Method and device for performing l1 / l2-based cell change and recovering connection in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. According to various embodiments of the present disclosure, a method performed by a user equipment in a wireless communication system may comprise the steps of: receiving, from a first central unit (CU), information for configuring L1 / L2 triggered mobility (LTM), wherein the information for configuring the LTM includes an identifier (ID) associated with the first CU and information on an LTM candidate cell; performing cell selection for selecting a first cell by detecting a radio link failure (RLF); when the first cell is the LTM candidate cell, determining whether an ID associated with the first cell is identical to the ID associated with the first CU; and when the ID associated with the first cell is identical to the ID associated with the first CU, performing LTM cell switching to the first cell.

Description

Method and apparatus for performing L1 / L2-based cell switching and restoring a connection in a wireless communication system

[0001] The present disclosure relates to the operation of a terminal and a base station in a wireless communication system. More specifically, the present disclosure relates to a method for performing a procedure to rapidly restore a connection when an L1 (layer 1) / L2 (layer 2) based cell change is performed, and an apparatus capable of performing the same.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in frequency bands below 6 GHz ('Sub 6 GHz'), such as 3.5 gigahertz (3.5 GHz), but also in ultra-high frequency bands called millimeter waves (mmWave), such as 28 GHz and 39 GHz ('Above 6 GHz'). In addition, for 6G mobile communication technology, which is referred to as a system beyond 5G, implementation in the terahertz (THX) band (e.g., the 3 terahertz band at 95 GHz) is being considered to achieve transmission speeds 50 times faster and ultra-low latency reduced to one-tenth compared to 5G mobile communication technology.

[0003] In the early stages of 5G mobile communication technology, aiming to satisfy service support and performance requirements for enhanced Mobile BroadBand (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), technologies such as beamforming and Massive MIMO to mitigate path loss and increase transmission distance in ultra-high frequency bands, support for various numerologies (such as the operation of multiple subcarrier spacings) and dynamic operation of slot formats for the efficient utilization of ultra-high frequency resources, initial access techniques to support multi-beam transmission and broadband, definition and operation of Band-Width Parts (BWP), Low Density Parity Check (LDPC) codes for high-volume data transmission, new channel coding methods such as Polar Codes for the reliable transmission of control information, and L2 pre-processing (L2 Standardization has been carried out for pre-processing, network slicing which provides a dedicated network specialized for specific services, and other methods.

[0004] Currently, discussions are underway to improve and enhance the performance of the initial 5G mobile communication technology, taking into account the services that the 5G mobile communication technology was intended to support. Additionally, standardization of the physical layer is in progress for technologies such as V2X (Vehicle-to-Everything), which helps autonomous vehicles make driving decisions and enhance user convenience based on their own location and status information transmitted by the vehicle; NR-U (New Radio Unlicensed), which aims for system operation in unlicensed bands to comply with various regulatory requirements; NR terminal low power consumption technology (UE Power Saving); Non-Terrestrial Network (NTN), which is direct terminal-satellite communication for securing coverage in areas where communication with the terrestrial network is impossible; and positioning.

[0005] In addition, standardization is underway in the field of wireless interface architecture / protocols for technologies such as the Industrial Internet of Things (IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) which provides nodes to expand network service areas by integrating wireless backhaul links and access links, Mobility Enhancement including Conditional Handover and Dual Active Protocol Stack (DAPS) Handover, and 2-step Random Access (2-step RACH for NR) which simplifies random access procedures. Standardization is also underway in the field of system architecture / services for 5G baseline architectures (e.g., Service based Architecture, Service based Interface) to incorporate Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC), which provides services based on the location of the terminal.

[0006] When such 5G mobile communication systems are commercialized, connected devices, which are increasing explosively, will be connected to communication networks. Accordingly, it is expected that there will be a need to enhance the functionality and performance of 5G mobile communication systems and to integrate the operation of connected devices. To this end, new research is planned to be conducted on 5G performance improvement and complexity reduction, support for AI services, support for metaverse services, and drone communication using eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] Furthermore, the advancement of these 5G mobile communication systems encompasses multi-antenna transmission technologies such as new waveforms, Full Dimensional MIMO (FD-MIMO), array antennas, and large-scale antennas to guarantee coverage in the terahertz band of 6G mobile communication technology; metamaterial-based lenses and antennas; high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM); and Reconfigurable Intelligent Surface (RIS) technology to improve terahertz band signal coverage; as well as full-duplex technology for enhancing frequency efficiency and system networks in 6G mobile communication technology; AI-based communication technologies that realize system optimization by utilizing satellites and Artificial Intelligence (AI) from the design stage and internalizing end-to-end AI support functions; and the realization of services of complexity exceeding the limits of terminal computing capabilities by utilizing ultra-high-performance communication and computing resources. It could serve as a foundation for the development of next-generation distributed computing technologies.

[0008] The present invention discloses a procedure for applying a pre-configuration for an LTM candidate cell configuration and a reference cell configuration when a terminal supports L1 / L2 triggered mobility (L1(layer 1) / L2(layer 2) triggered mobility, LTM) for different base stations (e.g., inter-CU(central unit)).

[0009] The technical problems to be solved by the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0010] According to various embodiments of the present disclosure, a method performed by a terminal (user equipment) in a wireless communication system may include: receiving information for setting LTM (L1 / L2 triggered mobility) from a first central unit (CU); the information for setting LTM includes an identifier (ID) associated with the first CU and information about an LTM candidate cell; performing cell selection for selecting a first cell by detecting a radio link failure (RLF); determining whether, if the first cell is the LTM candidate cell, the ID associated with the first cell is the same as the ID associated with the first CU; and, if the ID associated with the first cell is the same as the ID associated with the first CU, performing an LTM cell switching for the first cell.

[0011] According to various embodiments of the present disclosure, in a wireless communication system, a terminal (user equipment) comprises: at least one transceiver; and at least one processor communicatively coupled to the at least one transceiver; and may include at least one memory that is communicationally coupled to the at least one processor and stores instructions, and the instructions are executed individually or in any combination by the at least one processor so that the terminal: receives information for setting LTM (L1 / L2 triggered mobility) from a first CU (central unit), the information for setting LTM includes an ID (identifier) ​​associated with the first CU and information about an LTM candidate cell, performs cell selection for selecting a first cell by detecting a radio link failure (RLF), determines whether the ID associated with the first cell is the same as the ID associated with the first CU if the first cell is the LTM candidate cell, and performs LTM cell switching for the first cell if the ID associated with the first cell is the same as the ID associated with the first CU.

[0012] The present invention can reduce the signaling overhead of the pre-configuration for LTM by making the reference cell configuration available, according to the overall procedure of applying the LTM candidate cell configuration and the reference cell configuration when inter-CU LTM is supported.

[0013] Figure 1 illustrates the structure of a next-generation mobile communication system to which the present invention is applied.

[0014] FIG. 2 illustrates the wireless protocol structure of a next-generation mobile communication system to which the present invention can be applied.

[0015] FIG. 3 illustrates the structure of another next-generation mobile communication system to which the present invention can be applied.

[0016] FIG. 4 illustrates a scenario for inter-cell beam management according to embodiments of the present disclosure, in which a terminal transmits and receives data through the beam of a TRP (transmission and reception point) of a neighboring cell that supports L1 / L2-based beam switching while maintaining a connection state with a serving cell.

[0017] FIG. 5 illustrates a scenario in which a terminal changes the serving cell and beam to the TRP of a cell that supports L1 / L2-based beam changing according to embodiments of the present disclosure to transmit and receive data.

[0018] FIG. 6 illustrates the flow of signals for a terminal that has received an LTM setting in an intra-CU to perform a recovery procedure after a wireless link failure, according to various embodiments of the present disclosure.

[0019] FIG. 7 illustrates the flow of signals for a terminal that has experienced a wireless link failure to select an LTM candidate cell in a different CU and perform fast recovery, according to various embodiments of the present disclosure.

[0020] FIG. 8 illustrates the flow of terminal operations for performing fast recovery operations in LTMs within different CUs when an NCC value is transmitted through an LTM cell change MAC CE according to an embodiment of the present disclosure.

[0021] FIG. 9 illustrates the flow of terminal operations for performing fast recovery operations in LTMs within different CUs when an NCC value for an LTM candidate cell is transmitted via an RRC message, according to an embodiment of the present disclosure.

[0022] FIG. 10 illustrates the flow of base station operation according to embodiments of the present disclosure.

[0023] FIG. 11 illustrates the structure of a terminal according to embodiments of the present disclosure.

[0024] FIG. 12 illustrates the structure of a base station according to embodiments of the present disclosure.

[0025] The operating principle of the present invention will be described in detail below with reference to the attached drawings. In describing the present invention below, if it is determined that a detailed description of related known functions or configurations might unnecessarily obscure the essence of the invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. Terms used in the following description to identify connection 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 provided as examples for the convenience of explanation. Accordingly, the present invention is not limited to the terms described below, and other terms referring to objects having equivalent technical meanings may be used.

