Apparatus and method for preventing potential error that can occur when performing daps handover in next-generation mobile communication system

Abstract

This disclosure relates to: communication technologies for the convergence of IoT technology and fifth-generation (5G) or pre-5G communication systems, for supporting higher data transmission rates than fourth-generation (4G) communication systems such as LTE; and systems for use therein. Based on 5G communication technology and IoT-related technologies, this disclosure can be applied to smart services (e.g., smart homes, smart buildings, smart cities, smart cars or connected cars, healthcare, digital education, retail businesses, security and safety-related services, etc.). According to various embodiments of this disclosure, methods and apparatus can be provided for preventing potential errors that may occur during DAPS handover.

Description

Technical Field

[0001] This disclosure relates to the operation of terminals and base stations in mobile communication systems, and to errors that may occur when performing efficient handover methods (e.g., Dual Active Protocol Stack (DAPS) handover methods) that do not cause a pause in data transmission or reception during handover. This disclosure also relates to methods and apparatus capable of resolving errors in next-generation mobile communication systems. Background Technology

[0002] To meet the increased demand for wireless data services since the deployment of fourth-generation (4G) communication systems, efforts have been made to develop improved fifth-generation (5G) or pre-5G communication systems. Therefore, 5G or pre-5G communication systems are also referred to as "beyond 4G networks" or "post-LTE" systems.

[0003] 5G communication systems are considered to be implemented in ultra-high frequency (millimeter wave (mmWave)) bands (e.g., the 60 GHz band) to achieve higher data rates. To reduce radio wave propagation loss and increase transmission distance in ultra-high frequency bands, beamforming, massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and massive MIMO technologies are discussed in 5G communication systems.

[0004] In addition, in 5G communication systems, development is underway to improve system networks based on advanced small cells, cloud radio access networks (cloud RAN), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multipoint (CoMP), and receiver interference cancellation.

[0005] In 5G systems, hybrid FSK (Frequency Shift Keying) and QAM (Four-way Amplitude Modulation) modulation and sliding window superposition coding (SWSC) have also been developed as advanced coding and modulation (ACM), as well as filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) as advanced access technologies.

[0006] Compared to traditional 4G systems, 5G systems are considering supporting a wider range of services. For example, the most representative services may include ultra-wideband mobile communication services (enhanced mobile broadband (eMBB)), ultra-reliable / low-latency communication services (ultra-reliable and low-latency communication (URLLC)), massive device-to-device communication services (massive machine-type communication (mMTC)), and next-generation broadcast services (evolved multimedia broadcast / multicast service (eMBMS)). Systems providing URLLC services can be called URLLC systems, and systems providing eMBB services can be called eMBB systems. The terms "service" and "system" are used interchangeably.

[0007] Among these services, URLLC, as a new service under consideration in 5G systems, needs to meet the requirements of ultra-high reliability (e.g., a packet error rate of approximately 10⁻⁵) and low latency (e.g., approximately 0.5 milliseconds) compared to existing 4G systems. To meet these stringent requirements, URLLC services may need to apply shorter transmission time intervals (TTIs) than eMBB services, and various operational schemes for this service are under investigation.

[0008] The internet, a human-centric network of connections where humans generate and consume information, is now evolving into the Internet of Things (IoT), in which distributed entities (such as things) exchange and process information without human intervention. The Internet of Everything (IoE), combining IoT technology with cloud server connectivity and big data processing technologies, has emerged. As essential technological elements for realizing IoT, such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, and security technology, sensor networks, machine-to-machine (M2M) communication, and machine-type communication (MTC) have recently been studied.

[0009] Such an IoT environment can provide intelligent Internet of Things (IT) services, creating new value for human life by collecting and analyzing data generated between connected objects. Through the integration and combination of existing information technology (IT) and various industrial applications, IoT can be applied to a wide range of fields, including smart homes, smart buildings, smart cities, smart or connected cars, smart grids, healthcare, smart appliances, and advanced medical services.

[0010] Correspondingly, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as sensor networks, machine-type communication (MTC), and machine-to-machine (M2M) communication can be implemented using beamforming, MIMO, and array antennas. Cloud radio access networks (cloud RAN), as an application of the aforementioned big data processing technologies, can also be considered an example of the integration of 5G and IoT technologies. Summary of the Invention

[0011] Technical issues

[0012] In next-generation mobile communication systems, the Dual Active Protocol Stack (DAPS) handover method can be supported as an efficient handover approach to support services with no data interruption and low transmission latency. However, a method may be needed to analyze and resolve potential problems when the base station and terminal execute the DAPS handover method.

[0013] The technical topics pursued in this disclosure may not be limited to those described above, and other technical topics not mentioned will be clearly understood by those skilled in the art from the following description.

[0014] Technical solution

[0015] According to an embodiment for addressing the above-mentioned problem, a method performed by a terminal of a wireless communication system may include: receiving from a source base station a handover command message indicating a dual active protocol stack (DAPS) handover for at least one bearer; and before the DAPS handover is completed, receiving from the source base station a Media Access Control Protocol Data Unit (MAC PDU) including a MAC sub-PDU, the MAC sub-PDU including a logical channel identifier of a bearer not configured for DAPS handover, and discarding the MAC sub-PDU including the logical channel identifier of the bearer not configured for DAPS handover.

[0016] In addition, the method may also include sending data to or receiving data from the source base station through a protocol layer device corresponding to at least one bearer configured for DAPS handover at a time point up to the completion of the DAPS handover.

[0017] In addition, the method may also include generating a protocol layer device for a target base station corresponding to at least one bearer configured for DAPS handover, and performing a random access procedure with the target base station by using the protocol layer device for the target base station.

[0018] Furthermore, the method may also include: suspending uplink data transmission to the source base station via a protocol layer device corresponding to at least one bearer configured for DAPS handover, provided that a first condition is met; and sending uplink data to the target base station via a protocol layer device for the target base station.

[0019] In addition, the first condition may include at least one of the following: the random access procedure with the target base station is successfully completed; uplink resources are initially allocated from the target base station; uplink transmission resources are included in the handover command message when a handover indicating that no random access procedure is required is required; the handover command message indicates a two-step random access procedure; and the handover command message indicates a two-step random access procedure and the transmission resources configured for data transmission in the two-step random access procedure have a value greater than a pre-configured value.

[0020] Furthermore, the method may also include, upon satisfying a second condition, suspending downlink data reception from the source base station via a protocol layer device corresponding to at least one bearer configured for DAPS handover, and receiving downlink data from the target base station via a protocol layer device for the target base station.

[0021] In addition, the second condition may include at least one of the following: receiving a random access response message from the target base station, sending a handover completion message to the target base station, completing a random access procedure with the target base station and initially sending uplink data to the target base station, initially allocating uplink resources from the target base station, and the expiration of a pre-configured timer.

[0022] Furthermore, according to embodiments used to solve the above problems, the terminal of the wireless communication system may include a transceiver, and

[0023] The controller, connected to the transceiver, is configured to receive a handover command message from the source base station indicating a dual active protocol stack (DAPS) handover for at least one bearer, and before the DAPS handover is completed, receive from the source base station a Media Access Control Protocol Data Unit (MAC PDU) including a MAC sub-PDU, the MAC sub-PDU including a logical channel identifier for a bearer not configured for DAPS handover, and discard the MAC sub-PDU including the logical channel identifier for the bearer not configured for DAPS handover.

[0024] Beneficial effects

[0025] This disclosure proposes a DAPS handover method as an efficient handover approach. When performing handover in a next-generation mobile communication system, this method prevents data interruption due to handover, thereby supporting service without data interruption. Furthermore, it presents methods for analyzing potential problems when implementing the DAPS handover method and for resolving these problems.

[0026] The beneficial effects that can be obtained from this disclosure are not limited to those described above. Other effects not mentioned will be clearly understood by those skilled in the art to which this disclosure pertains from the following description. Attached Figure Description

[0027] Figure 1a The structure of an LTE system according to an embodiment of this disclosure is shown.

[0028] Figure 1b The radio protocol structure of an LTE system according to an embodiment of this disclosure is shown.

[0029] Figure 1c The structure of a next-generation mobile communication system according to an embodiment of this disclosure is shown.

[0030] Figure 1d The radio protocol structure of a next-generation mobile communication system according to an embodiment of this disclosure is shown.

[0031] Figure 1e The process of a terminal, according to an embodiment of the present disclosure, transferring from RRC idle mode to RRC connected mode and establishing a connection with the network is illustrated.

[0032] Figure 1f The signaling process for performing a handover according to an embodiment of this disclosure is illustrated.

[0033] Figure 1g The specific operation of a handover method for reducing data interruption time caused by handover, according to a first embodiment of the present disclosure, is shown.

[0034] Figure 1h The specific operation of a handover method for reducing data interruption time caused by handover, according to a second embodiment of the present disclosure, is shown.

[0035] Figure 1a The structure of a PDCP layer entity applied to a DAPS switching method according to a second embodiment of the present disclosure and a method for applying the structure are shown.

[0036] Figure 1ib The structure of a PDCP layer entity applied to a DAPS switching method according to a second embodiment of the present disclosure and a method for applying the structure are shown.

[0037] Figure 1j An embodiment of the present disclosure is shown in which a method carrying specific configuration information is applied when the DAPS switching method is configured.

[0038] Figure 1jaaA method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for the SRB, the bearer configured with the DAPS handover method, or the bearer not configured with the DAPS handover method.

[0039] Figure 1 jab A method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0040] Figure 1jba A method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0041] Figure 1jbb A method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0042] Figure 1jca A method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0043] Figure 1jcbA method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0044] Figure 1jda A method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0045] Figure 1jdb A method is shown in which a terminal that has received a message, when an RRCReconfiguration message or an RRCConnectionReconfiguration message indicates a DAPS handover method corresponding to a second embodiment of this disclosure for each bearer, operates the protocol layer entity of a different bearer for an SRB, a bearer configured with a DAPS handover method, or a bearer not configured with a DAPS handover method.

[0046] Figure 1k Terminal operation according to an embodiment of this disclosure is illustrated.

[0047] Figure 11 A method for processing received data when receiving data (e.g., MAC PDU) in a MAC layer entity of a base station or terminal, according to embodiments of the present disclosure, is illustrated.

[0048] Figure 1m This illustrates a problem that may occur in a terminal when performing the DAPS switching method according to embodiments of this disclosure.

[0049] Figure 1n This is a block diagram illustrating the structure of a terminal according to an embodiment of the present disclosure.

[0050] Figure 1o A block diagram configuration of a TRP in a wireless communication system according to an embodiment of the present disclosure is shown. Detailed Implementation

[0051] The operating principles of this disclosure will be described in detail below with reference to the accompanying drawings. In the following description of this disclosure, detailed descriptions of known functions or configurations incorporated herein will be omitted where it is determined that such description might unnecessarily obscure the subject matter of this disclosure. The terminology described below is defined in consideration of the functions in this disclosure and may vary depending on the user, the user's intent, or habits. Therefore, the definitions of terminology should be based on the entire contents of this specification. Embodiments of this disclosure will be described below with reference to the accompanying drawings.

[0052] In the following description, for convenience, terms used to identify access nodes, network entities, messages, interfaces between network entities, and various identification information are used illustratively. Therefore, this disclosure is not limited to the terms used below, and other terms relating to the subject matter with equivalent technical meaning may be used.

[0053] In the following description of this disclosure, for ease of description, the terms and names defined in the 3GPP LTE standard will be used. However, this disclosure is not limited to these terms and names and can be applied in the same manner to systems conforming to other standards. In this disclosure, the term "eNB" may be used interchangeably with the term "gNB". That is, a base station described as "eNB" may indicate "gNB".

[0054] This disclosure proposes a non-interrupted handover method that can minimize or reduce the data interruption time caused by handover in next-generation mobile communication systems to 0ms.

[0055] Specifically, the efficient handover method proposed in this disclosure may have one or more of the following features. Furthermore, regarding the efficient handover method proposed in this disclosure (e.g., the Dual Active Protocol Stack (DAPS) handover method), different handover methods can be applied to different bearers.

[0056] When a terminal performing data transmission or reception (uplink or downlink data transmission and reception) to or from a source base station via each protocol layer entity (PHY entity, MAC layer entity, RLC layer entity, or PDCP layer entity) of multiple first bearers receives a handover command message (e.g., a handover command message or a Radio Resource Control (RRC) reconfiguration message), the terminal can, based on the configuration information included in the handover command message, configure a new protocol layer entity (e.g., with the same bearer identifier) ​​for a new second bearer corresponding to the protocol layer entity of the first bearer (i.e., with the same bearer identifier) ​​using the bearer (e.g., the first bearer) configured with the indicator in the handover command message indicating the execution of the DAPS handover method. Furthermore, the terminal performs data transmission or reception (uplink or downlink data transmission and reception) without interruption but rather continues data transmission or reception (uplink or downlink data transmission and reception) to or from the source base station via multiple first bearers. In the above description, the first and second bearers can receive or transmit data through a single PDCP layer entity, and the data of the first bearer can be processed within the PDCP layer entity using the source base station's security key, security algorithm (encryption, decryption, or integrity protection or verification), or header compression protocol (or context). Alternatively, the data of the second bearer can be processed within the PDCP layer entity using the target base station's security key, security algorithm (encryption, decryption, or integrity protection or verification), or header compression protocol (or context). The aforementioned PDCP layer entity is proposed as the structure of the second PDCP layer entity and is described in detail in the following disclosure.

[0057] -Based on the bearer configuration information or multiple protocol layer entity information included in the handover command message, after receiving the handover command message, multiple newly configured protocol layer entities (PHY layer entity, MAC layer entity, RLC layer entity or PDCP layer entity) of the second bearer are configured to send data to the target base station and receive data from the target base station.

[0058] - In the above description, the terminal can perform a random access procedure to the target base station by using multiple protocol layer entities of the second bearer (e.g., MAC layer entities), while simultaneously performing data transmission or reception (uplink or downlink data transmission and reception) to or from the source base station by using multiple protocol layer entities of the first bearer. In the above description, 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., contention resolution of MAC CE or reception of uplink transmission resources), etc.

[0059] - In the above description, when the terminal performs data transmission or reception to or from the source base station by using multiple protocol layer entities of the first bearer, it can complete the random access procedure to the target base station by using multiple protocol layer entities of the second bearer (e.g., MAC layer entities), and can send a handover completion message to the target base station by using multiple protocol layer entities of the second bearer.

[0060] - In the above description, when the terminal performs data transmission or reception to or from the source base station by using multiple protocol layer entities of the first bearer, it can complete the random access procedure to the target base station by using multiple protocol layer entities of the second bearer (e.g., MAC layer entities), and can send a handover completion message to the target base station by using multiple protocol layer entities of the second bearer, and perform data transmission and reception (uplink or downlink).

[0061] - In the above description, when the random access procedure to the target base station is successfully completed, the terminal can suspend uplink data transmission to the source base station and hand over uplink data transmission by using multiple protocol layer entities of the first bearer, so as to send uplink data to the target base station through the second bearer.

[0062] - In the above description, when a handover command message is received, the terminal can continuously transmit or receive data to or from the source base station (uplink or downlink data transmission and reception) by using multiple protocol layer entities of the first bearer, and perform a random access procedure to the target base station by using multiple protocol layer entities of the second bearer. Upon successful completion of the random access procedure, the terminal can suspend uplink data transmission to the source base station by using multiple protocol layer entities of the first bearer, and perform uplink data transmission to the target base station by using only the protocol layer entities of the second multiple bearer. The terminal can continuously receive downlink data from the source base station by using multiple protocol layer entities of the first bearer, and also continuously receive downlink data from the target base station by using multiple protocol layer entities of the second bearer. Furthermore, in the above description, when it is necessary to send retransmissions, HARQ retransmissions, HARQ feedback, RLC control data, or PDCP control data to the source base station via the first bearer, the terminal can perform transmissions to the source base station.

[0063] In the above description, the first and second bearers can be configured as a structure of a second PDCP layer entity. In this structure, the first bearer (e.g., an RLC layer entity, MAC layer entity, or PHY layer entity) and the second bearer (e.g., an RLC layer entity, MAC layer entity, or PHY layer entity) for the source base station can all be connected to a single PDCP layer entity. Uplink data can be transmitted via one of the first and second bearers using the PDCP layer entity. That is, uplink data can be transmitted via the first bearer before the terminal performs and successfully completes a random access procedure to the target base station. If the terminal has already performed and successfully completed a random access procedure to the target base station, the terminal can suspend data transmission via the first bearer and perform a handover to transmit uplink data to the target base station via the second bearer. However, in the second PDCP layer entity structure, the terminal can receive downlink data from either the source or target base station via either the first or second bearer.

[0064] In this disclosure, a Dual Active Protocol Stack (DAPS) handover method and device are proposed as the aforementioned efficient handover method.

[0065] Furthermore, errors that may occur in the aforementioned DAPS switching method are described, and methods to resolve these errors are proposed.

[0066] Figure 1a The structure of an LTE system according to an embodiment of this disclosure is shown.

[0067] refer to Figure 1a The radio access network of an LTE system may include next-generation base stations (evolved Node B, hereinafter referred to as ENB, Node B, or base station) 1a-05, 1a-10, 1a-15, and 1a-20, a Mobility Management Entity (MME) 1a-25, and a Service Gateway (S-GW) 1a-30. User equipment (hereinafter referred to as UE or terminal) 1a-35 may access external networks via ENB 1a-05 to 1a-20 and S-GW 1a-30.

[0068] exist Figure 1aIn this context, ENBs 1a-05 to 1a-20 correspond to existing Node Bs in UMTS. ENBs 1a-05 to 1a-20 can connect to Terminal 1a-35 via radio channels and can perform more complex functions compared to existing Node Bs. All user services, including real-time services such as Voice over IP (VoIP) via the Internet Protocol, can be served through shared channels in the LTE system. Therefore, an entity may be needed to organize the state information of Terminal 1a-35 (such as buffer state information, available transmission power state information, and channel state information) and perform scheduling, and ENBs 1a-05 to 1a-20 can operate as such an entity. One of ENBs 1a-05 to 1a-20 typically controls multiple cells. For example, the LTE system uses radio access technologies such as Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM) on a 20MHz bandwidth to achieve a data rate of 100Mbps. Furthermore, Adaptive Modulation and Coding (hereinafter referred to as AMC) is applied in the LTE system to determine the modulation scheme and channel coding rate based on the channel state of Terminal 1a-35. S-GW 1a-30 is the entity used to provide data bearers and generates or removes data bearers under the control of MME 1a-25. MME 1a-25 is the entity used to perform mobility management functions and various control functions on terminal 1a-35 and is connected to multiple base stations 1a-05 to 1a-20.

[0069] Figure 1b The radio protocol structure of an LTE system according to an embodiment of this disclosure is shown.

[0070] Reference Figure 1b The radio protocol architecture of an LTE system may include Packet Data Convergence Protocol (PDCP) layers 1b-05 and 1b-40, Radio Link Control (RLC) layers 1b-10 and 1b-35, and Media Access Control (MAC) layers 1b-15 and 1b-30, respectively, for terminals and ENBs. PDCP layer 1b-05 or 1b-40 performs operations such as IP header compression / decompression. The main functions of PDCP layer 1b-05 or 1b-40 are summarized below.

[0071] -Header compression and decompression: ROHC only

[0072] -Transmission of user data

[0073] - Sequential delivery of upper-layer PDUs during PDCP reconstruction in RLC AM

[0074] - Separate bearer for DC (RLC AM only): PDCP PDU routing for transmission and PDCP PDU reordering for reception.

[0075] - Repeated detection of low-level SDUs during PDCP reconstruction of RLC AM

[0076] - For DC-based separate bearers, PDCP SDU retransmission during handover; and for RLC AM, PDCP PDU retransmission during PDCP data recovery.

[0077] - Encryption and decryption

[0078] - Timer-based SDUs are dropped in the uplink.

[0079] Radio Link Control (RLC) layer 1b-10 or 1b-35 can perform ARQ operations, etc., by reconfiguring PDCP protocol packet data units (PDUs) to have an appropriate size. The main functions of RLC layer 1b-10 or 1b-35 are summarized below.

[0080] -Transmission of upper-layer PDUs

[0081] - Error correction via ARQ (for AM data transmission only)

[0082] - Cascading, segmentation, and reassembly of RLC SDUs (for UM and AM data transmission only)

[0083] - Resegmentation of RLC data PDUs (for AM data transmission only)

[0084] - Reordering of RLC data PDUs (for UM and AM data transfer only)

[0085] - Duplicate detection (only for UM and AM data transfers)

[0086] - Protocol error detection (for AM data transmission only)

[0087] -RLC SDU discard (only for UM and AM data transfers)

[0088] -RLC Reconstruction

[0089] MAC layer 1b-15 or 1b-30 connects to multiple RLC layer entities configured for a terminal and performs operations such as multiplexing RLCPDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC layer 1b-15 or 1b-30 are summarized below.

[0090] Mapping between logical channels and transport channels

[0091] - Multiplexing MAC SDUs belonging to one or different logical channels into a transport block (TB) delivered to the physical layer on the transport channel / Demultiplexing MAC SDUs belonging to one or different logical channels from a transport block (TB) delivered by the physical layer on the transport channel.

[0092] - Scheduling Information Report

[0093] - Error correction via HARQ

[0094] Priority processing between logical channels of a UE

[0095] Priority processing among UEs is performed through dynamic scheduling.

[0096] -MBMS service identifier

[0097] -Transmission format selection

[0098] -filling

[0099] Physical layer 1b-20 or 1b-25 performs the following operations: performs channel coding and modulation on upper-layer data to generate OFDM symbols and transmits OFDM symbols via a wireless channel, or performs demodulation and channel decoding on OFDM symbols received via a wireless channel and delivers OFDM symbols to the upper layer.

[0100] Figure 1c The structure of a next-generation mobile communication system according to an embodiment of this disclosure is shown.

[0101] refer to Figure 1c The radio access network for next-generation mobile communication systems (hereinafter referred to as NR or 5G communication systems) includes a new radio node B (hereinafter referred to as NR gNB, NR base station, or gNB) 1c-10 and a new radio core network (NR CN) 1c-05. User equipment (new radio user equipment, hereinafter referred to as NR UE or terminal) 1c-15 accesses external networks via NR gNB 1c-10 and NR CN 1c-05.

[0102] exist Figure 1cIn this context, the NR gNB 1c-10 corresponds to the Evolved Node B (ENB) of a traditional LTE system. The NR gNB 1c-10 can connect to the NR UE 1c-15 via a radio channel and can provide better service than the existing Node B. In next-generation mobile communication systems, all user service data can be served through a shared channel, thus requiring an entity to organize the buffer state information, available transmission power state information, and channel state information of the UE 1c-15 and perform scheduling; the NR gNB 1c-10 operates as such an entity. A single NR gNB 1c-10 typically controls multiple cells. Compared to existing LTE systems, next-generation mobile communication systems can have bandwidth equal to or greater than the maximum bandwidth of existing LTE systems to achieve ultra-high data rates. Orthogonal Frequency Division Multiplexing (OFDM) can be used as the radio access technology, and beamforming technology can be combined with it. Furthermore, next-generation mobile communication systems employ Adaptive Modulation and Coding (AMC) to determine the modulation scheme and channel coding rate based on the channel state of the terminal 1c-15. The NR CN 1c-05 performs functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. The NR CN 1c-05 is an entity that performs not only mobility management functions for the terminal 1c-15 but also various control functions, and it connects to multiple base stations 1c-10. Furthermore, the next-generation mobile communication system can link with existing LTE systems, and the NR CN 1c-05 connects to the MME 1c-25 via a network interface. The MME 1c-25 connects to the ENB 1c-30, which serves as a legacy base station.

[0103] Figure 1d The radio protocol structure of a next-generation mobile communication system according to an embodiment of this disclosure is shown.

[0104] refer to Figure 1d The radio protocols of next-generation mobile communication systems may include NR 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 terminals and NR base stations, respectively.

[0105] The main functions of NR SDAP layer 1d-01 or 1d-45 may include some of the following functions.

[0106] -Transmission of user plane data

[0107] Mapping between QoS flows and DRB for both DL and UL

[0108] - Mark QoS flow IDs in both DL and UL groups

[0109] - Reflect QoS flow to UL SDAP PDU to DRB mapping.

[0110] Regarding SDAP layer entities, for each PDCP layer entity, each bearer, or each logical channel, the terminal can be configured via RRC messages to use either the SDAP layer entity header or its functionality. When the SDAP header is configured, the 1-bit NAS reflection QoS indicator and the 1-bit AS reflection QoS indicator in the SDAP header can instruct the terminal to update or reconfigure uplink and downlink QoS flow and data bearer mapping information. The SDAP header may include QoS flow ID information indicating QoS. QoS information can be used for data processing priority, scheduling information, etc., to support seamless service.

[0111] The main functions of NR PDCP layer 1d-05 or 1d-40 may include some of the following functions.

[0112] -Header compression and decompression: ROHC only

[0113] -Transmission of user data

[0114] - Sequential delivery of upper-layer PDUs

[0115] -Disordered delivery of upper-layer PDUs

[0116] - Reordering of received PDCP PDUs

[0117] -Repetition detection of low-level SDUs

[0118] -PDCP SDU retransmission

[0119] - Encryption and decryption

[0120] - Timer-based SDUs are dropped in the uplink.

[0121] The reordering function of the NR PDCP layer entity can instruct the reordering of PDCP PDUs received from lower layers based on the PDCP sequence number (SN). The reordering function can include delivering data to upper layers in the reordered order, or delivering data directly regardless of order, recording lost PDCP PDUs by reordering received PDCP PDUs, reporting the status information of lost PDCP PDUs to the transmitter, and requesting retransmission of lost PDCP PDUs.

[0122] The main functions of NR RLC layer 1d-10 or 1d-35 may include some of the following functions.

[0123] -Transmission of upper-layer PDUs

[0124] - Sequential delivery of upper-layer PDUs

[0125] -Disordered delivery of upper-layer PDUs

[0126] - Error correction via ARQ

[0127] Cascading, segmentation, and reassembly of RLC SDUs

[0128] - Resegmentation of RLC data PDUs

[0129] - RLC data PDU reordering

[0130] -Duplicate detection

[0131] -Protocol error detection

[0132] -RLC SDU discard

[0133] -RLC Reconstruction

[0134] The sequential delivery function of an NR RLC layer entity can instruct the sequential delivery of RLC SDUs received from a lower layer to an upper layer. Sequential delivery functions may include: reassembling and delivering the reassembled RLC SDU when multiple RLC SDUs segmented from a single RLC SDU are received; reordering received RLC PDUs based on their RLC serial number (SN) or PDCP serial number (SN); recording lost RLC PDUs by reordering received RLC PDUs; reporting the status information of lost RLC PDUs to the transmitter; requesting retransmission of lost RLC SDUs; delivering RLC SDUs to the upper layer sequentially only before the lost RLC SDU when a lost RLC SDU exists; delivering all RLC SDUs received before the timer started sequentially to the upper layer when a predetermined timer expires, even if a lost RLC SDU exists; or delivering all RLC SDUs received up to the current time sequentially to the upper layer when a predetermined timer expires, even if a lost RLC SDU exists. Furthermore, the NR RLC layer entity can process RLC PDUs sequentially according to their reception order (based on arrival order, regardless of sequence number or order number) and can deliver RLC PDUs to the PDCP entity regardless of their order (out-of-order delivery). In the case of fragmentation, the NR RLC layer entity can receive segments stored in a buffer or those to be received in the future, reconfigure the segments into a complete RLC PDU, process the RLCPDU, and then deliver it to the PDCP device. The NR RLC layer entity may not include concatenation functionality, and this functionality can be performed in the NRMAC layer or replaced by multiplexing functionality of the NR MAC layer.

