Method and apparatus for performing handover in a wireless communication system

Abstract

A method for a user equipment (UE) to perform a dual active protocol stack (DAPS) handover in a wireless communication system, comprising: receiving a radio resource control (RRC) reconfiguration message including DAPS configuration information from a source base station, the DAPS configuration information indicating at least one bearer for the DAPS handover; reconfiguring a packet data convergence protocol (PDCP) entity corresponding to at least one bearer for the DAPS handover for the DAPS handover; and establishing a protocol entity for a target cell corresponding to at least one bearer for the DAPS handover.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for effectively performing handover without interrupting data transmission and reception when performing handover in a next-generation mobile communication system. Background Art

[0002] After the commercialization of the fourth-generation (4G) communication system, in order to meet the growing demand for wireless data services, efforts have been made to develop a fifth-generation (5G) or pre-5G communication system. To this end, the 5G or pre-5G communication system is referred to as an "ultra 4G network" communication system or a "post-long term evolution (post-LTE)" system. The 5G communication system defined by the Third Generation Partnership Project (3GPP) is referred to as a New Radio (NR) system. In order to achieve high data rates, it is being considered to implement the 5G communication system in the ultra-high frequency millimeter wave (mmWave) band (e.g., 60 gigahertz (GHz) band). In order to reduce the path loss of radio waves and increase the transmission distance of radio waves in the ultra-high frequency band of the 5G communication system, various technologies such as beamforming, massive multiple-input multiple-output (massive MIMO), full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive antennas are being studied and applied to the NR system. In order to improve the system network for the 5G communication system, various technologies have been developed, such as evolved small cells, advanced small cells, cloud radio access network (cloud RAN), ultra-dense network, device-to-device communication (D2D), wireless backhaul, mobile network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation. In addition, for the 5G communication system, advanced coding modulation (ACM) technologies such as hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC) have been developed, as well as advanced access technologies such as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA).

[0003] The Internet has evolved from a human - based network for creating and consuming information to the Internet of Things (IoT), in which distributed elements such as objects exchange information with each other to process information. The Internet of Everything (IoE) technology has emerged, in which IoT technology is combined with technologies such as those for processing big data through connection to a cloud server. To implement IoT, various technical elements are required, such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, and security technology. Therefore, in recent years, technologies related to sensor networks for connecting objects, machine - to - machine (M2M) communication, and machine - type communication (MTC) have been studied. In the IoT environment, intelligent Internet technology (IT) services can be provided to collect and analyze data obtained from connected objects, thereby creating new value in human life. With the mutual integration and combination of existing information technology (IT) and various industries, IoT can be applied to various fields, such as smart homes, smart buildings, smart cities, smart cars, or connected cars, smart grids, healthcare, smart home appliances, and advanced medical services.

[0004] Various attempts are being made to apply the 5G communication system to IoT networks. For example, technologies related to sensor networks, M2M communication, and MTC are being implemented through 5G communication technologies using beamforming, MIMO, and array antennas. Cloud radio access network (cloud RAN), as an application of the above - mentioned big - data processing technology, can be an example of the integration of 5G communication technology and IoT technology. SUMMARY OF THE INVENTION

[0005] SOLUTION TO THE PROBLEM

[0006] According to the present disclosure, an efficient handover method is provided for supporting services with low transmission latency and no data interruption in a next - generation mobile communication system.

[0007] Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the presented embodiments of the present disclosure.

[0008] According to an embodiment of the present disclosure, a method for a user equipment (UE) to perform dual - active protocol stack (DAPS) handover in a wireless communication system includes: receiving, from a source base station, a radio resource control (RRC) reconfiguration message including DAPS configuration information indicating at least one bearer for DAPS handover; reconfiguring a packet data convergence protocol (PDCP) entity corresponding to at least one bearer for DAPS handover for DAPS handover; and establishing a protocol entity for a target cell corresponding to at least one bearer for DAPS handover.

[0009] According to an embodiment of the present disclosure, a user equipment (UE) performing dual active protocol stack (DAPS) handover in a wireless communication system includes: a transceiver; and at least one processor. The at least one processor is connected to the transceiver and is configured to: receive a radio resource control (RRC) reconfiguration message including DAPS configuration information from a source base station, the DAPS configuration information indicating at least one bearer for DAPS handover; reconfigure a packet data convergence protocol (PDCP) entity corresponding to at least one bearer for DAPS handover for DAPS handover; and establish a protocol entity for a target cell corresponding to at least one bearer for DAPS handover. Description of the Drawings

[0010] From the following description with reference to the drawings, the above and other aspects, features, and advantages of certain embodiments of the present disclosure will become more apparent, where:

[0011] Figure 1A is a diagram showing the configuration of a Long Term Evolution (LTE) system according to an embodiment of the present disclosure;

[0012] Figure 1B is a diagram showing the radio protocol architecture of an LTE system according to an embodiment of the present disclosure;

[0013] Figure 1C is a diagram showing a next-generation mobile communication system according to an embodiment of the present disclosure;

[0014] Figure 1D is a diagram showing the radio protocol architecture of a New Radio (NR) or fifth-generation (5G) mobile communication system according to an embodiment of the present disclosure;

[0015] Figure 1E is a diagram for describing the process of a user equipment (UE) switching from radio resource control (RRC) idle mode to RRC connected mode and establishing a connection with a network according to an embodiment of the present disclosure;

[0016] Figure 1F is a diagram showing the signaling process for performing handover in a next-generation mobile communication system according to an embodiment of the present disclosure;

[0017] Figure 1G shows specific operations of Embodiment 1 of an effective handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure;

[0018] Figure 1H shows specific operations of Embodiment 2 of an effective handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure;

[0019] Figure 1I It shows the architecture of an efficient Packet Data Convergence Protocol (PDCP) layer to be applied to a Dual Active Protocol Stack (DAPS) handover method as an embodiment 2 of an efficient handover method according to the present disclosure, and a method of applying this architecture;

[0020] Figure 1J It shows the architecture of an efficient Service Data Adaptation Protocol (SDAP) layer to be applied to a DAPS handover method as an embodiment 2 of an efficient handover method according to the present disclosure, and a method of applying this architecture;

[0021] Figure 1K It is a diagram showing the operation of a User Equipment (UE) according to an embodiment of the present disclosure;

[0022] Figure 1L It is a diagram showing the configuration of a UE to which an embodiment of the present disclosure is applicable;

[0023] Figure 1M It is a diagram showing the configuration of a Base Station (BS) to which an embodiment of the present disclosure is applicable. Detailed Description

[0024] Before proceeding with the following description, it may be advantageous to clarify the definitions of certain words and phrases used throughout this patent document: The terms "comprising" and "including" and their derivatives mean including without limitation; the term "or" is inclusive and means and / or; the phrases "associated with" and "associated therewith" and their derivatives may mean including, being included within, interconnected with, containing, being contained within, connected to or coupled with, coupled to or associated with, communicable with, cooperating with, interlacing, juxtaposing, adjacent, bound to or associated with, having its characteristics, etc.; and the term "controller" represents any device, system or part thereof that controls at least one operation, and such a device may be implemented in hardware, firmware or software or some combination of at least two of them. It should be noted that the functions associated with any particular controller may be centralized or distributed, whether local or remote.

[0025] In addition, the various functions described below can be implemented or supported by one or more computer programs, each formed of computer-readable program code and embodied in a computer-readable medium. The terms "application" and "program" refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or portions thereof suitable for implementation in a suitable computer-readable program code. The phrase "computer-readable program code" includes any type of computer code, including source code, object code, and executable code. The phrase "computer-readable medium" includes any type of medium that can be accessed by a computer, such as read-only memory (ROM), random access memory (RAM), hard disk drive, optical disc (CD), digital versatile disc (DVD), or any other type of memory. A "non-transitory" computer-readable medium does not include a wired, wireless, optical, or other communication link that transmits transitory electrical or other signals. Non-transitory computer-readable media include media that can permanently store data and media that can store data and later rewrite it, such as rewritable optical discs or erasable storage devices.

[0026] Certain words and phrases are defined throughout this patent document, and those of ordinary skill in the art should understand that, in many instances if not most, such definitions apply to both the prior and future use of such defined words and phrases.

[0027] As discussed below Figures 1A to 1M and the various embodiments used in this patent document to describe the principles of the present disclosure are merely exemplary and should not be construed in any way as limiting the scope of the present disclosure. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any suitably arranged system or device.

[0028] Throughout the disclosure, the expression "at least one of a, b, or c" only means only a, only b, only c, a and b, a and c, b and c, all of a, b, and c, or variants thereof.

[0029] Examples of terminals may include user equipment (UE), mobile station (MS), cellular phone, smart phone, computer, multimedia system capable of performing communication functions, and the like.

[0030] In the present disclosure, the controller may also be referred to as a processor.

[0031] Throughout the specification, a layer (or layer device) may also be referred to as an entity.

[0032] In the following, the operating principle of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or configurations are not described in detail because they would obscure the present disclosure with unnecessary details. The terms used in the specification are defined in consideration of the functions used in the present disclosure and may be changed according to the intention of the user or operator or the common method. Therefore, the definition of the terms should be understood based on the entire description of this specification.

[0033] In the following description of the present disclosure, well-known functions or configurations are not described in detail because they would obscure the present disclosure with unnecessary details. In the following, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0034] In the following, for ease of explanation, terms for identifying access nodes, terms for representing network entities, terms for representing messages, terms for representing interfaces between network entities, and terms for representing various identification information used in the following description are exemplified. Therefore, the present disclosure is not limited to the terms to be described below, and other terms representing objects with the same technical meaning may be used.

[0035] For ease of description, the present disclosure uses terms and names defined in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) standard. However, the present disclosure is not limited to these terms and names and can be equally applied to communication systems conforming to other standards. In the present disclosure, for ease of description, evolved Node B (eNB) may be used interchangeably with next generation Node B (gNB). That is, the BS described as eNB may represent gNB.

[0036] In the present disclosure, a seamless handover method is provided that can minimize the data interruption time due to handover or make the data interruption time 0 milliseconds in a next generation mobile communication system.

[0037] Specifically, the effective handover method provided in the present disclosure may have one or more of the following multiple features.

[0038] When the UE receives a handover command message (e.g., a handover command message or a Radio Resource Control (RRC) reconfiguration message) from the source BS, the UE performs data transmission or reception (uplink (UL) or downlink (DL) data transmission and reception) to or from the source BS via the protocol layers of each of the multiple first bearers (i.e., the Physical (PHY) layer, the Medium Access Control (MAC) layer, the Radio Link Control (RLC) layer, and the Packet Data Convergence Protocol (PDCP) layer). The UE may configure the protocol layers of multiple new second bearers corresponding to the protocol layers of the multiple first bearers (e.g., having the same bearer identifier), and may perform data transmission or reception (UL or DL data transmission and reception) without interruption but maintaining the data transmission or reception (UL or DL data transmission and reception) to or from the source BS via the multiple first bearers.

[0039] In the above case, after the UE receives the handover command message, based on the bearer configuration information or protocol layer information included in the handover command message, the protocol layers (PHY layer, MAC layer, RLC layer, and PDCP layer) of the multiple second bearers to be newly configured are configured for data transmission and reception to and from the target BS.

[0040] In the above case, the UE may be configured to perform data transmission or reception (UL or DL data transmission and reception) to or from the source BS via the protocol layers of the multiple first bearers, and perform a random access procedure to the target BS via the protocol layers of the multiple second bearers (e.g., the MAC layer). In the above case, the random access procedure may include the transmission of a preamble, the reception of a random access response, the transmission of Message 3, the reception of Message 4 (e.g., a contention resolution MAC control element (CE) element or the reception of UL transmission resources), etc.

[0041] In the above case, the UE may be configured to perform data transmission or reception to or from the source BS via the protocol layers of the multiple first bearers, complete the random access procedure to the target BS via the protocol layers of the multiple second bearers (e.g., the MAC layer), and send a handover completion message to the target BS via the protocol layers of the multiple second bearers.

[0042] In the above case, the UE may be configured to perform data transmission or reception to or from the source BS via the protocol layers of the multiple first bearers, complete the random access procedure to the target BS via the protocol layers of the multiple second bearers (e.g., the MAC layer), send a handover completion message to the target BS via the protocol layers of the multiple second bearers, and perform data transmission and reception (UL or DL).

[0043] In the above case, the UE can be configured in such a way that when the UE successfully completes the random access procedure for the target BS and then initially receives the UL transmission resource from the target BS, the UE stops data transmission via the protocol layers of the plurality of first bearers to the source BS, switches the UL transmission, and then transmits data to the target BS via the plurality of second bearers.

[0044] In the above case, the UE can be configured in such a way that when the UE receives the handover command message, the UE continuously performs data transmission or reception (UL or DL data transmission and reception) to or from the source BS, and performs a random access procedure for the target BS via the protocol layers of the plurality of second bearers; when the UE successfully completes the random access procedure and then initially receives the UL transmission resource from the target BS, the UE stops data transmission via the protocol layers of the plurality of first bearers to the source BS and performs UL data transmission to the target BS only via the protocol layers of the plurality of second bearers. In addition, the UE can be configured to continuously receive DL data from the source BS via the protocol layers of the plurality of first bearers and continuously receive DL data from the target BS via the protocol layers of the plurality of second bearers.

[0045] In the above case, the first bearer and the second bearer can constitute a second PDCP layer architecture, and in the second PDCP layer architecture, the first bearer (e.g., RLC layer, MAC layer, or PHY layer) of the source BS and the second bearer (e.g., RLC layer, MAC layer, or PHY layer) of the target BS are both connected to one PDCP layer, and UL data can be transmitted via one of the first bearer or the second bearer of the PDCP layer. That is, before the UE performs a random access procedure for the target BS, successfully completes the random access procedure, and initially receives the UL transmission resource from the target BS, the UE transmits UL data via the first bearer, and when the UE performs a random access procedure for the target BS, successfully completes the random access procedure, and initially receives the UL transmission resource from the target BS, the UE can stop data transmission via the first bearer, can switch the data transmission, and thus can transmit UL data to the target BS via the second bearer. In this regard, the UE in the second PDCP layer architecture can be configured to receive DL data from the source BS or the target BS via the first bearer or the second bearer.

[0046] Hereinafter, in the present disclosure, based on the foregoing features, an effective handover process without a data interruption time is provided.

[0047] Figure 1A is a diagram showing the configuration of an LTE system according to an embodiment of the present disclosure.

[0048] Refer to Figure 1A, the radio access network (RAN) of an LTE system includes multiple evolved Node Bs (eNBs) (or Node Bs or base stations) 1a-05, 1a-10, 1a-15, and 1a-20, a mobility management entity (MME) 1a-25, and a serving gateway (S-GW) 1a-30. A UE (or terminal) 1a-35 can access an external network through eNBs 1a-05, 1a-10, 1a-15, or 1a-20 and S-GW 1a-30.

[0049] In Figure 1A , eNBs 1a-05, 1a-10, 1a-15, or 1a-20 can correspond to existing Node Bs of a Universal Mobile Telecommunications System (UMTS). eNBs 1a-05, 1a-10, 1a-15, or 1a-20 can be connected to a UE 1a-35 through a radio channel and can perform complex functions compared to existing Node Bs. All user service data including real-time services (such as Voice over Internet Protocol (VoIP)) can be served through a shared channel in the LTE system, so an entity for collating UE status information (such as buffer status information, available transmission power status information, and channel status information) and performing scheduling may be required, and eNBs 1a-05, 1a-10, 1a-15, or 1a-20 can operate as such an entity. One eNB usually controls multiple cells. For example, the LTE system can use radio access technologies such as Orthogonal Frequency Division Multiplexing (OFDM) with a bandwidth of 20 MHz to achieve a data rate of 100 Mbps. Adaptive Modulation and Coding (AMC) can be used to determine a modulation scheme and a channel coding rate according to the channel status of a UE. S-GW 1a-30 is an entity for providing data bearers and can establish and release data bearers under the control of MME 1a-25. MME 1a-25 is an entity for performing mobility management functions and various control functions on a UE1a-35 and is connected to multiple eNBs1a-05, 1a-10, 1a-15, and 1a-20.

[0050] Figure 1B is a diagram showing the radio protocol architecture of an LTE system according to an embodiment of the present disclosure.

[0051] Refer to Figure 1B , the radio protocol architecture of an LTE system can include a Packet Data Convergence Protocol (PDCP) layer 1b-05 and 1b-40, a Radio Link Control (RLC) layer 1b-10 and 1b-35, and a Media Access Control (MAC) layer 1b-15 and 1b-30 for a UE and an eNB, respectively. The PDCP layer 1b-05 or 1b-40 can perform, for example, IP header compression / decompression. The main functions of the PDCP layer 1b-05 or 1b-40 are summarized as follows.

[0052] - Header compression and decompression: Robust Header Compression (ROHC only)

[0053] - Transmission of user data

[0054] - Sequential transfer of upper layer Packet Data Units (PDUs) during PDCP re - establishment procedure in RLC acknowledged mode (AM)

[0055] - For split bearers in DC (RLC AM only supported): Routing of PDCP PDUs for transmission and re - ordering of PDCP PDUs for reception

[0056] - Duplicate detection of lower layer Service Data Units (SDUs) during PDCP re - establishment process in RLC AM

[0057] - Retransmission of PDCP PDUs during handover and, for split bearers in DC, retransmission of PDCP PDUs during PDCP data recovery process in RLC AM

[0058] - Encryption and decryption

[0059] - Timer - based SDU discard in the uplink

[0060] RLC layer 1b - 10 or 1b - 35 can perform operations such as Automatic Repeat reQuest (ARQ) by reconstructing the Packet Data Convergence Protocol Packet Data Unit (PDCP PDU) into an appropriate size. The main functions of RLC layer 1b - 10 or 1b - 35 can be summarized by example as follows.

[0061] - Transmission of upper layer PDUs

[0062] - Error correction by ARQ (only applicable to AM data transmission)

[0063] - Concatenation, segmentation, and reassembly of RLC SDUs (only applicable to unacknowledged mode (UM) and AM data transmission)

[0064] - Re - segmentation of RLC data PDUs (only applicable to AM data transmission)

[0065] - Re - ordering of RLC data PDUs (only applicable to UM and AM data transmission)

[0066] - Duplicate detection (only applicable to UM and AM data transmission)

[0067] - Protocol error detection (only applicable to AM data transmission)

[0068] - RLC SDU discard (only applicable to UM and AM data transmission)

[0069] - RLC re - establishment

[0070] The MAC layer 1b-15 or 1b-30 can be connected to multiple RLC layers configured in a UE, can multiplex RLC PDUs into MAC PDUs, and demultiplex MAC PDUs into RLC PDUs. The main functions of the MAC layer 1b-15 or 1b-30 can be summarized as follows.

[0071] - Mapping between logical channels and transport channels

[0072] - Multiplexing MAC SDUs belonging to one or different logical channels into transport blocks (TBs) transmitted to the physical layer on the transport channel / Demultiplexing MAC SDUs belonging to one or different logical channels from the transport blocks (TBs) received from the physical layer on the transport channel

[0073] - Scheduling information reporting

[0074] - Error correction through hybrid ARQ (HARQ)

[0075] - Priority handling between logical channels of a UE

[0076] - Priority handling between UEs through dynamic scheduling

[0077] - Multimedia broadcast / multicast service (MBMS) service identification

[0078] - Transmission format selection

[0079] - Padding

[0080] The physical (PHY) layer 1b-20 or 1b-25 can encode and modulate the upper layer data channel into OFDM symbols, transmit the OFDM symbols through the radio channel, or demodulate the OFDM symbols received through the radio channel, perform channel decoding on them, and transmit them to the upper layer.

[0081] Figure 1C It is a diagram showing a next-generation mobile communication system according to an embodiment of the present disclosure.

[0082] Reference Figure 1C , as shown in the figure, the radio access network of the next-generation mobile communication system (hereinafter referred to as NR or 5G communication system) includes a new radio node B (NR gNB, NR NB or gNB) 1c-10 and a new radio core network (NRCN) 1c-05. The NR UE (or terminal) 1c-15 accesses the external network through the NR gNB 1c-10 and the NR CN 1c-05.

[0083] In Figure 1CIn this case, NR gNB 1c-10 corresponds to the eNB in a traditional LTE system. NR gNB 1c-10 can be connected to NR UE 1c-15 via a radio channel and can provide better services compared to existing Node Bs. All user traffic data can be served via a shared channel in the NR or 5G mobile communication system. Therefore, an entity may be required to collate the buffer status information, available transmission power status information, and channel status information of the UE and perform scheduling, and NR gNB 1c-10 can operate as such an entity. One NR gNB typically controls multiple cells. The NR or 5G communication system may have a larger bandwidth than the maximum bandwidth of the existing LTE system to achieve ultra-high data rates compared to the existing LTE system, may use OFDM as the radio access technology, and may additionally use beamforming technology. Furthermore, NR gNB 1c-10 uses AMC to determine the modulation scheme and channel coding rate according to the channel status of NR UE 1c-15. NR CN 1c-05 performs functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. NR CN 1c-05 is an entity for performing mobility management functions and various control functions on NR UE 1c-15 and is connected to multiple base stations. The NR or 5G mobile communication system can cooperate with the existing LTE system, and NR CN 1c-05 can be connected to MME 1c-25 via a network interface. MME1c-25 is connected to eNB 1c-30, which is an existing base station.

