WO2015020507A1

WO2015020507A1 - Method and apparatus for reordering pdcp in dual connectivity system

Info

Publication number: WO2015020507A1
Application number: PCT/KR2014/007456
Authority: WO
Inventors: 정명철; 권기범; 허강석; 안재현
Original assignee: 주식회사 팬택
Priority date: 2013-08-09
Filing date: 2014-08-11
Publication date: 2015-02-12

Abstract

The present invention relates to a method and an apparatus for reordering a packet data convergence protocol (PDCP) in a wireless communication system supporting dual connectivity. According to the present invention, provided is a method for reordering PDCP service data units (SDU) by a PDCP entity of user equipment (UE) to which dual connectivity between a master eNB and a secondary eNB is configured. According to the present invention, when the dual connectivity is configured to the user equipment, even if the PDCP PDUs are received non-sequentially by the PDCP entity of the user equipment, the PDCP SDUs can be reordered based on a timer, the PDCP SDUs can be delivered to an upper layer in ascending order, and transmission efficiency can be improved.

Description

Method and apparatus for rearranging PDCP in dual connectivity system

The present invention relates to wireless communication, and more particularly, to a method and apparatus for PDCP reordering in a wireless communication system supporting dual connectivity.

In particular areas, such as hot spots inside the cell, there is a great demand for communication, and in certain areas such as cell edges or coverage holes, the reception sensitivity of radio waves may be reduced. With the development of wireless communication technology, small cells, such as pico cells, within a macro cell for the purpose of enabling communication in areas such as hot spots, cell boundaries, and coverage holes. (Pico Cell), femto cell (Femto Cell), micro cell (Micro Cell), remote radio head (RRH), relay (relay), repeater (repeater) is installed together. Such a network is called a heterogeneous network (HetNet). In a heterogeneous network environment, a macro cell is a large coverage cell, and a small cell such as a femto cell and a pico cell is a small coverage cell. Compared to macro cells, small cells such as femto cells and pico cells use low power and are also referred to as low power networks (LPNs). Coverage overlap occurs between multiple macro cells and small cells in a heterogeneous network environment.

The terminal may configure dual connectivity through two or more base stations among the base stations configuring at least one serving cell. Dual connectivity is an operation in which the terminal consumes radio resources provided by at least two different network points (eg, macro base station and small base station) in a radio resource control connection (RRC_CONNECTED) mode. In this case, the at least two different network points may be connected by non-ideal backhaul.

In this case, one of the at least two different network points may be called a macro base station (or a master base station or an anchor base station), and the rest may be called small base stations (or secondary base stations or assisting base stations or slave base stations).

In general, a wireless communication system has a single flow structure in which a service is provided to a terminal through one radio bearer (RB) for one EPS bearer service. However, in a wireless communication system supporting dual connectivity, one EPS bearer may provide a service to a terminal through two RBs configured in a macro cell and a small cell instead of one RB. That is, the service may be provided to the terminal through multi-flow. In the above, one RB may be provided through only the macro cell, and the other RB may be configured through two base stations corresponding to the macro cell and the small cell. In other words, one RB may be configured in a single base station and the other RB may be configured in a bearer split into two base stations.

In the case of an RLC acknowlegdged mode (AMC), when a received RLC packet data unit (RDU PDU) is received out of order in downlink, the RLC entity reorders the RLC PDUs. In the case of RLC AM, the missing RLC PDU may be retransmitted at the receiver. The RLC entity reassembles an RLC Service Date Unit (SDU) based on the rearranged RLC PDUs and sequentially delivers them to a higher layer (ie, PDCP entity). In the case of RLC AM, sequential delivery is possible through reordering and retransmission of the RLC PDU. In other words, the PDCP entity should receive the RLC SDUs sequentially, except for re-establishment of the lower layer. However, in case of a UE configured with multi-flow, an RLC entity for a small base station and an RLC entity for a macro base station may be divided to receive each RLC PDU, and the RLC SDU may be delivered to a higher layer (ie, a PDCP layer). If the PDCP entity does not expect the sequential reception of the RLC SDU. Therefore, in case of a UE configured with multi-flow, a PDCP rearrangement method for ascending delivery of PDCP SDUs to a higher layer in a PDCP entity is required.

The present invention provides a method and apparatus for rearranging PDCP in a dual connectivity system.

Another technical problem of the present invention is to provide a method and apparatus for transmitting a PDCP SDU to an upper layer in an ascending order by a receiving end of a PDCP entity in a multiflow structure.

Another technical problem of the present invention is to perform PDCP rearrangement based on a timer in a multiflow structure.

According to an aspect of the present invention, in a Packet Data Convergence Protocol (PDCP) entity of a UE configured for dual connectivity with a macro base station (Macro eNB) and a small eNB (small eNB), multi-flow A method of reordering PDCP Service Data Units (SDUs) considering multi-flow is provided. The PDCP SDU rearrangement method, when sequentially receiving PDCP sequence number (PDCP SN) PD PD packet data units (PDUs), delivers a corresponding PDCP SDU to a higher layer and starts / restarts a rearrangement timer. And if the PDCP PDUs of PDCP SN n + 1, which are expected to be sequentially received before the rearrangement timer expires, are received, restarting the rearrangement timer.

According to another aspect of the present invention, there is provided a method of transmitting a PDCP PDU in consideration of multi-flow from a PDCP entity of a macro base station to a PDCP entity of a terminal having dual connectivity with a macro base station and a small base station. The PDCP PDU transmission method may include generating PDCP PDUs by processing PDCP SDUs for a packet received from an upper layer, and generating the PDCP PDUs to an RLC entity of the macro base station and an RLC entity of the small base station according to a predetermined rule. And distributing the packet to a PDCP entity of the terminal, and if a service gap occurs in which a packet is not received from a higher layer for a predetermined time, the service is delivered to the PDCP entity of the terminal for the first time after the service disconnection. PDCP PDU is characterized in that for transmitting through the RLC entity of the macro base station.

According to the present invention, when the terminal is dual-connected with the master base station and the secondary base station, in performing the multi-flow downlink reception, even if PDCP PDUs are received out of sequence in the PDCP entity of the terminal, based on a timer The rearrangement of PDCP SDUs can be performed, ascending order of PDCP SDUs can be performed to an upper layer, and transmission efficiency can be improved.

In addition, even when a service disconnection occurs, the first PDCP PDU after the service disconnection is delivered to the PDCP entity of the terminal through both the master base station with a short path delay or the duplicated RLC entity of the master base station and the secondary base station RLC entity. By doing so, it is possible to support timely reception of the PDCP PDU.

In addition, since the standby timer may be driven based on non-sequentially received PDCP PDUs, PDCP SDU rearrangement may be smoothly performed even if a time delay occurs while receiving a packet due to service interruption.

1 shows a wireless communication system to which the present invention is applied.

FIG. 2 is a block diagram illustrating a radio protocol architecture for a user plane.

3 is a block diagram illustrating a radio protocol structure for a control plane.

4 is a diagram illustrating an outline of an example of an RLC sublayer model to which the present invention is applied.

5 is a diagram illustrating an outline of an example of a PDCP sublayer model to which the present invention is applied.

6 shows an example of a dual connection situation of a terminal applied to the present invention.

7 shows an example of an EPS bearer structure when a single flow is configured.

8 shows an example of a network structure of a macro base station and a small base station in a single flow in a dual connectivity situation.

9 shows an example of an EPS bearer structure when a multi flow is configured in a dual connection situation.

10 shows an example of the network structure of the macro base station and the small base station in the multi-flow.

11 illustrates a packet forwarding process in the case of a single flow when considering dual connectivity.

12 illustrates a packet forwarding process in the case of multi-flow when considering dual connectivity.

13 shows an example of a PDCP PDU reception timing in a PDCP entity of a terminal.

14 shows another example of a PDCP PDU reception timing in a PDCP entity of a terminal.

15A to 15E illustrate examples of PDCP SDU rearrangement through rearrangement timer operation according to the present invention.

16A to 16B illustrate other examples of PDCP SDU rearrangement using the rearrangement timer operation according to the present invention.

17 shows an example of transmission of PDCP SDUs to a higher layer when the rearrangement timer according to the present invention expires.

18A to 18B illustrate an example of applying a PDCP SDU removal decision method according to the present invention.

19 is a flowchart example of a PDCP SDU rearrangement using the rearrangement timer operation according to the present invention.

20 is a diagram illustrating a case in which packets are intermittently transmitted due to service interruption.

21A to 21B illustrate another example of PDCP PDU reception timing in a PDCP entity of the UE.

22 shows an example of a PDCP PDU transmission scheme considering service disconnection according to the present invention.

23 shows another example of a PDCP PDU transmission scheme considering service disconnection according to the present invention.

24 is a diagram illustrating a case where a packet is intermittently received due to service disconnection.

25A to 25C illustrate a PDCP SDU rearrangement method in consideration of multiflow according to an embodiment of the present invention.

26 is a flowchart illustrating a PDCP SDU rearrangement method using a wait timer according to another embodiment of the present invention.

27 is a block diagram of a macro base station, a small base station and a terminal according to the present invention.

Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings and examples, together with the contents of the present disclosure. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even though they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that a detailed description of a related well-known configuration or function may obscure the gist of the present specification, the detailed description thereof will be omitted.

In addition, the present specification describes a wireless communication network, the operation performed in the wireless communication network is performed in the process of controlling the network and transmitting data in the system (for example, the base station) that is in charge of the wireless communication network, or the corresponding wireless Work may be done at the terminal coupled to the network.

1 shows a wireless communication system to which the present invention is applied. This may be a network structure of an Evolved-Universal Mobile Telecommunications System. The E-UMTS system may be a Long Term Evolution (LTE) or LTE-A (Advanced) system. Wireless communication systems include Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), and OFDM-FDMA Various multiple access schemes such as OFDM, TDMA, and OFDM-CDMA may be used.

Referring to FIG. 1, the E-UTRAN provides a base station 20 (evolved NodeB: eNB) which provides a control plane (CP) and a user plane (UP) to a user equipment (UE). Include.

The terminal 10 may be fixed or mobile and may be called by other terms such as mobile station (MS), advanced MS (AMS), user terminal (UT), subscriber station (SS), and wireless device (Wireless Device). .

The base station 20 generally refers to a station communicating with the terminal 10, and includes a base station (BS), a base transceiver system (BTS), an access point, and a femto-eNB. It may be called other terms such as a pico base station (pico-eNB), a home base station (Home eNB), a relay (relay). The base stations 20 may be connected to each other through an X2 interface. The base station 20 is connected to a Serving Gateway (S-GW) through an MME (Mobility Management Entity) and an S1-U through an Evolved Packet Core (EPC) 30, more specifically, an S1-MME through an S1 interface. The S1 interface exchanges OAM (Operation and Management) information for supporting the movement of the terminal 10 by exchanging signals with the MME.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway (P-GW). The MME has access information of the terminal 10 or information on the capability of the terminal 10, and this information is mainly used for mobility management of the terminal 10. The S-GW is a gateway having an E-UTRAN as an endpoint, and the P-GW is a gateway having a PDN (Packet Data Network) as an endpoint.

Integrating the E-UTRAN and the EPC 30 may be referred to as an EPS (Evoled Packet System), and the traffic flows from the radio link that the terminal 10 connects to the base station 20 to the PDN connecting to the service entity are all IP. It works based on (Internet Protocol).

The radio interface between the terminal and the base station is called a Uu interface. The layers of the radio interface protocol between the terminal and the network are based on the lower three layers of the Open System Interconnection (OSI) reference model, which are well known in a communication system. It may be divided into a second layer L2 and a third layer L3. Among these, the physical layer belonging to the first layer provides an information transfer service using a physical channel, and the RRC (Radio Resource Control) layer located in the third layer exchanges an RRC message for the UE. Control radio resources between network and network.

FIG. 2 is a block diagram showing a radio protocol architecture for a user plane, and FIG. 3 is a block diagram showing a radio protocol architecture for a control plane. The user plane is a protocol stack for user data transmission, and the control plane is a protocol stack for control signal transmission.

2 and 3, a physical layer (PHY) layer provides an information transfer service to a higher layer using a physical channel. The physical layer is connected to a medium access control (MAC) layer, which is an upper layer, through a transport channel. Data is transmitted through a transport channel between the MAC layer and the physical layer. Transport channels are classified according to how data is transmitted over the air interface.

In addition, data is transmitted through a physical channel between different physical layers (ie, between physical layers of a transmitter and a receiver). The physical channel may be modulated by an orthogonal frequency division multiplexing (OFDM) scheme and utilizes time and frequency as radio resources.

For example, the physical downlink control channel (PDCCH) of the physical channel informs the UE of resource allocation of a paging channel (PCH) and downlink shared channel (DL-SCH) and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry an uplink scheduling grant informing the UE of resource allocation of uplink transmission. In addition, a physical control format indicator channel (PCFICH) informs the UE of the number of OFDM symbols used for PDCCHs and is transmitted every subframe. In addition, the PHICH (physical hybrid ARQ Indicator Channel) carries a HARQ ACK / NAK signal in response to uplink transmission. In addition, the physical uplink control channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request, and CQI for downlink transmission. In addition, a physical uplink shared channel (PUSCH) carries an uplink shared channel (UL-SCH).