[0135] The non-sequential function (out-of-order delivery) of NR RLC layer entities is the function of directly transmitting RLC SDUs received from lower layers to upper layers, regardless of the order of RLC SDUs. It may include the function of reassembling and transmitting RLC PDUs when an original RLC SDU is divided into multiple RLCSDUs and then received, as well as the function of storing the RLC SN or PDCPSN of the received RLC PDUs, reordering RLC PDUs, and recording lost RLC PDUs.

[0136] NR MAC layer 1d-15 or 1d-30 can connect to multiple NR RLC layers configured for a single terminal, and the main functions of the NR MAC layer can include some of the following functions.

[0137] Mapping between logical channels and transport channels

[0138] - MAC SDU multiplexing / demultiplexing

[0139] - Scheduling Information Report

[0140] - Error correction via HARQ

[0141] Priority processing between logical channels of a UE

[0142] Priority processing among UEs is performed through dynamic scheduling.

[0143] -MBMS service identifier

[0144] -Transmission format selection

[0145] -filling

[0146] The NR PHY layer 1d-20 or 1d-25 can perform the following operations: perform channel coding and modulation on the upper layer data to generate OFDM symbols and transmit the OFDM symbols via the radio channel, or perform demodulation and channel decoding on the OFDM symbols received via the radio channel and deliver the OFDM symbols to the upper layer.

[0147] Figure 1e The process of a terminal, according to an embodiment of the present disclosure, transferring from RRC idle mode to RRC connected mode and establishing a connection with the network is illustrated.

[0148] exist Figure 1e In this system, when a terminal configured to send and receive data in RRC connection mode fails to send or receive data for a predetermined reason or within a predetermined time, the base station can send an RRCConnectionRelease message to the terminal to allow it to hand over to RRC idle mode (Operation 1e-01). Subsequently, when a currently unconnected terminal (hereinafter referred to as an idle mode UE) has data to send, the terminal can execute an RRC connection establishment procedure with the base station. The terminal establishes reverse transmission synchronization with the base station through a random access procedure and sends an RRCConnectionRequest message to the base station (Operation 1e-05). The RRCConnectionRequest message includes the terminal's identifier, the reason for establishment, etc. The base station sends an RRCConnectionSetup message to allow the terminal to establish an RRC connection (Operation 1e-10).

[0149] The message includes configuration information for each service / bearer / RLC layer, each logical channel, or each bearer, and may include information on whether ROHC is used for each bearer / logical channel, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information from the base station instructing the terminal to report PDCP status), drb-ContinueROHC information (which corresponds to configuration information indicating that ROHC configuration information is maintained and used without change, and may be sent to be included in the PDCP layer entity configuration information (pdcp-config), etc. Furthermore, the message includes RRC connection configuration information, etc. The bearer used for RRC connection is called the Signaling Radio Bearer (SRB) and is used for sending and receiving RRC messages as control messages between the terminal and the base station.

[0150] A terminal that has been configured with an RRC connection sends an RRCConnectionSetupComplete message (Operation 1e-15) to the base station. This message includes control messages, such as a Service Request message for the bearer to be configured with a predetermined service by the terminal requesting the MME / AMF. The base station sends the Service Request message included in the RRCConnectionSetupComplete message to the MME or AMF (Operation 1e-20), and the MME or AMF determines whether to provide the service requested by the terminal. As a result of this determination, if the service requested by the terminal is to be provided, the MME or AMF sends an Initial Context Setup Request message to the base station (Operation 1e-25). This message includes information such as Quality of Service (QoS) information to be applied in configuring the Data Radio Bearer (DRB) and security-related information (e.g., security keys or security algorithms) to be applied to the DRB.

[0151] Furthermore, when the base station fails to receive terminal capability information from the MME or AMF, the base station can send a terminal capability information request message to the terminal to determine the terminal capability information (Operation 1e-26). When the terminal receives the terminal capability information request message, the terminal can configure and generate a terminal capability information message and report it to the base station (Operation 1e-27). The terminal capability information message may include information about the types of handover methods supported by the terminal. For example, the terminal can report information about its capabilities to the base station via an indicator indicating whether the terminal supports the efficient handover method (i.e., Dual Active Protocol Stack (DAPS)) proposed in this disclosure. When the base station identifies the terminal capability information, when the base station instructs the terminal to handover, for each handover method, the base station can instruct the terminal to handover by defining an indicator that indicates the type of handover to be indicated in the handover command message. For example, the base station can instruct the terminal to handover using the efficient handover method (DAPS handover method) proposed in this disclosure, or it can configure the DAPS handover method for each bearer (DRB or SRB). When the base station configures the DAPS handover method for the terminal, it also instructs other handover methods (e.g., a conditional handover method (configuring multiple target cells and multiple conditions for the terminal, and performing a handover to a target cell when the terminal meets the conditions in the cell selection or reselection process), or a handover method without a random access procedure) to prevent data loss or transmission delays that may occur during handover. The terminal can perform the handover to the target base station according to the handover method indicated in the handover command message.

[0152] To configure security with the terminal, the base station exchanges a SecurityModeCommand message (operation 1e-30) and a SecurityModeComplete message (operation 1e-35). When security configuration is complete, the base station sends an RRCConnectionReconfiguration message (operation 1e-40) to the terminal.

[0153] The message includes configuration information for each service / bearer / RLC layer, each logical channel, or each bearer, and may include information on whether ROHC is used for each bearer / logical channel, ROHC configuration information (e.g., ROHC version, initial information, etc.), statusReportRequired information (information from the base station instructing the terminal to report PDCP status), drb-ContinueROHC information (which corresponds to configuration information indicating that ROHC configuration information is maintained and used without change, and may be sent to be included in the PDCP layer entity configuration information (pdcp-config), etc. Furthermore, the message includes RRC connection configuration information, etc. The bearer used for RRC connection is called the Signaling Radio Bearer (SRB) and is used for sending and receiving RRC messages as control messages between the terminal and the base station.

[0154] This message includes configuration information for the DRB, in which user data will be processed. The terminal uses this information to configure the DRB and sends an RRCConnectionReconfigurationComplete message to the base station (Operation 1e-45). The base station, having completed the DRB configuration with the terminal, sends an INITIAL CONTEXT SETUP COMPLETE message to the MME or AMF (Operation 1e-50). The MME or AMF that has received this message can exchange S1 Bearer SETUP and S1 Bearer SETUP RESPONSE messages with the S-GW to configure the S1 bearer (Operations 1e-55 and 1e-60). The S1 bearer refers to the connection configured between the S-GW and the base station for data transmission, corresponding one-to-one with the DRB. Once all the above processes are complete, the terminal sends data to or receives data from the base station through the S-GW (Operations 1e-65 and 1e-70). Therefore, the general data transmission process mainly includes three stages: RRC connection configuration, security configuration, and DRB configuration. In addition, the base station can send an RRC connection reconfiguration message to the terminal to update, add, or change the configuration for predetermined reasons (Operation 1e-75).

[0155] In this disclosure, the bearers may include SRBs and DRBs, where SRBs represent signaling radio bearers and DRBs represent data radio bearers. SRBs are primarily used for sending and receiving RRC messages for RRC layer entities, while DRBs are primarily used for sending and receiving various user layer data. Furthermore, UM DRBs indicate the use of DRBs for RLC layer entities operating in unacknowledged (UM) mode, and AM DRBs indicate the use of DRBs for RLC layer entities operating in acknowledged (AM) mode.

[0156] In this disclosure, a bearer configured with a DAPS handover method can refer to or indicate a bearer having an identifier configured in an RRC message that is included in a list of bearers configured with a DAPS handover method, a bearer having an identifier that is not included in a list of bearers without a DAPS handover method, a bearer having bearer configuration information that includes a DAPS handover method configuration indicator, or a bearer having a DAPS handover method configuration indicator configured in PDCP layer configuration information.

[0157] In this disclosure, a bearer without a configured DAPS handover method may refer to or indicate a bearer having an identifier configured in an RRC message that is not included in the list of bearers with a configured DAPS handover method, a bearer having an identifier included in the list of bearers without a configured DAPS handover method, a bearer having bearer configuration information that does not include a DAPS handover method configuration indicator, or a bearer having a DAPS handover method configuration indicator that is not configured in the PDCP layer configuration information.

[0158] In this disclosure, a source base station may be interpreted as a source cell (primary cell (PCell), special cell (SpCell), or secondary cell (SCell)) or a source cell group (cell group or primary cell group), and a target base station may be interpreted as a target cell (pCell, SpCell, or SCell) or a target cell group (cell group or primary cell group).

[0159] Figure 1f The signaling process for performing a handover according to an embodiment of this disclosure is illustrated.

[0160] Terminal 1f-01, in RRC connected mode, periodically reports cell measurement information (cell measurement report) to the current source base station (source ENB) 1f-02 (operation 1f-05) or when a specific event is met. Source base station 1f-02 determines whether the terminal needs to perform a handover to a neighboring cell based on the measurement information. Handover refers to the technique of changing the source base station 1f-20 providing service to the terminal in connected mode to another base station (or another cell within the same base station). When source base station 1f-02 determines a handover, it requests the handover by sending a handover (HO) request message (e.g., a handover preparation information message) to the new base station (i.e., the target base station (target ENB) 1f-03) that will provide service to terminal 1f-01 (operation 1f-10). When the handover request is accepted, target base station 1f-03 sends an HO request Ack message (e.g., a handover command message) to source base station 1f-02 (operation 1f-15). The source base station 1f-02, having received the message, can send a handover command message (HO command message, or an RRCReconfiguration message included in the DCCH of the HO request Ack message) to the terminal 1f-01 (operation 1f-20). The source base station 1f-02 can extract the handover command (HO command) message from the message received from the target base station 1f-03 and send it to the terminal 1f-01 using the RRC connection reconfiguration message (operation 1f-20).

[0161] In this disclosure, a method is proposed to determine an efficient DAPS handover method by using these two messages when the source base station 1f-02 sends a handover preparation information message (operation 1f-10) and in response, the target base station 1f-03 sends a handover command message to the source base station 1f-02 (operation 1f-15).

[0162] The first embodiment of the method for determining efficient DAPS switching proposed in the above disclosure is as follows.

[0163] In the first embodiment, the entity used to determine the DAPS handover method may be the source base station 1f-02. Furthermore, in the first embodiment, when the source base station 1f-02 requests the DAPS handover method, the target base station 1f-03 may always instruct or execute the DAPS handover method.

[0164] Source base station 1f-02 can define a new indicator in the handover preparation information message to indicate to target base station 1f-03 that it intends to execute the DAPS handover method proposed in this disclosure, and can also request the DAPS handover method. The handover preparation information message may include the current bearer configuration information, security key information, cell group configuration information, terminal capability information, etc. of terminal 1f-01. In the above description, source base station 1f-02 can be implemented to pre-share the capabilities of target base station 1f-03 to pre-identify whether target base station 1f-03 supports the DAPS handover method. In the above description, source base station 1f-02 can indicate to target base station 1f-03 that it intends to execute the DAPS handover method, to notify target base station 1f-03 that it can quickly or early perform early data forwarding, and to instruct target base station 1f-03 so that target base station can prepare to receive and process data forwarding. In the above description, source base station 1f-02 can also request the DAPS handover method for each bearer (DRB or SRB).

[0165] - In the above description, when the target base station 1f-03 receives the handover preparation information message and recognizes that it includes an indicator requesting a DAPS handover method, when configuring the RRCReconfiguration message for instructing the terminal 1f-01 to perform the handover, the target base station 1f-03 can configure the RRCReconfiguration message by including the indicator indicating the DAPS handover method and including bearer configuration information, bearer configuration information, security key information, cell group configuration information, or system information required when the terminal 1f-01 performs the DAPS handover method. Furthermore, the target base station can transmit the RRCReconfiguration message to the source base station 1f-02 by including the RRCReconfiguration message in the DL-DCCH message of the handover command message. In the above description, the target base station 1f-03 can also indicate the DAPS handover method for each bearer (DRB or SRB).

[0166] - In the above description, when a handover command message is received, the source base station 1f-02 can extract the RRCReconfiguration message included in the handover command message, or send the RRCReconfiguration message to the terminal 1f-01 to indicate the handover. In the above description, the source base station 1f-02 can also perform the DAPS handover method for each bearer (DRB or SRB) by identifying the indicated DAPS handover method for each bearer.

[0167] In the above description, the second embodiment of the method for determining efficient DAPS switching proposed in this disclosure is as follows.

[0168] In the second embodiment, the entity used to determine the DAPS handover method may be the target base station 1f-03. Furthermore, in the second embodiment, when the source base station requests a DAPS handover method from the target base station 1f-03 via an indicator, the target base station 1f-03 may refuse or accept the request, or may indicate another handover method to the source base station 1f-02 via a handover command message.

[0169] Source base station 1f-02 can define a new indicator in the handover preparation information message to indicate to target base station 1f-03 that it intends to execute the DAPS handover method proposed in this disclosure, and can also request the DAPS handover method. The handover preparation information message may include the current bearer configuration information, security key information, cell group configuration information, terminal capability information, etc. of terminal 1f-01. In the above description, source base station 1f-02 can be implemented to pre-share the capabilities of target base station 1f-03 to pre-identify whether target base station 1f-03 supports the DAPS handover method. In the above description, source base station 1f-02 can indicate to target base station 1f-03 that it intends to execute the DAPS handover method to notify target base station 1f-03 that it can quickly perform early data forwarding, and can instruct target base station 1f-03 to prepare to receive and process data forwarding. In the above description, source base station 1f-02 can also request the DAPS handover method for each bearer (DRB or SRB).

[0170] - In the above description, when the target base station 1f-03 receives a handover preparation information message and recognizes that it includes an indicator requesting a DAPS handover method, the target base station 1f-03 may reject or accept the request for a DAPS handover method, or indicate another handover method based on whether the target base station 1f-03 can support the DAPS handover method, the amount of current transmission resources, or scheduling. In the above description, the target base station 1f-03 may send a handover command message to the source base station 1f-02 by including an indicator for rejecting the request for a DAPS handover method, an indicator for accepting the request for a DAPS handover method, or an indicator indicating another type of handover method. In the above description, when configuring the RRCReconfiguration message to indicate a handover to terminal 1f-01, target base station 1f-03 can configure the RRCReconfiguration message by including an indicator indicating a DAPS handover method when a DAPS handover request is accepted, an indicator indicating another handover method when a DAPS handover request is rejected, and bearer configuration information, security key information, cell group configuration information, or system information required for the terminal to execute the DAPS handover method or another handover method. Furthermore, the target base station can transmit the configured RRCReconfiguration message to source base station 1f-02 via a DL-DCCH message that includes a handover command message. In the above description, target base station 1f-03 can also indicate the DAPS handover method for each bearer (DRB or SRB).

[0171] In the above description, when a handover command message is received, the source base station 1f-02 can identify whether the request for the DAPS handover method is accepted or rejected by recognizing the indicator included in the handover command message. If the request is accepted, the source base station 1f-02 can also execute the DAPS handover method and indicate the handover by extracting the RRCReconfiguration message included in the handover command message or sending an RRCReconfiguration message to the terminal 1f-01. However, if the indicator included in the handover command message is recognized, and the request for the DAPS handover method is rejected or another handover message is indicated, the source base station 1f-02 can also execute another handover method indicated by the target base station 1f-03. Furthermore, the source base station indicates the handover by extracting the RRCReconfiguration message included in the handover command message or sending an RRCReconfiguration message to the terminal 1f-01. As another method, even if the handover command message does not include a separate indicator, the source base station 1f-02 can identify the type of handover message indicated by the target base station 1f-03 by reading the RRCReconfiguration message included in the handover command message, and can identify whether the request for the DAPS handover method is accepted or rejected. The source base station 1f-02 can also execute the handover method indicated in the RRCReconfiguration message (e.g., the DAPS handover method or another handover method). In the above description, the source base station can also execute the DAPS handover method for each bearer (DRB or SRB) by identifying the indicated DAPS handover method for each bearer.

[0172] In the above description, the third embodiment of the method for determining efficient DAPS switching proposed in this disclosure is as follows.

[0173] In the third embodiment, the entity used to determine the DAPS handover method may be the target base station 1f-03. Furthermore, in the third embodiment, the target base station 1f-03 can identify the capabilities of the terminal 1f-01 and can determine the handover method (e.g., the DAPS handover method) based on whether the target base station can support the DAPS handover method, the amount of current transmission resources, or scheduling.

[0174] Source base station 1f-02 can send a handover preparation information message, including the terminal's current bearer configuration information, security key information, cell group configuration information, and terminal capability information, to request a handover from target base station 1f-03. In the above description, source base station 1f-02 can be implemented to pre-share the capabilities of target base station 1f-03 to identify in advance whether target base station 1f-03 supports the DAPS handover method. Furthermore, when target base station 1f-03 instructs the execution of the DAPS handover method, source base station 1f-02 can quickly or prematurely perform early data forwarding.

[0175] - In the above description, target base station 1f-03 can receive handover preparation information messages and determine the handover method (e.g., DAPS handover method) based on the capability information of terminal 1f-01, whether the target base station supports the DAPS handover method, and the current amount or scheduling of transmission resources. In the above description, when determining the DAPS handover method, target base station 1f-03 can send a handover command message by including an indicator of the DAPS handover method in an indication message. In the above description, when configuring the RRCReconfiguration message to indicate the handover to terminal 1f-01, target base station 1f-03 can configure the RRCReconfiguration message by including an indicator indicating the DAPS handover method when determining the DAPS handover, including an indicator indicating another handover method when determining a handover method other than the DAPS handover method, and including necessary bearer configuration information, bearer configuration information, security key information, cell group configuration information, or system information when terminal 1f-01 executes the DAPS handover method or another handover method. Furthermore, the target base station can transmit the RRCReconfiguration message to the source base station 1f-02 by including the handover command message in the DL-DCCH message. In the above description, the target base station 1f-03 can also indicate the DAPS handover method for each bearer (DRB or SRB).

[0176] In the above description, when a handover command message is received, the source base station 1f-02 can identify the indicator included in the handover command message to determine whether a DAPS handover method has been determined. If a DAPS handover method is indicated, the source base station 1f-02 can also execute the DAPS handover method, and can indicate the handover by extracting the RRCReconfiguration message included in the handover command message or by sending an RRCReconfiguration message to the terminal 1f-01. However, if the indicator included in the handover command message is identified, and the DAPS handover method is not determined or another handover method is indicated, the source base station 1f-02 can also execute another handover method indicated by the target base station 1f-03. Furthermore, the source base station can indicate the handover by extracting the RRCReconfiguration message included in the handover command message or by sending an RRCReconfiguration message to the terminal 1f-01. As another method, when the handover command message does not include a separate indicator, the source base station 1f-02 can identify the type of handover message indicated by the target base station 1f-03 by reading the RRCReconfiguration message included in the handover command message, and can also identify whether a DAPS handover method has been determined. If another handover method is indicated, the source base station 1f-02 can also execute the indicated handover method. In the above description, the source base station 1f-02 can also execute the DAPS handover method for each bearer (DRB or SRB) by identifying the indicated DAPS handover method for each bearer.

[0177] New embodiments can be extended by combining the methods of the first, second, or third embodiments of the method for determining efficient DAPS switching proposed in this disclosure.

[0178] According to embodiments of this disclosure, the base station can indicate the efficient handover method (DAPS handover method) proposed in this disclosure to terminal 1f-01 in an RRCReconfiguration message. Alternatively, the base station can configure the DAPS handover method for each bearer (DRB or SRB) of terminal 1f-01. For example, a new indicator indicating the efficient handover method (DAPS handover method) can be defined in the RRCReconfiguration message in the bearer configuration information, PDCP configuration information, or RLC configuration information for each bearer identifier or logical channel identifier. The base station can use this indicator to indicate an efficient handover message for each bearer or logical channel identifier to terminal 1f-01. When the DAPS handover method is configured for terminal 1f-01, the base station also indicates other handover methods (e.g., conditional handover method (a method that configures multiple target cell configurations and multiple conditions for the terminal, and when the conditions are met during cell selection or reselection, terminal 1f-01 performs a handover to a target cell), or handover without a random access procedure), thereby preventing data loss or transmission delay that may occur during handover. Upon receiving the RRCReconfiguration message, terminal 1f-01 suspends or continues sending or receiving data to or from source base station 1f-02 according to the configured handover method, and starts timer T304 (operation 1f-25). If terminal 1f-01 fails to successfully hand over to target base station 1f-03 within a predetermined time (e.g., when timer T304 expires), T304 causes terminal 1f-01 to return to its original configuration and transition to the RRC idle state. Furthermore, terminal 1f-01 can trigger the RRC connection reconstruction process, and as another method, when an efficient handover method is configured and the connection to source base station 1f-02 is valid, the terminal can also report the handover failure to source base station 1f-02 by performing a fallback. Source base station 1f-02 transmits the sequence number (SN) status of uplink / downlink data for each bearer (e.g., each RLC UM bearer or each RLC AM bearer), and transmits downlink or uplink data to target base station 1f-03 when downlink or uplink data is available (operations 1f-30 and 1f-35). Terminal 1f-01 attempts random access to the target cell indicated by source base station 1f-02 (operation 1f-40). Random access is performed to notify terminal 1f-01 of the handover to target cell 1f-03 and simultaneously match uplink synchronization. For random access, terminal 1f-01 sends a preamble to target cell 1f-03 corresponding to the preamble ID provided by source base station 1f-02 or a randomly selected preamble ID.After sending the preamble and after a time interval corresponding to a specific number of subframes, terminal 1f-01 monitors whether a Random Access Response (RAR) message has been sent from target cell 1f-03. The time interval used to monitor RAR messages is called the Random Access Response window (RAR window). When a RAR message is received during the RAR window (operation 1f-45), terminal 1f-01 sends a handover completion (HO completion) message to target base station 1f-03 via an RRC reconfiguration completion message (operation 1f-55). When a RAR message is successfully received from target base station 1f-03, terminal 1f-01 stops or ends timer T304 (operation 1f-50). In order to hand over the path of the bearer configured for source base station 1f-02, target base station 1f-03 requests the handover of the bearer path from MME, S-GW, or AMF 1f-04 (operations 1f-60 and 1f-65) and notifies source base station 1f-02 to discard the UE context of terminal 1f-01 (operation 1f-70). Furthermore, the target base station 1f-03 can send an RRC message (e.g., an RRCReconfiguration message (operation 1f-71)) to terminal 1f-01 to indicate the release of the connection to the source base station 1f-02 using an indicator. Alternatively, the target base station can also indicate the release of the connection link to the source base station 1f-02 by sending MAC control information, RLC control information, or PDCP control information to terminal 1f-01. Therefore, terminal 1f-01 attempts to receive data from the target base station 1f-03 from the start of the RAR window, and after receiving the RAR message, it begins sending data to or receiving data from the target base station 1f-03 by sending an RRC reconfiguration completion message and receiving downlink or uplink transmission resources (operation 1f-75).

[0179] When base station 1f-02 or 1f-03 configures or instructs terminal 1f-01 on or by using a handover command message or RRC message (e.g., RRCReconfiguration message), the following methods can be applied. In this disclosure, when base station 1f-02 or 1f-03 configures the DAPS handover method for terminal 1f-01, or when terminal 1f-01 has received a handover command message configuring the DAPS handover method from base station 1f-02 or 1f-03, the method obtained by applying one or more of the following methods can be executed.

[0180] Method 1-1: When indicating or configuring a handover to or for terminal 1f-01, the base station (source base station 1f-02, target base station 1f-03, LTE base station, or NR base station) can indicate the DAPS handover method for each bearer by including mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message, and defining an indicator in the DRB-ToAddMod of the SRB-ToAddMod or SRB-ToAddModList or DRB-ToAddModList in the bearer configuration information (dedicated to radio resource configuration or radio bearer). Alternatively, as described above, the base station can indicate the DAPS handover method for each bearer by defining an indicator in the pdcp-config of the SRB-ToAddMod or DRB-ToAddMod. As another approach, as described above, when the LTE base station instructs or configures an LTE RRCReconfiguration message for or to terminal 1f-01, since pdcp-config is not defined in SRB-ToAddMod, but the use of the default pdcp layer entity configuration is defined in LTE, the LTE base station can configure the DAPS handover method for each bearer by defining an indicator about the SRB in SRB-ToAddMod, and can also configure the DAPS handover method for each bearer by defining an indicator in pdcp-config in DRB-ToAddMod. When terminal 1f-01 receives the handover command message (RRCReconfiguration message) configured as above, terminal 1f-01 can, according to the configuration and for each bearer, execute the DAPS handover method for bearers configured with the DAPS handover method, and execute the general handover method for bearers without the DAPS handover method configured. Furthermore, when an indicator for the handover method type of terminal 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) is included in the mobility control information or reconfiguration with synchronization configuration information in the handover command message, and a DAPS handover method is configured for each bearer, when terminal 1f-01 performs a handover procedure for each bearer, terminal 1f-01 may preferentially apply the DAPS handover method to other handover method types.For example, depending on the configuration and for each bearer, terminal 1f-01 can perform a DAPS handover method for bearers in which a DAPS handover method is configured, and can also perform a handover method for bearers in which a DAPS handover method is not configured. The handover method is configured according to an indicator indicating or configuring the handover method type (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) for terminal 1f-01 in the mobility control information of the handover command message or in the reconfiguration with synchronization configuration information. Alternatively, to reduce the complexity of the terminal implementation, when a DAPS handover method is configured for at least one bearer or bearer, the mobility control information of the handover command message or the reconfiguration with synchronization configuration information can be configured not to indicate or configure another handover method type (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) for terminal 1f-01. Furthermore, when terminal 1f-01 receives the handover command message (RRCReconfiguration message) configured as above, when a DAPS handover method is configured for at least one bearer or for each bearer, terminal 1f-01 can apply the processing methods of the RRC layer entity, SDAP layer entity, MAC layer entity, PHY layer entity, or SRB proposed in this disclosure for performing the DAPS handover method, and for each bearer configured with the DAPS handover method, the processing methods of the PDCP layer entity or RLC layer entity proposed in this disclosure for performing the DAPS handover method can be applied.