[0026] For convenience of explanation below, the present invention uses terms and names defined in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard. However, the present invention is not limited by the above terms and names and can be applied in the same way to systems conforming to other standards.

[0027] Figure 1 illustrates the structure of a next-generation mobile communication system to which the present invention is applied.

[0028] Referring to FIG. 1, as illustrated, the wireless access network of a next-generation mobile communication system consists of a next-generation base station (New Radio Node B, hereinafter NR NB) (110) and an NR CN (New Radio Core Network) (or Next Generation Core Network, NG CN) (105). A user terminal (New Radio User Equipment) (hereinafter NR UE or terminal) (115) connects to an external network through the NR NB (110) and the NR CN (105).

[0029] In FIG. 1, the NR NB (110) corresponds to the eNB (Evolved Node B) of the existing LTE system. The NR NB is connected to the NR UE (115) via a wireless channel and can provide superior service compared to the existing Node B. In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device is required to collect status information such as the buffer status, available transmission power status, and channel status of the UEs and perform scheduling, and this is handled by the NR NB (110). A single NR NB typically controls multiple cells. To achieve ultra-high-speed data transmission compared to existing LTE, the next-generation mobile communication system can have a maximum bandwidth greater than that of the existing system, and can additionally incorporate beamforming technology by using Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology. In addition, an Adaptive Modulation & Coding (AMC) method can be applied to determine the modulation scheme and channel coding rate according to the channel conditions of the terminal. The NR CN (105) performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN is a device responsible for various control functions as well as mobility management functions for the terminal, and is connected to multiple base stations. In addition, the next-generation mobile communication system can be interoperable with the existing LTE system, and the NR CN is connected to the MME (125) via a network interface. The MME is connected to the existing base station eNB (130).

[0030] FIG. 2 illustrates the wireless protocol structure of a next-generation mobile communication system to which the present invention can be applied.

[0031] Referring to FIG. 2, the wireless protocol of the next-generation mobile communication system consists of NR SDAP (201, 245), NR PDCP (205, 240), NR RLC (210, 235), and NR MAC (215, 230) at the terminal and the NR base station, respectively.

[0032] The main functions of NR SDAP (201, 245) may include some of the following functions.

[0033] - User data transfer function (transfer of user plane data)

[0034] - Mapping function between a QoS flow and a DRB for both DL and UL for uplink and downlink

[0035] - Marking QoS flow ID for uplink and downlink (marking QoS flow ID in both DL and UL packets)

[0036] - Function to map reflective QoS flow to data bearers for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

[0037] For SDAP layer devices, the terminal may receive a setting via an RRC message regarding whether to use the SDAP layer device header or the SDAP layer device function for each PDCP layer device, bearer, or logical channel. If the SDAP header is set, the terminal may be instructed to update or reset the mapping information for the uplink and downlink QoS flows and data bearers using a 1-bit indicator for NAS QoS reflection (e.g., NAS reflective QoS) and a 1-bit indicator for AS QoS reflection (e.g., AS reflective QoS) in the SDAP header. The SDAP header may include QoS flow ID information indicating QoS. The QoS information may be used for data processing priority, scheduling information, etc., to support seamless service.

[0038] The main functions of NR PDCP (205, 240) may include some of the following functions.

[0039] - Header compression and decompression features (ROHC only)

[0040] - User data transfer function (Transfer of user data)

[0041] - Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0042] - Out-of-sequence delivery of upper layer PDUs

[0043] - Reordering function (PDCP PDU reordering for reception)

[0044] - Duplicate detection function (Duplicate detection of lower layer SDUs)

[0045] - Retransmission of PDCP SDUs

[0046] - Encryption and decryption functions (Ciphering and deciphering)

[0047] - Timer-based SDU discard in uplink.

[0048] The reordering function of the NR PDCP device refers to a function of reordering PDCP PDUs received from a lower layer in order based on the PDCP SN (sequence number), and may include a function of transmitting data to an upper layer in the reordered order, or a function of transmitting immediately without considering the order, or a function of recording lost PDCP PDUs by reordering, or a function of reporting the status of lost PDCP PDUs to the transmitting side, or a function of requesting retransmission of lost PDCP PDUs.

[0049] The main functions of NR RLC (210, 235) may include some of the following functions.

[0050] - Data transfer function (Transfer of upper layer PDUs)

[0051] - Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0052] - Out-of-sequence delivery of upper layer PDUs

[0053] - ARQ function (Error Correction through ARQ)

[0054] - Concatenation, segmentation, and reassembly functions of RLC SDUs

[0055] - Re-segmentation function (Re-segmentation of RLC data PDUs)

[0056] - Reordering function (Reordering of RLC data PDUs)

[0057] - Duplicate detection

[0058] - Error detection function (Protocol error detection)

[0059] - RLC SDU discard function

[0060] RLC re-establishment function

[0061] The in-sequence delivery function of an NR RLC device refers to the function of delivering RLC SDUs received from a lower layer to an upper layer in sequence; it may include a function to reassemble and deliver them if a single RLC SDU is received split into multiple RLC SDUs; it may include a function to rearrange received RLC PDUs based on an RLC SN (sequence number) or PDCP SN (sequence number); it may include a function to record lost RLC PDUs after rearrangement; it may include a function to report the status of lost RLC PDUs to the transmitting side; it may include a function to request retransmission of lost RLC PDUs; and if there are lost RLC SDUs, it may include a function to deliver only the RLC SDUs prior to the lost RLC SDU to the upper layer in sequence; or, even if there are lost RLC SDUs, if a predetermined timer has expired, it may include a function to deliver all RLC SDUs received before the timer started to the upper layer in sequence; or It may include a function that delivers all RLC SDUs received up to the present to the upper layer in order once a predetermined timer has expired, even if there are lost RLC SDUs. Additionally, the RLC PDUs mentioned above may be processed in the order they are received (e.g., in the order of arrival, regardless of the sequence number) and delivered to the PDCP device out of order (out-of-sequence delivery). In the case of segments, segments stored in a buffer or to be received later may be received, reconstructed into a single complete RLC PDU, processed, and then delivered to the PDCP device.The NR RLC layer may not include a concatenation function, or the function may be performed by the NR MAC layer or replaced by the multiplexing function of the NR MAC layer.

[0062] The out-of-sequence delivery function of an NR RLC device refers to the function of delivering RLC SDUs received from a lower layer directly to an upper layer regardless of order. It may include a function of reassembling and delivering RLC SDUs when a single RLC SDU is received divided into multiple RLC SDUs, and may include a function of storing the RLC SN or PDCP SN of the received RLC PDUs and sorting the order to record the lost RLC PDUs.

[0063] The NR MAC (215, 230) can be connected to multiple NR RLC layer devices configured in a terminal, and the main functions of the NR MAC may include some of the following functions.

[0064] - Mapping function (Mapping between logical channels and transport channels)

[0065] - Multiplexing and demultiplexing functions (Multiplexing / demultiplexing of MAC SDUs)

[0066] - Scheduling information reporting function

[0067] - HARQ function (Error correction through HARQ)

[0068] - Priority handling between logical channels of one UE

[0069] - Priority handling between UEs by means of dynamic scheduling

[0070] - MBMS service identification function

[0071] - Transport format selection function

[0072] - Padding

[0073] The NR PHY layer (220, 225) can perform the operation of channel coding and modulating upper layer data, creating OFDM symbols and transmitting them to the wireless channel, or demodulating OFDM symbols received through the wireless channel and channel decoding them to transmit them to the upper layer.

[0074] FIG. 3 illustrates the structure of another next-generation mobile communication system to which the present invention can be applied.

[0075] Referring to FIG. 3, a cell serviced by a beam-based NR gNB (305) may be composed of multiple TRPs (Transmission and Reception Points) (310, 315, 320, 325, 330, 335, 340). The TRPs (310–340) represent blocks from which some functions of transmitting and receiving physical signals from an existing NR base station (eNB) have been separated, and may be composed of multiple antennas. The NR gNB (305) may be represented as a CU (Central Unit), or the TRPs may be represented as a DU (Distributed Unit). The functions of the NR gNB (305) and the TRPs may be configured by separating each layer from the PDCP / RLC / MAC / PHY layer (345). That is, TRPs (315, 325) can perform the functions of the corresponding layer using only the PHY layer, or TRPs (310, 335, 340) can perform the functions of the corresponding layers using only the PHY layer and the MAC layer, or TRPs (320, 330) can perform the functions of the corresponding layers using only the PHY layer, the MAC layer, and the RLC layer. In particular, TRPs (310~340) can use beamforming technology to transmit and receive data by generating narrow beams in multiple directions using multiple transmitting and receiving antennas. The user terminal (350) connects to the NR gNB (305) and the external network through the TRPs (310~340). The NR gNB (305) collects state information such as the buffer status, available transmission power status, and channel status of terminals to schedule them for service to users, and supports the connection between terminals and the core network (CN) (especially AMF / SMF (355)).