The MAC layer may perform multiplexing or demultiplexing into a transport block provided as a physical channel on a transport channel of a MAC service data unit (SDU) belonging to the logical channel and mapping between the logical channel and the transport channel. The MAC layer provides a service to a Radio Link Control (RLC) layer through a logical channel. The logical channel may be divided into a control channel for transmitting control region information and a traffic channel for delivering user region information.

Functions of the RLC layer include concatenation, segmentation, and reassembly of RLC SDUs. In order to guarantee the various quality of service (QoS) required by the radio bearer (RB), the RLC layer has a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (Acknowledged Mode). Three modes of operation (AM).

The RLC SDUs are supported in various sizes, and for example, may be supported in units of bytes. RLC protocol data units (PDUs) are defined only when a transmission opportunity is notified from a lower layer (eg, MAC layer), and when the transmission opportunity is notified, the RLC PDUs are delivered to the lower layer. The transmission opportunity may be informed with the size of the total RLC PDUs to be transmitted. Hereinafter, the RLC layer will be described in detail with reference to FIG. 4.

Functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include delivery of user data, header compression, and ciphering. Functions of the PDCP layer in the user plane include the transfer of control plane data and encryption / integrity protection.

The RRC layer is responsible for the control of logical channels, transport channels, and physical channels in connection with configuration, re-configuration, and release of RBs. RB means a logical path provided by the first layer (PHY layer) and the second layer (MAC layer, RLC layer, PDCP layer) for data transmission between the terminal and the network. The configuration of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and operation method. The RB may be further classified into a signaling RB (SRB) and a data RB (DRB). The SRB is used as a path for transmitting RRC messages and non-access stratum (NAS) messages in the control plane, and the DRB is used as a path for transmitting user data in the user plane.

The NAS layer is located above the RRC layer and performs functions such as session management and mobility management.

If there is an RRC connection between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in an RRC connected state, otherwise it is in an RRC idle state.

The downlink transmission channel for transmitting data from the network to the UE includes a BCH (Broadcast Channel) for transmitting system information and a downlink shared channel (SCH) for transmitting user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH or may be transmitted through a separate downlink multicast channel (MCH). Meanwhile, the uplink transport channel for transmitting data from the terminal to the network includes a random access channel (RACH) for transmitting an initial control message and an uplink shared channel (SCH) for transmitting user traffic or control messages.

It is located above the transport channel, and the logical channel mapped to the transport channel is a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH), and a multicast traffic (MTCH). Channel).

The physical channel is composed of several symbols in the time domain and several sub-carriers in the frequency domain. One sub-frame consists of a plurality of OFDM symbols in the time domain. One subframe consists of a plurality of resource blocks, and one resource block consists of a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific symbols (eg, the first symbol) of the corresponding subframe for the physical downlink control channel (PDCCH). The transmission time interval (TTI), which is a unit time for transmitting data, is 1 ms corresponding to one subframe.

4 is a diagram illustrating an example of an example of an RLC sublayer model to which an embodiment of the present invention is applied.

Referring to FIG. 4, certain RLC entities are classified into different RLC entities according to data transmission schemes. For example, there is a TM RLC entity 400, a UM RLC entity 420, and an AM RLC entity 440.

The UM RLC entity 400 may be configured to receive or forward RLC PDUs over logical channels (eg, DL / UL DTCH, MCCH or MTCH). In addition, the UM RLC entity may deliver or receive a UMD PDU (Unacknowledged Mode Data PDU).

The UM RLC entity consists of a sending UM RLC entity or a receiving UM RLC entity.

The transmitting UM RLC entity receives the RLC SDUs from the upper layer and sends the RLC PDUs to the peer receiving UM RLC entity via the lower layer. When the sending UM RLC entity constructs UMD PDUs from the RLC SDUs, the total size of the RLC PDUs indicated by the lower layer by segmenting or concatenating the RLC SDUs when a specific transmission opportunity is notified by the lower layer. The UMD PDUs are configured to be within and the related RLC headers are included in the UMD PDU.

The receiving UM RLC entity delivers the RLC SDUs to the upper layer and receives the RLC PDUs from the peer receiving UM RLC entity through the lower layer. When the receiving UM RLC entity receives UMD PDUs, the receiving UM RLC entity detects whether the UMD PDUs have been received in duplicate, removes the duplicate UMD PDUs, and when the UMD PDUs are received out of sequence. Reorder the UMD PDUs, detect loss of UMD PDUs in the lower layer to avoid excessive reordering delays, reassemble RLC SDUs from the rearranged UMD PDUs, and In addition, the reassembled RLC SDUs are delivered to an upper layer in an ascending order of an RLC sequence number, and UMD PDUs cannot be reassembled into an RLC SDU due to a loss of UMD PDUs belonging to a specific RLC SDU in a lower layer. Can be removed. Upon RLC re-establishment, the receiving UM RLC entity, if possible, reassembles the RLC SDUs from the received UMD PDUs out of sequence and forwards them to the higher layer, and the remaining UMD PDUs that could not be reassembled into RLC SDUs. Remove all, initialize the relevant state variables and stop the associated timers.

Meanwhile, the AM RLC entity 440 may be configured to receive or deliver RLC PDUs through logical channels (eg, DL / UL DCCH or DL / UL DTCH). The AM RLC entity delivers or receives an AMD PDU or ADM PDU segment, and delivers or receives an RLC control PDU (eg, a STATUS PDU).

AM RLC entity 440 delivers STATUS PDUs to peer AM RLC entities to provide positive and / or negative acknowledgment of RLC PDUs (or portions thereof). This may be called STATUS reporting. A polling procedure may be involved from the peer AM RLC entity to trigger STATUS reporting. That is, an AM RLC entity may poll the peer AM RLC entity to trigger STATUS reporting at its peer AM RLC entity.

If a STATUS report is triggered and the t-StatusProhibit is not running or has expired, the STATUS PDU is sent at the next transmission opportunity. Accordingly, the UE estimates the size of the STATUS PDU and considers the STATUS PDU as data available for transmission in the RLC layer.

The AM RLC entity is composed of a transmitting side and a receiving side.

The transmitter of the AM RLC entity receives the RLC SDUs from the upper layer and sends the RLC PDUs to the peer AM RLC entity via the lower layer. When the transmitter of the AM RLC entity configures AMD PDUs from RLC SDUs, it splits the RLC SDUs to fit within the total size of the RLC PDU (s) indicated by the lower layer when a particular transmission opportunity is notified by the lower layer. Segment or concatenate to configure AMD PDUs. The transmitter of the AM RLC entity supports retransmission of RLC data PDUs (ARQ). If the RLC data PDU to be retransmitted does not fit within the total size of the RLC PDU (s) indicated by the lower layer when a particular transmission opportunity is informed by the lower layer, then the AM RLC entity repartitions the RLC data PDU into AMD PDU segments. (re-segment)

At this time, the number of re-segmentation is not limited. When the transmitter of the AM RLC entity creates AMD PDUs from RLC SDUs received from the upper layer or AMD PDU segments from RLC data PDUs to be retransmitted, the relevant RLC headers are included in the RLC data PDU.

The receiver of the AM RLC entity delivers the RLC SDUs to the upper layer and receives the RLC PDUs from the peer AM RLC entity via the lower layer.

When the receiver of the AM RLC entity receives the RLC data PDUs, the receiver detects whether the RLC data PDUs are received in duplicate, removes the duplicate RLC data PDUs, and removes the RLC data PDUs out of sequence. Reorder the order of RLC data PDUs, detect the loss of RLC data PDUs occurring in the lower layer, request retransmission to the peer AM RLC entity, and reassemble RLC SDUs from the rearranged RLC data PDUs. reassemble, and deliver the reassembled RLC SDUs to an upper layer in reassembled order.

When resetting the RLC, the receiver of the AM RLC entity, possibly out of sequence, reassembles the RLC SDUs from the received RLC data PDUs and delivers them to the higher layer, all remaining RLC data PDUs that cannot be reassembled into RLC SDUs. Remove it, initialize the relevant state variables and stop the associated timers.

The PDCP sublayer includes at least one PDCP entity 500. Each RB (eg, DRB and SRB, except SRB0) is associated with one PDCP entity 500. Each PDCP entity may be associated with one or two RLC entity (s) depending on the characteristics of the RB and the RLC mode.

The PDCP entity 500 receives user data from a higher layer (eg an application layer) or passes user data to a higher layer. The user data here is an IP packet. User data may be delivered via a Service Access Point (PDCP-SAP). The PDCP layer receives a PDCP configuration request (PDCP_CONFIG_REQ) message, which is signaling data, from the RRC layer. The PDCP configuration request message may be delivered through a control-service access point (C-SAP). The PDCP configuration request message is a message requesting to configure PDCP according to the PDCP configuration parameters.

The transmitting side of the PDCP entity 500 starts a discard timer upon receipt of user data from a higher layer. User data (i.e. PDCP SDU) is subject to PDCP headers (i.e., RLC SDUs) through header compression, flawless protection (in the control plane), and encryption. The transmitter PDCP delivers the PDCP PDU to the lower layer (eg, RLC layer). The PDCP PDU may include a PDCP Data PDU and a PDCP Control PDU. The PDCP Data PDU carries user plane data, control plane data, and the like, and carries a PDCP SDU Sequence Number (SN). PDCP SDU SN may be called PDCP SN. The PDCP Control PDU carries a PDCP status report and header compression control information.

The RLC SDU may be delivered to the RLC layer through the RLC-SAP. If the user data is not transmitted until the removal timer expires, the transmitting PDCP removes the user data (PDCP SDU including the user data).

The receiving side of the PDCP entity 500 receives an RLC SDU (ie PDCP PDU) from a lower layer. PDCP PDUs become PDCP SDUs through PDCP header decompression, deciphering, and integrity verification (in the control domain). The receiving end of the PDCP entity 500 delivers the PDCP SDUs to higher layers (eg, application layers).

The receiving end of the PDCP entity 500 generally expects to receive sequentially RLC SDUs (ie, PDCP PDUs), except for re-establishment of lower layers. Accordingly, except when the receiving end of the PDCP entity 500 receives the RLC SDU through the resetting of the lower layer, when the PDCP PDU is received, the receiving end of the PDCP entity 500 may transmit the corresponding PDCP SDU to the upper layer in ascending order. If there are stored PDCP SDUs, they are delivered to the upper layer in ascending order. For example, if the PDCP entity 500 receives a PDCP PDU for reasons other than resetting the lower layer, the PDCP entity 500 forwards all stored PDCP SDU (s) with a count value lower than the count value of the received PDCP SDU to the upper layer in ascending order. And start with the count value of the received PDCP SDU and deliver all stored PDCP SDU (s) of the continuously associated count value to the upper layer in ascending order.

6 shows an example in which a dual connection is configured in a terminal to which an embodiment of the present invention is applied.

Referring to FIG. 6, a terminal 650 located in a service area of a macro cell in a macro base station (or a master base station or an anchor base station 600) may be a small base station (or a secondary base station or an assisting base station or a slave base station, 610). In this case, the mobile station enters an area overlaid with the service area of the small cell.

In order to support additional data service through the small cell in the small base station while maintaining the existing wireless connection and data service connection through the macro cell in the macro base station, the network configures dual connectivity for the terminal.

Accordingly, the user data arriving at the macro cell may be delivered to the terminal through the small cell in the small base station. Specifically, the F2 frequency band may be allocated to the macro base station, and the F1 frequency band may be allocated to the small base station. In this case, the terminal may receive the service through the F2 frequency band from the macro base station and at the same time receive the service through the F1 frequency band from the small base station.

7 shows an example of an EPS bearer structure when a single flow is configured.

Referring to FIG. 7, an RB is a bearer provided in a Uu interface to support a service of a user. In the wireless communication system, each bearer is defined for each interface to ensure independence between the interfaces.

Bearers provided by the wireless communication system are collectively referred to as EPS (Evolved Packet System) bearers. The EPS bearer is a transmission path generated between the UE and the P-GW. The P-GW may receive IP flows from the Internet or send IP flows to the Internet. One or more EPS bearers may be configured per terminal, each EPS bearer may be divided into an E-UTRAN Radio Access Bearer (E-RAB) and an S5 / S8 bearer, and the E-RAB may be a Radio Bearer (RB) or an S1. Can be divided into bearers. That is, one EPS bearer corresponds to one RB, S1 bearer, and S5 / S8 bearer, respectively. Depending on which service (or application) is used, the IP flow may have different Quality of Service (QoS) characteristics, and IP flows having different QoS characteristics may be mapped and transmitted for each EPS bearer. The EPS bearer may be classified based on an EPS bearer identity. The EPS bearer identifier is allocated by the UE or MME.

P-GW (Packet Gateway) is a network node connecting between a wireless communication network (for example, LTE network) and another network according to the present invention. EPS bearer is defined between the terminal and the P-GW. EPS bearer is further subdivided between nodes, defined as RB between UE and BS, S1 bearer between BS and S-GW, and S5 / S8 bearer between S-GW and P-GW in EPC. do. Each bearer is defined through QoS. QoS is defined through data rate, error rate, delay, and the like.

Therefore, once the QoS that the wireless communication system should provide as a whole is defined as an EPS bearer, each QoS is determined for each interface. Each interface establishes a bearer according to the QoS that it must provide. Since bearers of each interface provide QoS of all EPS bearers by interface, EPS bearers, RBs, and S1 bearers are basically in a one-to-one relationship.