[0181] Method 1-2: When instructing or configuring a handover to or for terminal 1f-01, the base station (source base station 1f-02, target base station 1f-03, LTE base station, or NR base station) can indicate the DAPS handover method for each bearer (DRB) by including mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message, and defining an indicator in the DRB-ToAddMod-ToAddModList of the DRB in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message, and without introducing a separate indicator for the configuration of the DAPS handover method of the SRB. That is, when terminal 1f-01 receives the handover command message (RRCReconfiguration message) configured as above, when a DAPS handover method is configured for at least one bearer (DRB) or for each bearer (DRB), the SRB processing method for performing the DAPS handover method proposed in this disclosure can be applied. As another approach, as described above, the base station can indicate the DAPS handover method for each bearer by defining an indicator in the pdcp-config of DRB-ToAddMod. When terminal 1f-01 receives the handover command message (RRCReconfiguration message) configured as above, terminal 1f-01 can perform the DAPS handover method for bearers configured with the DAPS handover method, and can perform the general handover method for bearers without the DAPS handover method configured, according to the configuration and for each bearer. Furthermore, if an indicator indicating or configuring the handover method type for terminal 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) is included in the mobility control information or reconfiguration with synchronization configuration information of the handover command message, and a DAPS handover method is configured for each bearer, terminal 1f-01 can preferentially apply the DAPS handover method instead of other handover method types when performing the handover process for each bearer. For example, depending on the configuration and for each bearer, terminal 1f-01 can perform a DAPS handover method for bearers in which a DAPS handover method is configured, and can perform a handover method for bearers in which a DAPS handover method is not performed. The handover method is configured according to an indicator indicating or configuring the handover method type (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) of terminal 1f-01 in the mobility control information of the handover command message or in the reconfiguration with synchronization configuration information.As another approach, to reduce the complexity of terminal implementation, when a DAPS handover method is configured for at least one bearer or bearer, the mobility control information or reconfiguration with synchronization configuration information in the handover command message can be configured not to indicate or configure another handover method type for the terminal (e.g., MakeBeforeBreak handover, rach-skip handover, rach-free handover, or conditional handover (CHO)). Furthermore, when terminal 1f-01 receives a handover command message (RRCReconfiguration message), when a DAPS handover method is configured for at least one bearer or one bearer for each bearer in the handover command message (RRCReconfiguration message), the processing methods of the RRC layer entity, SDAP layer entity, MAC layer entity, PHY layer entity, or SRB proposed in this disclosure for performing the DAPS handover method can be applied. And for each bearer configured with the DAPS handover method, the processing methods of the PDCP layer entity or RLC layer entity proposed in this disclosure for performing the DAPS handover method can be applied.

[0182] Method 2-1: When indicating or configuring a handover to or for terminal 1f-01, the base station (source base station 1f-02, target base station 1f-03, LTE base station, or NR base station) can indicate that a DAPS handover method has been configured for at least one bearer by including mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message, and by defining and including an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration. Furthermore, the DAPS handover method for each bearer (SRB or DRB) can be indicated by defining an indicator in the SRB-ToAddMod or DRB-ToAddMod of the SRB-ToAddModList or DRB-ToAddMod in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message. Alternatively, as described above, the base station can indicate the DAPS handover method for each bearer by defining an indicator in the pdcp-config within the SRB-ToAddMod or DRB-ToAddMod. As another approach, as described above, when the LTE base station indicates or configures handover to or for terminal 1f-01 using the LTE RRCReconfiguration message, since pdcp-config is not defined in SRB-ToAddMod, but the use of the default pdcp layer configuration is defined in LTE, the LTE base station can configure the DAPS handover method for each bearer by defining an indicator about the SRB in SRB-ToAddMod, and can also configure the DAPS handover method for each bearer by defining an indicator in the pdcp-config of the DRB. When a handover command message (RRCReconfiguration message) configured as above is received, terminal 1f-01 can execute the DAPS handover method for bearers configured with the DAPS handover method according to the configuration and for each bearer, and can execute the general handover method for bearers without the DAPS handover method configured. Furthermore, if an indicator indicating or configuring the handover method type for the terminal (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) is included in the mobility control information or reconfiguration with synchronization configuration information in the handover command message, and if the DAPS handover method is configured for each bearer, the terminal 1f-01 may preferentially apply the DAPS handover method instead of other handover method types when performing a handover procedure for each bearer.For example, depending on the configuration and for each bearer, UE 1f-01 can perform a DAPS handover method for bearers in which a DAPS handover method is configured, and can perform a handover method for bearers in which a DAPS handover method is not configured, based on an indicator in the mobility control information of the handover command message or a reconfiguration with synchronization configuration information indicating or configuring the handover method type (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) for terminal 1f-01. Alternatively, to reduce the complexity of terminal implementation, when a DAPS handover method is configured for at least one bearer or for a bearer, the mobility control information of the handover command message or a reconfiguration with synchronization configuration information can be configured not to indicate or configure another handover method type (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) for terminal 1f-01. Furthermore, when terminal 1f-01 receives a handover command message (RRCReconfiguration message), when an indicator indicating or configuring the DAPS handover method is included or configured in the mobility control information for synchronous reconfiguration in the handover command message (RRCReconfiguration message), the processing methods of the RRC layer entity, SDAP layer entity, MAC layer entity, PHY layer entity, or SRB for performing the DAPS handover method proposed in this disclosure can be applied. And for each bearer configured with the DAPS handover method, the processing methods of the PDCP layer entity or RLC layer entity for performing the DAPS handover method proposed in this disclosure can be applied.

[0183] - Method 2-2: When indicating or configuring a handover to or for terminal 1f-01, the base station (source base station 1f-02, target base station 1f-03, LTE base station, or NR base station) can indicate that a DAPS handover method has been configured for at least one bearer by including mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message and by defining and including an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration. The DAPS handover method for each bearer (DRB) can be indicated by defining an indicator in the DRB-ToAddMod of the DRB-ToAddModList in the bearer configuration information (dedicated radio resource configuration or radio bearer configuration) of the RRCReconfiguration message, and a separate indicator for configuring the DAPS handover method for the SRB can be omitted. In other words, when terminal 1f-01 has received a handover command message (RRCReconfiguration message), and when a DAPS handover method is configured for at least one bearer (DRB) or for each bearer (DRB), the SRB processing method proposed in this disclosure can be applied to execute the DAPS handover method. Alternatively, as described above, the base station can indicate the DAPS handover method for each bearer by defining an indicator in the pdcp-config of DRB-ToAddMod. When terminal 1f-01 receives the handover command message (RRCReconfiguration message) configured as above, terminal 1f-01 can execute the DAPS handover method for bearers configured with a DAPS handover method, and can execute a general handover method for bearers without a configured DAPS handover method. Furthermore, if an indicator indicating or configuring the handover method type for terminal 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) is included in the mobility control information or reconfiguration with synchronization configuration information in the handover command message, and a DAPS handover method is configured for each bearer, when terminal 1f-01 performs a handover procedure for each bearer, terminal 1f-01 may preferentially apply the DAPS handover method instead of other handover method types.For example, based on this configuration and for each bearer, terminal 1f-01 can perform a DAPS handover method for bearers configured with a DAPS handover method, and can also perform a handover method for bearers not configured with a DAPS handover method. The handover method is configured according to the indicator in the mobility control information that indicates or configures the handover method type for terminal 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) or the synchronization configuration information of the handover command message. Alternatively, to reduce the complexity of the terminal implementation, when a DAPS handover method is configured for at least one bearer or for a bearer, the mobility control information in the handover command message or the reconfiguration with synchronization configuration information can be configured not to indicate or configure another handover method type for terminal 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)). Furthermore, when terminal 1f-01 has received the handover command message (RRCReconfiguration message) configured as above, when an indicator indicating or configuring the DAPS handover method is included or configured in the mobility control information for synchronous reconfiguration in the handover command message (RRCReconfiguration message), the processing methods of the RRC layer entity, SDAP layer entity, MAC layer entity, PHY layer entity, or SRB for performing the DAPS handover method proposed in this disclosure can be applied. And for each bearer configured with the DAPS handover method, the processing methods of the PDCP layer entity or RLC layer entity for performing the DAPS handover method proposed in this disclosure can be applied.

[0184] Method 3-1: When instructing or configuring a handover for terminal 1f-01, the base station (source base station 1f-02, target base station 1f-03, LTE base station, or NR base station) can indicate that a DAPS handover method has been configured for at least one bearer by including mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message, and by defining and including an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration. It can also indicate whether a DAPS handover method has been configured for each bearer by configuring and including a list of bearers with configured DAPS handover methods and including the identifier (SRB or DRB) of the bearers with configured DAPS handover methods in the bearer list. Alternatively, as described above, the base station can indicate whether a DAPS handover method has been configured for each bearer by configuring and including a list of bearers without configured DAPS handover methods and including the identifier (SRB or DRB) of the bearers without configured DAPS handover methods in the bearer list. When terminal 1f-01 receives the handover command message (RRCReconfiguration message) configured as above, terminal 1f-01 can perform the DAPS handover method according to the configuration and for each bearer, for bearers configured with the DAPS handover method, bearers with identifiers included in the bearer list configured with the DAPS handover method, or bearers with identifiers not included in the bearer list not configured with the DAPS handover method. It can also perform the general handover method for bearers not configured with the DAPS handover method, bearers with identifiers not included in the bearer list configured with the DAPS handover method, or bearers with identifiers included in the bearer list not configured with the DAPS handover method. Furthermore, if an indicator indicating or configuring the handover method type for the terminal (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) is included in the mobility control information or reconfiguration with synchronization configuration information in the handover command message, and a DAPS handover method is configured for each bearer, when terminal 1f-01 performs a handover procedure for each bearer, terminal 1f-01 may preferentially apply the DAPS handover method instead of other handover method types.For example, depending on the configuration and for each bearer, terminal 1f-01 can perform a DAPS handover method for a bearer configured with a DAPS handover method, a bearer with an identifier included in the list of bearers configured with a DAPS handover method, or a bearer with an identifier not included in the list of bearers without a DAPS handover method. It can also perform a handover method for a bearer without a DAPS handover method, a bearer with an identifier not included in the list of bearers configured with a DAPS handover method, or a bearer with an identifier included in the list of bearers without a DAPS handover method. The handover method (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)) is configured according to the mobility control information in the handover command message or the reconfiguration with synchronization configuration information. As an alternative approach, to reduce the complexity of terminal implementation, when a DAPS handover method is configured for at least one bearer or bearer, the mobility control information of the handover command message or the reconfiguration with synchronization configuration information can be configured not to indicate or configure another handover method type for the terminal (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)). Furthermore, when terminal 1f-01 has received the handover command message (RRCReconfiguration message) configured as above, when an indicator indicating or configuring the DAPS handover method is included or configured in the mobility control information of the synchronous reconfiguration of the handover command message (RRCReconfiguration message), the processing methods of the RRC layer entity, SDAP layer entity, MAC layer entity, PHY layer entity, or SRB for performing the DAPS handover method proposed in this disclosure can be applied. For each bearer, the processing methods of the PDCP layer entity or RLC layer entity for performing the DAPS handover method proposed in this disclosure can be applied to bearers configured with the DAPS handover method, bearers with identifiers included in the bearer list configured with the DAPS handover method, or bearers with identifiers not included in the bearer list not configured with the DAPS handover method.

[0185] Method 3-2: When instructing or configuring a handover for terminal 1f-01, the base station (source base station 1f-02, target base station 1f-03, LTE base station, or NR base station) can indicate that a DAPS handover method has been configured for at least one bearer by including mobility control information or reconfiguration with synchronization configuration information in the RRCReconfiguration message, and by defining and including an indicator indicating or configuring a DAPS handover method in the mobility control information or synchronization reconfiguration. It can also indicate whether a DAPS handover method has been configured for each bearer by configuring and including a list of bearers with configured DAPS handover methods, and including the identifier (SRB or DRB) of the bearers with configured DAPS handover methods in the bearer list. Furthermore, for SRBs, a separate indicator for configuring a DAPS handover method may not be introduced. Alternatively, as described above, the base station can indicate whether a DAPS handover method has been configured for each bearer by configuring and including a list of bearers without configured DAPS handover methods, and including the identifier (SRB or DRB) of the bearers without configured DAPS handover methods in the bearer list. That is, when terminal 1f-01 has received the handover command message (RRCReconfiguration message) configured as above, and when a DAPS handover method is configured for at least one bearer (DRB) or for each bearer (DRB), the SRB processing method for executing the DAPS handover method proposed in this disclosure can be applied. When the handover command message (RRCReconfiguration message) configured as above is received, terminal 1f-01 can, according to the configuration and for each bearer, execute the DAPS handover method for bearers configured with the DAPS handover method, bearers having identifiers included in the list of bearers configured with the DAPS handover method, or bearers having identifiers not included in the list of bearers not configured with the DAPS handover method. It can also execute a general handover method for bearers not configured with the DAPS handover method, bearers having identifiers not included in the list of bearers configured with the DAPS handover method, or bearers having identifiers included in the list of bearers not included with the DAPS handover method. Furthermore, if an indicator indicating or configuring the handover method type for terminal 1f-01 (e.g., MakeBeforeBreak handover, Rach-skip handover, RACH-less handover, or conditional handover CHO) is included in the mobility control information or reconfiguration with synchronization configuration information in the handover command message, and if the DAPS handover method is configured for each bearer, terminal 1f-01 may preferentially apply the DAPS handover method instead of other handover method types when performing a handover procedure for each bearer.For example, depending on the configuration and for each bearer, terminal 1f-01 can perform a DAPS handover method for a bearer configured with a DAPS handover method, a bearer with an identifier included in the list of bearers configured with a DAPS handover method, or a bearer with an identifier not included in the list of bearers not configured with a DAPS handover method, and can also perform a handover method for a bearer not configured with a DAPS handover method, a bearer with an identifier not included in the list of bearers configured with a DAPS handover method, or a bearer with an identifier included in the list of bearers not configured with a DAPS handover method, configuring the handover method according to an indicator indicating or configuring the handover method type (e.g., MakeBeforeBreak handover, Rach-skip handover, RACH-less handover, or Conditional Handover CHO) in the mobility control information of the handover command message or in the reconfiguration with synchronization configuration information. As an alternative approach, to reduce the complexity of terminal implementation, when a DAPS handover method is configured for at least one bearer or bearer, the mobility control information or reconfiguration with synchronization configuration information in the handover command message can be configured not to indicate or configure another handover method type for terminal 1f-01 (e.g., MakeBeforeBreak handover, rach-skip handover, RACH-less handover, or conditional handover (CHO)). Furthermore, when terminal 1f-01 has received the handover command message (RRCReconfiguration message) configured as above, when an indicator indicating or configuring the DAPS handover method is included or configured, the processing method of the RRC layer entity, SDAP layer entity, MAC layer entity, PHY layer entity, or SRB proposed in this disclosure for performing the DAPS handover method can be applied in the mobility control information for synchronous reconfiguration. For each bearer, the processing method of the PDCP layer entity or RLC layer entity proposed in this disclosure for performing the DAPS handover method can be applied to bearers configured with the DAPS handover method, bearers with identifiers included in the bearer list configured with the DAPS handover method, or bearers with identifiers not included in the bearer list not configured with the DAPS handover method.

[0186] This disclosure proposes a non-interrupted handover method that can reduce data interruption time caused by handover or reduce data interruption time to 0ms in next-generation mobile communication systems.

[0187] The terminal can be configured with multiple first bearers with the source base station, and can perform data transmission and reception (uplink or downlink data transmission and reception) by using protocol layer entities (PHY layer entity, MAC layer entity, RLC layer entity or PDCP layer entity) for each bearer. However, in this disclosure, for the sake of convenience, it is assumed that the terminal has one bearer in the figures and description.

[0188] Figure 1g The specific operation of a handover method for minimizing data interruption time caused by handover, according to a first embodiment of the present disclosure, is shown.

[0189] refer to Figure 1g In a first embodiment of the general handover method, during the first operation 1g-01, when terminal 1g-20 receives a handover command message from source base station 1g-05 while sending or receiving data from source base station 1g-05, upon receiving the handover command message according to the handover method indicated by the handover command message (e.g., an RRCReconfiguration message), terminal 1g-20 may release the connection to source base station 1g-05, perform a random access procedure to target base station 1g-10, and perform the handover procedure. Alternatively, to minimize data interruption time during handover according to the indicated handover method, terminal 1g-20 may continuously send and receive data from source base station 1g-05.

[0190] exist Figure 1g In the first embodiment of the general handover method, in the second operation 1g-02, when the process of random access to the target base station 1g-10 is performed according to the handover method indicated by the handover command message, the preamble is sent, or data is initially transmitted in the uplink transmission resources by using the Physical Uplink Control Channel (PUCCH) or Physical Uplink Shared Channel (PUSCH) transmission resources, the terminal 1g-20 may suspend sending data to the source base station 1g-05 and receiving data from the source base station 1g-05 (uplink data transmission and downlink data reception).

[0191] exist Figure 1g In the first embodiment of the general handover method, in the third operation 1g-03, terminal 1g-20 can complete the random access procedure with respect to target base station 1g-10, send a handover completion message, and start sending data to and receiving data from target base station 1g-10 (uplink data transmission and downlink data reception).

[0192] The first embodiment of the efficient handover method disclosed above can describe the handover method executed when the DAPS handover method is not configured.

[0193] Figure 1h The specific operation of a handover method for reducing data interruption time caused by handover, according to a second embodiment of the present disclosure, is shown.

[0194] As a second embodiment of this disclosure, specific operations of an efficient dual-active protocol stack (DAPS) handover method for minimizing data interruption time caused by handover are described.

[0195] exist Figure 1hIn the DAPS handover method, specifically in the second embodiment, when terminal 1h-20 receives a handover command message from source base station 1h-05 during the first operation 1h-01, if the handover command message indicates the second embodiment of the efficient handover method proposed in this disclosure (e.g., the DAPS handover method) or indicates the handover of each bearer, the terminal can continuously send data to or receive data from source base station 1h-05 through the protocol layer entity 1h-22 for the first bearer, thereby minimizing the data interruption time that occurs during the handover even when a handover command message is received. Furthermore, when the RRC layer entity recognizes an indication of the second embodiment of the efficient handover method (e.g., the DAPS handover method) proposed in this disclosure in the handover command message, or when it identifies an indicator of the DAPS handover method for each bearer, the RRC layer entity can transmit the indicator to the PDCP layer entity corresponding to each bearer or the bear to which the DAPS handover method is indicated. When the PDCP layer entity receives the indicator, it can transfer the data from the first PDCP layer entity structure 1i-11 or 1i-12 to the second PDCP layer entity structure 1i-20. The first operation 1h-01 above describes the operation of terminal 1h-20 receiving a handover command message (RRCReconfiguration message) from base station 1h-05. Furthermore, when the configuration is transferred to the second PDCP layer entity structure according to the received handover command message, the protocol layer entity (PHY layer entity, MAC layer entity, RLC layer entity or PDCP layer entity) 1h-21 of the second bearer of the target base station 1h-10 can be pre-configured or established, the security key of the target base station 1h-10 can be exported and updated, and the header (or data) compression context of the target base station 1h-10 can be configured. Furthermore, when terminal 1h-20 receives a handover command message indicating the DAPS handover method proposed in this disclosure or indicating a DAPS handover method for a specific bearer, or when the PDCP realignment timer value is newly configured, when a handover from the first PDCP layer entity structure or function (1i-11 or 1i-12) proposed in this disclosure to the second PDCP layer entity structure or function (1i-20) is performed for each bearer or for the bear indicating the DAPS handover method, terminal 1h-20 can update the variables used for realignment to the PDCP sequence number or the expected next reception count (COUNT) value, stop the realignment timer, and restart the realignment timer. Additionally, as described above, when a handover command message (e.g., an RRCReconfiguration message) is received, the RRC layer entity of terminal 1h-20 can start a first timer (e.g., T304).Furthermore, when the terminal performs a random access procedure to the target base station 1h-10 to perform a handover and the random access procedure is successfully completed (e.g., when the first condition set forth in this disclosure is met), the first timer can be stopped, and in the event of a handover failure and the first timer therefore expiring, when the connection to the source base station 1h-05 is valid, the terminal 1h-20 can report the handover failure to the source base station 1h-5 and attempt to restore the connection by performing a fallback, and when the connection to the source base station 1h-05 is invalid, the terminal can perform an RRC connection reconstruction procedure.

[0196] The handover command message can instruct the second bearer to be configured and established with the same bearer identifier as the first bearer to prevent data interruption for each bearer. Furthermore, in the second embodiment described above, the PDCP layer entity of the first bearer and the PDCP layer entity of the second bearer can logically operate as a single PDCP layer entity; see Figure 1i for details. Additionally, in the second embodiment described above, when terminal 1h-20 is configured to send uplink data to both source base station 1h-05 and target base station 1h-10, in this second embodiment, uplink data can be sent only to one of the source base station 1h-05 and target base station 1h-10 to avoid coverage reduction due to insufficient transmission power of terminal 1h-20, or to address the issue of determining which base station to request transmission resources from and to which the uplink data will be sent when sending uplink data (link selection). More specifically, in the second embodiment described above, when terminal 1h-20 does not have the capability to simultaneously transmit uplink data to different base stations at different frequencies or the same frequency (dual uplink transmission), the terminal can transmit uplink data to only one of the source base station 1h-05 and the target base station 1h-10 within a single time unit. Therefore, terminal 1h-20 can request scheduling from only one of the source base station 1h-05 and the target base station 1h-10, can send a report (e.g., a buffer status report) to only one of the source base station 1h-05 and the target base station 1h-10 regarding the size of multiple data items to be transmitted by the PDCP layer entity, and can receive uplink transmission resources, thereby transmitting uplink data to only one base station. Furthermore, even when a handover command message is received from the source base station 1h-05, terminal 1h-20 may not initialize the MAC layer entity used for the first bearer to prevent data loss by continuing data transmission and reception during HARQ retransmission. Additionally, the RLC layer entity in AM mode can continuously perform RLC retransmissions. As another method, when the handover command message indicates the second embodiment (DAPS handover method) of the efficient handover method proposed in this disclosure for each bearer, the terminal 1h-20 may continuously send or receive data from the source base station 1h-05 only for the PDCP layer entity, RLC layer entity or MAC layer entity corresponding to the bearer or logical channel identifier indicated in the handover command message for the second embodiment (DAPS handover method), or only for the data corresponding to the bearer or logical channel identifier.Furthermore, when the first condition proposed in this disclosure is met (e.g., when uplink data transmission is transferred to the target base station 1h-10), terminal 1h-20 may also continuously send or receive RLC control data (RLC status report), PDCP control data (ROHC feedback or PDCP status report), or HARQ retransmissions only to the PDCP layer entity, RLC layer entity, or MAC layer entity corresponding to the bearer or logical channel identifier indicated in the handover command message as the second embodiment (DAPS handover method). Additionally, when the handover command message indicates the second embodiment (DAPS handover method) of the efficient handover method proposed in this disclosure for each bearer, terminal 1h-20 may suspend sending data to or receiving data from the source base station 1h-05 for the PDCP layer entity, RLC layer entity, or MAC layer entity corresponding to the bearer or logical channel identifier not indicated in the handover command message as the second embodiment (DAPS handover method). Furthermore, in the above description, when terminal 1h-20 receives a handover command message, and the handover command message indicates the DAPS handover method proposed in this disclosure, or indicates a DAPS handover method for a specific bearer, or indicates that a DAPS handover method has been configured for at least one bearer, or indicates that a DAPS handover method has been configured for a bearer, or indicates that QoS flow and bearer mapping information has been newly configured, terminal 1h-20 can transfer the first SDAP layer entity structure or function 1j-10 to the second SDAP layer entity structure or function 1j-20 proposed in this disclosure for each bearer or the bear indicated by the DAPS handover method. Furthermore, in the second SDAP layer entity structure 1j-20, the existing first QoS flow and existing bearer mapping information for the source base station 1h-05 are maintained, allowing uplink data to be sent to the source base station 1h-05 and downlink data to be received from the source base station 1h-05 to be processed. The newly configured second QoS flow and bearer mapping information in the handover command message can be configured for the target base station 1h-10 and can be used to process uplink data to be sent to the target base station 1h-10 and downlink data to be received from the target base station 1h-10. In other words, in the second SDAP layer entity structure 1j-20 proposed in this disclosure, the first QoS flow and bearer mapping information for the source base station 1h-05 or the second QoS flow and bearer mapping information for the target base station 1h-10 can be maintained, allowing data for the source base station 1h-05 and data for the target base station 1h-10 to be processed separately. In the second SDAP layer entity structure, the SDAP layer entity can distinguish whether the data received from the lower layer is received from the source base station 1h-05 or the target base station 1h-10 by using the 1-bit indicator in the SDAP header, the 1-bit indicator in the PDCP header, or the information indicated by the PDCP layer entity.Furthermore, when the base station indicates the DAPS handover method for each bearer to the terminal 1h-20 using a handover command message, the base station can always indicate the DAPS handover method for the default bearer (default DRB), so that when data appears in a new QoS flow that does not correspond to the QoS flow and bearer mapping information during the DAPS handover process, uplink data is always sent through the default bearer. When no DAPS handover method is configured for the default bearer, uplink data transmission of the new QoS flow that appears during the handover is unavailable, which may result in data interruption time. As another method, in the above description, when the terminal 1h-20 receives a handover command message (e.g., an RRCReconfiguration message), the second embodiment (DAPS handover method) is indicated, and the SDAP layer configuration information or the second QoS flow and bearer mapping information for the target base station is configured in the RRC message. When the first condition proposed in this disclosure is met, the terminal 1h-20 can apply the SDAP layer configuration information or the second QoS flow and bearer mapping information. Furthermore, in the above description, when the handover command message indicates the second embodiment (DAPS handover method) for each bearer, when the first QoS flow and bearer mapping information of the source base station 1h-05 is maintained, the terminal 1h-20 may only maintain and apply the first QoS flow and bearer mapping information corresponding to the bearer indicated in the second embodiment, and may release or not apply the first QoS flow and bearer mapping information corresponding to the bearer not indicated in the second embodiment. And when the SDAP layer configuration information or the second QoS flow and bearer mapping information of the target base station 1h-10 is configured in the RRC message, when the first condition proposed in this disclosure is met, the terminal 1h-20 may apply the SDAP layer configuration information or the second QoS flow and bearer mapping information to data transmission to or from the target base station 1h-10.

[0197] exist Figure 1h In a second embodiment of the efficient handover method, in the second operation 1h-02, when a random access procedure is performed on the target base station 1h-10 indicated in the handover command message through the protocol layer entity 1h-21 for the second bearer, the terminal 1h-20 can also continue to send or receive data (uplink data transmission or downlink data reception) to or from the source base station 1h-05 through the protocol layer entity 1h-22 for the first bearer. In the above description, the second operation can describe the process in which the terminal 1h-20 performs a cell selection or reselection procedure and executes a random access procedure on the target cell 1h-10 indicated by the handover command message (RRCReconfiguration message) received from the source base station 1h-05.

[0198] exist Figure 1h In the second embodiment of the efficient handover method, when the first condition is met in the third operation 1h-03, terminal 1h-20 can suspend uplink data transmission to source base station 1h-05 through protocol layer entity 1h-22 for the first bearer in the bearer configured with the DAPS handover method, and transmit uplink data to target base station 1h-10 through protocol layer entity 1h-21 for the second bearer. It can also continuously receive downlink data from source base station 1h-05 and target base station 1h-10 through protocol layer entity 1h-22 for the first bearer and protocol layer entity 1h-21 for the second bearer. In the above description, the third operation describes the operation in which terminal 1h-20 satisfies the first condition and therefore transfers uplink transmission from source base station 1h-05 to target base station 1h-10. More specifically, it describes the operation in which terminal 1h-20 sends uplink data to source base station 1h-05 via the first bearer until the first condition is met. When the first condition is met, terminal 1h-20 suspends sending uplink data to source base station 1h-05 via the first bearer and begins sending uplink data to target base station 1h-10 via the second bearer. Specifically, in the second PDCP layer entity structure proposed in this disclosure for a bearer configured with the DAPS handover method, when the PDCP layer entity transmits uplink data via the first bearer, the first condition is met, and an indicator is received from either a lower-layer entity (when the MAC layer entity successfully accesses the target base station during random access) or an upper-layer entity (when the first timer in the RRC layer entity expires). This allows the suspension of uplink data transmission via the first bearer and the execution of a handover, thereby enabling the commencement of uplink data transmission via the second bearer. Furthermore, as in the PDCP layer entity structure proposed with reference to Figure 1i, the receiving PDCP layer entity 1h-21 for the second bearer and the receiving PDCP layer entity 1h-22 for the first bearer can operate as a single entity. The receiving PDCP layer entity 1h-21 can continuously receive data from the source base station 1h-05 or the target base station 1h-10 without interruption by using stored transmit / receive data, sequence number information, or information such as header compression and decompression context. In the above description, the first condition can be one of the following conditions. The first condition proposed below sets an uplink data transmission handover time point at which transmission resources can be used most efficiently and data interruption time can be minimized.

