Method and apparatus for performing handover in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method for processing a control signal in a wireless communication system of the present disclosure may include: receiving a first control signal transmitted from a base station; processing the received first control signal; generating a second signal based on the processing; and transmitting the generated second control signal to the base station.

Description

Technical Field

[0001] The present disclosure relates to a wireless communication system or a mobile communication system, and more particularly to a method and apparatus for performing handover in a wireless communication system. Background Art

[0002] Fifth-generation (5G) mobile communication technology defines a wide frequency band, enabling high transmission rates and new services. This technology is achievable not only in "sub-6 GHz" frequency bands such as 3.5 GHz, but also in "above 6 GHz" frequency bands, known as millimeter waves, including 28 GHz and 39 GHz. Furthermore, consideration is being given to implementing 6G mobile communication technology (referred to as a "super 5G system") in terahertz (THz) frequency bands (e.g., the 95 GHz to 3 THz band) in order to achieve transmission rates fifty times faster than 5G mobile communication technology and ultra-low latency one-tenth that of 5G mobile communication technology.

[0003] At the start of the development of 5G mobile communication technology, in order to support services and meet performance requirements related to enhanced mobile broadband (eMBB), ultra-reliable low-latency communications (URLLC), and massive machine-type communications (mMTC), there has been ongoing standardization on beamforming and massive MIMO for mitigating radio wave path loss and increasing radio wave transmission range in millimeter waves, support for dynamic operation of parameter sets (e.g., operating multiple subcarrier spacings) and time slot formats for efficient utilization of millimeter wave resources, initial access technology for supporting multi-beam transmission and wideband, definition and operation of BWP (bandwidth part), new channel coding methods such as LDPC (low-density parity-check) codes for large-scale data transmission and polar codes for highly reliable transmission of control information, L2 preprocessing, and network slicing for providing dedicated networks tailored for specific services.

[0004] Currently, there are ongoing discussions on improvements and performance enhancements to initial 5G mobile communication technologies in view of the services to be supported by 5G mobile communication technologies, and there has been standardization of physical layers regarding technologies such as: V2X (Vehicle-to-Everything) for assisting driving decisions of autonomous vehicles based on information on the position and status of vehicles transmitted by vehicles and for enhancing user convenience, NR-U (Unlicensed New Radio) for system operation that is designed to comply with various regulatory requirements within unlicensed frequency bands, NR UE energy saving, Non-Terrestrial Networks (NTN) as UE-satellite direct communication for providing coverage in areas where communication with terrestrial networks is not possible, and positioning.

[0005] In addition, in the air interface architecture / protocol area, standardization is already underway for technologies such as the Industrial Internet of Things (IIoT), which supports new services through interconnection and integration with other industries; IAB (Integrated Access and Backhaul), which provides nodes for network service area expansion by integrating wireless backhaul links and access links; mobility enhancements including conditional handover and DAPS (Dual Active Protocol Stack) handover; and two-step random access (two-step RACH for NR) to simplify the random access procedure. In the system architecture / service area, standardization is also underway for the following: a 5G baseline architecture (e.g., a service-based architecture or service-based interface) for incorporating network function virtualization (NFV) and software-defined networking (SDN) technologies; and mobile edge computing (MEC) for receiving services based on UE location.

[0006] With the commercialization of 5G mobile communication systems, the already exponentially growing number of connected devices will be connected to communication networks, and accordingly, it is expected that enhanced functionality and performance of 5G mobile communication systems and the integrated operation of connected devices will become necessary. To this end, new research is being planned on extending reality (XR) to effectively support AR (augmented reality), VR (virtual reality), MR (mixed reality), etc., improving 5G performance and reducing complexity through the use of artificial intelligence (AI) and machine learning (ML), supporting AI services, supporting metaverse services, and drone communications.

[0007] Furthermore, such development of 5G mobile communication systems will serve as the foundation for the development of not only new waveforms for providing terahertz band coverage for 6G mobile communication technology, multi-antenna transmission technologies such as full-dimensional MIMO (FD-MIMO), array antennas, and massive antennas, metamaterial-based lenses and antennas for improving terahertz band signal coverage, high-dimensional spatial multiplexing technology using OAM (orbital angular momentum), and RIS (Reconfigurable Smart Surfaces), but also full-duplex technology for improving the frequency efficiency of 6G mobile communication technology and improving system networks, AI-based communication technology for leveraging satellites and AI (artificial intelligence) to achieve system optimization and internalize end-to-end AI support functions from the design stage, and next-generation distributed computing technology for implementing services at a complexity level that exceeds the operational capabilities of UEs by utilizing ultra-high-performance communication and computing resources.

[0008] The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with respect to the present disclosure. Summary of the Invention

[0009] Technical issues

[0010] Based on the above discussion, the present disclosure is to provide an apparatus and method capable of effectively providing services in a wireless communication system.

[0011] More specifically, the present disclosure provides a method and apparatus in which, when a terminal is receiving service from a current serving cell via a specific beam, a beam belonging to another cell can be measured and reported, and if the beam of a neighboring cell becomes better, a cell change to the neighboring cell can be indicated and performed via Layer 1 / Layer 2 (L1 / L2) signaling.

[0012] Solution to the problem

[0013] The present disclosure relates to a method for processing a control signal in a wireless communication system, the method comprising: receiving a first control signal transmitted from a base station; processing the received first control signal; generating a second signal based on the processing; and transmitting the generated second control signal to the base station.

[0014] Through the method and apparatus for effectively managing L1 / L2 triggered mobility (LTM) and an existing layer 3-based handover operation provided in the present disclosure, two different handover requests are not transmitted to a terminal, so that the terminal can perform a more reliable handover operation.

[0015] Advantageous effects obtainable from the present disclosure may not be limited to the above-mentioned effects, and other effects that are not mentioned may be clearly understood by those skilled in the art to which the present disclosure pertains through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0017] Figure 1 The structure of a wireless communication system according to various embodiments of the present disclosure is shown;

[0018] Figure 2 The radio protocol structure of a wireless communication system according to various embodiments of the present disclosure is shown;

[0019] Figure 3 A network including a radio protocol for a wireless communication system according to various embodiments of the present disclosure is shown;

[0020] Figure 4 1. A scenario in which a terminal connected to a serving cell transmits and receives data via a beam of a TRP of a target cell according to various embodiments of the present disclosure is shown;

[0021] Figure 5A scenario in which a terminal according to various embodiments of the present disclosure transmits and receives data by changing a serving cell and a beam to a TRP of a cell supporting L1 / L2-based beam changing is shown;

[0022] Figure 6 shows the overall operation in which L1 / L2-based handover is successfully performed according to various embodiments of the present disclosure;

[0023] Figure 7 shows the overall operation in which L1 / L2 based handover is performed and fails according to various embodiments of the present disclosure;

[0024] Figure 8 1. The overall operation of triggering L1 / L2-based handover in a serving cell (DU) and transmitting corresponding triggering information from the serving cell (DU) to a base station CU according to various embodiments of the present disclosure is shown;

[0025] Figure 9 1. Shows the overall operation of the existing layer 3 handover being triggered in the base station CU and the corresponding triggering information being transmitted from the base station CU to the serving cell (DU) according to various embodiments of the present disclosure;

[0026] Figure 10 shows the overall operation of the base station CU and the serving cell (DU) transmitting the handover triggering information according to various embodiments of the present disclosure;

[0027] Figure 11 The operation of performing L1 / L2-based beam changing and terminal switching according to various embodiments of the present disclosure is shown;

[0028] Figure 12 illustrates base station operations according to various embodiments of the present disclosure;

[0029] Figure 13 shows the structure of a terminal according to various embodiments of the present disclosure; and

[0030] Figure 14 The structure of a base station according to various embodiments of the present disclosure is shown. DETAILED DESCRIPTION

[0031] Hereinafter, the operating principle of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description of the present disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the description may make the subject matter of the present disclosure unnecessarily unclear. The terms to be described below are terms defined in consideration of the functions in the present disclosure, and may vary according to the user, the user's intention or habit. Therefore, the definition of terms should be based on the content in the entire specification. In the following description, for the convenience of description, terms for identifying access nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, etc. are illustratively used. Therefore, the present disclosure is not limited to the terms used below, and other terms referring to subjects with equivalent technical meanings may be used.

[0032] In the following description of the present disclosure, for the sake of convenience, terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard will be used. However, the present disclosure is not limited to these terms and names and can be applied in the same manner to systems conforming to other standards.

[0033] Because existing Layer 3-based handovers can operate simultaneously, two types of handover signals may be indicated simultaneously. This may occur because the entities that determine L1 / L2 Triggered Mobility (LTM) and existing handover operations differ, and ultimately, the base station handover instructions to the terminal do not match, which may cause the terminal to question which operation to perform. The present disclosure describes a method and apparatus for efficiently managing L1 / L2-based handovers and Layer 3-based handovers in a wireless communication system to address the aforementioned issues.

[0034] Figure 1 The structure of a wireless communication system according to various embodiments of the present disclosure is shown.

[0035] refer to Figure 1 The radio access network of the wireless communication system may include a next-generation base station (new radio node B, hereinafter referred to as NR NB) 110, and a new radio core network (NR CN) or next-generation core network (NG CN) 105. A user terminal (new radio user equipment, hereinafter referred to as NR UE or NR terminal) 115 may access an external network via the NR NB 110 and the NR CN 105.

[0036] exist Figure 1In this example, NR NB 110 corresponds to the evolved Node B (eNB) of a conventional LTE system. Alternatively, NR NB 110 may comprise a gNode B (gNB) of an NR system. NR NB 110 can connect to NR UE 115 via a radio channel and provide superior service compared to conventional Node Bs. In wireless communication systems or mobile communication systems, since all user traffic is served over a shared channel, the NR NB 110 can serve as a device that collects status information (such as the UE's buffer status, available transmit power, and channel status) and performs scheduling accordingly. Typically, one NR NB 110 can control multiple cells. To achieve ultra-high-speed data transmission exceeding existing LTE, wireless communication systems or mobile communication systems can provide bandwidths wider than the existing maximum bandwidth, employ orthogonal frequency division multiplexing (OFDM) as a radio access technology, and integrate beamforming technology. Furthermore, wireless communication systems or mobile communication systems can employ adaptive modulation and coding (AMC) schemes to determine the modulation scheme and channel coding rate based on the UE's channel status. The NR CN 105 can perform functions such as mobility support, bearer configuration, and QoS configuration. The NR CN 105 is a device responsible for various control functions and UE mobility management functions and can be connected to multiple base stations. In addition, the wireless communication system or mobile communication system can interoperate with the existing LTE system, and the NR CN 105 can be connected to the MME 125 via a network interface. The MME 125 can be connected to the eNB 130, which is an existing base station.

[0037] Figure 2 A radio protocol structure of a wireless communication system according to various embodiments of the present disclosure is shown.

[0038] refer to Figure 2 , the radio protocol of the wireless communication system may include an NR SDAP layer 201 or 245, an NR PDCP layer 205 or 240, an NR RLC layer 210 or 235, and an NR MAC layer 215 or 230 in each of the UE and the NR base station.

[0039] The main functions of the NR SDAP layer 201 or 245 may include but are not limited to the following:

[0040] -Transmission of user data (transmission of user plane data);

[0041] - Mapping between QoS flows and data bearers for uplink and downlink (mapping between QoS flows and DRBs for both DL and UL);

[0042] - marking the QoS Flow ID in both uplink and downlink (marking the QoS Flow ID in both DL and UL packets); and / or

[0043] - Mapping of Reflective QoS flows to data bearers with respect to UL SDAP PDUs (Reflective QoS flow to DRB mapping for UL SDAP PDUs).

[0044] According to an embodiment, the UE can be configured to use the header of the SDAP layer device or the functions of the SDAP layer device through an RRC message for each PDCP layer device, each bearer, or each logical channel. In addition, when the SDAP header is configured, the SDAP header's one-bit NAS QoS reflection configuration indicator (NAS Reflective QoS) and one-bit AS QoS reflection configuration indicator (AS Reflective QoS) can instruct the UE to update or reconfigure the mapping information related to QoS flows and data bearers for uplink and downlink. The SDAP header can include QoS flow ID information indicating QoS. QoS information can be used to smoothly support services, such as data processing priority and scheduling information.

