KR20200115202A - Method for transmitting and receiving data in handover procedure - Google Patents

Abstract

According to the present invention, an operation method of a terminal performing handover between a source base station and a target base station comprises the steps of: receiving first packet data units from the source base station, and receiving second packet data units from the target base station; receiving, by a first packet data convergence protocol (PDCP) layer of the terminal, the first packet data units from a lower layer of the first PDCP layer; receiving, by a second PDCP layer of the terminal, the second packet data units from a lower layer of a second PDCP; and rearranging the first packet data units and the second packet data units by an upper layer of the first PDCP layer and the second PDCP based on a PDCP sequence number. The first packet data units and the second packet data units are transmitted to the upper layer according to the PDCP sequence number. Accordingly, the performance of a communication system may be increased.

Description

Data transmission/reception method and apparatus in handover procedure {METHOD FOR TRANSMITTING AND RECEIVING DATA IN HANDOVER PROCEDURE}

The present invention relates to a method of transmitting and receiving data in a handover procedure, and more particularly, to a method and apparatus for transmitting and receiving data in a handover procedure performed in a mobile communication system.

When the terminal moves in the communication system and moves to the coverage of the target base station through the coverage of the source base station, handover may occur. When a handover occurs due to movement of the terminal, the terminal may release the connection with the source base station and attempt to connect to the target base station.

In this case, the terminal may not be able to perform data communication from the time when the terminal receives the handover command from the source base station to the time when the target base station receives the handover completion message from the terminal. That is, data disconnection time may occur. In general, the disconnection time is several tens of ms. If the terminal is using an application that requires a real-time service, the corresponding service may not be provided smoothly because interaction with the network is impossible during the disconnection time. For example, when the terminal uses a video call or video conference service, a video interruption phenomenon may occur. Data disconnection time can be seen as a major factor that makes real-time interaction with the network difficult. In addition, when the terminal performs handover according to the LTE (Long-Term Evolution) or NR (New Radio) standard, the data disconnection time may additionally increase due to an operation of reordering data sequence numbers.

An object of the present invention for solving the above problems is to provide a data transmission method and apparatus capable of reducing a data disconnection time occurring in a process of performing a handover.

In accordance with the present invention for achieving the above object, a method of operating a terminal for performing handover between a source base station and a target base station includes receiving a message for handover from the source base station to the target base station, and Performing a connection establishment procedure to the target base station while maintaining the connection with the source base station, receiving first packet data units (PDUs) from the source base station, and second packet data from the target base station Receiving units, a first PDCP (Packet Data Convergence Protocol) layer of the terminal receiving the first packet data units from a lower layer of the first PDCP layer, the second PDCP layer of the terminal 2 receiving the second packet data units from a lower layer of PDCP, and an upper layer of the first PDCP layer and the second PDCP based on the first packet data units and the second packet data units based on a PDCP sequence number. And performing reordering, wherein the first packet data units and the second packet data units are transmitted to an upper layer according to the PDCP sequence number.

According to embodiments of the present invention, by transmitting data to an upper layer without performing rearrangement of data sequence numbers in the RLC (Radio Link Control) layer with the source base station of the terminal and/or the RLC layer with the target base station, It is possible to minimize the data disconnection time occurring during the handover process. That is, the terminal may perform handover with reduced latency and improved performance. In addition, the terminal can provide a handover service with high data transmission efficiency and a minimized service disconnection time.

The accompanying drawings, which are included as part of the detailed description to aid in understanding of the present invention, provide embodiments for the present invention, and describe the technical idea of the present invention together with the detailed description.
1 is a conceptual diagram illustrating a communication network.
2 is a block diagram showing a communication node.
3 is a state transition diagram of a terminal in a handover procedure.
4 is a flow chart showing a first embodiment of a handover procedure.
5 is a flow chart showing a second embodiment of a handover procedure.
6 to 11 are conceptual diagrams illustrating a process of performing a handover by a terminal based on a dual active protocol stack.
12 is a flowchart illustrating a method of operating a terminal.
13 is a conceptual diagram illustrating an operation performed in a Radio Link Control (RLC) layer of a terminal in Long Term Evolution (LTE).
14 to 17 are conceptual diagrams illustrating operations performed in a packet data convegence protocol (PDCP) layer of a terminal in an LTE system.
18 to 20 are conceptual diagrams illustrating operations performed in a PDCP layer of a terminal in a New Radio (NR) system.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to a specific embodiment, it is to be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in the present application. Does not.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, in order to facilitate an overall understanding, the same reference numerals are used for the same elements in the drawings, and duplicate descriptions for the same elements are omitted.