[0076] The TRP in the present invention is described based on a structure (315, 325) that has only a PHY layer and can perform the functions of that layer.

[0077] FIG. 4 illustrates a scenario for inter-cell beam management according to embodiments of the present disclosure, in which a terminal transmits and receives data through the beam of a TRP (transmission and reception point) of a neighboring cell that supports L1 / L2-based beam switching while maintaining a connection state with a serving cell.

[0078] FIG. 4 describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2) (410, 415) exist within a single DU (Distributed unit, 405), but the general content of the present invention is also applicable to inter-DU cases (e.g., each DU constitutes a single TRP-Cell). Furthermore, throughout the present invention, non-serving cells (e.g., TRP 2, Cell 2) that support L1 / L2-based mobility (e.g., beam change and serving cell change) are referred to interchangeably as neighbor cells, non-serving cells, and additional cells with a physical cell identity (PCI) different from the serving cell.

[0079] In the existing terminal beam change procedure (445), the terminal (420) can transmit and receive data in a connected state through the TRP 1 (410) of serving cell 1 and can be aligned to the optimal beam, TCI state 1 (425, 430). At this stage, the terminal can receive instructions for setting information for L3 channel measurement (radio resource management, RRM) for an additional cell (TRP 2-Cell 2) (415) that has a different PCI from the serving cell through RRC setting information from the serving cell (410), and can perform an L3 measurement operation (446) for the corresponding frequency and cell. Subsequently, the serving cell (TRP 1-Cell 1) (410) can instruct (447) a handover to the corresponding cell (TRP 2-Cell 2) (415) based on the reported measurement value. After the handover is completed, additional RRC configuration information may be transmitted (448) to the terminal (420) via TRP 2-Cell 2 (415). The RRC configuration information may include UL / DL configuration information in the cell, L1 measurement related settings (e.g., CSI-RS measurement and reporting), and in particular, TCI state configuration information for PDCCH and PDSCH channels. The terminal performs L1 measurement according to the configuration (449), and the base station may update the TCI state through L1 / L2 signaling according to the measurement report (450). Here, the optimal beam, TCI state 2 (440), may be indicated. At this stage, the serving cell is Cell 1 until the handover, and Cell 2 may become the serving cell after the handover. That is, even after the handover, many procedures and time may be required until the optimal beam is indicated.

[0080] Unlike the existing terminal beam change procedure (445), the improved beam change technique (455) considered in the present invention is as follows. The terminal can transmit a beam setting associated with an additional cell (TRP 2-Cell 2) (415) with a different PCI from the serving cell by referencing the serving cell through RRC setting information (456) from the serving cell (410). A method of indicating a beam setting associated with an additional cell (TRP 2-Cell 2) (415) with a different PCI from the serving cell (e.g., the part that associates the TCI state corresponding to TRP2) by associating a new cell ID (Physical cell ID, PCI; additionalPCI-r17) as follows may be applied.

[0081]

[0082] In addition, a unified TCI state framework may be applied for beam management between the cells. The unified TCI state framework applies a common TCI state framework to the uplink and downlink, and to the common channel and dedicated channel, and can be configured as either Joint UL / DL mode or separate UL / DL mode.

[0083]

[0084] 1. Joint UL / DL Mode: UL and DL can be configured to share the same TCI settings (in PDSCH-Config)

[0085]

[0086] 2. Separate UL / DL mode: Separate TCI settings may be provided for the UL and DL. The TCI state for the DL follows the settings in dl-OrJoint-TCIStateList-r17 (in PDSCH-Config), and the TCI state for the UL may follow ul-TCI-StateList-r17 (in BWP-UplinkDedicated).

[0087]

[0088] In the RRC connection state for serving cell 1, after the configuration for TRP 2-Cell 2 is provided, the terminal performs an L1 measurement for the TRP 2-Cell 2 according to the configuration and reports the result to the serving cell (Cell 1) (410) (457). If the serving cell determines that a change is necessary from the serving cell beam (TCI state 1) (425, 430) to a specific beam (TCI state 2) (435, 440) of TRP 2 (Cell 2) (415) based on the measurement result, it triggers a beam change and instructs the terminal via L1 / L2 signaling (458). Through the instruction, the terminal changes the beam to the specific beam (TCI state 2) (440) of TRP 2 (Cell 2) (415) and performs physical channel configuration and upper layer configuration operations associated with the configured beam. From this stage, the terminal remains connected to the serving cell (Cell 1) (410), but performs data transmission and reception using the channel link of TRP 2 (Cell 2) (415) (e.g., receiving PDCCH / PDSCH, transmitting PUCCH / PUSCH). That is, transmission and reception for the common control channel is performed through the serving cell (Cell 1) (410). Subsequently, the terminal performs L3 measurement operations according to the measurement settings set in the independent serving cell (459), and can change the serving cell to Cell 2 by receiving a handover command message from the serving base station (Cell 1) (460). Through this technique (455), the terminal performs data transmission and reception with a specific TRP 2 of Cell 2 that supports L1 / L2-based mobility while connected to the serving cell, and can continue to use the beam even after the handover.

[0089] For reference, the RRC settings regarding the settings and operations related to L1 measurement and report in step 457 are described as follows. This content is basically applied to the following embodiments of the present invention, and enhancement techniques may be added in future embodiments.

[0090] 1. L1 measurement settings (CSI-ResourceConfig) (Set within the serving cell; Set within ServingCellConfig IE)

[0091] - CSI-RS / SSB resources and resource pools requiring measurement (nzp-CSI-RS, csi-IM, csi-SSB)

[0092] - Configuration of CSI-RS / SSB resources requiring measurement (aperiodic, semi-persistent) and triggering settings

[0093] - When a CSI-RS resource references an SSB resource, additional PCI information is provided to enable L1 measurement from neighboring cells (up to 7 neighboring cells (PCI) can be added from a single serving cell).

[0094]

[0095] 2. L1 report settings (configured within the serving cell, ServingCellConfig, configured within IE)

[0096] - Report Type: Periodic Report, Semi-periodic Report with PUCCH, Semi-periodic Report with PUSCH, Aperiodic Report with PUSCH

[0097] - Report quantity

[0098] - Other settings required for reporting

[0099] FIG. 5 illustrates a scenario in which a terminal changes the serving cell and beam to the TRP of a cell that supports L1 / L2-based beam changing according to embodiments of the present disclosure to transmit and receive data.

[0100] FIG. 5 describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2) (510, 515, 540, 545) exist within a single DU (Distributed Unit) (505, 535), but the overall content of the present invention is also applicable to inter-DU within an intra-CU (e.g., each DU constitutes a single TRP-Cell).

[0101] Unlike the conventional terminal beam changing procedure (445, 455) described in FIG. 4, the improved beam changing technique (525, 575) considered in these embodiments is as follows.

[0102] 1. Operation 1 (525): After performing the inter-cell beam management (change) operation, perform L1 / L2 handover.

[0103] 2. Action 2(575): Perform L1 / L2 handover immediately

[0104] First, to describe the overall operation of operation 1, the terminal can receive common configuration and dedicated configuration information for an additional cell (TRP 2-Cell 2) (515) that has a different PCI from the serving cell (510) through RRC configuration information (526). That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon, and ServingCellConfig may be provided in advance. The configuration information may be provided in the form of pre-configuration in the RRC configuration and may include configuration information for multiple cells. In addition, the configuration may include all configuration information (e.g., cell configuration, bearer configuration, security key configuration, etc.) that is applied when the terminal moves to the cell (e.g., handover). The configuration may include enhanced configurations by referring to the unified TCI state configuration and L1 measurement and report related configurations described in step 456. More specifically, for continuous LTM, an enhanced unified TCI state setting and L1 measurement and report settings are included, which are described in detail in the drawings below of the present invention.

[0105] In the RRC connection state for serving cell 1, after the configuration for TRP 2-Cell 2 (515) is provided, the terminal performs an L1 measurement for the TRP 2-Cell 2 (515) according to the configuration received in step 527 and reports the result to the serving cell (Cell 1) (510). If the serving cell determines that a change to a specific beam (TCI state 2) (540) of TRP 2 (Cell 2) (515) is necessary from the serving cell beam (TCI state 1) (525) based on the measurement result, it triggers a beam change in step 528 and instructs the terminal via L1 / L2 signaling. The terminal performs a beam change to TRP 2 (Cell 2) (515) via the instruction and transmits and receives data through the TRP 2 (Cell 2) (515). At this time, no change in serving cell occurs, and the terminal may still be connected to the serving cell (Cell 1) (510) via RRC. Subsequently, the terminal may still perform an L1 measurement for TRP 2-Cell 2 (515) and report the result to the serving cell (Cell 1) (510). If the L1 measurement reported by the terminal satisfies the triggering condition for a handover to TRP 2-Cell 2 (515) (detailed operation described below), the serving cell (Cell 1) (510) instructs the terminal to perform a handover. This instruction may be an L1 / L2 message. That is, the MAC CE may contain an indicator instructing the handover.