[0084] Figure 1D is a diagram showing the radio protocol architecture of an NR or 5G mobile communication system according to an embodiment of the present disclosure.

[0085] Refer to Figure 1D , the radio protocol architecture of the NR or 5G mobile communication system may include NR service data adaptation protocol (SDAP) layers 1d-01 and 1d-45, NR PDCP layers 1d-05 and 1d-40, NR RLC layers 1d-10 and 1d-35, and NR MAC layers 1d-15 and 1d-30 for the UE and NR gNB, respectively.

[0086] The main functions of the NR SDAP layer 1d-01 or 1d-45 may include some of the following functions.

[0087] - Transmission of user plane data

[0088] - Mapping between QoS flows and data radio bearers (DRBs) for both DL and UL

[0089] - Marking QoS flow identifiers (IDs) in both DL and UL packets

[0090] - Mapping of Reflective QoS Flows to DRBs for UL SDAP PDUs

[0091] For the SDAP layer, via RRC messages, the UE can be configured to use the SDAP layer header or the SDAP layer functions for each PDCP layer, each bearer, or each logical channel. When the SDAP header is configured, the 1-bit non-access stratum (NAS) reflective QoS indicator and the 1-bit access stratum (AS) reflective QoS indicator of the SDAP header can indicate to the UE to update or reconfigure the mapping information between QoS flows and data bearers for both UL and DL. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority information or scheduling information for appropriately supporting services.

[0092] The main functions of the NR PDCP layer 1d-05 or 1d-40 can include some of the following functions.

[0093] - Header Compression and Decompression: Only ROHC

[0094] - Transfer of User Data

[0095] - Sequential Delivery of Upper Layer PDUs

[0096] - Unordered Delivery of Upper Layer PDUs

[0097] - Reordering of Received PDCP PDUs

[0098] - Duplicate Detection of Lower Layer SDUs

[0099] - Retransmission of PDCP SDUs

[0100] - Encryption and Decryption

[0101] - Timer-based SDU Discard in the Uplink

[0102] The reordering function of the NR PDCP layer 1d-05 or 1d-40 can indicate the function of reordering the PDCP PDUs received from the lower layer based on the PDCP sequence number (SN). The reordering function can include the function of delivering the reordered data to the upper layer in order or delivering the reordered data to the upper layer regardless of order, the function of reordering the lost PDCP PDUs by reordering the received PDCP PDUs, the function of reporting the status information of the lost PDCP PDUs to the transmitter, or the function of requesting retransmission of the lost PDCP PDUs.

[0103] The main functions of the NR RLC layer 1d-10 or 1d-35 can include some of the following functions.

[0104] - Transmission of upper layer PDU

[0105] - Sequential transfer of upper layer PDU

[0106] - Unordered transfer of upper layer PDU

[0107] - Error correction by ARQ

[0108] - Concatenation, segmentation and reassembly of RLC SDU

[0109] - Re-segmentation of RLC data PDU

[0110] - Re-ordering of RLC data PDU

[0111] - Duplicate detection

[0112] - Protocol error detection

[0113] - RLC SDU discard

[0114] - RLC reconstruction

[0115] The in-sequence delivery function of the NR RLC layer 1d-10 or 1d-35 can represent the function of delivering the RLC SDUs received from the lower layer to the upper layer in sequence. The in-sequence delivery function can include: the function of reassembling the RLC SDUs when multiple RLC SDUs segmented from one RLC SDU are received and delivering the reassembled RLC SDU; the function of reordering the received RLC PDUs based on the RLC SN or PDCP SN; the function of reordering the lost RLC PDUs by reordering the received RLC PDUs; the function of reporting the status information of the lost RLC PDUs to the transmitter; the function of requesting retransmission of the lost RLC PDUs; the function of delivering only the RLC PDUs before the lost RLC SDU to the upper layer in sequence when the lost RLC SDU exists; the function of delivering all the RLC PDUs received before the start of the timer to the upper layer in sequence when a specific timer expires despite the existence of lost RLC PDUs; or the function of delivering all the RLC PDUs received within the current time to the upper layer in sequence when a specific timer expires despite the existence of lost RLC PDUs. The NR RLC layer 1d-10 or 1d-35 can process the RLC PDUs in the received order and deliver the RLC PDUs to the NR PDCP layer 1d-05 or 1d-40 regardless of the SN (out-of-sequence delivery), and when a segment is received, the NR RLC layer 1d-10 or 1d-35 can recombine the segment with other segments stored in the buffer or received later into a complete RLC PDU and can deliver the RLC PDU to the NR PDCP layer 1d-05 or 1d-40. The NR RLC layer 1d-10 or 1d-35 may not have the concatenation function, and the concatenation function can be performed by the NR MAC layer 1d-15 or 1d-30, or replaced by the multiplexing function of the NR MAC layer 1d-15 or 1d-30.

[0116] The out-of-sequence delivery function of the NR RLC layer 1d-10 or 1d-35 can include: the function of directly delivering the RLC SDUs received from the lower layer to the upper layer out of sequence; the function of reassembling the multiple RLC SDUs segmented from one RLC SDU and delivering the reassembled RLC SDU when the segmented RLC SDUs are received; or the function of reordering the received RLC SDUs and reordering the lost RLC PDUs by storing the RLC SN or PDCP SN of the received RLC SDUs.

[0117] The NR MAC layer 1d-15 or 1d-30 can be connected to multiple NR RLC layers configured for one UE, and the main functions of the NR MAC layer 1d-15 or 1d-30 can include some of the following functions.

[0118] - Mapping between logical channels and transport channels

[0119] - Multiplexing / demultiplexing of MAC SDUs

[0120] - Scheduling information reporting

[0121] - Error correction by HARQ

[0122] - Priority handling between logical channels of a UE

[0123] - Priority handling between UEs by dynamic scheduling

[0124] - MBMS service identification

[0125] - Transmission format selection

[0126] - Padding

[0127] The NR PHY layer 1d-20 or 1d-25 can encode and modulate the upper layer data channel into OFDM symbols, send the OFDM symbols through the radio channel, or demodulate the OFDM symbols received through the radio channel, perform channel decoding on the OFDM symbols, and deliver them to the upper layer.

[0128] Figure 1E is a diagram for describing the process in which a UE according to an embodiment of the present disclosure switches from the RRC idle mode to the RRC connected mode and establishes a connection with the network.

[0129] Reference Figure 1E , when a UE configured to send and receive data in the RRC connected mode does not send or receive data due to a predetermined reason or for a predetermined time, the gNB can send an RRCConnectionRelease message to the UE to cause the UE to transition to the RRC idle mode (operation 1e-01). After that, when a UE that is not currently configured for connection (hereinafter, also referred to as an idle mode UE) has data to send, the UE can perform an RRC connection establishment process on the gNB. The UE establishes reverse transmission synchronization with the gNB through a random access process and sends an RRCConnectionRequest message to the gNB (operation 1e-05). The RRCConnectionRequest message may include an identifier of the UE, a reason for establishment, etc. The gNB sends an RRCConnectionSetup message to cause the UE to establish an RRC connection (operation 1e-10).

[0130] The RRCConnectionSetup message includes configuration information for each service / bearer / RLC layer or each logical channel or each bearer. The PDCP layer configuration information (pdcp-config) may include information on whether ROHC is to be used for each bearer / logical channel, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information for the BS to indicate PDCP status reports to the UE), and drb-ContinueROHC information (configuration information indicating the continued and unchanged use of ROHC configuration information) and may be sent. In addition, RRCConnectionSetup may include RRC connection configuration information. The bearer used for the RRC connection is called the signaling radio bearer (SRB) and is used to send and receive RRC messages, i.e., control messages between the UE and the gNB.

[0131] The UE that establishes the RRC connection sends an RRCConnectionSetupComplete message to the gNB (operation 1e-15). The RRCConnectionSetupComplete message may include a control message, such as a SERVICE REQUEST message, for the UE to request the MME or the access and mobility management function (AMF) to configure a bearer for a specific service. The gNB sends the SERVICE REQUEST message included in the RRCConnectionSetupComplete message to the MME or the AMF (operation 1e-20), and the MME or the AMF may determine whether to provide the service requested by the UE. As a result of the determination, when the service requested by the UE is to be provided, the MME or the AMF sends an INITIAL CONTEXT SETUP REQUEST message to the gNB (operation 1e-25). The INITIALCONTEXT SETUP REQUEST message may include QoS information to be applied when configuring the DRB, security information to be applied to the DRB (e.g., security key, security algorithm, etc.), and so on.

[0132] When the gNB does not receive UE capability information from the MME or AMF, the gNB may send a UE capability information request message to the UE to check the UE capability information (operation 1e-26). When the UE receives the UE capability information request message, the UE may configure, generate, and report a UE capability information message to the gNB (operation 1e-27). The UE capability information may include information on which types of handover methods the UE supports. For example, the UE may report information on the UE capability to the gNB via an indicator that indicates whether the UE supports the effective handover method provided in the present disclosure (i.e., the dual active protocol stack (DAPS) handover method). The gNB checks the UE capability information and then indicates a handover to the UE. According to each handover method, the gNB may indicate the handover by defining an indicator indicating the handover in the handover command message. For example, the gNB may indicate the effective handover method (DAPS handover method) provided in the present disclosure to the UE, or may configure the DAPS handover method for the UE according to each bearer (DRB or SRB). When the gNB configures the DAPS handover method for the UE, the gNB also indicates other handover methods (e.g., the conditional handover method (configuring multiple target cells and multiple conditions for the UE, and when the UE meets the conditions in the cell selection process or the cell reselection process, the UE performs a handover process on one of the target cells) or the handover method without a random access process), thereby preventing data loss or transmission delay that may occur during the handover. The UE may perform a handover process to the target gNB according to the handover method indicated in the handover command message.

[0133] To configure security with the UE, the gNB exchanges a SecurityModeCommand message (operation 1e-30) and a SecurityModeComplete message (operation 1e-35). When the security configuration is completed, the gNB sends an RRCConnectionReconfiguration message to the UE (operation 1e-40).

[0134] The RRCConnectionReconfiguration message includes configuration information for each service / bearer / RLC layer or each logical channel or each bearer. The PDCP layer configuration information (pdcp-config) may include information on whether ROHC is to be used for each bearer / logical channel, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information by which the BS indicates PDCP status reports to the UE), and drb-ContinueROHC information (configuration information indicating continued and unchanged use of ROHC configuration information) and may be sent. In addition, RRCConnectionReconfiguration may include RRC connection configuration information. The bearer used for the RRC connection is called an SRB, which is used for the transmission and reception of RRC messages, which are control messages between the UE and the gNB.

[0135] The RRCConnectionReconfiguration message includes configuration information for the DRB in which user data will be processed. The UE configures the DRB by using the configuration information of the DRB and sends an RRCConnectionReconfigurationcomplete message to the gNB (operation 1e-45). When the DRB configuration for the UE is complete, the gNB sends an INITIALCONTEXT SETUP COMPLETE message to the MME or AMF (operation 1e-50), and upon reception, the MME or AMF may exchange S1BEARER SETUP messages and S1 BEARER SETUP RESPONSE messages with the S-GW to configure the S1 bearer (operations 1e-55 and 1e-60). The S1 bearer is a connection for data transmission, which is configured between the S-GW and the eNB and corresponds to the DRB in a one-to-one manner. After the above processes are completed, the UE may send or receive data to or from the gNB through the S-GW (operations 1e-65 and 1e-70). Therefore, the general data transmission process mainly includes three steps: RRC connection establishment, security setup, and DRB configuration. In addition, for some reason, the gNB may send an RRCConnectionReconfiguration message to the UE to update, add, or change the configuration (operation 1e-75).

[0136] In the present disclosure, the bearers may include SRBs and DRBs, where SRB represents Signaling Radio Bearer and DRB represents Data Radio Bearer. SRBs are mainly used to send and receive RRC messages of the RRC layer, and DRBs are mainly used to send and receive multiple pieces of user plane data. UM DRB refers to a DRB configured to use the RLC layer operating in the Unacknowledged Mode (UM), and the Acknowledged Mode (AM) DRB refers to a DRB configured to use the RLC layer operating in AM.

[0137] Figure 1F FIG. is a diagram showing a signaling procedure for performing handover in a next-generation mobile communication system according to an embodiment of the present disclosure.

[0138] The UE 1f-01 in the RRC connected mode state reports a cell measurement report to the current source gNB 1f-02 in a periodic manner or when a specific event is satisfied (operation 1f-05). The source gNB 1f-02 determines whether the UE1f-01 is to perform a handover to an adjacent cell based on the cell measurement report. Handover is a technique of switching the source BS to another BS (or another cell in the same BS), and the source BS provides services to the UE in the connected mode state. When the source gNB 1f-02 determines a handover, the source gNB1f-02 requests the handover by sending a handover request message (e.g., a handover preparation information message) to the target gNB 1f-03 as the new BS to provide services to the UE 1f-01 (operation 1f-10). When the target gNB1f-03 accepts the handover request, the target gNB1f-03 sends a handover request acknowledgment (Ack) message (e.g., a handover command message) to the source gNB 1f-02 (operation 1f-15). When receiving this message, the source gNB 1f-02 sends a handover command message (an RRCReconfiguration message included in the dedicated control channel (DCCH) of the handover request Ack message) to the UE 1f-01 (operation 1f-20). The source gNB1f-02 extracts the handover command message from the message received from the target gNB1f-03 and sends the handover command message to the UE 1f-01 by using the RRC connection reconfiguration message (operation 1f-20).

[0139] In the present disclosure, a method for determining an effective DAPS handover method by using two messages (i.e., a handover preparation information message (operation 1f-10) and a handover command message (operation 1f-15)) when the source gNB 1f-02 sends a handover preparation information message (operation 1f-10) is provided, and in response thereto, the target gNB 1f-03 sends a handover command message to the source gNB 1f-02 (operation 1f-15).

[0140] Embodiment 1 of the method for determining an effective DAPS handover provided in the present disclosure will now be described.

[0141] In Embodiment 1 of the present disclosure, the entity for determining the DAPS handover method may be the source BS. In addition, in Embodiment 1 of the present disclosure, in the case where the source BS requests the DAPS handover method from the target BS, the target BS may always indicate or execute the DAPS handover method.

[0142] The source BS may indicate to the target BS that the source BS will execute the DAPS handover method provided in the present disclosure and may request the DAPS handover method by defining a new indicator in the handover preparation information message. The handover preparation information message may include the current bearer configuration information of the UE, security key information, cell group configuration information, UE capability information, etc. The source BS is configured to pre-share the capabilities of the target BS, so it can know in advance whether the target BS supports the DAPS handover method. The source BS may indicate to the target BS that the source BS will execute the DAPS handover method, may indicate to the target BS that the source BS can perform early data forwarding quickly or in advance, and may indicate to the target BS to prepare to receive data forwarding and perform processing. The source BS may indicate a request for the DAPS handover method for each bearer (DRB or SRB).

[0143] In the case where the target BS receives the handover preparation information message and identifies that it includes an indicator requesting the DAPS handover method, when the target BS configures the RRCReconfiguration message to indicate a handover to the UE, the target BS may add an indicator requesting the DAPS handover method, the bearer configuration information required for the UE to execute the DAPS handover method, bearer configuration information, security key information, cell group configuration information, or system information to the RRCReconfiguration message. In addition, the target BS may add the RRCReconfiguration message to the DL-DCCH message of the handover command message and may send the handover command message to the source BS. The target BS may perform an indication of the DAPS handover method for each bearer (DRB or SRB).

[0144] When the source BS receives the handover command message, the source BS may extract the RRCReconfiguration message included in the handover command message and may send the RRCReconfiguration message to the UE, thereby indicating a handover. The source BS may identify the indicated DAPS handover method for each bearer and may perform the DAPS handover method for each bearer (DRB or SRB).

[0145] Embodiment 2 of the method for determining an effective DAPS handover provided in the present disclosure will now be described.

[0146] In Embodiment 2 of the present disclosure, the entity for determining the DAPS handover method may be the target BS. Further, in Embodiment 2 of the present disclosure, in the case where the source BS requests the DAPS handover method from the target BS, the target BS may reject or accept the request from the source BS, or may indicate another handover method to the source BS via a handover command message indicating another handover method.

[0147] The source BS may indicate to the target BS that the source BS will perform the DAPS handover method provided in the present disclosure and may request the DAPS handover method by defining a new indicator in the handover preparation information message. The handover preparation information message may include the current bearer configuration information of the UE, security key information, cell group configuration information, UE capability information, etc. The source BS is configured to pre-share the capabilities of the target BS and thus may know in advance whether the target BS supports the DAPS handover method. The source BS may indicate to the target BS that the source BS will perform the DAPS handover method, may indicate to the target BS that the source BS may perform early data forwarding, and may indicate to the target BS to prepare to receive data forwarding and perform processing. The source BS may indicate a request for the DAPS handover method for each bearer (DRB or SRB).

[0148] In the case where the target BS receives the handover preparation information message and identifies an indicator requesting the DAPS handover method included therein, the target BS may reject or accept the request for the DAPS handover method from the source BS based on whether the target BS can support the DAPS handover method, the amount of current transmission resources, or scheduling, or may indicate another handover method to the source BS. The target BS may add an indicator rejecting the request for the DAPS handover method, an indicator accepting the request for the DAPS handover method, or an indicator indicating another handover method to the handover command message, and may send the handover command message. In the case where the target BS configures the RRCReconfiguration message to indicate handover to the UE, the target BS may configure the RRCReconfiguration message such that when the DAPS handover request is accepted, the RRCReconfiguration message includes an indicator indicating the DAPS handover method, or when the DAPS handover request is rejected, the RRCReconfiguration message includes an indicator indicating another handover method, and the RRCReconfiguration message includes bearer configuration information, bearer configuration information, security key information, cell group configuration information, or system information required for the UE to perform the DAPS handover method or other handover methods. In addition, the target BS may add the RRCReconfiguration message to the DL-DCCH message of the handover command message, and may send the handover command message to the source BS. The target BS may perform an indication of the DAPS handover method for each bearer (DRB or SRB).

[0149] When the source BS receives a handover command message, the source BS may check an indicator included in the handover command message, and thus may identify whether a request for the DAPS handover method is accepted or rejected. When the request for the DAPS handover method is accepted, the source BS may execute the DAPS handover method, may extract the RRCReconfiguration message included in the handover command message, may send the RRCReconfiguration message to the UE, and thus may indicate the handover. When the source BS checks the indicator included in the handover command message, when the request for the DAPS handover method is rejected or another handover message is indicated, the source BS may execute another handover method indicated by the target BS. In addition, the source BS may extract the RRCReconfiguration message included in the handover command message, may send the RRCReconfiguration message to the UE, and thus may indicate the handover. As another method, when there is no separate indicator in the handover command message, the source BS may check the type of the handover message indicated by the target BS by reading the RRCReconfiguration message included in the handover command message, and may identify whether a request for the DAPS handover method is accepted or rejected. The source BS may execute the handover method indicated in the RRCReconfiguration message (e.g., the DAPS handover method or another handover method). The source BS may identify the indicated DAPS handover method for each bearer, and may execute the DAPS handover method for each bearer (DRB or SRB).

[0150] Embodiment 3 for determining an effective DAPS handover method provided in the present disclosure will now be described.

[0151] In Embodiment 3 of the present disclosure, the entity for determining the DAPS handover method may be the target BS. In addition, in Embodiment 3 of the present disclosure, the target BS may check the UE's capabilities, and may determine the handover method (e.g., the DAPS handover method) based on whether the target BS can support the DAPS handover method, the amount of current transmission resources, or scheduling.

[0152] The source BS may add the UE's current bearer configuration information, security key information, cell group configuration information, UE capability information, etc. to the handover preparation information message, and may send the handover preparation information message to request the target BS to perform a handover. The source BS is configured to pre-share the capabilities of the target BS, and thus may know in advance whether the target BS supports the DAPS handover method. When the target BS indicates to execute the DAPS handover method, the source BS may perform early data forwarding quickly or in advance.

[0153] The target BS can receive the handover preparation information message and can determine a handover method (e.g., the DAPS handover method) based on UE capability information, whether the target BS can support the DAPS handover method, the amount or scheduling of the current transmission resources. When the target BS determines the DAPS handover method, the target BS can add an indicator indicating the DAPS handover method to the handover command message and can send the handover command message. In the case where the target BS configures the RRCReconfiguration message to indicate handover to the UE, the target BS can configure the RRCReconfiguration message such that when the DAPS handover request is determined, the RRCReconfiguration message includes an indicator indicating the DAPS handover method, or when the DAPS handover request is determined, the RRCReconfiguration message includes an indicator indicating another handover method, and the RRCReconfiguration message includes bearer configuration information, bearer configuration information, security key information, cell group configuration information, or system information required for the UE to perform the DAPS handover method or other handover methods. In addition, the target BS can add the RRCReconfiguration message to the DL-DCCH message of the handover command message and can send the handover command message to the source BS. The target BS can perform an indication of the DAPS handover method for each bearer (DRB or SRB).