[0199] - If terminal 1h-20 successfully completes the random access process to target base station 1h-10 for the second bearer through layer entity 1h-21 (e.g., MAC layer entity), and if terminal 1h-20 successfully completes the random access process to target base station 1h-10 for the second bearer through layer entity 1h-21 (e.g., MAC layer entity) and receives the allocation of the first uplink transmission resources from target base station 1h-10, or if uplink transmission resources are initially indicated to terminal 1h-20, it can be determined that the first condition is met.

[0200] ■ For example, when terminal 1h-20 receives a handover command message from source base station 1h-05 and receives an indication of random access to target base station 1h-10, if the indicated random access is contention-free random access (CFRA) (e.g., when a pre-specified preamble or terminal cell identifier (e.g., C-RNTI) is assigned),

[0201] ◆When terminal 1h-20 sends a pre-specified preamble to the target base station 1h-10's cell and receives a Random Access Response (RAR) message, the random access procedure can be considered successfully completed. Therefore, when the first uplink transmission resource allocated, included, or indicated in the RAR message is received, it can be determined that the first condition is met. Alternatively, when uplink transmission resources are initially received after receiving the RAR message, it can be determined that the first condition is met.

[0202] ■ When terminal 1h-20 receives a handover command message from source base station 1h-05 and receives an indication of random access to target base station 1h-10, if the indicated random access is based on contention-based random access (CBRA) (e.g., when no pre-assigned preamble or terminal cell identifier (e.g., C-RNTI) has been assigned),

[0203] ◆When terminal 1h-20 sends a preamble (e.g., a random preamble) to the cell of target base station 1h-10 and receives a Random Access Response (RAR) message, it sends message 3 (e.g., a handover completion message) using uplink transmission resources allocated, included, or indicated in the RAR message, and receives it from target base station 1h-10 via message 4, indicating a contention-resolved MAC CE (contention-resolved MAC CE) or receiving uplink transmission resources via the PDCCH corresponding to the C-RNTI of terminal 1h-20. Therefore, thereafter, when terminal 1h-20 monitors the PDCCH and initially receives or is initially indicated to receive uplink transmission resources via the PDCCH corresponding to the C-RNTI of terminal 1h-20, it can be determined that the first condition is met. Alternatively, when the size of the uplink transmission resources allocated in the RAR message is sufficient and therefore terminal 1h-20 can send message 3 and additionally send uplink data, it can be determined that the uplink transmission resources are initially received, and it can also be determined that the first condition is met. In other words, when a RAR is received, it can be determined that uplink transmission resources have been initially received, and it can also be determined that the first condition is met.

[0204] -When the handover command message received by terminal 1h-20 indicates a handover method that does not require a random access procedure (RACH-less handover),

[0205] ■ When the handover command message includes uplink transmission resources for the target base station 1h-10,

[0206] ◆When terminal 1h-20 sends message 3 (e.g., a handover completion message or an RRCReconfigurationComplete message) using the uplink transmission resources of target base station 1h-10, receives a UE identifier confirmation MAC CE from target base station 1h-10 via message 4, or receives uplink transmission resources via the PDCCH corresponding to the C-RNTI of terminal 1h-20, it can be determined that the random access procedure has been successfully completed and the first condition is met. Alternatively, when the first uplink transmission resource is received via the PDCCH corresponding to the C-RNTI of terminal 1h-20 after the random access procedure has been successfully completed, it can be determined that the first condition is met.

[0207] ■ When the handover command message does not include the uplink transmission resources of the target base station 1h-10,

[0208] ◆When terminal 1h-20 monitors the PDCCH of target base station (or cell) 1h-10 and receives uplink transmission resources via the PDCCH corresponding to the C-RNTI of terminal 1h-20, or when terminal sends message 3 (e.g., handover completion message or RRCReconfigurationComplete message) using uplink transmission resources and receives UE identifier confirmation MACCE from base station 1h-10, or receives uplink transmission resources via the PDCCH corresponding to the C-RNTI of terminal 1h-20, it can be determined that the random access procedure has been successfully completed and the first condition is met. Alternatively, when the first uplink transmission resource is received via the PDCCH corresponding to the C-RNTI of terminal 1h-20 after the random access procedure has been successfully completed, it can be determined that the first condition is met.

[0209] -1> When the DAPS handover method is indicated to terminal 1h-20 via a handover command message, and the handover command message (e.g., RRCReconfiguration message) configures or indicates a two-step random access procedure,

[0210] -1> Alternatively, even if the handover command message (e.g., RRCReconfiguration message) does not configure or indicate a 2-step random access procedure, if terminal 1h-20 supports a 2-step random access procedure through its terminal capabilities, and if information about the 2-step random access procedure (e.g., random access resources or thresholds for determining whether to perform or not perform the 2-step random access procedure) is broadcast in the system information of target cell 1h-10, or if terminal 1h-20 receives the system information and performs a 2-step random access procedure on target cell 1h-10, this is because the signal strength is better or has a value greater than the threshold broadcast in the system information.

[0211] ■2>When the above two-step random access process is successfully completed, terminal 1h-20 can determine that the first condition is met.

[0212] ■2> Specifically, the two-step random access procedure can be performed using either the contention-based random access (CBRA) method or the contention-free random access (CFRA) method.

[0213] ◆3> When terminal 1h-20 executes the CBRA-based two-step random access procedure,

[0214] ●4> Terminal 1h-20 may send a preamble in transport resources used for the two-step random access procedure (e.g., PRACH timing, transport resources configured by the base station via RRC messages, or transport resources broadcast in system information), and send data (e.g., MsgAMAC PDU) in transport resources used for data transmission (e.g., PUSCH timing). This data may include MAC control information (C-RNTI MAC CE), which includes a terminal identifier (C-RNTI) or an RRC message (RRCReconfigurationComplete message or handover completion message).

[0215] ●4> Terminal 1h-20 can monitor PDCCH scrambled by the terminal identifier (C-RNTI) or the first identifier (MsgB-RNTI) caused by the time or frequency of sending the preamble.

[0216] ●4> When terminal 1h-20 receives a PDCCH scrambled with the terminal identifier, receives the allocation of downlink transmission resources in the PDCCH, or receives MAC control information (timing advance command MAC CE) used to control the timing of downlink transmission resources,

[0217] ■5> Terminal 1h-20 can confirm that it has successfully completed the two-step random access process and met the first condition.

[0218] ●4> When the terminal receives a PDCCH scrambled with the first identifier (MsgB-RNTI), receives the allocation of downlink transmission resources in the PDCCH, or receives a back-off random access response to the preamble sent by the terminal in the downlink transmission resources (i.e., when the base station receives the preamble but fails to receive MsgA, the back-off RAR indicates that MsgA should be sent through another transmission resource), 1h-20

[0219] ■5> Terminal 1h-20 can send data (MsgAMAC PDU) by reverting to the transmission resources indicated by the random access response.

[0220] ■5> Terminal 1h-20 can monitor PDCCH scrambled by the terminal identifier (C-RNTI).

[0221] ■5> When terminal 1h-20 receives a PDCCH scrambled with the terminal identifier or allocates uplink transmission resources in the PDCCH, terminal 1h-20 can determine that it has successfully completed the two-step random access procedure and that the first condition is met.

[0222] ◆3> When terminal 1h-20 executes the CFRA-based two-step random access procedure,

[0223] ●4> Terminal 1h-20 can send a preamble in transport resources used for the two-step random access procedure (e.g., PRACH timing or transport resources specified by the base station via RRC messages), and send data (e.g., MsgA MAC PDU) in transport resources used for data transmission (e.g., PUSCH timing). This data may include MAC control information (C-RNTI MACCE), which includes a terminal identifier (C-RNTI) or an RRC message (RRCReconfigurationComplete message or handover completion message).

[0224] ●4> Terminal 1h-20 can monitor PDCCH scrambled by the terminal identifier (C-RNTI) or the first identifier (MsgB-RNTI) caused by the time or frequency of sending the preamble.

[0225] ●4> When terminal 1h-20 receives a PDCCH scrambled with a terminal identifier, receives the allocation of downlink transmission resources in the PDCCH, or receives MAC control information (timing advance command MAC CE) used to control the timing in the downlink transmission resources,

[0226] ■5> Terminal 1h-20 can confirm that it has successfully completed the two-step random access process and that the first condition is met.

[0227] ●4> When terminal 1h-20 receives a PDCCH scrambled with the first identifier (MsgB-RNTI), receives the allocation of downlink transmission resources in the PDCCH, or receives a back-off random access response to the preamble sent by terminal 1h-20 in the downlink transmission resources (i.e., when the base station receives the preamble but fails to receive MsgA, the back-off RAR indicates that MsgA should be sent through another transmission resource),

[0228] ■5> Terminal 1h-20 can confirm that it has successfully completed the two-step random access process and that the first condition is met.

[0229] ■5> Terminal 1h-20 can send data (MsgAMAC PDU) by reverting to the transmission resources indicated by the random access response.

[0230] -1> As another method, when the DAPS handover method is indicated to terminal 1h-20 via a handover command message and the handover command message (e.g., RRCReconfiguration message) configures or indicates a two-step random access procedure, terminal 1h-20 can determine that the first condition is met. For example, in the above case, terminal 1h-20 can determine that the first condition is met before the two-step random access procedure begins.

[0231] -1> As another method, when instructing the DAPS handover method to terminal 1h-20 via a handover command message, terminal 1h-20 can determine that a first condition is met: the handover command message (e.g., an RRC configuration message) configures or indicates a two-step random access procedure, and the transmission resources (PUSCH) configured for data transmission during the two-step random access procedure have a value greater than a first threshold, or the RRC message includes a configuration value (timing advance value) for controlling timing. In the above description, the first threshold can be configured by the base station via an RRC message (e.g., RRCReconfiguration), can be broadcast in system information, or can be configured by terminal 1h-20 having the size of the data to be transmitted. For example, in the above case, terminal 1h-20 can determine that the first condition is met before the two-step random access procedure begins. As another method, when the configuration value (timing advance value) used to control timing is included in the RRC message or a two-step random access procedure is configured, terminal 1h-20 can directly transmit data in the configured transmission resources (e.g., transmission resources configured in the RRC message or transmission resources indicated by the PDCCH of the target base station 1h-20 and monitored by terminal 1h-20) without transmitting a preamble. Therefore, in the above case, terminal 1h-20 can determine that the first condition is met before the start of the two-step random access procedure, when transmitting data, or before transmitting data. As another method, when the configuration value (timing advance value) used to control timing is included in the RRC message or a two-step random access procedure is configured, terminal 1h-20 can directly transmit data in the configured transmission resources (PUSCH) (e.g., transmission resources configured in the RRC message or transmission resources indicated by the PDCCH of the target base station 1h-10 and monitored by terminal 1h-20) without transmitting a preamble. In the above circumstances, when the configured transmission resource (PUSCH) (e.g., the transmission resource configured in the RRC message or the transmission resource indicated by the PDCCH of the target base station 1h-10 and monitored by the terminal 1h-20) has a value greater than the first threshold, or when the RRC message includes a configuration value (timing advance value) for controlling timing, the terminal 1h-20 may determine that the first condition is met before the start of the 2-step random access procedure, when the data is sent, or before the data is sent.

[0232] The following describes a method for efficiently transferring uplink data from source base station 1h-05 to target base station 1h-10 in the DAPS handover method proposed in this disclosure. In the above description, the MAC layer entity or RRC layer entity of the second bearer corresponding to the target base station 1h-10 can determine or identify whether a first condition is met according to one of the following methods, and these methods can be combined and extended to form new methods.

[0233] - First method: For example, when terminal 1h-20 receives an RRCReconfiguration message indicating DAPS handover, terminal 1h-20 can configure a MAC layer entity for the target base station 1h-10 corresponding to the second bearer, and the MAC layer entity can perform a random access procedure and identify whether a first condition is met. Furthermore, when the first condition is met, the MAC layer entity can use an indicator to indicate the upper-layer entity (e.g., a PDCP layer entity) used for the bearer, in which the DAPS handover method is configured to transfer uplink data transmission from the source base station 1h-05 via the first bearer to the target base station 1h-10 via the second bearer in the DAPS handover method proposed in this disclosure.

[0234] A second method: As another method, for example, when the RRCReconfiguration message received by terminal 1h-20 indicates DAPS handover, terminal 1h-20 can configure a MAC layer entity for the target base station 1h-10 corresponding to the second bearer, and the MAC layer entity can perform a random access procedure and identify whether the first condition is met. Furthermore, when the first condition is met, the MAC layer entity can also indicate to the upper-layer entity (e.g., the RRC layer entity) that the first condition is met. Additionally, the upper-layer entity (e.g., the RRC layer entity) can use an indicator to indicate the lower-layer entity (e.g., the PDCP layer entity) used for the bearer, in which the DAPS handover method is configured to transfer uplink data transmission from the source base station 1h-05 via the first bearer to the target base station 1h-10 via the second bearer in the DAPS handover method proposed in this disclosure. In the above description, when the first condition set forth in this disclosure is met or the random access procedure to the target base station 1h-10 is successfully executed, the upper-layer entity (e.g., the RRC layer entity) can stop the first timer. Therefore, when the first timer stops, the RRC layer entity can use an indicator to indicate the PDCP layer entity used for the bearer, in which the DAPS handover method is configured to hand over uplink data transmission.

[0235] The third method: When the RRCReconfiguration message received by terminal 1h-20 indicates DAPS handover, terminal 1h-20 can configure a MAC layer entity for the target base station 1h-10 corresponding to the second bearer. When the RRC layer entity of terminal 1h-20 instructs a lower-layer entity (e.g., a MAC layer entity) to perform DAPS handover by using an indicator, the MAC layer entity can perform a random access procedure and identify whether a first condition is met. When the first condition is met, the MAC layer entity can use an indicator to instruct the upper-layer entity (e.g., a PDCP layer entity) used for the bearer, in which the DAPS handover method is configured to transfer uplink data transmission from the source base station 1h-05 via the first bearer to the target base station 1h-10 via the second bearer in the DAPS handover method proposed in this disclosure.

[0236] Fourth method: As another method, when the RRC configuration message received by terminal 1h-20 indicates DAPS handover, terminal 1h-20 can configure a MAC layer entity for the target base station 1h-10 corresponding to the second bearer. When the RRC layer entity of terminal 1h-20 instructs a lower-layer entity (e.g., a MAC layer entity) to perform DAPS handover using an indicator, the MAC layer entity can perform a random access procedure and can identify whether the first condition is met. Furthermore, when the first condition is met, the MAC layer entity can also indicate to the upper-layer entity (e.g., the RRC layer entity) that the first condition has been met. When the indicator is recognized, and the first condition proposed in this disclosure is met or the random access procedure for the target base station 1h-10 is successfully performed, the upper-layer entity (e.g., the RRC layer) can stop the first timer, thus stopping the first timer. Furthermore, upper-layer entities (e.g., RRC layer entities) can use indicators to indicate lower-layer entities (e.g., PDCP layer entities) used for the bearer, in which, in the DAPS handover method proposed in this disclosure, the DAPS handover method is configured to transfer uplink data transmission from source base station 1h-05 via a first bearer to target base station 1h-10 via a second bearer.

[0237] According to the first, second, third, or fourth method described above, when a PDCP layer entity receives an indicator from an upper-layer entity (e.g., an RRC layer entity) or a lower-layer entity (e.g., a MAC layer entity) indicating that a first condition is met, or an indicator indicating that uplink data transmission will be transferred from source base station 1h-05 to target base station 1h-10 (e.g., when indicating a DAPS handover method), the PDCP layer entity can perform the protocol layer operations described below to efficiently perform the handover of uplink data transmission, and can perform one or more of the following operations to prevent data loss due to uplink data transmission. The following operations can be applied to PDCP layer entities connected to AM DRBs or UM DRBs (RLC layer entities operating in AM mode or RLC layer entities operating in UM mode). In the above description, before the first condition is met or before receiving an indicator indicating that the first condition is met, the PDCP layer entity can, when the buffer stores data to be transmitted, indicate the existence of data to be transmitted to the MAC layer entity of the first bearer of the source base station 1h-05 by indicating the size or quantity of the data to be transmitted (e.g., PDCP data volume), and can then perform uplink data transmission to the source base station 1h-05. Subsequently, the MAC layer entity of the first bearer for the source base station 1h-05 can execute a scheduling request or buffer status report procedure to receive the allocation of uplink transmission resources from the source base station 1h-05. However, when the first condition is met or an indicator indicating that the first condition is met is received, the handover of uplink data transmission to the target base station 1h-10 can be performed on the bearer configured with the DAPS handover method.

[0238] The uplink or downlink ROHC context of the source base station 1h-05 can be left uninitialized and used without modification. The uplink or downlink ROHC context of the target base station 1h-10 can be initialized, and the terminal can start in the initial state (e.g., the IR state in U mode).

[0239] In the above description, in order to transfer uplink data transmission from the first bearer for source base station 1h-05 to the second bearer for target base station 1h-10, the PDCP layer entity can indicate to the MAC layer entity of the first bearer for source base station 1h-05 that the size or quantity of data to be transmitted is 0 (or none). That is, the PDCP layer entity can indicate to the MAC layer entity of the first bearer that the amount of data in the PDCP layer entity (PDCP data amount) is 0, thereby indicating that no more data needs to be transmitted (even when the buffer actually stores multiple data items to be transmitted, in order to hand over uplink data transmission, the PDCP layer entity can indicate to the MAC layer entity of the first bearer of source base station 1h-05 that no more data needs to be transmitted).

[0240] However, as proposed in this disclosure, when the handover method (DAPS handover method) of the second embodiment of this disclosure is indicated, when the bearer of the handover method (DAPS handover method) of the second embodiment of this disclosure is indicated, or when the first condition is met, when RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback) of the source base station 1h-05 is generated, the PDCP layer entity of the bearer can indicate the amount of data corresponding to the RLC control data or PDCP control data to the MAC layer entity of the source base station 1h-05, and can perform data transmission to the source base station 1h-05 or the RLC layer entity of the source base station 1h-05. However, as proposed in this disclosure, when the handover method (DAPS handover method) of the second embodiment of this disclosure is indicated, when the bearer of the handover method (DAPS handover method) of the second embodiment of this disclosure is indicated, or when the first condition is met, when RLC control data (RLC status report) or PDCP control data (PDCP status report or ROHC feedback) of the target base station 1h-10 is generated, the PDCP layer entity of the bearer can indicate the amount of data corresponding to the RLC control data or PDCP control data to the MAC layer entity of the target base station 1h-10, and can perform data transmission to the target base station 1h-10 or the RLC layer of the target base station 1h-10. When the first condition is not met, the PDCP layer entity can indicate the amount of data corresponding to the generated data (PDCP data PDU or PDCP control PDU) to the MAC layer entity of the source base station 1h-05, and can perform data transmission to the source base station 1h-05 or the RLC layer entity of the source base station 1h-05. Therefore, in the second PDCP layer entity structure proposed for a bearer configured with the DAPS handover method, when an indicator indicating that the first condition is met is received and the second PDCP layer entity indicates the amount of data to the MAC layer entity of the target base station 1h-10, the second PDCP layer entity may indicate the amount of data to the MAC layer entity of the target base station 1h-10, excluding the amount or size of PDCP control data or RLC control data to be sent to the bearer or the MAC layer entity of the source base station 1h-05.

[0241] - In the above description, based on the header context of the target base station 1h-10, the PDCP layer entity connected to the AM DRB (i.e., the RLC layer operating in AM mode) (where all pre-stored PDCP PDUs are discarded (e.g., PDCP SDUs are not discarded to prevent loss of original data)) can perform a new header compression process for multiple data items (PDCP SDUs in the buffer) in ascending order, receiving a count value (or PDCP sequence number) assigned before a first condition is met or an indicator indicating that the first condition is met. This ascending order starts from the first data (e.g., PDCP SDU) that was not acknowledged for successful transmission by the lower layer entity (e.g., the RLC layer entity corresponding to the first bearer of the source base station 1h-05). The integrity process or encryption process can be re-executed by applying the security key of the target base station 1h-10. The PDCP header can be configured and transmitted to the lower layer entity (the RLC layer entity of the second bearer of the target base station 1h-10) to perform retransmission or transmission. In other words, the PDCP layer entity performs cumulative retransmission of data starting from the first data that was not acknowledged for successful transmission. As an alternative approach, when a PDCP layer entity performs a retransmission, the PDCP layer entity may only retransmit multiple data items that have not been acknowledged as successfully transmitted by the lower layer entity (e.g., the RLC layer entity of the first bearer of the source base station 1h-05). More specifically, the PDCP layer entity connected to the AM DRB (or the RLC layer entity operating in AM mode) (where all stored PDCP PDUs can be discarded to be sent to the source base station 1h-05 using the first protocol layer entity previously connected to the PDCP layer entity (e.g., PDCP SDUs can be retained to prevent loss of original data)) can perform a new header or data compression process for multiple data (e.g., PDCP SDUs) that were not acknowledged by the lower layer entity (e.g., the RLC layer entity) acting as the first protocol layer entity of the source base station 1h-05) by applying a header compression (or data compression) protocol context or security key corresponding to the target base station 1h-10. Based on the count value (or PDCP sequence number) assigned before the first condition is met or an indicator indicating that the first condition is met is received, the integrity process or encryption process can be re-executed, the PDCP header can be configured, and it can be transmitted to the lower layer entity acting as the second protocol layer entity for transmission to the target base station 1h-10, thereby performing a retransmission or transmission. In other words, to prevent the waste of transmission resources, PDCP layer entities can also selectively retransmit only for multiple data items that were successfully transmitted but not acknowledged. Alternatively, transmission or retransmission can be performed after the lower-layer entity (e.g., the transmit or receive RLC layer entity or MAC layer entity) that is the first protocol layer entity used to send data to the source base station 1h-05 has been released.When the transmission or retransmission process is extended to the UM DRB, the PDCP layer entity connected to the RLC layer operating in UM mode can treat multiple data items—data that have not yet been transmitted to the lower-layer entity, data whose PDCP drop timers have not expired, or data items that have already been assigned PDCP sequence numbers (or count values)—as received from or newly received from the upper-layer entity. It can avoid restarting the PDCP drop timer for each data item and can perform header (or data) compression on multiple data items using the header (or data) compression context or security key of the target base station 1h-10. Alternatively, the PDCP layer entity can perform encryption or integrity protection processes, generate a PDCP header and concatenate it with multiple data items, then perform transmission or retransmission. It can also process the data in ascending order of the count values ​​assigned before the process was triggered, and then perform transmission or retransmission. The window state variables of the PDCP layer entity connected to the UM DRB or AMDRB can be left uninitialized and can remain unchanged and be used.

[0242] - In the above description, when the buffer stores data to be transmitted, the PDCP layer entity can indicate the presence of data to be transmitted to the MAC layer entity of the second bearer of the target base station 1h-10 by indicating the size or amount of data to be transmitted (e.g., PDCP data volume), and can perform the handover of uplink data transmission to the target base station 1h-10. Thereafter, the MAC layer entity of the second bearer for the target base station 1h-10 can execute a scheduling request or buffer status reporting procedure to receive the allocation of uplink transmission resources from the target base station 1h-10.

[0243] - In the above description, for a bearer that indicates (or configures) the second embodiment (or DAPS handover method), when the first condition is met, the configuration information or context of the data compression protocol (for source base station 1h-05) (e.g., uplink data compression protocol) can be released. Alternatively, when the first condition is met, the upper-layer entity of terminal 1h-20 (e.g., RRC layer entity) can instruct or reconfigure the PDCP layer entity to release the configuration information or context of the data compression protocol (e.g., uplink data compression protocol). However, for a bearer that does not indicate (or configure) the second embodiment (or DAPS handover method), when a handover command message is received, terminal 1h-20 can release the configuration information or context of the data compression protocol (e.g., uplink data compression protocol). Alternatively, when a handover command message is received, the upper-layer entity of terminal 1h-20 (e.g., RRC layer entity) can instruct or reconfigure the PDCP layer entity to release the configuration information or context for the data compression protocol (for source base station 1h-05) (e.g., uplink data compression protocol). This is because, for bearers configured with the DAPS handover method, it is necessary to compress the data and send the compressed data to the source base station 1h-05 by using the configuration information or context of the data compression protocol used by the source base station 1h-05 until the first condition is met.

[0244] In the above description, if a DAPS handover method is configured for at least one of the bearers configured for terminal 1h-20, if a DAPS handover method is configured for a bearer, if a first condition is met, or if an indicator indicating that the first condition is met is received, terminal 1h-20 may perform one of the following methods for a bearer for which a DAPS handover method is not configured.

[0245] - First method: When the first condition is met as described above, the upper-layer entity of terminal 1h-20 (e.g., the RRC layer entity) can trigger or request a PDCP reconstruction process for one or more bearers that are not configured with a DAPS handover method (even when the target base station 1h-10 configures a PDCP reconstruction process for the bearer in the handover command message, the PDCP reconstruction process can still be executed when the first condition is met). The PDCP layer entity that has received the request for the PDCP reconstruction process can execute a different PDCP reconstruction process for each bearer. For example, for UM DRB, the PDCP layer entity can initialize window state variables, compress the context or security key based on the header (or data) of the target base station 1h-10, and perform transmission or retransmission by compressing or encrypting multiple data items that have not yet been sent to the lower layer entity or multiple data items whose PDCP discard timers have not yet expired in ascending order of count values, or by performing integrity protection. It can stop and initialize the reorder timer when it is running, and can process the received data (PDCP SDU or PDCP PDU) sequentially to send the processed data to the upper layer entity. For AM DRB, the PDCP layer may not initialize window state variables, and can perform transmission or retransmission by compressing the context or security key based on the header (or data) of the target base station 1h-10, in ascending order of the count value or PDCP sequence number of the first data item (PDCP SDU or PDCP PDU) that was successfully transmitted but not acknowledged from the lower layer entity, by performing compression or encryption or performing integrity protection. In the above description, when a handover command message is received for a bearer without a configured DAPS handover method, the PDCP reconstruction process is not executed. The reason for executing the PDCP reconstruction process when the first condition is met is that if the handover process to the target base station 1h-10 fails, a fallback to the source base station 1h-05 can be performed. However, much of the data, which the bearer processes by compressing the data into the header (or data) compression context of the target base station 1h-10 during the PDCP reconstruction process, and which uses the security key of the target base station 1h-10 for encryption or integrity protection, becomes useless when a fallback is needed and is therefore discarded. Furthermore, this is because when a fallback is needed, the PDCP reconstruction process needs to be performed again on the bearer, thereby compressing the data using the header (or data) compression context of the source base station 1h-05 for data transmission, and requiring the use of the security key of the source base station 1h-05 for encryption or integrity protection again, resulting in unnecessary processing.Therefore, when the terminal executes the DAPS handover method from 1h to 20h, upon receiving a handover command message, for bearers without a configured DAPS handover method, the PDCP reconstruction process may not be triggered or executed. Alternatively, the target base station may not configure the PDCP reconstruction process for the bearer in the handover command message from 1h to 10h, and the PDCP reconstruction process may be triggered or executed when the first condition is met. Furthermore, for bearers with a configured DAPS handover method, the PDCP reconstruction process is not executed.