That is, the LTE wireless communication system is basically a single flow structure, one RB is configured for one EPS bearer. In other words, one EPS bearer is mapped with the S1 bearer through one RB. In the case of a single flow, one EPS bearer is serviced through one RB. In this case, one RB (eg, PDCP entity, RLC entity, MAC entity, PHY layer) is configured for the corresponding EPS bearer, and one RB is configured in the terminal.

8 shows an example of a network structure of a macro base station and a small base station in a single flow in a dual connectivity situation. 8 illustrates a case where a service is provided to a terminal through two EPS bearers.

Referring to FIG. 8, a macro base station includes two PDCP entities, an RLC entity, a MAC entity, and a PHY layer, while a small base station includes an RLC entity, a MAC entity, and a PHY layer. The EPS bearer # 1 800 provides a service to the terminal through the RB (PDCP / RLC / MAC / PHY) configured in the macro base station. On the other hand, the EPS bearer # 2 850 provides a service to the terminal through the PDCP entity configured in the macro base station and the RB (RLC / MAC / PHY) configured in the small base station. Therefore, a service is provided through one RB per EPS bearer in a single flow.

Referring to FIG. 9, when multi-flow is configured, a service is provided through two RBs configured for the macro base station and the small base station instead of one RB for one EPS bearer. The terminal may simultaneously receive a service through one RB configured in the macro base station and one RB configured in the small base station for one EPS bearer. This is a form in which one EPS bearer provides a service through two RBs. As described above, when one EPS bearer provides a service to a terminal through two or more RBs, it may be regarded that multi-flow is configured in the terminal. Alternatively, the multi-flow may be configured when the RB providing the service only through the macro base station and another RB providing the RB divided into the macro base station and the small base station are simultaneously provided to the terminal. The case of providing a service to a terminal through a macro base station and a small base station by dividing one RB may be referred to as bearer split.

Referring to FIG. 10, a macro base station includes a PDCP entity, an RLC entity, a MAC entity, and a PHY layer, while a small base station includes an RLC entity, a MAC entity, and a PHY layer. In FIG. 10, unlike FIG. 8, an RB is configured at a macro base station and a small base station for one EPS bearer 1000 to provide a service to a terminal. That is, a macro base station and a small base station provide a service to a terminal through multiflow for one EPS bearer.

On the other hand, in consideration of dual connectivity, in the case of single flow and multi-flow, the packet forwarding process may be represented as follows.

Referring to FIG. 11, the macro base station 1130 receives packets for each of two EPS bearers through the P-GW and the S-GW. Here, the flow through which packets are sent is mapped to each EPS bearer. Packets transmitted through the EPS bearer # 1 are called packet 1, and packets transmitted through the EPS bearer # 2 are assumed to be packet 2.

The PDCP 1135-1 of the macro base station 1130 receives Packet 1 from the S-GW, and the PDCP 1135-2 receives Packet 2 from the S-GW. The PDCP 1135-1 generates PDCP PDU1 based on Packet 1, and the PDCP PDU1 is delivered to the RLC 1140 of the macro base station 1130, and each entity and the MAC 1145 through the PHY 1150. It is transformed into a form suitable for a layer and transmitted to the terminal 1100.

The PDCP 1135-2 of the macro base station 1130 generates a PDCP PDU2 based on Packet 2, and delivers the PDCP PDU2 to the RLC 1170 of the small base station 1160, and sends the MAC 1175 and the PHY 1180. ) Is transformed into a format suitable for each entity and layer and transmitted to the terminal 1100.

In the terminal 1100, a radio protocol entity exists for each of the EPS bearer # 1 and the EPS bearer # 2. In other words, the PDCP / RLC / MAC / PHY entity (or layer) exists in the EPS bearer # 1 and the PDCP / RLC / MAC / PHY entity (or layer) exists in the EPS bearer # 2. . In more detail, PHY 1105-1, MAC 1110-1, RLC 1115-1, and PDCP 1120-1 exist with respect to EPS bearer # 1. To deal with. The PHY 1105-2, the MAC 1110-2, the RLC 1115-2, and the PDCP 1120-2 exist for the EPS bearer # 2, and service data and packets for the EPS bearer # 2 are present. Process.

Meanwhile, the macro base station 1130 and the small base station 1160 may be connected through an X2 interface. That is, the macro base station 1130 transmits the PDCP PDU2 of the PDCP 1135-2 to the RLC 1140 of the small base station 1160 through the X2 interface. Herein, the X2 interface may use other expressions indicating an X3 interface or an interface between other macro base stations and small base stations. In this case, when the X2 interface between the macro base station 1130 and the small base station 1160 is configured with a non-ideal backhaul, a transmission delay of about 20 to 60 ms may occur. The size of the transmission delay may be changed according to a transmission line or a method as an example.

However, even in this case, the terminal 1100 includes the RLC 1115-1 for the EPS bearer # 1, the PDCP 1120-1 for the EPS bearer # 2, and the RLC 1115-2 for the EPS bearer # 2 and the PDCP 1120-2. Since it is configured separately, no problem occurs even when sequential delivery of RLC SDUs is performed from the RLC entity of the AM to the PDCP entity. In other words, each PDCP entity corresponding to PDCP 1120-1 and PDCP 1120-2 is sequentially processed if it is processed in the order transmitted from each RLC entity corresponding to RLC 1115-1 and RLC 1115-2. Problem does not occur.

Referring to FIG. 12, the macro base station 1230 receives packets for one EPS bearer through the P-GW and the S-GW. The macro base station 1230 and the small base station 1260 each constitute an RB for the one EPS bearer. Specifically, the macro base station 1230 constitutes a PDCP 1235, an RLC 1240, a MAC 1245, and a PHY 1250, and the small base station 1240 is an RLC 1270, a MAC 1275, and a PHY 1280. ). The RB configured by the small base station 1240 shares the PDCP 1235 configured by the macro base station 1230. Therefore, one RB is divided into a macro base station 1230 and a small base station 1260.

The PDCP 1235 of the macro base station 1230 receives the packet from the S-GW. The PDCP 1235 generates PDCP PDUs based on packets, and generates the PDCP PDUs according to a predefined rule or any method according to the RLC 1240 of the macro base station 1230 and the RLC 1270 of the small base station 1260. Properly distribute to For example, PDCP PDUs having odd SNs among PDCP PDUs are transmitted to the RLC 1240 of the macro base station 1230, and PDCP PDUs having even SNs are transmitted to the RLC 1270 of the small base station 1260. Can be.

The RLC 1240 generates an RLC PDU1 (s), and the RLC PDU1 (s) is transformed into a format suitable for each entity and layer through the MAC 1245 and the PHY 1250 and transmitted to the terminal 1200. In addition, the RLC 1270 generates an RLC PDU2 (s), and the RLC PDU2 (s) is transformed into a format suitable for each entity and layer through the MAC 1275 and the PHY 1280 and transmitted to the terminal 1200. do.

The terminal 1200 has two radio protocol entities for the EPS bearer. In other words, the terminal 1200 includes a PDCP / RLC / MAC / PHY entity (or layer) as an RB corresponding to the macro base station 1230, and an RLC / MAC / PHY entity (as an RB corresponding to the small base station 1260). Or hierarchy). In detail, the PHY 1205-1, the MAC 1210-1, the RLC 1215-1, and the PDCP 1220 corresponding to the macro base station 1230 exist for the EPS bearer, and the small base station 1260 is present. There is a corresponding PHY 1205-2, MAC 1210-2, and RLC 1215-2. The PDCP 1220 is a PDCP entity corresponding to the macro base station 1230 and the small base station 1260 simultaneously. That is, in this case, two RLC entities 1215-1 and 1215-2 exist at the terminal 1200, but the two RLC entities 1215-1 and 1215-2 are one PDCP entity 1220. Corresponds to.

As described above, the macro base station 1230 and the small base station 1260 may be connected through an X2 (or Xn) interface. That is, the macro base station 1230 transfers some of the PDCP PDUs of the PDCP 1235-2 to the RLC 1240 of the small base station 1260 through the X2 interface. Herein, the X2 interface may use other expressions indicating an Xn interface or an interface between other macro base stations and small base stations. In this case, when the X2 interface between the macro base station 1230 and the small base station 1260 is configured with a non-ideal backhaul, a transmission delay of about 20 to 60 ms may occur. The PDCP entity 1220 of the UE 1200 should receive RLC SDUs (ie, PDCP PDUs) from two RLC entities 1215-1 and 1215-2, respectively, generate PDCP SDUs, and deliver them to a higher layer. Due to the transmission delay, a time difference occurs between the RLC SDUs (ie, PDCP PDUs) received by the PDCP entity 1220 from those received from the RLC entity 1215-1, and from the RLC entity 1215-2. The PDCP entity 1220 may have problems in performing ascending transmission to the upper layer of the PDCP SDU.

As shown in FIG. 12, one PDCP 1235 exists in the macro base station 1230 and one PDCP entity 1220 exists in the UE 1200 for multi-flow in a dual connectivity environment. In addition, the

RLC entities

1240 and 1270 are present in the macro base station 1230 and the small base station 1230, respectively, and two RLC entities 1215-1 and 1215-2 are also present in the terminal 1200. . That is, in the RLC entities 1215-1 and 1215-2 of the terminal 1210, in-sequence delivery to the upper layer may be guaranteed. However, at the PDCP entity 1220 end of the terminal 1210, RLC SDUs (ie PDCP PDUs) are transmitted from two RLC entities 1215-1 and 1215-2 instead of one RLC entity. Thus, sequential delivery at the RLC entity 1215-1, 1215-2 end does not guarantee sequential reception of PDCP PDUs at the PDCP entity end. In addition, the transmission of the PDCP PDU (s) from the PDCP entity 1235 of the macro base station 1230 to the RLC entity 1270 of the small base station 1260 may involve a transmission delay of about 20 to 60 ms. There may be a time delay between the transmission of the PDCP PDU (s) towards the RLC entity 1240 of 1230 and the transmission of the PDCP PDU (s) towards the RLC entity 1270 of the small base station 1230. As a result, even when the PDCP PDU (s) transmitted from the PDCP entity 1235 of the macro base station 1230 is received by the PDCP entity 1220 of the terminal 1200, transmission and small through the RLC sub-terminal of the macro base station 1230 are performed. In the transmission through the RLC stage of the base station 1260, a difference occurs in the reception time, and the PDCP entity 1220 of the terminal 1200 is difficult to expect the sequential reception of the PDCP PDU (s).

13 shows an example of a PDCP PDU reception timing in a PDCP entity of a terminal. 13 exemplarily shows a time when a PDCP PDU transmitted through a macro base station and a PDCP PDU transmitted through a small base station arrive at a PDCP entity of a terminal. The macro base station may determine a PDCP PDU to be transmitted through the macro base station and a PDCP PDU to be transmitted through the small base station for the service for one EPS bearer. In FIG. 13, PDCP PDUs associated with an odd number of PDCP sequence numbers are transmitted through a macro base station, and PDCP PDUs associated with an even number are transmitted through a small base station.

Referring to FIG. 13, there is a time delay difference between a reception time at a terminal of a PDCP PDU transmitted through a macro base station and a reception time at a terminal of a PDCP PDU transmitted through a small base station. A transmission delay of about 20 to 60 ms may occur in the PDCP PDU transmitted through the small base station. This is mainly caused by transmission delay occurring in the X2 (or Xn) interface when the PDCP PDU is transmitted from the macro base station to the small base station. In this case, due to the time difference between the RLC (AMD) SDUs received from the two RLC entities, the PDCP entity of the terminal receives the PDCP PDUs out of order, and the PDCP entity processes them to a higher layer (for example, an application layer). In case of transmission, it is difficult to guarantee ascending transmission. That is, since the PDCP PDUs transmitted from one PDCP entity of the macro base station in the multi-flow structure are transmitted through the RLC entity of the macro base station and the RLC entity of the small base station, the PDCP PDU of the UE receives a time delay. Therefore, a problem arises in performing ascending transmission of the PDCP SDU from the PDCP entity to the higher layer.

The PDCP entity of the UE reads the received PDCP PDU and performs header decompression, and transmits the PDCP SDU to the upper layer. At this time, if the PDCP SDU of the SN smaller than the SN (sequence number) of the current PDCP SDU is stored, the PDCP SDU is transmitted to the upper layer in order from the smallest SN to the largest SN.

Meanwhile, the transmission side of the PDCP entity may operate a discard timer. The duration of the removal timer may be configured from a higher layer, and the timer is started when the PDCP SDU is received from the higher layer. When the removal timer expires, the PDCP entity removes the corresponding PDCP SDU. Accordingly, due to expiration of the removal timer, PDCP SDUs of a specific SN may be removed, and the receiving end of the PDCP entity may transmit all PDCP SDUs in ascending order without having to sequentially transmit to the upper layer.

However, when supporting the multi-flow in the aforementioned dual connectivity situation, the PDCP entity may receive RLC SDUs (PDCP PDUs) from the two RLC entities with which it is associated. In this case, PDCP PDUs (particularly, RLC AMD SDUs) are not sequentially received at the PDCP entity, and PDCP PDUs having a larger PDCP SN may be first received due to transmission path reception delay.

When RLC SDUs (ie, PDCP PDUs) are received out of order in a PDCP entity, one of two cases may be determined. However, the PDCP entity may not be distinguished in any of the following two cases.