[0106] To describe the overall operation of Operation 2, the terminal can receive common and dedicated configuration information for an additional cell (TRP 2-Cell 2) (545) with a different PCI from the serving cell (540) through RRC configuration information from the serving cell (540) (576). That is, the ServingCellID or candidateCellID (cell ID associated with PCI) and configuration information corresponding to the candidate LTM cell may be provided in advance. The configuration information may be provided in the form of pre-configuration in the RRC configuration and may include configuration information for multiple cells. In addition, the configuration may include all configuration information (e.g., cell configuration, bearer configuration, channel measurement configuration, etc.) that is applied when the terminal moves to the corresponding cell (e.g., handover). In the configuration, the unified TCI state configuration and settings related to L1 measurement and report described in step 456 may be modified and included to support consecutive LTMs. The L1 measurement and report and TCI state configurations applied in the present invention are described in detail below.

[0107] In the RRC connection state for serving cell 1, after the configuration for TRP 2-Cell 2 (545) is provided, the terminal performs an L1 measurement for the TRP 2-Cell 2 (545) according to the configuration received in step 577 and reports the result to the serving cell (Cell 1) (540). If the serving cell determines that a handover is required to change the beam from the serving cell beam (TCI state 1) (545) to a specific beam (TCI state 2) (570) of TRP 2 (Cell 2) (545) and simultaneously change the beam (TCI state 2) (570) based on the measurement result, it triggers the beam change and handover in step 578 and instructs the terminal via L1 / L2 signaling. Through the instruction, the terminal performs a handover to the TRP 2 (Cell 2) (515) and simultaneously changes the beam (TRP 2) (515) and transmits and receives data through the TRP 2 (Cell 2) (515). At this time, the terminal may apply the configuration information for the target cell where the handover is to be performed, which was pre-configured in step 576. Depending on whether uplink synchronization is required in that step, the terminal may perform random access, or random access to the target cell may be omitted. Detailed operation is described in the drawings below.

[0108] In particular, as described above, a detailed method for setting the unified TCI state and L1 measurement and report for candidate cells surrounding an LTM to support the continuous LTM proposed in the present invention is described. As explained in Figure 4, in conventional inter-cell beam management (ICBM), L1 measurement resource settings for cells requiring measurement can be provided in the CSI-ResourceConfig of the ServingCellConfig IE within the serving cell settings. In particular, to indicate resources for surrounding cells, the PCI of the cell where the corresponding L1 measurement resource is set can be indicated in the servingAdditionalPCIList.

[0109] Detailed settings for L1 measurement and reporting settings for LTM can be provided through L1 measurement resource settings applied to LTM candidate cells as follows. To this end, during the preprocessing stage, it is necessary to share and determine the L1 measurement resources and reporting settings for LTM among the LTM candidate cells. The entire procedure is described together in the following examples. The following examples are described by referring to the relevant settings.

[0110] 1. L1 measurement resource configuration (configured within LTM-CSI-ResourceConfig and LTM-Config)

[0111] - CSI Resource configuration index exists to specify CSI resource settings (LTM-CSI-ResourceConfigId-r18)

[0112] - CSI resource set containing CSI-RS or SSB resources requiring measurement

[0113] - A single CSI resource set can be multiple SSB resources or CSI-RS resources existing within an LTM candidate cell.

[0114] 2. L1 report settings (configured within LTM-Config)

[0115] - CSI Report configuration index exists to specify CSI reporting settings (LTM-CSI-ReportConfig-r18)

[0116] - Report Type: Periodic Report, Semi-periodic Report with PUCCH, Semi-periodic Report with PUSCH, Aperiodic Report with PUSCH

[0117] - Report Content (Number of cells to report, number of resources to report, etc.)

[0118] In particular, the present invention describes in detail the fast recovery operation for an LTM candidate cell performed by a terminal according to the attemptLTM-Switch-r18 field configured within the LTM-Config below. attemptLTM-Switch-r18 is an indicator configured by the base station that instructs the terminal to perform fast recovery on a cell if the cell selected by the terminal during the RRC connection re-establishment procedure is an LTM candidate cell. The detailed operation is explained again in Fig. 6 below.

[0119]

[0120]

[0121]

[0122]

[0123]

[0124]

[0125] FIG. 6 illustrates the flow of signals for a terminal that has received an LTM setting in an intra-CU to perform a recovery procedure after a wireless link failure, according to various embodiments of the present disclosure.

[0126] In particular, in an intra-CU, a single base station CU (603) manages multiple DUs, and the RRC security between the DUs follows the security generated by the CU. That is, even if a cell change occurs between DUs / cells within the CU, no security key update is required, so additional consideration of security may be unnecessary. In particular, the present invention describes details regarding how the rapid recovery operation varies depending on the influence of security when a terminal selects a new cell after a wireless link failure and performs rapid recovery to that cell.

[0127] In step 610, the terminal (601) in the RRC connection state performs data transmission and reception with source cell 1 (602), and can transmit layer 3 measurement values ​​for the serving cell and surrounding cells to source cell 1 (602) according to the configured layer 3 measurement and report. At this time, the actual measurement values ​​can be transmitted to the base station CU (603). This is because the base station CU (603) is responsible for processing RRC messages and determining mobility.

[0128] In step 615, the base station CU (603) may generate and transmit a message (e.g., UE Context Setup Request or UE Context Modification Request) requesting configuration information for L1 / L2-based handover to LTM candidate surrounding cells (604, 605) based on the measurement report received from the terminal, through the F1 interface. Referring to FIG. 6, the candidate cell is indicated in association with the DU, but in reality, the candidate cell and the DU may be mapped 1:1, or multiple candidate cells may be included in a single DU. The message requesting configuration information for L1 / L2-based handover may request the surrounding cells to be determined as L1 / L2-based handover candidate cells, and at the same time, request RRC configuration information that is applied when an L1 / L2-based handover is performed to the cell. At this time, the source base station CU (603) may transmit the configuration information of the source cell and separate reference cell configuration information. Although omitted in FIG. 6, if the source base station CU (603) fails to generate a reference cell configuration from the surrounding LTM candidate cells (604, 605) at that stage, it may request an IE requesting a reference cell configuration. That is, two methods can be used for the setting of the IE below (e.g., using the CHOICE structure).

[0129] 1. Request for reference cell setting (request for lower layer setting of LTM candidate cells): That is, it can be used as a preprocessing procedure for LTM coordination.

[0130]

[0131] 2. Provide reference cell settings (provide reference cell settings to LTM candidate cells (in the form of CellGroupConfig): can be used when requesting LTM settings.

[0132] In response to this, the source base station CU (603) can receive a lower layer setting that can be a reference cell setting from the LTM candidate surrounding cells (604, 605).

[0133]

[0134] According to one embodiment, step 625 (e.g., UE Context Setup / Modification Response message) may be used as a preprocessing procedure for LTM coordination, in which case the message transmitted from the LTM candidate cells (604, 605) of step 625 to the source base station CU (603) as described above may include lower layer setting information of each LTM cell.

[0135] According to one embodiment, when step 625 (e.g., UE Context Setup / Modification Response message) is used as an LTM setup request, the terminal can generate a candidate cell configuration applied to each LTM candidate cell in step 620 based on the received reference cell configuration, and check whether the candidate cell configuration is complete (e.g., LTM Complete Configuration Indicator) and transmit it as a response message. Here, whether the candidate cell configuration is complete may mean whether the configuration information of the LTM candidate cell is generated based on the configuration information after receiving the reference cell configuration from the source base station CU (603). For example, if it is generated according to a delta configuration based on the reference cell configuration, the configuration of the cell may be said not to be complete. The terminal can check the LTM Complete Configuration Indicator as complete and transmit it only when the LTM candidate cell configuration information provided by the cell is generated completely, regardless of the reference cell configuration.

[0136] According to one embodiment, the reference cell configuration information transmitted by the source base station CU (603) to each candidate cell (604, 605) may include common configuration information that can be applied to multiple target candidate cells in order to reduce signaling overhead when target candidate cells provide configuration information for LTM, and this may include measurement configuration, bearer configuration, or, if the cells belong to the same CellGroup, configurations set at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.). Alternatively, if the source base station CU (603) has a procedure to roughly know or know the configuration information for each candidate cell (604, 605), the reference cell configuration may be determined through a separate procedure to identify the reference cell configuration information based thereon.

