into the baseband signal. For example, the RF processor 1310 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and the like. Although only one antenna is shown in fig. 13, the terminal may have a plurality of antennas. In addition, the RF processor 1310 may include a plurality of RF chains. In addition, the RF processor 1310 may perform beamforming. To perform beamforming, the RF processor 1310 may adjust the phase and amplitude of signals transmitted and received through multiple antennas or antenna elements. In addition, the RF processor may perform MIMO, and may receive multiple layers when performing MIMO operation. The RF processor 1310 may perform receive beam scanning by appropriately setting a plurality of antennas or antenna elements under the control of a controller, or may adjust the direction and beam width of the receive beam so that the receive beam is coordinated with the transmit beam.
The baseband processor 1320 performs the function of converting between baseband signals and bit strings according to the physical layer specification of the system. For example, in the case of data transmission, the baseband processor 1320 encodes and modulates a transmission bit string, thereby generating complex symbols. In addition, when receiving data, the baseband processor 1320 demodulates and decodes the baseband signal provided from the RF processor 1310, thereby recovering the received bit string. For example, in case of applying an Orthogonal Frequency Division Multiplexing (OFDM) scheme, when transmitting data, the baseband processor 1320 generates complex symbols by encoding and modulating a transmission bit string, maps the complex symbols to subcarriers, and then configures OFDM symbols through an Inverse Fast Fourier Transform (IFFT) operation and Cyclic Prefix (CP) insertion. In addition, when receiving data, the baseband processor 1320 divides a baseband signal provided from the RF processor 1310 into OFDM symbol units, restores a signal mapped to subcarriers through a Fast Fourier Transform (FFT) operation, and then restores a received bit string through demodulation and decoding.
The baseband processor 1320 and the RF processor 1310 transmit and receive signals as described above. Accordingly, the baseband processor 1320 and the RF processor 1310 may be referred to as a "transmitter," receiver, "" transceiver, "or" communication unit. In addition, at least one of baseband processor 1320 and RF processor 1310 may include a plurality of communication modules to support a plurality of different radio access technologies. In addition, at least one of the baseband processor 1320 and the RF processor 1310 may include different communication modules to process signals of different frequency bands. For example, the different radio access technologies may include LTE networks, NR networks, and so on. In addition, the different frequency bands may include an ultrahigh frequency (SHF) (e.g., 2.5Ghz or 5 Ghz) frequency band and a millimeter wave (e.g., 60 Ghz) frequency band.
The storage unit 1330 stores data such as basic programs, application programs, and configuration information for the operation of the terminal. The storage unit 1330 provides the stored data in response to a request from the controller 1340.
A controller 1340 controls the overall operation of the terminal. For example, the controller 1340 transmits and receives signals through the baseband processor 1320 and the RF processor 1310. In addition, the controller 1340 records data in and reads data from the storage unit 1330. To this end, the controller 1340 may include at least one processor. For example, the controller 1340 may include a Communication Processor (CP) for controlling communication and an Application Processor (AP) for controlling upper layers such as an application program. In some embodiments, controller 1340 includes a multi-connection processor 1342.
Fig. 14 shows a block diagram of TRP in a wireless communication system to which the embodiment can be applied.
As shown in fig. 14, the base station includes an RF processor 1410, a baseband processor 1420, a backhaul transceiver 1430, a storage unit (or memory) 1440, and a controller 1450.
The RF processor 1410 performs functions of transmitting and receiving signals through a radio channel, such as frequency band conversion and amplification of signals. That is, the RF processor 1410 up-converts the baseband signal supplied from the baseband processor 1420 into an RF band signal, thereby transmitting the RF band signal through an antenna, and down-converts the RF band signal received through the antenna into the baseband signal. For example, the RF processor 1410 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and the like. Although only one antenna is shown in the figures, the first access node may have multiple antennas. In addition, the RF processor 1410 may include a plurality of RF chains. In addition, the RF processor 1410 may perform beamforming. To perform beamforming, the RF processor 1410 may adjust the phase and amplitude of signals transmitted and received through multiple antennas or antenna elements. The RF processor may perform downlink MIMO operation by transmitting one or more layers.