[0246] -Second method: When a handover command message is received for a bearer that is not configured with a DAPS handover method, the upper-layer entity of terminal 1h-20 (e.g., the RRC layer entity) can trigger or request a PDCP reconstruction process. The PDCP layer entity that has received the request for the PDCP reconstruction process can perform a different PDCP reconstruction process for each bearer. For example, for UM DRB, the PDCP layer entity can initialize window state variables, compress the context or security key based on the header (or data) of the target base station 1h-10, and perform transmission or retransmission by compressing or encrypting multiple data items that have not yet been transmitted to the lower-layer entity or multiple data items whose PDCP discard timers have not yet expired in ascending order of count values, or by performing integrity protection. It can stop and initialize the reorder timer when it is running, and can process the received data (PDCP SDU or PDCP PDU) sequentially to send the processed data to the upper-layer entity. Alternatively, for AM DRB, the PDCP layer entity may not initialize window state variables, and can perform transmission or retransmission by compressing the context or security key based on the header (or data) of the target base station 1h-10, and performing integrity protection by performing compression or encryption or performing integrity protection, based on the count value or PDCP sequence number of the first data item (PDCP SDU or PDCPPDU) that was successfully transmitted but not acknowledged from the lower-layer entity. In the above description, upon receiving a handover command message for a bearer without a configured DAPS handover method, since the data is compressed using the header (or data) compression context of the target base station 1h-10, and processed through the PDCP reconstruction process by performing encryption or integrity protection using the security key of the target base station 1h-10, when terminal 1h-20 fails to execute the handover process to the target base station 1h-10 (e.g., when the first timer expires or when the radio connection to the target base station 1h-10 fails), and when a fallback to the source base station 1h-05 is possible and therefore executed, the upper-layer entity of terminal 1h-20 (e.g., the RRC layer) can instruct the bearer whose DAPS handover method is not indicated to discard the data (PDCP) processed based on the configuration information (security key or header (or data) compression context) of the target base station 1h-10. The bearer may discard multiple data items (e.g., PDCP PDU) or reconfigure the PDCP reconstruction process or configuration information (security key or header (or data) compression context) of the source base station 1h-05, and request or indicate the regeneration and reprocessing of data based on the source base station configuration information, so that the bearer can discard multiple data items (e.g., PDCP PDU) and reprocess multiple data items (e.g., PDCP SDU) based on the header (or data) compression context or security key of the source base station 1h-05.

[0247] In a second embodiment of the efficient handover method proposed in this disclosure (e.g., the DAPS handover method), even after receiving a handover command message (e.g., an RRCReconfiguration message), terminal 1h-20 can continue to receive downlink data from source base station 1h-05 or target base station 1h-10 through the protocol layer entity for the first bearer of source base station 1h-05 or the second bearer of target base station 1h-10. For AM bearers, RLC status reports instead of data can be continuously sent to source base station 1h-05 (or target base station 1h-10) via the uplink through the protocol layer entities 1h-22 and 1h-21 of the first bearer (or the second bearer), so that downlink data can be seamlessly received from source base station 1h-05 (or target base station 1h-10), or downlink data can be seamlessly sent from source base station 1h-05 (or target base station 1h-10). In other words, even when the first condition is met and terminal 1h-20 hands over uplink data transmission to target base station 1h-10, if terminal 1h-20 needs to send an RLC status report, HARQ ACK or NACK, or PDCP control data (PDCP ROHC feedback or PDCP status report) to source base station 1h-05, the terminal can still allow data transmission via the first bearer used by source base station 1h-05. This is because, in the case of the AM bearer, after data is sent to the sender, if the RLC status report does not indicate successful transmission (i.e., when no RLC status report is received), data transmission cannot continue. Specifically, in Figure 1h In the second embodiment of the efficient handover method, in the third operation 1h-03, even when the first condition is met and terminal 1h-20 stops sending uplink data to source base station 1h-05 through protocol layer entity 1h-22 for the first bearer and performs a handover to start sending uplink data to target base station 1h-10 through protocol layer entity 1h-21 for the second bearer, terminal 1h-20 can continue to send HARQ ACK or HARQ NACK information, RLC status reports (ACK or NACK information), or PDCP control data (e.g., PDCP status reports or ROHC feedback information) through the protocol layer entity of the first bearer (or the second bearer), thereby seamlessly receiving downlink data from source base station 1h-05 (or target base station 1h-10), or seamlessly sending downlink data from source base station 1h-05 (or target base station 1h-10). Furthermore, in Figure 1hIn the second embodiment of the efficient handover method, in the third operation 1h-03, even when the first condition is met and terminal 1h-20 stops sending uplink data to source base station 1h-05 through protocol layer entity 1h-22 for the first bearer and performs handover to start sending uplink data to target base station 1h-10 through protocol layer entity 1h-21 for the second bearer, terminal 1h-20 can continue data transmission due to HARQ retransmission of MAC layer entity, or due to retransmission of AM mode RLC layer entity, to prevent data loss to source base station 1h-05. In the above description, in Figure 1h In the second embodiment of the efficient handover method, in the third operation 1h-03, when the first condition is met and terminal 1h-20 stops sending uplink data to source base station 1h-05 through protocol layer entity 1h-22 for the first bearer and performs a handover to start sending uplink data to target base station 1h-10 through protocol layer entity 1h-21 for the second bearer, source base station 1h-05 or target base station 1h-10 can allocate transmission resources to terminal 1h-20 through time-segmentation to prevent conflicts between uplink transmission resources to target base station 1h-10 and uplink transmission resources to source base station 1h-05. When uplink transmission resources to target base station 1h-10 and uplink transmission resources to source base station 1h-05 conflict and overlap, terminal 1h-20 can prioritize the uplink transmission resources to source base station 1h-05 and perform data transmission to source base station 1h-05 to maintain downlink data transmission or to continuously receive downlink data from source base station 1h-05 without problems. Alternatively, when uplink transmission resources to target base station 1h-10 and uplink transmission resources to source base station 1h-05 conflict and overlap, terminal 1h-20 can prioritize the uplink transmission resources to target base station 1h-10 and perform data transmission to target base station 1h-10 to maintain downlink data transmission from target base station 1h-10.

[0248] Specifically, when terminal 1h-20 receives a handover command message, if a handover corresponding to the second embodiment of this disclosure (e.g., DAPS handover) is indicated, or if a handover is indicated for each bearer, UE 1h-20 or the bearer indicating the DAPS handover can execute a scheduling request through the first protocol layer entity 1h-22 until a first condition is met. In this case, a buffer status report can be sent to the source base station 1h-05 to receive uplink transmission resources and send uplink data to the source base station 1h-05, and downlink data can be received from the source base station 1h-05. However, when the first condition is met, terminal 1h-20 may no longer send data to the source base station 1h-05, and can hand over the uplink through the second protocol layer entity 1h-21 to execute the scheduling request. It can also send a buffer status report to the target base station 1h-10 to receive uplink transmission resources and send uplink data to the target base station 1h-10. However, terminal 1h-20 can continuously receive downlink data from source base station 1h-05, and even after uplink transmission handover, it can continuously send HARQ ACK or HARQ NACK, RLC status report, or PDCP control data (e.g., PDCP status report or ROHC feedback information) corresponding to the downlink data to source base station 1h-05. Furthermore, even when the first condition is met, terminal 1h-20 can continuously receive downlink data from either source base station 1h-05 or target base station 1h-10.

[0249] exist Figure 1h In the second embodiment of the efficient handover method, in the fourth operation 1h-04, when the second condition is met, terminal 1h-20 can stop receiving downlink data from source base station 1h-05 through protocol layer entity 1h-22 for the first bearer, and can release the connection with source base station 1h-05. In the above description, the second condition can be one of the following conditions. Furthermore, PDCP layer entity 1h-21 for the second bearer can continuously perform seamless data transmission or reception with target base station 1h-10 by using information stored in PDCP layer entity 1h-22 for the first bearer, such as data transmission or reception information, sequence number information, or header compression and decompression context.

[0250] - When the random access procedure to the target base station 1h-10 is performed through the second bearer layer entity 1h-21 and a random access response is received, the terminal 1h-20 can determine that the second condition is met.

[0251] - When the random access procedure to the target base station 1h-10 is performed, the random access response is received, and the handover completion message is configured and sent to the target base station 1h-10 through the layer entity used for the second bearer, the terminal 1h-20 can determine that the second condition is met.

[0252] - When the random access procedure to the target base station 1h-10 is completed through the layer entity used for the second bearer and data is transmitted for the first time using PUCCH or PUSCH uplink transmission resources, or when PUCCH or PUSCH uplink transmission resources are received for the first time, the terminal 1h-20 can determine that the second condition is met.

[0253] -When the base station configures a separate timer for terminal 1h-20 via RRC message and the timer has expired, the terminal can determine that the second condition is met.

[0254] ■ The timer can be started when terminal 1h-20 receives a handover command message from source base station 1h-05, when it begins random access to target base station 1h-10 (when sending a preamble), when it receives a random access response from target base station 1h-10, when it sends a handover completion message to target base station 1h-10, or when it first uses PUCCH or PUSCH uplink transmission resources to send data.

[0255] -When terminal 1h-20 performs a random access procedure to target base station 1h-10 for the second bearer through layer entity 1h-21, receives a random access response, and configures and sends a handover completion message to target base station 1h-10, and the MAC layer entity (HARQ ACK) or RLC layer entity (RLC ACK) confirms the successful transmission of the handover completion message, the terminal can determine that the second condition has been met.

[0256] - When uplink transmission resources are allocated from target base station 1h-10 for the first time, or when uplink transmission resources are first indicated by terminal 1h-20 after it performs a random access procedure to target base station 1h-10, receives a random access response, or configures and sends a handover completion message to target base station 1h-10 through the layer entity for the second bearer, the terminal can determine that the second condition is met.

[0257] When the source base station 1h-05 performs the efficient handover as described in this disclosure, the source base station 1h-05 can determine when to stop sending downlink data to the terminal 1h-20 or when to release the connection with the terminal 1h-20. For example, this determination can be made using a predetermined method (e.g., when a predetermined timer has expired (the timer can be started after the handover instruction), or when the source base station 1h-05 receives an instruction from the target base station 1h-10 that the terminal 1h-20 has successfully performed the handover to the target base station 1h-10). Additionally, if no downlink data is received from the source base station 1h-05 within a predetermined time, the terminal 1h-20 can determine that a second condition has been met, confirm that the connection with the source base station 1h-05 has been released, and can release the connection.

[0258] When terminal 1h-20 receives an indication from target base station 1h-10 to release the connection with source base station 1h-05 (e.g., RRC message (e.g., RRC configuration message), MAC CE, RLC control PDU, or PDCP control PDU), terminal 1h-20 can determine that the second condition is met.

[0259] - If the terminal fails to receive downlink data from the source base station 1h-05 within the predetermined time, the terminal can determine that the second condition is met.

[0260] - When terminal 1h-20 successfully completes the random access procedure to target base station 1h-10 through the second bearer layer entity 1h-21 (e.g., MAC layer entity), when terminal 1h-20 successfully completes the random access procedure to target base station 1h-10 through the second bearer layer entity and receives the allocation of the first uplink transmission resource from target base station 1h-10, or when the uplink transmission resource is first indicated to terminal 1h-20, terminal 1h-20 can determine that the second condition is met.

[0261] ■For example, more specifically, when terminal 1h-20 receives a handover command message from source base station 1h-05 and indicates random access to target base station 1h-10, if the indicated random access is a contention-free random access (CFRA) procedure (e.g., when a pre-specified preamble or terminal cell identifier (e.g., C-RNTI) is assigned),

[0262] ◆When terminal 1h-20 sends a pre-specified preamble to the cell of target base station 1h-10 and receives a Random Access Response (RAR) message, the random access procedure can be considered successfully completed. Therefore, when it receives the first uplink transmission resource allocated, included, or indicated in the RAR message, terminal 1h-20 can determine that the second condition is met. Alternatively, terminal 1h-20 can also determine that the second condition is met when it receives uplink transmission resources for the first time after receiving the RAR.

[0263] ■ When terminal 1h-20 receives a handover command message from source base station 1h-05, and when random access to target base station 1h-10 is indicated, and the indicated random access is based on a contention-based random access (CBRA) procedure (e.g., when no pre-specified preamble or terminal cell identifier (e.g., C-RNTI) is assigned),

[0264] ◆When terminal 1h-20 sends a preamble (e.g., a random preamble) to the cell of target base station 1h-10, receives a random access response (RAR) message, sends message 3 (e.g., a handover completion message) using uplink transmission resources allocated, included, or indicated in the random access response message, and receives a MAC CE indicating that contention has been resolved (contention resolution MAC CE) from target base station 1h-10 via message 4, or when the terminal receives uplink transmission resources via the PDCCH corresponding to the C-RNTI of terminal 1h-20, terminal 1h-20 can determine that the random access procedure to target base station 1h-10 has been successfully completed. Therefore, when terminal 1h-20 monitors the PDCCH and receives uplink transmission resources for the first time via the PDCCH corresponding to the C-RNTI of terminal 1h-20, or when terminal 1h-20 receives an indication of uplink transmission resources for the first time, the terminal can determine that the second condition is met. As another method, if the size of the uplink transmission resources allocated in the random access message is sufficient to send message 3 and terminal 1h-20 can send additional uplink data, the terminal can determine that it has received uplink transmission resources for the first time and that the second condition is met. That is, when the RAR is received, terminal 1h-20 can determine that it has received uplink transmission resources for the first time and that the second condition is met.

[0265] - In cases where the handover command message received by terminal 1h-20 indicates a handover method that does not require a random access procedure (RACH-less handover),

[0266] ■ When the uplink transmission resources of the target base station 1h-10 are included in the handover command message,

[0267] ◆When the terminal sends message 3 (e.g., a handover completion message or an RRCReconfigurationComplete message) through the uplink transmission resources of the target base station 1h-10 and receives the UE identifier confirmation MACCE from base station 1h-10 via message 4, or when terminal 1h-20 receives uplink transmission resources through the PDCCH corresponding to the C-RNTI of terminal 1h-20, terminal 1h-20 can determine that the random access procedure has been successfully completed and that the second condition is met. Alternatively, after the random access procedure has been successfully completed, when terminal 1h-20 performs PDCCH monitoring and receives the first uplink transmission resources through the PDCCH corresponding to the C-RNTI of terminal 1h-20, the terminal can determine that the second condition is met.

[0268] ■ When the uplink transmission resources of the target base station 1h-10 are not included in the handover command message

[0269] ◆When terminal 1h-20 performs PDCCH monitoring on target base station (or cell) 1h-10 and receives uplink transmission resources through the PDCCH corresponding to the C-RNTI of terminal 1h-20, when the terminal sends message 3 (e.g., a handover completion message or an RRCReconfigurationComplete message) and receives a UE identifier confirmation MAC CE from base station 1h-10, or when the terminal receives uplink transmission resources through the PDCCH corresponding to the C-RNTI of terminal 1h-20, terminal 1h-20 can determine that the random access procedure has been successfully completed and that the second condition is met. Alternatively, after the random access procedure has been successfully completed, when terminal 1h-20 performs PDCCH monitoring and receives the first uplink transmission resource through the PDCCH corresponding to the C-RNTI of terminal 1h-20, terminal 1h-20 can determine that the second condition is met.

[0270] In the above description, when terminal 1h-20 executes the second embodiment of the efficient handover method proposed in this disclosure (e.g., the DAPS handover method), if it is identified that the RRC layer entity, MAC layer entity, or RLC layer entity of the first bearer of the source base station 1h-05 for terminal 1h-20 or the RRC layer entity, MAC layer entity, or RLC layer entity of the second bearer of the target base station 1h-10 meets the second condition proposed in this disclosure, an indicator indicating that the second condition is met can be indicated to the PDCP layer entity of the bearer or to terminal 1h-20 executing the DAPS handover method. When the PDCP layer entity of terminal 1h-20 receives an indication indicating that the second condition is met from a lower-layer entity or an upper-layer entity, or when the second condition is met, the second embodiment of the efficient handover method proposed in this disclosure can be successfully completed by executing one or more of the following processes on terminal 1h-20, which is configured with the DAPS handover method.

[0271] Terminal 1h-20 can release the first bearer used by source base station 1h-05 and release the connection with source base station 1h-05. Before releasing the first bearer of source base station 1h-05, an RLC reconstruction process can be performed on the RLC layer entity corresponding to the first bearer of source base station 1h-05 (e.g., when the reordering timer is running, the timer can be stopped or initialized; when received data is stored in the buffer, multiple data items can be processed and sent to the upper layer; or when there is data to be sent in the buffer, the data can be discarded), or the MAC layer can be initialized.

[0272] When the connection with the source base station 1h-05 is released, the terminal 1h-20 can trigger the PDCP status reporting process to report the reception status of multiple downlink data received from the source base station 1h-05 to the target base station 1h-10. The PDCP status reporting can be configured and the PDCP status report can be sent to the target base station 1h-10.

[0273] When the second condition is met, terminal 1h-20 can transfer from the second PDCP layer entity structure or function 1i-20 to the first PDCP layer entity structure or function 1i-11 or 1i-12 proposed in this disclosure. For each bearer or for the bearer indicated by the DAPS handover method, a reordering variable can be initialized, a reordering timer can be stopped and initialized, and a decryption process or header (or data) decompression can be performed by applying the security key or header decompression context of the source base station 1h-05 to multiple data items stored in the buffer for reordering (e.g., multiple data items received from the source base station 1h-05), and then discarding the security key or header decompression context of the source base station 1h-05. Furthermore, the terminal can also transmit the processed multiple data items to the upper layer in ascending order. In other words, when the second condition is met, terminal 1h-20 can perform a decryption process or header (or data) decompression by applying the security key or header decompression context of source base station 1h-05 to multiple data items stored in the buffer for reordering (e.g., multiple data items received from source base station 1h-05), and then discard the security key or header decompression context of source base station 1h-05. Alternatively, as described above, when the second condition is met, for each bearer or bearer indicated by the DAPS handover method, terminal 1h-20 can transfer from the second PDCP layer entity structure or function 1i-20 to the third PDCP layer entity structure or function 1i-30 proposed in this disclosure, and can continue to use the reordering variables and reordering timers without stopping or initializing them. However, the terminal can perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source base station 1h-05 to multiple data items stored in a buffer for reordering (e.g., multiple data items received from the source base station 1h-05), and then discard the security key or header decompression context of the source base station 1h-05. Furthermore, the terminal can transmit the processed multiple data items to the upper layer in ascending order. That is, in the above description, when the second condition is met, the terminal 1h-20 can perform a decryption process or header (or data) decompression by applying the security key or header decompression context of the source base station 1h-05 to multiple data items stored in a buffer for reordering (e.g., multiple data items received from the source base station 1h-05), and then discard the security key or header decompression context of the source base station 1h-05. In the above description, terminal 1h-20 can release the QoS mapping information of the SDAP layer entity of the source base station 1h-05, the security key information of the source base station 1h-05 of the PDCP layer entity, the header (or data) compression context information of the source base station 1h-05, or the RLC layer entity or MAC layer entity of the source base station 1h-05.In the above description, for each bearer or for a bearer indicating a DAPS handover method, the transfer from the second PDCP layer entity structure or function 1i-20 to the first PDCP layer entity structure or function proposed in this disclosure may mean a PDCP layer reconfiguration, and a reconfiguration can be performed when a reconfiguration indicator for a PDCP layer entity is received from an upper-layer entity (e.g., an RRC layer entity). For example, when terminal 1h-20 receives a handover command message, the upper-layer entity (e.g., an RRC layer entity) sends a PDCP layer entity reconfiguration indicator to the PDCP layer entity of the bearer, such that for a bearer configured with a DAPS handover method, the first PDCP layer entity structure or function can be reconfigured to the second PDCP layer entity structure or function, and when a second condition is met, the upper-layer entity (e.g., an RRC layer entity) sends the PDCP layer entity reconfiguration indicator to the PDCP layer entity of the bearer, such that the second PDCP layer entity structure or function can be reconfigured to the first PDCP layer entity structure or function. For example, whenever a PDCP layer entity reconfiguration indicator is received from an upper-level entity (e.g., an RRC layer entity) in a triggered manner, the carrying PDCP layer entity can reconfigure the first PDCP layer entity structure or function to the second PDCP layer entity structure or function, or it can reconfigure the second layer entity structure or function to the first PDCP layer entity structure or function.

[0274] When the second condition proposed in this disclosure is met during the execution of the DAPS handover method proposed in this disclosure, terminal 1h-20 can release the first bearer used by the source base station 1h-05 and can again transfer from the second SDAP layer entity structure and function 1j-20 applied to each bearer or the bearer indicated by the DAPS handover method to the first SDAP layer entity structure and function 1j-10 and apply the same functions. Furthermore, when the second condition is met, terminal 1h-20 can transfer from the second SDAP layer entity structure or function 1j-20 to the first SDAP layer entity structure or function 1j-10 proposed in this disclosure. For each bearer or for the bearer indicated by the DAPS handover method, the second mapping information between the QoS flow and the bearer and the second bearer of the target base station 1h-10 can be maintained. Before releasing the first bearer of the source base station 1h-05 or the first mapping information between the QoS flow and the bearer, data processing can be completed by applying the first mapping information between the QoS flow and the bearer to multiple data received from the source base station (e.g., all data received from the source base station 1h-05). Then, the first mapping information between the QoS flow and the bearer or the first bearer can be released. In addition, the terminal can transmit the processed multiple data to the upper layer in ascending order. In other words, when the second condition is met, terminal 1h-20 can perform data processing (e.g., based on the first mapping information between the QoS flow and the bearer, reading SDAP header information and updating the mapping information, configuring the SDAP header, or routing or transmitting it to the appropriate upper-layer or lower-layer entity), and then can discard the first mapping information between the QoS flow and the bearer of source base station 1h-05. In the above description, the SDAP layer entity can define and apply a 1-bit indicator of the new SDAP header, a 1-bit indicator of the PDCP header, SDAP control data (e.g., downlink end marker), or information indicated by the PDCP layer entity, and can base its data on the new SDAP header. The type of the last data received from source base station 1h-05 is identified by a 1-bit indicator in the DAP header, a 1-bit indicator in the PDCP header, SDAP control data, or information indicated by the PDCP layer entity. Therefore, after performing data processing by applying the first mapping information between the QoS stream and bearer of source base station 1h-05 to the last data received from source base station 1h-05, the first mapping information between the QoS stream and bearer of source base station 1h-05 can be discarded. Furthermore, the SDAP layer entity can continue to maintain the second mapping information between the QoS stream and bearer and process uplink or downlink data to target base station 1h-10 based on this mapping information.

[0275] - When the MAC layer entity of the source base station 1h-05 is initialized, and the second PDCP layer entity structure of the bearer configured with the DAPS handover method is transferred to the first PDCP layer entity structure, the RLC layer reconstruction or release process can be performed for the RLC layer entity of the source base station 1h-05 in the second PDCP layer entity structure.

[0276] ■ In this disclosure, when the second condition is met, or when an indicator indicating that the second condition is met is received from an upper-layer entity (e.g., an RRC layer entity) or a lower-layer entity (e.g., a MAC layer entity), the RLC layer reconstruction or release process of the first bearer of the source base station 1h-05 may follow one of the following methods.

[0277] ◆First Method: For a bearer configured with the DAPS handover method, when the RLC layer entity of the first bearer of source base station 1h-05 is an LTE RLC layer entity, the upper-layer entity (e.g., an RRC layer entity) can instruct the LTE RLC layer entity to perform a reconstruction process. Specifically, when the reordering timer is running in the LTE RLC layer entity, the reordering timer can be stopped or initialized, and when there are stored multiple data items, the stored multiple data items are processed and transmitted to the upper-layer entity, thereby reducing the transmission delay caused by the reordering timer. Furthermore, variables can be initialized, and multiple data items used for transmission can be discarded. Afterward, the upper-layer entity (e.g., the RRC layer entity) can instruct the release of the LTE RLC layer entity. However, in the above description, when the RLC layer entity of the first bearer used for source base station 1h-05 is an NR RLC layer entity, the upper-layer entity (e.g., the RRC layer entity) can instruct the NR RLC layer entity to be released immediately without reconstruction. This is because there is no stored data, as the NR RLC layer entity always performs out-of-order delivery, and even when stored data exists, the data can be segmented, so discarding the stored data is not a problem. As mentioned above, different procedures can be applied depending on the RLC layer entity configured for each bearer.

[0278] ◆Second Method: For bearers configured with the DAPS handover method, when the RLC layer entity of the first bearer of source base station 1h-05 is an LTE RLC layer entity, the upper-layer entity (e.g., an RRC layer entity) can instruct the LTE RLC layer entity to perform a reconstruction process. Specifically, when the reordering timer is running in the LTE RLC layer entity, the reordering timer can be stopped or initialized, and when there are stored multiple data items, the stored multiple data items are processed and transmitted to the upper-layer entity, thereby reducing transmission delay caused by the reordering timer. Furthermore, variables can be initialized, and multiple data items used for transmission can be discarded. Alternatively, the upper-layer entity (e.g., the RRC layer entity) can release the LTE RLC layer entity. However, when the RLC layer entity of the first bearer used for source base station 1h-05 is an NR RLC layer entity, the upper-layer entity (e.g., the RRC layer entity) can instruct the NR RLC layer entity to be released immediately without reconstruction. This is because since the NR RLC layer always performs out-of-order delivery, there may be no stored data, and even if stored data exists, the data may be segmented, so discarding the data is not a problem. As mentioned above, different processes can be applied depending on the RLC layer entity configured for each bearer.

[0279] ◆Third Method: In the above description, for a bearer configured with the DAPS handover method, when the RLC layer entity of the first bearer of the source base station 1h-05 is an LTE RLC layer entity, when the target base station 1h-10 sends an RRC message (e.g., RRCReconfiguration) to the terminal 1h-20, including an indication to release the connection with the source base station 1h-05 or to release the first bearer of the source base station 1h-05, the indication for rebuilding the LTE RLC layer entity (e.g., reestablishRLC) can be sent through the configuration information (e.g., rlc-config) of the LTE RLC layer entity for the bearer included in the RRC message (or may also include an indication to release the LTE RLC layer entity). Therefore, when an indication to release the connection with the source base station 1h-05 is received, or when the second condition is met, the upper-layer entity (e.g., the RRC layer entity) can read the RRC message and instruct the LTE RLC layer entity to perform the reconstruction process according to the indication for the LTE RLC reconstruction (or release) process. Specifically, when the reordering timer is running in the LTE RLC layer entity, the reordering timer can be stopped or initialized, and when there are stored multiple data items, the stored multiple data items are processed and transmitted to the upper layer entity, thereby reducing the transmission delay caused by the reordering timer. Furthermore, variables can be initialized, and multiple data items used for transmission can be discarded. Afterwards, the upper layer entity (e.g., the RRC layer entity) can release the LTE RLC layer entity. For bearers configured with the DAPS handover method, when the RLC layer entity of the first bearer of the source base station 1h-05 is an NR RLC layer entity, when the target base station 1h-10 sends an RRC message (e.g., RRCReconfiguration) to the terminal 1h-10 including an indication to release the connection with the source base station 1h-05 or to release the first bearer of the source base station 1h-05, the indication to release the NR RLC layer entity can be sent through the configuration information (e.g., rlc-config) of the NR RLC layer entity for the bearer included in the RRC message. As described above, the target base station 1h-10 can indicate different procedures via RRC messages according to the RLC layer entity configured for each bearer, and therefore, the terminal 1h-20 can apply these procedures to each bearer.