Throughout the specification, a network is, for example, a wireless Internet such as WiFi (wireless fidelity), a mobile Internet such as WiBro (wireless broadband internet) or WiMax (world interoperability for microwave access), and a global system for mobile communication (GSM). ) Or a 2G mobile communication network such as code division multiple access (CDMA), a 3G mobile communication network such as wideband code division multiple access (WCDMA) or CDMA2000, a high speed downlink packet access (HSDPA) or a high speed uplink packet access (HSUPA). It may include a 3.5G mobile communication network, a 4G mobile communication network such as a long term evolution (LTE) network or an LTE-Advanced network, and a 5G mobile communication network.

Throughout the specification, a terminal is a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, user equipment, and an access terminal. And the like, and may include all or part of functions such as a terminal, a mobile station, a mobile terminal, a subscriber station, a mobile subscriber station, a user equipment, and an access terminal.

Here, a desktop computer, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smart phone, and a smart watch that can communicate with a terminal. (smart watch), smart glass, e-book reader, PMP (portable multimedia player), portable game console, navigation device, digital camera, DMB (digital multimedia broadcasting) player, digital voice Recorder (digital audio recorder), digital audio player (digital audio player), digital video recorder (digital picture recorder), digital video player (digital picture player), digital video recorder (digital video recorder), digital video player (digital video player) ) Can be used.

Throughout the specification, a base station is an access point, a radio access station, a node B, an evolved node B, a base transceiver station, and an MMR. mobile multihop relay)-BS, or the like, and may include all or part of functions such as a base station, an access point, a radio access station, a nodeB, an eNodeB, a transmission/reception base station, and MMR-BS.

1 is a conceptual diagram showing a communication network according to an embodiment of the present invention. Referring to FIG. 1, the communication network 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes is a communication protocol based on code division multiple access (CDMA), a communication protocol based on wideband CDMA (WCDMA), a communication protocol based on time division multiple access (TDMA), and frequency division multiple access (FDMA). access) based communication protocol, OFDM (orthogonal frequency division multiplexing) based communication protocol, OFDMA (orthogonal frequency division multiple access) based communication protocol, SC (single carrier)-FDMA based communication protocol, NOMA (non-orthogonal multiple) access)-based communication protocol, space division multiple access (SDMA)-based communication protocol, etc. may be supported. Each of the plurality of communication nodes may have the following structure.

2 is a block diagram showing a communication node according to an embodiment of the present invention. Referring to FIG. 2, the communication node 200 may include at least one processor 210, a memory 220, and a transmission/reception device 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, and a storage device 260. Each of the components included in the communication node 200 may be connected by a bus 270 to perform communication with each other.

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260. The processor 210 may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may be configured with at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory 220 may be formed of at least one of a read only memory (ROM) and a random access memory (RAM).

1 is a conceptual diagram showing a communication network according to an embodiment of the present invention. Referring to FIG. 1, the communication network 100 includes a plurality of communication nodes 110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes is a communication protocol based on code division multiple access (CDMA), a communication protocol based on wideband CDMA (WCDMA), a communication protocol based on time division multiple access (TDMA), and frequency division multiple access (FDMA). access) based communication protocol, OFDM (orthogonal frequency division multiplexing) based communication protocol, OFDMA (orthogonal frequency division multiple access) based communication protocol, SC (single carrier)-FDMA based communication protocol, NOMA (non-orthogonal multiple) access)-based communication protocol, space division multiple access (SDMA)-based communication protocol, etc. may be supported. Each of the plurality of communication nodes may have the following structure.

2 is a block diagram showing a communication node according to an embodiment of the present invention. Referring to FIG. 2, the communication node 200 may include at least one processor 210, a memory 220, and a transmission/reception device 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, and a storage device 260. Each of the components included in the communication node 200 may be connected by a bus 270 to perform communication with each other.