[0045] The main functions of the NR PDCP layer 205 or 240 may include but are not limited to the following:

[0046] - Header compression and decompression (ROHC only);

[0047] -Transmission of user data;

[0048] - In-sequence delivery (in-sequence delivery of upper layer PDUs);

[0049] - Out-of-order delivery (out-of-order delivery of upper layer PDUs);

[0050] - Reordering (for received PDCP PDU reordering);

[0051] - Duplicate detection (duplicate detection of lower layer SDUs);

[0052] -Retransmission (retransmission of PDCP SDU);

[0053] - encryption and decryption; and / or

[0054] - Timer-based SDU discard (Timer-based SDU discard in uplink).

[0055] Reordering of NR PDCP equipment refers to the function of reordering PDCP PDUs received from lower layers in an order based on the PDCP sequence number (SN). Reordering of NR PDCP equipment may include the function of delivering data to higher layers according to the reordered order, the function of directly delivering data without considering the order, the function of reordering to record lost PDCP PDUs, the function of reporting the status of lost PDCP PDUs to the transmitting side, or the function of requesting retransmission of lost PDCP PDUs.

[0056] The main functions of the NR RLC layer 210 or 235 may include but are not limited to the following functions:

[0057] -Data transmission (transmission of upper layer PDU);

[0058] - In-sequence delivery (in-sequence delivery of upper layer PDUs);

[0059] - Out-of-order delivery (out-of-order delivery of upper layer PDUs);

[0060] -ARQ (error correction through ARQ);

[0061] - Concatenation, segmentation and reassembly (concatenation, segmentation and reassembly of RLC SDUs);

[0062] - Resegmentation (resegmentation of RLC data PDUs);

[0063] - Reordering (reordering of RLC data PDUs);

[0064] - Repeated testing;

[0065] - Error detection (protocol error detection);

[0066] - RLC SDU discard; and / or

[0067] -RLC reconstruction.

[0068] The in-sequence delivery of the NR RLC device may indicate a function of sequentially delivering an RLC SDU received from a lower layer to an upper layer. In addition, the in-sequence delivery may include a function of reassembling the plurality of RLC SDUs and delivering the reassembled RLC SDUs if one original RLC SDU is divided into a plurality of RLC SDUs and then the RLC SDUs are received, may include a function of rearranging the received RLC PDUs according to an RLC sequence number (SN) or a PDCP sequence number (SN), may include a function of rearranging the order to record lost RLC PDUs, may include a function of reporting the status of lost RLC PDUs to a transmitting side, may include a function of requesting retransmission of lost RLC PDUs, may include a function of sequentially delivering only the RLC SDUs preceding the lost RLC SDU to an upper layer if there is a lost RLC SDU, may include a function of sequentially delivering all RLC SDUs received before the timer is started to an upper layer if a predetermined timer has expired despite the presence of a lost RLC SDU, or may include a function of sequentially delivering all RLC SDUs received so far to an upper layer if a predetermined timer has expired despite the presence of a lost RLC SDU. In addition, the NR RLC device can process the RLC PDUs in the order in which they were received (the order in which the RLC PDUs have arrived, regardless of the order based on the sequence number), and then deliver the processed RLC PDUs to the PDCP device regardless of the order (out-of-order delivery). In the case of segmentation, the NR RLC device can receive segments stored in the buffer or to be received in the future, reconfigure the segments into a complete RLC PDU, then process the RLC PDU, and deliver the processed RLC PDU to the PDCP device. The NR RLC layer may not include a concatenation function, and the concatenation function may be performed in the NR MAC layer or replaced by a multiplexing function of the NR MAC layer.

[0069] The out-of-order delivery function of the NR RLC device may indicate a function of immediately transmitting the RLC SDU received from the lower layer regardless of its order. In addition, the out-of-order delivery function may include the following functions: if one original RLC SDU is divided into several RLC SDUs and then the RLC SDUs are received, the several RLC SDUs are reassembled and the reassembled RLC SDUs are transmitted, and may include storing the RLC sequence number (SN) or PDCP sequence number (SN) of the received RLC PDU and arranging the sequence to record the lost RLC PDU.

[0070] The NR MAC layer 215 or 230 may be connected to several NR RLC layer devices configured in a single UE, and main functions of the NR MAC layer 215 or 230 may include the following:

[0071] - Mapping (mapping between logical channels and transport channels);

[0072] -Multiplexing and demultiplexing (MAC SDU multiplexing / demultiplexing);

[0073] -Dispatch information report;

[0074] -HARQ (error correction through HARQ);

[0075] - Priority handling between logical channels (priority handling between logical channels of a UE);

[0076] Priority handling between UEs (priority handling between UEs with the help of dynamic scheduling);

[0077] -MBMS service identifier;

[0078] - transport format selection; and / or

[0079] -filling.

[0080] The NR PHY layer 220 or 225 may perform channel coding and modulation of higher-layer data to make the data into OFDM symbols and transmit the OFDM symbols through a wireless channel, or may perform demodulation and channel decoding of OFDM symbols received through a wireless channel and then transmit the OFDM symbols to a higher layer.

[0081] Figure 3 A network including a radio protocol of a wireless communication system according to various embodiments of the present disclosure is shown.

[0082] refer to Figure 3A cell served by a beam-based NR gNB 305 may include multiple transmit receive points (TRPs) 310, 315, 320, 325, 330, 335, and 340. TRPs 310, 315, 320, 325, 330, 335, and 340 represent blocks that separate some of the functionality for transmitting and receiving physical signals from a traditional NR base station (eNB) and may include multiple antennas. The NR gNB 305 may also be denoted as a central unit (CU), and the TRPs may also be denoted as distributed units (DUs). The functionality of the NR gNB 305 and TRPs may be configured separately within each of the PDCP / RLC / MAC / PHY layers 345. That is, TRPs 315 and 325 may only have a PHY layer and perform the functions of the corresponding layers, TRPs 310, 335, and 340 may only have a PHY layer and a MAC layer and perform the functions of the corresponding layers, and TRPs 320 and 330 may only have a PHY layer, a MAC layer, and an RLC layer and perform the functions of the corresponding layers. In particular, TRPs 310, 315, 320, 325, 330, 335, and 340 may use beamforming technology to generate narrow beams in multiple directions using multiple transmit / receive antennas to transmit and receive data. User terminals 350 can access NR gNB 305 and external networks via TRPs 310, 315, 320, 325, 330, 335, and 340. In order to provide services to users, the NR gNB 305 can collect terminal status information such as buffer status, available transmission power status and channel status, and support the connection between the terminal and the core network (CN) (especially AMF / SMF) (e.g., user terminal 350) by scheduling the collected status information.

[0083] The TRP in the present disclosure may include structures 315 and 325 , wherein the TRP may have only a PHY layer and perform functions of a corresponding layer.

[0084] Figure 4 The present invention illustrates a scenario in which a terminal connected to a serving cell transmits and receives data via a beam of a transmit reception point (TRP) of a target cell according to various embodiments of the present disclosure. Specifically, Figure 4 A diagram illustrating a scenario for inter-cell beam management according to an embodiment and illustrating a scenario in which a terminal transmits and receives data via a beam of a TRP of a neighboring cell that supports L1 / L2-based beam change while maintaining connection with a serving cell is shown. According to various embodiments of the present disclosure, the cell to which the terminal is currently connected may be referred to as a serving cell, and the cell for handover may be referred to as a target cell or an object cell. According to an embodiment, a neighboring cell or another cell that is a non-serving cell may include a target cell or an object cell to which the terminal performs handover.

[0085] Figure 4 The present invention illustrates a case where multiple cells (TRP1-cell 1 and TRP2-cell 2) 410 and 415 exist within a single distributed unit (DU) 405. However, the overall content of the present disclosure is also applicable to the case where multiple DUs are located between each other (e.g., each DU constitutes a TRP-cell). In addition, in the present disclosure, a cell (TRP 2, cell 2) that is not a serving cell and supports L1 / L2-based mobility (beam change and serving cell change) may be referred to as a neighboring cell, a non-serving cell, an additional cell having a different physical cell identifier (PCI) from the serving cell, etc.

[0086] refer to Figure 4 The existing terminal beam change procedure 445 may include enabling the terminal 420 to transmit and receive data in a connected state via TRP 1 410 of the serving cell 1, using TCI state 1 425 or 430 as the best beam. The terminal may receive an indication of configuration information for L3 channel measurement (radio resource management (RRM)) on an additional cell (TRP 2-cell 2) 415 having a PCI different from that of the serving cell via RRC configuration information from the serving cell 410, and may perform L3 measurement operations 446 for the corresponding frequency and cell. The serving cell (TRP 1-cell 1) 410 may then instruct a handover to the corresponding cell (TRP 2-cell 2) 415 based on the reported measurement values ​​in operation 447, and after the handover is complete, the additional RRC configuration information may be transmitted to the terminal 420 via TRP 2-cell 2 415 in operation 448. The RRC configuration information may include UL / DL configuration information and L1 measurement-related configuration (CSI-RS measurement and reporting) in the corresponding cell, and specifically may include TCI state configuration information for PDCCH and PDSCH. The terminal may perform L1 measurement in operation 449 according to the configuration, and the base station may update the TCI state in operation 450 via L1 / L2 signaling based on the measurement report. During this process, TCI state 2 440 may be indicated as the best beam. In the above operation, cell 1 may be the serving cell before the handover, and cell 2 may be the serving cell after the handover. That is, multiple processes and additional time may be required before the best beam is indicated, even after the handover.

[0087] According to an embodiment of the present disclosure, unlike the existing terminal beam changing process 445, the improved beam changing technique 455 considered in the present disclosure may include the following: The terminal may receive a beam configuration associated with an additional cell (TRP 2-cell 2) 415 having a PCI different from that of the serving cell 410 via RRC configuration information (e.g., operation 456) from the serving cell 410. For the beam configuration associated with the additional cell (TRP 2-cell 2) 415 having a PCI different from that of the serving cell, that is, the portion associated with the TCI state corresponding to TRP 2, a method of associating and indicating a new cell ID (physical cell ID, PCI; additional PCI-r17) is applied, as shown in [Table 1].

[0088] [Table 1]

[0089]

[0090] In addition, a unified TCI status framework can be applied to beam management between corresponding cells.

[0091] According to an embodiment of the present disclosure, a unified TCI status framework may be a framework for applying a common TCI status framework in uplink, downlink, common channels, and dedicated channels, and may be configured as shown in [Table 2] in one of a joint UL / DL mode and a separate UL / DL mode.

[0092] [Table 2]

[0093]

[0094] 1. Joint UL / DL mode: UL and DL are configured to share the same TCI configuration (in PDSCH-Config), as shown in [Table 3].

[0095] [Table 3]

[0096]

[0097] 2. Separate UL / DL mode: Separate TCI configurations are provided for UL and DL. The TCI state for DL ​​complies with the configuration in dl-OrJoint-TCIStateList-r17 (in PDSCH-Config), and the TCI state for UL complies with ul-TCI-StateList-r17 (in BWP-UplinkDedicated), as shown in [Table 4].

[0098] [Table 4]

[0099]

[0100] After the terminal is provided with a TRP 2-Cell 2 configuration while RRC-connected to serving cell 1, in operation 457, the terminal may perform L1 measurements on TRP 2-Cell 2 based on the received TRP 2-Cell 2 configuration and report the performance results to serving cell (Cell 1) 410. If the measurement results determine that a change to a specific beam (TCI state 2) 435 or 440 of TRP 2 (Cell 2) 415 is required, rather than the serving cell beam (TCI state 1) 425 or 430, the serving cell may trigger a beam change in operation 458 and instruct the terminal via L1 / L2 signaling. Based on the beam change instruction from the serving cell, the terminal may perform a beam change on the specific beam (TCI state 2) 440 of TRP 2 (Cell 2) 415 and perform physical channel configuration and higher layer configuration operations associated with the configured beam. Afterwards, the terminal can remain connected to the serving cell (cell 1) 410, but can transmit and receive data (PDCCH / PDSCH reception and PUCCH / PUSCH transmission) using the channel link of TRP 2 (cell 2) 415. That is, transmission and reception on the common control channel can be performed via the serving cell (cell 1) 410. The terminal can then perform L3 measurement operation 459 according to the measurement configuration configured in the independent serving cell, and can receive a handover command message from the serving base station (cell 1) and change the serving cell to cell 2 in operation 460. Through technique 455, the terminal can perform data transmission and reception to and from the specific TRP 2 of cell 2 supporting L1 / L2-based mobility while connected to the serving cell, and can continue to use the corresponding beam even after handover.