The baseband processor 1420 performs a function of converting between baseband signals and bit strings according to a physical layer specification of the first radio access technology. For example, in the case of data transmission, baseband processor 1420 encodes and modulates a transmission bit string, thereby generating complex symbols. In addition, when receiving data, the baseband processor 1420 demodulates and decodes the baseband signal provided from the RF processor 1410, thereby recovering a received bit string. For example, in case of applying the OFDM scheme, when transmitting data, the baseband processor 1420 generates complex symbols by encoding and modulating a transmission bit string, maps the complex symbols to subcarriers, and then configures the OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processor 1420 divides a baseband signal supplied from the RF processor 1410 into OFDM symbol units, restores a signal mapped to subcarriers through an FFT operation, and then restores a received bit string through demodulation and decoding. The baseband processor 1420 and the RF processor 1410 transmit and receive signals as described above. Accordingly, the baseband processor 1420 and the RF processor 1410 may be referred to as a "transmitter," receiver, "" transceiver, "" communication unit, "or" wireless communication unit.
The transceiver 1430 provides an interface for performing communication with other nodes in the network.
The storage unit 1440 stores data such as basic programs, application programs, and configuration information for the operation of the main base station. Specifically, the storage unit 1440 may store information on bearers allocated to the connected terminals, measurement results reported from the connected terminals, and the like. In addition, the storage unit 1440 may store information as a standard for determining whether multiple connections are provided to a terminal or released. In addition, the storage unit 1440 provides the stored data in response to a request from the controller 1450.
The controller 1450 controls the overall operation of the main base station. For example, the controller 1450 transmits and receives signals through the baseband processor 1420 and the RF processor 1410 or the backhaul transceiver 1430. In addition, the controller 1450 records data in and reads data from the storage unit 1440. To this end, the controller 1450 may include at least one processor. In some embodiments, controller 1450 includes a multi-connection processor 1452.
Meanwhile, the order in which the methods of the present disclosure are explained with reference to the drawings does not necessarily correspond to the order in which the methods are performed, and the order thereof may be changed or performed in parallel.
Alternatively, only some elements may be included in the drawings describing the methods of the present disclosure and some elements omitted therefrom without departing from the scope of the present disclosure.
In addition, methods of the present disclosure may be performed in conjunction with some or all of the content included in various embodiments without departing from the scope of the present disclosure.
Further, the information contained in the messages of the present disclosure is intended to explain examples of the present disclosure, and some information may be omitted therefrom, or additional information may be included therein.
While the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. The disclosure is intended to embrace such alterations and modifications that fall within the scope of the appended claims.
Claims (12)
1. A method performed by a terminal in a communication system, the method comprising:
receiving a radio resource control, RRC, message from a first base station for handover to a second base station, the RRC message comprising configuration information for bearers for dual protocol stack handover;
Executing a random access process to the second base station, and executing uplink data transmission to the first base station until the random access process is successfully completed;
Switching uplink data transmission to the second base station after the random access procedure is completed and performing uplink data transmission to the second base station based on the switching, and
Performing downlink data reception on downlink data from the first base station until connection with the first base station is released by a release command from the second base station,
Wherein after the handover, continuing to perform uplink transmission of feedback information associated with the downlink data to the first base station, and
Wherein the feedback information associated with the downlink data includes at least one of hybrid automatic repeat request, HARQ, feedback information, radio link control, RLC, status report, or robust header compression, ROHC, feedback information.
2. The method of claim 1, further comprising:
Generating a medium access control, MAC, entity for the second base station;
establishing a radio link control, RLC, entity for the second base station for the bearer, and
Reconfiguring a packet data convergence protocol PDCP entity for the bearer with secure and robust header compression ROHC header decompression functions for the first base station and the second base station, respectively.
3. The method according to claim 1,
Wherein the medium access control MAC entity for the first base station is not reset.
4. The method according to claim 1,
Wherein the state variables of the packet data convergence protocol PDCP entity are not reset, and
Wherein the bearer is a radio link control unacknowledged mode RLC-UM bearer or an RLC acknowledged mode RLC-AM bearer.
5. A method performed by a first base station in a communication system, the method comprising:
transmitting a radio resource control, RRC, message for handover to a second base station to the terminal, the RRC message including a configuration for bearers for dual protocol stack handover;
Performing downlink data transmission of downlink data to the terminal until the connection between the terminal and the first base station is released by a release command from the second base station, and
Performing uplink data reception from the terminal until the random access procedure to the second base station is successfully completed;
Wherein after the terminal switches uplink data transmission to the second base station, uplink reception of feedback information associated with downlink data is continued from the terminal, and
Wherein the feedback information associated with the downlink data includes at least one of hybrid automatic repeat request, HARQ, feedback information, radio link control, RLC, status report, or robust header compression, ROHC, feedback information.