First, the discard timer may be expired. The transmitting end of the PDCP entity drives a discard timer for each PDCP SDU processed by the PDCP entity. If the amount of packets flowing into the PDCP is greater than a certain standard due to the removal of the timer, the unprocessed packets are removed within the duration of the removal timer, and the corresponding packet is based on a retransmission request performed by a higher layer. Processing may be newly performed.

Second, it may be the case of reception delay of PDCP PDU transmission path. The PDCP entity of the macro base station may separate and transmit the PDCP PDU through the macro base station and the small base station due to the multi-flow. In this case, a time difference may occur when the PDCP PDU is received by the PDCP entity of the UE due to a delay caused by different paths. The opposite is also true. In this case, the order of PDCP SDUs is reversed and may be transmitted to a higher layer.

Accordingly, there is a need for a method of transmitting PDCP SDUs to an upper layer in an ascending order from a PDCP entity of a terminal, in which the case of multiflow transmission path reception delay is distinguished from the case of PDCP removal timer expiration.

The PDCP rearrangement and PDCP SDU ascending order transfer to higher layers according to an embodiment of the present invention are as follows.

In the present invention, the PDCP entity drives a reordering timer upon reception of the PDCP PDU. The PDCP entity waits for a reception delay of the PDCP PDU based on the rearrangement timer, rearranges the PDCP PDUs received within a predetermined time, and performs ascending order of PDCP SDUs to a higher layer. This is to prevent PDCP PDUs having a large PDCP SN first arriving at the PDCP entity and being transmitted to the higher layer, and PDCP PDUs having a smaller PDCP SN arriving at the PDCP entity later and being transmitted to the higher layer. The PDCP entity waits for a certain amount of time in consideration of the delay time and, when the PDCP PDU of the missing PDCP SN (or count value) arrives, carries out an ascending order to the upper layer, including the PDCP of the missing PDCP SN within a certain time. If the PDU does not arrive, the PDCP PDU is considered to have been removed due to the expiration of the removal timer, and the ascending order is performed to the upper layer except the PDCP PDU.

The PDCP rearrangement method based on the rearrangement timer may be specifically performed as follows.

First, the basic operation of the rearrangement timer is as follows.

The receiving end of the PDCP entity starts the reordering timer when the reordering timer is not running (or not on duration) upon receiving the PDCP PDU.

When the receiving end of the PDCP entity receives the PDCP PDU sequentially when the PDCP PDU is received,

If the rearrangement timer is not running, start the rearrangement timer.

-If the rearrangement timer is running (or running), restart the rearrangement timer.

That is, the PDCP entity initially starts a reordering timer upon receiving the PDCP PDU or when the PDCP PDU is not running.

The rearrangement timer corresponds to a wait timer for waiting for a PDCP PDU that can be received sequentially in a received (or stored) PDCP PDU.

If the reorder timer is running,

If a PDCP PDU is received in-sequence, the corresponding (or associated) PDCP SDU is forwarded to the upper layer.

If a PDCP PDU is received out-of-sequence, the PDCP SDU corresponding to the PDCP PDU is stored and is not delivered to the upper layer.

If a PDCP PDU is received after the rearrangement timer expires, only PDCP SDUs that are sequentially received (except for PDCP SNs of PDCP SDUs expected to be received sequentially) among the stored PDCP SDUs are delivered to a higher layer. do. Alternatively, among PDCP SDUs stored at the time when the rearrangement timer expires, only PDCP SDUs sequentially received (based on the rest of the PDCP SDUs expected to be sequentially received) are transferred to a higher layer.

The rearrangement timer may be determined in consideration of the transmission delay time between the macro base station and the small base station having dual connectivity to the terminal. For example, when considering the delay time of the X2 (or Xn) interface using the non-ideal backhaul between the macro base station and the small base station, the rearrangement timer may be set to, for example, 20 to 60 ms. As described above, the delay time may be changed and the rearrangement timer value may be changed according to a difference in a transmission line or a scheme.

The PDCP entity may identify the PDCP SN of the PDCP SDU (ie, received PDCP SDU) corresponding to the received PDCP PDU. By comparing the PDCP SN of the received PDCP SDU with the PDCP SN of the last PDCP SDU transmitted to the upper layer, it is possible to determine whether the PDCP PDU (or PDCP SDU) is sequentially received. The PDCP entity may restart the rearrangement timer if the received PDCP PDUs were received sequentially. If the PDCP entity has not received the received PDCP PDUs sequentially, the PDCP entity keeps a rearrangement timer and stores the PDCP SDUs corresponding to the received PDCP PDUs. If the PDCP PDU of the next PDCP SN of the last PDCP PDU sent to the higher layer does not arrive until the rearrangement timer expires, the PDCP entity determines that the PDCP PDU (or PDCP SDU) has been removed by expiration of the purge timer. And the remaining sequentially received (or stored) PDCP SDUs in ascending order to the upper layer. The PDCP entity may compare the PDCP SNs of the received PDCP SDUs with the PDCP SNs of the PDCP SDUs last transmitted to the upper layer, and may determine that they are sequentially received if they are in order.

If the PDCP SN of the last PDCP SDU transmitted to the upper layer is defined as Last_Submitted_PDCP_RX_SN and the PDCP SN of the PDCP SDU expected to be sequentially received next is defined as Next_PDCP_RX_SN, Next_PDCP_RX_SN is represented by Equation 1 and Equation 2 below. You can follow either.

Equation 1

Equation 2

In Equation 2, Maximum_PDCP_SN represents the maximum value of the allowed PDCP SN. That is, Equation 2 indicates that the number starts again from 0 after the maximum value of the PDCP SN.

Meanwhile, the start / restart method of the rearrangement timer is as follows. The PDCP entity starts or restarts the rearrangement timer when the PDCP PDUs are sequentially received according to whether the rearrangement timer is running. For example, if the rearrangement timer is not running, the PDCP entity starts the rearrangement timer when it receives a PDCP PDU, and restarts the rearrangement timer if the rearrangement timer is running.

In addition, when the rearrangement timer is running or on duration, the PDCP entity stores PDCP SDUs corresponding to PDCP PDUs that are not sequentially received. This is in case the PDCP PDU with the smaller PDCP SN is received later.

On the other hand, the rearrangement timer may not be restarted if the PDCP PDUs are not sequentially received, but may be maintained and expired. If the rearrangement timer expires, when the rearrangement timer expires or when the PDCP PDU is received after the rearrangement timer expires, the PDCP entity is selected from among the stored PDCP SDUs. Sequential PDCP SDUs are transmitted to a higher layer except for Next_PDCP_RX_SN The present invention can be applied to both a DL data transfer procedure and an UL data transfer procedure. Explain the delivery process.

For example, in case of downlink data transmission, the receiving PDCP is the PDCP entity 1120 of the terminal, and the transmitting PDCP is the PDCP entity 1135 of the macro base station.

For example, in the case of uplink data transmission, the receiving PDCP is a PDCP entity 1135 of the macro base station, and the transmitting PDCP is a PDCP entity 1120 of the UE.

For uplink data transfer, the PDCP entity 1120 of the UE is responsible for each RLC (PDC RDU: 1115-1, small base station RLC: 1115-2) responsible for transmitting PDCP PDUs to the macro base station and the small base station. To send). The macro base station RLC 1140 and the small base station RLC 1170 respectively receive a PDCP PDU (RLC SDU) of the UE transmitted from the macro base station RLC 1115-1 and the small base station RLC 1115-2. Receive.

In this case, a PDCP PDU received by the PDCP entity 1135 of the macro base station from the small base station RLC 1170 may have a difference in reception time due to a transmission time difference between the base stations. Accordingly, the PDCP entity 1135 of the base station may generate a PDCP PDU. In-sequence reception cannot be guaranteed at the time of reception.

Therefore, the UE should consider a scheme for receiving PDCP in-sequence in the PDCP entity 1135 of the base station even when transmitting uplink data. This may be applied in the same manner as that for the base station to receive in-sequence in the PDCP entity 1120 of the terminal during downlink data transmission.

14 shows another example of a PDCP PDU reception timing in a PDCP entity of a terminal. 14 is a multi-flow transmission scenario, and assumes that transmission of PDCP PDUs for one RB occurs at the same time in the macro base station and the small base station. That is, the PDCP PDUs are divided and transmitted from the PDCP entity of the macro base station to the RLC entity of the macro base station and the RLC entity of the small base station. 14 shows PDCP PDUs associated with 1, 2, 3, 4, 5, 11, 12, 13, 17, 18, 19, 20, 21, 22, 26, 27, 33, 34, and 35 of the PDCP SN. PDCP PDUs transmitted through a base station (of RLC entity) and associated with 6, 7, 8, 9, 10, 14, 15, 16, 23, 24, 25, 28, 29, 30, 31, 32 are small base stations Assume a case of transmitting through (an RLC entity of).

Referring to FIG. 14, no PDCP PDCP is transmitted through a small base station while a PDCP PDU up to

PDCP SNs

1, 2, 3, 4, 5, 11, and 12 is received at a PDCP entity of a terminal through a macro base station. Not received by the PDCP entity. Thereafter, PDCP PDUs from PDCP SN 6 begin to be received by the PDCP entity of the UE through the small base station. This is because the PDCP PDU transmitted through the small base station is transmitted from the PDCP entity of the macro base station via the RLC entity of the small base station, resulting in a path delay. Here, it is assumed that the occurrence of delay difference in the wireless section is almost the same or not.

As described above, when the PDCP entity of the terminal receives the PDCP PDU of the PDCP SN 11 immediately after the PDCP PDU of the PDCP SN 5 is received, the PDCP entity of the terminal is the PDCP PDU of the PDCP SN 6 which is different from the PDCP SN 6 which expected the reception. It is necessary to distinguish whether the PDCP PDU of PDCP SN # 6 is removed due to the removal timer expiration or is received later due to the multiflow reception delay.

15 shows an example of PDCP SDU rearrangement through the rearrangement timer operation according to the present invention. FIG. 15A illustrates a case in which the PDCP entity of the UE completes reception of PDCP PDUs of PDCP SN 11 after receiving PDCP PDUs of PDCP SNs 1 to 5 in the example of FIG. 14.

Referring to FIG. 15A, the PDCP entity of the UE starts a rearrangement timer upon reception of PDCP PDU of PDCP SN # 1. Since the rearrangement timer does not operate when the PDCP entity of the terminal receives the PDCP PDU of PDCP SN # 1, the rearrangement timer starts when the PDCP PDU of PDCP SN # 1 is received. The PDCP entity of the terminal maintains the rearrangement timer according to the rearrangement timer value RT. The rearrangement timer value may be transmitted from the macro base station or the small base station to the terminal. For example, the rearrangement timer value may be included in the configuration information when the dual connection (or multiflow) is configured in the terminal and transmitted to the terminal. The rearrangement timer is maintained for RT time after startup, or until the rearrangement timer is restarted by receiving a PDCP PDU of the sequential PDCP SN. On the other hand, the received PDCP SN 1 is delivered to the upper layer.

Thereafter, the PDCP entity of the terminal restarts the rearrangement timer upon receiving the PDCP PDU of PDCP SN 2, and delivers the PDCP SDU corresponding to the PDCP PDU of PDCP SN 2 to a higher layer. This assumes that a PDCP PDU of a sequential PDCP SN is received before the rearrangement timer expires. Thereafter, the PDCP entity of the terminal restarts the rearrangement timer every time PDCP PDUs of PDCP SN 3 to 5 are received. Meanwhile, PDCP SDUs corresponding to PDCP PDUs of PDCP SNs 3 to 5 that are sequentially received are delivered to a higher layer.

Since the PDCP layer of the terminal receives the PDCP PDUs out of sequence when receiving PDCP PDUs of PDCP SN 11, the PDCP layer does not restart the rearrangement timer and maintains them. When the PDCP layer of the UE receives PDCP PDUs of PDCP SN 5, it is expected to receive PDCP PDUs of PDCP SN 6. However, the PDCP SN of the PDCP PDU received is 11, which corresponds to non-sequential reception, not sequential reception. Therefore, do not restart the rearrangement timer in this case. PDCP SDUs corresponding to PDCP PDUs received out of order while the rearrangement timer is running are stored in a buffer. Therefore, in this case, PDCP SDUs corresponding to PDCP PDUs of PDCP SN 11 are stored in a buffer. In this case, the rearrangement timer is maintained.

FIG. 15B assumes a case in which a PDCP entity of a UE completes reception of PDCP PDUs of PDCP SN 12 after FIG. 15A.

Referring to FIG. 15B, the PDCP entity of the terminal still determines that PDCP PDU reception of PDCP SN 12 is still out of order. Because the PDCP SN of the last PDCP SDU delivered to the upper layer is 5, the PDCP entity of the UE expects to receive the PDCP PDU of PDCP SN # 6, which is next to the PDCP SN of the last PDCP SDU delivered to the upper layer. Because. Thus, in this case, the rearrangement timer continues to expire.

FIG. 15C assumes a case in which a PDCP entity of a UE completes reception until PDCP PDU of PDCP SN 6 after FIG. 15B.