[0101] According to an embodiment of the present disclosure, the RRC configuration for configuration and operation related to L1 measurement and reporting in operation 457 includes the following content. This content can also be basically applied to other embodiments of the present disclosure, and improved technologies can be added in future embodiments.

[0102] 1. CSI measurement configuration

[0103] - CSI-RS resources and resource pools required for measurement (nzp-CSI-RS, csi-IM, and csi-SSB); and / or

[0104] - CSI-RS resource configuration (aperiodic, semi-persistent) and trigger configuration required for measurement.

[0105] When CSI-RS resources are based on SSB resources, additional PCI information is provided to enable L1 measurements from neighboring cells (up to 7 neighboring cells (PCIs) can be added in one serving cell), as shown in [Table 5] and [Table 6].

[0106] [Table 5]

[0107]

[0108] [Table 6]

[0109]

[0110] 2. CSI Report Configuration

[0111] - Reporting type: periodic reporting, semi-persistent reporting via PUCCH, semi-persistent reporting via PUSCH, and aperiodic reporting via PUSCH (periodic, semi-persistent for PUCCH, semi-persistent for PUSCH, and aperiodic);

[0112] - Report quantity; and / or

[0113] - Reports additional configuration required.

[0114] Figure 5 A scenario is shown in which a terminal according to various embodiments of the present disclosure transmits and receives data by changing a serving cell and a beam to a TRP of a cell supporting L1 / L2-based beam changing.

[0115] Figure 5 The case where multiple cells (TRP1-cell 1 and TRP2-cell 2) 510, 515, 540 and 545 exist within a single distributed unit (DU) 505 or 535 is shown, but the overall content of the present disclosure is also applicable to the case between DUs (for example, each DU constitutes a TRP-cell).

[0116] refer to Figure 5 , and the existing terminal beam changing process (e.g., Figure 4 Unlike 445 and 455 in the embodiments, the improved beam changing techniques 525 and 575 considered in the embodiments are as follows.

[0117] 1. Embodiment 1 525: After performing inter-cell beam management (change), perform L1 / L2 switching.

[0118] 2. Example 2 575: Execute L1 / L2 switching immediately.

[0119] First, in order to describe the overall operation of Example 1, in operation 526, the terminal 520 may receive public configuration and dedicated configuration information for an additional cell (TRP 2-cell 2) 515 having a PCI different from the PCI of the serving cell from the serving cell 510 via RRC configuration information. That is, the terminal 520 may receive configuration information corresponding to ServingCellConfig and ServingCellConfigCommon, and ServingCellID or candidateCellID (cell ID associated with PCI) from the serving cell 510 in advance. The configuration information may be provided in a pre-configured form in the RRC configuration, and may include configuration information for multiple cells. In addition, the configuration includes all configuration information (cell configuration, bearer configuration, measurement-related configuration, security key configuration, etc.) that is applied when the terminal moves (performs handover) to an additional cell having a PCI different from the PCI of the serving cell. In addition, the configuration may include configuration related to L1 measurement and reporting as well as Figure 4 The unified TCI state configuration described in operation 456.

[0120] Various embodiments of the present disclosure provide a detailed description of a structure for pre-providing configurations of candidate neighboring cells on which L1 / L2 handover can be performed, specifically, a method for configuring L3 measurement-related configurations (MeasConfig), radio bearer configurations (RadioBearerConfig), and cell group configurations (CellGroupConfig) including cell configurations. Specifically, the present disclosure provides a method that can efficiently transmit configuration information when transmitting the configuration information to the terminal, compared to when only specific configuration information of a specific LTM candidate cell is updated. In addition, the present disclosure also provides a method for effectively configuring RLC bearer configurations, logical channel configurations, MAC configurations, etc. to reduce signaling overhead when the RLC bearer configurations, logical channel configurations, MAC configurations, etc. are generally applicable even within a cell group configuration. In addition, in various embodiments of the present disclosure, not only intra-CU scenarios but also inter-CU scenarios are considered.

[0121] After receiving a configuration for TRP 2-Cell 2 515 while being RRC-connected to serving cell 1 510, the terminal may perform L1 measurements on TRP 527-Cell 2 515 based on the received configuration for TRP 2-Cell 2 in operation 527 and report the performance results to serving cell (Cell 1) 510. If the measurement results determine that a change to a specific beam (TCI state 2) 540 of TRP 2 (Cell 2) 515 is necessary, rather than the serving cell beam (TCI state 1) 525, serving cell 510 may trigger a beam change in operation 528 and instruct the terminal via L1 / L2 signaling. Terminal 520 may perform a beam change to TRP 2 (Cell 2) 515 in response to the beam change instruction received from serving cell 510, and transmit and receive data via TRP 2 (Cell 2) 515. In this case, the serving cell is not changed, and the terminal remains RRC-connected to serving cell (Cell 1) 510. Terminal 520 then performs L1 measurements on TRP 2-Cell 2 515 and reports the corresponding results to serving cell (Cell 1) 510. When the L1 measurements reported by terminal 520 meet the triggering conditions for handover to TRP 2-Cell 2 515 (the detailed operation will be described in detail below), serving cell (Cell 1) 510 may instruct the terminal to perform the handover. The handover indication from the serving cell to the terminal may be transmitted via L1 / L2 messaging. In other words, a MAC CE or DCI may include an indicator indicating the handover.

[0122] To describe the overall operation of Embodiment 2, in operation 576, the terminal 550 may receive, from the serving cell 540 via RRC configuration information, common configuration and dedicated configuration information for an additional cell (TRP 2-cell 2) 545 having a PCI different from that of the serving cell. That is, the terminal 550 may receive configuration information corresponding to ServingCellConfig and ServingCellConfigCommon, as well as ServingCellID or candidateCellID (a cell ID associated with the PCI) from the serving cell 540. The configuration information for the cell may be a cell group-level configuration (CellGroupConfig) rather than a cell-level configuration, or may be provided via configuration according to an RRC configuration message (RRCReconfiguration).

[0123] According to an embodiment of the present disclosure, configuration information may be provided in a pre-configured form in an RRC configuration and may include configuration information for multiple cells. In addition, the configuration may include all configuration information (cell configuration, bearer configuration, security key configuration, etc.) applied when the terminal moves (performs handover) to the corresponding cell. In addition, the configuration may include Figure 4 The unified TCI state configuration and the configuration related to L1 measurement and reporting described in operation 456 of the present disclosure are described. The embodiments of the present disclosure provide a description of a structure for pre-providing configurations of candidate neighboring cells for which L1 / L2 handover can be performed, and specifically provide a method for applying configuration information and incremental configuration of a reference cell to the configuration of a candidate neighboring cell.

[0124] According to an embodiment of the present disclosure, after providing a configuration on TRP 2-Cell 2 545 while being RRC-connected to serving cell 1 540, terminal 550 may perform L1 measurement on TRP 2-Cell 2 545 based on the received configuration in operation 577 and report the corresponding result to serving cell (Cell 1) 540. If it is determined based on the measurement result that a beam change to a specific beam (TCI state 2) 570 of TRP 2 (Cell 2) 545 rather than the serving cell beam (TCI state 1) 560 is required while simultaneously performing handover, serving cell 540 may trigger a beam change and handover in operation 578 and instruct terminal 550 of the beam change via L1 / L2 signaling. Based on the beam change instruction received from serving cell 540, terminal 550 may perform handover while simultaneously performing a beam change to TRP 2 (Cell 2) 545 and transmit and receive data via TRP 2 (Cell 2) 545. In this case, the terminal 550 may apply the configuration information of the target cell for which the handover is to be performed, which has been pre-configured in operation 576. In this case, the terminal may perform random access according to whether uplink synchronization is required, and may omit random access to the target cell. The detailed operation will be described below with reference to the accompanying drawings.

[0125] The existing Layer 3 handover techniques used in various embodiments of the present disclosure can all be applied to various handover techniques (Conditional Handover (CHO), Dual Active Protocol Stack (DAPS) handover, and Conditional PSCell Addition and Change (CPAS)), including basic handover (instructed by the base station by transmitting a Handover Command RRC message) used since Rel-15. That is, although omitted in this disclosure, in the description of LTM and existing Layer 3 handover operations, in particular, the operation of preventing simultaneous handover triggering can include all existing handover techniques.

[0126] Furthermore, in various embodiments of the present disclosure, regarding the operation of a terminal when LTM and an existing Layer 3 handover are triggered and transmitted simultaneously to the terminal, it is assumed that the terminal operates based on the handover signaling received first. Furthermore, if a terminal can receive multiple handover messages simultaneously, it may be necessary to define which signal to prioritize. In one approach, LTM may be applied first, while in another approach, the existing Layer 3 handover may be processed first.

[0127] Figure 6 The overall operation of successfully performing L1 / L2-based switching according to various embodiments of the present disclosure is shown. Specifically, as scenario 1 described in the present disclosure, Figure 6 The overall operation of successfully performing L1 / L2 based handover is shown.

[0128] refer to Figure 6 In operation 610, the RRC-connected terminal 601 may transmit and receive data to and from the source cell 1 602, and then transmit layer 3 measurement values ​​of neighboring cells and the serving cell to the source cell 1 602 according to the configured layer 3 measurement and reporting. In this case, the terminal 601 may transmit the layer 3 measurement values ​​of the neighboring cells and the serving cell to the base station's CU 603 according to the actually configured layer 3 measurement and reporting. This is because the base station CU 603 is responsible for RRC message processing and determining mobility.

[0129] In operation 615, the base station CU 603 may generate a message for requesting configuration information for L1 / L2-based handover (L1 / L2 configuration request message), and transmit the message to the LTM candidate neighbor cells 604 and 605 via the F1 interface according to the measurement value report received from the terminal 601. Figure 6 , candidate cells are shown in association with DUs, but candidate cells and DUs may be mapped 1:1, or multiple candidate cells may be included in one DU. In addition, the message for requesting configuration information for L1 / L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, or the like, and may be a new F1 or Xn message. The message for requesting configuration information for L1 / L2-based handover may be a message for requesting a cell to be determined as a candidate cell for L1 / L2-based handover from a neighboring cell, and may simultaneously be a message for requesting RRC configuration information to be applied when performing L1 / L2-based handover on the corresponding cell. The RRC configuration information (CellGroupConfig 1, ..., CellGroupConfig N) to be applied when performing L1 / L2-based handover may be transmitted in one of a cell-level structure, a cell group-level structure, and an RRC message-level structure. The message for requesting configuration information for L1 / L2-based handover may be used to simultaneously transmit configuration and information about a reference cell, and the message for requesting configuration information for L1 / L2-based handover may include an indicator for requesting that the configuration information for L1 / L2-based handover be transmitted to the candidate neighboring cells 604 and 605 by applying incremental configuration. The indicator for requesting that the configuration information for handover be transmitted by applying incremental configuration may be requested for each cell or may be requested jointly for all cells.

[0130] In operation 620, the candidate neighboring cells 604 and 605 that have received the message requesting configuration information for L1 / L2-based handover may generate configuration information of each candidate neighboring cell when L1 / L2-based handover is applied based on the transmitted configuration information of the reference cell, based on the incremental configuration.

[0131] In operation 625 , each candidate neighboring cell 604 or 605 may include the generated configuration information for L1 / L2-based handover in a configuration information response message for L1 / L2-based handover (L1 / L2 configuration response message) and send the response message to the base station CU 603 .

[0132] In operation 630, the base station CU 603 may generate an RRC message and transmit it to the source cell 602, and the source cell 602 may transmit the RRC message to the terminal 601. The RRC message may include configuration information (Pre-Config1, ..., Pre-ConfigN) of neighboring candidate cells for applying L1 / L2-based handover (LTM). The Pre-Config included in the RRC message may include the bearer configuration of the LTM candidate cell generated by the base station, the Layer 3 (L3) measurement configuration, and the CellGroupConfig configuration received from the LTM candidate cell in operation 625.