[0280] ◆Fourth Method: For a bearer configured with the DAPS handover method, when the RLC layer entity of the first bearer of the source base station 1h-05 is an LTE RLC layer entity, when the target base station 1h-10 sends an RRC message (e.g., RRCReconfiguration) to the terminal 1h-05, including an indicator indicating the release of the connection with the source base station 1h-05 or the release of the first bearer of the source base station 1h-05, the indicator for rebuilding the LTE RLC layer entity (e.g., reestablishRLC) can be sent through the configuration information (e.g., rlc-config) of the LTE RLC layer entity for the bearer included in the RRC message (or may also include an indicator indicating the release of the LTE RLC layer entity). Therefore, when an indication to release the connection with the source base station 1h-05 is received, or when the second condition is met, the upper-layer entity (e.g., the RRC layer entity) can read the RRC message and instruct the LTE RLC layer entity to perform the reconstruction process according to the indication for the LTE RLC reconstruction (or release) process. Specifically, when the reordering timer is running in the LTE RLC layer entity, the reordering timer can be stopped or initialized, and when there are stored multiple data items, the stored multiple data items are processed and transmitted to the upper layer entity, thereby reducing the transmission delay caused by the reordering timer. Furthermore, variables can be initialized, and multiple data items used for transmission can be discarded. Alternatively, the upper layer entity (e.g., the RRC layer entity) can release the LTE RLC layer entity. For bearers configured with the DAPS handover method, when the RLC layer entity of the first bearer of the source base station 1h-05 is an NR RLC layer entity, when the target base station 1h-10 sends an RRC message (e.g., RRCReconfiguration) to the terminal 1h-20 including an indicator indicating the release of the connection with the source base station 1h-05 or the release of the first bearer of the source base station 1h-05, the indicator indicating the release of the NR RLC layer entity of the bearer or the indicator indicating the reconstruction of the NR RLC layer entity can be sent by including it in the RRC message. As described above, the target base station 1h-10 can indicate different procedures via RRC messages according to the RLC layer entity configured for each bearer, and therefore, the terminal 1h-20 can apply these procedures to each bearer.

[0281] - The receiving PDCP layer entity can process or store data received due to the reconstruction process of lower layer entities (e.g., RLC layer entities), and can perform header decompression based on header compression context (robust header compression (ROHC) or Ethernet header compression (EHC)) for UM DRB, for multiple stored data (received from source base station 1h-05) or all stored data (for source base station 1h-05).

[0282] - The receiving PDCP layer entity can process or store data received due to the reconstruction process of lower layer entities (e.g., RLC layer entities), and can perform header decompression based on header compression context (robust header compression (ROHC) or Ethernet header compression (EHC)) for AM DRB, for multiple stored data (received from source base station 1h-05) or all stored data (for source base station 1h-05).

[0283] - As an alternative approach, the receiving PDCP layer entity can process or store data received due to the reconstruction process of lower-layer entities (e.g., RLC layer entities), and for UM DRB or AM DRB, when the indicator indicating continuous use of header compression context (drb-Continue ROHC or drb-Continue Ethernet Header Compression (EHC)) is not configured, the receiving PDCP layer entity can perform header decompression for multiple stored data (received from source base station 1h-05) or all stored data based on header compression context (robust header compression (ROHC) or Ethernet header compression (EHC)).

[0284] - After performing the above process, the sending or receiving PDCP layer entity can discard or release the security key or header compression context of the source base station 1h-05.

[0285] In this disclosure Figure 1fIn this context, when a handover command message 1f-20 is sent to terminal 1f-01, base station 1f-02 can define an indicator of the embodiments proposed in this disclosure in the handover command message (e.g., an RRCReconfiguration message). This indicator can specify the embodiment of the handover process to be triggered for terminal 1f-01 or 1h-20. Terminal 1f-01 or 1h-20 can then execute the handover process according to the handover method indicated in the handover command message. For example, it can execute a second embodiment of the efficient handover method proposed in this disclosure (DAPS handover method) to perform a handover to the target base station 1f-03 or 1h-10 while minimizing data interruption time. Alternatively, the handover command message can define an indicator of the embodiments proposed in this disclosure for each bearer, and can more specifically indicate the embodiment to be applied to the bearer during handover and the bearer to which that embodiment is applied during handover. For example, it can indicate that the second embodiment of this disclosure applies only to AM bearers where RLC layer entities operate in AM mode, or it can be extended and applied to UM bearers where RLC layer entities operate in UM mode. Furthermore, it can be assumed that the embodiments proposed in this disclosure are applicable to DRBs. However, if necessary (for example, if terminal 1f-01 or 1h-1 maintains the SRB of source base station 1f-02 or 1h-05 and fails to perform a handover to target base station 1f-03 or 1h-10, and can report a handover failure message to the SRB of source base station 1f-02 or 1h-05 or restore the message), it can also be extended and applied to the SRB.

[0286] In embodiments of this disclosure, when terminal 1h-20 performs data transmission and reception to or from source base station 1h-05 via a protocol layer entity for the first bearer, and performs data transmission and reception to or from target base station 1h-10 via a protocol layer entity for the second bearer, each of the MAC layer entities for the first bearer and the MAC layer entities for the second bearer can operate a separate discontinuous reception (DRX) cycle to reduce battery consumption of terminal 1h-20. That is, even after receiving a handover command message, terminal 1h-20 can continue to apply the DRX cycle of the MAC layer entity while transmitting and receiving data via the protocol layer entity of the first bearer, and can stop discontinuous reception (DRX) according to the first or second condition of this disclosure. Furthermore, terminal 1h-20 can independently apply the DRX cycle to the MAC layer entity of the second bearer according to the instruction of target base station 1h-10.

[0287] Furthermore, in this disclosure, when terminal 1h-20 stops uplink transmission to source base station 1h-05 via the protocol layer entity used for the first bearer and stops receiving downlink data from source base station 1h-05, it means that terminal 1h-20 reconstructs, initializes, or releases the protocol layer entity (PHY layer entity, MAC layer entity, RLC layer entity, or PDCP layer entity) used for the first bearer.

[0288] In the embodiments of this disclosure, for ease of description, it has been described that terminal 1h-20 configures a first bearer for source base station 1h-05 or a second bearer for target base station 1h-10. This can be easily extended to the case where terminal 1h-20 configures multiple first bearers for source base station 1h-05 or multiple second bearers for target base station 1h-10, thus allowing the same approach to be applied. According to another method, this can be easily extended to the case where multiple bearers are configured for multiple target gNBs 1h-10, and the same approach can be applied. For example, terminal 1h-20 can perform a handover to a first target base station to configure a second bearer; if the handover fails, it can perform a handover to a second target base station to configure a second bearer. This allows the terminal itself to search for and determine cells from multiple target base stations that meet predetermined conditions (e.g., predetermined signal strength or higher), and to perform a handover process on the determined cell.

[0289] Figure 1a and Figure 1ib The structure of a PDCP layer entity applied to a DAPS switching method according to a second embodiment of the present disclosure and a method for applying the structure are shown.

[0290] Figure 1a and Figure 1ib The specific structure and function of an efficient PDCP layer entity for a DAPS handover method corresponding to the second embodiment of the efficient handover method proposed in this disclosure are proposed. Furthermore, regarding the PDCP layer entity structure proposed below, different PDCP layer entity structures can be applied to each bearer at different time points during the DAPS handover process.

[0291] For example, before receiving a handover command message from a base station, the terminal processes, sends, or receives data (operation 1i-01) by applying the first PDCP layer entity structure and function 1i-11 or 1i-12 proposed in this disclosure to each bearer.

[0292] However, when a terminal receives a handover command message from a base station and the handover command message indicates the DAPS handover method proposed in this disclosure, or indicates a DAPS handover method for a specific bearer, the terminal processes and sends or receives data by applying the second PDCP layer entity structure or function 1i-20 proposed in this disclosure to each or more bearers to which the DAPS handover method is indicated (operation 1i-02). That is, when a terminal receives a handover command message and the handover command message indicates the DAPS handover method proposed in this disclosure, or indicates a DAPS handover method for a specific bearer, the terminal can transfer from the first PDCP layer entity structure or function 1i-11 or 1i-12 already used for each bearer to the second PDCP layer entity structure or function 1i-20 proposed in this disclosure for each bearer (e.g., Dual Active Protocol Stack (DAPS) PDCP), or switch to the bearer indicating the DAPS handover method. As another method, when the first condition set forth in this disclosure is met, for each bearer or the bearer indicated by the DAPS handover method, the terminal can transfer from the first PDCP layer entity structure or function li-11 or 1i-12 already used for each bearer to the second PDCP layer entity structure or function 1i-20 proposed in this disclosure (operation 1i-02). Furthermore, in the above description, when the terminal receives a handover command message and indicates the DAPS handover method proposed in this disclosure in the handover command message, or indicates the DAPS handover method for a specific bearer, or when the PDCP reordering timer value is reconfigured, when the terminal transfers from the first PDCP layer entity structure or function 1i-11 or 1i-12 proposed in this disclosure to the second PDCP layer entity structure or function 1i-20, for each bearer or the bear indicated by the DAPS handover method, the terminal can update the reordering variable with the PDCP sequence number or the expected count value to be received next, and can stop and restart the reordering timer. The second PDCP layer entity structure proposed in this disclosure may be referred to as a DAPS PDCP layer entity.

[0293] Furthermore, when the DAPS handover method described above in this disclosure is executed and the second condition described in this disclosure is met, the terminal can release the first bearer used by the source base station and can again transfer from the second PDCP layer entity structure and function 1i-20, which has been applied to each bearer or the bearer indicated by the DAPS handover method, to the first PDCP layer entity structure and function 1i-11 or 1i-12, and apply the same functions. Additionally, in the above description, when the second condition is met when the terminal transfers from the second PDCP layer entity structure or function 1i-20 to the first PDCP layer entity structure or function 1i-11 or 1i-12 as described in this disclosure, for each bearer or for the bearer indicated by the DAPS handover method, the terminal can initialize a reordering variable and stop and initialize a reordering timer. It can perform a decryption process or header (or data) decompression by applying the source base station's security key or header decompression context to multiple data items (e.g., multiple data items received from the source base station) stored in a buffer for reordering. The source base station's security key or header decompression context can then be discarded. Furthermore, the terminal can also transmit multiple processed data items to the upper-layer entity in ascending order. That is, when the second condition is met, the terminal can perform a decryption process or header (or data) decompression by applying the source base station's security key or header decompression context to multiple data items (e.g., multiple data items received from the source base station) stored in a buffer for reordering, and then can discard the source base station's security key or header decompression context.

[0294] As another method, when the second condition proposed in this disclosure is met while executing the DAPS handover method proposed in this disclosure, the terminal can release the bearer of the source base station and can transfer from the second PDCP layer entity structure and function or DAPS PDCP layer entity structure 1i-20, which has been applied to each bearer or the bearer indicated by the DAPS handover method, to the third PDCP layer entity structure and function 1i-30, and apply the same structure and function. In the above description, when the terminal transfers from the second PDCP layer entity structure or function or DAPS PDCP layer entity 1i-20 to the third PDCP layer entity structure or function 1i-30 proposed in this disclosure, for each bearer or for the bearer indicated by the DAPS handover method, the terminal can continuously use the reordering variables and reordering timers without stopping or initializing them. However, the terminal can perform a decryption process or header (or data) decompression by applying the source base station's security key or header decompression context to multiple data items (e.g., multiple data items received from the source base station) stored in a buffer for reordering, and then discard the source base station's security key or header decompression context. Furthermore, the terminal can also transmit the processed multiple data items to the upper layer in ascending order. That is, in the above description, when the second condition is met, the terminal can perform a decryption process or header (or data) decompression by applying the source base station's security key or header decompression context to multiple data items (e.g., multiple data items received from the source base station) stored in a buffer for reordering, and then discard the source base station's security key or header decompression context.

[0295] As presented in Figure 1i above, when the terminal performs a handover by applying different first PDCP layer structures and functions 1i-11 or 1i-12, second PDCP layer structures and functions 1i-20, and third PDCP layer structures and functions 1i-30 to each bearer at different times, the data interruption time can be minimized without data loss.

[0296] The first PDCP layer entity structure 1i-11 or 1i-12 proposed in Figure 1i may have the (1-1)th PDCP layer entity structure, (1-2)th PDCP layer entity structure, (1-3)th PDCP layer entity structure or (1-4)th PDCP layer entity structure proposed in the following disclosure, and may have the following features.

[0297] -1>(In the case of the (1-1) PDCP layer entity structure), for example, when the terminal applies the first PDCP layer entity structure and function 1i-11 to the PDCP layer entity (e.g., E-UTRA PDCP layer entity or LTE PDCP layer entity) connected to the AM RLC layer entity (e.g., E-UTRA AM RLC layer entity), the following features may be present.

[0298] ■2> The receiving PDCP layer entity can first perform out-of-window data detection or duplicate data detection on multiple received data items. (RLC AM has retransmission capabilities, and the sizes of the LTE RLC SN and PDCP SN may differ from each other, therefore duplicate data or out-of-window data may be received. The window indicates the area of ​​the count value or PDCP sequence number of the received valid data.)

[0299] ◆3> Before discarding out-of-window or duplicate data, the terminal performs a decryption and header decompression process, and then discards them. (This may include useful information used in the header decompression process (e.g., IR packets or header compression information), thus allowing out-of-window or duplicate data to be identified and discarded.)

[0300] ■2> Without performing sorting, the terminal can directly perform decryption and header decompression on multiple received data items without discarding them. This is because the E-UTRA AM RLC layer entity performs data sorting and transmits multiple data items to the PDCP layer entity.

[0301] ■2> In addition, when multiple data items are transmitted to the upper layer, they are sent in ascending order of their count values.

[0302] -1>(In the case of the (1-2)th PDCP layer entity structure), for example, when the terminal applies the first PDCP layer entity structure and function 1i-11 to the PDCP layer entity (e.g., E-UTRA PDCP layer entity or LTE PDCP layer entity) connected to the UM RLC layer entity (e.g., E-UTRA UM RLC layer entity), the following characteristics may exist.

[0303] ■2> The out-of-window data detection or duplicate data detection process is not performed. This is because the UM E-UTRA RLC layer entity does not have a retransmission process.

[0304] ■2> For the multiple data received above, the decryption process is executed directly, and the header decompression process is also executed.

[0305] ■2> A reordering process can be performed to send data to the upper layer (e.g., in ascending order).

[0306] -1> (in the case of the first PDCP layer entity structure (1-3)), for example, when the terminal applies the first PDCP layer entity structure and function 1i-11 to a PDCP layer entity (e.g., E-UTRA PDCP layer entity or LTE PDCP layer entity) configured as a separate bearer, packet replication bearer or LWA bearer, a reordering process and a reordering timer are always applied, and the following characteristics may exist.

[0307] ■2> Out-of-window data detection for duplicate data detection can be performed first on the received data. (This is because RLC AM may experience retransmissions, or data may be received from different RLC layer entities at different times. The sizes of the LTE RLC SN and PDCPSN may also differ, thus potentially resulting in out-of-window or duplicate data being received.)

[0308] ◆3> Perform the decryption process. However, the header decompression process is not performed. (This is because E-UTRA PDCP cannot be configured with a header compression protocol for split bearers or LWQ bearers.)

[0309] ◆3> After the integrity protection or verification process is performed, the data is discarded. When the integrity verification process fails, the data can be discarded, and a report can be made to the upper-level entity.

[0310] ◆3> Data outside the window or duplicate data is discarded.

[0311] ■2> When the aforementioned data is not discarded, the decryption process is executed directly without sorting the received data items. Furthermore, when integrity protection or verification is configured, integrity verification is performed. After the integrity protection or verification process is executed, the data is discarded. If the integrity verification process fails, the data can be discarded, and a report can be sent to the upper layer.

[0312] ■2> When multiple data items are sorted and the PDCP sequence numbers or count values ​​are ordered consecutively in ascending order without gaps, a header compression process is performed, and (if a header compression or decompression process is configured) the data is sent to the upper-layer entity in ascending order.

[0313] ■2> When the reordering timer is running

[0314] ◆3> When data corresponding to a count value that is the same as the value obtained by subtracting 1 from the value held by the reordering variable is sent to the upper-level entity, or when all data is sent to the upper level without gaps in the PDCP sequence number (or count value),

[0315] ●4> Stop and initialize the reordering timer.

[0316] ■2> When the reordering timer is not running

[0317] ◆3> When the buffer contains data that has not been sent to the upper-layer entity, or when there are gaps in the PDCP sequence number (or count value),

[0318] ●4> The reordering timer starts.

[0319] ●4> The reordering variable is updated with the expected PDCP sequence number or count value to be received next.

[0320] ■2> When the reordering timer expires

[0321] ◆3> When the header decompression process is configured in ascending order according to the PDCP sequence number or the count value less than the reorder variable value, the header decompression process is executed and the stored data is sent to the upper-level entity.

[0322] ◆3> When the header decompression process is configured in ascending order according to the PDCP sequence number or count value for the reordered variable value that is equal to or greater than the stored multiple data items, the header decompression process is executed and the stored multiple data items are sent to the upper-level entity.

[0323] ◆3> In addition, update the variable value of the last data transmitted to the upper-level entity with the PDCP sequence number or the count value of the last transmitted data.

[0324] ◆3> When the buffer contains data that has not been sent to the upper-layer entity, or when there are gaps in the PDCP sequence number (or count value),

[0325] ●4> The reordering timer starts.

[0326] ●4> In addition, the reordering variable is updated with the expected PDCP sequence number or count value to be received next.

[0327] -1>(In the case of the (1-4)th PDCP layer entity structure), for example, when the terminal applies the first PDCP layer entity structure and function 1i-12 to the NR PDCP layer entity, the reordering process and reordering timer are always applied, and the following characteristics may exist.

[0328] ■2> First, the received data is decrypted.

[0329] ■2> When an integrity protection or verification process is configured, the received data can be protected or verified. If the integrity verification process fails, the data can be discarded and reported to the upper layer.

[0330] ■2> Perform out-of-window data detection or duplicate data detection on the received data. (After performing the above decryption process, out-of-window data detection or duplicate detection can be performed. Alternatively, the decryption process can only be performed if integrity protection or verification is configured, followed by out-of-window data detection or duplicate detection. When integrity protection or verification is not configured, out-of-window data detection or duplicate detection can be performed, and then the decryption process can be performed on multiple data items that have not been discarded.)

[0331] ◆3> Data outside the window or duplicate data is discarded.

[0332] ■2> When the data is not discarded, the received data items are sorted, and when the PDCP sequence number or count value is sorted in ascending order without gaps, the header compression process can be performed, and (when the header compression or decompression process is configured) the data can be transmitted to the upper-level entity in ascending order.

[0333] ■2> In addition, when multiple data items are transmitted to the upper-level entity, the multiple data items are transmitted in ascending order of their count values.

[0334] ■2> When the reordering timer is running

[0335] ◆3> When data corresponding to a count value that is the same as the value obtained by subtracting 1 from the value held by the reordering variable is transmitted to the upper-level entity, when all data is sent to the upper-level entity without gaps in the PDCP sequence number (or count value), or when the value of the variable storing the PDCP sequence number or the count value of the data to be transmitted to the upper-level entity is greater than or equal to the value of the reordering variable,

[0336] ●4> Stop and initialize the reordering timer.

[0337] ■2> When the reordering timer is not running

[0338] ◆3> When the buffer stores data that has not been transmitted to the upper-level entity, when there are gaps in the PDCP sequence number (or count value), or when the value of the variable storing the count value of the first data that has not been transmitted to the upper-level entity is less than the reordering variable value,

[0339] ●4> In addition, the reordering variable is updated with the expected PDCP sequence number or count value to be received next.

[0340] ●4> The reordering timer starts.

[0341] ■2> When the reordering timer expires

[0342] ◆3> When the header decompression process is configured in ascending order according to the PDCP sequence number or the count value less than the reorder variable value, the header decompression process is executed and the stored data is transmitted to the upper-level entity.

[0343] ◆3> When the header decompression process is configured in ascending order according to the PDCP sequence number or count value for a value that is equal to or greater than the value of the reordering variable of the stored data, the header decompression process is executed and the stored data is transmitted to the upper layer.

[0344] ◆3> In addition, the variable values ​​of the first data that have not been transmitted to the upper layer are updated using the PDCP sequence number or count value of the first data that have not been transmitted to the upper layer entity.

[0345] ◆3> When the buffer stores data that has not been transmitted to the upper-level entity, when there are gaps in the PDCP sequence number (or count value), or when the value of the variable storing the count value of the first data that has not been transmitted to the upper-level entity is less than the reordering variable value,

[0346] ●4> In addition, the reordering variable is updated with the expected PDCP sequence number or count value to be received next.

[0347] ●4> The reordering timer starts.

[0348] The second PDCP layer entity structure 1i-20 proposed in Figure 1i may have the (2-1)th or (2-2)th PDCP layer entity structure proposed below in this disclosure, and may have the following characteristics.

[0349] This disclosure proposes a second PDCP layer entity structure for efficient handover, as shown in 1i-20. This second PDCP layer entity structure can be applied to a second embodiment of the efficient handover method for minimizing data interruption time proposed in this disclosure.

[0350] In the second PDCP layer entity structure, the terminal can perform data transmission or reception from the source base station 1i-21 through the protocol layer entity used for the first bearer (e.g., SDAP layer entity, PDCP layer entity, RLC layer entity, or MAC layer entity), and can perform data transmission or reception from the target base station 1i-22 through the protocol layer entity used for the second bearer (e.g., SDAP layer entity, PDCP layer entity, RLC layer entity, or MAC layer entity).

[0351] In the above description, each of the PDCP layer entities used for the first bearer and the PDCP layer entities used for the second bearer can be configured in the terminal, but logically, they can operate as a single PDCP layer entity, as shown in 1i-20. Specifically, a single PDCP layer entity can divide the functions of the PDCP layer entity, implementing the functions of the higher-level PDCP layer entity (e.g., sequence number allocation, reordering, in-order delivery, or duplicate detection) and the functions of two lower-level PDCP layer entities (e.g., decryption or encryption, header (or data) compression or header (or data) decompression, integrity protection or verification, or duplicate detection) for each source base station and each target base station. Furthermore, as mentioned above, in the DAPS handover method, when the terminal sends uplink data to the source base station and meets the first condition, the terminal can perform a handover to the target base station and can continuously receive downlink data from both the source and target base stations. Therefore, for the uplink, the header (or data) compression protocol context can be maintained and applied by only one context for either the source or target base station, while for the downlink, two contexts can be maintained and applied by either the source or target base station.

[0352] Based on the second PDCP layer entity structure proposed above, the (2-1)th PDCP layer entity structure proposed in this disclosure (e.g., the E-UTRAPDCP layer entity for DAPS switching method) may have the following characteristics.

[0353] In the above description, the upper-level transport PDCP layer entity can perform the task of assigning PDCP sequence numbers to multiple data received from the upper-level entity. Furthermore, the two lower-level transport PDCP layer entity functions 1i-21 and 1i-22 for each source base station and each target base station can apply a header (or data) compression context or security key configured for the source base station to the data to be sent to the source base station, and a header (or data) compression context or security key configured for the target base station to the data to be sent to the target base station, using separate security keys configured for each source base station and each target base station. This ensures that when header (or data) compression is configured, a header (or data) compression process is applied; and when integrity protection is configured, encryption and integrity protection processes are applied to the PDCP header and data (PDCP SDU). For the first bearer, the data to be sent to the source base station is transmitted to the transport RLC layer entity; for the second bearer, the data to be sent to the target base station is transmitted to the transport RLC layer entity. In the above description, the two lower transport PDCP layer entity functions 1i-21 and 1i-22 can perform parallel data processing, where header compression, integrity protection, or encryption processes can be executed in parallel to accelerate data processing. Furthermore, within the two lower transport PDCP layer entity functions 1i-21 and 1i-22, the integrity protection or encryption processes can be performed using different security keys. Logically, different data item compression, integrity protection, or encryption processes can be performed by applying different security keys or security algorithms within a single transport PDCP layer entity.

[0354] In the above description, in the PDCP layer entity function, for multiple data received from each lower-layer entity—specifically, for multiple data received from two RLC layer entities of each source base station and each target base station—out-of-window data detection or duplicate detection procedures can be performed independently for the multiple data received from each RLC layer entity based on the PDCP sequence number or count value in the lower-layer PDCP layer entity functions 1i-21 and 1i-22 of the source base station or target base station. Alternatively, for ease of implementation, out-of-window data detection or duplicate detection procedures can be performed on all received data based on the PDCP sequence number or count value without distinguishing between the corresponding RLC layer entities. As another method, for more accurate duplicate detection, out-of-window data detection can be performed on all received data based on the PDCP sequence number or count value without distinguishing between the corresponding RLC layer entities, and duplicate detection procedures can be performed independently for data received from the corresponding RLC layer entities. As another approach, when multiple data received from different base stations are copied, out-of-window data detection can be performed on all received data based on the PDCP sequence number or count value without distinguishing between individual RLC layer entities. Furthermore, a copy detection process can be performed on the entire data after performing a decryption process, an integrity protection process, or a header (or data) decompression process on the multiple data received from each RLC layer entity, in order to prevent data loss of the header compression protocol.

[0355] The lower functions of receiving PDCP layer entities can be achieved by using a compression context or security key configured for each source base station and each target base station, applying the decryption process directly to the received data, and applying the integrity verification process to the PDCP header and data (PDCP SDU) when integrity protection is configured.

[0356] In the (2-1)th PDCP layer entity structure, for multiple data items received from the RLC layer entity of the first bearer of each source base station, the header (or data) decompression process can be performed directly without sorting. Furthermore, for multiple data items received from the RLC layer entity of the second bearer of each target base station, the header (or data) decompression process can be performed directly without sorting. Additionally, to distinguish between multiple data items received from the RLC layer entity of the first bearer of each source base station and multiple data items received from the RLC layer entity of the second bearer of each target base station, an indicator can be defined for each data item to distinguish whether the data was received from the source base station or the target base station. Alternatively, a 1-bit indicator in the PDCP header, SDAP header, or RLC header can be defined to distinguish whether the data was received from the source base station or the target base station. Furthermore, for all multiple data items received from the RLC layer entity of the first bearer of the source base station (which has already undergone header (or data) compression) and from the RLC layer entity of the second bearer of the target base station, a duplicate detection process can be performed based on the PDCP sequence number or count value (a process of discarding all data except one item (applicable to data previously received or transmitted to the upper layer) for each PDCP sequence number or count value). Additionally, for all multiple data items received from the RLC layer entity of the first bearer of the source base station and from the RLC layer entity of the second bearer of the target base station, a reordering process can be performed in ascending order based on the PDCP sequence number or count value, and the data can be sequentially sent to the upper layer entity. In the above description, a single PDCP layer entity can receive data from different base stations, i.e., data can be received from the first or second bearer in any order, therefore a reordering process may always be necessary.

[0357] Two lower-receive PDCP layer entity functions can perform parallel data processing, including header compression, integrity protection, or encryption, based on PDCP sequence numbers or count values, to accelerate data processing. They can perform integrity protection, encryption, or decompression processes using different header (or data) compression contexts or security keys. Furthermore, logically, different data integrity protection, encryption, or decompression processes can be performed by applying different header (or data) compression contexts, security keys, or security algorithms within a single transport PDCP layer. Additionally, within the lower-receive PDCP layer entity functions, out-of-order decryption or integrity verification can be performed on each of the received data items, regardless of the order of the PDCP sequence numbers or count values.