Referring to FIG. 15C, when the PDCP entity of the UE receives the PDCP PDU of PDCP SN 6, it determines that the PDCP PDU is sequentially received. This is because the PDCP PDU of PDCP SN 6, which is next to PDCP SN 5 of the last PDCP PDU delivered to the upper layer, is received. In this case, the terminal restarts the rearrangement timer, and delivers the PDCP SDU corresponding to the PDCP PDU of PDCP SN 6 to a higher layer. If the PDCP entity of the terminal does not receive PDCP PDUs of PDCP SN 6 until the rearrangement timer expires, the PDCP SDU corresponding to PDCP PDUs of PDCP SN 6 is considered to have been removed by expiration of the removal timer.

FIG. 15D assumes a case in which a PDCP entity of the UE completes reception until PDCP PDU of PDCP SN 19 after FIG. 15C.

Referring to FIG. 15D, the PDCP entity of the terminal receives PDCP PDUs in the order of 13, 7, 17, 8, 18, 9, 19 after PDCP SN 6 PDCP PDU reception. In this case, the PDCP entity of the UE regards PDCP PDUs of

PDCP SN

6, 7, 8, and 9 sequentially and delivers corresponding PDCP SDUs to a higher layer. In this case, the PDCP entity of the terminal restarts the rearrangement timer every time PDCP PDUs of

PDCP SN

6, 7, 8, and 9 are received.

As such, the PDCP entity of the UE delivers corresponding PDCP SDUs to the upper layer because PDCP PDUs of

PDCP SNs

11, 12, 13, 17, 18, and 19 are not sequentially received (PDCP PDUs of PDCP SN 10 are not received). Instead, store it in a buffer. In this case, the rearrangement timer is maintained without restarting.

FIG. 15E assumes a case in which a PDCP entity of the UE completes reception until PDCP PDU of PDCP SN 10 after FIG. 15D.

Referring to FIG. 15E, upon reception of a PDCP PDU of PDCP SN # 10, the PDCP entity of the terminal delivers a corresponding PDCP SDU and PDCP SDUs associated with stored

PDCP SNs

11, 12, and 13 to a higher layer. Due to reception of PDCP PDUs of PDCP SN 10, the PDCP entity of the UE may deliver all of the PDCP SDUs corresponding to the consecutive order starting from PDCP SN 10 to a higher layer at a time.

The PDCP entity of the UE determines that the received PDCP PDUs of

PDCP SN

17, 18 and 19 are out of order until receiving PDCP PDUs of

PDCP SN

14, 15 and 16, and PDCP PDUs of

PDCP SN

17, 18 and 19. The PDCP SDUs corresponding to the PCP SDUs are stored in the buffer without being transferred to the upper layer. That is, since PDCP PDUs of

PDCP SNs

17, 18 and 19 are not in sequential order until PDCP PDUs of

PDCP SNs

14, 15 and 16 are received, corresponding PDCP SDUs are not delivered to the upper layer. In other words, for higher layer delivery of PDCP SDUs corresponding to PDCP PDUs of

PDCP SN

17, 18 and 19, PDCP PDUs of

PDCP SN

14, 15 and 16 should be received or removed. Ascending order to the upper layer of the PDCP SDU can be guaranteed based on the rearrangement timer according to the above criteria.

16 shows another example of PDCP SDU rearrangement through the rearrangement timer operation according to the present invention. FIG. 16A illustrates a PDCP PDU of

PDCP SN

13 and 7 without receiving PDCP PDUs of PDCP SN 6 after PDCP entity of the UE receives PDCP PDUs of PDCP SNs 1 to 5 and 11 and 12 in FIG. 14. This is the case.

Referring to FIG. 16A, the PDCP entity of the terminal according to the present invention delivers corresponding PDCP SDUs to a higher layer whenever PDCP SNs 1 to 5 PDCP PDUs are received, and starts / restarts a rearrangement timer. However, upon receiving

PDCP SN

11, 12, 13, and 7 PDCP PDUs, the PDCP PDUs of PDCP SN 6 have not yet been received (ie, out of sequence), so that the corresponding PDCP SDUs are stored and re-created. Keep the array timer. In this case, the PDCP entity of the terminal cannot clearly distinguish whether the PDCP PDU of PDCP SN 6 is removed due to the removal timer expiration or arrives late due to a path delay. The PDCP entity of the terminal determines that the PDCP SDU corresponding to the PDCP PDU of the PDCP SN 6 is removed when the PDCP SN of the PDCP SN 6 is not received even if the rearrangement timer waits until the rearrangement timer expires.

FIG. 16b assumes that after FIG. 16a, the PDCP entity of the terminal has completed reception up to the PDCP PDU of PDCP SN 19. After the PDCP entity of the terminal receives PDCP SN 13, PDCP PDUs of

PDCP SN

13 and 7 without receiving PDCP SN of PDCP SN 6, the rearrangement timer expires, and then the PDCP entity of the UE receives PDCP PDU of PDCP SN 17 One case.

Referring to FIG. 16B, when the rearrangement timer expires, the PDCP PDU of the UE determines that the PDCP SDU corresponding to the PDCP PDU of PDCP SN 6 is removed. This is because the rearrangement timer means a time that the PDCP PDU of the PDCP SN, which is expected to be sequentially received, can wait as much as possible in consideration of a path delay. Therefore, when the rearrangement timer expires, it is determined that the PDCP SDU corresponding to the PDCP PDU of the corresponding PDCP SN is removed. In general, packet loss is regarded as no packet loss in the X2 (or Xn) interface section between the macro base station and the small base station. When using the RLC AM, transmission without packet loss between the base station and the terminal is performed even if there is a delay time. It is considered possible. Therefore, even though the rearrangement timer has elapsed, when the PDCP entity of the UE does not receive the PDCP PDU of the PDCP SN that expected the next sequential reception, it is reasonable to consider that the PDCP SDU corresponding to the PDCP PDU has been removed.

Accordingly, the PDCP entity considers the PDCP PDUs of PDCP SN 7 to be sequential because the PDCP SDUs associated with PDCP SN 6 have been removed. This is because the PDCP SDU associated with PDCP SN 6 is removed and cannot be received by the PDCP entity of the UE. Therefore, even if the PDCP SDU associated with PDCP SN 7 is delivered to a higher layer, there is no problem in ascending order. Therefore, except for the PDCP SDU thus removed, it is possible to grasp the sequential reception (or ascending order). The PDCP entity may transmit a PDCP SDU associated with PDCP SN 7 to a higher layer, but may transmit the PDCP SDU associated with PDCP SN 7 to a higher layer when the rearrangement timer expires, or first receive after the rearrangement timer expires. Upon receiving the PDCP PDU of PDCP SN 17, the PDCP SDU associated with PDCP SN 7 may be delivered to a higher layer. In addition, the rearrangement timer is not started when the PDCP PDU of PDCP SN 17 is received, and thus the rearrangement timer is started.

17 shows an example of transmission of PDCP SDUs to a higher layer when the rearrangement timer according to the present invention expires. 17, in the example of FIG. 14, after the PDCP entity of the UE receives PDCP PDUs of PDCP SNs 1 to 5, 11 and 12, PDCP SN 13 and PDCPs of

PDCP SN

13 and 7 are received without receiving PDCP PDUs of PDCP SN 6. After the rearrangement timer expires, the rearrangement timer is started when the PDCP entity of the UE receives the PDCP SN # 17 PDCP PDU, and without the PDCP SN # 8 PDCP PDU,

PDCP SN

18, 9, 19, 10 PDCP PDUs have been received and the rearrangement timer has expired.

According to the standard for the PDCP layer, when the PDCP entity receives the PDCP PDU, it describes on which criteria the corresponding PDCP SDU is transmitted to the upper layer. However, there is no description of the behavior of the PDCP entity when the rearrangement timer expires. The PDCP entity may perform the next operation immediately when the reordering timer expires, or may perform the next operation upon receiving the PDCP PDU after the reordering timer expires. For example, a PDCP entity may forward PDCP SDUs treated as sequential reception to a higher layer except for PDCP SDUs that are treated as removed when the rearrangement timer expires. Alternatively, when the PDCP PDU is received after the rearrangement timer expires, the PDCP entity may deliver PDCP SDUs treated as sequential receptions to a higher layer except for the PDCP SDUs that are treated as removed by the rearrangement timer expiration. That is, when the rearrangement timer expires, delivering the PDCP SDUs treated as sequential receptions among the stored PDCP SDUs to a higher layer may be triggered immediately when the rearrangement timer expires, or After the rearrangement timer expires, it may be triggered at the time the PDCP PDU is received.

On the other hand, the larger the rearrangement timer value, it can be clearly determined whether the missing PDCP SDU has been removed or not yet received, but the time delay occurs because the transfer to the upper layer of the remaining PDCP SDUs is reserved during the rearrangement timer time. In addition, as the rearrangement timer value is smaller, the time delay is reduced, but it may be less accurate to determine whether the missing PDCP SDU is removed or not received yet. Therefore, the rearrangement timer should be appropriately set in consideration of the above problem.

PDCP PDUs may be transmitted via a macro base station or a small base station. At this time, the time interval between successive PDCP PDUs is determined to be insignificant. Also, the time that the PDCP removal timer is driven and progressed is about the same in successive PDCP PDUs. Therefore, it is sufficient to consider only the delay due to the difference in transmission paths between PDCP PDUs transmitted from the macro base station's PDCP entity through the macro base station's RLC entity or the small base station's RLC entity. For example, if it is assumed that the difference in the transmission delay in the radio section is insignificant, the main path delay will correspond to the delay time in the X2 (or Xn) path existing between the macro base station and the small base station. Therefore, the rearrangement timer value RT may be set to any value within 20 to 60 ms corresponding to the X2 (or Xn) path delay. The rearrangement timer value RT may be signaled from a base station to a terminal in a dedicated or broadcast manner.

On the other hand, when the rearrangement timer expires, in order to increase the accuracy of the determination of whether the missing PDCP SDU is removed or not yet received, additional PDCP SDU removal confirmation method may be used.

18 shows an example of applying a PDCP SDU removal determination method according to the present invention. FIG. 18A illustrates, after the PDCP entity of the UE receives PDCP PDUs of PDCP SNs 1 to 5, 11 and 12, the PDCP entity of the UE does not receive PDCP PDUs of PDCP SN 6 to PDCP SN 13 in FIG. 14. After receiving 7 PDCP PDUs, the rearrangement timer expires, and then the PDCP entity of the UE receives PDCP PDUs of PDCP SN 17 afterwards.

When the PDCP entity of the terminal receives the PDCP PDU of PDCP SN 17, the PDCP SDU corresponding to the PDCP PDU of PDCP SN 7 is transferred to a higher layer and starts a rearrangement timer. The PDCP entity stores the corresponding PDCP SDU (associated with PDCP SN 17) since the PDCP PDUs of PDCP SN 17 are not sequential receptions.

FIG. 18B illustrates a case in which a PDCP entity of the UE receives PDCP SN 18, PDPD # 9 without receiving PDCP PDUs of PDCP SN 8 after FIG. 18A.

Referring to FIG. 18B, the PDCP entity of the terminal receives PDCP SN 18 and PDCP PDUs in sequence 9 without receiving PDCP PDUs of PDCP SN 8.

In a multi-flow environment, assuming that a PDCP entity of a terminal can distinguish PDCP SNs of PDCP PDUs transmitted through an RLC entity of a macro base station and PDCP SNs of PDCP PDUs transmitted through an RLC entity of a small base station. When the rearrangement timer expires, the PDCP entity may determine the PDCP SDU removal according to the following method.

The PDCP SN of a specific PDCP PDU expected to be received sequentially through one base station (for example, a small base station) to the PDCP entity of the terminal is called X, and the PDCP PDU received from another base station (for example, macro base station) If the maximum PDCP SN is Y, if the PDCP entity of the UE is Y> X, it may be determined that the PDCP PDU (or PDCP SDU) having the PDCP SN corresponding to X is removed. A description with reference to FIG. 18B is as follows.

When the rearrangement timer expires without receiving the PDCP PDUs of the DCP SN 8, the PDCP entity of the UE is PDCP SN 6 of the PDCP PDU, which was expected to be sequentially received through the small base station, and the PDCP PDU received through the macro base station. Compare 20 times the maximum PDCP SN of, and since 20> 6, determine that the PDCP SDU associated with the corresponding PDCP SN 6 has been removed.

Referring to FIG. 19, when the PDCP entity of the terminal sequentially receives PDCP SN n PDCP PDUs, the PDCP entity forwards the corresponding PDCP SDU to the upper layer, and if the rearrangement timer is not running, starts the rearrangement timer. If the rearrangement timer is in operation, the rearrangement timer is restarted (S1900). In this case, the PDCP entity of the terminal restarts the rearrangement timer every time the PDCP PDU is sequentially received while the rearrangement timer is being driven. Here, the rearrangement timer corresponds to a waiting timer for waiting for the PDCP PDUs that are expected to be sequentially received after the last sequentially received PDCP PDUs. The PDCP entity of the UE may check whether the corresponding PDCP PDUs are sequentially received based on the PDCP SN of the corresponding PDCP PDU.

The PDCP entity of the UE checks whether the PDCP PDU of PDCP SN n + 1 is received before the rearrangement timer expires (S1910). Although the PDCP entity of the terminal receives PDCP PDUs of PDCP SN n + 2 and PDCP SN n + 3, it is determined that the PDCP PDUs are not sequential reception and are determined to be PDCP PDUs of PDCP SN n + 2 and PDCP SN n + 3. Store the corresponding PDCP SDUs and maintain the rearrangement timer.