[0133] In operation 635, the terminal 601 that has received the RRC message may perform a process of decoding and processing the RRC message. The processing process of the terminal 601 may include ASN.1 decoding and validity determination of the received message, a method of storing and managing configuration details, and the like.

[0134] In operation 640, terminal 601 may perform layer 1 (L1) measurements and reporting for each candidate neighboring cell, and may also simultaneously perform layer 3 (L3) measurements and reporting in operation 645, depending on the configuration. Having received the L1 measurement report, the source cell may determine handover based on the corresponding measurement values ​​and, in operation 650, indicate L1 / L2 handover to terminal 601. In operation 640, DCI and MAC CE including a handover indicator may be used for L1 / L2 signaling. The transmission of L1 measurement values ​​for determining L1 / L2 handover and the handover determination in operations 640 and 650 may be performed by the source cell (DU) or source base station CU 603. If base station CU 603 makes all determinations, source cell 602 may transmit the L1 measurement values ​​received from terminal 601 to base station CU 603 and, in accordance with the handover determination indicated by base station CU 603, transmit L1 / L2 signaling to the terminal. However, when the source cell makes the final determination, the source cell can determine the handover by itself and transmit L1 / L2 signaling to the terminal without transmitting the L1 measurement value to the base station based on the measurement value criteria (threshold and measurement value range) for handover determination of each candidate neighboring cell received from the previous base station.

[0135] In operation 655, when the L1 / L2 switching indication is transmitted to the terminal, the terminal may start the switching process and drive the timer for L1 / L2 switching. The timer for L1 / L2 switching may be a newly configured timer for LTM, or the existing T304 timer may be reused.

[0136] In operation 660 , the terminal 601 may apply a configuration on the target cell to which the L1 / L2 handover is applied. The configuration may be one of the LTM candidate neighbor cell configurations previously received in operation 630 .

[0137] In operation 665, depending on the applied configuration, the terminal may perform random access when the target cell requires random access, and may omit the random access procedure when random access is neither indicated nor required (when uplink synchronization has already been performed or configured). Furthermore, while performing this procedure, base station CU 603 may determine an existing Layer 3 handover for the terminal based on the results of the L3 measurement and reporting in operation 645, and may transmit a handover indication to the terminal in operation 670. For LTM, this may be the case when the serving cell (DU) triggers LTM, and no information is exchanged with the serving cell (DU). That is, since base station CU 603 cannot identify whether the serving cell (DU) has already indicated LTM to terminal 601, a handover indication to the terminal may be provided via a separate L3 measurement and reporting procedure.

[0138] In operation 675, the terminal may perform a handover completion procedure with the target cell. The handover completion procedure may be a handover completion procedure for LTM or a handover completion procedure for an existing L3 handover. In the scenarios of the present disclosure, a description is provided for the case where LTM is indicated first, and thus a handover completion procedure for LTM is described. This procedure may vary depending on the handover completion indication method, and when the configuration of the target cell is received at the RRC message level, the procedure may be the transmission of an RRCReconfigurationComplete message. However, when a cell-level or cell group-level configuration is received, a new handover completion indication message (a new RRC message or a MAC CE) may replace this procedure.

[0139] Furthermore, since the present disclosure considers applications within a CU, in operation 680, the target cell (DU) 604, having received the handover complete message, may transmit the received handover complete message to the base station CU 603. In this case, the target cell (DU) 604 may transmit the received handover complete message to the base station CU 603 via the F1 interface as is, or may process the message based on the received information and transmit it. Thereafter, in operation 685, the base station CU 603 may transmit information regarding the handover complete to the source cell 602, instructing the release of the terminal context.

[0140] Figure 7 FIG2 shows the overall operation of the L1 / L2-based handover being performed and failing according to various embodiments of the present disclosure. Specifically, as scenario 2 described in the present disclosure, Figure 7 The overall operation is shown where an L1 / L2 based handover is performed and fails.

[0141] In operation 710, the RRC-connected terminal 701 may transmit and receive data to and from the source cell 1 702, and then transmit layer 3 measurement values ​​of neighboring cells and the serving cell to the source cell 1 702 according to the configured layer 3 measurement and reporting. In this case, the terminal 701 may transmit the layer 3 measurement values ​​of the neighboring cells and the serving cell to the base station's CU 703 according to the actually configured layer 3 measurement and reporting. This is because the base station CU 703 is responsible for RRC message processing and determining mobility.

[0142] In operation 715, the base station CU 703 may generate a message for requesting configuration information for L1 / L2-based handover (L1 / L2 configuration request message), and transmit the message to the LTM candidate neighbor cells 704 and 705 via the F1 interface according to the measurement value report received from the terminal. Figure 7, candidate cells are shown in association with DUs, but candidate cells and DUs may be mapped 1:1, or multiple candidate cells may be included in one DU. In addition, the message for requesting configuration information for L1 / L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, or the like, and may be a new F1 or Xn message. The message for requesting configuration information for L1 / L2-based handover may be a message for requesting a cell to be determined as a candidate cell for L1 / L2-based handover from a neighboring cell, and may simultaneously be a message for requesting RRC configuration information to be applied when performing L1 / L2-based handover on the corresponding cell. The RRC configuration information (CellGroupConfig 1, ..., CellGroupConfig N) to be applied when performing L1 / L2-based handover may be transmitted in one of a cell-level structure, a cell group-level structure, and an RRC message-level structure. The message for requesting configuration information for L1 / L2-based handover may be used to simultaneously transmit configuration and information about a reference cell, and the message for requesting configuration information for L1 / L2-based handover may include an indicator for requesting that the configuration information for L1 / L2-based handover be transmitted to the candidate neighboring cells 704 and 705 by applying incremental configuration. The indicator for requesting that the configuration information for L1 / L2-based handover be transmitted by applying incremental configuration may be requested for each cell or may be requested jointly for all cells.

[0143] In operation 720, the candidate neighboring cells 704 and 705 that have received the message for requesting configuration information for L1 / L2-based handover may generate, based on the incremental configuration, configuration information of each candidate neighboring cell when L1 / L2-based handover is applied based on the transmitted configuration information of the reference cell.

[0144] In operation 725 , each candidate neighboring cell 704 or 705 may include the generated configuration information for L1 / L2-based handover in a configuration information response message for L1 / L2-based handover (L1 / L2 configuration response message) and send the response message to the base station CU 703 .

[0145] In operation 730, the base station CU 703 may generate an RRC message and transmit it to the source cell 702, and the source cell 702 may transmit the RRC message to the terminal 701. The RRC message may include configuration information (Pre-Config1, ..., Pre-ConfigN) of neighboring candidate cells for applying L1 / L2-based handover (LTM). The Pre-Config included in the RRC message may include the bearer configuration of the LTM candidate cell generated by the base station, the Layer 3 (L3) measurement configuration, and the CellGroupConfig configuration received from the LTM candidate cell in operation 725.

[0146] In operation 735, the terminal 701 that has received the RRC message may perform a process of decoding and processing the RRC message. The processing of the terminal 701 may include ASN.1 decoding and validity determination of the received message, a method for storing and managing configuration details, and the like.

[0147] In operation 740, terminal 701 may perform Layer 1 (L1) measurements and reporting for each candidate neighboring cell, and may also simultaneously perform L3 measurements and reporting in operation 745, depending on the configuration. Having received the L1 measurement report, the source cell may determine handover based on the corresponding measurement values ​​and, in operation 750, indicate L1 / L2 handover to the terminal. In operation 740, DCI and MAC CE including a handover indicator may be used for L1 / L2 signaling. The transmission of L1 measurement values ​​for determining L1 / L2 handover and the handover determination in operations 740 and 750 may be performed by the source cell (DU) or the source base station (CU). If base station CU 703 makes all determinations, source cell 702 may transmit the L1 measurement values ​​received from terminal 701 to base station CU 703 and, in accordance with the base station CU's indication of the handover determination, transmit L1 / L2 signaling to the terminal. However, when the source cell makes the final determination, the source cell can determine the handover by itself and transmit L1 / L2 signaling to the terminal without transmitting the L1 measurement value to the base station based on the measurement value criteria (threshold and measurement value range) for handover determination of each candidate neighboring cell received from the previous base station.

[0148] In operation 755, when the L1 / L2 switching indication is transmitted to the terminal, the terminal may start the switching process and drive the timer for L1 / L2 switching. The timer for L1 / L2 switching may be a newly configured timer for LTM, or the existing T304 timer may be reused.

[0149] In operation 760 , the terminal 701 may apply a configuration on the target cell to which the L1 / L2 handover is applied. The configuration may be one of the LTM candidate neighbor cell configurations previously received in operation 730 .

[0150] In operation 765, depending on the applied configuration, the terminal may perform random access when the target cell requires random access, and may omit the random access procedure when random access is neither indicated nor required (when uplink synchronization has already been performed or configured). Furthermore, while performing this procedure, base station CU 703 may determine an existing Layer 3 handover for the terminal based on the results of the L3 measurement and reporting in operation 745, and may transmit a handover indication to the terminal in operation 770. For LTM, this may be the case when the serving cell (DU) triggers LTM, and no information is exchanged with the serving cell (DU). That is, since base station CU 703 cannot identify whether the serving cell (DU) has already indicated LTM to terminal 701, a handover indication may be provided to the terminal via a separate L3 measurement and reporting procedure.

[0151] In operation 775, the terminal may fail in the LTM handover to the target cell. The reasons for the LTM handover failure may include expiration of the timer for LTM handover or expiration of the existing T304 timer, failure of random access to the target cell performing LTM handover, etc. As an operation performed when the terminal fails in the LTM handover, the following operations may be performed in operation 780. However, the operation is not limited thereto.

[0152] When LTM fails, Terminal 701 can fall back to the previous source cell 702 and attempt to connect. To this end, Terminal 701 may need to maintain the configuration information for the source cell even when LTM is triggered. Furthermore, even after falling back to source cell 702, LTM configuration information for the LTM target cell may be maintained. This allows LTM to be retriggered based on the existing configuration.

[0153] If fallback to the source cell 702 cannot be fully performed, the terminal 701 may enter the RRC re-establishment procedure to reselect a connectable cell. If the cell found via cell reselection is one of the LTM candidate cells, the terminal 701 may attempt to connect by applying the pre-configured RRC configuration to the cell.

[0154] In operation 785, the terminal may generate a handover failure report message in the connected cell (source cell or target cell) and transmit the message to the base station CU 703. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Furthermore, the handover failure may be reported via a new MAC CE or uplink control signal (uplink control information (UCI)). The information included in the handover failure report message may include the following information. However, the information is not limited thereto.

[0155] - An indicator indicating that the switch failed due to LTM failure.

[0156] - Information of the target cell where LTM has been attempted and has failed: LTM cell configuration index or actual cell index (physical cell index (PCI)) information.

[0157] In the embodiments of the present disclosure, Figure 6 and Figure 7 The scenario described in [1], specifically, involves the simultaneous triggering of LTM and existing handovers. It's unclear how the terminal should operate in these situations, so clearly defined operations are required. This will be discussed in detail in the following embodiments. Furthermore, in the following embodiments, the description is extended to inter-CU scenarios to address more general situations.

[0158] Figure 8 The overall operation of triggering L1 / L2-based handover in a serving cell (DU) and transmitting corresponding trigger information from the serving cell (DU) to the base station CU according to various embodiments of the present disclosure is shown. Specifically, as embodiment 1 described in the present disclosure, Figure 8 A method of triggering L1 / L2-based handover in a serving cell (DU) and transmitting corresponding triggering information from the serving cell (DU) to a base station CU and its overall operation are shown.

[0159] In operation 810, the RRC connection terminal 801 may perform data transmission and reception to and from the source cell 1 802, and then transmit layer 3 measurement values ​​of neighboring cells and the serving cell to the source cell 1 802 according to the configured layer 3 measurement and reporting. In this case, according to the actually configured layer 3 measurement and reporting, the layer 3 measurement values ​​of the neighboring cells and the serving cell may be transmitted to the base station CU1 803. This is because the base station CU1 803 is responsible for RRC message processing and determining mobility.