[0154] When the source BS receives a handover command message, the source BS may check an indicator included in the handover command message, and thus may identify whether the DAPS handover method is determined. When the DAPS handover method is indicated, the source BS may perform the DAPS handover method, may extract the RRCReconfiguration message included in the handover command message, may send the RRCReconfiguration message to the UE, and thus may indicate the handover. When the source BS checks the indicator included in the handover command message, when the DAPS handover method is not determined or another handover message is indicated, the source BS may perform another handover method indicated by the target BS. In addition, the source BS may extract the RRCReconfiguration message included in the handover command message, may send the RRCReconfiguration message to the UE, and thus may indicate the handover. As another method, when there is no separate indicator in the handover command message, the source BS may check the type of handover message indicated by the target BS by reading the RRCReconfiguration message included in the handover command message, and may identify whether the DAPS handover method is determined. When another handover method is indicated, the source BS may perform the indicated another handover method. The source BS may identify the indicated DAPS handover method for each bearer, and may perform the DAPS handover method for each bearer (DRB or SRB).

[0155] By combining the methods of Embodiment 1, Embodiment 2, or Embodiment 3 for determining an effective DAPS handover method, a new embodiment can be obtained.

[0156] According to an embodiment of the present disclosure, the BS may indicate an effective handover method (DAPS handover method) provided in the present disclosure to the UE through the RRCReconfiguration message, or in another method, the BS may configure the DAPS handover method for each bearer (DRB or SRB) of the UE. For example, a new indicator for indicating bearer configuration information, DPC PDCP configuration information, or RLC configuration information indicating each bearer identifier or each logical channel identifier may be defined in the RRCReconfiguration message, and the BS may indicate an effective handover message for each bearer or logical channel identifier to the UE by using the new identifier. When the BS configures the DAPS handover method for the UE, the BS also indicates other handover methods (for example, a conditional handover method (configuring multiple target cells and multiple conditions for the UE, and when the UE meets the conditions in the cell selection process or the cell reselection process, the UE performs a handover process on one target cell) or a handover method without a random access process), thereby preventing data loss or transmission delay that may occur during handover.

[0157] When the UE 1f-01 receives an RRCReconfiguration message, the UE 1f-01 interrupts or continues data transmission and reception with the source gNB 1f-02 by using the configured handover method and starts the T304 timer. When the UE 1f-01 fails to successfully hand over to the target gNB 1f-03 within a preset time (e.g., when the T304 timer expires), the T304 timer returns the UE1f-01 to the initial configuration of the UE 1f-01 and causes the UE 1f-01 to transition to the RRC idle state. In addition, the UE 1f-01 can trigger an RRC connection reestablishment process, and when an effective handover method is configured and the connection to the source gNB 1f-02 is active, the UE 1f-01 can fallback and report the handover failure of the UE to the source gNB 1f-02. The source gNB 1f-02 provides the sequence number (SN) status of UL / DL data for each bearer (e.g., for each RLC UM bearer or each RLC AM bearer), and when DL data or UL data exists, the source gNB 1f-02 sends the DL data or UL data to the target gNB 1f-03 (Operations 1f-30 and 1f-35). The UE 1f-01 attempts to randomly access the target cell indicated by the source gNB 1f-02 (Operation 1f-40). The UE 1f-01 performs random access to notify the UE 1f-01 of the handover to the target cell while matching UL synchronization. For random access, the UE1f-01 sends a preamble to the target cell, which corresponds to the preamble ID provided by the source gNB 1f-02 or a randomly selected preamble. After sending the preamble and then sending a specific number of subframes, the UE 1f-01 listens for whether a random access response (RAR) message is sent from the target cell. The time interval for listening for the RAR message is called the RAR window. When the RAR message is received during the RAR window (Operation 1f-45), the UE 1f-01 sends a handover completion message to the target gNB 1f-03 in the RRC reconfiguration complete message (Operation 1f-55). When the UE 1f-01 successfully receives the RAR message from the target gNB 1f-03, the UE 1f-01 stops the T304 timer (Operation 1f-50).

[0158] To switch to the bearer path configured by the source gNB 1f-02, the target gNB 1f-03 requests the core network 1f-04 (e.g., MME / S-GW / AMF) to perform a bearer path switch (Operations 1f-60 and 1f-65), and instructs the source gNB 1f-02 to discard the UE context of UE1f-01 (Operation 1f-70). The target gNB 1f-03 may send an RRC message (e.g., RRCReconfiguration message 1f-71) to the UE 1f-01, and may use an indicator to instruct the UE 1f-01 to release the connection with the source gNB1f-02. As another method, the target gNB 1f-03 may send MAC control information, RLC control information, or PDCP control information to the UE 1f-01, thereby instructing the UE 1f-01 to release the connection with the source gNB 1f-02. The UE 1f-01 attempts to receive data from the target gNB 1f-03 at the start point of the RAR window, and after receiving the RAR message, the UE 1f-01 sends an RRC reconfiguration complete message and receives a DL transmission resource or a UL transmission resource, thereby starting to send data to the target gNB 1f-03 and receive data from the target gNB 1f-03.

[0159] In the following, in the present disclosure, a non-interruptive handover method is provided that can make the data interruption time 0 ms or minimize the data interruption time due to handover in the next-generation mobile communication system.

[0160] The UE may configure multiple first bearers with the source BS, and may perform data transmission and reception (UL or DL data transmission and reception) via the protocol layers (PHY layer, MAC layer, RLC layer, PDCP layer, etc.) of each of the multiple first bearers. In the present disclosure, for ease of description, it is assumed in the drawings and the description that the UE has one bearer.

[0161] Figure 1G Embodiment 1 of a specific operation of an effective handover method for minimizing the data interruption time due to handover according to an embodiment of the present disclosure is shown.

[0162] According to an embodiment of the present disclosure, in Figure 1GIn Embodiment 1 of the effective handover method, when UE 1g-20 transmits data to or receives data from source BS 1g-05 in the first operation 1g-01 and then receives a handover command message, UE 1g-20 can release the connection with source BS 1g-05, perform a random access procedure on target BS 1g-10, and perform a handover procedure based on the handover method indicated by the handover command message (e.g., RRCReconfiguration message). As another method, in order to minimize the data interruption time occurring during handover based on the indicated handover method, UE 1g-20 can continuously transmit data to and receive data from source BS 1g-05.

[0163] According to an embodiment of the present disclosure, in the second operation 1g-02, when UE 1g-20 performs a random access procedure on target BS 1g-10 by using the handover method indicated by the handover command message received from source BS 1g-05, transmits a preamble to target BS 1g-10, or initially transmits data in the UL transmission resource by using PUCCH or PUSCH transmission resources, UE 1g-20 can stop transmitting data to and receiving data from target BS 1g-05 (UL data transmission and DL data reception).

[0164] According to an embodiment of the present disclosure, in the third operation 1g-03, UE 1g-20 can complete the random access procedure for target BS 1g-10, transmit a handover completion message to target BS 1g-10, and start transmitting data to and receiving data from target BS 1g-10 (UL data transmission and DL data reception).

[0165] Figure 1H Shows specific operations of Embodiment 2 of the effective handover method for minimizing data interruption time due to handover according to an embodiment of the present disclosure.

[0166] According to an embodiment of the present disclosure, in Figure 1HIn Embodiment 2 of the effective handover method, in the first operation 1h-01, when the UE 1h-20 transmits and / or receives data with the source BS 1h-05, the UE 1h-20 may receive a handover command message from the source BS 1h-05. When the source BS 1h-05 indicates in the handover command message the handover method according to Embodiment 2 of the effective handover method provided in the present disclosure (e.g., the DAPS handover method) or the handover method for each bearer, even when the UE 1h-20 has received the handover command message, the UE 1h-20 may continuously transmit data to and receive data from the source BS 1h-05 via the protocol layer 1h-22 of the first bearer to minimize the data interruption time occurring during the handover.

[0167] In addition, when the RRC layer of the UE 1h-20 recognizes an indication regarding the handover method according to Embodiment 2 of the effective handover method provided in the present disclosure (e.g., the DAPS handover method) in the handover command message, or recognizes an identifier regarding the DAPS handover method for each bearer, the RRC layer may provide the indication to the PDCP layer of each bearer or the bearer indicating the DAPS handover method. When the PDCP layer receives the indicator, the PDCP layer may switch the first PDCP layer architecture 1i-11 or 1i-12 (see Figure 1I ) to the second PDCP layer architecture 1i-20 (see Figure 1I ).

[0168] Figure 1HThe first operation 1h-01 can be described as an operation where the UE 1h-20 receives a handover command message (RRCReconfiguration message) from the BS. When the UE 1h-20 switches to the second PDCP layer architecture 1i-20 according to the configuration included in the received handover command message, the UE 1h-20 can pre-configure or pre-set the protocol layers (PHY layer, MAC layer, RLC layer, or PDCP layer) 1h-21 of the second bearer for the target BS 1h-10, can derive and update the security key for the target BS 1h-10, and can configure the header (or data) compression context for the target BS 1h-10. In addition, the UE 1h-20 can receive the handover command message from the source BS 1h-05, and in the handover command message, when the source BS 1h-05 indicates the DAPS handover method provided in the present disclosure, when the source BS 1h-05 indicates the DAPS handover method for a specific bearer, or when the PDCP re-calibration timer value is newly configured, the UE 1h-20 can switch the first PDCP layer architecture or function 1i-11 or 1i-12 to the second PDCP layer architecture or function 1i-20 provided in the present disclosure for each bearer or for the bearer indicating the DAPS handover method. When the UE 1h-20 switches the first PDCP layer architecture or function 1i-11 or 1i-12 to the second PDCP layer architecture or function 1i-20 provided in the present disclosure, the UE 1h-20 can update the variable for re-calibration to the PDCP SN or COUNT value (count value) expected to be received next time, can stop the re-calibration timer, and can restart the timer.

[0169] When the UE 1h-20 receives a handover command message (e.g., RRCReconfiguration message), the RRC layer of the UE 1h-20 can start a first timer (e.g., T304). When the UE 1h-20 performs a random access procedure on the target BS 1h-10 to perform the handover and the random access procedure is successfully completed (e.g., when the first condition provided in the present disclosure is met), the first timer can be stopped. In the case of a handover failure and thus the expiration of the first timer, when the connection with the source BS 1h-05 is active, the UE 1h-20 can fallback and report the handover failure of the UE to the source BS 1h-05 and can attempt connection recovery, and when the connection with the source BS 1h-05 is inactive, the UE 1h-20 can perform an RRC connection re-establishment procedure.

[0170] The handover command message received by the UE 1h-20 from the source BS 1h-05 may include information by which a second bearer is configured to have the same identifier as the first bearer and then established such that a data interruption time does not occur in each bearer. In Embodiment 2 of the present disclosure, the PDCP layer of the first bearer and the PDCP layer of the second bearer may operate logically as one PDCP layer, and a detailed description of the operation will now be provided with reference to Figure 1I to provide a detailed description of the operation.

[0171] In Embodiment 2 of the present disclosure, when the UE is configured to transmit UL data to both the source BS and the target BS, in order to avoid a coverage reduction problem due to insufficient transmission power of the UE or to prevent link selection, when the UE transmits UL data, the UE must determine to which BS the UE must request transmission resources and transmit UL data. The UE in Embodiment 2 of the present disclosure may transmit UL data only to one of the source BS and the target BS. Specifically, in Embodiment 2 of the present disclosure, when the UE does not have the ability to transmit UL data to different BSs simultaneously at different frequencies or the same frequency (dual uplink transmission), the UE may transmit UL data only to one of the source BS and the target BS within one time unit. Therefore, the UE may perform a scheduling request only to one of the source BS and the target BS, may transmit a report (e.g., buffer status report) on the size of a plurality of data items to be transmitted by the PDCP layer to one of the source BS and the target BS, may receive UL transmission resources, and thus may transmit UL data only to one BS. In addition, even when the UE receives a handover command message from the source BS, the UE may not initialize the MAC layer of the first bearer in order to prevent data loss by continuing data transmission and reception through HARQ retransmission. In addition, the RLC layer in the AM mode may continuously perform RLC retransmission.

[0172] As another method, when the handover command message indicates Embodiment 2 (DAPS handover method) of the valid handover method provided in the present disclosure for each bearer, the UE may continuously transmit data to or receive data from the source BS only for the PDCP layer, RLC layer, or MAC layer corresponding to the bearer or logical channel identifier that indicates Embodiment 2 (DAPS handover method) in the handover command message, or only for the data corresponding to the bearer or logical channel identifier. In addition, when the first condition provided in the present disclosure is satisfied (for example, when UL data transmission is switched to the target BS), the UE may continuously transmit or receive RLC control data (RLC status report), PDCP control data (ROHC feedback or PDCP status report), or HARQ retransmission from the source BS only for the PDCP layer, RLC layer, or MAC layer corresponding to the bearer or logical channel identifier that indicates Embodiment 2 (DAPS handover method) in the handover command message. In addition, when the handover command message indicates Embodiment 2 (DAPS handover method) of the valid handover method provided in the present disclosure for each bearer, the UE may stop transmitting or receiving data from the source BS for the PDCP layer, RLC layer, or MAC layer corresponding to the bearer or logical channel identifier that does not indicate Embodiment 2 (DAPS handover method) in the handover command message.

[0173] In addition, in the case where the UE receives a handover command message and the handover command message indicates the DAPS handover method provided in the present disclosure, when the DAPS handover method is indicated for a specific bearer and QoS flow and bearer mapping information are newly configured, the UE may switch the first SDAP layer architecture or function 1j-10 (see Figure 1J ) to the second SDAP layer architecture or function 1j-20 (see Figure 1J)。In addition, in the second SDAP layer architecture, the existing first QoS and existing bearer mapping information of the source BS are maintained, so that the UL data to be sent to the source BS and the DL data to be received from the source BS can be processed. The newly configured second QoS flow and bearer mapping information in the handover command message are configured for the target BS and can be used to process the UL data to be sent to the target BS and the DL data to be received from the target BS. That is, in the second SDAP layer architecture provided in the present disclosure, the first QoS flow and bearer mapping information of the source BS or the second QoS flow and bearer mapping information of the target BS are maintained, so that the data of the source BS and the data of the target BS can be processed separately. In the second SDAP layer architecture, the SDAP layer can identify whether the data received from the lower layer is the data received from the source BS or the data received from the target BS by using a 1-bit indicator in the SDAP header, a 1-bit indicator in the PDCP header, or the information indicated by the PDCP layer. When the source BS indicates the DAPS handover method for each bearer to the UE by using a handover command message, the DAPS handover method for the default DRB is always indicated, and when data appears in a new QoS that does not correspond to the QoS flow and bearer mapping information during the execution of the DAPS handover process, the UE can be instructed to always send the UL data via the default bearer. When the DAPS handover method is not configured for the default bearer, it is impossible to send the UL data for the new QoS flow that appears during the handover, resulting in a possible data interruption time.

[0174] As another method, when the UE receives a handover command message (RRCReconfiguration message) indicating Embodiment 2 (DAPS handover method) and the SDAP layer configuration information or the second QoS flow and bearer mapping information of the target BS is configured in the RRC message, the UE can apply the SDAP layer configuration information or the second QoS flow and bearer mapping information when the first condition provided in the present disclosure is met. In addition, when the DAPS handover method (Embodiment 2) is indicated for each bearer in the handover command message, the UE can only maintain and apply the first QoS flow and bearer mapping information corresponding to the bearer indicating Embodiment 2 from the first QoS flow and bearer mapping information of the source BS, and can release or not apply the first QoS flow and bearer mapping information corresponding to the bearer that does not indicate Embodiment 2. In addition, when the SDAP layer configuration information or the second QoS flow and bearer mapping information of the target BS is configured in the RRC message, when the first condition provided in the present disclosure is met, the UE can apply the SDAP layer configuration information or the second QoS flow and bearer mapping information to the data transmission or reception to or from the target BS.

[0175] According to an embodiment of the present disclosure, in Figure 1HIn Embodiment 2 of the effective handover method, in the second operation 1h-02, the UE 1h-20 may perform a random access procedure on the target BS 1h-10 via the protocol layer of the second bearer, and the target BS 1h-10 is indicated in the handover command message. When performing the random access procedure via the protocol layer of the second bearer, the UE 1h-20 may continue to send or receive data (UL data transmission or DL data reception) to or from the source BS 1h-05 via the protocol layer of the first bearer. The second operation 1h-02 may be described as an operation in which the UE 1h-20 performs a cell selection procedure or a cell reselection procedure, and performs a random access procedure on the target cell indicated by the handover command message (RRCReconfiguration message) received from the source BS 1h-05.

[0176] According to an embodiment of the present disclosure, in Figure 1H In Embodiment 2 of the effective handover method, when a first condition to be described below is satisfied in the third operation 1h-03, the UE 1h-20 may stop UL data transmission to the source BS 1h-05 via the protocol layer 1h-22 of the first bearer, and may transmit UL data to the target BS 1h-10 via the protocol layer 1h-21 of the second bearer. In view of this, the UE 1h-20 may continuously receive DL data from the source BS 1h-05 and the target BS 1h-10 via the protocol layers of the first and second bearers. The third operation 1h-03 may be an operation in which the UE 1h-20 satisfies the first condition and thus switches UL transmission from the source BS 1h-05 to the target BS 1h-10. Specifically, in the operation, the UE 1h-20 transmits UL data to the source BS 1h-05 via the first bearer until the UE 1h-20 satisfies the first condition, and when the UE 1h-20 satisfies the first condition, the UE 1h-20 stops transmitting UL data to the source BS 1h-05 via the first bearer, and starts transmitting UL data to the target BS 1h-10 via the second bearer.

[0177] Specifically, in the second PDCP layer architecture provided in the present disclosure, in the case where the PDCP layer transmits UL data via the first bearer and satisfies the first condition to receive an indicator from the lower layer (when the random access procedure to the target BS in the MAC layer is successful) or the upper layer (when the first timer in the RRC layer expires), the PDCP layer may stop transmitting UL data via the first bearer, may perform a handover, and may start transmitting UL data via the second bearer. In addition, as in the reference Figure 1IIn the provided PDCP layer structure, the receiving PDCP layer 1h-21 of the second bearer and the receiving PDCP layer 1h-22 of the first bearer can operate as one entity, and the receiving PDCP layer 1h-21 can continuously receive data from the source BS 1h-05 or the target BS 1h-10 by using the stored transmitted and / or received data, SN information, or information such as header compression and decompression context. The first condition can be one of the following conditions. The following first condition presents the UL data transmission handover time point at which the transmission resources can be maximized and effectively utilized, and the data interruption time can be minimized.

[0178] It can be determined that the first condition is satisfied when the UE successfully completes the random access procedure to the target BS via the layer of the second bearer (e.g., MAC layer), when the UE successfully completes the random access procedure to the target BS via the layer of the second bearer (e.g., MAC layer) and receives the allocation of the first UL transmission resource from the target BS, or when the UL transmission resource is first indicated to the UE.

[0179] For example, when the UE receives a handover command message from the source BS and receives an indication of random access to the target BS, when the indicated random access is contention-free random access (CFRA) (e.g., when a predefined preamble or a UE cell identifier (e.g., cell radio network temporary identifier (C-RNTI)) is allocated), and when the UE transmits the predefined preamble to the cell of the target BS and receives the RAR message, it can be determined that the random access procedure is successfully completed. Therefore, when the UE receives (is allocated) the first UL transmission resource allocated (or included or indicated) in the RAR message, it can be determined that the first condition is satisfied. As another method, when the UE first receives the UL transmission resource after receiving the RAR message, it can be determined that the first condition is satisfied.

[0180] In the case where the UE receives a handover command message from the source BS and receives an indication of random access to the target BS, when the indicated random access is contention-based random access (CBRA) (e.g., when no predefined preamble or UE cell identifier (e.g., C-RNTI) is allocated), it can be determined that when the UE sends a preamble (e.g., a random preamble) to the cell of the target BS and receives a RAR message, sends message 3 (e.g., a handover completion message) to the target BS by using the UL transmission resource allocated (or included or indicated) in the RAR message, and receives a contention resolution MAC CE indicating contention resolution from the target BS via message 4, or receives the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI. Therefore, when the UE monitors the PDCCH and first receives (or is first indicated) the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the first condition is satisfied. As another method, when the size of the UL transmission resource allocated in the RAR message is large enough and thus the UE can send message 3 and additionally send UL data, the UE can determine that the UE first receives the UL transmission resource, and thus can determine that the first condition is satisfied. That is, when the UE receives the RAR message, the UE can determine that the UE first receives the UL transmission resource, and thus can determine that the first condition is satisfied.

[0181] When a handover method that does not request a random access procedure (rach-less handover) is also indicated in the handover command message received by the UE, it can be determined that the first condition is satisfied in the following cases.

[0182] When the handover command message includes the UL transmission resource for the target BS, the UE sends message 3 (e.g., a handover completion message or an RRCReconfigurationComplete message) by using the UL transmission resource for the target BS, and when the UE receives the UE identity confirmation MAC CE from the BS via message 4, or receives the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the random access procedure is successfully completed and the first condition is satisfied. As another method, after the random access procedure is successfully completed, the UE performs PDCCH monitoring and receives the first UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the first condition is satisfied.

[0183] When the handover command message does not include the UL transmission resource for the target BS, the UE performs PDCCH monitoring for the target BS (or cell), and when the UE receives the UL transmission resource through the PDCCH corresponding to the UE's C-RNTI or sends Message 3 (e.g., handover complete message or RRCReconfigurationComplete message) by using the UL transmission resource and receives the UE identity confirmation MAC CE from the BS or receives the UL transmission resource through the PDCCH corresponding to the UE's C-RNTI, it can be determined that the random access procedure is successfully completed and the first condition is satisfied. As another method, after the random access procedure is successfully completed, the UE performs PDCCH monitoring and receives the first UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, and it can be determined that the first condition is satisfied.