If the PDCP entity of the UE receives PDCP SN n + 1 PDCP PDUs before the rearrangement timer expires in S1910, the PDCP entity of the UE continuously starts from PDCP SN n + 1 and is continuously associated with PDCP SN. All stored PDCP SDUs of the value are transmitted to the upper layer in ascending order (S1920).

If the rearrangement timer expires in S1910, that is, if the PDCP entity of the terminal does not receive PDCP SN n + 1 PDCP PDUs until the rearrangement timer expires, the PDCP entity of the terminal PDPD SN n + 1 The PDCP SDUs associated with are reported to have been removed, and starting with PDCP SN n + 2, all stored PDCP SDUs of consecutively associated PDCP SN values are delivered to the upper layer in ascending order (S1930). As an example, the PDCP entity of the UE may deliver all stored PDCP SDUs of consecutively associated PDCP SN values starting from PDCP SN n + 2 at the time of reordering timer to the upper layer in ascending order. As another example, the PDCP entity of the terminal is the first time any PDCP PDU received after the rearrangement timer expires, starting from PDCP SN n + 2 to the upper layer in the ascending order all the stored PDCP SDUs of the associated PDCP SN value I can deliver it.

Meanwhile, various communication services provided to a user may have a service gap for various reasons. The service disconnection refers to a phenomenon in which the packet transmission is not continuously and continuously interrupted or discontinuously transmitted for a specific time in providing Internet services. Services provided on the Internet may be transmitted from the application server to the user via the Internet network. At this time, the packet transmitted to the user may be discontinuously transmitted according to the load condition of the network. Incoming packets can also be introduced discontinuously from various nodes in the network. In addition, depending on the application, a packet may be generated discontinuously instead of continuously generating a packet.

Even in a network (eg, LTE network) of the wireless communication system according to the present invention, packets for a service flowing into a base station are not continuously received continuously, and packet flow may be interrupted due to service disconnection.

Referring to FIG. 20, a packet is transmitted from a GW (gateway) 2060 to a base station 2030 for a service provided to the terminal 2000. The application service may be provided through a server or the like, which is transmitted to the wireless network and transmitted to the base station 2030 in the form of a packet via the GW 260. Packet traffic is then generally transmitted continuously from the GW 2060 to the base station 2030. However, service disconnection may occur in which packets are not transmitted at regular or random intervals according to network conditions or applications.

Although shown in FIG. 20, there is a slight gap from packet 1 to packet 4, this is to illustrate the flow of packets explicitly, and in practice, there is little gap or little time difference between packets. However, between packet 4 and packet 5, no packet is transmitted during the relatively long time interval corresponding to gap 1. In addition, between

packets

8 and 9, packets are not transmitted during the relatively long time interval corresponding to Gap 2. Here, Gap1 and Gap2 may be treated as service interruptions. The base station 2030 receives the transmitted packets in order from packet # 1. The received packets correspond to PDCP SDUs. That is, the received packet is stored in the PDCP buffer in the form of PDCP SDU in the PDCP entity of the PDCP layer. At this time, the PDCP SDUs stored in the buffer are sequentially processed as PDCP PDUs and transferred to the lower layer. As described above, if a time interval in which packets are received by the base station 2030 due to service disconnection occurs, the time interval may also occur in a time when PDCP PDUs are delivered to a lower layer in a PDCP entity of the base station 2030. That is, PDCP PDUs in which PDCP SDUs corresponding to

packets

4 and 5 and

packets

8 and 9 received by the base station 2030 at intervals of Gap1 and Gap2 are processed may also be delivered to a lower layer with a time difference. Can be.

When dual connectivity is configured in the terminal, in case of a single flow situation, generally one PDCP entity is associated with one RLC entity. Therefore, even if service disconnection occurs, there may be a time interval between PDCP PDUs received by the PDCP entity of the UE, but this situation does not cause a problem in the sequential reception of PDCP PDUs in the PDCP entity. The PDCP PDU generated in the PDCP entity is delivered through the RLC entity in the lower layer, especially in the case of RLC AM, which supports sequential delivery. Therefore, the incoming PDCP PDUs should be processed after a certain period of time, and the service disconnection does not cause any special problems in system performance.

However, when the dual connection is configured in the terminal, in the case of a multi-flow situation, the terminal may receive the packets through two different transmission paths. In other words, for one EPS bearer configured in the terminal and the network, the terminal receives the service through the macro base station and the small base station. For example, if one PDCP entity exists in the macro base station and one RLC entity exists in the macro base station and the small base station for one EPS bearer, the PDCP PDUs delivered by the PDCP entity of the macro base station are RLC of the macro base station. It is delivered to the PDCP entity of the terminal via the RLC entity of the entity or the small base station. Accordingly, the PDCP entity of the terminal receives PDCP PDUs that have experienced different path delays. In this case, a problem may occur such that a PDCP PDU having a large PDCP SN arrives before a PDCP PDU having a small PDCP SN, and thus, a method of rearranging PDCP SDUs in a PDCP entity should be considered. In order to rearrange PDCP SDUs in a PDCP entity, a timer considering path delay time may be used. However, additional PDCP PDU transmission delays due to service interruption may also need to be considered to rearrange PDCP SDUs.

By using the rearrangement timer according to the present invention as described above, the PDCP SDUs may be rearranged in the PDCP entity in such a manner as to secure the time that the PDCP PDU can be received in consideration of the path delay. In this case, the rearrangement timer value could be set in consideration of the path delay time. However, when a time interval occurs due to service disconnection, the service disconnection time may be much larger than the path delay time, and in this case, it may be difficult to perform PDCP SDU rearrangement using only the rearrangement timer considering the path delay time.

21 shows another example of a PDCP PDU reception timing in a PDCP entity of a terminal. FIG. 21 shows PDCP PDUs associated with 1, 2, 3, 4, 5, 6, 7, and 8 of the PDCP SNs are transmitted through the small base station (the RLC entity), and 9, 10, 14, 15, 16, 23 Assume that PDCP PDUs associated with No. 24 are transmitted through a macro base station (the RLC entity of).

21A illustrates reception of PDCP PDUs in the absence of service disruption.

Referring to FIG. 21A, the PDCP entity of the UE receives PDCP PDUs of PDCP SNs 1 to 7, delivers corresponding PDCP SDUs to a higher layer, and starts / restarts a rearrangement timer for each reception. In the absence of service disconnection, PDCP PDUs of PDCP SN 8 may be received at the PDCP entity after PDCP SN 9 PDCP PDUs are received before the rearrangement timer expires. In this case, the PDCP entity may deliver PDCP SDUs associated with

PDCP SNs

9 and 10 to a higher layer.

21B illustrates reception of PDCP PDUs when there is a service disruption. 21B illustrates a case where service disconnection occurs after PDCP PDUs of PDCP SN 7 are transmitted (or received).

Referring to FIG. 21B, when the PDCP entity of the terminal receives the PDCP PDU of PDCP SN # 7, the PDCP entity transfers the corresponding PDCP SDU to the higher layer and restarts the rearrangement timer. As service interruption occurs, the delay due to service interruption is generated in addition to the path delay in receiving the PDCP PDU. Accordingly, PDCP PDUs of PDCP SN 8 are not received and the rearrangement timer expires. This is because the rearrangement timer is designed in consideration of the path delay time and does not consider the delay time due to service disconnection. In this case, due to expiration of the rearrangement timer, PDCP SN 8 PDCP PDUs (or PDCP SDUs) are considered to have been removed, so that a series of processing is performed (

e.g. PDCP SN

9, 10 PDCP SDUs are higher layers). PDCP PDUs of PDCP SN 8 may be received. In such a case, the PDCP entity of the UE may not be able to guarantee the ascending delivery of PDCP SDUs to higher layers.

Therefore, there is a need for a method for PDCP SDU rearrangement that can be additionally applied in case of service disconnection, which can be performed as follows.

For example, when a service disconnection occurs, the PDCP entity of the base station may transmit a PDCP PDU delivered for the first time after the service interruption occurs through a path having a relatively short path delay time. For example, when the PDCP PDU is delivered to the PDCP entity of the UE via the RLC entity of the macro base station, the path delay is relatively shorter than when the PDCP PDU is delivered to the PDCP entity of the UE via the RLC entity of the UE. It can be seen that you have time. As such, when the first PDCP PDU delivered after a service disconnection is delivered through a path having a relatively (or the shortest) path delay time, the PDCP PDU of the UE before the rearrangement timer expires. Can increase the likelihood of receiving.

22 shows an example of a PDCP PDU transmission scheme considering service disconnection according to the present invention. 22 shows PDCP PDUs associated with Nos. 1, 2, 3, 4, 5, 6, 7, and 8 of the PDCP SNs are transmitted through the small base station (the RLC entity of) and 9, 10, 14, 15, 16, 23 Assume that PDCP PDUs associated with No. 24 are transmitted through a macro base station (the RLC entity of). In addition, FIG. 22 assumes a case where service disconnection occurs after transmission of PDCP PDUs of PDCP SN # 7.

Assuming that FIG. 22 shows that the PDCP entity of the base station transmits PDCP SN # 7 PDCP PDUs, if a service disconnection occurs, the PDCP PDUs of PDCP SN # 8 may not use the small base station (the RLC entity) but the macro base station (the RLC entity). Through the PDCP entity of the terminal through. This is the case where the path delay time through the small base station is larger than the path delay time through the macro base station. In general, it may be assumed that a transmission through a small base station including an X2 (or Xn) path delay is larger than a transmission through a macro base station. However, in some cases, the path delay of the transmission through the small base station may be smaller than the path delay of the transmission through the macro base station, and the macro base station may determine which path path is short.

In this case, PDCP PDUs of PDCP SN # 8 transmitted through the macro base station may be received by the PDCP entity of the UE before the rearrangement timer expires, and the PDCP entity of the UE may ensure the ascending delivery of PDCP SDUs to higher layers. Can be.

As another example, when a service break occurs, the PDCP entity of the base station first delivers the PDCP PDU delivered after the service break occurs to the RLC entity of the macro base station and the RLC entity of the small base station, respectively. As such, when a PDCP PDU delivered for the first time after the service disconnection is duplicated and delivered to the RLC entity of the macro base station and the RLC entity of the small base station, the PDCP entity of the UE may receive and process the PDCP PDU delivered first. As a result, it is possible to increase the likelihood of receiving the PDCP PDU before the rearrangement timer expires. In this case, the PDCP entity of the UE may receive a PDCP PDU that arrives first among the duplicate PDCP PDUs, perform a process such as storage or forwarding to a higher layer, and remove the second received PDCP PDU.

23 shows another example of a PDCP PDU transmission scheme considering service disconnection according to the present invention. FIG. 23 shows PDCP PDUs associated with 1, 2, 3, 4, 5, 6, 7, and 8 of the PDCP SNs are transmitted through the small base station (the RLC entity), and 9, 10, 14, 15, 16, 23 Assume that PDCP PDUs associated with No. 24 are transmitted through a macro base station (the RLC entity of). In addition, FIG. 23 assumes a case where a service disconnection occurs after transmission of PDCP PDUs of PDCP SN # 7.

Referring to FIG. 23, if a service disconnection occurs after PDCP SN # 7 PDCP PDU transmission, the PDCP entity duplicates the PDCP PDU # 8 of PDCP SN # 8 and the small base station (RLC entity of) and macro base station (RLC entity of). Through the PDCP entity of the terminal through the transmission. As such, when the PDCP PDUs of PDCP SN No. 8 that are first transmitted after the service disconnection are repeatedly transmitted through the macro base station and the small base station, the PDCP PDU transmitted through the base station having the smallest path delay is first received by the PDCP entity of the UE. Can be. In this case, the PDCP entity of the terminal may receive PDCP PDUs of PDCP SN 8 before the rearrangement timer expires. When the PDCP entity of the terminal first receives a PDCP PDU of PDCP SN # 8, the PDCP entity transmits a corresponding PDCP SDU to a higher layer and restarts the rearrangement timer. Since the PDCP PDU of PDCP SN # 8 received later corresponds to duplicate reception, it can be removed.

Even in a network (for example, an LTE network) of a wireless communication system according to the present invention, packets for a service flowing into a base station (for example, a macro base station) are not continuously received continuously, and packet flow may be interrupted due to service disconnection. It may be.

Referring to FIG. 24, a packet is transmitted from a GW (gateway) 2460 to a base station 2430 for a service provided to the terminal 1400. The base station 2430 may be, for example, a macro base station. The application service may be provided through a server or the like, which is transmitted to the wireless network and transmitted to the base station 2430 in the form of a packet via the GW 2460. Packet traffic is then generally transmitted continuously from the GW 2460 to the base station 2430. However, service disconnection may occur in which packets are not transmitted at regular or random intervals according to network conditions or applications.