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260. The processor 210 may mean a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may be configured with at least one of a volatile storage medium and a nonvolatile storage medium. For example, the memory 220 may be formed of at least one of a read only memory (ROM) and a random access memory (RAM).

3 is a state transition diagram of a terminal in a handover procedure.

Referring to Figure 3, the terminal is in the RRC idle state (RRC_IDLE state, 310) through the RRC connection establishment (RRC connection establishment) procedure (S310) through the RRC connection (RRC connection) setup with the base station is normally completed when the RRC connection state ( RRC_CONNECTED state) can be transitioned to (320).

The terminal in the RRC connection state 320 may transition back to the RRC idle state 310 when the RRC connection setting with the base station is released through the RRC connection release procedure (S320). In addition, when the terminal in the RRC connection state 320 performs a handover and changes the serving base station (or cell) to reset the RRC connection with the changed serving base station (ie, target base station), the RRC connection state with the changed serving base station Can keep. Meanwhile, a data interruption time occurs in the process of the terminal performing handover, that is, changing the connection from the current serving base station (i.e., source base station) to a new serving base station (i.e., target base station). I can.

4 is a flow chart showing a first embodiment of a handover procedure.

Referring to FIG. 4, the source base station 420 may perform measurement configuration so that the terminal 410 may measure neighbor base stations including the target base station 420. Next, the terminal 410 performs measurement on the signal strength of the neighboring base stations including the source/target base station (S401), and when the measurement result satisfies a predetermined condition, the terminal 410 sends a measurement report to the source base station 420. ) Can be reported (S402). At this time, the reported measurement result may include signal measurement results of neighboring base stations.

Based on the received measurement result, the source base station 420 determines a handover to the target base station 430 and transmits a handover preparation request message to the target base station 430 to the target base station 430. Handover preparation can be instructed (S403). In this case, the source base station 420 may include the measurement result of the target base station 430 received from the terminal 410 in the handover preparation request message and transmit it to the target base station 430.

Meanwhile, the target base station 430 may determine whether to accept the handover of the terminal through admission control (S404), and when it is determined to accept the handover of the terminal, the source base station 420 A handover preparation acknowledgment message may be transmitted (S405).

The source base station 420 may transmit a handover command message to the terminal 410 (S406). In this case, the handover command message may be transmitted as, for example, a'RRCConnectionReconfiguration' message which is an RRC signaling message. In addition, the handover command message may include information on a resource to be used by the terminal 410 in a random access (RA) procedure for the target support station 430, which is included in the handover preparation approval message and received. .

Upon receiving the handover command message, the terminal 410 may perform handover immediately. Accordingly, the terminal 410 acquires downlink synchronization with the target base station 430 (S408), releases the connection with the source base station 420 (S409), and accesses the target base station 430 You can try (S410, S411). Meanwhile, the source base station 420 may forward the data to be transmitted to the terminal 410 to the target base station 430 (S407).

Thereafter, the terminal 410 may attempt random access based on information on a resource to be used in a random access procedure provided by the target base station 430 included in the handover command message (S410). The target base station 430 may transmit a random access response (RAR) in response to the RACH (S411). When the access procedure for the target base station 430 is completed, the terminal 410 may transmit a handover complete message to the target base station 430 (S412). The target base station 430 receiving the handover completion message from the terminal 410 may transmit data to the terminal 410 (S413).

Meanwhile, in this handover method, the terminal 410 completes handover to the target base station 430 from a time point before or after the time point at which the source base station 420 forwards data to the target base station 430, and the target base station 430 From) to the point in time when data can be received, a disconnection time in which data cannot be received may occur.

5 is a flow chart showing a second embodiment of a handover procedure.

Referring to FIG. 5, in order to reduce the disconnection time occurring in the handover procedure as shown in FIG. 4, the terminal maintains a connection with the source base station during handover and disconnects the source base station after the connection to the target base station is completed. Handover procedure can be performed. That is, in the handover procedure, the UE can maintain the RRC connection with the source base station or the target base station, maintain the connection with the source base station or the target base station, and perform handover.

Referring to FIG. 5, in the same manner as the handover method described with reference to FIG. 4, the source base station 520 is configured to measure so that the terminal 510 can perform measurements on neighboring base stations including the target base station 530. (measurement configuration) can be performed. Next, the terminal 510 performs measurement on the signal strength of neighboring base stations including the source base station 520 and the target base station 530 (S501), and when the measurement result satisfies a predetermined condition, the source base station 520 ) May report a measurement report (S502). At this time, the reported measurement result may include a signal measurement result of the neighboring base station.