[0137] According to various embodiments, the purpose of the source base station CU (603) transmitting the reference cell settings to each candidate cell (604, 605) is to allow each candidate cell to transmit only the additional setting information based on the reference cell settings to the source base station CU (603) so that a delta configuration (e.g., a method of configuring a perfect setting by applying a setting added on top of the reference cell settings, or a method of configuring a perfect setting by applying a setting over the reference cell settings in the target cell) can be applied. This is subsequently transmitted to the terminal as is, thereby having the effect of reducing the signaling of RRC messages transmitted to the terminal.

[0138] According to the method described above, candidate surrounding cells (604, 605) that receive a message requesting configuration information for L1 / L2-based handover in step 620 generate configuration information for each candidate surrounding cell when L1 / L2-based handover is applied, either based on delta configuration or without applying it, based on the configuration information of the transmitted reference cell.

[0139] Subsequently, in step 625, each candidate surrounding cell (604, 605) can store the generated configuration information for L1 / L2-based handover in an L1 / L2-based handover configuration information response message (e.g., UE Context Setup Response or UE Context Modification Response) and transmit it to the base station CU (603).

[0140] In step 630, the source cell (602) can receive an RRC message generated by the base station CU (603) based on configuration information received from each candidate cell, and can transmit it to the terminal. The RRC message is a message containing configuration information for surrounding candidate cells to which L1 / L2-based handover (LTM) is applied. For example, the RRC message is a message containing CellGroupConfig settings received from LTM candidate cells, bearer settings for LTM candidate cells generated by the base station, or Layer 3 (Layer 3, L3) measurement settings.

[0141] In step 635, the terminal that receives the RRC message may perform a procedure to decode and process the RRC message. The processing procedure may include ASN.1 decoding of the received message, validation, and a method for storing and managing the configuration content. Additionally, the terminal may store the LTM configuration information for each candidate cell decoded in that step as complete configuration information in the terminal's buffer (memory), and simultaneously store and manage the received reference cell configuration information in the terminal's buffer (memory) as well. According to one embodiment, the RRC message (or configuration information for each LTM candidate cell) in step 630 may provide an indicator indicating whether the reference cell configuration information and the configuration information for each candidate cell are complete.

[0142] In step 640, the terminal can perform L1 (layer 1) measurements and reports for each candidate surrounding cell, and simultaneously, in step 645, can also perform L3 measurements and reports according to the settings received from the base station. The source cell that receives the L1 measurement report can make a handover decision based on the measurement value and instruct the terminal to perform an L1 / L2 handover. For the L1 / L2 signaling in the above steps, a MAC CE instructing a handover may be used.

[0143] In various embodiments of the present disclosure, a case in which a radio link failure (RLF) occurs before the above-described LTM cell change instruction or during the LTM cell change operation is described (650).

[0144] In step 650, if the terminal receives a notification of a wireless link failure from a lower layer, the terminal detects the wireless link failure. The reasons for this may include the following causes.

[0145] - When an out-of-sync indicator (N311) at the physical layer is received more than a specified number of times, and the period has elapsed longer than a specified time (T310)

[0146] - If beam failure recovery fails

[0147] - If a problem occurs with random access

[0148] - If more than a specified number of RLC transmissions fail

[0149] For the reasons mentioned above, the terminal can detect a radio link failure (RLF) and enter into an RRC connection re-establishment procedure in step 655.

[0150] For example, the terminal can start the T311 timer (660) and, while the timer is running, can find a suitable cell and perform an action to re-establish the connection.

[0151] In step 665, the terminal may perform a cell selection procedure, which may mean an action to find a suitable cell among the received signals of surrounding cells that the terminal receives. The cell selected in the cell selection procedure may be an LTM candidate cell that was set in the previous source cell or the previous source cell, or it may be a cell other than an LTM candidate cell.

[0152] In Fig. 6, we consider a case where the base station provides LTM configuration and LTM candidate cell configuration, and attemptsLTM-Switch-r18 is configured within LTM-Config to instruct fast recovery operations for LTM candidate cells.

[0153] - Case 1: When the source cell is selected

[0154] The terminal can apply the settings of the corresponding source cell and establish a connection. The terminal can fall back to the source cell.

[0155] - Case 2: When an LTM candidate cell is selected

[0156] * In step 670, the terminal can apply the settings of the LTM candidate cell.

[0157] - Case 3: When a cell that is neither a source cell nor an LTM candidate cell is selected

[0158] The terminal can send an RRCReestablishmentRequest message to the cell in accordance with the RRC reestablishment procedure, receive an RRCReestablishment message in response, send an RRCReestablishmentComplete message, and re-establish the connection.

[0159] In step 675, the terminal may perform a random access procedure to establish a connection to the corresponding LTM candidate cell. If a RACH-less setting and a TA (timing advance) value for the cell already exist, the random access procedure may be omitted.

[0160] In step 680, the terminal may transmit a handover completion message to the target cell, which may include a message (RRCReconfigurationComplete) indicating LTM cell switch complete.

[0161] In step 685, the target cell (DU) (604) that receives this can transmit the received message to the base station CU (603). At this time, the target cell (604) may transmit the handover completion message received through the F1 interface as is, or may generate and transmit a new message based on the received information.

[0162] In step 690, the base station CU (603) can instruct the source cell (602) to transmit information about the completion of the handover and to release the terminal context.

[0163] Various embodiments of the present invention support subsequent LTM operations. To this end, the terminal can store the LTM configuration information received in step 630 (e.g., configuration information for target candidate cells and reference cell configuration information, etc.) as is, so that the terminal can continue to perform the LTM procedure unless the LTM configuration information is changed, disabled, or added through a separate RRC configuration. If it is necessary to update the reference cell configuration information, the update can be performed by delivering new RRC configuration information to the terminal. That is, the procedures described in FIG. 6 can be triggered and executed again.

[0164] FIG. 7 illustrates the flow of signals for a terminal that has experienced a wireless link failure to select an LTM candidate cell in a different CU and perform fast recovery, according to various embodiments of the present disclosure.

[0165] Referring to FIG. 7, particularly in the inter-CU, multiple base station CUs (703, 706) each manage multiple DUs, and the RRC security between cells where the corresponding CUs differ needs to be updated when changing cells. For example, since a security key update is required even when a cell change occurs between DUs / cells of each CU, additional consideration regarding security may be required. In particular, the present invention explains details regarding how the rapid recovery operation varies depending on the influence of security when a terminal selects a new cell after a wireless link failure and performs rapid recovery on that cell.

[0166] In step 710, the terminal (701) in the RRC connection state performs data transmission and reception with source cell 1 (702), and can transmit Layer 3 measurement values ​​for the serving cell and surrounding cells to the source base station (703) according to the configured Layer 3 measurement and reporting. At this time, the actual measurement values ​​can be transmitted to the base station CU (703). This is because the base station CU (703) is responsible for processing RRC messages and determining mobility.

[0167] In step 715, the base station CU (703) can generate a message (e.g., UE Context Setup Request or UE Context Modification Request) requesting configuration information for L1 / L2-based handover to intra-CU LTM candidate surrounding cells (704, 705) based on the measurement report received from the terminal, and transmit it through the F1 interface.

[0168] The information that may be included in the message is summarized as follows. The following message content may also be used as the composition of the message in steps 715 and 735.

[0169] - LTM candidate ID

[0170] - Mapping information between the LTM candidate ID and the corresponding cell ID

[0171] - Beam information (TCI state) to be used by each candidate

[0172] In this case, the meaning of 'use' or 'beam to be used' may include the meaning of a beam linked to a RACH occasion when performing DL and / or UL synchronization, and / or a beam to be used for first UL data transmission. If necessary, a cell switch may be performed accompanied by an indicator for each case.

[0173] - RACH preamble index

[0174] - SSB index: An index of the SSB used to determine the RACH occasion in each candidate cell, which can represent the occasion of the RACH preamble of CFRA.

[0175] The above information may include information that needs to be displayed when issuing a cell switch command MAC CE instruction to a candidate cell that has made an LTM decision.

[0176] - Reference cell setting information (e.g., may include one of the following two contents as a CHOICE structure) (e.g., refer to Fig. 6)

[0177] * Request to set reference cell

[0178] * Provides reference cell settings

[0179] - CSI resource request information for each candidate cell

[0180] It may be requested during the pre-configuration preprocessing section for LTM candidate cells.

[0181] ** Indicator for whether it is a request for initial preparation (e.g., initiation) or for a modification request after the initial one

[0182] In particular, when the relevant request information is included, lower layer setting information of this message, etc., may not be transmitted.

[0183] If CSI resource information is transmitted from candidate cells via the relevant request information, the CSI resource settings of each of the following candidate cells may be transmitted instead of the resource request. For example, a CSI resource setting preprocessing procedure of at least 2 steps is required.

[0184] - CSI report configuration considering the CSI resources of each candidate cell

[0185] If a candidate DU creates and transmits the information to a CU, this information may be used as the CSI report configuration within the target cell configuration (RRCReconfiguration) of the concerned cell (e.g., target cell) created by the CU. Alternatively, the information may not be transmitted separately but may be included within the target cell configuration (RRCReconfiguration).