Although shown in FIG. 24, there is a slight gap from packet 1 to packet 4, this is to illustrate the flow of the packet explicitly, and in practice, there is little or no time difference between the packets. However, between packet 4 and packet 5, no packet is transmitted during the relatively long time interval corresponding to gap 1. In addition, between

packets

8 and 9, packets are not transmitted during the relatively long time interval corresponding to Gap 2. Here, Gap1 and Gap2 may be treated as service interruptions. The base station 2430 side receives the transmitted packets in order from packet # 1. The received packets correspond to PDCP SDUs. That is, the received packet is stored in the PDCP buffer in the form of PDCP SDU in the PDCP entity of the PDCP layer. At this time, the PDCP SDUs stored in the buffer are sequentially processed as PDCP PDUs and transferred to the lower layer. As described above, if a time interval in which packets are received at the base station 2430 due to service disconnection occurs, the time interval may also occur at a time when PDCP PDUs are delivered to a lower layer in the PDCP entity of the base station 2430. That is, PDCP PDUs in which PDCP SDUs corresponding to

packets

4 and 5 and

packets

8 and 9 received by the base station 2430 at intervals of Gap1 and Gap2 are processed may also be delivered to a lower layer with a time difference. Can be.

When dual connectivity is configured in the terminal, in case of a single flow situation, generally one PDCP entity is associated with one RLC entity. Therefore, even if service disconnection occurs, a time interval between PDCP PDUs received by the PDCP entity of the UE may exist, but this situation does not cause a problem. The PDCP PDU generated in the PDCP entity is delivered through the RLC entity in the lower layer, especially in the case of RLC AM, which supports sequential delivery. Therefore, the incoming PDCP PDUs should be processed after a certain period of time, and the service disconnection does not cause any special problems in system performance.

As such, when a time interval occurs due to service disconnection, the service disconnection time may be much greater than the path delay time. Accordingly, there is a need for a PDCP SDU rearrangement method capable of delivering PDCP SDUs to an upper layer in ascending order in consideration of service interruption as well as path delay.

Hereinafter, in another embodiment of the present invention, in consideration of situations such as reception delay and service disconnection through multipath, a standby timer that is driven when the PDCP entity receives the PDCP PDU out-of-sequence ( Based on the wait timer), we propose a method of performing PDCP SDU rearrangement. The wait timer may be referred to as an out-of-sequence timer. The present invention can be applied to both a downlink data transfer procedure and an uplink data transfer procedure, and the following description will focus on the downlink data transfer procedure.

25 illustrates a PDCP SDU rearrangement method in consideration of multiflow according to another embodiment of the present invention. 25 shows that PDCP PDUs of PDCP SNs 1 to 8 are delivered through an RLC entity of a macro base station, and PDCP PDUs of

PDCP SNs

9, 10, 14, 15, 16, 23 and 24 are delivered through an RLC entity of a small base station. Assume the case In addition, FIG. 15 assumes that other PDCP PDUs are not delivered for a certain time due to service disconnection after the PDCP PDUs of PDCP SN 7 are delivered.

FIG. 25A illustrates a case in which PDCP PDUs of PDCP SN 9 are received without PDCP PDUs of PDCP SN 8 after

PDCP SN

1,2, 3, 4, 5, 6, and 7 PDCP PDUs are received by the PDCP entity of the UE.

Referring to FIG. 25A, a PDCP entity of a terminal sequentially receives PDCP PDUs of PDCP SNs 1 to 7. The PDCP entity of the terminal processes the received PDCP PDUs and delivers corresponding PDCP SDUs to a higher layer. When the PDCP PDUs are sequentially received, the PDCP entity of the terminal does not run the wait timer. After the PDCP entity of the terminal does not receive other PDCP PDUs for a predetermined time, the PDCP entity receives the PDCP PDU of PDCP SN # 9. Since the PDCP entity of the UE has not yet received PDCP PDUs of PDCP SN 8, PDCP PDUs of PDCP SN 9 are determined to be out of sequence and drive a standby timer.

In this case, the sequential reception may be determined based on, for example, the following criteria. If the PDCP SN of the last PDCP SDU delivered to the upper layer is defined as Last_Submitted_PDCP_RX_SN and the PDCP SN of the PDCP SDU expected to be sequentially received next is defined as Next_PDCP_RX_SN, Next_PDCP_RX_SN is represented by

Equations

1 and 2 above. You can follow either.

In addition, the wait timer may mean a timer waiting for reception of a sequential PDCP PDU by a PDCP entity receiving an out of sequence PDCP PDU. The wait timer may be set to, for example, a value of 20 to 60 ms in consideration of the path delay time of the X2 (or Xn) interface between the macro base station and the small base station.

As described above, when the standby timer is driven based on the non-sequential reception of the PDCP PDU, it is possible to prevent the timer from expiring due to time delay due to service disconnection. For example, a timer for rearranging PDCP SDUs may be operated based on sequential reception of PDCP PDUs, but in this case, in case of such service disconnection, the timer may undesirably expire and may be received when waiting longer. PDCP PDUs can be incorrectly treated as removed. However, by operating the standby timer based on the non-sequential reception of the PDCP PDU as described above, it is possible to solve the problem caused by the time delay due to service disconnection.

FIG. 25B assumes that, after FIG. 25A, the PDCP entity of the UE receives PDCP PDUs of PDCP SN 8 after the waiting timer expires after receiving

PDCP SNs

10 and 14 PDCP PDUs.

Referring to FIG. 25B, the PDCP entity of the UE determines that PDCP PDUs of

PDCP SN

10 and 14 are still out of order. Subsequently, if PDCP PDUs of PDCP SN # 8 are received, this is determined as sequential reception. The PDCP entity of the terminal stops the wait timer when a PDCP PDU of PDCP SN 8 is received. Then, starting from PDCP SN 8, all stored PDCP SDUs of consecutively related PDCP SN values are delivered to the upper layer in ascending order. For example, the PDCP

entities PDCP SN

8, 9, and 10 PDCP SDUs of the UE are delivered to the upper layer in ascending order.

FIG. 25C assumes a case where the PDCP entity of the UE receives the PDCP PDU of PDCP SN 15 after FIG. 25B.

Referring to FIG. 25C, when the PDCP entity of the UE receives the PDCP PDU of PDCP SN 15, it determines that the PDCP PDU is out of order and drives the standby timer again. The PDCP entity of the terminal waits for the PDCP PDU of PDCP SN 11, which is expected to receive sequentially, until the waiting timer expires.

If the PDCP PDUs of the PDCP SN 11 are not received until the wait timer expires, for example, the PDCP entity of the terminal does not store all of the PDCP SN values continuously associated with the PDCP SN 11 starting from the PDCP SN 11 when the wait timer expires. PDCP SDUs (eg PDCP SDUs of

PDCP SNs

11, 12, 13) that have not been determined are removed and then all stored PDCP PDUs of successively associated PDCP SN values starting with the PDCP SN (eg, For example, PDCP SDUs of PDCP SN 14 and 15) are transmitted to an upper layer.

As another example, when the PDCP entity of the UE receives a PDCP PDU for the first time after the waiting timer expires, it is determined that all unsaved PDCP SDUs of consecutively related PDCP SN values starting from the PDCP SN 11 are removed, and then the PDCP SN Starting from then, all stored PDCP PDUs of consecutively related PDCP SN values are transmitted to the upper layer.

According to the present invention as described above, when the terminal is configured for dual connection with the macro base station and the small base station, when performing the multi-flow downlink reception, due to the transmission path delay, out of order to the PDCP entity of the terminal Even if PDCP PDUs are received, rearrangement of PDCP SDUs may be performed based on a waiting timer, ascending order of PDCP SDUs to an upper layer, and transmission efficiency may be improved.

In addition, since the standby timer is driven based on the non-sequentially received PDCP PDU, the PDCP SDU rearrangement can be smoothly performed even if a time delay occurs while the packet is received by the macro base station due to service disconnection.

Referring to FIG. 26, when a PDCP entity of a terminal sequentially receives PDCP PDUs of PDCP SN n, the PDCP entity transmits a corresponding PDCP SDU to an upper layer (S2600). The PDCP entity of the UE may check whether the corresponding PDCP PDUs are sequentially received based on the PDCP SN of the received PDCP PDU.

When the PDCP entity of the UE receives a PDCP PDU of PDCP SN n + k (k is a natural number other than 1) instead of PDCP SN n + 1, which is expected to be sequentially received, the PDCP entity drives a standby timer (S2610). . The wait timer may refer to a timer waiting for a PDCP entity receiving a non-sequential PDCP PDU to receive a sequential PDCP PDU.

For example, in FIG. 25A, after receiving a PDCP PDU corresponding to PDCP SN 7, the UE may be in a state of receiving 8 PDCP PDUs of PDCP SN 7 + 1. In this case, the UE receives a PDCP PDU corresponding to SN 9 instead of PDCP SN 8, which is expected to receive after a predetermined time elapses. The terminal drives the timer to wait for the reception of PDCP PDU 8 after the reception of PDCP PDU 9. When the terminal receives the PDCP PDU corresponding to PDCP SN 9, the PDCP PDU corresponding to PDCP SN 7 is transmitted to a higher layer and is no longer stored in the terminal. However, the terminal may store the SN of the PDCP PDU transmitted to the upper layer and may know the PDCP SN that it expects to receive next.

In addition, referring to FIG. 25B, the terminal transmits all PDCP PDUs corresponding to

PDCP SNs

8, 9, and 10 to the upper layer upon reception of PDCP PDU # 8. Accordingly, the terminal corresponds to PDCP corresponding to PDCP SN # 10. It is understood that the PDU is transmitted to a higher layer. At this time, the UE is aware of the PDCP SN 11 expected to receive the next time. In FIG. 25C, when the UE receives a PDCP PDU corresponding to PDCP SN 15, the UE differs from PDCP SN 11, which was expected to be received next, so that the UE drives a standby timer to wait for reception of PDCP PDU corresponding to PDCP SN 11. . In this case, the UE stores PDCP PDU Nos. 14 and 15. Although PDCP SN 11 is expected to receive the wait timer, it is reasonable to determine that

PDCP PDUs

12 and 13 were transmitted through macro or small base stations before

PDCP PDUs

14 and 15. Therefore, when the terminal receives the PDCP PDU No. 15, it is appropriate to receive within the waiting timer operation period. If not received, it is considered discarded. Therefore, PDCP PDUs that do not arrive at the time when the waiting timer, which is driven by the UE when the PDCP PDU 15 is received, may be determined to have been removed.

The PDCP entity of the UE checks whether the PDCP PDU of PDCP SN n + 1 is received before the waiting timer expires (S2620). The PDCP entity of the terminal does not start / restart the standby timer even if the standby timer receives another out of sequence PDCP PDU during operation.

If the PDCP entity of the UE receives PDCP SN n + 1 PDCP PDUs before the timer expires in S2620, the PDCP entity of the UE stops the standby timer and starts from PDCP SN n + 1. All stored PDCP SDUs of consecutively related PDCP SN values are delivered to the upper layer in ascending order (S2630).

If the wait timer expires in S2620, that is, if the PDCP entity of the terminal does not receive PDCP SN n + 1 PDCP PDU until the wait timer expires, the PDCP entity of the terminal is smaller than PDCP SN n + k times All PDCP SDUs associated with PDCP SN values that have not yet been received are considered to have been removed (S2640). That is, the PDCP entity of the UE removes PDCP SDUs except for the PDCP SDUs currently stored among the associated PDCP SDUs having a PDCP SN value smaller than the PDCP SN value n + k starting from the PDCP SN value n + 1 expected to be sequentially received. Can be considered. In this case, the PDCP entity of the terminal delivers all stored PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n + k to a higher layer (S2650), starting with PDCP SN n + k and having all consecutive PDCP SN values. The stored PDCP SDUs are transferred to an upper layer (S2660). As an example, the PDCP entity of the terminal delivers all stored PDCP SDUs associated with PDCP SN values less than PDCP SN n + k times to the upper layer in ascending order at the time of waiting timer expiration, and starts continuously from n + k times All stored PDCP SDUs of SN value may be delivered to the upper layer in ascending order. As another example, the PDCP entity of the terminal forwards all stored PDCP SDUs associated with the PDCP SN value less than PDCP SN n + k to the upper layer at the time of receiving any PDCP PDU for the first time after the rearrangement timer expires, Starting from n + k, all stored PDCP SDUs of consecutively related PDCP SN values may be delivered to the upper layer in ascending order.

Or all unsaved PDCP SDUs starting with PDCP SN n + 1 up to successively associated PDCP SN values PDCP SN n + m are considered to have been removed and the last (largest) PDCP SN value of the PDCP SDUs considered to have been removed. Starting from +1 of n + m, all stored PDCP SDUs of consecutively associated PDCP SN values may be delivered to the upper layer in ascending order. FIG. 27 is an example of a block diagram of a macro base station, a small base station, and a terminal according to the present invention. to be.

Referring to FIG. 27, the terminal 2700 according to the present invention may configure dual connectivity with the macro base station 2730 and the small base station 2760. In addition, the terminal 2700, the macro base station 2730 and the small base station 2760 according to the present invention supports the above-described multi-flow.

The macro base station 2730 includes a macro transmitter 2735, a macro receiver 2740, and a macro processor 2750.

The macro receiver 2740 receives a packet for one EPS bearer from the S-GW. The macro processor 2750 controls the PDCP entity of the macro base station 2730 to process PDCP SDUs corresponding to the received packet and generate PDCP PDUs. The macro processor 2750 distributes the PDCP PDUs according to a reference, transfers (or transmits) a part of the PDCP PDUs to the RLC entity of the macro base station 2740, and transmits the PDCP PDUs to the terminal through the macro transmitter 2735. The macro processor 2750 transmits (or forwards) the remaining part to the RLC entity of the small base station 2760 through the macro transmitter 2735. In this case, PDCP SDUs corresponding to PDCP PDUs may be identified and indicated as PDCP SN.