Based on the received measurement result, the source base station 520 determines a handover to the target base station 530 and transmits a handover preparation request message to the target base station 530 to prepare for handover to the target base station. Can be indicated (S503). In this case, the source base station 520 may include the measurement result of the target base station 530 received from the terminal 510 in the handover preparation request message and transmit it to the target base station 530.

The target base station 530 determines whether to accept the handover of the terminal through admission control (S504), and when it is determined to accept the handover of the terminal, the source base station 520 acknowledges handover preparation (handover preparation). Acknowledgment) message can be transmitted (S505). The source base station 520 may transmit a handover command message to the terminal 510 (S506). In this case, the handover command message may be transmitted as, for example, a'RRCConnectionReconfiguration' message which is an RRC signaling message.

Unlike in the example of FIG. 4 that the terminal 510 receiving the handover command message immediately performs the handover, the handover method according to FIG. 5 is when the terminal 510 receiving the handover command message executes handover. Is determined (S507), and a handover execution procedure can be performed.

Upon receiving the handover command from the source base station 520, the terminal 510 may perform downlink synchronization with the target base station 530 when the actual handover execution time is determined (S507) ( S508). Thereafter, the terminal 510 may transmit a first handover indication message to the source base station 520 (S509), and the source base station 520 transmits the received first handover message to the target base station 530 ) Can be delivered (S510). At this time, the first handover indication message is a message for indicating the actual handover execution time determined by the UE, and indicates the time when data forwarding is started from the source base station to the target base station, and the terminal attempts connection access to the target base station. I can.

The terminal 510 may perform a random access procedure with the target base station 530 without releasing the connection with the source base station 520 (S512 and S513). Thereafter, when the connection with the target base station 530 is successfully completed, the terminal 510 transmits a handover complete message to the target base station 530 (S514), and to the source base station 520 A second handover indication message instructing release of the connection to the source base station may be transmitted (S516). Thereafter, the terminal 510 may release the connection with the source base station 520 (S517).

Since the terminal 510 maintains a connection with the source base station 520 during the handover process to the target base station 530, the terminal 510 can continuously receive data from the source base station 520. After the target base station 530 receives the handover completion message from the terminal 510 (S514), the terminal 510 may receive data from the target base station 530 (S515). Meanwhile, in the case of handover through contention-free random access, the target base station may transmit data to the terminal faster after receiving the corresponding random access preamble. A process in which the terminal 510 transmits data to the target base station 530 and/or the source base station 520 will be described.

The terminal 510 may transmit and receive data with the source base station 520 and the target base station 530 based on a dual active protocol stack.

6 to 11 are conceptual diagrams illustrating a process of performing a handover by a terminal based on a dual active protocol stack.

6 to 11, a separate PDCP entity may be set for each of the source base station 520 and the target base station 530 in the PDCP of the terminal 510. The PDCP entity of the target base station 530 may be set as a primary entity (primary entity or new entity), and the PDCP entity of the source base station 520 may be set as a secondary entity (secondary entity or old entity). That is, for one bearer, the PDCP entity may have a connection with the source base station 520 and a connection with the target base station 530, and for data transfer to an upper layer according to data sequence number rearrangement and sequence number. , Logically, it can operate as one entity.

A primary entity that is a PDCP layer entity connected to the target base station 530 may manage a data transfer operation, and manage and perform a data sequence number rearrangement operation. A secondary entity, which is a PDCP layer entity connected to the source base station 520, may inform the received data unit (eg, PDCP PDU) to the primary entity.

Robust header compression (ROHC) and security context in the PDCP layer with the source base station 520 and the PDCP layer with the target base station 530 may be individually managed in each PDCP layer. Accordingly, the PDCP layer entity connected to the source base station can perform compression and decompression by continuously maintaining the ROHC state, and encryption and integrity by using an existing security key. Protection (integrity protection) can be performed.