[0184] In the following, a method for effectively switching UL data from the source BS to the target BS is provided, and this method is performed when the DAPS handover method provided in the present disclosure is executed. The MAC layer or RRC layer of the second bearer of the target BS can check or identify whether the first condition is satisfied by using one or a combination of the methods to be described below.

[0185] First method: For example, when the RRCReconfiguration message received by the UE indicates DAPS handover, the UE can configure the MAC layer of the second bearer for the target BS, and the MAC layer of the target BS can perform the random access procedure and can identify whether the first condition is satisfied. When the first condition is satisfied, in the DAPS handover method provided in the present disclosure, the MAC layer of the target BS can use an indicator to indicate the upper layer (e.g., PDCP layer) to switch the UL data transmission from the source BS via the first bearer to the target BS via the second bearer.

[0186] Second method: As another method, for example, when the RRCReconfiguration message received by the UE indicates a DAPS handover, the UE may configure the MAC layer of the second bearer for the target BS, and the MAC layer of the target BS may perform a random access procedure and may identify whether the first condition is met. When the first condition is met, the MAC layer of the target BS may indicate to the upper layer (e.g., the RRC layer) that the first condition is met. In addition, in the DAPS handover method provided in the present disclosure, the upper layer (e.g., the RRC layer) may use an indicator to indicate to the lower layer (e.g., the PDCP layer) to switch the UL data transmission from the source BS via the first bearer to the target BS via the second bearer. When the first condition provided in the present disclosure is met or the random access procedure is successfully performed on the target BS, the upper layer (e.g., the RRC layer) may stop the first timer, and when the first timer stops, the RRC layer may use an indicator to indicate to the PDCP layer to perform the handover.

[0187] Third method: When the RRCReconfiguration message received by the UE indicates a DAPS handover, the UE may configure the MAC layer of the second bearer for the target BS. When the RRC layer of the UE uses an indicator to indicate to the lower layer (e.g., the MAC layer) to perform a DAPS handover, the MAC layer of the target BS may perform a random access procedure and may check whether the first condition is met. When the first condition is met, in the DAPS handover method provided in the present disclosure, the MAC layer of the target BS may use an indicator to indicate to the upper layer (e.g., the PDCP layer) to switch the UL data transmission from the source BS via the first bearer to the target BS via the second bearer.

[0188] Fourth method: As another method, when the RRCReconfiguration message received by the UE indicates a DAPS handover, the UE may configure the MAC layer of the second bearer for the target BS. When the RRC layer of the UE uses an indicator to indicate to the lower layer (e.g., the MAC layer) to perform a DAPS handover, the MAC layer of the target BS may perform a random access procedure and may check whether the first condition is met. When the first condition is met, the MAC layer may indicate to the upper layer (e.g., the RRC layer) that the first condition is met. When the indicator is recognized, when the first condition provided in the present disclosure is met or the random access procedure is successfully performed on the target BS, the upper layer (e.g., the RRC layer) may stop the first timer. In addition, in the DAPS handover method provided in the present disclosure, the upper layer (e.g., the RRC layer) may use an indicator to indicate to the lower layer (e.g., the PDCP layer) to switch the UL data transmission from the source BS via the first bearer to the target BS via the second bearer.

[0189] When the PDCP layer receives an indicator indicating that the first condition is satisfied or an indicator indicating a handover of UL data transmission from a source BS to a target BS from an upper layer (e.g., the RRC layer) or a lower layer (e.g., the MAC layer) according to the first method, the second method, the third method, or the fourth method, the PDCP layer may perform the protocol layer operations provided below to effectively perform the handover of UL data transmission, and may perform one or more operations from the following operations to prevent data loss due to UL data transmission.

[0190] The following operations may be applied to the PDCP layer connected to an AM DRB or a UM DRB (the RLC layer operating in the AM mode or the RLC layer operating in the UM mode). Before the first condition is satisfied or before receiving an indicator indicating that the first condition is satisfied, the PDCP layer may indicate the size or quantity of the data to be transmitted (e.g., the PDCP data volume) to the MAC layer of the first bearer of the source BS when storing the data to be transmitted in the buffer, and may perform UL data transmission to the source BS. Then, the MAC layer of the first bearer of the source BS may perform a scheduling request or a buffer status report procedure to receive an allocation of UL transmission resources from the source BS. When the first condition is satisfied or an indicator indicating that the first condition is satisfied is received, the UL data transmission may be handed over to the target BS in the manner described below.

[0191] To hand over the UL data transmission from the first bearer of the source BS to the second bearer of the target BS, the PDCP layer may indicate to the MAC layer of the first bearer of the source BS that the size or quantity of the data to be transmitted is 0 (or none). That is, the PDCP layer may indicate to the MAC layer of the first bearer that the data volume (PDCP data volume) of the PDCP layer is 0, thereby indicating that there is no more data to be transmitted (even when the buffer actually stores multiple data items to be transmitted, for the purpose of handing over the UL data transmission, the PDCP layer may indicate to the MAC layer of the first bearer of the source BS that there is no more data to be transmitted). However, in the case of indicating the handover method (DAPS handover method) of Embodiment 2 provided in the present disclosure, when generating RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback), the UE may indicate the data volume corresponding to the RLC control data or the PDCP control data to the MAC layer and may perform data transmission to the source BS.

[0192] The PDCP layer connected to the AM DRB (i.e., the RLC layer operating in the AM mode) (discarding all pre-stored PDCP PDUs (e.g., not discarding PDCP PDUs to prevent loss of original data)) can perform a new header compression process on multiple data items (PDCP SDUs in the buffer) arranged in ascending order of COUNT value (or PDCP SN) assigned before meeting the first condition or receiving an indicator indicating that the first condition is met. This ascending order starts from the first data (e.g., PDCP SDU) not acknowledged as successfully transmitted by the lower layer (e.g., the RLC layer of the first bearer of the source BS). The PDCP layer can re-perform an integrity-related process or an encryption process on the multiple data items that have undergone the new header compression process by applying a security key for the target BS, can configure the PDCP header, and can provide the PDCP header to the lower layer (the RLC layer of the second bearer of the target BS) to perform retransmission or transmission.

[0193] That is, the PDCP layer can perform cumulative retransmission on the data starting from the first data not acknowledged as successfully transmitted. As another method, when the PDCP layer performs retransmission, the PDCP layer can perform retransmission only on multiple data items not acknowledged as successfully transmitted by the lower layer (e.g., the RLC layer of the first bearer of the source BS). Specifically, the PDCP layer connected to the AM DRB (or the RLC layer operating in the AM mode) (PDCP PDUs stored to be sent to the source BS via the first protocol layer previously connected to the PDCP layer are all discarded (e.g., PDCP PDUs may not be discarded to prevent loss of initial data)) can be performed by applying the header compression (or data compression) protocol context or security key corresponding to the target BS, and perform a new header or data compression process on multiple data items (e.g., PDCP SDUs) not acknowledged as successfully transmitted by the lower layer (e.g., the RLC layer), which is the first protocol layer of the source BS, based on the COUNT value (or PDCP SN) assigned before meeting the first condition or receiving an indicator indicating that the first condition is met. The PDCP layer can re-perform an integrity-related process or an encryption process on the multiple data items that have undergone the new header or data compression process, can configure the PDCP header, and can provide the PDCP header to the lower layer, which is the second protocol layer, for transmission to the target BS to perform retransmission or transmission. That is, to prevent waste of transmission resources, the PDCP layer can perform selective retransmission only on multiple data items not acknowledged as successfully delivered. As another method, transmission or retransmission can be performed after the lower layer (e.g., the transmitting or receiving RLC layer or MAC layer), which is the first protocol layer for sending data to the source BS, is released.

[0194] When the transmission or retransmission process extends to the UM DRB, the PDCP layer connected to the RLC layer operating in the UM mode may consider data that has not been sent to the lower layer, data for which the PDCP discard timer has not expired, or multiple data items for which PDCP SN (or COUNT value) has been allocated as data received from or newly received from the upper layer. In addition, the PDCP layer may not restart the PDCP discard timer for the data considered to be received from or newly received from the upper layer, may perform header (or data) compression, encryption, or integrity protection processes on multiple data items by using the header (or data) compression context or security key of the target BS, may generate and combine PDCP headers, and then may perform transmission or retransmission. In addition, the PDCP layer may process data in ascending order of the allocated COUNT value before the process is triggered and may perform transmission or retransmission. The window status variable of the PDCP layer connected to the UM DRB or AM DRB may not be initialized but may be maintained.

[0195] When the buffer stores data to be transmitted, the PDCP layer may indicate the presence of data to be transmitted to the MAC layer of the second bearer of the target BS by indicating the size or quantity of the data to be transmitted (e.g., PDCP data volume), and may perform a handover of UL data transmission to the target BS. Then, the MAC layer of the second bearer of the target BS may perform a scheduling request or buffer status report process to receive an allocation of UL transmission resources from the target BS.

[0196] According to Embodiment 2 of the effective handover method (e.g., DAPS handover method) provided in the present disclosure, even after the UE receives a handover command message (e.g., RRCReconfiguration message), the UE may continuously receive DL data from the source BS or the target BS via the protocol layer of the first bearer of the source BS or the second bearer of the target BS. In addition, according to Embodiment 2 of the present disclosure, in order for the UE to smoothly receive DL data from the source BS (or target BS), or for the source BS (or target BS) to smoothly send DL data to the UE, for the AM bearer, the UE may continuously perform RLC status reporting on the source BS (or target BS) via the protocol layer of the first bearer (or second bearer) instead of UL transmission of data. That is, even when the first condition is satisfied and thus the UE switches to UL data transmission of the target BS, when the UE has to send an RLC status report, HARQ ACK or NACK, or PDCP control data (PDCP ROHC feedback or PDCP status report) to the source BS, the UE may be made to perform data transmission via the first bearer of the source BS. In the case of the AM bearer, when data is sent to the transmitting end and then it is not indicated that successful transmission has occurred by using the RLC status report (i.e., when no RLC status report is received), the data cannot be continuously transmitted thereafter.

[0197] Specifically, when the first condition is satisfied in the third operation 1h-03 of Embodiment 2 of the effective handover method in Figure 1H , the UE 1h-20 stops UL data transmission via the protocol layer 1h-22 of the first bearer to the source BS 1h-05, performs a handover, and then starts UL data transmission via the protocol layer 1h-21 of the second bearer to the target BS 1h-10. The UE 1h-20 can continuously transmit HARQ ACK or HARQ NACK information, RLC status reports (ACK or NACK information), or PDCP control data (e.g., PDCP status reports or PDCP ROHC feedback information) via the protocol layer of the first bearer (or the second bearer) in order to smoothly receive DL data from the source BS 1h-05 (or the target BS 1h-10), or to enable the source BS 1h-05 (or the target BS 1h-10) to smoothly transmit DL data.

[0198] In detail, in Figure 1H the third operation 1h-03 in Embodiment 2 of the effective handover method in

[0199] even when the first condition is satisfied and thus the UE 1h-20 stops UL data transmission via the protocol layer 1h-22 of the first bearer to the source BS 1h-05, performs a handover, and then starts UL data transmission via the protocol layer 1h-21 of the second bearer to the target BS 1h-10, the UE 1h-20 can continuously perform data transmission caused by HARQ retransmission of the MAC layer or data transmission caused by retransmission of the RLC layer in the AM mode to prevent data loss at the source BS 1h-05. Figure 1H In detail, in the third operation 1h-03 in Embodiment 2 of the effective handover method in

[0200] As another method, when the UL transmission resource to the target BS conflicts with the UL transmission resource to the source BS and thus overlaps with the UL transmission resource to the source BS, the UE may perform data transmission to the target BS by assigning a priority to the UL transmission resource to the target BS in order to maintain the DL data transmission from the target BS.

[0201] Specifically, when the UE receives a handover command message (in which the handover corresponding to Embodiment 2 of the present disclosure (DAPS handover method) is indicated or the handover corresponding to Embodiment 2 of the present disclosure (DAPS handover method) is indicated for each bearer), the UE or the bearer indicating the DAPS handover may perform a scheduling request via the first protocol layer, may receive a UL transmission resource by sending a buffer status report to the source BS, may send UL data, and may receive DL data from the source BS until the first condition is satisfied. However, when the first condition is satisfied, the UE no longer sends data to the source BS, may perform a scheduling request by switching the UL via the second protocol layer, may receive a UL transmission resource by sending a buffer status report to the target BS, and may send UL data to the target BS. However, the UE may continuously receive DL data from the source BS, and even after the UL transmission handover, the UE may continuously send a HARQ ACK or HARQ NACK, an RLC status report, or PDCP control data (e.g., a PDCP status report or ROHC feedback information) corresponding to the DL data. In addition, even when the first condition is satisfied, the UE may continuously receive DL data from the source BS or the target BS.

[0202] When Figure 1H When the second condition is satisfied in the fourth operation 1h-04 in Embodiment 2 of the effective handover method, the UE 1h-20 may stop receiving DL data from the source BS 1h-05 via the protocol layer 1h-22 of the first bearer, or may release the connection with the source BS 1h-05. The second condition may be one of the following conditions. In addition, the PDCP layer 1h-21 of the second bearer may continuously perform data transmission or reception to or from the target BS without interruption by using the data to be sent or received, SN information, or header compression and decompression context stored in the PDCP layer 1h-22 of the first bearer.

[0203] When the UE 1h-20 performs a random access procedure to the target BS via the layer 1h-21 of the second bearer and receives a RAR message, it may be determined that the second condition is satisfied.

[0204] When the UE 1h-20 performs a random access procedure on the target BS via the layer 1h-21 of the second bearer, receives the RAR message, configures the handover completion message and sends it to the target BS, it can be determined that the second condition is satisfied.

[0205] When the UE 1h-20 performs a random access procedure on the target BS via the layer 1h-21 of the second bearer, and for the first time sends data by using the PUCCH or PUCCH UL transmission resource, or receives the PUCCH or PUCCH UL transmission resource for the first time, it can be determined that the second condition is satisfied.

[0206] When the BS configures an independent timer for the UE by using the RRC message and the independent timer expires, it can be determined that the second condition is satisfied. When the UE receives the handover command message from the source BS, the UE starts the random access to the target BS (sends the preamble), the UE receives the RAR message from the target BS, the UE sends the handover completion message to the target BS, or the UE first sends data by using the PUCCH or PUCCH UL transmission resource, a separate timer can be started.

[0207] When the UE performs a random access procedure on the target BS via the protocol layer of the second bearer, receives the RAR message, configures and sends the handover completion message to the target BS, and then receives an acknowledgement of the successful transmission of the handover completion message via the MAC layer (HARQ ACK) or the RLC layer (RLC ACK), it can be determined that the second condition is satisfied.

[0208] When the UE performs a random access procedure on the target BS via the protocol layer of the second bearer, receives the RAR message, or configures and sends the handover completion message to the target BS, and then receives the allocation of the UL transmission resource from the target BS for the first time, or receives the indication of the UL transmission resource for the first time, it can be determined that the second condition is satisfied.

[0209] When the source BS performs an effective handover provided in the present disclosure, the source BS can determine when to stop sending the DL data to the UE or when to release the connection with the UE. For example, when a specific timer expires (the timer can start after indicating the handover) or the source BS receives an indication from the target BS indicating that the UE has successfully performed the handover to the target BS, the source BS can determine whether to stop sending the DL data or when to release the connection with the UE. When the UE does not receive the DL data from the source BS within a specific time period, the UE can determine that the second condition is satisfied, and can determine that the connection with the source BS is released, so the connection can be released.

[0210] When the UE receives an indication (e.g., an RRC message (e.g., an RRCReconfiguration message)) from the target BS indicating to release the connection with the source BS, or receives a MAC CE, an RLC control PDU, or a PDCP control PDU from the target BS, the UE may determine that the second condition is satisfied.

[0211] When the UE receives an indication (e.g., an RRC message (e.g., an RRCReconfiguration message)) from the source BS indicating to release the connection with the source BS, or receives a MAC CE, an RLC control PDU, or a PDCP control PDU from the target BS, the UE may determine that the second condition is satisfied.

[0212] When the UE does not receive DL data from the source BS within a specific time period, the UE may determine that the second condition is satisfied.

[0213] When the UE successfully completes the random access procedure to the target BS via the layer of the second bearer (e.g., the MAC layer), the UE successfully completes the random access procedure to the target BS via the layer of the second bearer, then receives the allocation of the first UL transmission resource from the target BS, or when the UE receives an indication of the UL transmission resource for the first time, the UE may determine that the second condition is satisfied.

[0214] For example, in the case where the UE receives a handover command message from the source BS and receives an indication of random access to the target BS, when the indicated random access is CFRA (e.g., when a predefined preamble or a UE cell identifier (e.g., C-RNTI) is allocated), it can be determined that when the UE sends a predefined preamble to the cell of the target BS and receives an RAR message, the random access procedure is successfully completed. Therefore, when the UE receives the first UL transmission resource allocated, included, or indicated in the RAR message, it can be determined that the first condition is satisfied. As another method, when the UE receives the UL transmission resource for the first time after receiving the RAR message, it can be determined that the second condition is satisfied.

[0215] In the case where the UE receives a handover command message from the source BS and receives an indication of random access to the target BS, when the indicated random access is CBRA (for example, when no predefined preamble or UE cell identifier (e.g., C-RNTI) is allocated), it can be determined that when the UE sends a preamble (e.g., a random preamble) to the cell of the target BS and receives a RAR message, sends message 3 (e.g., a handover completion message) to the target BS by using the UL transmission resource allocated (or included or indicated) in the RAR message, and receives a contention resolution MAC CE indicating contention resolution from the target BS via message 4, or receives the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the random access procedure to the target BS has been successfully completed. Therefore, when the UE monitors the PDCCH and first receives or is first indicated the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the second condition is satisfied.

[0216] As another method, when the size of the UL transmission resource allocated in the RAR message is large enough and thus the UE can send message 3 and additionally send UL data, the UE can determine that the UE has first received the UL transmission resource, and thus can determine that the second condition is satisfied. That is, when the UE receives the RAR message, the UE can determine that the UE has first received the UL transmission resource, and thus can determine that the second condition is satisfied.

[0217] When a handover method that does not request a random access procedure (RACH-less handover) is also indicated in the handover command message received by the UE, it can be determined that the second condition is satisfied in the following cases.

[0218] When the handover command message includes the UL transmission resource for the target BS, the UE sends message 3 (e.g., a handover completion message or an RRCReconfigurationComplete message) by using the UL transmission resource for the target BS, and when the UE receives the UE identity confirmation MAC CE from the BS via message 4 or receives the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the random access procedure has been successfully completed and the second condition is satisfied. As another method, after the random access procedure has been successfully completed, the UE performs PDCCH monitoring and receives the first UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the second condition is satisfied.

[0219] When the handover command message does not include the UL transmission resource for the target BS, the UE performs PDCCH monitoring for the target BS (or cell). When the UE receives the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, or sends Message 3 (e.g., handover complete message or RRCReconfigurationComplete message) by using the UL transmission resource, receives the UE identity confirmation MAC CE from the BS, or receives the UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the random access procedure is successfully completed and the second condition is satisfied. As another method, after the random access procedure is successfully completed, if the UE performs PDCCH monitoring and receives the first UL transmission resource via the PDCCH corresponding to the UE's C-RNTI, it can be determined that the second condition is satisfied.

[0220] In the case of Embodiment 2 in which the UE executes the effective handover method provided in the present disclosure (e.g., DAPS handover method), when it is recognized that the RRC layer, MAC layer, and RLC layer of the first bearer of the UE for the source BS and the RRC layer, MAC layer, and RLC layer of the second bearer of the UE for the target BS satisfy the second condition provided in the present disclosure, an indicator indicating that the second condition is satisfied can be indicated to the UE or the PDCP layer of the bearer that executes the DAPS handover method. When the PDCP layer of the UE receives an indicator indicating that the second condition is satisfied from the lower layer or the upper layer, the UE can perform one or more of the following processes to perform the operations of Embodiment 2 of the effective handover method provided in the present disclosure.

[0221] The UE can release the first bearer for the source BS and can release the connection with the source BS. Then, before the UE releases the first bearer for the source BS, the UE can perform an RLC re-establishment process for the RLC layer corresponding to the first bearer for the source BS. For example, when the recalibration timer is running, the UE can stop or reconfigure the timer, and when the received data is stored in the buffer, the UE can process the stored data and provide it to the upper layer. When there is data to be sent in the buffer, the UE can discard the data or can initialize the MAC layer.

[0222] When the UE releases the connection with the source BS, in order to report the reception status of multiple DL data received from the source BS to the target BS, the UE can trigger a PDCP status report process, can configure the PDCP status report, and can send the PDCP status report to the target BS.

[0223] When the second condition is satisfied, the UE can use the second PDCP layer architecture or function 1i-20 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method (see Figure 1I)Switch to the first PDCP layer architecture or functions 1i-11 or 1i-12 (see Figure 1I ). The UE may initialize variables for recalibration, may stop and reconfigure the recalibration timer, may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to a plurality of data items stored in a buffer for reordering (e.g., a plurality of data items received from the source BS), and may discard the security key or header decompression context of the source BS. The UE may provide a plurality of processed data items to the upper layer in ascending order. That is, when the second condition is satisfied, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to a plurality of data items stored in a buffer for reordering (e.g., a plurality of data items received from the source BS), and may discard the security key or header decompression context of the source BS.