In addition, the macro processor 2750 generates information on the rearrangement timer for the PDCP SDU and transmits the information to the terminal through the macro transmitter 2735. The information on the rearrangement timer may be signaled exclusively to the terminal 2700 or may be signaled in a broadcast manner. The macro transmitter 2735 may transmit the information on the rearrangement timer to the terminal 2700 through an RRC message (eg, an RRC connection reconfiguration message).

On the other hand, when a service gap occurs in which the packet is not received for a predetermined time or more, the macro processor 2750 receives the PDCP entity of the terminal 2700 for the first time after the service disconnection of the PDCP entity of the macro processor 2750. The PDCP PDU delivered to the entity may be controlled to be delivered through the RLC entity of the macro base station 2730. In addition, the macro processor 2750 may duplicate the PDCP PDU delivered by the PDCP entity to the PDCP entity of the terminal 2700 for the first time after the service disconnection, and thus the RLC entity and the small of the macro base station 2730. Control may be delivered via all of the RLC entities of base station 2760.

In addition, the macro processor 2750 may generate information on a wait timer for the PDCP SDU and transmit the information to the terminal 2700 through the macro transmitter 2735. The information on the wait timer may be signaled exclusively to the terminal 2700 or may be signaled in a broadcast manner. The macro transmitter 2735 may transmit the information on the wait timer to the terminal 2700 through an RRC message (eg, an RRC connection reconfiguration message).

The small base station 2760 includes a small transmitter 2765, a small receiver 2770, and a small processor 2780.

The small receiver 2770 receives the remaining PDCP PDUs from the macro base station 2730.

The small processor 2780 processes the PDCP PDU by controlling the RLC entity, the MAC entity, and the PHY layer of the small base station 2730, and transmits the PDCP PDU to the terminal through the small transmitter 2765.

The terminal 2700 includes a terminal receiver 2705, a terminal transmitter 2710, and a terminal processor 2720. The terminal processor 2720 performs the functions and controls necessary to implement the features of the present invention as described above.

The terminal receiver 2705 receives the information on the rearrangement timer from the macro base station 2730. The information on the rearrangement timer may be included in an RRC message (eg, an RRC connection reconfiguration message) and received by the terminal receiver 2705. In this case, the terminal transmitter 2710 may transmit an RRC connection reconfiguration complete message to the macro base station 2730.

The terminal receiver 2705 may receive information on a standby timer from the macro base station 2730. The information on the wait timer may be included in an RRC message (eg, an RRC connection reconfiguration message) and may be received by the terminal receiver 2705. In this case, the terminal transmitter 2710 may transmit an RRC connection reconfiguration complete message to the macro base station 2730.

In addition, the terminal receiving unit 2705 receives data for PDCP PDUs from the macro base station 2730 and the small base station 2760, respectively.

The terminal processor 2720 interprets the data and controls the PHY layer (s), the MAC entity (s), the RLC entity (s), and the PDCP entity of the terminal 2700 to obtain PDCP SDUs.

When the PDCP 2720 sequentially receives the PDCP SN n PDCP PDUs from the PDCP entity, the UE processor 2720 transfers the corresponding PDCP SDU to the higher layer. Here, the terminal processor 1720 may check whether the corresponding PDCP PDU is sequentially received by the PDCP entity based on the PDCP SN of the received PDCP PDU. For example, the PDCP SN value of the PDCP SDU (or PDU) which is expected to be sequentially received based on

Equation

1 or 2 may be determined. When the PDCP PDUs are sequentially received, the UE processor 2720 starts the rearrangement timer if the rearrangement timer is not running, and restarts the rearrangement timer if the rearrangement timer is running. In this case, the terminal processor 2720 restarts the rearrangement timer every time the PDCP PDU is sequentially received while the rearrangement timer is driven to the PDCP entity of the terminal. Here, the rearrangement timer corresponds to a timer for waiting for PDCP PDUs that are expected to be sequentially received after the last sequentially received PDCP PDUs. The terminal processor 2720 may determine whether the corresponding PDCP PDU is sequentially received by the PDCP entity based on the PDCP SN of the corresponding PDCP PDU.

The terminal processor 2720 checks whether PDCP SN n + 1 PDCP PDUs are received by the PDCP entity before the rearrangement timer expires. The terminal processor 2720 determines that the PDCP entity is not a sequential reception even though PDCP PDUs of PDCP SN n + 2 and PDCP SN n + 3 are received by the PDCP entity, and are not PDCP SN n + 2 and PDCP SN n. Store PDCP SDUs corresponding to +3 PDCP PDUs in a buffer and maintain a rearrangement timer.

If the PDCP entity receives PDCP SN n + 1 PDCP PDUs before the rearrangement timer expires, the terminal processor 2720 ascends all stored PDCP SDUs of consecutively associated PDCP SN values starting from PDCP SN n + 1. To the upper layer of the PDCP entity.

If the rearrangement timer expires, that is, if the PDCP PDU of PDCP SN n + 1 has not been received until the rearrangement timer expires in the PDCP entity of the terminal, the terminal processor 2720 is assigned to PDCP SN n + 1 The associated PDCP SDUs are considered to have been removed, and all PDCP SDUs of the associated PDCP SN value are delivered to the upper layer in ascending order starting from PDCP SN n + 2 stored in the PDCP entity. For example, the terminal processor 2720 may deliver all PDCP SDUs of consecutively related PDCP SN values to the upper layer starting from PDCP SN n + 2 stored in the PDCP entity at the time of reordering timer expiration in ascending order. As another example, the terminal processor 2720, in the ascending order of all PDCP SDUs of consecutively associated PDCP SN values starting from PDCP SN n + 2 stored in the PDCP entity, at the time of receiving any PDCP PDU for the first time after the rearrangement timer expires. Can be passed to the layer.

Meanwhile, when the PDCP PDU of PDCP SN n + k (where k is a natural number other than 1) is received instead of PDCP SN n + 1, which is expected to be sequentially received, the PD processor 1720 drives the standby timer. can do.

If a PDCP PDU of PDCP SN n + 1 is received at the PDCP entity before the wait timer expires, the UE processor 2720 stops the wait timer. The terminal processor 2720 transfers all stored PDCP SDUs of consecutively related PDCP SN values starting with PDCP SN n + 1 to the upper layer of the PDCP entity in ascending order.

If the wait timer expires, that is, if no PDCP PDUs of PDCP SN n + 1 are received until the PDCP entity expires, the terminal processor 2720 has a PDCP SN value of less than PDCP SN n + k times. All associated unreceived PDCP SDUs may be considered to have been removed.

In this case, the terminal processor 2720 transfers all stored PDCP SDUs associated with a PDCP SN value smaller than PDCP SN n + k times to an upper layer in ascending order. In addition, the terminal processor 2720 transfers all stored PDCP SDUs of PDCP SN values consecutively associated with PDCP SN n + k to the upper layer in ascending order.

For example, the terminal processor 2720 may deliver all stored PDCP SDUs associated with a PDCP SN value smaller than the PDCP SN n + k stored in the PDCP entity to the upper layer at the time of waiting timer expiration, starting from PDCP SN n + k. All PDCP SDUs of consecutively associated PDCP SN values may be delivered to the upper layer in ascending order. As another example, the terminal processor 2720, in the ascending order of all stored PDCP SDUs associated with a PDCP SN value less than PDCP SN n + k stored in the PDCP entity, at the time of receiving any PDCP PDU for the first time after the wait timer expires. All PDCP SDUs of PDCP SN values consecutively associated with PDCP SN n + k may be delivered to the upper layer in ascending order.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims

In a Packet Data Convergence Protocol (PDCP) entity of a UE configured with dual connectivity, as a method for reordering PDCP SDUs (Service Data Units),

When sequentially receiving PDCP sequence number (PDCP SN) packet data units (PDUs) n times, delivering a corresponding PDCP SDU to a higher layer and starting / restarting a rearrangement timer; And

And restarting the rearrangement timer when a PDCP PDU of the PDCP SN n + 1 times expected to be sequentially received before the rearrangement timer expires is restarted. .
The method of claim 1,

The value of the rearrangement timer is set to a value within 20ms ~ 60ms, PDCP SDU rearrangement method.
The method of claim 1,

If the PDCP SN n + 1 PDCP PDUs are received before the rearrangement timer expires, all PDCP SN values that have a contiguously associated PDCP SN starting from the PDCP SN n + 1 are received. Delivering the stored PDCP SDUs to the upper layer in ascending order.
The method of claim 3, wherein

And if the PDCP PDU of PDCP SN n + 1 is not received until the rearrangement timer expires, determining that the PDCP SDU associated with PDCP SN n + 1 is removed. How to rearrange SDUs.
The method of claim 4, wherein

If the PDCP SN n + 1 PDCP PDUs are not received until the rearrangement timer expires, the PDCP PDUs of PDCP SN n + 1 which are expected to be sequentially received are the RLCs of any one of a macro base station and a small base station. If it is expected to be received by the PDCP entity via an entity, compare n + 1 with k, which is the maximum PDCP SN value of PDCP PDUs received by the PDCP entity via an RLC entity configured in another base station, and k> n If +1, the PDCP SDU rearrangement method characterized in that it is determined that the PDCP SDU associated with PDCP SN n + 1 has been removed.
The method of claim 4, wherein

If the PDCP SN n + 1 PDCP PDUs are not received until the rearrangement timer expires, starting from PDCP SN n + 2, all stored PDCP SDUs of consecutively related PDCP SN values are delivered to the upper layer in ascending order. PDCP SDU arrangement method, characterized in that it comprises a step.
The method of claim 6,

And all stored PDCP SDUs of consecutively associated PDCP SN values starting from the PDCP SN n + 2 at the time when the rearrangement timer expires, to the upper layer in ascending order.
The method of claim 6,

At the time when any PDCP PDU is received for the first time after the rearrangement timer expires, all stored PDCP SDUs of consecutively related PDCP SN values are delivered to the upper layer in ascending order starting from the PDCP SN n + 2. PDCP SDU array method.
A dual connectivity (dual connectivity) is configured, the terminal (UE) to rearrange (reordering) PDCP Service Data Units (SDUs),

A receiver configured to receive PDCP PDUs from at least one of a master base station and a small base station having dual connectivity with the terminal;

A processor for delivering a corresponding PDCP SDU to a higher layer and starting / restarting a rearrangement timer when PDCP sequence number (PDCP PDU) packet data units (PDCP) n times among the received PDCP PDUs are sequentially received. Including,

And the processor restarts the rearrangement timer when a PDCP PDU of PDCP SN n + 1 received sequentially is received before the rearrangement timer expires.
In a Packet Data Convergence Protocol (PDCP) entity of a UE configured with dual connectivity, as a method for reordering PDCP SDUs (Service Data Units),

Sequentially receiving PDCP sequence number (SN) PDCP Packet Data Units (PDUs);

And when a PDCP PDU of PDCP SN n + k is received instead of PDCP SN n + 1, which is expected to receive the next sequential reception, driving a wait timer. Rearrangement method.
The method of claim 10,

The value of the wait timer is set to a value within 20ms ~ 60ms, PDCP SDU rearrangement method.
The method of claim 10,

The PDCP SDU rearrangement method is characterized in that the standby timer is driven only when the standby timer is not running even when a PDCP PDU of PDCP SN n + k, which is a non-sequential reception, is received.
The method of claim 10,

If the PDCP SN n + 1 PDCP PDUs are received before the wait timer expires, all stored with associated PDCP SN values starting from the PDCP SN n + 1 and continuously associated with them. Delivering the PDCP SDUs to the upper layer in ascending order.
The method of claim 13,

If the PDCP SN n + 1 PDCP PDUs are not received until the wait timer expires, the not yet received PDCP SDUs associated with the PDCP SN value less than the PDCP SN n + k times are removed. And determining the PDCP SDU rearrangement method.
The method of claim 14,

If the PDCP SN n + 1 PDCP PDUs are not received until the wait timer expires, forwarding all stored PDCP SDUs associated with a PDCP SN value less than PDCP SN n + k to an upper layer in ascending order. Characterized in that, PDCP SDU rearrangement method.
The method of claim 15,

At the time when the wait timer expires, deliver all stored PDCP SDUs having a PDCP SN value less than the PDCP SN n + k to an upper layer in ascending order.
The method of claim 15,

At the time when any PDCP PDU is received for the first time after the waiting timer expires, all stored PDCP SDUs of consecutively related PDCP SN values starting from the PDCP SN n + k are delivered to the upper layer in ascending order. PDCP SDU rearrangement method.
The method of claim 15,

If the PDCP SN n + 1 PDCP PDUs are not received until the wait timer expires, starting with PDCP SN n + k, all stored PDCP SDUs of consecutively related PDCP SN values are delivered to the upper layer in ascending order. PDCP SDU rearrangement method, characterized in that it comprises a step.
The method of claim 18,

And all stored PDCP SDUs associated with a PDCP SN value less than PDCP SN n + k are delivered to the upper layer in ascending order when the wait timer expires.
The method of claim 18,

At the time when any PDCP PDU is received for the first time after the waiting timer expires, all stored PDCP SDUs of consecutively related PDCP SN values are delivered to the upper layer in ascending order starting from the PDCP SN n + k. , PDCP SDU Rearrangement Method.