[0358] When distinguishing between the first bearer layer entity and the second bearer layer entity, a single PDCP layer can differentiate between the first bearer layer entity (or the first RLC layer entity) and the second bearer layer entity (or the second RLC layer entity) by considering that the layer entity is connected to different MAC layer entities, that the layer entity has different logical channel identifiers, that the layer entity is a different RLC layer entity connected to different MAC layer entities, or that different encryption keys are used. This allows for the use of different encryption keys to perform encryption or decryption processes on uplink and downlink data, and the use of different compression protocol contexts to perform compression or decompression.

[0359] Based on the second PDCP layer entity structure proposed above, the (2-2)th PDCP layer entity structure proposed in this disclosure (e.g., the NR PDCP layer of the DAPS switching method) may have the following characteristics.

[0360] In the above description, the upper-level transport PDCP layer entity can perform the task of assigning PDCP sequence numbers to multiple data received from the upper-level entity. Furthermore, the two lower-level transport PDCP layer entity functions 1i-21 and 1i-22 for each source base station and each target base station can apply a header (or data) compression context or security key configured for the source base station to the data to be sent to the source base station, and a header (or data) compression context or security key configured for the target base station to the data to be sent to the target base station, using separate security keys configured for each source base station and each target base station. This ensures that when header (or data) compression is configured, a header (or data) compression process is applied; and when integrity protection is configured, encryption and integrity protection processes are applied to the PDCP header and data (PDCP SDU). For the first bearer, the data to be sent to the source base station is transmitted to the transport RLC layer entity; for the second bearer, the data to be sent to the target base station is transmitted to the transport RLC layer entity. In the above description, the two lower transport PDCP layer entity functions 1i-21 and 1i-22 can perform parallel data processing, where header compression, integrity protection, or encryption processes can be executed in parallel to accelerate data processing. Furthermore, within the two lower transport PDCP layer entity functions 1i-21 and 1i-22, the integrity protection or encryption processes can be performed using different security keys. Logically, different data item compression, integrity protection, or encryption processes can be performed by applying different security keys or security algorithms within a single transport PDCP layer entity.

[0361] In the above description, in the receiving PDCP layer entity function, for multiple data received from each lower-layer entity, specifically, for multiple data received from the two RLC layer entities of each source base station and each target base station, based on the PDCP sequence number or count value in the lower receiving PDCP layer entity functions 1i-21 and 1i-22 of the source base station or target base station, an out-of-window data detection or duplicate detection process can be independently performed on the multiple data received from each RLC layer entity. Alternatively, for ease of implementation, an out-of-window data detection or duplicate detection process can be performed on all received data based on the PDCP sequence number or count value without distinguishing the corresponding RLC layer entity. Alternatively, for more accurate duplicate detection, an out-of-window data detection process can be performed on all received data based on the PDCP sequence number or count value without distinguishing the corresponding RLC layer entity, and a duplicate detection process can be performed independently on the data received from the corresponding RLC layer entity. As another approach, when multiple data received from different base stations are copied, out-of-window data detection can be performed on all received data based on the PDCP sequence number or count value without distinguishing between individual RLC layer entities. Furthermore, a copy detection process can be performed on the entire data after performing a decryption process, an integrity protection process, or a header (or data) decompression process on the multiple data received from each RLC layer entity, in order to prevent data loss of the header compression protocol.

[0362] The lower functions 1i-21 and 1i-22 of receiving PDCP layer entities can apply the decryption process directly to the received multiple data items by using a compression context or security key configured for each source base station and each target base station, and when integrity protection is configured, apply the integrity verification process to the PDCP header and data (PDCPSDU).

[0363] In the (2-2)th PDCP layer structure, after applying the reordering process to multiple data items received from the RLC layer entity of the first bearer of each source base station and multiple data items received from the RLC layer entity of the second bearer of each target base station, the header (or data) decompression process can be performed by applying the header (or data) compression context of each base station (source base station or target base station) to each data item received from each base station (source base station or target base station) in ascending order of PDCP sequence number or count value. Furthermore, to distinguish between multiple data items received from the RLC layer entity of the first bearer of each source base station and multiple data items received from the RLC layer entity of the second bearer of each target base station, an indicator can be defined for the corresponding data item to distinguish whether the data was received from the source base station or the target base station. Alternatively, a 1-bit indicator in the PDCP header, SDAP header, or RLC header can be defined to distinguish whether the data was received from the source base station or the target base station. Furthermore, for all multiple data items received from the RLC layer entity of the first bearer of the source base station (which has already undergone header (or data) compression) and from the RLC layer entity of the second bearer of the target base station, a duplicate detection process can be performed based on the PDCP sequence number or count value (for each PDCP sequence number or count value, the process of discarding all data except one item (applicable to data previously received or transmitted to the upper layer)). Additionally, for all multiple data items received from the RLC layer entity of the first bearer of the source base station and from the RLC layer entity of the second bearer of the target base station, the data can be sequentially sent to the upper layer entity based on the PDCP sequence number or count value. In the above description, a single PDCP layer entity can receive data from different base stations, i.e., data can be received from the first or second bearer in any order, therefore a reordering process may always be required.

[0364] The two lower-receive PDCP layer entity functions 1i-21 and 1i-22 can perform parallel data processing, including header compression, integrity protection, or encryption, based on PDCP sequence numbers or count values, to accelerate data processing. They can also perform integrity protection, encryption, or decompression processes using different header (or data) compression contexts or security keys. Furthermore, logically, different data integrity protection, encryption, or decompression processes can be performed by applying different header (or data) compression contexts, security keys, or security algorithms within a single transport PDCP layer. Additionally, in the lower-receive PDCP layer entity functions 1i-21 and 1i-22, out-of-order decryption or integrity verification processes can be performed on each of the received data items, regardless of the order of the PDCP sequence numbers or count values.

[0365] When distinguishing between the first bearer layer entity and the second bearer layer entity, a single PDCP layer can differentiate between the first bearer layer entity (or the first RLC layer entity) and the second bearer layer entity (or the second RLC layer entity) by considering that the layer entity is connected to different MAC layer entities, that the layer entity has different logical channel identifiers, that the layer entity is a different RLC layer entity connected to different MAC layer entities, or that different encryption keys are used. This allows for the use of different encryption keys to perform encryption or decryption processes on uplink and downlink data, and the use of different compression protocol contexts to perform compression or decompression.

[0366] This disclosure proposes an efficient third PDCP layer entity structure for handover, as shown in 1i-30. The third PDCP layer entity structure can be applied to the second embodiment of the efficient handover method for minimizing data interruption time proposed in this disclosure. Furthermore, the PDCP layer entity functions in the third PDCP layer entity structure proposed in this disclosure can be the same as those in the second PDCP layer structure proposed in this disclosure. However, the third PDCP layer entity structure corresponds to the structure obtained by releasing the first bearer for the source base station from the second PDCP layer entity structure. Specifically, the third PDCP layer entity structure proposed in this disclosure has the same functions as the aforementioned second PDCP layer entity structure, but may have a structure that releases the first bearer of the source base station (e.g., SDAP layer entity, PDCP layer entity, RLC layer entity, or MAC layer entity). Accordingly, in the third PDCP layer entity structure, the QoS mapping information of the SDAP layer entity of the source base station, the security key information of the source base station of the PDCP layer entity, the header (or data) compression context information of the source base station, or the RLC layer entity or MAC layer entity of the source base station may be released.

[0367] The following section describes how, when a terminal receives a handover command message and the application is included above... Figure 1f When the bearer configuration information is in the switching command message, the bearer configuration information is applied in different ways according to the switching type indicated in the switching command message.

[0368] - When the terminal receives a handover command message, if the handover command message, ReconfigWithSync information, or MobilityControlInfo information indicates a first handover method (e.g., the first embodiment of this disclosure or a general handover method), or if the second embodiment of this disclosure (DAPS handover method) is not configured, or if no bearer is configured in the bearer configuration information of the second embodiment of this disclosure (DAPS handover method),

[0369] ■ When a default bearer is configured in the SDAP layer entity configuration information configured in the handover command message, the default bearer of the source base station can be configured as the default bearer of the target base station indicated in the configuration information.

[0370] ■ When the second mapping information between QoS flows and bearers is configured in the SDAP layer entity configuration information configured in the handover command message, the first mapping information between QoS flows and bearers already applied to the source base station can be released, and the second mapping information between QoS flows and bearers can be applied. Alternatively, the first mapping information between QoS flows and bearers already applied to the source base station can be replaced with the second mapping information between QoS flows and bearers.

[0371] ■ When a data discard timer value is configured in the PDCP layer entity configuration information configured in the switching command message, the discard timer value can be directly applied to the PDCP layer entity corresponding to the bearer identifier of the configuration information.

[0372] ■ When the drb-ContinueROHC indicator is configured as "false" in the PDCP layer entity configuration information configured in the handover command message, the header compression or decompression protocol context can be initialized in the PDCP layer entity corresponding to the bearer identifier in the configuration information. When the drb-ContinueROHC indicator is configured as "true", the header compression or decompression protocol context is not initialized in the PDCP layer entity corresponding to the bearer identifier in the configuration information.

[0373] ■ When a reordering timer value is configured in the PDCP layer entity configuration information configured in the switching command message, the reordering timer value can be directly applied to the PDCP layer entity corresponding to the bearer identifier of the configuration information.

[0374] ■ When a handover command message is received, the PDCP layer entity can be reconstructed. For example, for an SRB, a window state variable can be initialized, in which stored multiple data items (PDCP SDUs or PDCP PDUs) can be discarded. For an UM DRB, a window state variable can be initialized, in which the compression context or security key of the header (or data) of the target base station can be used to perform compression, encryption, or integrity protection on multiple data items that have not yet been sent to the lower layer entity or multiple data items whose PDCP discard timers have not yet expired, in ascending order of count values. When the reordering timer is running, the reordering timer can be stopped and initialized, and the received multiple data items (PDCP SDUs or PDCP PDUs) can be processed sequentially and transmitted to the upper layer entity. For an AM DRB, the window state variable can be not initialized, in which the compression context or security key of the header (or data) can be used to perform compression, encryption, or integrity protection on ascending order of PDCP sequence numbers or count values, starting from the first data item (PDCP SDU or PDCP PDU) that the lower layer entity has not recognized as successfully transmitted.

[0375] ■ When security key-related configuration information or security algorithms are configured in the security configuration information configured in the switching command message, new security keys or security configuration information can be exported by using the configuration information, existing security keys or security configuration information can be released, or existing security keys or security configuration information can be replaced with new security keys or security configuration information.

[0376] ■ When a new logical channel identifier is configured in the RLC layer configuration information configured in the handover command message, the new logical channel identifier can be configured by releasing the existing logical channel identifier corresponding to the bearer identifier indicated in the RLC layer entity configuration information, or by replacing the existing logical channel identifier with the new logical channel identifier.

[0377] ■ When an RLC reconstruction process is configured in the RLC layer entity configuration information configured in the handover command message, the RLC reconstruction process of the RLC layer entity corresponding to the bearer identifier indicated in the RLC layer configuration information can be executed. Specifically, the RLC reconstruction process can be executed so that the transmitting RLC layer entity can discard all stored multiple data items. Furthermore, when the reordering timer is running, the receiving RLC layer entity can stop and initialize the reordering timer, and can process all stored multiple data items to send them to the upper-layer entity. Additionally, the MAC layer entity can be initialized. Furthermore, the MAC layer entity of the source base station can be initialized, and can also be used for the MAC layer entity of the target base station.

[0378] ■As described above, the MAC layer entity can be initialized, and data transmission or reception at the source base station and for each bearer can be suspended. Furthermore, the MAC layer entity can stop PDCCH monitoring of the first terminal identifier (C-RNTI) assigned from the source base station. Additionally, the MAC layer entity can stop the process of requesting scheduling from the source base station, or it can release transmission resources for scheduling. Furthermore, the PHY or MAC layer entity can perform a random access procedure to the target base station. When the handover to the target base station is successfully completed, the PHY or MAC layer entity can resume data transmission or reception at the target base station and can start PDCCH monitoring on the second terminal identifier (C-RNTI) assigned from the target base station. Furthermore, the PHY or MAC layer entity can receive the system frame number from the target base station and perform synchronization. Additionally, the PHY or MAC layer can start or execute a process of requesting scheduling from the target base station.

[0379] ■As described above, the PHY layer entity can stop performing channel measurements, channel measurement reports, or sending HARQ ACK or NACK to the source base station. Furthermore, the PHY layer performs a downlink synchronization process relative to the target base station. Additionally, the configuration information about the target base station (or Spcell or Pcell) received in the handover command message can be configured for lower-layer entities or the PHY layer entity. When the handover to the target base station is successfully completed, the PHY layer entity can begin sending or sending HARQ ACK or NACK information to the target base station. Furthermore, the PHY or MAC layer entity can receive the system frame number from the target base station and perform synchronization. Additionally, the PHY or MAC layer entity can begin or execute a process requesting scheduling from the target base station.

[0380] ■ When the RLC layer entity configuration information configured in the switching command message is newly configured, the RLC reconstruction process can be performed on the RLC layer entity corresponding to the bearer identifier indicated in the RLC layer configuration information.

[0381] ■ When a second priority of a logical channel is newly configured in the MAC layer configuration information configured in the switching command message, the configuration can be performed by releasing the first priority corresponding to the logical channel identifier indicated in the configuration information, or by replacing the first priority corresponding to the logical channel identifier with the newly configured second priority.

[0382] ■> When a new second priority bit rate (prioritized bit rate, PBR) for a logical channel is configured in the MAC layer entity configuration information configured in the handover command message, it can be configured by releasing the first priority bit rate (prioritized bit rate, PBR) corresponding to the logical channel identifier indicated in the configuration information, or by replacing the first priority bit rate (prioritized bit rate, PBR) corresponding to the logical channel identifier with the newly configured second priority bit rate (prioritized bit rate, PBR). In the above description, the priority bit rate is a value that increases for each logical channel every predetermined time (e.g., TTI). When uplink transmission resources are received, a logical channel prioritization (LCP) process can be performed, taking into account priority and priority bit rate when sending data for the logical channel. Higher priority or a larger priority bit rate allows for the transmission of more data.

[0383] ■> When a second bucket size (bucketSizeDuration) for a logical channel is newly configured in the MAC layer entity configuration information configured in the handover command message, it can be configured by either releasing the first bucket size (bucketSizeDuration) corresponding to the logical channel identifier indicated in the configuration information, or replacing the first bucket size (bucketSizeDuration) corresponding to the logical channel identifier with the newly configured second bucket size (bucketSizeDuration). In the above description, the bucket size indicates the maximum value that the priority bit rate may have when the priority bit rate is accumulated.

[0384] ■> When configuring the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period, or logical channel group configuration information in the MAC layer configuration information configured in the handover command message, you can release the previously configured first allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period, or logical channel group configuration information, or replace the previously configured first allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period, or logical channel group configuration information with the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period, or the newly configured logical channel group configuration information mentioned above.

[0385] - When a terminal receives a handover command message, when a second handover method (e.g., the second embodiment of this disclosure or the DAPS handover method) is indicated or configured in the handover command message, ReconfigWithSync information, or mobilityControlInfo information; when a DAPS handover method is indicated or configured for each bearer identifier; when the disclosed second embodiment (DAPS handover method) is configured for a bearer in the bearer configuration information; or when the second embodiment (DAPS handover method) proposed in this disclosure is configured for at least one bearer in the bearer configuration information.

[0386] ■ When a default bearer is configured in the SDAP layer entity configuration information configured in the handover command message, the DAPS handover method proposed above in this disclosure can be executed. A second SDAP layer entity structure can be applied to maintain the default bearer of the existing source base station, and the default bearer information indicated in the configuration information can be configured as the default bearer of the target base station. Alternatively, when the first condition proposed in this disclosure is met, the default bearer of the existing source base station can be transferred to the default bearer of the target base station indicated in the configuration information.

[0387] ■ When the second mapping information between QoS flows and bearers is configured in the SDAP layer entity configuration information configured in the handover command message, the DAPS handover method proposed above in this disclosure can be executed. A second SDAP layer entity structure can be applied to maintain the first mapping information between QoS flows and bearers already applied to the data of the source base station, and the second mapping information between QoS flows and bearers can be applied to the data of the target base station. Alternatively, when the first condition proposed in this disclosure is met, the second mapping information between QoS flows and bearers of the target base station can be applied.

[0388] ■ When a data discard timer value is configured in the PDCP layer entity configuration information configured in the handover command message, the DAPS handover method proposed in this disclosure can be executed. The discard timer value can be directly applied to the PDCP layer entity corresponding to the bearer identifier of the configuration information by applying the second PDCP layer entity structure.

[0389] ■ PDCP layer entities that have indicated or configured the DAPS handover method in the handover command message may not be rebuilt and can perform the following procedures. For example, for SRBs, window state variables can be initialized (the initialization of variables can be omitted so that a rollback can be performed in case of DAPS handover failure). Specifically, when the counter value or window state variable value is initialized, to address the security issue of using the same security key and reusing the same counter value from the beginning when performing the DAPS handover rollback procedure (the risk of security key exposure due to sending different data items using the same security key and the same counter value during the DAPS handover rollback procedure), the counter value, transmission window state variable (TX_NEXT), or reception window state variable (RX_NEXT and RX_DELIV) may not be initialized, and the values ​​of existing variables can be used continuously or retained. Alternatively, stored multiple data items (PDCP SDU or PDCP PDU) can be discarded. Alternatively, for UM DRBs configured with the DAPS handover method, the window state variable may not be initialized, and multiple data items that have not yet been sent to lower-level entities or data whose PDCP discard timers have not yet expired may be continuously sent to or received from the source base station. Alternatively, for AM DRBs configured with the DAPS handover method, the window state variable may not be initialized, and data may be continuously sent to or received from the source base station. Furthermore, more specifically, regarding the procedure for the SRB, the SRB for the source base station may be suspended, or the SRB for the target base station may be suspended. To address the security issue described above where the same count value is reused from the beginning when performing the DAPS handover rollback procedure, the existing count value of the source base station's SRB or the value of the transmit or receive window variable may be applied to or retained in the SRB established for the target base station (or by configuring the count value of the source base station's SRB or the value of the transmit or receive window variable to be the count value of the target base station's SRB or the value of the transmit or receive window variable). When a security key for the target base station is configured, the target base station's security key can be exported or applied to the target base station's SRB. The SRB's PDCP layer entity can then perform encryption, decryption, integrity protection, or verification processes by applying the target base station's security key. Furthermore, when a PDCP reconstruction process is configured in the handover command message, the PDCP reconstruction process can be performed on the SRB. Additionally, for the source base station's SRB, old data (e.g., the source base station's RRC messages) can be discarded. Procedures for the target base station's SRB can be defined as new procedures (e.g., DAPS SRB establishment or PDCP layer entity reconstruction procedures) and instructed, triggered, or executed. Furthermore, procedures for the SRB can be extended and applied to UM DRBs or AM DRBs that are not configured with a DAPS handover method.As an alternative approach, regarding the process for the SRB, the SRB for the source base station can be suspended, or when no security key for the target base station is configured, for the SRB for the target base station, to address the security issue mentioned above where the same count value is reused from the beginning during the DAPS handover backoff process, the existing count value or the value of the transmit or receive window variable of the source base station's SRB can be applied to the SRB established for the target base station or kept in use (or by configuring the count value or the value of the transmit or receive window variable of the source base station's SRB as the count value or the value of the transmit or receive window variable of the target base station's SRB). However, when the security key for the target base station is configured, the SRB for the target base station can be established by initializing the count value or the value of the transmit or receive window variable. Furthermore, when a PDCP reconstruction process is configured, a PDCP reconstruction process can be performed for the SRB.

[0390] ■ A PDCP layer entity that does not specify or configure a DAPS handover method in the handover command message can rebuild the PDCP layer entity. For example, for an SRB, a window state variable can be initialized, in which stored multiple data items (PDCPSDU or PDCP PDU) can be discarded. For an UM DRB, a window state variable can be initialized, in which the transmission or retransmission can be performed on multiple data items that have not yet been sent to the lower layer entity or multiple data items whose PDCP discard timers have not yet expired, based on the header (or data) compression context or security key of the target base station, by performing compression, encryption, or integrity protection on multiple data items that have not yet been sent to the lower layer entity in ascending order of count values. When the reordering timer is running, the reordering timer can be stopped and initialized, and the received multiple data items (PDCP SDU or PDCP PDU) can be processed sequentially and transmitted to the upper layer entity. For an AM DRB, a window state variable can be not initialized, in which the transmission or retransmission can be performed on the header (or data) compression context or security key by performing compression, encryption, or integrity protection in ascending order of PDCP sequence number or count value, starting from the first data item (PDCP SDU or PDCP PDU) that the lower layer entity did not recognize as successfully transmitted. In addition, the RLC layer entity can also perform the reconstruction process.

[0391] ■ When the drb-ContinueROHC indicator is configured as "false" in the PDCP layer configuration information indicating or configuring the DAPS handover method in the handover command message, the DAPS handover method described above in this disclosure can be executed. A second PDCP layer entity structure can be applied to use the header compression or decompression protocol context of the source base station without modification. In the PDCP layer entity corresponding to the bearer identifier of the configuration information, the header compression or decompression protocol context of the target base station is initialized, starting from an initial state (e.g., IR state). When the drb-ContinueROHC indicator is configured as "true", the DAPS handover method described above in this disclosure can be executed. A second PDCP layer entity structure can be applied to use the header compression or decompression protocol context of the source base station in the PDCP layer corresponding to the bearer identifier of the configuration information without modification, so that the header compression or decompression protocol context of the target base station is applied equivalently to the header compression or decompression protocol context of the source base station. For example, the header compression or decompression protocol context of the source base station can be applied without modification by being copied to the header compression or decompression protocol context of the target base station. As an alternative approach, the same header compression or decompression protocol context can be applied to either the target or source base station.

[0392] ■ When a reordering timer value is configured in the PDCP layer entity configuration information that indicates or configures the DAPS handover method in the handover command message, the DAPS handover method proposed in this disclosure can be executed, and a second PDCP layer entity structure can be applied to directly apply the reordering timer value to the PDCP layer entity corresponding to the bearer identifier of the configuration information.

[0393] ■ When the handover command message indicates or configures the security configuration information of the DAPS handover method and configures the security key-related configuration information or security algorithm, or when there is an indicator indicating a new process in the PDCP layer entity configuration information, the new security key or security configuration information can be derived by using the configuration information, the DAPS handover method proposed above in this disclosure can be executed, the second PDCP layer entity structure can be applied to maintain the existing security key or security configuration information of the source base station, and the security key or security configuration information of the target base station can be configured as a new security key or security configuration information.

[0394] ■ When a new logical channel identifier is configured in the RLC layer configuration information of the bearer that indicates or configures the DAPS handover method in the handover command message, the DAPS handover method proposed above in this disclosure can be executed. The second PDCP layer entity structure can be applied to maintain the existing logical channel identifier of the RLC layer entity or MAC layer entity of the first bearer of the source base station corresponding to the bearer identifier indicated in the RLC layer entity configuration information, and the new logical channel identifier indicated in the configuration information can be configured relative to the RLC layer entity or MAC layer entity of the second bearer of the target base station.

[0395] ■ In the RLC layer entity configuration information of the bearer that indicates or configures the DAPS handover method configured in the handover command message, the RLC reconstruction process may not be performed on the RLC layer entity of the source base station. Specifically, the transmitting RLC layer entity can continue to transmit multiple stored data items without performing the RLC reconstruction process, and furthermore, the receiving RLC layer entity can continuously process multiple stored data items along with the received data, thereby avoiding data interruption time. However, when the first condition proposed in this disclosure is met, according to the method proposed in this disclosure, the PDCP layer entity configured with the DAPS handover method can transmit a PDCP user data discard indicator (PDCP data PDU) to the RLC layer entity of the source base station to indicate the discard of data (PDCP data PDU) regarding the AM bearer or UM bearer. Therefore, the RLC layer entity of the source base station discards the PDCP data PDU, but can send the PDCP control PDU without discarding the PDCP control PDU.

[0396] ■ For RLC layer entities that bearer a DAPS handover method not specified in the handover command message, an RLC reconstruction procedure can be performed, or, if an RLC reconstruction procedure is configured, it can be performed. Specifically, an RLC reconstruction procedure can be performed, causing the transmitting RLC layer entity to discard all stored multi-function data (PDCP data PDUs or PDCP control PDUs). Furthermore, when a reordering timer is running, the receiving RLC layer entity can stop and initialize the reordering timer, and can process all stored multi-function data and send it to the upper-layer entity.

[0397] ■ When the RLC layer entity configuration information of the bearer that indicates or configures the DAPS handover method in the handover command message is newly configured, the DAPS handover method proposed in this disclosure can be executed, and the second PDCP layer structure can be applied, so that for the RLC layer entity of the first bearer of the source base station corresponding to the bearer identifier indicated in the RLC layer configuration information, the existing RLC configuration information can be maintained, and for the RLC layer entity of the second bearer of the target base station, the new RLC layer configuration information indicated in the configuration information can be configured.

[0398] ■ Can execute what will be disclosed in this publication Figure 1j Method 1, Method 2, or Method 3 for configuring MAC layer entities are proposed in the document.

[0399] ■ Can be executed in Figure 1k The proposed methods 1, 2, or 3 for configuring MAC layer entities allow for continuous data transmission or reception for bearers that have indicated or configured a DAPS handover method in the MAC layer entity, without initializing the MAC layer entity. For bearers that have not indicated or configured a DAPS handover method, data transmission or reception can be paused.

[0400] ■ PDCCH monitoring of the first terminal identifier (C-RNTI) assigned from the source base station can be performed continuously without initializing the MAC layer entity of the source base station. Furthermore, the MAC layer entity of the source base station can continue to execute the process of requesting scheduling from the source base station. Additionally, the PHY or MAC layer entity of the target base station can apply configuration using the configuration information received in the handover command message and execute the random access procedure to the target base station. When the handover to the target base station is successfully completed, the PHY or MAC layer entity of the target base station can begin sending or receiving data to the target base station and can begin PDCCH monitoring of the second terminal identifier (C-RNTI) assigned from the target base station. Furthermore, the PHY or MAC layer entity can receive the system frame number from the target base station and perform synchronization. Additionally, the PHY or MAC layer of the target base station can begin or execute the process of requesting scheduling from the target base station. In the above description, the terminal may perform PDCCH monitoring on the first terminal identifier allocated from the source base station in the PHY or MAC layer entity for the source base station, and may perform PDCCH monitoring on the second terminal identifier allocated from the target base station in the PHY or MAC layer entity for the target base station, until the connection with the source base station is released or until the second condition set forth in this disclosure is met. In the above description, when the connection with the source base station is released, or when the second condition set forth in this disclosure is met, the terminal may stop PDCCH monitoring on the first terminal identifier allocated from the source base station in the PHY or MAC layer entity for the source base station, or may release the transmission resources used for the scheduling request.