[0224] As another method, when the second condition is satisfied, the UE may switch the second PDCP layer architecture or function 1i-20 provided in the present disclosure to the third PDCP layer architecture or function 1i-30 for each bearer or for a bearer indicating the DAPS handover method (see Figure 1I ). In addition, instead of stopping and initializing, the UE may continuously use the variables for recalibration and the recalibration timer. However, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to a plurality of data items stored in a buffer for reordering (e.g., a plurality of data items received from the source BS), and may discard the security key or header decompression context of the source BS. In addition, the UE may provide a plurality of processed data items to the upper layer in ascending order. That is, when the second condition is satisfied, the UE may perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to a plurality of data items stored in a buffer for reordering (e.g., a plurality of data items received from the source BS), and may discard the security key or header decompression context of the source BS. The UE may release the QoS mapping information of the SDAP layer, the security key information of the PDCP layer of the source BS, the header (or data) compression context information of the source BS, or the header (or data) compression context information of the RLC layer or MAC layer of the source BS.

[0225] When the second condition provided in the present disclosure is satisfied when the UE executes the DAPS handover method, the UE may release the second SDAP layer architecture and function 1j-20 for the first bearer of the source BS, and the second SDAP layer architecture and function 1j-20 has been applied to each bearer or the bearer indicating the DAPS handover method, and may switch the second SDAP layer architecture and function 1j-20 to the first SDAP layer architecture or function 1j-10, and apply the first SDAP layer architecture or function 1j-10. In addition, when the second condition is satisfied, the UE may switch the second SDAP layer architecture and function 1j-20 to the first SDAP layer architecture or function 1j-10 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method. Here, the second bearer of the target BS or the second QoS flow and bearer mapping information may be maintained. In addition, before the UE releases the first bearer or the first QoS flow and bearer mapping information of the source BS, the UE may complete data processing by applying the first QoS flow and bearer mapping information to a plurality of data items received from the source BS (e.g., all data received from the source BS), and then may release the first QoS flow and bearer mapping information or the first bearer. In addition, the UE may provide the plurality of processed data items to the upper layer in ascending order.

[0226] That is, when the second condition is satisfied, the UE may process data by applying the first QoS flow and bearer mapping information of the source BS to a plurality of data items stored in the buffer (e.g., a plurality of data items received from the source BS). For example, based on the first QoS flow and bearer mapping information, the UE may perform a process of reading SDAP header information and updating mapping information or configuring the SDAP header, or routing or providing the processed information to an appropriate upper layer or lower layer. After that, the UE may discard the first QoS flow and bearer mapping information of the source BS.

[0227] The SDAP layer may define and apply a 1-bit indicator of a new SDAP header, a 1-bit indicator of a new PDCP header, SDAP control data (e.g., a DL end marker), or information indicated by the PDCP layer, and may identify which data is the data recently received from the source BS (or the last received data) based on this information. Therefore, the SDAP layer may perform data processing on the data that is recently received from the source BS by applying the first QoS flow and bearer mapping information of the source BS, and then may discard the first QoS flow and bearer mapping information of the source BS. In addition, the SDAP layer may continuously maintain the second QoS flow and bearer mapping information, and may process UL data or DL data for the target BS based on the second QoS flow and bearer mapping information.

[0228] When the present disclosure's Figure 1FWhen the source gNB 1f-02 sends a handover command message to the UE 1f-01 (operation 1f-20), the source gNB 1f-02 may define an indicator related to the embodiments of the present disclosure in the handover command message (e.g., RRCReconfiguration message), and may indicate to the UE 1f-01 which handover process corresponding to which embodiment will be triggered. The UE 1f-01 may perform the handover process according to the handover method indicated in the handover command message. For example, by executing Embodiment 2 (DAPS handover method) of the effective handover method provided in the present disclosure, the UE 1f-01 may perform the handover to the target gNB 1f-03 in a manner that minimizes the data interruption time of the UE 1f-01.

[0229] As another method, the source gNB 1f-02 may define an indicator for each bearer in the handover command message, which is related to the embodiments of the present disclosure, and may further specifically indicate which embodiment will be applied to which bearer in the handover. For example, the source gNB 1f-02 may indicate via the handover command message that Embodiment 2 of the present disclosure is only applied to the AM bearer for which the RLC layer operating in the AM mode is active, or Embodiment 2 may be widely applied to the UM bearer for which the RLC layer operating in the UM mode is active.

[0230] Assume that the embodiments of the present disclosure are applied to the DRB. However, when needed (e.g., in the case where the UE fails to perform the handover but the UE retains the SRB for the source BS, and thus the UE can report the handover failure or can recover via the SRB for the source BS), the embodiments of the present disclosure may be applied to the SRB.

[0231] In the embodiments of the present disclosure, when the UE performs data transmission and reception to and from the source BS via the protocol layer of the first bearer, and performs data transmission and reception to and from the target BS via the protocol layer of the second bearer, the MAC layer of the first bearer and the MAC layer of the second bearer may each operate a discontinuous reception (DRX) cycle, thereby reducing the battery consumption in the UE. That is, even after the UE receives the handover command message, the UE may continue to apply the DRX cycle of the MAC layer applied when transmitting and receiving data via the protocol layer of the first bearer, and may interrupt the DRX cycle according to the first condition or the second condition. In addition, in response to an indication from the target BS, the UE may manage whether to apply the DRX cycle to the MAC layer of the second bearer alone.

[0232] In the present disclosure, the meaning that the UE stops UL transmission to the source BS via the protocol layer of the first bearer and stops receiving DL data from the source BS may refer to the UE re-establishing, initializing, or releasing the protocol layer (PHY layer, MAC layer, RLC layer, or PDCP layer) of the first bearer.

[0233] In an embodiment of the present disclosure, for ease of description, it is described that the UE configures a first bearer for the source BS or a second bearer for the target BS, and the embodiments of the present disclosure can be easily extended and equally applied to the case where the UE configures multiple first bearers for the source BS or multiple second bearers for the target BS. In addition, the embodiments of the present disclosure can be extended and equally applied to the case of configuring multiple bearers for multiple target BSs. For example, the UE can configure a second bearer while performing a handover procedure for a first target BS, and when the handover fails, the UE can configure a second bearer while performing a handover procedure for a second target BS, so that the UE can autonomously detect and determine a cell that meets a specific condition (for example, a signal with an intensity equal to or greater than a specific value) from multiple cells, can select a cell, and then can perform a handover procedure on that cell.

[0234] Figure 1I The architecture of an effective PDCP layer to be applied to the DAPS handover method as an embodiment 2 of an effective handover method according to an embodiment of the present disclosure, and a method of applying this architecture are shown.

[0235] In Figure 1I this, the present disclosure proposes a specific architecture and function to be applied to the effective PDCP layer of the DAPS handover method, which is embodiment 2 of the effective handover method provided in the present disclosure, and the architecture of the PDCP layer provided below is characterized in that different PDCP layer architectures can be applied to each bearer at different time points when performing the DAPS handover procedure.

[0236] For example, before the UE receives a handover command message from the BS, the UE can process and send or receive data by applying the first PDCP layer architecture and functions 1i-11 or 1i-12 provided in the present disclosure to each bearer (operation 1i-01).

[0237] However, when the UE receives a handover command message from the BS and the DAPS handover method provided in the present disclosure is indicated in the handover command message or the DAPS handover method is indicated for a specific bearer, the UE can process and send or receive data by applying the second PDCP layer architecture and functions 1i-20 provided in the present disclosure for each bearer or for the bearer for which the DAPS handover method is indicated (operation 1i-02).

[0238] That is, when the UE receives a handover command message from the BS and the DAPS handover method provided in the present disclosure is indicated in the handover command message or the DAPS handover method is indicated for a specific bearer, the UE may switch the first PDCP layer architecture or function 1i-11 or 1i-12 for each bearer to the second PDCP layer architecture or function 1i-20 provided in the present disclosure for each bearer or for the bearer for which the DAPS handover method is indicated.

[0239] As another method, when the first condition provided in the present disclosure is satisfied, the UE may switch the first PDCP layer architecture or function 1i-11 or 1i-12 for each bearer to the second PDCP layer architecture or function 1i-20 provided in the present disclosure for each bearer or for the bearer for which the DAPS handover method is indicated (operation 1i-02).

[0240] In addition, in the case where the UE receives a handover command message from the BS and the DAPS handover method provided in the present disclosure is indicated in the handover command message, when the DAPS handover method is indicated for a specific bearer or a PDCP recalibration timer value is newly set, when the UE switches the first PDCP layer architecture or function 1i-11 or 1i-12 to the second PDCP layer architecture or function 1i-20 provided in the present disclosure for each bearer or for the bearer for which the DAPS handover method is indicated, the UE may update the variable for recalibration to the PDCP SN or COUNT value that is predicted to be received next, and may stop and restart the recalibration timer.

[0241] When the second condition provided in the present disclosure is satisfied and when the UE executes the DAPS handover method provided in the present disclosure, the UE may release the second PDCP layer architecture and function 1i-20 applied to each bearer or the bearer indicating the DAPS handover method from the first bearer of the source BS, and may switch back to the first PDCP layer architecture and function 1i-11 or 1i-12, and may apply the first PDCP layer architecture and function 1i-11 or 1i-12 to each bearer. When the second condition is satisfied and the UE switches the second PDCP layer architecture or function 1i-20 to the first PDCP layer architecture or function 1i-11 or 1i-12 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method, the UE may initialize the variable for recalibration, and may stop and reconfigure the recalibration timer. In addition, the UE may perform the decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to a plurality of data items stored in the buffer for reordering (e.g., a plurality of data items received from the source BS), and may discard the security key or header decompression context of the source BS. In addition, the UE may provide the plurality of processed data items to the upper layer in ascending order. That is, when the second condition is satisfied, the UE may perform the decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to a plurality of data items stored in the buffer for reordering (e.g., a plurality of data items received from the source BS), and may discard the security key or header decompression context of the source BS.

[0242] As another method, when the second condition provided in the present disclosure is satisfied and when the UE executes the DAPS handover method provided in the present disclosure, the UE may release the second PDCP layer architecture and function 1i-20 applied to each bearer or the bearer indicating the DAPS handover method from the bearer of the source BS, and may switch to the third PDCP layer architecture or function 1i-30, and may apply the third PDCP layer architecture or function 1i-30 to each bearer. When the second condition is satisfied and thus the UE switches the second PDCP layer architecture or function 1i-20 to the third PDCP layer architecture or function 1i-30 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method, the UE may not stop or initialize, but may continuously use the variable for recalibration and the recalibration timer.

[0243] However, the UE can perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to multiple data items stored in a buffer for reordering (e.g., multiple data items received from the source BS), and can discard the security key or header decompression context of the source BS. In addition, the UE can provide multiple processed data items to the upper layer in ascending order. That is, when the second condition is satisfied, the UE can perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source BS to multiple data items stored in a buffer for reordering (e.g., multiple data items received from the source BS), and can discard the security key or header decompression context of the source BS.

[0244] As provided in the Figure 1I present disclosure, the UE can apply different first PDCP layer architectures or functions 1i-11 or 1i-12, second PDCP layer architectures or functions 1i-20, or third PDCP layer architectures or functions 1i-30 to each bearer at different time points, so as to prevent data loss and minimize data interruption time when performing a handover.

[0245] Figure 1I The first PDCP layer architectures 1i-11 or 1i-12 provided in the present disclosure can have the 1-1 PDCP layer architecture, 1-2 PDCP layer architecture, 1-3 PDCP layer architecture, or 1-4 PDCP layer architecture provided in the present disclosure, and can have the features to be described below.

[0246] First, when the first PDCP layer architecture 1i-11 corresponds to the 1-1 PDCP layer architecture, the first PDCP layer architecture 1i-11 can have the following features.

[0247] 1> (When it is the 1-1 PDCP layer architecture) For example, when the UE applies the first PDCP layer architecture and function 1i-11 to the PDCP layer (e.g., E-UTRA PDCP layer or LTE PDCP layer) connected to the AM RLC layer (e.g., E-UTRA AM RLC layer), the PDCP layer can have the following features.

[0248] 2> The PDCP layer can first detect out-of-window data or duplicate data for multiple received data items. (Retransmissions may occur in RLC AM, and the sizes of LTE RLC SN and PDCP SN may be different, so duplicate data or out-of-window data may be received. Above, the window indicates the range of PDCP SN or COUNT values for which valid data has been received.)

[0249] 3>Before discarding data outside the PDCP discard window or duplicate data, the PDCP layer performs the decryption process and the header decompression process, and then performs the discard operation. (Since the data may include useful information for the header decompression process (e.g., initialization and refresh (IR) packets or header compression information), the PDCP layer can check and then discard the data.)

[0250] 2>The PDCP layer can decrypt multiple data items immediately without sorting. The data is received without being discarded, and the header decompression process can be performed. This is because the E-UTRA AM RLC layer performs sorting on multiple data items and provides the multiple data items to the PDCP layer.

[0251] 2>Then, the PDCP layer provides multiple data items to the upper layer in ascending order of the COUNT value.

[0252] Next, when the first PDCP layer architecture 1i-11 corresponds to the 1-2 PDCP layer architecture, the first PDCP layer architecture 1i-11 can have the following characteristics.

[0253] 1>(When it is the 1-2 PDCP layer architecture) For example, when the UE applies the first PDCP layer architecture and function 1i-11 to the PDCP layer (e.g., E-UTRA PDCP layer or LTE PDCP layer) connected to the UM RLC layer (e.g., E-UTRA UM RLC layer), the PDCP layer can have the following characteristics.

[0254] 2>The PDCP layer may not perform the process of detecting data outside the window or duplicate data. This is because the UM E-UTRARLC layer does not perform the retransmission process.

[0255] 2>Then, the PDCP layer can immediately perform the decryption process on multiple received data items, and then perform the header decompression process.

[0256] 2>Then, the PDCP layer can perform the reordering process and can provide multiple data items to the upper layer (e.g., in ascending order).

[0257] Next, when the first PDCP layer architecture 1i-11 corresponds to the 1-3 PDCP layer architecture, the first PDCP layer architecture 1i-11 can have the following characteristics.

[0258] 1> (When it is a 1-3 PDCP layer architecture) For example, when the UE applies the first PDCP layer architecture 1i-11 to the PDCP layer (e.g., the E-UTRA PDCP layer or the LTE PDCP layer) configured with a split bearer, a packet duplication bearer, or an LTE WLAN Aggregation (LWA) bearer, the reordering process and the re-calibration timer can always be applied, and the PDCP layer can have the following characteristics.

[0259] 2>The PDCP layer can first detect out-of-window data or duplicate data for multiple received data items. (Retransmissions may occur at the RLC AM, data may be received from different RLC layers at different time points, and the sizes of the LTE RLC SN and PDCP SN may be different, resulting in the possible reception of out-of-window data or duplicate data.)

[0260] 3>The PDCP layer performs the decryption process. However, the PDCP layer may not perform the header decompression process. (This is because the E-UTRA PDCP layer cannot configure a header compression protocol for a split bearer or an LWA bearer.

[0261] 3>When the integrity protection or verification process has been performed, the PDCP layer can perform the integrity protection verification process and then can discard the data. When the integrity verification process fails, the PDCP layer can discard the data and can report the failure to the upper layer.

[0262] 3>The PDCP layer discards out-of-window data or duplicate data.

[0263] 2>When the data is not discarded, the PDCP layer can immediately perform the decryption process without reordering the multiple received data items. After that, when the integrity protection or verification process is configured, the PDCP layer can perform the integrity verification. When the integrity protection or verification process is performed, the PDCP layer can perform the integrity protection or verification process and then can discard the data. When the integrity verification process fails, the PDCP layer can discard the data and can report the failure to the upper layer.

[0264] 2>After that, the PDCP layer can reorder the multiple received data items, and when the PDCP SN or COUNT value is arranged in ascending order without gaps in between, the PDCP layer can perform the header compression process (when the header compression process or the header decompression process is configured) and can provide the data to the upper layer in ascending order.

[0265] 2>In the case where the re-calibration timer is running,

[0266] 3> When data is provided to the upper layer, the data corresponding to the COUNT value has the same value as the value obtained by subtracting 1 from the value held by the variable for recalibration, or when multiple data items are all provided to the upper layer without gaps between PDCP SNs (COUNT values),

[0267] 4> The PDCP layer stops and reconfigures the recalibration timer.

[0268] 2> In the case where the recalibration timer is not running,

[0269] 3> When the buffer stores data that has not been provided to the upper layer, or when there are gaps between PDCP SNs (COUNT values),

[0270] 4> The PDCP layer starts the recalibration timer.

[0271] 4> Then, the PDCP layer updates the variable for recalibration to the PDCP SN or COUNT value expected to be received next.

[0272] 2> In the case where the recalibration timer expires,

[0273] 3> When the header decompression process is configured for multiple stored data item values that are less than the variable for recalibration, the PDCP layer performs the header decompression process and provides the data to the upper layer in ascending order of PDCP SN or COUNT value.

[0274] 3> When the header decompression process is configured for multiple stored data item values (equal to or greater than the variable for recalibration), the PDCP layer performs the header decompression process and provides the data to the upper layer in ascending order of PDCP SN or COUNT value.

[0275] 3> Then, the PDCP layer updates the variable value of the most recently provided data to the PDCP SN or COUNT value of the most recently provided data to the upper layer.

[0276] 3> When the buffer stores data that has not been provided to the upper layer, or when there are gaps between PDCP SNs (COUNT values),

[0277] 4> The PDCP layer starts the recalibration timer.

[0278] 4> Then, the PDCP layer updates the variable for recalibration to the PDCP SN or COUNT value expected to be received next.

[0279] First, when the first PDCP layer architecture 1i - 11 corresponds to the 1 - 4 PDCP layer architectures, the first PDCP layer architecture 1i - 11 can have the following characteristics.

[0280] 1> (When it is a 1-4 PDCP layer architecture) For example, when the UE applies the first PDCP layer architecture and functions 1i-11 to the PDCP layer (such as the E-UTRA PDCP layer or LTE PDCP layer) connected to the AM RLC layer (such as the E-UTRA AM RLC layer), the PDCP layer may have the following characteristics.

[0281] 2>The PDCP layer may first perform a decryption process on multiple received data items.

[0282] 2>When integrity protection or verification process is configured, the PDCP layer may perform integrity protection or verification process on the received data, and when the integrity verification process fails, the PDCP layer may discard the data and may report the failure to the upper layer.

[0283] 2>The PDCP layer performs detection of out-of-window data or duplicate data on the received data. (The feature of the present disclosure is that the decryption process is first performed, and then the detection of out-of-window data or duplicate data is performed. As another method, the decryption process may be performed only when integrity protection or verification process is configured. In the case where the detection of out-of-window data or duplicate data is performed but integrity protection or verification process is not configured, the decryption process may be performed only on multiple data items on which the detection of out-of-window data or duplicate data is performed and which are not discarded.)

[0284] 3>The PDCP layer discards out-of-window data or duplicate data.

[0285] 2>When the data is not discarded, the PDCP layer may perform reordering on multiple received data items, and when the PDCP SN or COUNT values are arranged in ascending order without gaps therebetween, the PDCP layer may perform a header compression process (when a header compression process or a header decompression process is configured), and may provide the data to the upper layer in ascending order.

[0286] 2>When the PDCP layer provides data to the upper layer, the PDCP layer provides the data in ascending order of the COUNT value.

[0287] 2>In the case where the recalibration timer is running,

[0288] 3>When the data is provided to the upper layer, when all multiple data items are provided to the upper layer without gaps between the PDCP SN (COUNT values), or when the value of the variable storing the PDCP SN or the COUNT value of the data to be provided to the upper layer is equal to or greater than the value of the variable for recalibration, the data corresponding to the COUNT value has the same value as the value obtained by subtracting 1 from the value of the variable for recalibration.

[0289] 4>The PDCP layer stops and reconfigures the recalibration timer.

[0290] 2>In the case where the recalibration timer is not running,

[0291] 3>When the buffer stores data not provided to the upper layer, when there is a gap between PDCP SNs (COUNT values), or when the value of the variable storing the COUNT value of the first data not provided to the upper layer is less than the value of the variable used for recalibration,

[0292] 4>The PDCP layer updates the variable used for recalibration to the PDCP SN or COUNT value expected to be received next.

[0293] 4>The PDCP layer starts the recalibration timer.

[0294] 2>In the case where the recalibration timer expires,

[0295] 3>When the header decompression process is configured for multiple stored data items whose values are less than the variable used for recalibration, the PDCP layer performs the header decompression process in ascending order of PDCP SN or COUNT value and provides the data to the upper layer.

[0296] 3>When the header decompression process is configured for multiple stored data items whose values are equal to or greater than the variable used for recalibration, the PDCP layer performs the header decompression process in ascending order of PDCP SN or COUNT value and provides the data to the upper layer.

[0297] 3>Then, the PDCP layer updates the variable value of the first data not provided to the upper layer to the PDCP SN or COUNT value of the first data not provided to the upper layer.

[0298] 3>When the buffer stores data not provided to the upper layer, or when there is a gap between PDCP SNs (COUNT values), or when the value of the variable storing the COUNT value of the first data not provided to the upper layer is less than the value of the variable used for recalibration,

[0299] 4>The PDCP layer updates the variable used for recalibration to the PDCP SN or COUNT value expected to be received next.

[0300] 4>The PDCP layer starts the recalibration timer.