Referring to FIG. 6, before the terminal 510 performs handover, only a source protocol and a source key connected to the source base station 520 may be used. Referring to FIG. 7, before a random-access channel (RACH), that is, when a terminal 510 receives a handover command, a source protocol and a source key connected to the source base station 520 and the target base station 530 are connected. Both a target protocol and a target key may exist. However, only the source protocol and source key can be used in this process.

Referring to FIG. 8, during RACH, both a source protocol and a source key connected to the source base station 520 and a target protocol and target key connected to the target base station 530 may exist. The source protocol and source key may be used in a process in which the terminal 510 receives data from the source base station 520 and transmits data to the source base station 520. Meanwhile, in the target protocol connected to the target base station 530, the PHY (Physical) layer and the MAC (Medium Access Control) layer may be used in the process of the UE 510 performing the RACH procedure to the target base station 530.

Referring to FIG. 9, in a transmission process while handover is completed, both a source protocol and a source key connected to the source base station 520 and a target protocol and target key connected to the target base station 530 may exist. The source protocol and source key may be used in a process in which the terminal 510 receives data from the source base station 520 and transmits data to the source base station 520. Meanwhile, in the target protocol connected to the target base station 530, the PHY layer, the MAC layer, the Radio Link Control (RLC) layer, and the PDCP layer may be used to transmit the RRCReconfigurationComplete message.

Referring to FIG. 10, after the RAR process, both a source protocol and a source key connected to the source base station 520 and a target protocol and target key connected to the target base station 530 may exist. The source protocol and source key may be used in a process in which the terminal 510 receives data from the source base station 520 and transmits data to the source base station 520. The target protocol and target key may be used in a process in which the terminal 510 receives data from the target base station 530 and transmits data to the target base station 530. Referring to FIG. 11, after the connection with the source base station 520 is released, the source protocol and the source key connected to the terminal 510 are deleted, and only the target protocol and the target key may be used.

On the other hand, when the terminal 510 transmits and receives data with the source base station 520 and/or the target base station 530, due to the data sequence number reordering operation performed in the RLC layer of the terminal 510, FIG. 5 Data disconnection time (or delay time) may also occur in the handover procedure such as

Therefore, in order to reduce the disconnection time, when the terminal 510 transmits and receives data with the source base station 520 (ie, before the connection between the terminal 510 and the source base station 520 is released (before S517)), the terminal When 510 transmits and receives data to and from the target base station 530 (that is, after the terminal 510 receives a handover completion message from the target base station 530 (after S514)), data sequence number rearrangement operation in the RLC layer You may need a way to avoid doing it.

12 is a flowchart illustrating a method of operating a terminal.

Referring to FIG. 12, the UE may determine a handover execution time point while maintaining a connection with a source base station and perform handover to a target base station. Specifically, the terminal may perform a connection setup procedure to the target base station (S1210). The terminal can receive first packet data units (PDUs) from the source base station and second packet data units from the target base station while maintaining the connection between the source base station and the target base station. (S1220).

The first Packet Data Convergence Protocol (PDCP) layer connected to the source base station in the terminal may receive first packet data units from a lower layer of the first PDCP layer. In addition, the second PDCP layer connected to the target base station in the terminal may receive second packet data units from a lower layer of the second PDCP layer. Thereafter, the upper layer of the first PDCP layer and the second PDCP may rearrange the first packet data units and the second packet data units according to the PDCP sequence number (or serial number) (S1230). In addition, the first packet data units and the second packet data units may be delivered to an upper layer in the order of PDCP sequence numbers (S1240).

Hereinafter, a data transmission procedure performed by the terminal in the handover process will be described.

13 is a conceptual diagram illustrating an operation performed in an RLC layer of a terminal in a Long Term Evolution (LTE) system.

13 is a re-establishment procedure of 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 36.322 5.4. Referring to FIG. 13, when a terminal is connected to a source base station and a target base station and a connection is added, the terminal The RRC layer of the UE requests to perform re-establishment for an Acknowledged Mode (AM) RLC entity, an Unacknowledged Mode (UM) RLC entity, and a Transparent Mode (TM) RLC entity to the RLC layer of the UE. A continue-DataTransfer 1310 and a continue-DataTransfer 1320 for the UM RLC entity may be set. The continue-DataTransfer (1310, 1320) may be an indicator that continuously transmits and receives a packet data unit through a corresponding entity.