[0160] In operation 815, the base station CU1 803 may generate a message for requesting configuration information for L1 / L2-based handover (L1 / L2 configuration request message), and transmit the message to the LTM candidate neighbor cells 804 and 805 via the F1 interface according to the measurement value report received from the terminal. Figure 8, candidate cells are shown in association with DUs, but candidate cells and DUs may be mapped 1:1, or multiple candidate cells may be included in one DU. In addition, the message for requesting configuration information for L1 / L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, or the like, and may be a new F1 or Xn message. The message for requesting configuration information for L1 / L2-based handover may be a message for requesting a cell to be determined as a candidate cell for L1 / L2-based handover from a neighboring cell, and may simultaneously be a message for requesting RRC configuration information to be applied when performing L1 / L2-based handover on the corresponding cell. The RRC configuration information (CellGroupConfig 1, ..., CellGroupConfig N) to be applied when performing L1 / L2-based handover may be transmitted in one of a cell-level structure, a cell group-level structure, and an RRC message-level structure. The message for requesting configuration information for L1 / L2-based handover may be used to simultaneously transmit configuration and information about a reference cell, and the message for requesting configuration information for L1 / L2-based handover may include an indicator for requesting that the configuration information for L1 / L2-based handover be transmitted to the candidate neighboring cells 804 and 805 by applying incremental configuration. The indicator for requesting that the configuration information for L1 / L2-based handover be transmitted by applying incremental configuration may be requested for each cell or may be requested jointly for all cells.

[0161] In operation 820, the candidate neighbor cells 804 and 805 that have received the message requesting configuration information for L1 / L2-based handover may generate configuration information of each candidate neighbor cell when L1 / L2-based handover is applied based on the transmitted configuration information of the reference cell based on incremental configuration.

[0162] In operation 825 , each candidate neighboring cell 804 or 805 may include the generated configuration information for L1 / L2-based handover in a configuration information response message for L1 / L2-based handover (L1 / L2 configuration response message) and send the response message to the base station CU1 803 .

[0163] In operation 830, base station CU1 803 may generate an RRC message and transmit it to source cell 802, and source cell 802 may transmit the RRC message to terminal 801. The RRC message may include configuration information (Pre-Config1, ..., Pre-ConfigN) of neighboring candidate cells for applying L1 / L2-based handover (LTM). The Pre-Config included in the RRC message may include the bearer configuration of the LTM candidate cell generated by the base station, the Layer 3 (L3) measurement configuration, and the CellGroupConfig configuration received from the LTM candidate cell in operation 825.

[0164] In operation 835, the terminal 801 that has received the RRC message performs a process of decoding and processing the RRC message. The process includes ASN.1 decoding and validity determination of the received message, a method for storing and managing configuration details, and the like.

[0165] In operation 840, terminal 801 may perform Layer 1 (L1) measurements and reporting for each candidate neighboring cell, and may also simultaneously perform Layer 3 (L3) measurements and reporting in operation 845, depending on the configuration. In operation 850, base station CU1 803, having received the L3 measurement reports, may perform a process to determine whether handover for terminal 801 is possible from neighboring base station CU2 (gNB2) 806, which can perform handover. In other words, a handover request for terminal 801 and a response thereto may be received. The response to the handover request may include RRC configuration information to be applied to the target cell when performing handover for terminal 801. Furthermore, in a corresponding operation, base station CU2 (gNB2) 806 may reject the handover request. In operation 840, source cell 802, having received the L1 measurement reports, may determine handover based on the corresponding measurement values ​​and, in operation 855, instruct terminal 801 to perform L1 / L2 handover. In this case, DCI and MAC CEs including a handover indicator may be used for L1 / L2 signaling. The L1 measurement value transmission and handover determination in operations 840 and 855 for determining L1 / L2 handover can be performed by the source cell (DU) or the source base station CU. If the base station CU makes all determinations, the source cell can transmit the L1 measurement values ​​received from the terminal and transmit L1 / L2 signaling to the terminal 801 based on the handover determination instruction from the base station CU. However, when the source cell makes the final determination, the source cell can determine the handover and transmit L1 / L2 signaling to the terminal based on the measurement value criteria (threshold and measurement value range) for the handover determination of each candidate neighboring cell received from the previous base station, without transmitting the L1 measurement values ​​to the base station. In the embodiments of the present disclosure, the source cell (DU) 802 determines the triggering of LTM handover.

[0166] In operation 860, when the L1 / L2 switching indication is transmitted to the terminal 801, the terminal 801 may start the switching process and drive the timer for the L1 / L2 switching. The timer for the L1 / L2 switching may be a newly configured timer for the LTM, or the existing T304 timer may be reused.

[0167] In operation 865, the source cell (DU) 802 may transmit information indicating that LTM has been triggered to the source base station (CU) 803. This may serve as a request to the source base station (CU) 803 to refrain from triggering operations related to the existing L3 measurement-based handover (L3 Handover Indication) due to the triggering of LTM. The LTM triggering information may be transmitted via the F1 interface and may include an indicator indicating that LTM has been triggered and an index to the LTM cell configuration (information that can indicate the target cell for which LTM has been performed). Furthermore, at the same time, the source base station (CU) 803 may instruct a handover in operation 866. In operation 867, the source cell (DU) may transmit the status of downlink data transmission from the target cell to the base station and may send a message including an indicator requesting that data transmission be stopped. This may be transmitted via an existing DL Delivery Status message or a new message. For reference, when the handover process is later completed, the base station that has received the message performs a process of receiving a status report on downlink data reception from the target cell and transmitting it to the source cell. When the provided operations are applied, the corresponding process may be omitted, thereby simplifying the process. In addition, the message serves to transmit the reception status of the downlink data message, and via this, the source base station CU1803 can determine whether to receive the downlink data and whether to support additional handover.

[0168] In operation 870, the source base station CU1 803 may transmit an inter-node message requesting to stop the ongoing handover process to the neighboring base station CU2 (gNB2) 806, which may perform Layer 3 handover, via an Xn interface. To this end, an existing handover cancel message may be reused, or a new message (e.g., a handover stop request message) may be adopted.

[0169] In operation 875, in response to the request for the handover stop procedure, neighboring base station CU2 (gNB2) 806 may generate an acceptance or rejection message and transmit it to source base station CU1 803. Through these procedures, in response to the handover stop request transmitted from source base station CU1 803, base station CU2 (gNB2) 806 releases handover-related resources for the terminal, further facilitating base station operations. If base station CU2 (gNB2) 806 accepts the handover stop procedure, the terminal context and handover-related procedures for terminal 801 may be released. If base station CU2 (gNB2) 806 rejects the handover stop procedure, this may be communicated to source base station CU1 803, allowing source base station CU1 803 to later re-trigger the handover procedure for terminal 801. In other words, base station CU2 (gNB2) 806 may maintain the context and related configurations for the terminal handover until the handover procedure is successful.

[0170] In operation 880 , the terminal 801 may apply the configuration on the target cell to which the L1 / L2 handover is applied. The configuration on the target cell to which the L1 / L2 handover is applied is one of the LTM candidate neighbor cell configurations previously received in operation 830 .

[0171] In operation 885 , according to the applied configuration, the terminal 801 may perform random access when the target cell requires random access, and may omit the random access procedure when random access is neither indicated nor required (when uplink synchronization has been performed or configured).

[0172] In operation 890, the terminal 801 may fail in LTM handover to the target cell. Causes of LTM handover failure may include expiration of a timer for LTM handover or an existing T304 timer, failure of random access to the target cell performing LTM handover, and the like.

[0173] In operation 893, the terminal 801 may perform the following operations as operations performed when the LTM switching fails. However, the operations are not limited thereto.

[0174] When LTM fails, the terminal performs a fallback to the previous source cell 802 and attempts to connect. To this end, even when LTM is triggered, the terminal may need to maintain the configuration information for the source cell. In addition, even after falling back to the source cell 802, the LTM configuration information of the LTM target cell may be maintained. This allows LTM to be retriggered based on the existing configuration.

[0175] If fallback to the source cell cannot be fully performed, the terminal may enter the RRC re-establishment procedure to reselect a connectable cell. If the cell found via cell reselection is one of the LTM candidate cells, the terminal may attempt to connect by applying the pre-configured RRC configuration to the cell.

[0176] In operation 895, the terminal 801 may generate a handover failure report message in the connected cell (source cell or target cell) and send the message to the base station CU 803. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Furthermore, the handover failure may be reported via a new MAC CE or an uplink control signal (uplink control information (UCI)). The information included in the handover failure report message may include the following information. However, the information is not limited thereto.

[0177] - An indicator indicating that the switch failed due to LTM failure.

[0178] - Information of the target cell where LTM has been attempted and has failed: LTM cell configuration index or actual cell index (physical cell index (PCI)) information.

[0179] In operation 897, source base station CU 803 may recognize, via the LTM triggering information in operation 865, that source cell DU 802 has triggered LTM, and may recognize, via the handover failure message in operation 895, that the LTM attempt has failed and fallback to the source cell has been performed. Therefore, source base station CU 703 may re-trigger the already suspended Layer 3 handover procedure. However, due to the influence of the determination of Layer 3 handover to the target cell based on the information included in the LTM failure message, this determination may not be performed. This is a network implementation, and for example, if the target cell information associated with the failed LTM is the same as the target cell for which an existing Layer 3 handover was performed, the handover may fail again, necessitating re-triggering or cancellation of the handover by updating to new configuration values. Furthermore, this handover procedure may be a handover procedure that was already suspended via operations 870 and 875, and the handover configuration and target cell may be changed mid-process based on new measurement values ​​and solutions (such as inter-node messaging with the base station).

[0180] This procedure allows the base station to avoid triggering repeated Layer 3 handovers even when LTM has already been triggered, and resolves uncertainty in terminal operation caused by multiple repeated handover requests. If the terminal receives an LTM MAC CE and maintains connection with the source cell even during the LTM process, and uplink / downlink transmission and reception are possible, a new handover message can be triggered even during the LTM handover process. In this case, the base station can request a handover instead of LTM if necessary.

[0181] Figure 9 The overall operation of triggering an existing layer 3 handover in a base station CU and transmitting corresponding trigger information from the base station CU to a serving cell (DU) according to various embodiments of the present disclosure is shown. Specifically, as embodiment 2 described in the present disclosure, Figure 9 An operation of requesting the serving cell not to perform LTM-related operations when an existing layer 3 handover is first triggered is shown.

[0182] refer to Figure 9 In operation 910, the RRC connection terminal 901 may perform data transmission and reception to and from the source cell 1 902, and then transmit the layer 3 measurement values ​​of the neighboring cells and the serving cell to the source cell 1 902 according to the configured layer 3 measurement and reporting. In this case, according to the actually configured layer 3 measurement and reporting, the layer 3 measurement values ​​of the neighboring cells and the serving cell may be transmitted to the base station CU1 903. This is because the base station CU1 903 is responsible for RRC message processing and determining mobility.

[0183] In operation 915, the base station CU1 903 may generate a message for requesting configuration information for L1 / L2-based handover (L1 / L2 configuration request message), and transmit the message to the LTM candidate neighbor cells 904 and 905 via the F1 interface according to the measurement value report received from the terminal. Figure 9, candidate cells are shown in association with DUs, but candidate cells and DUs may be mapped 1:1, or multiple candidate cells may be included in one DU. In addition, the message for requesting configuration information for L1 / L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, or the like, and may be a new F1 or Xn message. The message for requesting configuration information for L1 / L2-based handover may be a message for requesting a cell to be determined as a candidate cell for L1 / L2-based handover from a neighboring cell, and may simultaneously be a message for requesting RRC configuration information to be applied when performing L1 / L2-based handover on the corresponding cell. The RRC configuration information (CellGroupConfig 1, ..., CellGroupConfig N) to be applied when performing L1 / L2-based handover may be transmitted in one of a cell-level structure, a cell group-level structure, and an RRC message-level structure. The message for requesting configuration information for L1 / L2-based handover may be used to simultaneously transmit configuration and information about a reference cell, and the message for requesting configuration information for L1 / L2-based handover may include an indicator for requesting that the configuration information for L1 / L2-based handover be transmitted to the candidate neighboring cells 904 and 905 by applying incremental configuration. The indicator for requesting that the configuration information for L1 / L2-based handover be transmitted by applying incremental configuration may be requested for each cell or may be requested jointly for all cells.