[0301] Figure 1I The second PDCP layer architecture or functionality 1i - 20 provided in can have the 2 - 1 PDCP layer architecture or 2 - 2 PDCP layer architecture provided in this disclosure and can have the features to be described below.

[0302] In the present disclosure, a second PDCP layer architecture 1i-20 effective in handover is provided. The second PDCP layer architecture can be applied to Embodiment 2 of an effective handover method for minimizing data interruption time provided in the present disclosure.

[0303] In the second PDCP layer architecture, the UE can perform data transmission or reception from or to the source BS 1i-21 via the protocol layer of the first bearer (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer), and can perform data transmission or reception from or to the target BS 1i-22 via the protocol layer of the second bearer (e.g., SDAP layer, PDCP layer, RLC layer, or MAC layer).

[0304] The PDCP layer of the first bearer and the PDCP layer of the second bearer can each be configured in the UE, but can operate logically as one PDCP layer, as shown in 1i-20. Specifically, by differentiating the functions of the PDCP layer, one PDCP layer can be implemented as the functions of an upper PDCP layer (e.g., SN allocation function, reordering (recalibration) function, in-sequence delivery function, or duplicate detection function) and the functions of two lower PDCP layers for the source BS and the target BS, respectively (e.g., decryption or encryption function, header (or data) compression or decompression function, integrity protection or verification function, or duplicate detection function). In addition, as described above, when performing the DAPS handover method, the UE can send UL data transmission to the source BS, and when a first condition is satisfied, the UE can hand over to the target BS, and can continuously receive DL data from the source BS and the target BS. Therefore, only one header (or data) compression protocol context of the source BS or the target BS can be maintained and applied to UL, while two contexts of the source BS or the target BS can be maintained and applied to DL.

[0305] The 2-1 PDCP layer architecture (e.g., the E-UTRA PDCP layer for the DAPS handover method) provided in the present disclosure can have the following characteristics.

[0306] The upper transmit PDCP layer function can be used to assign PDCP SNs to multiple data items received from the upper layer. Two lower transmit PDCP layer functions 1i-21 and 1i-22, respectively for the source BS and the target BS, can apply the header (or data) compression context or security key configured by the source BS to the data to be sent to the source BS, and apply the header (or data) compression context or security key configured by the target BS to the data to be sent to the target BS, by using separate security keys configured in each of the source BS and the target BS, and when the header (or data) compression process is configured, the header (or data) compression process can be applied. In addition, when integrity protection is configured, the lower transmit PDCP layer functions 1i-21 and 1i-22 can apply the encryption process by applying the integrity protection process to the PDCP header and data (PDCP SDU), can provide the data to be sent to the source BS to the transmit RLC layer of the first bearer, and can provide the data to be sent to the target BS to the transmit RLC layer of the second bearer, so as to perform transmission.

[0307] To accelerate the data processing speed, the two lower transmit PDCP layer functions 1i-21 and 1i-22 can process the header compression, integrity protection, and encryption processes in parallel. In addition, the two lower transmit PDCP layer functions 1i-21 and 1i-22 can perform the integrity protection or encryption process by using different security keys. In addition, the two lower transmit PDCP layer functions 1i-21 and 1i-22 can perform the compression, integrity protection, or encryption process on multiple different data items by applying different compression contexts, different security keys, or different security algorithms in a logically single transmit PDCP layer.

[0308] The receive PDCP layer functions (i.e., the lower receive PDCP layer functions 1i-21 and 1i-22 of the source BS or the target BS) can each independently perform out-of-window data detection or duplicate detection processes on multiple data items received from each lower layer, particularly on multiple data items received from the two RLC layers of the source BS and the target BS, based on the PDCP SN or COUNT value. As another method, for ease of implementation, the receive PDCP layer functions can perform the out-of-window data detection or duplicate detection process on all received data based on the PDCP SN or COUNT value without distinguishing the RLC layers.

[0309] As another method, for more precise duplicate detection, the receiving PDCP layer function can perform out-of-window data detection based on the PDCP SN or COUNT values on all received data without distinguishing the RLC layer, and can perform the duplicate detection process separately on multiple data items received from each RLC layer. As another method, when multiple data items received from different BSs overlap with each other, to prevent data loss of the header compression protocol, the receiving PDCP layer function can perform out-of-window data detection on all received data based on the PDCP SN or COUNT values without distinguishing the RLC layer, and for multiple data items received from each RLC layer, perform the duplicate detection process on all data received after the decryption process, integrity protection process, or header (or data) decompression process.

[0310] When it is configured to immediately apply the decryption process and integrity protection to multiple received data items, which are performed by using a separate header (or data) compression context or security key configured separately from the source BS and the target BS, the sub-function of the receiving PDCP layer can apply the integrity protection process to the PDCP header and data (PDCP SDU).

[0311] In the 2-1 PDCP layer architecture, the header (or data) decompression process can be immediately performed on multiple data items received from the RLC layer of the first bearer of the source BS without reordering, and the header (or data) decompression process can be immediately performed on multiple data items received from the RLC layer of the second bearer of the target BS without reordering. In addition, to distinguish the data received from the RLC layer of the first bearer of the source BS from the data received from the RLC layer of the second bearer of the target BS, an indicator is defined for each data so that it can be identified whether the PDCP layer receives data from the source BS or from the target BS. As another method, a 1-bit indicator is defined in the PDCP header, SDAP header, or RLC header so that it can be identified whether the PDCP layer receives data from the source BS or from the target BS.

[0312] In addition, the PDCP layer may perform a duplicate detection process on all the multiple data items received from the RLC layer of the first bearer of the source BS and the multiple data items received from the RLC layer of the second bearer of the target BS based on the PDCP SN or COUNT value (in this process, only one data (including pre-received data or data provided to the upper layer) is assigned to each PDCP SN or each COUNT value, and other data is discarded), where the header (or data) compression process for the multiple data items has been completed. Then, the PDCP layer may perform a recalibration process on all the multiple data items received from the RLC layer of the first bearer of the source BS and the multiple data items received from the RLC layer of the second bearer of the target BS in ascending order based on the PDCP SN or COUNT value, and may provide the multiple data items to the upper layer sequentially. Since the PDCP layer may receive data from different BSs (i.e., from the first bearer or the second bearer) in an unordered manner, the PDCP layer may always have to perform the recalibration process.

[0313] To accelerate the data processing speed, the two downlink PDCP layer functions 1i-21 and 1i-22 may perform the header compression, integrity protection, and encryption processes in parallel based on each PDCP SN or each COUNT value. In addition, the two downlink PDCP layer functions 1i-21 and 1i-22 may perform the integrity protection, encryption process, or header decompression process by using different header (or data) compression contexts or different security keys. In addition, the two downlink PDCP layer functions 1i-21 and 1i-22 may perform the integrity protection, encryption process, or decompression process on multiple different data items by applying different header (or data) compression contexts, different security keys, or different security algorithms in a logically single transmit PDCP layer. In addition, the two downlink PDCP layer functions 1i-21 and 1i-22 may perform the unordered decryption or integrity verification process on each of the received multiple data items, regardless of the order of the PDCP SN or COUNT value.

[0314] When the PDCP layer differentiates between the layer of the first bearer and the layer of the second bearer, considering that the layer of the first bearer and the layer of the second bearer are connected to different MAC layers, have different logical channel identifiers, the layer of the first bearer and the layer of the second bearer are different RLC layers connected to different MAC layers, or use different encryption keys, the PDCP layer may differentiate between the layer of the first bearer (or the first RLC layer) and the layer of the second bearer (or the second RLC layer). By doing so, the encryption process or decryption process may be performed on the UL data and DL data by using different security keys, and the UL data and DL data may be compressed or decompressed by using different compression protocol contexts.

[0315] Based on the second PDCP layer architecture, the 2-2 PDCP layer architecture provided in the present disclosure (e.g., the NR PDCP layer for the DAPS handover method) may have the following characteristics.

[0316] The upper transmit PDCP layer function can be used to assign PDCP SNs to multiple data items received from the upper layer. Two lower transmit PDCP layer functions 1i-21 and 1i-22 for the source BS and the target BS respectively can apply the header (or data) compression context or security key configured by the source BS and the target BS to the data to be sent to the source BS and the data to be sent to the target BS by using separate security keys configured in each of the source BS and the target BS, and when the header (or data) compression process is configured, the header (or data) compression process can be applied. In addition, when integrity protection is configured, the lower transmit PDCP layer functions 1i-21 and 1i-22 can apply the encryption process by applying the integrity protection process to the PDCP header and data (PDCP SDU), can provide the data to be sent to the source BS to the transmit RLC layer of the first bearer, and can provide the data to be sent to the target BS to the transmit RLC layer of the second bearer, so as to perform transmission.

[0317] To accelerate the data processing speed, the two lower transmit PDCP layer functions 1i-21 and 1i-22 can process the header compression, integrity protection, and encryption processes in parallel. In addition, the two lower transmit PDCP layer functions 1i-21 and 1i-22 can perform the integrity protection or encryption process by using different security keys. In addition, the two lower transmit PDCP layer functions 1i-21 and 1i-22 can perform the compression, integrity protection, or encryption process on multiple different data items by applying different compression contexts, different security keys, or different security algorithms in a logically single transmit PDCP layer.

[0318] The receive PDCP layer function (i.e., the lower receive PDCP layer functions 1i-21 and 1i-22 for the source BS or the target BS) can independently perform out-of-window data detection or duplicate data detection processes on multiple data items received from each lower layer, especially on multiple data items received from the two RLC layers of the source BS and the target BS, based on the PDCP SN or COUNT value. As another method, for ease of implementation, the receive PDCP layer function can perform out-of-window data detection or duplicate detection processes on all received data based on the PDCP SN or COUNT value without distinguishing the RLC layers.

[0319] As another method, for more precise duplicate detection, the receiving PDCP layer function may perform out-of-window data detection on all received data based on the PDCP SN or COUNT value, without differentiating between RLC layers, and may perform the duplicate detection process separately on multiple data items received from each RLC layer. As another method, when multiple data items received from different BSs overlap with each other, to prevent data loss in the header compression protocol, the receiving PDCP layer function may perform out-of-window data detection on all received data based on the PDCP SN or COUNT value, without differentiating between RLC layers, and may perform the duplicate detection process on all data received after the decryption process, integrity protection process, or header (or data) decompression process for multiple data items received from each RLC layer.

[0320] When configured to immediately apply the decryption process and integrity protection to multiple received data items, which are performed by using separate header (or data) compression contexts or security keys separately configured by the source BS and the target BS, the sub-function of the receiving PDCP layer may apply the integrity protection process to the PDCP header and data (PDCP SDU).

[0321] In the 2-2 PDCP layer architecture, a reordering process can be performed on multiple data items received from the RLC layer of the first bearer of the source BS and multiple data items received from the RLC layer of the second bearer of the target BS, and a header (or data) decompression process can be performed on multiple data items received from each BS (source BS or target BS) in ascending order of PDCP SN or COUNT values by applying the header (or data) compression context of each BS (source BS or target BS). In addition, in order to distinguish data received from the RLC layer of the first bearer of the source BS from data received from the RLC layer of the second bearer of the target BS, an indicator is defined for each data, so that it can be identified whether the PDCP layer receives data from the source BS or from the target BS. As another method, a 1-bit indicator is defined in the PDCP header, SDAP header, or RLC header, so that it can be identified whether the PDCP layer receives data from the source BS or from the target BS. In addition, the PDCP layer can perform a duplicate detection process on all multiple data items received from the RLC layer of the first bearer of the source BS and multiple data items received from the RLC layer of the second bearer of the target BS based on the PDCP SN or COUNT value (in this process, only one data (including pre-received data or data provided to the upper layer) is allocated for each PDCP SN or each COUNT value, and other data is discarded), where the header (or data) compression process for multiple data items has been completed. Then, the PDCP layer can sequentially provide all multiple data items received from the RLC layer of the first bearer of the source BS and multiple data items received from the RLC layer of the second bearer of the target BS to the upper layer in ascending order based on the PDCP SN or COUNT value. Since the PDCP layer can receive data disorderly from different BSs (i.e., from the first bearer or the second bearer), the PDCP layer may have to always perform a re-calibration process.

[0322] To accelerate data processing speed, the two downlink PDCP layer functions 1i-21 and 1i-22 can perform header compression, integrity protection, and encryption processes in parallel based on each PDCP SN or each COUNT value. In addition, the two downlink PDCP layer functions 1i-21 and 1i-22 can perform integrity protection, encryption processes, or header decompression processes by using different header (or data) compression contexts or different security keys. In addition, the two downlink PDCP layer functions 1i-21 and 1i-22 can perform integrity protection, encryption processes, or decompression processes on multiple different data items by applying different header (or data) compression contexts, different security keys, or different security algorithms in a logically single transmit PDCP layer. In addition, the two downlink PDCP layer functions 1i-21 and 1i-22 can perform an out-of-order decryption or integrity verification process on each of the multiple received data items, regardless of the order of the PDCP SN or COUNT values.

[0323] When the PDCP layer differentiates between the layer of the first bearer and the layer of the second bearer, considering that the layer of the first bearer and the layer of the second bearer are connected to different MAC layers, have different logical channel identifiers, the layer of the first bearer and the layer of the second bearer are different RLC layers connected to different MAC layers, or use different encryption keys, the PDCP layer can differentiate between the layer of the first bearer (or the first RLC layer) and the layer of the second bearer (or the second RLC layer). By doing so, an encryption process or a decryption process can be performed on UL data and DL data by using different security keys, and UL data and DL data can be compressed or decompressed by using different compression protocol contexts.

[0324] In the present disclosure, a third PDCP layer architecture 1i-30 effective in handover is provided. The third PDCP layer architecture can be applied to Embodiment 2 of the effective handover method provided in the present disclosure for minimizing data interruption time. The PDCP layer function in the third PDCP layer architecture provided in the present disclosure can be equal to the second PDCP layer architecture provided in the present disclosure.

[0325] However, the third PDCP layer architecture can correspond to the architecture of the first bearer that releases the source BS in the second PDCP layer architecture. Specifically, the third PDCP layer architecture provided in the present disclosure can have the same function as the second PDCP layer architecture, but can have an architecture that releases the first bearer (such as the SDAP layer, PDCP layer, RLC layer, or MAC layer) of the source BS in the second PDCP layer architecture. Therefore, the third PDCP layer architecture is characterized by releasing the QoS mapping information of the SDAP layer of the source BS, the security key information of the PDCP layer of the source BS, the header (or data) compression context information of the PDCP layer of the source BS, or the RLC layer or MAC layer of the source BS.

[0326] Figure 1J Shows the architecture of an effective SDAP layer to be applied to the DAPS handover method of Embodiment 2 as an effective handover method according to an embodiment of the present disclosure, and a method of applying this architecture.

[0327] In Figure 1J this disclosure proposes a specific architecture and function of an effective SDAP layer to be applied to the DAPS handover method, which is Embodiment 2 of the effective handover method provided in this disclosure, and the architecture of the SDAP layer provided below is characterized in that different SDAP layer architectures can be applied to each bearer at different time points when performing the DAPS handover process.

[0328] For example, before the UE receives a handover command message from the BS, the UE can process and send or receive data by applying the first SDAP layer architecture and function 1j-10 provided in this disclosure to each bearer (Operation 1j-01).

[0329] In the first SDAP layer architecture, the SDAP layer can perform data processing (e.g., reading SDAP header information and updating mapping information or configuring the SDAP header, or routing or providing the processed information to a suitable upper layer or lower layer based on the first QoS flow and bearer mapping information) on multiple UL data items to be sent or multiple received DL data items (e.g., multiple data items received from the source BS) by maintaining and applying the first QoS flow and bearer mapping information for the source BS.

[0330] However, when the UE receives a handover command message from the BS and the DAPS handover method provided in this disclosure is indicated in the handover command message, or the DAPS handover method is indicated for a specific bearer, the UE can process and send or receive data by applying the second PDCP layer architecture and function 1j-20 provided in this disclosure to each bearer or the bearer for which the DAPS handover method is indicated (Operation 1j-02).

[0331] That is, when the UE receives a handover command message from the BS and the DAPS handover method provided in this disclosure is indicated in the handover command message or for each bearer for which the DAPS handover method is indicated, the UE can switch the first SDAP layer architecture or function 1j-10 for each bearer to the second SDAP layer architecture or function 1j-20 for each bearer or the bearer for which the DAPS handover method is indicated provided in this disclosure.

[0332] As another method, when the first condition provided in the present disclosure is satisfied, the UE may switch the first SDAP layer architecture or function 1j-10 for each bearer to the second SDAP layer architecture or function 1j-20 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method (operation 1j-02).

[0333] In addition, when the UE receives a handover command message from the BS and the DAPS handover method provided in the present disclosure is indicated in the handover command message, the DAPS handover method is indicated for a specific bearer, or new QoS flow and bearer mapping information are newly configured, the UE may switch the first SDAP layer architecture or function 1j-10 to the second SDAP layer architecture or function 1j-20 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method.

[0334] In addition, in the second SDAP layer architecture, the existing first QoS and the existing bearer mapping information for the source BS are maintained so that the UL data to be sent to the source BS and the DL data to be received from the source BS can be processed. In addition, in the second SDAP layer architecture, the second QoS flow and the bearer mapping information newly configured in the handover command message are configured for the target BS and can be used to process the UL data to be sent to the target BS and the DL data to be received from the target BS.

[0335] That is, in the second SDAP layer architecture provided in the present disclosure, the first QoS flow and the bearer mapping information of the source BS or the second QoS flow and the bearer mapping information of the target BS are maintained so that the data of the source BS and the data of the target BS can be processed separately. In the second SDAP layer architecture, the SDAP layer may identify whether the data received from the lower layer is the data received from the source BS or the data received from the target BS by using a 1-bit indicator of the SDAP header, a 1-bit indicator of the PDCP header, or the information indicated by the PDCP layer.

[0336] When the source BS indicates the DAPS handover method for each bearer to the UE by using the handover command message, the DAPS handover method is always indicated for the default DRB, and when the DAPS handover process is executed, when data appears in the new QoS not corresponding to the QoS flow and the bearer mapping information, the UE may be indicated to always send the UL data via the default bearer. When the DAPS handover method is not configured for the default bearer, it is impossible to send the UL data for the new QoS that appears during the handover, and thus a data interruption time may occur.

[0337] When the second condition provided in the present disclosure is satisfied, when the UE executes the DAPS handover method provided in the present disclosure, the UE may release the second SDAP layer architecture and function 1j-20 applied to each bearer or the bearer indicating the DAPS handover method from the first bearer of the source BS, and may switch back to the first SDAP layer architecture and function 1j-10, and may apply the first SDAP layer architecture and function 1j-10 to each bearer. When the second condition is satisfied, the UE may switch the second SDAP layer architecture or function 1j-20 to the first SDAP layer architecture or function 1j-10 provided in the present disclosure for each bearer or the bearer indicating the DAPS handover method. In addition, it is characterized in that the UE maintains the second bearer or the second QoS flow and bearer mapping information of the target BS, and before the UE releases the first bearer or the first QoS flow and bearer mapping information of the source BS, the UE may complete the data processing for a plurality of data items received from the source BS (for example, all data received from the source BS), and then may release the first QoS flow and bearer mapping information or the first bearer. In addition, the UE may provide the plurality of processed data items to the upper layer in ascending order.

[0338] That is, when the second condition is satisfied, the UE may perform data processing (for example, the UE performs a process of reading SDAP header information and updating mapping information or configuring an SDAP header, and routing or providing the processed information to an appropriate upper layer or lower layer based on the first QoS flow and bearer mapping information) by applying the first QoS flow and bearer mapping information of the source BS to a plurality of data items stored in a buffer (for example, a plurality of data items received from the source BS), and may discard the first QoS flow and bearer mapping information of the source BS.

[0339] The SDAP layer may define and apply an indicator of 1 bit of a new SDAP header, an indicator of 1 bit of a new PDCP header, SDAP control data (for example, a DL end marker), or information indicated by the PDCP layer, and may identify which data has been recently received from the source BS based on this information. Therefore, the SDAP layer may perform data processing on the data that has been recently received from the source BS by applying the first QoS flow and bearer mapping information of the source BS, and then may discard the first QoS flow and bearer mapping information of the source BS. Then, the SDAP layer may continuously maintain the second QoS flow and bearer mapping information, and may process UL data or DL data for the target BS based on the second QoS flow and bearer mapping information.

[0340] Hereinafter, according to an embodiment of the present disclosure, there is provided a method of applying bearer configuration information using different schemes according to a handover type indicated in a handover command message when the UE receives a handover command message and applies the bearer configuration information included in the Figure 1F handover command message.

[0341] In the case where the UE receives a handover command message, when the ReconfigWithSync information indicates the first handover method (e.g., Embodiment 1 of the present disclosure or the normal handover method), the UE can apply the bearer configuration information by using the following Method 1. When the default bearer is configured in the SDAP layer configuration information configured in the handover command message, the UE can configure the default bearer of the source BS as the default bearer of the target BS indicated in the configuration information.

[0342] 2) When the second QoS flow and bearer mapping information are configured in the SDAP layer configuration information configured in the handover command message, the UE can release the first QoS flow and bearer mapping information applied for the source BS, and can apply the second QoS flow and bearer mapping information. As another method, the UE can replace the first QoS flow and bearer mapping information applied for the source BS with the second QoS flow and bearer mapping information.