[0186] For example, when a terminal moves from another cell to the concerned cell, the information can be used as a CSI report configuration with the concerned cell as the serving cell. More specifically, it can be used to include it in the target cell configuration without exchanging a separate L1 configuration for Subsequent LTM.

[0187] - RACH configuration and lower layer setting information to be used in the concerned cell

[0188] The information can be transmitted from the candidate DU to the CU, generated for the settings required for performing RACH within the target cell configuration of the concerned cell, the lower layer settings to be applied when moving to the cell, and / or reference settings including them, and can be transmitted to the terminal.

[0189] In particular, some of the RACH settings may be used to include Rach preamble index, Mask, and occasion determination information in the cell switch command MAC CE described above.

[0190] According to various embodiments, for the application and configuration requests for LTM candidate cells, a step of generating LTM pre-configuration by exchanging messages between the base station CU and the LTM candidate cells via the F1 interface may be required. Referring to FIG. 7, although this is indicated as a single procedure as in step 715, it is understood that this step can be applied to multiple procedures (procedures 715 and 735). The multiple procedures that can be performed for L1 measurement resource and reporting configuration are as follows. For example, procedures 715 and 735 can be described as follows.

[0191] Step 1: LTM candidate cells may be requested to set up L1 measurement resources and reference cells.

[0192] Step 2: LTM candidate cells can transmit a response containing lower layer setting information for setting the L1 measurement resource and reference cell of the cell to the source base station CU (703). In connection with this procedure, the UE Context Setup Response message can be transmitted to the source base station through the F1 interface.

[0193] Step 3: The source base station CU (703) can transmit L1 measurement resource settings and reference cell settings for continuous LTM support to each candidate cell based on the settings for each collected candidate cell. In connection with this procedure, a UE Context Modification Request message can be transmitted through the F1 interface.

[0194] Step 4: The source base station CU (703) can finally set up L1 measurement reports for LTM candidate cells and exchange configuration information (CellGroupConfig) applied to the LTM candidate cells. In connection with this procedure, a UE Context Modification Response message can be transmitted through the F1 interface.

[0195] Step 5: LTM-related settings can be transmitted to the terminal. The source base station can aggregate all LTM-related settings received from LTM candidate cells and store them in an RRCReconfiguration message, and transmit the corresponding RRC setting information to the terminal. For example, pre-configuration information for LTM candidate cells can be transmitted to the terminal.

[0196] According to various embodiments, the source base station CU (703) may transmit the source cell configuration information and separate reference cell configuration information together. The reference cell configuration information transmitted by the source base station CU (703) to each candidate cell (704, 705) may include common configuration information that can be applied to multiple target candidate cells in order to reduce signaling overhead when target candidate cells provide configuration information for LTM. This may include measurement configuration, bearer configuration, or configurations set at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.) in the case of cells belonging to the same CellGroup. Alternatively, if the source base station CU (703) has a procedure to roughly know or know the configuration information for each candidate cell (704, 705), the reference cell configuration may be determined through a separate procedure to obtain the reference cell configuration information.

[0197] According to various embodiments, the purpose of the source base station CU (703) transmitting a reference cell setting to each candidate cell (704, 705) is to allow each candidate cell to transmit only the additional setting information based on the reference cell setting to the source base station CU (703) so that a delta configuration (e.g., a method of configuring a complete setting by applying a setting added on top of the reference cell setting, or a method of configuring a complete setting by applying a setting over the reference cell setting in the target cell) can be applied. This is subsequently transmitted to the terminal as is, thereby having the effect of reducing the signaling of RRC messages transmitted to the terminal. Additionally, when the source base station CU (703) transmits the reference cell setting to each candidate cell (704, 705), the above procedure may be omitted, and in this case, a complete RRC setting may be provided for the candidate cell setting.

[0198] Additionally, in step 720, the base station CU (703) may generate a message (e.g., Handover Request or new message) requesting configuration information for an L1 / L2-based handover to the target base station (CU2) (706) for an LTM candidate cell configuration request for an LTM surrounding cell (707) of the inter-CU based on a measurement report received from the terminal, and may transmit this through the X2 interface.

[0199] Subsequently, in step 725, the target base station (CU2) (706) may generate and transmit a message requesting configuration information for L1 / L2-based handover (e.g., UE Context Setup Request or UE Context Modification Request) for an LTM candidate cell (707) belonging to the CU through the F1 interface, and may receive a response message requesting configuration information for L1 / L2-based handover (e.g., UE Context Setup Response or UE Context Modification Response). This procedure may refer to the LTM configuration preprocessing procedure of step 715.

[0200] Subsequently, in step 730, the target base station (CU2) (706) can generate a message (e.g., Handover Response or new response message) containing LTM candidate configuration information transmitted by the LTM candidate cell (707) belonging to the CU, and transmit it to the source base station (CU) (703) via the X2 interface.

[0201] The following is a summary of the contents that may be newly added to the LTM configuration request message through the X2 interface of step 720 according to various embodiments.

[0202] - Indicator for LTM execution

[0203] Additionally, an indicator of whether the request is for initial preparation (e.g., initiation) or for modification after the initial request.

[0204] - Device ID

[0205] - Source CU and / or Source DU ID, and / or Source DU's TNL address (e.g., IP (Internet Protocol) address)

[0206] - ID of the requested candidate cell (e.g., PCI or NR CGI with NR ARFCN)

[0207] - LTM configuration ID of this candidate cell (if accepted, the source DU can use the LTM config ID when cell switching to the target cell)

[0208] - LTM configuration ID mapping list (information to inform the candidate DU of the mapping relationships between the candidate DU's currently available LTM configurations and its cells when delivered to the candidate DU)

[0209] * Opt 1. The aforementioned list of candidate cells may be a list of candidate cells operated by all candidate CUs for the terminal concerned; or

[0210] * Opt 2. It may be a list containing only candidate cells operated by the source CU that transmits the HO request message.

[0211] - Request information for CSI resource configuration for LTM L1 measurement

[0212] - An indicator requesting PRACH resource information for target candidate cells

[0213] - An indicator requesting a lower layer setting for target candidate cells

[0214] - Request reference cell settings or provide reference cell settings

[0215] - Encryption key settings applied to LTM candidate cells (NCC value: NextHopChainingCount): Parameter used to update the master key, the KgNB key.

[0216] In addition to the information described above, the content that can be newly added to the LTM configuration request message may include information previously used in HO request messages. The table below may be referenced regarding this.

[0217]

[0218]

[0219] In addition, the LTM setting response message through the X2 interface of step 730 may additionally include LTM-related setting information of the LTM target cell within the corresponding CU.

[0220] - Set up CSI resources in response to requested CSI resources

[0221] - CSI reporting configuration information

[0222] If the CSI resource request is omitted and the configuration information of the CSI resources being transmitted by all currently configured candidate cells is delivered, the CSI reporting settings with those settings applied can be delivered as is.

[0223] - RACH configuration and lower layer setting information to be used in the concerned cell

[0224] The information described above can be transmitted from the LTM candidate DU within the CU to the CU, and can be generated as a setting required to perform RACH within the target cell configuration of the concerned cell, a lower layer setting to be applied when moving to the cell, and / or a reference setting including these, and can be transmitted to the terminal.

[0225] In particular, some of the RACH settings can be used to include the Rach preamble index, Mask, and occasion determination information in the cell switch command MAC CE described above.

[0226] Beam information (TCI state) to be used by each candidate

[0227] ** In this case, the meaning of 'use' or 'beam to be used' may include the meaning of a beam linked to a RACH occasion when performing DL and / or UL synchronization, and / or a beam to be used for first UL data transmission. If necessary, a cell switch may be performed accompanied by an indicator for each case.

[0228] In addition, the configuration information transmitted by the DU is configuration information applied after the handover is completed, and can be composed of complete configuration information.

[0229] - An indicator that indicates whether the reference cell setting information and candidate cell settings are complete

[0230] In step 735, the source base station (702) may trigger steps 715 and 720 again based on the information of LTM-related candidate cells received from the target base station (706). In response to this, step 730 may also be performed. The detailed procedure described above is described separately for each option.

[0231] In step 740, the source base station (702) can collect all LTM-related configurations received from LTM candidate cells and store them in an RRCReconfiguration message transmitted to the terminal, and can transmit the RRC configuration information to the terminal. For example, pre-configuration information for LTM candidate cells can be transmitted to the terminal. At this time, the source base station CU (703) can include the configuration information of the source cell and separate reference cell configuration information in the RRC configuration information and transmit them.