[0184] In operation 920, the candidate neighboring cells 904 and 905 that have received the message for requesting configuration information for L1 / L2-based handover may generate, based on the incremental configuration, configuration information of each candidate neighboring cell when L1 / L2-based handover is applied based on the transmitted configuration information of the reference cell.

[0185] In operation 925 , each candidate neighboring cell 904 or 905 may include the generated configuration information for L1 / L2-based handover in a configuration information response message for L1 / L2-based handover (L1 / L2 configuration response message) and send the response message to the base station CU1 903 .

[0186] In operation 930, base station CU1 903 may generate an RRC message and transmit it to source cell 902, and source cell 902 may transmit the RRC message to terminal 901. The RRC message may include configuration information (Pre-Config1, ..., Pre-ConfigN) of neighboring candidate cells for applying L1 / L2-based handover (LTM). The Pre-Config included in the RRC message may include the bearer configuration of the LTM candidate cell generated by the base station, the Layer 3 (L3) measurement configuration, and the CellGroupConfig configuration received from the LTM candidate cell in operation 925.

[0187] In operation 935, the terminal 901 that has received the RRC message performs a process of decoding and processing the RRC message. The processing process of the terminal may include ASN.1 decoding and validity determination of the received message, a method for storing and managing configuration details, and the like.

[0188] In operation 940, terminal 901 may perform Layer 1 (L1) measurements and reporting for each candidate neighboring cell, and may also simultaneously perform Layer 3 (L3) measurements and reporting in operation 945, depending on the configuration. In operation 950, base station CU1 903, having received the L3 measurement report, may perform a process to determine whether handover for terminal 901 is possible from neighboring base station CU2 (gNB2) 906, which can perform handover. In other words, a handover request for terminal 901 and a response thereto may be received. The response to the handover request may include RRC configuration information to be applied to the target cell when performing handover for the terminal. In this case, base station CU2 (gNB2) 906 may reject the handover request. Therefore, base station CU 903 may determine whether to indicate Layer 3 handover based on the measurement report results in operation 945, and may indicate handover in operation 955. When the L3 handover indication is transmitted to terminal 901 via an RRC message, terminal 901 may initiate a handover procedure in operation 960 and activate timer T304 for handover.

[0189] In operation 965, the base station CU 903 may transmit a message to the source cell (DU) 902, including an indicator requesting that LTM-related operations be stopped due to the triggering of a Layer 3 handover. To this end, the source base station CU 903 may request that operations related to LTM-related L1 measurement-based handover (LTM Handover Indication) not be triggered due to the triggering of the handover. The LTM triggering information may be transmitted via the F1 interface and may include an indicator indicating that a Layer 3 handover has been triggered and an index of the target cell to which the handover has been triggered (information capable of indicating the target cell indicated for the handover). Even if the source cell is not requested to trigger handover-related operations (LTM Handover Indication), the configuration on the LTM candidate cell may be maintained. This is because LTM can be retriggered when LTM to another cell is indicated or the handover fails.

[0190] In operation 966, the source cell (DU) 902 may generate a response message regarding the indication in operation 965 and transmit the response message to the base station CU 903. The response message may include acceptance / rejection information of the source cell (DU) 902 to the request.

[0191] In operation 970 , the terminal 901 may apply a configuration on a target cell to which layer 3 handover is applied, and the terminal 901 may perform random access to the target cell according to the applied configuration.

[0192] In operation 975, the terminal 901 may fail in handover to the target cell. The reason for the handover failure to the target cell may include expiration of the timer T304 for handover, failure of random access to the target cell for handover, etc. As the operation performed when the terminal fails in handover, the following operations may be performed. However, the operation is not limited thereto.

[0193] - The terminal generates a handover failure report message in the connected cell (source cell or target cell) and transmits the message to the base station CU 903. The handover failure report message may be a UEInformationResponse or another uplink RRC message.

[0194] When the base station recognizes that the handover has failed, the base station may transmit information about the handover failure to the source cell DU. This information may also include an indicator indicating that the layer 3 handover has failed and an index of the target cell for which the handover has been performed (information that can indicate the target cell indicated for the handover).

[0195] - The source cell DU 902 having received the information may initiate the LTM operation process by reapplying the previously stored LTM configuration information.

[0196] Figure 10FIG2 shows the overall operation of the base station CU and the serving cell (DU) transmitting the handover trigger information according to various embodiments of the present disclosure. Figure 8 and Figure 9 Compared with the operations of Example 1 and Example 2 described in the present disclosure, as Example 3 described in the present disclosure, Figure 10 Operation is shown where the serving cell performs reporting only upon receiving a request from the base station, rather than triggering LTM and transmitting the information immediately.

[0197] In operation 1010, the RRC connection terminal 1001 may perform data transmission and reception to and from the source cell 1 1002, and then transmit the layer 3 measurement values ​​of the neighboring cells and the serving cell to the source cell 1 1002 according to the configured layer 3 measurement and reporting. In this case, according to the actually configured layer 3 measurement and reporting, the layer 3 measurement values ​​of the neighboring cells and the serving cell may be transmitted to the base station CU1 1003. This is because the base station CU1 1003 is responsible for RRC message processing and determining mobility.

[0198] In operation 1015, the base station CU1 1003 may generate a message for requesting configuration information for L1 / L2-based handover (L1 / L2 configuration request message), and transmit the message to the LTM candidate neighboring cells 1004 and 1005 via the F1 interface according to the measurement value report received from the terminal. Figure 10, candidate cells are shown in association with DUs, but candidate cells and DUs may be mapped 1:1, or multiple candidate cells may be included in one DU. In addition, the message for requesting configuration information for L1 / L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, or the like, and may be a new F1 or Xn message. The message for requesting configuration information for L1 / L2-based handover may be a message for requesting a cell to be determined as a candidate cell for L1 / L2-based handover from a neighboring cell, and may simultaneously be a message for requesting RRC configuration information to be applied when performing L1 / L2-based handover on the corresponding cell. The RRC configuration information (CellGroupConfig 1, ..., CellGroupConfig N) to be applied when performing L1 / L2-based handover may be transmitted in one of a cell-level structure, a cell group-level structure, and an RRC message-level structure. The message for requesting configuration information for L1 / L2-based handover may be used to simultaneously transmit configuration and information about a reference cell, and the message may include an indicator for requesting that the configuration information for L1 / L2-based handover be transmitted to the candidate neighboring cells 1004 and 1005 by applying incremental configuration. The indicator for requesting that the configuration information for L1 / L2-based handover be transmitted by applying incremental configuration may be requested for each cell or may be requested for all cells collectively.

[0199] In operation 1020, the candidate neighboring cells 1004 and 1005 that have received the message requesting configuration information for L1 / L2-based handover may generate configuration information of each candidate neighboring cell when L1 / L2-based handover is applied based on the transmitted configuration information of the reference cell based on incremental configuration.

[0200] In operation 1025 , each candidate neighboring cell 1004 or 1005 may include the generated configuration information for L1 / L2-based handover in a configuration information response message for L1 / L2-based handover (L1 / L2 configuration response message) and send the response message to the base station CU1 1003 .

[0201] In operation 1030, base station CU1 1003 may generate an RRC message and transmit it to source cell 1002, and source cell 1002 may transmit the RRC message to terminal 1001. The RRC message may include configuration information (Pre-Config1, ..., Pre-ConfigN) of neighboring candidate cells for applying L1 / L2-based handover (LTM). The Pre-Config included in the RRC message is a message including the bearer configuration of the LTM candidate cell generated by the base station, the Layer 3 (L3) measurement configuration, and the CellGroupConfig configuration received from the LTM candidate cell in operation 1025.

[0202] In operation 1035, the terminal 1001 that has received the RRC message performs a process of decoding and processing the RRC message. The processing process of the terminal may include ASN.1 decoding and validity determination of the received message, a method for storing and managing configuration details, and the like.

[0203] In operation 1040, terminal 1001 may perform Layer 1 (L1) measurements and reporting for each candidate neighboring cell, and may also simultaneously perform Layer 3 (L3) measurements and reporting in operation 1045, depending on the configuration. In operation 1050, base station CU1 1003, having received the L3 measurement reports, may perform a process to determine whether handover for terminal 1001 is possible from neighboring base station CU2 (gNB2) 1006, which can perform handover. In other words, a handover request for terminal 1001 and a response thereto may be received. The response to the handover request may include RRC configuration information to be applied to the target cell when performing handover for terminal 1001. In this case, base station CU2 (gNB2) 1006 may reject the handover request. In operation 1040, source cell 1002, having received the L1 measurement reports, may determine handover based on the corresponding measurement values ​​and, in operation 1055, instruct the terminal to perform L1 / L2 handover. In operation 1050, DCI and MAC CE including a handover indicator may be used for L1 / L2 signaling. The L1 measurement value transmission for determining L1 / L2 handover and the handover determination in operations 1040 and 1055 can be performed by either the source cell (DU) or the source base station (CU). If the CU makes all determinations, the source cell may transmit the L1 measurement values ​​received from the terminal and, based on the handover determination indication from the CU, transmit L1 / L2 signaling to the terminal. However, when the source cell makes the final determination, it may, based on the measurement value criteria (threshold and measurement value range) used for handover determination for each candidate neighboring cell received from the previous base station, independently determine the handover and transmit L1 / L2 signaling to the terminal 1001 without transmitting the L1 measurement values ​​to the base station. In embodiments of the present disclosure, the triggering of LTM handover by the source cell (DU) is described. When the L1 / L2 handover indication is transmitted to the terminal, in operation 1060, the terminal may initiate the handover process and start a timer for L1 / L2 handover. This timer may be a newly configured timer for LTM, or the existing T304 timer may be reused.

[0204] In operation 1065 , the terminal 1001 applies a configuration of a target cell to which the L1 / L2 handover is applied. This configuration may be one of the LTM candidate neighbor cell configurations previously received in operation 1030 .

[0205] In operation 1070 , according to the applied configuration, the terminal 1001 may perform random access when the target cell requires random access, and may omit the random access procedure when random access is neither indicated nor required (when uplink synchronization has been performed or configured).

[0206] In operation 1075, the base station CU 903 may determine whether to indicate a Layer 3 handover based on the result of the measurement report received from the terminal 1001 in operation 1045, and instruct the terminal 1001 to perform the handover. This is because the base station independently determines and triggers the handover because it does not have information about whether the source cell DU has triggered the LTM. Although the L3 handover instruction is transmitted to the terminal via the RRC message, the terminal 1001 may not perform the corresponding Layer 3 handover operation due to the ongoing handover process.

[0207] In operation 1080, the base station CU 1003 may transmit a message to the source cell DU 1002, including an indicator requesting that LTM-related operations be stopped due to the triggering of a Layer 3 handover. To this end, the source base station CU 1003 may request that operations related to LTM-related L1 measurement-based handover (LTM Handover Indication) not be triggered due to the triggering of the handover. The LTM trigger information may be transmitted via the F1 interface and may include an indicator indicating that a Layer 3 handover has been triggered and an index of the target cell to which the handover has been triggered (information capable of indicating the target cell indicated for the handover). Even if the source cell receives this request from the base station, the configuration on the LTM candidate cell may be maintained. This is because LTM can be retriggered when LTM to another cell is indicated or the handover fails.

[0208] Furthermore, in operation 1083, the source cell (DU) 1002 may generate a response message regarding the indication of the base station CU 1003 in operation 1080 and transmit the response message to the base station CU 1003. The response message may include acceptance / rejection information of the source cell (DU) 1002 to the request.

[0209] In operation 1085, source cell DU 1002, having received the indication from base station CU 1003, may report to base station CU 1003 that LTM has been triggered in operation 1085. This may serve to inform source base station CU 1003 that LTM has been triggered and that a base station-triggered Layer 3 handover may not be performed. Furthermore, this may also serve as a request to avoid triggering operations related to existing L3 measurement-based handovers (L3 handover indications). LTM trigger information may be transmitted via the F1 interface and may include an indicator indicating that LTM has been triggered and an index for an LTM cell configuration (information capable of indicating the target cell for which LTM has been performed).