[0343] 3) When the data discard timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE can apply the discard timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0344] 4) When the UE receives a handover command message, the UE can re - establish the PDCP layer. For example, the UE can initialize the window state variable for the SRB, and can discard multiple stored data items (PDCP SDU or PDCP PDU). In addition, the UE can initialize the window state variable for the UM DRB, can perform compression, encryption, or integrity protection on multiple data items that have not been sent to the lower layer or for which the PDCP discard timer has not expired, in ascending order of the COUNT value, based on the header (or data) compression context or security key of the target BS, and then can send or re - transmit the data. In addition, when the recalibration timer is running, the UE can stop and re - configure the recalibration timer, can process multiple received data items (PDCP SDU or PDCP PDU) in sequence, and can provide the data to the upper layer. In addition, the UE does not initialize the window state variable for the AM DRB, and can perform compression, encryption, or integrity protection on the data starting from the first data (not successfully acknowledged by the lower layer) (PDCP SDU or PDCP PDU) in ascending order of the PDCP SN or COUNT value, based on the header (or data) compression context or security key of the target BS.

[0345] 5) When the drb-ContinueROHC indicator in the PDCP layer configuration information configured in the handover command message is configured to False, the UE may initialize the context of the header compression or decompression protocol in the PDCP layer corresponding to the bearer identifier of the configuration information. When the drb-ContinueROHC indicator is configured to True, the UE does not initialize the context of the header compression or decompression protocol in the PDCP layer corresponding to the bearer identifier of the configuration information.

[0346] 6) When the recalibration timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE may apply the recalibration timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0347] 7) When the security key configuration information or security algorithm is configured in the security configuration information configured in the handover command message, the UE may derive a new security key or new security configuration information by using the configuration information, may release the existing security key or existing security configuration information, or may replace the existing security key or existing security configuration information with the new security key or new security configuration information.

[0348] 8) When a new logical channel identifier is configured in the RLC layer configuration information configured in the handover command message, the UE may release the existing logical channel identifier corresponding to the bearer identifier indicated in the RLC layer configuration information, or may replace the existing logical channel identifier with the new logical channel identifier.

[0349] 9) When the RLC reconstruction process is configured in the RLC layer configuration information configured in the handover command message, the UE may perform the RLC reconstruction process on the RLC layer corresponding to the bearer identifier indicated in the RLC layer configuration information.

[0350] 10) When the RLC layer configuration information configured in the handover command message is newly configured, the UE may perform the RLC reconstruction process on the RLC layer corresponding to the bearer identifier indicated in the RLC layer configuration information.

[0351] 11) When a new second priority for a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may release the first priority corresponding to the identifier of the logical channel indicated in the configuration information, or may replace the first priority corresponding to the logical channel identifier with the newly configured second priority.

[0352] 12) When a second prioritisedBitRate (PBR) for a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may release the first prioritisedBitRate (PBR) corresponding to the identifier of the logical channel indicated in the configuration information, or may replace the first prioritisedBitRate (PBR) corresponding to the identifier of the logical channel with the newly configured second prioritisedBitRate (PBR). The prioritisedBitRate refers to a value that is incremented for each logical channel at a preset time interval (e.g., in each TTI). When the UE receives UL transmission resources, considering the priority and the prioritisedBitRate, the UE may perform a logical channel prioritization (LCP) process and may transmit data for the logical channel. In view of this, the higher the priority, or the larger the value of the prioritisedBitRate, the more data can be transmitted.

[0353] 13) When a second bucketSizeDuration for a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may release the first bucketSizeDuration corresponding to the identifier of the logical channel indicated in the configuration information, or may perform the configuration by replacing the first bucketSizeDuration corresponding to the identifier of the logical channel with the newly configured second bucketSizeDuration. In the above description, the bucket size indicates the maximum value that the prioritisedBitRate value can have when the prioritisedBitRate accumulates.

[0354] 14) When the second available SCell information, available subcarrier spacing information, maximum PUSCH duration, or logical channel group configuration information is configured in the MAC layer configuration information configured in the handover command message, the UE may release the pre-configured first available SCell information, pre-configured available subcarrier spacing information, pre-configured maximum PUSCH duration, or pre-configured logical channel group configuration information, or may perform the configuration by replacing the pre-configured first available SCell information, pre-configured available subcarrier spacing information, pre-configured maximum PUSCH duration, or pre-configured logical channel group configuration information with the newly configured second available SCell information, newly configured available subcarrier spacing information, newly configured maximum PUSCH duration, or newly configured logical channel group configuration information.

[0355] In the case where the UE receives a handover command message, when the ReconfigWithSync information indicates the second handover method (e.g., Embodiment 2 of the present disclosure or the DAPS handover method) or indicates the DAPS handover method for each bearer, the UE can apply the bearer configuration information by using the following methods.

[0356] 1) When a default bearer is configured in the SDAP layer configuration information configured in the handover command message, the UE can perform the DAPS handover method provided in the present disclosure, can maintain the existing default bearer of the source BS by applying the second SDAP layer architecture 1j-20, and can configure the default bearer information indicated in the configuration information as the default bearer of the target BS. As another method, when the first condition provided in the present disclosure is satisfied, the UE can switch the existing default bearer of the source BS to the default bearer of the target BS indicated in the configuration information.

[0357] 2) When the second QoS flow and bearer mapping information are configured in the SDAP layer configuration information configured in the handover command message, the UE can perform the DAPS handover method provided in the present disclosure, can maintain the first QoS flow and bearer mapping information of the source BS by applying the second SDAP layer architecture 1j-20, and can apply the second QoS flow and bearer mapping information to the data of the target BS. In addition, when the first condition provided in the present disclosure is satisfied, the UE can apply the second QoS flow and bearer mapping information for the target BS.

[0358] 3) When a data discard timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE can perform the DAPS handover method provided in the present disclosure, and can apply the discard timer value to the PDCP layer corresponding to the bearer identifier of the configuration information by applying the second PDCP layer architecture.

[0359] 4) When the UE receives a handover command message, the UE can not re-establish the PDCP layer indicating the DAPS handover method, and can perform the following procedures. For example, the UE can initialize the window state variable for the SRB (when the DAPS handover fails, the variable initialization can be skipped to perform a fallback), or can discard multiple stored data items (PDCP SDU or PDCPPDU). In addition, the UE can not initialize the window state variable for the UM DRB, and can continuously perform data transmission or reception to or from the source BS for multiple data items that have not been sent to the lower layer or for which the PDCP discard timer has not expired. In addition, the UE can not initialize the window state variable for the AD DRB, and can continuously perform data transmission or reception to or from the source BS.

[0360] 5) When the drb-ContinueROHC indicator in the PDCP layer configuration information configured in the handover command message is configured to False, the UE may perform the DAPS handover method provided in the present disclosure, and may, by applying the second PDCP layer architecture, invariantly use the header compression or decompression protocol context of the source BS in the PDCP layer corresponding to the bearer identifier of the configuration information, initialize the header compression or decompression protocol context of the target BS, and start in the initial state (e.g., IR state). When the drb-ContinueROHC indicator is configured to True, the UE may perform the DAPS handover method provided in the present disclosure, and may, by applying the second PDCP layer architecture, invariantly use the header compression or decompression protocol context of the source BS in the PDCP layer corresponding to the bearer identifier of the configuration information, and may equally apply the header compression or decompression protocol context of the target BS as the header compression or decompression protocol context of the source BS. For example, the UE may copy the header compression or decompression protocol context of the source BS and invariantly apply it to the header compression or decompression protocol context of the target BS. As another method, the UE may apply the same header compression or decompression protocol context to the target BS or the source BS.

[0361] 6) When a recalibration timer value is configured in the PDCP layer configuration information configured in the handover command message, the UE may perform the DAPS handover method provided in the present disclosure, and may, by applying the second PDCP layer architecture, apply the recalibration timer value to the PDCP layer corresponding to the bearer identifier of the configuration information.

[0362] 7) When security key configuration information or a security algorithm is configured in the security configuration information configured in the handover command message, or when an indicator indicating a new procedure is included in the PDCP layer configuration information, the UE may derive a new security key or new security configuration information by using the configuration information, and may perform the DAPS handover method provided in the present disclosure. In view of this, the UE may maintain the existing security key or existing security configuration information of the source BS by applying the second PDCP layer architecture, and may configure the security key or security configuration information of the target BS as the new security key or new security configuration information.

[0363] 8) When a new logical channel identifier is configured in the RLC layer configuration information configured in the handover command message, the UE can execute the DAPS handover method provided in the present disclosure. In addition, by applying the second PDCP layer architecture, the UE can maintain the existing logical channel identifier corresponding to the bearer identifier indicated in the RLC layer configuration information for the RLC layer or MAC layer of the first bearer of the source BS, and can configure the new logical channel identifier indicated in the configuration for the RLC layer or MAC layer of the second bearer of the target BS.

[0364] 9) When an RLC reestablishment procedure is configured in the RLC layer configuration information configured in the handover command message, the UE can execute the DAPS handover method provided in the present disclosure, and can execute the RLC reestablishment procedure on the RLC layer of the first bearer of the source BS corresponding to the bearer identifier indicated in the RLC layer configuration information by applying the second PDCP layer architecture.

[0365] 10) When the RLC layer configuration information configured in the handover command message is newly configured, the UE can execute the DAPS handover method provided in the present disclosure, and can maintain the existing RLC configuration information of the RLC layer of the first bearer of the source BS corresponding to the bearer identifier indicated in the RLC layer configuration information by applying the second PDCP layer architecture, and can configure the RLC layer of the second bearer of the target BS as the new RLC layer configuration information indicated in the configuration information.

[0366] 11) When a second priority for a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE can execute the DAPS handover method provided in the present disclosure and can apply the second PDCP layer architecture. In view of this, the UE can maintain the existing configuration information of the MAC layer of the first bearer of the source BS corresponding to the bearer identifier indicated above, can configure the new logical channel identifier indicated in the configuration information for the MAC layer of the second bearer of the target BS, and can configure the newly configured second priority corresponding to the logical channel identifier indicated in the configuration information. As another method, when the first condition provided in the present disclosure is satisfied, the UE can apply the priority order to the MAC layer of the second bearer of the target BS according to each logical channel identifier.

[0367] 12) When a second prioritisedBitRate (PBR) for a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method provided in the present disclosure. In view of this, the UE may apply the second PDCP layer architecture and maintain the existing configuration information of the MAC layer of the first bearer for the source BS, which corresponds to the bearer identifier indicated above, may configure a new logical channel identifier for the MAC layer of the second bearer for the target BS, the new logical channel identifier is indicated in the configuration information, and may configure a newly configured second prioritisedBitRate (PBR) corresponding to the new logical channel identifier indicated in the configuration information. As another method, after the first condition provided in the present disclosure is satisfied, the UE may start applying the second prioritisedBitRate to the new logical channel identifier in the MAC layer of the second bearer for the target BS (by doing so, UL transmission resources may be fairly allocated when different handover methods are indicated for each bearer). The prioritisedBitRate refers to a value that is incremented for each logical channel at a preset time interval (e.g., in each TTI) when the prioritisedBitRate is applied to each logical channel identifier. When the UE receives UL transmission resources, considering the priority and the prioritisedBitRate, the UE may perform the LCP process and may transmit data for the logical channel. In view of this, the higher the priority or the larger the value of the prioritisedBitRate, the more data may be transmitted.

[0368] 13) In the case where the DAPS handover method is applied in the above description, when the UE needs to transmit UL data via the first bearer of the source BS because the first condition provided in the present disclosure is not satisfied, the UE may select the MAC layer of the first bearer as the target of the LCP process only for the logical channel identifier for which the DAPS handover method is carried or indicated (or the handover method that can continuously transmit data to the source BS even after receiving the handover command message), and may perform the LCP process. This is because when the UE receives a handover command message for a bearer or logical channel identifier for which the DAPS handover method is not applied, the UE cannot transmit UL data to the source BS and the UE cannot select the bearer or logical channel identifier as the target of the LCP process.

[0369] 14) When a second bucketSizeDuration for a logical channel is newly configured in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method provided in the present disclosure. In view of this, the UE may apply the second PDCP layer architecture and maintain the existing configuration information of the MAC layer for the first bearer of the source BS, which corresponds to the bearer identifier indicated above, may configure a new logical channel identifier for the MAC layer of the second bearer of the target BS, the new logical channel identifier is indicated in the configuration information, and may configure the newly configured second bucketSizeDuration corresponding to the new logical channel identifier indicated in the configuration information. As another method, after satisfying the first condition provided in the present disclosure, the UE may start applying the second bucketSizeDuration to the new logical channel identifier in the MAC layer of the second bearer of the target BS (by doing so, UL transmission resources can be fairly allocated when different handover methods are indicated for each bearer). In the above description, the bucket size indicates the maximum value that the prioritisedBitRate value may have when the prioritisedBitRate accumulates.

[0370] 15) When second available Scell information, available subcarrier spacing information, maximum PUSCH duration or logical channel group configuration information is configured in the MAC layer configuration information configured in the handover command message, the UE may perform the DAPS handover method provided in the present disclosure. In view of this, the UE may apply the second PDCP layer architecture and maintain the existing configuration information related to the MAC layer of the first bearer of the source BS corresponding to the bearer identifier described above, and may configure the second available Scell information, available subcarrier spacing information, maximum PUSCH duration or logical channel group configuration information for the MAC layer of the second bearer of the target BS.

[0371] As described above, when the UE receives a handover command message and the second handover message is indicated in the ReconfigWithSync information (e.g., Embodiment 2 of the present disclosure or the DAPS handover method), or when the DAPS handover method is indicated for each bearer identifier or each logical channel identifier, after the UE receives the handover command message, the UE may continuously perform data transmission or reception to or from the source BS only for the bearers (AM bearers or UM bearers) for which the DAPS handover method is indicated, and then until the first condition provided in the present disclosure is satisfied. When the first condition is satisfied, the UE may switch the BS for receiving UL data from the source BS to the target BS, but may receive DL data from the source BS until the connection with the source BS is released. However, for the bearers for which the DAPS handover method is not indicated, the UE cannot perform data transmission or reception to or from the source BS in a continuous manner or after the UE receives the handover command message, and then until the first condition provided in the present disclosure is satisfied. Therefore, in order to enable the UE to perform the operations provided in the present disclosure, one or more methods described below may be applied.

[0372] Method 1: As provided in the present disclosure, when the UE receives a handover command message and the second handover message is indicated in the ReconfigWithSync information (e.g., Embodiment 2 of the present disclosure or the DAPS handover method), or when the DAPS handover method is indicated for each bearer identifier or each logical channel identifier, for example, when the MAC layer of the UE in the source BS starts transmitting data when performing the LCP process to receive the handover command message from the UE, the MAC layer of the UE in the source BS may only select the logical channel identifiers corresponding to the bearers for which the DAPS handover method is indicated as a candidate group, and may perform the LCP process.

[0373] In addition, the MAC layer of the UE in the source BS may only maintain the logical channel identifiers for which the DAPS handover method is indicated or the prioritisedBitRate or bucket size duration corresponding to the logical channel identifiers. In addition, the MAC layer of the UE in the source BS may release, may not use, or may not apply the logical channel identifiers or the prioritisedBitRate or bucket size duration corresponding to the logical channel identifiers, where the logical channel identifiers correspond to the bearers for which the DAPS handover method is not indicated.

[0374] In addition, the UE may perform a PDCP re - establishment process or an RLC re - establishment process on a bearer that does not indicate a DAPS handover method, and may apply the bearer configuration information (such as logical channel identifier, prioritisedBitRate or bucket size duration) configured for the target BS to the MAC layer of the target BS with respect to the bearer that does not indicate a DAPS handover method in the handover message. In addition, the UE may switch the connection of the bearer corresponding to the PDCP layer or RLC layer that does not indicate a DAPS handover method from the MAC layer of the source BS to the MAC layer of the target BS. That is, the UE may release the configuration information of the PDCP layer, RLC layer or MAC layer of the bearer that does not indicate a DAPS handover method from the MAC layer of the source BS, and may perform application or connection to the MAC layer of the target BS according to the bearer configuration of the target BS.

[0375] In addition, the UE may perform data transmission or reception to or from the source BS until the first condition provided in this disclosure is met, may initialise the prioritisedBitRate for the logical channel identifier in the MAC layer of the source BS that corresponds to the bearer that does not indicate a DAPS handover method, and may release or stop the bearer without applying the prioritisedBitRate cumulative calculation process. In addition, the MAC layer of the UE of the source BS may continuously maintain the prioritisedBitRate for the logical channel identifier corresponding to the bearer that indicates a DAPS handover method, and may perform an accumulation calculation process.

[0376] When the first condition is met, the UE may perform a handover of data transmission to the target BS, and the MAC layer of the target BS may initialise the prioritisedBitRate for the newly configured logical channel identifier, or may start the accumulation calculation (as another method, when the UE receives a handover command message for the MAC layer of the target BS, the UE may initialise the prioritisedBitRate and may start the accumulation calculation). In addition, when the bearer that does not indicate a DAPS handover method is interrupted, the UE may resume the bearer, may start data transmission or reception to or from the target BS, and may initialise the prioritisedBitRate or start the accumulation calculation. When the first condition is met, the UE may initialise the prioritisedBitRate for the logical channel identifier configured in the MAC layer of the source BS, and may stop the accumulation calculation.

[0377] In addition, the UE may perform data reception from the source BS or the target BS until a second condition provided in this disclosure is met, may initialize the MAC layer of the source BS when the second condition is met, and may release the RLC layer, the PDCP layer, or the bearer configuration information of the bearer that is connected to the MAC layer of the source BS and corresponds to the bearer that does not indicate the DAPS handover method from the MAC layer of the source BS. In addition, the UE may release the RLC layer or the bearer configuration information corresponding to the bearer that indicates the DAPS handover method from the second PDCP layer architecture or the MAC layer of the source BS.

[0378] Method 2: As provided in this disclosure, when the UE receives a handover command message and a second handover message (e.g., Embodiment 2 of this disclosure or the DAPS handover method) is indicated in the ReconfigWithSync information, or when the DAPS handover method is indicated for each bearer identifier or each logical channel identifier, the upper layer (e.g., the RRC layer) of the UE may indicate to perform MAC reconfiguration on the MAC layer of the source BS based on the configuration information that excludes the configuration information related to the bearer for which the DAPS handover method is not indicated in the handover command message from the configuration information of the current MAC layer.

[0379] As another method, the upper layer (e.g., the RRC layer) of the UE may indicate to perform MAC reconfiguration on the MAC layer of the source BS based on the configuration information that includes only the configuration information related to the bearer for which the DAPS handover method is indicated in the handover command message from the configuration information of the current MAC layer. When the UE reconfigures the MAC layer of the source BS, the MAC layer of the UE in the source BS may only retain the logical channel identifier corresponding to the bearer that indicates the DAPS handover method or the prioritisedBitRate or bucket size duration corresponding to the logical channel identifier, and may release, may not use, or may not apply the logical channel identifier, or the prioritisedBitRate or bucket size duration corresponding to the logical channel identifier, or the logical channel identifier corresponding to the bearer for which the DAPS handover method is not indicated.

[0380] The upper layer of the UE (e.g., the RRC layer) may instruct the MAC layer of the target BS to perform a PDCP re-establishment process or an RLC re-establishment process on a bearer for which the DAPS handover method is not indicated, and apply bearer configuration information such as the logical channel identifier, prioritisedBitRate, or bucket size duration configured for the target BS to the MAC layer of the target BS for a bearer for which the DAPS handover method is not indicated in the handover message. In addition, the upper layer of the UE (e.g., the RRC layer) may switch the connection to the PDCP layer or the RLC layer from the MAC layer of the source BS to the MAC layer of the target BS, where the PDCP layer or the RLC layer corresponds to a bearer for which the DAPS handover method is not indicated. For example, when the MAC layer of the UE of the source BS starts transmitting data when performing an LCP process to hand over from the connection, the MAC layer of the UE of the source BS may select only the logical channel identifier corresponding to the bearer for which the DAPS handover method is indicated as the candidate group and may perform the LCP process. The process of reconfiguring the MAC layer for the source BS, i.e., the process performed by the upper layer (e.g., the RRC layer), may include a process in which the MAC layer of the source BS is reconfigured by a partial MAC CE and thus performs the same process. For example, the upper layer (e.g., the RRC layer) may initialise, release, or stop using the configuration information of the MAC layer for a bearer for which the DAPS handover method is not indicated.

[0381] In addition, the UE may perform data transmission or reception to or from the source BS until the first condition provided in this disclosure is met. The prioritisedBitRate for the logical channel identifier in the MAC layer of the source BS corresponding to the bearer that does not indicate the DAPS handover method may be initialised, and the bearer may be released or stopped without applying the prioritisedBitRate cumulative calculation process. Further, the MAC layer of the UE of the source BS may continuously maintain the prioritisedBitRate for the logical channel identifier corresponding to the bearer that indicates the DAPS handover method, and may perform the cumulative calculation process. When the first condition is met, the UE may perform the handover of data transmission to the target BS, and the MAC layer of the target BS may initialise the prioritisedBitRate for the newly configured logical channel identifier, or may start the cumulative calculation (as another method, when the UE receives the handover command message for the MAC layer of the target BS, the UE may initialise the prioritisedBitRate and may start the cumulative calculation). In addition, when the bearer that does not indicate the DAPS handover method is interrupted, the UE may resume the bearer, may start data transmission or reception to or from the target BS, and may initialise the prioritisedBitRate or start the cumulative calculation. When the first condition is met, the UE may initialise the prioritisedBitRate for the logical channel identifier configured in the MAC layer of the source BS, and may stop the cumulative calculation.