Meanwhile, when the terminal releases the connection with the source base station while the source base station and the target base station are connected, the RRC layer of the terminal requests RLC release for each RLC entity of the RLC layer of the terminal connected to the source base station. I can. The terminal RRC may release the rlc-OutOfOrderDelivery setting for the AM RLC entity connected to the target base station of the terminal RLC layer. The terminal RRC may release the rlc-OutOfOrderDelivery setting more quickly, if necessary.

14 to 17 are conceptual diagrams illustrating operations performed in a PDCP layer of a terminal in an LTE system. 14 to 17 are related to the Re-establishment procedure of 3GPP TS 36.323 5.2, 14 to 16 are related to UL (Uplink) Data Transfer Procedures, and Figure 17 is related to DL (Downlink) Data Transfer Procedures.

14 to 17, the UE RRC requests the PDCP layer of the UE to perform re-establishment, while continue-DataTransfer (1410, 1420, 1430, 1440, 1450, 1460) for an AM or UM PDCP entity. ) Can be set. That is, when continue-DataTransfer is set to true, the terminal may transfer data units transmitted from the lower layer to the upper layer in order according to the PDCP sequence number.

Meanwhile, when the terminal is disconnected from the source base station while the source base station and the target base station are connected, the terminal RRC is an AM unit (secondary) PDCP entity and a UM unit (secondary) PDCP that perform the function of the PDCP layer configured with the source base station. It is possible to request an entity to perform PDCP release.

18 to 20 are conceptual diagrams illustrating operations performed in a PDCP layer of a terminal in a New Radio (NR) system. When the terminal is connected to the source base station and the connection with the target base station is added, the operation of the RLC layer of the terminal may be the same as the operation of the RLC layer of the terminal performed in the conventional NR. In addition, when the terminal is disconnected from the source base station while the source base station and the target base station are connected, the terminal RRC may request RLC release for each RLC entity connected to the source base station of the terminal RLC layer.

Meanwhile, FIGS. 18 to 20 relate to the PDCP entity re-establishment procedure of 3GPP TS 36.323 5.1.2, and referring to FIGS. 18 to 20, the UE RRC performs re-establishment to the PDCP layer of the UE. Upon request, continue-DataTransfer (1810, 1820, 1830, 1840) can be set for the AM or UM PDCP entity. That is, when continue-DataTransfer is set to true, the terminal may transfer data units transmitted from the lower layer to the upper layer in order according to the PDCP sequence number.

On the other hand, when the terminal is connected to the source base station and the connection with the target base station is added, the terminal transmits data to a higher layer without rearranging data sequence numbers in the RLC layer of the source base station and/or the target base station, or stores the data in the reception buffer I can. In this case, since the source base station or the target base station can receive data first, it is possible to quickly perform a data sequence number rearrangement operation, thereby minimizing a data disconnection time occurring in a handover. Therefore, the terminal can minimize the data disconnection time in the application layer while the data disconnection time satisfies 0 ms from the viewpoint of the physical layer during handover.

The methods according to the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like alone or in combination. The program instructions recorded on the computer-readable medium may be specially designed and configured for the present invention, or may be known and usable to those skilled in computer software.

Examples of computer-readable media include hardware devices specially configured to store and execute program instructions, such as rom, ram, flash memory, and the like. Examples of program instructions include not only machine language codes such as those produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The above-described hardware device may be configured to operate as at least one software module to perform the operation of the present invention, and vice versa.

Although described with reference to the above embodiments, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention described in the following claims. I will be able to.

Claims (1)

As an operating method of a terminal performing handover between a source base station and a target base station,
Receiving a message for handover from the source base station to the target base station, and performing a connection setup procedure with the target base station while maintaining connection with the source base station;
Receiving first packet data units (PDUs) from the source base station, and receiving second packet data units from the target base station;
Receiving, by a first Packet Data Convergence Protocol (PDCP) layer of the terminal, the first packet data units from a lower layer of the first PDCP layer;
Receiving, by a second PDCP layer of the terminal, the second packet data units from a lower layer of the second PDCP; And
A step of rearranging the first packet data units and the second packet data units based on a PDCP sequence number by an upper layer of the first PDCP layer and the second PDCP, wherein the first packet data units And the second packet data units are delivered to an upper layer according to the PDCP sequence number.

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