[0401] ■In the above description, the PHY layer entity of the source base station can maintain its configuration information or continue to perform channel measurements, channel measurement reports, or send HARQ ACK or NACK for the source base station. Furthermore, the PHY or MAC layer entity of the target base station performs downlink synchronization procedures with respect to the target base station. Additionally, the configuration information of the target base station (or Spcell or Pcell) received in the handover command message can be configured for the target base station's lower-layer entities or PHY layer entities. When the handover to the target base station is successfully completed, the PHY or MAC layer entity of the target base station can begin sending or send HARQ ACK or NACK information to the target base station. Furthermore, the PHY or MAC layer entity of the target base station can receive the system frame number from the target base station and perform synchronization. Furthermore, the PHY or MAC layer entity of the target base station can begin or perform procedures such as requesting scheduling from the target base station, performing channel measurements, or reporting channel measurement results. In the above description, the terminal may perform PDCCH monitoring on the first terminal identifier allocated from the source base station in the PHY or MAC layer entity for the source base station, and may perform PDCCH monitoring on the second terminal identifier allocated from the target base station in the PHY or MAC layer entity for the target base station, until the connection with the source base station is released or until the second condition set forth in this disclosure is met. In the above description, when the connection with the source base station is released, or when the second condition set forth in this disclosure is met, the terminal may cease PDCCH monitoring on the first terminal identifier allocated to the source base station in the PHY or MAC layer entity, or may release the transmission resources used for the scheduling request.

[0402] ■ Can execute what will be disclosed in this publication Figure 1j Method 1, Method 2, or Method 3 for configuring or processing SRBs are proposed in the document.

[0403] ■ When a new logical channel priority is configured in the MAC layer entity configuration information configured in the handover command message, the DAPS handover method proposed in this disclosure can be executed, and a second PDCP layer entity structure can be applied. For the MAC layer entity of the first bearer of the source base station corresponding to the aforementioned bearer identifier, the existing configuration information can be maintained. For the MAC layer entity of the second bearer of the target base station, a new logical channel identifier indicated in the configuration information can be configured, and a newly configured second priority corresponding to the logical channel identifier indicated in the configuration information can be configured. Alternatively, when the first condition proposed in this disclosure is met, for each logical channel identifier, the priority can be applied to the MAC layer entity of the second bearer of the target base station.

[0404] ■ When a new priority bit rate (PBR) for a logical channel is configured in the MAC layer entity configuration information configured in the handover command message, the DAPS handover method proposed in this disclosure can be executed, and a second PDCP layer structure can be applied. For the MAC layer entity of the first bearer of the source base station corresponding to the indicated bearer identifier, the existing configuration information can be maintained. For the MAC layer entity of the second bearer of the target base station, a new logical channel identifier indicated in the configuration information can be configured, and a newly configured second priority bit rate corresponding to the logical channel identifier indicated in the configuration information can be configured. Alternatively, when the first condition proposed in this disclosure is met, the second priority bit rate can be applied to the logical channel identifier in the MAC layer entity of the second bearer of the target base station (thus, uplink transmission resources can be allocated fairly when a different handover method is indicated for each bearer). In the above description, when each logical channel identifier is first applied, the priority bit rate is a value that increases for each logical channel every predetermined time (e.g., TTI). When uplink transmission resources are received, a Logical Channel Prioritization (LCP) process can be performed. Priorities and priority bit rates can be considered when sending data on the logical channel. As the priority is higher or the priority bit rate is larger, more data can be sent.

[0405] ■ Furthermore, when applying the DAPS handover method, if the first condition proposed in this disclosure is not yet met, and therefore the terminal needs to send uplink data to the source base station via the first bearer, the MAC layer entity of the first bearer can select only the bearer or logical channel identifier when performing the LCP procedure, wherein the DAPS handover method (or a handover method that allows data to be continuously sent to the source base station even after receiving the handover command message) is indicated as the target of the LCP procedure, and the LCP procedure is executed. This is because for a bearer or logical channel identifier for which the DAPS handover method is not applied, uplink data cannot be sent to the source base station when the handover command message is received, therefore the bearer or logical channel identifier should not be selected as the target of the LCP procedure.

[0406] ■ When a new second bucket size (bucketSizeDuration) for the logical channel is configured in the MAC layer entity configuration information configured in the handover command message, the DAPS handover method proposed in this disclosure can be executed, and a second PDCP layer structure can be applied. Specifically, for the MAC layer entity of the first bearer of the source base station corresponding to the aforementioned bearer identifier, the existing configuration information can be maintained. For the MAC layer entity of the second bearer of the target base station, a new logical channel identifier indicated in the configuration information can be configured, and a newly configured second bucket size corresponding to the logical channel identifier indicated in the configuration information can be configured. Alternatively, when the first condition proposed in this disclosure is met, the second bucket size can be applied to the logical channel identifier in the MAC layer entity of the second bearer of the target base station (thus, uplink transmission resources can be fairly allocated when a different handover method is indicated for each bearer). The bucket size indicates the maximum value that the priority bit rate may have when the priority bit rate accumulates.

[0407] ■ When the MAC layer entity configuration information configured in the handover command message includes the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period or logical channel group configuration information, the DAPS handover method proposed above in this disclosure can be executed. The second PDCP layer structure can be used to maintain the existing configuration information of the MAC layer entity of the first bearer of the source base station corresponding to the above-mentioned bearer identifier, and configure the second allowed SCell information, allowed subcarrier spacing information, maximum PUSCH period or logical channel group configuration information indicated in the configuration information of the MAC layer entity of the second bearer of the target base station.

[0408] Figure 1j An embodiment of the present disclosure illustrates a method for applying specific configuration information when a DAPS switching method is configured.

[0409] As in this disclosure Figure 1jThe proposed method allows the terminal to generate or establish a MAC layer entity of the target base station (or target cell) at the time of receiving the handover command message (operation 1j-01), when the ReconfigWithSync information indicates a second handover method (e.g., the second embodiment of this disclosure or the DAPS handover method), when a DAPS handover method is indicated for each bearer identifier or logical channel identifier, when a DAPS handover method is configured for at least one bearer, or when a DAPS handover method is configured for a bearer. The terminal can continue to send data to or receive data from the source base station only for bearers (AM bearers or UM bearers) whose MAC layer entities indicate a DAPS handover method through the source base station (or source cell), until the first condition proposed in this disclosure is met from the time of receiving the handover command message. When the first condition is met, the terminal can switch uplink data to the target base station and receive downlink data from the source base station until the connection with the source base station is released. However, for bearers without a specified DAPS handover method, the terminal cannot continuously or previously perform data transmission or reception to or from the source base station until the first condition set forth in this disclosure is met from the time the handover command message is received. Therefore, to enable the terminal to perform the operations set forth in this disclosure, one or more of the following methods can be applied, and modeling as shown in operation 1j-21 or 1j-22 can be performed. When the second condition set forth in this disclosure is met and the source base station is thus released, modeling as shown in operation 1j-31 or 1j-32 can be performed.

[0410] As described above in this disclosure, when a terminal receives a handover command message, when a second handover method (e.g., the second embodiment of this disclosure or the DAPS handover method) is indicated in the ReconfigWithSync information, when a DAPS handover method is indicated for each bearer identifier or logical channel identifier, when a DAPS handover method is configured for at least one bearer, or when a DAPS handover method is configured for a bearer, the SRB configured in the MAC layer entity of the source base station can be suspended, and the terminal's upper-layer entity (e.g., the RRC layer entity) can instruct the MAC layer entity of the source base station to perform a reconfiguration (MAC reconfiguration) using configuration information that remains after excluding configuration information related to bearers for which a DAPS handover method is not indicated in the handover command message from the current MAC layer entity's configuration information. Alternatively, the terminal's upper-layer entity (e.g., the RRC layer entity) can instruct the MAC layer entity of the source base station to perform a reconfiguration (MAC reconfiguration) using configuration information that includes only configuration information related to bearers for which a DAPS handover method is indicated in the handover command message, which is derived from the configuration information of the current MAC layer entity. When a terminal reconfigures the MAC layer entity of the source base station, the MAC layer entity of the source base station retains only the logical channel identifier that indicates the DAPS handover method, or the priority bit rate or bucket size corresponding to the logical channel identifier, and releases, no longer uses, or no longer applies the logical channel identifier corresponding to the bearer that does not indicate the DAPS handover method, or the priority bit rate or bucket size corresponding to the logical channel identifier. Furthermore, in the above description, the upper-layer entity of the terminal (e.g., the RRC layer entity) can perform a PDCP reconstruction procedure or an RLC reconstruction procedure for a bearer that does not indicate a DAPS handover method, can apply the PDCP configuration information or RLC configuration information configured in the handover message, stop the bearer, stop the bearer in the MAC layer entity of the source base station, or configure the bearer for the MAC layer of the target base station (when the first condition is met, the bearer can be configured for the MAC layer entity of the target base station), can instruct the MAC layer entity of the target base station so that the bearer configuration information (such as logical channel identifier, priority bit rate, or bucket size) configured for the target base station for the bearer that does not indicate a DAPS handover method in the handover command message is configured or applied to the MAC layer entity of the target base station, and can establish a connection by transferring the connection of the PDCP layer entity or RLC layer entity corresponding to the bearer that does not indicate a DAPS handover method from the MAC layer entity of the source base station to the MAC layer entity of the target base station. Subsequently, for example, when the MAC layer entity of the terminal's source base station performs a Logical Channel Prioritization (LCP) procedure for data transmission starting from that point in time, only the logical channel identifier corresponding to the bearer indicating the DAPS handover method can be selected as a candidate group, and the LCP procedure can be performed.The process of reconfiguring the MAC layer entity for the source base station, performed by an upper-layer entity (e.g., the RRC layer), can partially reset (a partial MAC reset can be performed) the MAC layer entity of the source base station to perform the same process. For example, the configuration information of the MAC layer entity of a bearer that does not indicate a DAPS handover method can be initialized or released, or its application can be suspended. Furthermore, data transmission or reception to or from the source base station can be performed until the first condition set forth in this disclosure is met. In the above description, for a logical channel identifier corresponding to a bearer that does not indicate a DAPS handover method, the MAC layer entity of the source base station can first initialize the bit rate, may no longer apply the priority bit rate accumulation calculation process, and may release or stop the bearer; for a logical channel identifier corresponding to a bearer that indicates a DAPS handover method, the MAC layer entity of the source base station can continue to maintain the priority bit rate and may perform the accumulation calculation process. When the first condition is met, data transmission can be transferred to the target base station. The MAC layer entity of the target base station can first initialize the priority bit rate of the newly configured logical channel identifier (the logical channel identifier corresponding to the bearer indicating the DAPS handover method or the bearer not indicating the DAPS handover method), or can start the cumulative calculation (as another method, when a handover command message for the MAC layer entity of the target base station is received, the priority bit rate can be initialized first, and the cumulative calculation can be started). When no bearer indicating the DAPS handover method has been configured or suspended, the MAC layer entity for the target base station can be configured or resumed to perform data transmission or reception to or from the target base station, and can initialize the priority bit rate or start the cumulative calculation. Furthermore, data reception can be performed from either the source base station or the target base station until the second condition set forth in this disclosure is met. When the second condition is met (operation 1j-03), the MAC layer entity of the source base station can be initialized. In this initialization, the RLC layer entity, the PDCP layer entity, or the bearer configuration information corresponding to the bearer of the DAPS handover method not indicating connection to the MAC layer entity of the source base station can be released from the MAC layer entity of the source base station. The RLC layer entity or the bearer configuration information corresponding to the bearer indicating the DAPS handover method can be released from the second PDCP layer entity structure or the MAC layer entity of the source base station (operation 1j-31 or 1j-32).When the handover process fails but the connection with the source base station is valid, as described in this disclosure, the terminal can perform a fallback procedure to the source base station (operation 1j-02), restore the SRB configured in the MAC layer entity of the source base station, report the handover failure, apply the existing bearer configuration information of the source base station before receiving the handover command message again, apply the configuration information of the original MAC layer entity (e.g., the RRC layer entity can reconfigure the MAC layer entity configuration information used before receiving the handover command message for MAC layer entity configuration), and resume data transmission or reception with the source base station for each bearer (operation 1j-10). Alternatively, the terminal's upper-layer entity (e.g., the RRC layer entity) can instruct an RLC reconstruction procedure for bearers indicating a DAPS handover method or bearers not indicating a DAPS handover method. Alternatively, the configuration information of the source base station's MAC layer entity to be applied when the source base station performs the DAPS handover method can also be configured via RRC messages.

[0411] In the method proposed in this disclosure, when a terminal receives a handover command message, when the ReconfigWithSync information indicates a second handover method (e.g., the second embodiment of this disclosure or the DAPS handover method), when the DAPS handover method is indicated for each bearer identifier or each logical channel identifier, when the DAPS handover method is configured for at least one bearer, or when the DAPS handover method is configured for a bearer, the SRB configured for the MAC layer entity of the source base station is applied by applying one or more of the following methods.

[0412] - When the terminal receives a handover command message, if the ReconfigWithSync information indicates a second handover method (e.g., the second embodiment of this disclosure or the DAPS handover method), if the DAPS handover method is indicated for each bearer identifier or each logical channel identifier, if the DAPS handover method is configured for at least one bearer, or if the DAPS handover method is configured for a bearer,

[0413] ■Method 1: The SRB can be suspended in the MAC layer entity of the source base station. Alternatively, the window state variable can be initialized by performing an RLC layer entity reconstruction procedure or a PDCP layer entity reconstruction procedure for the SRB, and stored multiple data items (PDCP SDU, PDCP PDU, RLC SDU, or RLC PDU) can be discarded. Alternatively, the SRB can be configured for the MAC layer entity of the target base station according to the configuration received in the handover message. As another method, the SRB of the MAC layer entity of the source base station can be configured according to the configuration received in the handover message, and can be switched and connected to the MAC layer entity of the target base station. When the terminal fails to perform the handover procedure and performs the fallback procedure, the terminal can restore the SRB suspended in the MAC layer entity of the source base station, or reconfigure the SRB configured for the target base station to the existing configuration of the source base station, and restore the SRB by handing over and connecting to the MAC layer entity of the source base station.

[0414] ■Method 2: The SRB can be suspended in the MAC layer entity of the source base station. Alternatively, the RLC layer entity reconstruction process or the PDCP layer entity reconstruction process of the SRB can be suspended and not executed. Alternatively, the SRB can be configured for the MAC layer entity of the target base station according to the configuration received in the handover message. As another method, the SRB of the MAC layer entity of the source base station can be configured according to the configuration received in the handover message and can be switched and connected to the MAC layer entity of the target base station. When the terminal fails to perform the handover procedure and performs a fallback procedure, the terminal can restore the suspended SRB in the MAC layer entity of the source base station, or reconfigure the SRB configured in the target base station to the existing configuration of the source base station, and restore the SRB by performing a handover and connecting to the MAC layer entity of the source base station.

[0415] ■Method 3: The SRB can be suspended in the MAC layer entity of the source base station. Alternatively, the RLC layer entity reconstruction process can be performed without executing the PDCP layer entity reconstruction process of the SRB, and the window state variables can be uninitialized, but stored multiple data items (PDCP SDU, PDCP PDU, RLC SDU, or RLC PDU) can be discarded (to prevent unsent RRC messages from being unnecessarily transmitted later). Alternatively, the SRB can be configured for the MAC layer entity of the target base station according to the configuration received in the handover message. As another method, the SRB of the MAC layer entity of the source base station can be configured according to the configuration received in the handover message, and can be switched and connected to the MAC layer entity of the target base station. When the terminal fails to perform the handover process and performs the fallback process, the terminal can restore the SRB suspended in the MAC layer entity of the source base station, or reconfigure the SRB configured for the target base station to the existing configuration of the source base station, and restore the SRB by performing a handover and connecting to the MAC layer entity of the source base station. Furthermore, more specifically, for the SRB process, the SRB for the source base station can be suspended, or the SRB for the target base station can be suspended, to address the security issue arising from reusing the same count value from the outset when performing a DAPS handover fallback procedure, as described above. The existing count value or the value of the transmit or receive window variable of the source base station's SRB can be applied to or retained in the SRB established for the target base station (or by configuring the count value or the value of the transmit or receive window variable of the source base station's SRB to the count value or the value of the transmit or receive window variable of the target base station's SRB). Additionally, for the target base station's SRB, the target base station's security key can be derived or applied, and the PDCP layer entity of the SRB can perform encryption, decryption, integrity protection, or authentication processes by applying the target base station's security key. Furthermore, for the source base station's SRB, old data (e.g., the source base station's RRC messages) can be discarded. The procedure for the target base station's SRB can be defined as a new procedure (e.g., DAPS SRB establishment or PDCP layer entity reconstruction procedure) and instructed, triggered, or executed. The procedure for the SRB can be extended and applied to UM DRBs or AM DRBs that are not configured with a DAPS handover method. More specifically, when a terminal fails to perform a handover procedure and performs a fallback procedure, the terminal can restore the source base station's SRB or release the target base station's SRB. Alternatively, to address the security issues arising from reusing the same count value from the outset, the existing count value or the value of the transmit or receive window variable of the target base station's SRB can be applied to or retained in the source base station's SRB (or by configuring the target base station's SRB's count value or the value of the transmit or receive window variable to match the source base station's SRB's count value or the value of the transmit or receive window variable), and the target base station's SRB can be released.Furthermore, for the source base station's SRB, the source base station's security key can be applied, and the SRB's PDCP layer entity can perform encryption, decryption, integrity protection, or authentication processes by applying the source base station's security key. Additionally, for the source base station's SRB, old data (e.g., the source base station's RRC messages) can be discarded. The procedures for the SRB can be extended and applied to UM DRBs or AM DRBs that are not configured with a DAPS handover method. Alternatively, the source base station's SRB can be suspended, or the target base station's SRB can be suspended when no security key is configured for it, to address the security issue mentioned above where the same count value is reused from the beginning during a DAPS handover rollback process. The existing count value of the source base station's SRB, or the value of the transmit or receive window variable, can be applied to the SRB established for the target base station or retained (or by configuring the source base station's SRB's count value or the transmit or receive window variable value as the target base station's SRB's count value or transmit or receive window variable value). However, when configuring the security key for the target base station, the SRB can be established by initializing the count value or the value of the transmit or receive window variable when establishing the target base station's SRB. Furthermore, when the PDCP reconstruction procedure is configured, the PDCP reconstruction procedure can be performed for the SRB.

[0416] Furthermore, in the case where the terminal executes the second embodiment (DAPS handover method) of the efficient handover method proposed in this disclosure, when the terminal fails to perform a handover, a method is proposed to quickly perform a fallback to the source base station and reconfigure the connection by using the features of the DAPS handover method proposed above. Specifically, the features of the DAPS handover method proposed in this disclosure mean that data transmission or reception is performed while maintaining the connection with the source base station even during the handover process, and even in the event of a handover failure, a fallback using the existing wireless connection established with the source base station is specifically proposed in the following disclosure.

[0417] For reference to this disclosure Figure 1h In the second embodiment of the efficient handover method (DAPS handover method) described herein, even when the terminal receives a handover command message from the source base station, the terminal can still perform the handover to the target base station while maintaining data transmission or reception with the source base station, as proposed in Operation 1h-02. Furthermore, this disclosure proposes a fallback to the source base station procedure when the handover to the target base station procedure fails.

[0418] As mentioned above, when a terminal fails to perform the handover to the target base station and attempts to fall back to the source base station, a method is needed to determine whether the wireless connection between the terminal and the source base station is valid. This is because if the wireless connection between the terminal and the source base station is invalid, the fallback process also fails when the terminal fails to perform the handover and attempts to fall back to the source base station, resulting in excessively increased data interruption time and significant data loss. Furthermore, when the wireless connection between the terminal and the source base station is valid, the SRB configured in both the terminal and the source base station needs to be maintained.

[0419] First, this disclosure proposes new timers applicable to handover methods and outlines the specific operation of each timer. Furthermore, the specific operations of the timers can differ from one another depending on the type of handover method indicated by the handover command message in the base station. Additionally, methods for releasing or maintaining the connection configured with the source base station or SRB according to the handover method are proposed.

[0420] To efficiently execute the handover process, this disclosure proposes introducing a first timer (e.g., T304), a second timer (e.g., T310), a third timer (e.g., T312), or a fourth timer (e.g., a timer for rollback), and driving and applying these timers during the handover process. The first timer (e.g., T304), second timer (e.g., T310), third timer (e.g., T312), or fourth timer (e.g., a timer for rollback) proposed in this disclosure is proposed to perform different operations depending on the type of handover method indicated by the handover command message. In the above description, the first timer (e.g., T304) is a timer for determining whether the handover has been successfully executed, the second timer (e.g., T310) is a timer for determining whether the wireless connection is valid, the third timer (e.g., T312) is an auxiliary timer for determining whether the wireless connection is valid, and a timer for triggering the frequency measurement process and reporting the frequency measurement results. Furthermore, the fourth timer (e.g., a timer for rollback) is used to execute the rollback to the source base station process when the handover fails during the execution of the second embodiment of the efficient handover method (DAPS handover method) proposed in this disclosure, to send a message to the source base station indicating that the handover has failed, and to determine whether the rollback process has been successfully executed or has failed.

[0421] According to the indicated switching method, the specific operation of the first timer (e.g., T304), the second timer (e.g., T310), the third timer (e.g., T312), or the fourth timer (e.g., a timer for rollback) that supports the efficient switching method proposed in this disclosure is proposed as follows.

[0422] -1> If the terminal receives an asynchrony indication from a lower-layer entity (e.g., a MAC layer entity or a PHY layer entity) indicating a predetermined number of synchronization mismatches in the radio connection signal (e.g., this number can be configured by the base station), and detects a problem in the physical layer entity, the terminal may start a second timer (e.g., T310) when the first timer (e.g., T304) has not run. Furthermore, when the terminal receives a synchronization indication from a lower-layer entity indicating a predetermined number of good synchronization matches in the radio connection signal (e.g., this number can be configured by the base station), the terminal stops the second timer when a handover process is triggered (started), or when an RRC connection reconstruction process begins. When the second timer expires, the terminal triggers or starts the RRC connection reconstruction process. Alternatively, the terminal switches to RRC idle mode and triggers or starts the RRC connection reconstruction process.

[0423] -1> When the second timer (e.g., T310) is running, and a frequency measurement procedure is triggered for a frequency measurement identifier configured for a third timer (e.g., T312), the terminal starts the third timer. Furthermore, when the terminal receives a synchronization indication from a lower-layer entity indicating a predetermined number of good synchronization matches for the radio connection signal (e.g., this number can be configured by the base station), when a handover procedure is triggered (started), or when an RRC connection re-establishment procedure begins, the terminal stops the third timer. When the third timer expires, the terminal triggers or starts the RRC connection re-establishment procedure. Alternatively, the terminal switches to RRC idle mode and triggers or starts the RRC connection re-establishment procedure.

[0424] -1> In the case where the handover command message received by the terminal from the base station (including the handover indication message in the Mobility Control Info or Reconfiguration With Sync or RRC Reconfiguration message) indicates a first handover method (e.g., the first embodiment or a general handover method), in the case where the terminal receives a handover command message and the first handover method (e.g., the first embodiment or a general handover method of this disclosure) is indicated in the handover command message, Reconfig With Sync information, or Mobility Control Info information, in the case where the second embodiment (DAPS handover method) proposed in this disclosure is not configured, or in the case where the second embodiment (DAPS handover method) proposed in this disclosure is not configured to carry the bearer in the configuration information,

[0425] ■2> In this disclosure, when a handover command message is received (the message includes a handover indication in a Mobility Control info or ReconfigurationWithSync message or an RRCReconfiguration message), the terminal triggers the handover process and starts a first timer (e.g., T304).

[0426] ■2> When the handover process is triggered, the terminal releases the SRB (e.g., SRB1) configured for the source base station and configures the SRB (e.g., SRB1) for the target base station based on the configuration information configured in the handover command message.

[0427] ■2> When a handover process is triggered, the terminal may stop the second timer while it is running (e.g., T310). Even if the conditions for starting the second timer while the first timer (e.g., T304) is running are met (when the asynchronous indicator of the radio connection signal is received from the lower-level entity a predetermined number of times), the terminal may not start the second timer. That is, the second timer may not be used while the first timer is running.

[0428] ■2> When a switching process is triggered and the third timer (e.g., T312) is running, the terminal can stop the third timer. Furthermore, the terminal can start the third timer if the condition that the third timer only starts when the second timer (e.g., T310) is running is met (when a frequency measurement process is triggered for a frequency measurement identifier configured with the third timer). That is, since the second timer is not used when the first timer (e.g., T304) is running, the third timer can also be left unused.

[0429] ■2> When the terminal successfully completes the handover to the target base station, or when the terminal successfully completes the random access process, the terminal stops the first timer (e.g., T304).

[0430] ■2> When the first timer (e.g., T304) expires (e.g., when the handover to the target base station fails), the terminal executes the RRC...

Claims

1. A method performed by a terminal of a wireless communication system, the method comprising: Receive a handover command message from the source base station indicating a handover of at least one dual active protocol stack (DAPS) bearer; During DAPS handover, a Media Access Control (MAC) Sub-Protocol Data Unit (PDU) is received from the source base station, which includes MAC sub-PDUs of bearers not configured for DAPS handover. and Discard DAPS to switch MAC subPDUs that are not configured for the bearer.

2. The method of claim 1, wherein, The MAC sub-PDU for DAPS handover of an unconfigured bearer includes the Logical Channel Identifier (LCID) or Extended LCID (eLCID) value for the unconfigured bearer.

3. The method of claim 1, wherein, During DAPS handover, the terminal performs data transmission or reception with the source base station by using the protocol layer device for the source base station, and performs data transmission or reception with the target base station by using the protocol layer device for the target base station.

4. The method according to claim 1, further comprising: Create a protocol layer device for the target base station corresponding to at least one bearer configured for DAPS handover; and The random access procedure with the target base station is performed by using a protocol layer device for the target base station.

5. The method according to claim 1, further comprising: If the first condition is met, uplink data is sent to the target base station other than the source base station through the protocol layer device used by the target base station.

6. The method of claim 5, wherein, The first condition includes that the random access process to the target base station has been successfully completed.

7. The method according to claim 1, further comprising: Receive downlink data from the source base station until the second condition is met.

8. The method according to claim 7, wherein, The second condition includes the connection to the source base station being released via an explicit release command from the target base station.

9. A terminal for a wireless communication system, the terminal comprising: transceiver; and The controller, coupled to the transceiver, is configured to: Receive a handover command message from the source base station indicating a handover of at least one dual active protocol stack (DAPS) bearer; During DAPS handover, a Media Access Control (MAC) Sub-Protocol Data Unit (PDU) is received from the source base station, which includes MAC sub-PDUs of bearers not configured for DAPS handover. and Discard DAPS to switch MAC subPDUs that are not configured for the bearer.

10. The terminal according to claim 9, wherein, The MAC sub-PDU for DAPS handover of an unconfigured bearer includes the Logical Channel Identifier (LCID) or Extended LCID (eLCID) value for the unconfigured bearer.

11. The terminal according to claim 9, wherein During DAPS handover, the controller performs data transmission or reception with the source base station by using the protocol layer device for the source base station, and performs data transmission or reception with the target base station by using the protocol layer device for the target base station.

12. The terminal of claim 9, wherein, The controller is configured as follows: Create a protocol layer device for the target base station corresponding to at least one bearer configured for DAPS handover; and The random access procedure with the target base station is performed by using a protocol layer device for the target base station.

13. The terminal of claim 9, wherein, The controller is configured as follows: If the first condition is met, uplink data is sent to the target base station other than the source base station through the protocol layer device used by the target base station.

14. The terminal according to claim 13, wherein, The first condition includes that the random access process to the target base station has been successfully completed.

15. The terminal of claim 9, wherein, The controller is configured as follows: Receive downlink data from the target base station from the source base station until the second condition is met.

16. The terminal of claim 15, wherein, The second condition includes the connection to the source base station being released via an explicit release command from the target base station.

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