[0382] In addition, the UE may perform data reception from the source BS or the target BS until the second condition provided in this disclosure is met. The MAC layer of the source BS may be initialised when the second condition is met, and the RLC layer, PDCP layer, or bearer configuration information connected to the MAC layer of the source BS and corresponding to the bearer that does not indicate the DAPS handover method may be released from the MAC layer of the source BS. Further, the RLC layer or bearer configuration information corresponding to the bearer that indicates the DAPS handover method may be released from the second PDCP layer architecture or the MAC layer of the source BS.

[0383] Method 3: As provided in the present disclosure, when the UE receives a handover command message, a second handover message (e.g., Embodiment 2 of the present disclosure or the DAPS handover method) may be indicated in the ReconfigWithSync information, or the DAPS handover method may be indicated for each bearer identifier or each logical channel identifier. In view of this, for example, when the MAC layer of the UE of the source BS starts sending data when performing the LCP process to receive the handover command message from the UE, the UE may indicate to the MAC layer of the source BS that there is no data to be sent in the buffer of the PDCP layer corresponding to the bearer for which the DAPS handover method is not indicated, or the PDCP data volume is 0, so that the LCP process may be performed only on the logical channel identifier corresponding to the bearer for which the DAPS handover method is indicated. Therefore, the MAC layer of the source BS may determine that there is no data to be sent for the non-indicated DAPS handover method, and may not perform the LCP process on the logical channel identifier corresponding to the bearer for which the DAPS handover method is not indicated.

[0384] In addition, the UE may perform a PDCP re-establishment process or an RLC re-establishment process on the bearer for which the DAPS handover method is not indicated, and may apply the bearer configuration information (e.g., logical channel identifier, prioritisedBitRate, or bucket size duration) configured for the target BS to the MAC layer of the target BS with respect to the bearer for which the DAPS handover method is not indicated in the handover message. In addition, the UE may switch the connection of the PDCP layer or the RLC layer corresponding to the bearer for which the DAPS handover method is not indicated from the MAC layer of the source BS to the MAC layer of the target BS. That is, the UE may release the configuration information of the PDCP layer, the RLC layer, or the MAC layer of the bearer for which the DAPS handover method is not indicated from the MAC layer of the source BS, and may perform the application or connection to the MAC layer of the target BS according to the bearer configuration of the target BS.

[0385] In addition, the UE may perform data transmission or reception to or from the source BS until the first condition provided in the present disclosure is met, may initialise the prioritisedBitRate for the logical channel identifier in the MAC layer of the source BS corresponding to the bearer for which the DAPS handover method is not indicated, and may release or stop the bearer without applying the prioritisedBitRate cumulative calculation process. In addition, the MAC layer of the UE of the source BS may continuously maintain the prioritisedBitRate for the logical channel identifier corresponding to the bearer for which the DAPS handover method is indicated, and may perform the accumulation calculation process.

[0386] When the first condition is satisfied, the UE may perform a handover for data transmission to the target BS, and the MAC layer of the target BS may initialize the prioritisedBitRate for the newly configured logical channel identifier, or may start cumulative calculation (as another method, when the UE receives a handover command message for the MAC layer of the target BS, the UE may initialize the prioritisedBitRate and may start cumulative calculation). In addition, when a bearer that does not indicate the DAPS handover method is interrupted, the UE may resume the bearer, may start data transmission or reception to or from the target BS, and may initialize the prioritisedBitRate or start cumulative calculation. When the first condition is satisfied, the UE may initialize the prioritisedBitRate for the logical channel identifier configured in the MAC layer of the source BS and may stop cumulative calculation.

[0387] In addition, the UE may perform data reception from the source BS or the target BS until the second condition provided in the present disclosure is satisfied, may initialize the MAC layer of the source BS when the second condition is satisfied, and may release the RLC layer, the PDCP layer, or the bearer configuration information connected to the MAC layer of the source BS and corresponding to a bearer that does not indicate the DAPS handover method. In addition, the UE may release the RLC layer or the bearer configuration information corresponding to a bearer that indicates the DAPS handover method from the second PDCP layer architecture or the MAC layer of the source BS.

[0388] Figure 1K is a diagram showing the operation of the UE 1k-01 according to an embodiment of the present disclosure.

[0389] In Figure 1K the UE 1k-01 may perform data transmission or reception to or from the source BS for each bearer through the first PDCP layer architecture. When the handover command message received by the UE 1k-01 (operation 1k-05) indicates the DAPS handover method of Embodiment 2 provided in the present disclosure or indicates the DAPS handover method for each bearer, the UE 1k-01 may switch the first PDCP layer architecture to the second PDCP layer architecture for the target BS indicated in the handover command message, for each bearer, or for a bearer that indicates the DAPS handover method. In addition, the UE 1k-01 may configure and establish the protocol layers of the second bearer and may perform a random access procedure to the target BS via the established protocol layers. When the UE 1k-01 performs a random access procedure to the target BS (operations 1k-10 and 1k-15), the UE 1k-01 may continuously perform data transmission or reception to or from the source BS (UL data transmission and DL data reception) via the protocol layers of the first bearer (operation 1k-20).

[0390] When the first condition of the present disclosure is satisfied (operation 1k-25), the UE 1k-01 may stop UL data transmission via the protocol layer of the first bearer to the source BS and may switch the UL data transmission, so that UL data can be transmitted to the target BS via the protocol layer of the second bearer. In view of this, the UE 1k-01 may continuously receive DL data from the source BS and the target BS via the protocol layers of the first and second bearers (operation 1k-30). In addition, the PDCP layer of the second bearer may continuously perform data transmission or reception to or from the target BS without interruption by using the data, SN information, or information such as header compression and decompression context stored in the PDCP layer of the first bearer.

[0391] When the first condition is not satisfied, the UE 1k-01 may continuously check the first condition while continuously executing the ongoing process.

[0392] When the second condition is satisfied, the UE 1k-01 may stop receiving DL data from the source BS via the protocol layer of the first bearer (operation 1k-45). In addition, the PDCP layer of the second bearer of the UE 1k-01 may continuously perform data transmission or reception to or from the target BS by using the data, SN information, or information such as header compression and decompression context stored in the PDCP layer of the first bearer.

[0393] When the second condition is not satisfied, the UE 1k-01 may continuously check the second condition while continuously executing the ongoing process (operation 1k-50).

[0394] According to an embodiment of the present disclosure, the PDCP layer provided in the present disclosure may perform different processes according to the handover type indicated in the handover command message received by the UE.

[0395] When the handover indicated in the handover command message received by the UE from the source BS is the handover of Embodiment 1 (for example, a conventional handover method), the UE may perform a PDCP re-establishment process on the PDCP layer for each bearer.

[0396] When the handover indicated in the handover command message received by the UE from the source BS is the handover of Embodiment 2 (or indicated for each bearer), the UE may perform a process on each bearer (or for the bearer indicated for Embodiment 2) that is provided in the present disclosure under the condition that the first condition is satisfied.

[0397] When the source BS indicates to the UE a handover in which the embodiments provided in the present disclosure are applied, the source BS may start forwarding data to the target BS when the following third condition is satisfied. The third condition according to an embodiment of the present disclosure may mean that one or more of the following conditions are satisfied.

[0398] In the case where the UE receives an indication from the target BS indicating that the handover has been successfully completed

[0399] In the case where the source BS sends a handover command message to the UE

[0400] In the case where the source BS sends a handover command message to the UE and identifies a successful transmission (HARQ ACK or NACK or RLC ACK or NACK) of the handover command message

[0401] In the case where the source BS receives an indication from the UE (e.g., an RRC message (e.g., an RRCReconfiguration message)) that indicates the release of the connection with the source BS, or receives a MAC CE, an RLC control PDU, or a PDCP control PDU from the UE

[0402] In the case where the source BS sends a handover command message to the UE and drives a certain timer, and then the timer expires

[0403] In the case where an acknowledgement (HARQ ACK or NACK or RLC ACK or NACK) for a successful transmission of DL data is not received from the UE within a certain time

[0404] Figure 1L is a diagram showing the configuration of a UE to which an embodiment of the present disclosure is applicable.

[0405] Reference Figure 1L , the UE may include a radio frequency (RF) processor 1l-10, a baseband processor 1l-20, a memory 1l-30, and a controller 1l-40 including a multi-connection processor 1l-42. However, the configuration of the UE is not limited to Figure 1L the configuration shown.

[0406] The RF processor 1l-10 performs functions of transmitting and receiving signals through a wireless channel, e.g., frequency band conversion and amplification of signals. That is, the RF processor 1l-10 up-converts the baseband signal provided from the baseband processor 1l-20 into an RF band signal, then transmits the RF band signal through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processor 1l-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Although in Figure 1LOnly one antenna is shown, but the UE may include multiple antennas. The RF processor 1l-10 may include multiple RF chains. In addition, the RF processor 1l-10 may perform beamforming. For beamforming, the RF processor 1l-10 may adjust the phase and intensity of the respective signals transmitted or received through multiple antennas or antenna elements. The RF processor 1l-10 may perform MIMO operations and may receive multiple layers in MIMO operations. The RF processor 1l-10 may perform receive beam scanning by appropriately configuring multiple antennas or antenna elements, or may adjust the direction and beam width of the receive beam in coordination with the transmit beam under the control of the controller 1l-40.

[0407] The baseband processor 1l-20 performs the conversion between the baseband signal and the bit stream based on the physical layer specifications of the system. For example, for data transmission, the baseband processor 1l-20 generates complex symbols by encoding and modulating the transmit bit stream. For data reception, the baseband processor 1l-20 reconstructs the received bit stream by demodulating and decoding the baseband signal provided by the RF processor 1l-10. For example, according to the OFDM scheme, for data transmission, the baseband processor 1l-20 generates complex symbols by encoding and modulating the transmit bit stream, maps the complex symbols to subcarriers, and then configures the OFDM symbols by performing the inverse fast Fourier transform (IFFT) and inserting a cyclic prefix (CP). For data reception, the baseband processor 1l-20 divides the baseband signal provided by the RF processor l-10 into OFDM symbol units, reconstructs the signal mapped to the subcarriers by performing fast Fourier transform (FFT) calculations, and then reconstructs the received bit stream by demodulating and decoding the signal.

[0408] The baseband processor 1l-20 and the RF processor 1l-10 transmit and receive signals in the above manner. Therefore, the baseband processor 1l-20 and the RF processor 1l-10 may also be referred to as a transmitter, a receiver, a transceiver, or a communicator. At least one of the baseband processor 1l-20 or the RF processor 1l-10 may include multiple communication modules to support a variety of different radio access technologies. At least one of the baseband processor 1l-20 or the RF processor 1l-10 may include different communication modules to process signals in different frequency bands. For example, different radio access technologies may include an LTE network, an NR network, etc. Different frequency bands may include super high frequency (SHF) (e.g., 2.5 GHz or 5 GHz) bands and millimeter wave (mmWave) (e.g., 60 GHz) bands.

[0409] The memory 1l-30 may store basic programs, application programs, and data for UE operations, such as configuration information. The memory 1l-30 may provide the stored data according to the request of the controller 1l-40.

[0410] The controller 1l-40 controls the overall operation of the UE. According to an embodiment of the present disclosure, the controller 1l-40 controls the operation of the UE. For example, the controller 1l-40 transmits and receives signals through the baseband processor 1l-20 and the RF processor 1l-10. The controller 1l-40 records data on the memory 1l-30 or reads data from the memory 1l-30. To this end, the controller 1l-40 may include at least one processor. For example, the controller 1l-40 may include a communication processor (CP) for controlling communication and an application processor (AP) for controlling upper layers such as applications.

[0411] Figure 1M is a diagram showing the configuration of a BS to which an embodiment of the present disclosure is applicable.

[0412] Reference Figure 1M , the base station may include an RF processor 1m-10, a baseband processor 1m-20, a communicator 1m-30, a memory 1m-40, and a controller 1m-50 including a multi-connection processor 1m-52. However, the configuration of the BS is not limited to Figure 1M the configuration shown.

[0413] The RF processor 1m-10 performs functions of transmitting and receiving signals through a wireless channel, for example, frequency band conversion and amplification of signals. That is, the RF processor 1m-10 up-converts the baseband signal provided by the baseband processor 1m-20 into an RF band signal, then transmits the RF band signal through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processor 1m-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in Figure 1M , the BS may include multiple antennas. The RF processor 1m-10 may include multiple RF chains. In addition, the RF processor 1m-10 may perform beamforming. For beamforming, the RF processor 1m-10 may adjust the phase and intensity of the corresponding signals transmitted or received through multiple antennas or antenna elements. The RF processor 1m-10 may perform DL MIMO operations by transmitting one or more layers.

[0414] The baseband processor 1m-20 performs the conversion between baseband signals and bitstreams based on the physical layer specifications of the first radio access technology. For example, for data transmission, the baseband processor 1m-20 can generate complex symbols by encoding and modulating the transmission bitstream. For data reception, the baseband processor 1m-20 reconstructs the received bitstream by demodulating and decoding the baseband signal provided by the RF processor 1m-10. For example, according to the OFDM scheme, for data transmission, the baseband processor 1m-20 generates complex symbols by encoding and modulating the transmission bitstream, maps the complex symbols to subcarriers, and then configures OFDM symbols by performing IFFT and inserting CP. For data reception, the baseband processor 1m-20 divides the baseband signal provided by the RF processor 1m-10 into OFDM symbol units, reconstructs the signal mapped to the subcarriers by performing FFT calculations, and then reconstructs the received bitstream by demodulating and decoding the signal. The baseband processor 1m-20 and the RF processor 1m-10 transmit and receive signals as described above. Thus, the baseband processor 1m-20 and the RF processor 1m-10 can also be referred to as a transmitter, a receiver, a transceiver, a communicator, or a wireless communicator.

[0415] The communicator 1m-30 provides an interface for communicating with other nodes in the network.

[0416] The memory 1m-30 can store basic programs, application programs, and data for BS operations, such as configuration information. In particular, the memory 1m-40 can store information such as information about the bearers allocated to the connected UEs and measurement results reported from the connected UEs. The memory 1m-40 can store standard information for determining whether to provide or release multi-connections to or from the UEs. The memory 1m-40 provides the stored data according to the request of the controller 1m-50.

[0417] The controller 1m-50 controls the overall operation of the BS. According to an embodiment of the present disclosure, the controller 1m-50 controls the operation of the BS. For example, the controller 1m-50 transmits and receives signals through the baseband processor 1m-20 and the RF processor 1m-10 or the communicator 1m-30 including a backhaul communicator. The controller 1m-50 records data on the memory 1m-40 or reads data from the memory 1m-40. To this end, the controller 1m-50 can include at least one processor.

[0418] The method according to an embodiment of the present disclosure described herein or in the following claims can be implemented as hardware, software, or a combination of hardware and software.

[0419] When implemented as software, a computer-readable storage medium or a computer program product storing one or more programs (e.g., software modules) can be provided. The one or more programs stored in the computer-readable storage medium or the computer program product are configured to be executed by one or more processors in an electronic device. The one or more programs include instructions that direct the electronic device to execute a method according to an embodiment of the present disclosure as described herein or in the following claims.

[0420] The program (e.g., software module or software) can be stored in a non-volatile memory including random access memory (RAM) or flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk storage device, compact disc (CD-ROM), digital versatile disc (DVD), another optical storage device, or magnetic tape. Alternatively, the program can be stored in a memory including a combination of some or all of the above storage media. Multiple such memories can be included.

[0421] In addition, the program can be stored in an attachable storage device accessible through any communication network such as the Internet, intranet, local area network (LAN), wide LAN (WLAN), and storage area network (SAN), or a combination thereof. Such a storage device can be accessed via an external port by the electronic device for executing an embodiment of the present disclosure. In addition, an additional storage device on the communication network can access the electronic device to execute an embodiment of the present disclosure.

[0422] In the present disclosure, various effective handover methods are provided to prevent data interruption time due to handover when performing handover in a next-generation mobile communication system, so that a service without data interruption can be supported.

[0423] In the above embodiments of the present disclosure, according to the embodiments of the present disclosure, one or more elements included in the present disclosure are represented in singular or plural forms. However, for the sake of convenience of description, the singular or plural form is appropriately selected. The present disclosure is not limited to the singular or plural form, and an element expressed in the singular form can include multiple elements, and an element expressed in the plural form can include a single element.

[0424] It should be understood that the embodiments disclosed in the specification and the drawings should be considered only as descriptive and not for the purpose of limitation. That is, those of ordinary skill in the art will understand that various changes can be made in form and detail based on the technical concept of the present disclosure. In addition, when necessary, the embodiments of the present disclosure can be combined to be implemented. For example, a part of an embodiment of the present disclosure is combined with a part of another embodiment of the present disclosure. The embodiments of the present disclosure can also be applied to other communication systems, such as LTE systems, 5G or NR systems, etc., and various modifications can be made based on the technical concept of the embodiments of the present disclosure.

[0425] Although the present disclosure has been described with various embodiments, various changes and modifications can be suggested to those skilled in the art. The present disclosure is intended to embrace these changes and modifications that fall within the scope of the appended claims.

Claims

1. A method for a source base station to perform Dual Active Protocol Stack (DAPS) handover in a wireless communication system, the method comprising: Sending a handover request to a target base station, the handover request including a first indicator indicating a request for the DAPS handover for a bearer; Receiving a handover request confirmation message from the target base station, the handover request confirmation message including a Radio Resource Control (RRC) reconfiguration message for a User Equipment (UE) and a second indicator indicating whether the DAPS handover for the bearer is accepted or not; And Sending the RRC reconfiguration message received in the handover request confirmation message to the UE, Wherein, when the second indicator indicates that the DAPS handover is accepted by the target base station, the RRC reconfiguration message includes the DAPS configuration information of the bearer, and Wherein, the DAPS handover indicates a handover process that maintains the connection between the source base station and the UE after the UE receives the RRC reconfiguration message and until the UE releases the source base station after successful random access from the UE to the target base station.

2. The method according to claim 1, wherein, When the second indicator indicates that the DAPS handover is not accepted by the target base station, the RRC reconfiguration message includes the bearer configuration information required for the UE to perform other handovers.

3. A source base station for performing Dual Active Protocol Stack (DAPS) handover in a wireless communication system, the source base station comprising: A transceiver; And At least one processor, the at least one processor being connected to the transceiver and configured to: Send a handover request to a target base station, the handover request including a first indicator indicating a request for the DAPS handover for a bearer; Receive a handover request confirmation message from the target base station, the handover request confirmation message including a Radio Resource Control (RRC) reconfiguration message for a User Equipment (UE) and a second indicator indicating whether the DAPS handover for the bearer is accepted or not; And Send the RRC reconfiguration message received in the handover request confirmation message to the UE, Wherein, when the second indicator indicates that the DAPS handover is accepted by the target base station, the RRC reconfiguration message includes the DAPS configuration information of the bearer, and Wherein, the DAPS handover indicates a handover process that maintains the connection between the source base station and the UE after the UE receives the RRC reconfiguration message and until the UE releases the source base station after successful random access from the UE to the target base station.

4. The source base station according to claim 3, wherein, When the second indicator indicates that the DAPS handover is not accepted by the target base station, the RRC reconfiguration message includes the bearer configuration information required for the UE to perform other handovers.

5. A method for a target base station to perform Dual Active Protocol Stack (DAPS) handover in a wireless communication system, the method comprising: Receive a handover request from a source base station, the handover request including a first indicator indicating a request for a bearer for which the DAPS handover is requested; And Send a handover request confirmation message to the source base station, the handover request confirmation message including a radio resource control (RRC) reconfiguration message for a user equipment (UE) and a second indicator indicating whether the DAPS handover for the bearer is accepted or not accepted, Wherein, in the case where the second indicator indicates that the DAPS handover is accepted by the target base station, the RRC reconfiguration message includes the DAPS configuration information of the bearer, and Wherein, the DAPS handover indicates a handover process that maintains the connection between the source base station and the UE after the UE receives the RRC reconfiguration message and until the UE releases the source base station after successful random access of the UE to the target base station.

6. The method according to claim 5, wherein In the case where the second indicator indicates that the DAPS handover is not accepted by the target base station, the RRC reconfiguration message includes the bearer configuration information required for the UE to perform other handovers.

7. A target base station for performing a dual active protocol stack (DAPS) handover in a wireless communication system, the target base station comprising: A transceiver; And At least one processor, the at least one processor being connected to the transceiver and configured to: Receive a handover request from a source base station, the handover request including a first indicator indicating a request for a bearer for which the DAPS handover is requested; And Send a handover request confirmation message to the source base station, the handover request confirmation message including a radio resource control (RRC) reconfiguration message for a user equipment (UE) and a second indicator indicating whether the DAPS handover for the bearer is accepted or not accepted, Wherein, in the case where the second indicator indicates that the DAPS handover is accepted by the target base station, the RRC reconfiguration message includes the DAPS configuration information of the bearer, and Wherein, the DAPS handover indicates a handover process that maintains the connection between the source base station and the UE after the UE receives the RRC reconfiguration message and until the UE releases the source base station after successful random access of the UE to the target base station.

8. The target base station according to claim 7, wherein, In the case where the second indicator indicates that the DAPS handover is not accepted by the target base station, the RRC reconfiguration message includes the bearer configuration information required for the UE to perform other handovers.

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