[0210] In operation 1087, the source cell DU 1002 may transmit the status of downlink data transmission from the target cell to the base station CU 1003, and may send a message including an indicator for requesting to stop data transmission. The message including the indicator for requesting to stop data transmission may be transmitted via an existing DL delivery status message or a new message. For reference, when the handover process is completed later, the base station that has received the message may perform a process of receiving a status report on downlink data reception from the target cell and transmitting it to the source cell, wherein when the provided operation is applied, the corresponding process may be omitted, thereby simplifying the process. In addition, the role of the message is to transmit the reception status of the downlink data message, and via this, the source base station CU1 1003 may determine whether to receive downlink data and whether to support additional handover.

[0211] In operation 1089, the source base station CU1 1003 may transmit an inter-node message for requesting to stop the ongoing handover process to the neighboring base station CU2 (gNB2) 1006 that may perform layer 3 handover via the Xn interface.

[0212] In operation 1091, neighboring base station CU2 (gNB2) 1006 may generate an acceptance or rejection message in response to a request received from source base station CU1 1003 to stop the handover procedure and transmit the acceptance or rejection message to source base station CU1 1003. In response to the handover stop request transmitted from source base station CU1 1003, base station CU2 (gNB2) 1006 may release handover-related resources for the terminal, thereby effectively operating the base station. If base station CU2 (gNB2) 1006 accepts the handover stop request, the terminal context and handover-related procedures for the terminal may be released. If base station CU2 (gNB2) 1006 rejects the handover stop request, this may be communicated to source base station CU1 1003, allowing source base station CU1 1003 to re-trigger the handover procedure for the terminal at a later time. In other words, base station CU2 (gNB2) 1006 may maintain the context and related configurations for the terminal handover until the handover procedure is successful.

[0213] In operation 1093, the terminal 1001 may fail in the LTM handover to the target cell. The reasons for the LTM handover failure may include expiration of the timer for LTM handover or expiration of the existing T304 timer, failure of random access to the target cell performing LTM handover, etc. As an operation performed when the terminal 1001 fails in the LTM handover, the following operation may be performed in operation 1095. However, the operation is not limited thereto.

[0214] When LTM fails, the terminal performs a fallback to the previous source cell 1002 and attempts to connect. To this end, even when LTM is triggered, the terminal may need to maintain the configuration information for the source cell. In addition, even after falling back to the source cell 1002, the LTM configuration information of the LTM target cell is maintained. This is to allow LTM to be retriggered based on the existing configuration.

[0215] If fallback to the source cell cannot be fully performed, the terminal enters the RRC re-establishment procedure to reselect a connectable cell. If the cell found via cell reselection is one of the LTM candidate cells, the terminal may attempt to connect by applying the pre-configured RRC configuration to the cell.

[0216] Then, in operation 1097, terminal 1001 may generate a handover failure report message in the connected cell (source cell or target cell) and transmit the message to base station CU 1003. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Furthermore, the handover failure may be reported via a new MAC CE or uplink control signal (uplink control information (UCI)). The information included in the handover failure report message may include the following information.

[0217] - An indicator indicating that the switch failed due to LTM failure.

[0218] - Information of the target cell where LTM has been attempted and has failed: LTM cell configuration index or actual cell index (physical cell index (PCI)) information.

[0219] In operation 1099, source base station CU 1003 may recognize, via the LTM triggering information in operation 1055, that source cell DU 1002 has triggered LTM, and may recognize, via the handover failure message in operation 1097, that the LTM attempt has failed and fallback to the source cell has been performed. Therefore, source base station CU 1003 may re-trigger the already pending Layer 3 handover procedure. However, due to the influence of the determination of Layer 3 handover to the target cell based on the information included in the LTM failure message, this determination may not be performed. This is a matter of network implementation, and for example, if the target cell information associated with the failed LTM is the same as the target cell for the existing Layer 3 handover, the handover may fail again, necessitating re-triggering or cancellation of the handover by updating to new configuration values. For reference, this handover procedure may be a handover procedure that was already pending via operations 1093 and 1095, and the handover configuration and target cell may be changed mid-flight based on new measurement values ​​and solutions (such as inter-node messaging with the base station).

[0220] This embodiment allows the base station to manage repeated Layer 3 handovers even when LTM has been triggered, resolving uncertainty in terminal and base station operations caused by multiple repeated handover requests. When a terminal receives an LTM MAC CE and maintains connection to the source cell even during the LTM process, and uplink / downlink transmission and reception are possible, the existing handover message allows Layer 3 operations triggered during the LTM handover process. In this case, the base station can request a handover instead of LTM if necessary.

[0221] Figure 11 The operation of performing L1 / L2-based beam changing and terminal switching according to various embodiments of the present disclosure is shown. Specifically, the terminal operation of the present disclosure includes an operation for resolving the situation where LTM and layer 3 switching are redundantly instructed.

[0222] In operation 1105, the connected terminal may receive configuration information in the neighboring cell from the serving cell via an RRC reconfiguration message, the configuration information being applied after indicating L1 / L2 based mobility. For detailed configuration methods and details, refer to Figures 6 to 10 Description. Additionally, although omitted, the terminal may have already received a basic RRC configuration from the base station before the RRC configuration information is transmitted, and the terminal may report Layer 3 measurements for neighboring cells. Specifically, the configuration information for the neighboring cell received in operation 1105 may be transmitted by applying incremental configuration based on the configuration of a reference cell, which is applied after indicating L1 / L2-based mobility. The terminal can identify the reference cell and configuration information for the reference cell previously notified or indicated in the RRC configuration. Since only the portions that differ from the reference cell are configured and transmitted, configuration for neighboring cells other than the reference cell can result in less signaling overhead. The terminal may decode the received configuration for the neighboring cell based on the configuration of the reference cell in the corresponding operation and store and manage the actually applied configuration in a separate buffer and list (i.e., storing the configuration based on the incremental configuration applied to the reference cell as a full configuration configured with reference to the reference cell). Alternatively, the terminal may store and manage the received RRC configuration based on the reference cell as in a buffer, without decoding the received configuration and storing and managing the actually applied configuration. In corresponding operations, when the configuration on the neighboring cell is decoded based on the reference cell and the actually applied configuration is stored, thereby indicating the actual L1 / L2-based handover, the handover to the corresponding cell can be immediately applied without additional delay time.

[0223] In operation 1110, the terminal may perform L1 measurements associated with candidate neighboring cells while maintaining a connection with the serving cell, and may report corresponding measurement results according to a pre-configured L1 measurement report configuration method. Furthermore, independently of the operation, the terminal may measure neighboring cells according to an L3 measurement configuration and report corresponding measurement results to the base station according to the L3 measurement report configuration. The serving cell may determine whether to perform beam change and handover of the terminal based on the received measurement results, and when it is determined that a change to a specific beam of the neighboring cell rather than a specific beam of the serving cell is required, handover and beam change of the terminal may be instructed via L1 / L2 signaling in operation 1115. Figure 11 The case where L1 / L2 signaling is MAC CE and DCI is shown, where the information indicating the change of specific cells of the serving cell and the neighboring cell can be indicated in the MAC CE (when the MAC CE only indicates one beam), and then in the transmitted DCI, the switching can be indicated by selecting one of the multiple beams of the neighboring cell activated in the MAC CE.

[0224] In operation 1120, the terminal may check whether handover is indicated according to the MAC CE and DCI signaling received in operation 1115, and perform an LTM handover operation. When the received MAC CE and DCI indicate handover (when the MAC CE itself indicates handover, or when the MAC CE activates multiple beams and the DCI indicates handover while indicating one of the beams), the terminal may perform handover to a cell associated with the indicated TCI state.

[0225] When random access is successfully performed and thus switching is successful in operation 1125, the terminal can also apply the configuration on the corresponding target cell in operation 1130, which has been stored as a pre-configuration for reception on the adjacent cell, and connect to the cell, thereby performing data transmission and reception using the indicated beam.

[0226] If the terminal fails in the LTM handover in operation 1125, then in operation 1135, the terminal can fall back to the previous source cell and attempt to connect. In order to fall back to the previous source cell and attempt to connect, the terminal may need to maintain the configuration information for the source cell even when LTM is triggered. In addition, even after falling back to the source cell, the LTM configuration information for the LTM target cell can be maintained. This is to allow LTM to be re-triggered based on the existing configuration. If the fallback to the source cell cannot be fully performed, the terminal can enter the RRC re-establishment process to reselect a connectable cell. If the cell found via cell reselection is one of the LTM candidate cells, the terminal can attempt to connect by applying the pre-configured RRC configuration to the cell.

[0227] Then, in operation 1140, the terminal may generate a handover failure report message in the connected cell (source cell or target cell) and transmit the message to the base station. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Furthermore, the handover failure may be reported via a new MAC CE or uplink control signal (uplink control information (UCI)). The information included in the handover failure report message may include the following information. However, the information is not limited thereto.

[0228] - An indicator indicating that the switch failed due to LTM failure.

[0229] - Information of the target cell where LTM has been attempted and has failed: LTM cell configuration index or actual cell index (physical cell index (PCI)) information.

[0230] Then, in operation 1140, the source base station may recognize that the LTM attempt has failed and that fallback to the corresponding cell has been performed via a handover failure message report. Therefore, the source base station may re-trigger the already suspended layer 3 handover process. Due to the influence of the determination of the layer 3 handover to the target cell based on the information included in the LTM failure message, the determination by the source base station to re-trigger the handover process may not be performed. This is a network implementation, and for example, if the target cell information associated with the failed LTM is the same as the target cell for performing the existing layer 3 handover, the handover may fail again, so that the handover may be re-triggered or canceled by updating to the new configuration value.

[0231] Although omitted in this figure, if the terminal is able to receive an RRC message from the source cell even when performing LTM handover to the target cell (if equipped with the corresponding capability) in operation 1120, the terminal may perform a handover operation in response to the received Layer 3 handover request. This operation may be performed by one of the following methods.

[0232] - Perform high priority handover operations (LTM or Layer 3 handover: priority is specified in the standard or provided via signaling);

[0233] -Continue to execute the currently running handover process; and / or

[0234] - Execute the newly indicated handover procedure (stop the existing handover procedure).

[0235] Figure 12 Base station operations according to various embodiments of the present disclosure are illustrated.

[0236] In operation 1205 , the base station may receive an L3 measurement value report from the terminal, and may identify whether the terminal needs handover and which cells are handover candidate cells based on the terminal's measurement values ​​relative to neighboring frequencies and cells.

[0237] In operation 1210, the base station may request configuration information for L1 / L2-based handover from a neighboring cell and receive a response from the cell. In operation, the base station receives RRC configuration information from the neighboring cell based on incremental configuration, and the base station may notify the neighboring cell of a reference cell and reference cell configuration, and receive configuration information for L1 / L2-based handover for other neighboring cells based on the reference cell configuration. Although omitted in this figure, prior to operation, configurations related to L3 measurement configuration and basic RRC configuration are provided.

[0238] In operation 1215, the base station may transmit the generated RRC configuration message to the connected terminal, the RRC configuration message including the neighbor cell configuration information received in operation 1210. That is, the configuration information in the neighbor cell applied after the L1 / L2-based mobility is instructed may be transmitted from the serving cell via the RRC reconfiguration message. Figures 6 to 10 Provide a specific description.

[0239] Then, in operation 1220, the base station may receive a report on L1 and L3 measurement values ​​from the terminal. In this case, the L1 measurement value can be used to support neighboring cells (non-serving cells) that support L1 / L2-based mobility. The serving cell can determine whether to perform beam change and handover for the terminal based on the received measurement results. When it is determined that a change to a specific beam of a neighboring cell rather than a specific beam of the serving cell is required, the base station can instruct the terminal to perform LTM handover via L1 / L2 signaling in operation 1225. The L1 / L2 signaling can be a MAC CE or DCI and can include information indicating a change to a specific beam of a neighboring cell. In addition, during operation, existing handovers via RRC messages can also be independently executed and instructed. This may occur because the base station and the serving cell independently determine LTM and Layer 3 handovers.