6. The method according to claim 5,
Wherein the performing of uplink data reception from the terminal is stopped in response to successful completion of the random access procedure.
7. A terminal in a communication system, the terminal comprising:
Transceiver, and
A controller configured to:
receiving a radio resource control, RRC, message for handover to a second base station from the first base station via the transceiver, the RRC message including configuration information on bearers for dual protocol stack handover,
Performing a random access procedure to the second base station and performing uplink data transmission to the first base station via the transceiver until the random access procedure is successfully completed, switching uplink data transmission to the second base station after the random access procedure is completed and performing uplink data transmission to the second base station via the transceiver based on the switching, and
Performing downlink data reception on downlink data from the first base station via the transceiver until connection with the first base station is released by a release command from the second base station,
Wherein after the handover, continuing to perform uplink transmission of feedback information associated with the downlink data to the first base station, and
Wherein the feedback information associated with the downlink data includes at least one of hybrid automatic repeat request, HARQ, feedback information, radio link control, RLC, status report, or robust header compression, ROHC, feedback information.
8. The terminal of claim 7, wherein the controller is configured to:
Generating a medium access control MAC entity for said second base station,
Establishing a radio link control, RLC, entity for the second base station for the bearer, and
Reconfiguring a packet data convergence protocol PDCP entity for the bearer with secure and robust header compression ROHC header decompression functions for the first base station and the second base station, respectively.
9. The terminal according to claim 7,
Wherein the Medium Access Control (MAC) entity for the first base station is not reset.
10. The terminal according to claim 7,
Wherein the state variables of the packet data convergence protocol PDCP entity are not reset, and
Wherein the bearer is a radio link control unacknowledged mode RLC-UM bearer or an RLC acknowledged mode RLC-AM bearer.
11. A first base station in a communication system, the first base station comprising:
Transceiver, and
A controller configured to:
Transmitting a radio resource control, RRC, message for handover to the second base station to the terminal via said transceiver, the RRC message including a configuration of bearers for dual protocol stack handover,
Performing downlink data transmission of downlink data to the terminal via the transceiver until the connection between the terminal and the first base station is released by a release command from the second base station, and
Uplink data reception from the terminal is performed via the transceiver, until the random access procedure to the second base station is successfully completed,
Wherein after the terminal switches uplink data transmission to the second base station, continuing to perform uplink reception of feedback information associated with the downlink data from the terminal, and
Wherein the feedback information associated with the downlink data includes at least one of hybrid automatic repeat request, HARQ, feedback information, radio link control, RLC, status report, or robust header compression, ROHC, feedback information.
12. The first base station of claim 11,
Wherein the performing of uplink data reception from the terminal is stopped in response to successful completion of the random access procedure.
Applications Claiming Priority (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR10-2019-0035805 | 2019-03-28 | ||
| KR20190035805 | 2019-03-28 | ||
| KR10-2019-0046156 | 2019-04-19 | ||
| KR20190046156 | 2019-04-19 | ||
| KR10-2019-0115518 | 2019-09-19 | ||
| KR1020190115518A KR20200114994A (en) | 2019-03-28 | 2019-09-19 | Method and apparatus for handover without stopping of data transmission or reception in a next generation mobile communication system |
| PCT/KR2020/004358 WO2020197361A1 (en) | 2019-03-28 | 2020-03-30 | Method and apparatus for handover without interruption of transmission and reception of data in next-generation mobile communication system |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN113767671A CN113767671A (en) | 2021-12-07 |
| CN113767671B true CN113767671B (en) | 2025-02-25 |
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|---|---|---|---|---|
| WO2016140757A1 (en) * | 2015-03-04 | 2016-09-09 | Qualcomm Incorporated | Dual link handover |
| WO2017138977A1 (en) * | 2016-02-12 | 2017-08-17 | Intel IP Corporation | Systems and methods for reducing interruptions in data transmissions due to handover operations |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2016140757A1 (en) * | 2015-03-04 | 2016-09-09 | Qualcomm Incorporated | Dual link handover |
| WO2017138977A1 (en) * | 2016-02-12 | 2017-08-17 | Intel IP Corporation | Systems and methods for reducing interruptions in data transmissions due to handover operations |
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