[0232] In particular, in step 740, various parameters associated with the fast recovery operation of the present invention are described in relation to the inter-CU LTM configuration. According to various embodiments of the present disclosure, the next hop chaining count (NCC) value, which is a parameter used to update the KgNB key—a master key applied when changing cells to a candidate cell of the inter-CU LTM—needs to be transmitted to the terminal. Only when the NCC value is transmitted can the terminal receive the RRC configuration for the corresponding LTM candidate cell and pass through security procedures (e.g., integrity, encryption). In the case of a conventional handover, the NCC value may be transmitted via an RRC message instructing the handover, and the terminal establishes AS security using the value after moving to the target cell. In the case of the Inter-CU LTM, the following methods for transmitting the NCC value are possible.

[0233] 1. First NCC transmission method: Transmits the NCC value applied to the target LTM cell via an RRC message.

[0234] A. Delivered before LTM cell change is performed

[0235] B. Delivered via the target cell's RRC message after the LTM cell change is instructed

[0236] 2. Second NCC Delivery Method: Delivery of the NCC value applied to the target LTM cell within the LTM cell change MAC CE

[0237] Regarding the above-described method, while one method may be selected and applied in the Inter-CU LTM, both methods may be supported depending on the network implementation, and the method of transmitting the NCC value may vary depending on the base station's selection. In this case, the base station may include an indicator within the RRC message indicating how the NCC value applied to the inter-CU LTM candidate cell is transmitted. For example, an indicator using 1 bit to distinguish between the RRC method and the MAC CE method may be included. That is, according to such an indicator, if the NCC is included in the RRC message, it means the RRC method, and if it is not included, it means it is transmitted via MAC CE. Alternatively, signaling may be added to distinguish cases where the NCC value is transmitted first or later through the RRC message.

[0238] In addition, corresponding to attemptLTM-Switch-r18, which indicates whether LTM fast recovery in the intra-CU described in Fig. 6 is supported, a new parameter (e.g., attemptLTM-Switch-InterCU-r19) indicating whether LTM fast recovery in the inter-CU is supported may be introduced. Additionally, depending on the NCC delivery method, an identifier to distinguish Inter-CU LTM candidate cells may be included. This can be logically mapped to a CU identifier (Rel-19 CU ID), and a different identifier may be assigned for distinction even within the same CU. Each LTM candidate cell may be configured to include a single Rel-19 CU ID.

[0239] In step 740, the source cell (702) can receive and transmit to the terminal an RRC message generated by the base station CU (703) based on configuration information received from each candidate cell. The RRC message may include configuration information for surrounding candidate cells to which L1 / L2-based handover (LTM) is applied. For example, the RRC message may include CellGroupConfig settings received from LTM candidate cells, bearer settings for LTM candidate cells generated by the base station, or Layer 3 (Layer 3, L3) measurement settings.

[0240] In step 745, the terminal that receives the RRC message may perform a procedure to decode and process the RRC message. The processing procedure may include ASN.1 decoding of the received message, validation, and methods for storing and managing the configuration content. Additionally, the terminal may store the LTM configuration information for each candidate cell decoded in that step as complete configuration information in the terminal's buffer (memory), and simultaneously store and manage the received reference cell configuration information in the terminal's buffer (memory) as well. According to one embodiment, the RRC message (or configuration information for each LTM candidate cell) in step 740 may provide an indicator indicating whether the reference cell configuration information and the configuration information for each candidate cell are complete.

[0241] In step 750, the terminal may perform L1 (layer 1) measurements and reports for each candidate surrounding cell, and simultaneously, in step 755, may also perform L3 measurements and reports according to the settings received from the base station. The source cell that receives the L1 measurement report may make a handover decision based on the measurement value and instruct the terminal to perform an L1 / L2 handover. For the L1 / L2 signaling in the above steps, a MAC CE that instructs a handover may be used.

[0242] In various embodiments of the present disclosure, a case in which a radio link failure (RLF) occurs before the above-described LTM cell change instruction or during the LTM cell change operation is described (760).

[0243] In step 760, if the terminal receives a notification of a wireless link failure from a lower layer, the terminal detects the wireless link failure. The reasons for this may include the following causes.

[0244] - When an out-of-sync indicator (N311) at the physical layer is received more than a specified number of times, and the period has elapsed longer than a specified time (T310)

[0245] - If beam failure recovery fails

[0246] - If a problem occurs with random access

[0247] - If more than a specified number of RLC transmissions fail

[0248] For the reasons mentioned above, the terminal can detect a radio link failure (RLF) and enter into an RRC connection re-establishment procedure in step 765.

[0249] For example, the terminal can start the T311 timer (770) and, while the timer is running, can find a suitable cell and perform an action to re-establish the connection.

[0250] In step 775, the terminal may perform a cell selection procedure, which may mean an action to find a suitable cell among the received signals of surrounding cells that the terminal receives. The cell selected in the cell selection procedure may be an LTM candidate cell that was set in the previous source cell or the previous source cell, or it may be a cell other than an LTM candidate cell.

[0251] In Fig. 7, we consider a case where the base station provides LTM settings and LTM candidate cell settings, and attemptsLTM-Switch-r18 and attemptsLTM-Switch-InterCU-r19 are configured within LTM-Config to instruct fast recovery operations for LTM candidate cells.

[0252] - Case 1: When the source cell is selected

[0253] The terminal can apply the settings of the corresponding source cell and establish a connection. The terminal can fall back to the source cell.

[0254] - Case 2: When an LTM candidate cell is selected

[0255] * Selection of cell to which Fast recovery is applied: In step 780, the terminal can apply the settings of an LTM candidate cell.

[0256] * Select cell where Fast recovery is not applied: The terminal can operate as in Case 3.

[0257] - Case 3: When a cell that is neither a source cell nor an LTM candidate cell is selected

[0258] The terminal can send an RRCReestablishmentRequest message to the cell in accordance with the RRC reestablishment procedure, receive an RRCReestablishment message in response, send an RRCReestablishmentComplete message, and re-establish the connection.

[0259] In particular, as in Case 2 described above, the terminal can determine which cells are to which Fast recovery is applied and which are not to which Fast recovery is applied, and decide to operate differently. More detailed information regarding this is described through the following embodiments. To this end, reference may be made to FIGS. 8 and 9.

[0260] For example, depending on whether it is a first NCC transmission method (e.g., RRC method) or a second NCC transmission method (e.g., MAC CE), subsequent operations may differ, and in particular, in the case of a second NCC transmission method, when cell selection to a cell belonging to a different CU is performed, the terminal may define the cell as a cell to which Fast recovery is not applied and perform different operations.

[0261] In step 785, the terminal may perform a random access procedure to establish a connection to the corresponding LTM candidate cell. If a RACH-less setting and TA value, etc., for the cell already exist, the random access procedure may be omitted.

[0262] In step 790, the terminal may transmit a handover completion message to the target cell, which may include a message (RRCReconfigurationComplete) indicating LTM cell switch complete.

[0263] In step 795, the target cell (DU) (707) that receives this can forward the received message to the target base station CU (706), which can then be forwarded to the source base station CU (703). At this time, the target cell (DU) (707) may forward the handover completion message received through the Xn and F1 interfaces as is, or may create and forward a new message based on the received information.

[0264] In step 7100, the base station CU (706) can transmit information about the completion of the handover to the source cell (702) and instruct it to release the terminal context.

[0265] Various embodiments of the present invention support subsequent LTM operations. To this end, the terminal can store the LTM configuration information received in step 740 (e.g., configuration information for target candidate cells and reference cell configuration information, etc.) as is, so that the terminal can continue to perform the LTM procedure unless the LTM configuration information is changed, disabled, or added through a separate RRC configuration. If it is necessary to update the reference cell configuration information, the update can be performed by delivering new RRC configuration information to the terminal. That is, the procedures described in FIG. 7 can be triggered and executed again.

[0266] FIG. 8 illustrates the flow of terminal operations for performing fast recovery operations in LTMs within different CUs when an NCC value is transmitted through an LTM cell change MAC CE according to various embodiments of the present disclosure.

[0267] In step 805, the connected terminal may receive an RRC reset message from the serving cell containing configuration information in a neighboring cell that is applied after L1 / L2-based movement is directed. According to one embodiment, the configuration information received by the terminal may include an LTM configuration in which attemptLTM-Switch-r18, indicating whether LTM fast recovery in the intra-CU described in FIG. 7 is supported, and / or a new parameter (e.g., attemptLTM-Switch-InterCU-r19), indicating whether LTM fast recovery in the inter-CU is supported, is set. Additionally, according to one embodiment, an identifier for distinguishing Inter-CU LTM candidate cells may be included in the configuration information, depending on the NCC transmission method. This may be logically mapped to a CU identifier (Rel-19 CU ID), and a different identifier may be assigned to each LTM candidate cell to distinguish them even within the same CU. Each LTM candidate cell may be configured to include one Rel-19 CU ID. For detailed configuration methods and content, refer to FIG. 7. In addition, as a procedure for transferring the RRC setting information described above, although omitted in FIG. 8, the terminal may have received basic RRC settings from the base station and may perform an operation of reporting layer 3 measurement values ​​for surrounding cells. In particular, the terminal according to various embodiments receives settings for LTM candidate cells within the inter-CU, stores them, and applies them when an LTM cell change is instructed.