[0240] In operation 1230, in order to solve such a problem, the base station CU and the serving cell DU may transmit the handover information triggered by the corresponding entity to another node in order to prevent repeated handover indications. That is, in the case where the handover is triggered, the source base station CU may send the existing handover trigger information to the source cell DU. When the LTM is triggered, the source cell DU may send the LTM trigger information to the source base station CU. As handover related information, an indicator indicating that the layer 3 handover or LTM has been triggered and an index of the target cell to which the handover has been triggered (information capable of indicating the target cell indicated for handover) may be included. For detailed operations, reference may be made to the diagrams showing embodiments 1, 2, and 3. Figure 8 、 Figure 9 and Figure 10 .

[0241] Then, in operation 1235, the base station may receive a handover failure report message from the terminal including information regarding the handover failure. This may be a message indicating that the terminal has attempted to reconnect to the corresponding cell after the handover failure. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Furthermore, the handover failure may be reported via a new MAC CE or uplink control signal (uplink control information (UCI)). The information included in the handover failure report message may include the following information. However, the information is not limited thereto.

[0242] - An indicator indicating that the switch failed due to LTM failure.

[0243] - Information of the target cell where LTM has been attempted and has failed: LTM cell configuration index or actual cell index (physical cell index (PCI)) information.

[0244] The source base station can identify that the LTM attempt has failed and has performed a fallback to the corresponding cell via a handover failure message report. Therefore, the source base station can re-trigger the already suspended Layer 3 handover process. Due to the influence of the determination of the Layer 3 handover to the target cell based on the information included in the LTM failure message, the determination to re-trigger the handover process may not be performed. This is a network implementation, and for example, if the target cell information associated with the failed LTM is the same as the target cell for the existing Layer 3 handover, the handover may fail again, so that the handover can be re-triggered or canceled by updating to the new configuration value.

[0245] Figure 13 The structure of a terminal according to various embodiments of the present disclosure is shown.

[0246] refer to Figure 13The terminal includes a radio frequency (RF) processor 1310 , a baseband processor 1320 , a storage unit 1330 , and a controller 1340 .

[0247] The RF processor 1310 can perform functions for transmitting and receiving signals via wireless channels, such as signal frequency band conversion and amplification. That is, the RF processor 1310 can up-convert the baseband signal provided by the baseband processor 1320 into an RF frequency band signal, transmit the converted RF frequency band signal via the antenna, and then down-convert the RF frequency band signal received via the antenna into a baseband signal. For example, the RF processor 1310 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), etc. Figure 13 In the figure, only one antenna is shown, but the terminal may have multiple antennas. The RF processor 1310 may include multiple RF chains. In addition, the RF processor 1310 may perform beamforming. To perform beamforming, the RF processor 1310 may adjust the phase and amplitude of each signal transmitted and received via multiple antennas or antenna elements. The RF processor 1310 may perform MIMO and may receive multiple layers when performing MIMO operations.

[0248] The baseband processor 1320 can perform conversion functions between baseband signals and bit streams according to the system's physical layer specifications. For example, during data transmission, the baseband processor 1320 can generate complex symbols by encoding and modulating the transmit bit stream. Furthermore, during data reception, the baseband processor 1320 can reconstruct the received bit stream by demodulating and decoding the baseband signal provided by the RF processor 1310. For example, when using an orthogonal frequency division multiplexing (OFDM) scheme, during data transmission, the baseband processor 1320 can generate complex symbols by encoding and modulating the transmit bit stream, mapping the complex symbols to subcarriers, and then configuring OFDM symbols through an inverse fast Fourier transform (IFFT) operation and cyclic prefix (CP) insertion. Furthermore, during data reception, the baseband processor 1320 can divide the baseband signal provided by the RF processor 1310 into OFDM symbols, reconstruct the signals mapped to the subcarriers through a fast Fourier transform (FFT), and then reconstruct the received bit stream through demodulation and decoding.

[0249] As described above, the baseband processor 1320 and the RF processor 1310 can transmit and receive signals. Therefore, the baseband processor 1320 and the RF processor 1310 can be referred to as transmitters, receivers, transceivers, or communication units. Furthermore, at least one of the baseband processor 1320 and the RF processor 1310 can include multiple communication modules to support a variety of different radio access technologies. Furthermore, at least one of the baseband processor 1320 and the RF processor 1310 can include different communication modules to process signals in different frequency bands. For example, the different radio access technologies can include wireless LANs (e.g., IEEE 802.11), cellular networks (e.g., LTE), and the like. Furthermore, the different frequency bands can include super high frequency (SHF) (e.g., 2.0 GHz, nHz) bands and millimeter wave (e.g., 60 GHz) bands.

[0250] The storage unit 1330 may store data used for the operation of the terminal, such as basic programs, applications, configuration information, etc. Specifically, the storage unit 1330 may store information about a second access node that performs wireless communication using a second radio access technology. In addition, the storage unit 1330 may provide the stored data in response to a request from the controller 1340.

[0251] The controller 1340 can control the overall operation of the terminal. For example, the controller 1340 can transmit and receive signals via the baseband processor 1320 and the RF processor 1310. Furthermore, the controller 1340 can store and read data in the storage unit 1340. To this end, the controller 1340 may include at least one processor. For example, the controller 1340 may include a communication processor (CP) configured to perform control for communication, and an application processor (AP) configured to control higher layers (such as application programs).

[0252] Figure 14 The structure of a base station according to various embodiments of the present disclosure is shown.

[0253] refer to Figure 14 The base station includes an RF processor 1410 , a baseband processor 1420 , a backhaul communication unit 1430 , a storage unit 1440 , and a controller 1450 .

[0254] The RF processor 1410 can perform functions for transmitting and receiving signals via wireless channels, such as signal frequency band conversion and amplification. That is, the RF processor 1410 can up-convert the baseband signal provided by the baseband processor 1420 into an RF frequency band signal, transmit the converted RF frequency band signal via the antenna, and then down-convert the RF frequency band signal received via the antenna into a baseband signal. For example, the RF processor 1410 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Figure 14 In the figure, only one antenna is shown, but the first access node may include multiple antennas. The RF processor 1410 may include multiple RF chains. In addition, the RF processor 1410 may perform beamforming. To perform beamforming, the RF processor 1410 may adjust the phase and amplitude of each signal transmitted and received via the multiple antennas or antenna elements. The RF processor 1410 may perform downlink MIMO operations by transmitting one or more layers.

[0255] The baseband processor 1420 performs conversion between baseband signals and bit streams according to the physical layer specifications of the first radio access technology. For example, during data transmission, the baseband processor 1420 can generate complex symbols by encoding and modulating the transmit bit stream. Furthermore, during data reception, the baseband processor 1420 can reconstruct the received bit stream by demodulating and decoding the baseband signal provided by the RF processor 1410. For example, when conforming to the OFDM scheme, during data transmission, the baseband processor 1420 can generate complex symbols by encoding and modulating the transmit bit stream, mapping the complex symbols to subcarriers, and then configuring OFDM symbols through an IFFT operation and CP insertion. Furthermore, during data reception, the baseband processor 1420 can divide the baseband signal provided by the RF processor 1410 into units of OFDM symbols, reconstruct the signals mapped to the subcarriers through an FFT operation, and then reconstruct the received bit stream through demodulation and decoding. The baseband processor 1420 and the RF processor 1410 can transmit and receive signals as described above. Therefore, the baseband processor 1420 and the RF processor 1410 may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0256] The backhaul communication unit 1430 may provide an interface for performing communications with other nodes within the network. That is, the backhaul communication unit 1430 may convert a bit stream transmitted from the master base station to another node (e.g., a secondary base station and a core network) into a physical signal, and may convert a physical signal received from another node into a bit stream.

[0257] The storage unit 1440 may store data used for base station operations, such as basic programs, applications, and configuration information. Specifically, the storage unit 1440 may store information about bearers allocated to connected terminals, measurement results reported from connected terminals, and the like. Furthermore, the storage unit 1440 may store information used as a criterion for determining whether to provide multiple connections to a terminal or to suspend multiple connections. The storage unit 1440 may provide the stored data in response to a request from the controller 1450.

[0258] The controller 1450 may control the overall operation of the master base station. For example, the controller 1450 may send and receive signals via the baseband processor 1420 and the RF processor 1410. In addition, the controller 1450 may record and read data in the storage unit 1440. To this end, the controller 1450 may include at least one processor.

[0259] Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

Claims

1. A method performed by a distributed unit (DU) of a base station in a wireless communication system, the method comprising: Identifying that Layer Triggered Mobility (LTM) is triggered based on measurement reports received from a user equipment (UE); as well as A first message for notifying that the LTM is triggered is sent to a central unit (CU) of the base station.

2. The method according to claim 1, wherein The first message includes an indicator associated with LTM-based cell switching.

3. The method according to claim 1, wherein The method further comprises: receiving, from the CU of the base station, a second message for notifying that a layer 3 (L3) handover is triggered, wherein the second message is received within a predetermined time period based on the transmission of the first message; and Recognize that LTM has higher priority than L3 switching, The second message includes an indicator for instructing to stop sending data to the UE.

4. A method performed by a central unit (CU) of a base station in a wireless communication system, the method comprising: receiving a first message for notifying that layer triggered mobility (LTM) is triggered from a distributed unit (DU) of a base station, Among them, the LTM is identified by the DU of the base station based on the measurement report received from the user equipment (UE).

5. The method according to claim 4, wherein The method further comprises: sending a second message for notifying a DU of a base station that a layer 3 (L3) handover is triggered, wherein the second message is received within a predetermined time period based on reception of the first message, Among them, LTM is recognized by the DU of the base station as having a higher priority than L3 handover. The second message includes an indicator for instructing to stop sending data to the UE.

6. The method according to claim 4, wherein: In case that the third message for notifying that the L3 handover is triggered is received before the LTM is triggered, the L3 handover has a higher priority than the LTM.

7. A distributed unit (DU) of a base station in a wireless communication system, the DU of the base station comprising: transceiver; and a controller coupled to the transceiver and configured to: Identifying that Layer Triggered Mobility (LTM) is triggered based on measurement reports received from a User Equipment (UE), and A first message for notifying that the LTM is triggered is sent to a central unit (CU) of the base station.

8. The DU according to claim 7, wherein: The first message includes an indicator associated with LTM-based cell switching.

9. The DU according to claim 7, wherein: The controller is also configured to: receiving, from the CU of the base station, a second message for notifying that a layer 3 (L3) handover is triggered, wherein the second message is received within a predetermined time period based on the transmission of the first message; and Recognize that LTM has higher priority than L3 switching, The second message includes an indicator for instructing to stop sending data to the UE.

10. The DU according to claim 7, wherein: In case that the third message for notifying that the L3 handover is triggered is received before the LTM is triggered, the L3 handover has a higher priority than the LTM.

11. A central unit (CU) of a base station in a wireless communication system, the CU of the base station comprising: transceiver; and a controller coupled to the transceiver and configured to: receiving a first message for notifying that layer triggered mobility (LTM) is triggered from a distributed unit (DU) of a base station, Among them, the LTM is identified by the DU of the base station based on the measurement report received from the user equipment (UE).

12. The CU according to claim 11, wherein: The controller is also configured to: transmitting a second message including a second message for notifying that a layer 3 (L3) handover is triggered to a DU of a base station, wherein the second message is received within a predetermined time period based on reception of the first message, Among them, LTM is recognized by the DU of the base station as having a higher priority than L3 handover. The second message includes an indicator for instructing to stop sending data to the UE.

13. The CU according to claim 11, wherein: In case that the third message for notifying that the L3 handover is triggered is received before the LTM is triggered, the L3 handover has a higher priority than the LTM.

14. A method performed by a user equipment (UE) in a wireless communication system, the method comprising: Send measurement reports to the distributed unit (DU) of the base station; Receive a handover command message based on Layer Triggered Mobility (LTM) from the DU of the base station, Among them, LTM is triggered based on measurement reports. Here, in case that the LTM is triggered before the triggering of the layer 3 (L3) handover, the LTM has a higher priority than the L3 handover.

15. A user equipment (UE) in a wireless communication system, the UE comprising: transceiver; and a controller coupled to the transceiver and configured to: Send measurement reports to the distributed unit (DU) of the base station, Receive a handover command message based on Layer Triggered Mobility (LTM) from the DU of the base station, Among them, LTM is triggered based on measurement reports. Here, in case that the LTM is triggered before the triggering of the layer 3 (L3) handover, the LTM has a higher priority than the L3 handover.

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