[0268] In step 810, the terminal can decode the settings for the received LTM candidate cells based on the settings of the reference cell, and store and manage the complete settings that are actually applied (e.g., the operation of saving a delta-configured setting based on the reference cell as a complete configuration by referring to the reference cell settings) in a separate buffer and list. Alternatively, the terminal may decode the received settings based on the reference cell criteria and store and manage the settings that are actually applied, but instead store and manage the received RRC settings as they are in the buffer. The advantage of decoding the settings for surrounding cells based on the reference cell criteria and storing the settings that are actually applied in this step is that when an actual L1 / L2-based handover is instructed, the handover for the corresponding cell can be applied immediately, so there is no additional delay.

[0269] In step 815, the terminal can perform an L1 measurement configured with an SSB or CSI-RS resource associated with a candidate neighbor cell while maintaining a connection with the serving cell, and can report the measurement results to the serving cell according to a pre-configured L1 measurement reporting method. In this step, the base station can control the reporting of L1 measurement resources to LTM neighbor cells requiring measurement through RRC settings and L1 / L2 signaling. The terminal can perform L1 measurement resource reporting according to the settings and instructions of the base station. Additionally, independently of this operation, the terminal can measure neighbor cells according to L3 measurement settings and report the measurement results to the base station according to L3 measurement reporting settings. The serving cell can determine whether to change the terminal's beam and hand over based on the received measurement results. If the serving cell determines that a change to a specific beam of a neighbor cell is necessary from a specific beam of the serving cell, it can instruct the terminal to hand over and change the beam through L1 / L2 signaling. FIG. 8 describes the case where the L1 / L2 signaling described above is a MAC CE. The base station may indicate all information instructing a specific beam of a surrounding cell and a serving cell change through the MAC CE (e.g., when the MAC CE indicates only one beam), or it may indicate a specific plurality of beams of an LTM target cell through the MAC CE, and then select one of the plurality of beams of the activated surrounding cell through the subsequently transmitted MAC CE to instruct a handover. According to various embodiments, with reference to FIG. 8, when a cell change to an LTM candidate cell belonging to an inter-CU is instructed by a MAC CE, a method is described in which the MAC CE is transmitted including an NCC value used for the cell change to the instructed LTM candidate cell.

[0270] In step 820, the terminal can detect RLF based on the cause of the wireless link failure. The cause of the RLF is described in detail in FIG. 7. The terminal can start the T311 timer and enter the connection re-establishment procedure.

[0271] In step 825, the terminal can perform a cell selection operation by finding a suitable cell based on the measurement results of surrounding cells while the T311 timer is operating. The measurement used for the cell selection may include an operation to find a cell with a high signal strength of surrounding cells.

[0272] In step 830, the terminal can check the type of the selected cell. The terminal can check whether there is a new parameter (e.g., attemptLTM-Switch-InterCU-r19) indicating whether LTM fast recovery in inter-CU is supported in the LTM setting of the RRC setting received in step 810. This operation can be performed in the same way if the existing attemptLTM-Switch-r18 is defined and used to apply to the case of Inter-CU as well, or if it is indicated by the new field attemptLTM-Switch-InterCU-r19. For example, the terminal can determine whether the cell is capable of fast recovery through the CU identifier (Rel-19 CU ID) to which the candidate cell belongs within the LTM candidate cell setting of the RRC setting received in step 810.

[0273] According to one embodiment, if the CU identifier (Rel-19 CU ID) of the LTM candidate cell selected by cell selection is the same as the CU identifier (Rel-19 CU ID) of the source cell (e.g., a cell within the same CU), the terminal can apply the settings for the LTM target cell stored in step 835 and perform a cell change to that cell because it has a security key for the corresponding CU. That is, the terminal can perform fast recovery to that cell. In step 840, the terminal can connect to the designated LTM target cell, transmit and receive data using the designated beam, perform channel measurement reporting according to the LTM settings, and continue to perform continuous LTM operations.

[0274] According to one embodiment, if the cell selected by the terminal in step 830 is not an LTM candidate cell, or if it is an LTM candidate cell but its CU identifier (Rel-19 CU ID) is different from the source cell's CU identifier (Rel-19 CU ID) (e.g., a cell within a different CU), the terminal may not perform a fast recovery operation for the selected cell. In step 845, the terminal may set and transmit an RRC re-establishment request message to the cell. In step 850, the terminal may perform data transmission and reception after completing the RRC re-establishment procedure (e.g., completing the reception of the RRC re-establishment message and the transmission of the RRC re-establishment complete message) and restoring the connection to the cell. In this case, the terminal may clear all LTM settings in the cell (e.g., including release, discard, etc.).

[0275] According to one embodiment, if the cell found through cell re-selection after the RRC Re-Establishment procedure is a cell other than an LTM candidate cell, or if it is an LTM candidate cell but the CU identifier (Rel-19 CU ID) of the cell is different from the CU identifier (Rel-19 CU ID) of the source cell (e.g., a cell within a different CU), the terminal may retain the LTM configuration information and reference cell configuration information that were stored in that cell as well. Alternatively, in such a case, the terminal may release the stored LTM-related configuration information and reference cell configuration information. Alternatively, the base station may explicitly specify an operation to the terminal through a setting.

[0276] FIG. 9 illustrates the flow of terminal operations for performing fast recovery operations in LTMs within different CUs when an NCC value for an LTM candidate cell is transmitted via an RRC message according to various embodiments of the present disclosure. With reference to FIG. 9, the difference from the embodiment according to the previous figure is that the NCC value for an Inter-CU LTM candidate cell is transmitted via an RRC setting rather than an LTM cell change MAC CE.

[0277] In step 905, the connected terminal may receive an RRC reset message from the serving cell containing configuration information in a neighboring cell that is applied after L1 / L2-based movement is directed. According to one embodiment, the configuration information received by the terminal may include an LTM setting in which attemptLTM-Switch-r18, indicating whether LTM fast recovery in the intra-CU described in FIG. 7 is supported, and / or a new parameter (e.g., attemptLTM-Switch-InterCU-r19), indicating whether LTM fast recovery in the inter-CU is supported, is set. Additionally, according to one embodiment, an identifier for distinguishing Inter-CU LTM candidate cells may be included in the configuration information, depending on the NCC transmission method. This may be logically mapped to a CU identifier (Rel-19 CU ID), and a different identifier may be assigned to each LTM candidate cell to distinguish them even within the same CU. Each LTM candidate cell may be configured to include one Rel-19 CU ID. For detailed configuration methods and content, refer to FIG. 7. In addition, as a procedure prior to the RRC setting information described above, although omitted in FIG. 9, the terminal may have received basic RRC settings from the base station and may perform an operation of reporting layer 3 measurement values ​​for surrounding cells. In particular, the terminal according to various embodiments receives settings for LTM candidate cells within the inter-CU, stores them, and applies them when an LTM cell change is instructed.

[0278] In step 910, the terminal can decode the settings for the received LTM candidate cells based on the settings of the reference cell, and store and manage the complete settings that are actually applied (e.g., the operation of saving a delta-configured setting based on the reference cell as a complete configuration by referring to the reference cell settings) in a separate buffer and list. Alternatively, the terminal may decode the received settings based on the reference cell criteria and store and manage the settings that are actually applied, but instead store and manage the received RRC settings as they are in the buffer. The advantage of decoding the settings for surrounding cells based on the reference cell criteria and storing the settings that are actually applied in this step is that when an actual L1 / L2-based handover is instructed, the handover for the corresponding cell can be applied immediately, so there is no additional delay.

[0279] In step 915, the terminal can perform an L1 measurement configured with an SSB or CSI-RS resource associated with a candidate neighbor cell while maintaining a connection with the serving cell, and can report the measurement results to the serving cell according to a pre-configured L1 measurement reporting method. In this step, the base station can control the reporting of L1 measurement resources to LTM neighbor cells requiring measurement through RRC settings and L1 / L2 signaling. The terminal can perform L1 measurement resource reporting according to the settings and instructions of the base station. Additionally, independently of this operation, the terminal can measure neighbor cells according to L3 measurement settings and report the measurement results to the base station according to L3 measurement reporting settings. The serving cell can determine whether to change the terminal's beam and hand over based on the received measurement results. If the serving cell determines that a change to a specific beam of a neighbor cell is necessary from the serving cell's specific beam, it can instruct the terminal to hand over and change the beam through L1 / L2 signaling. FIG. 8 describes the case where the L1 / L2 signaling described above is MAC CE. The base station may indicate all information instructing a specific beam of a surrounding cell and a serving cell change through the corresponding MAC CE (e.g., when the MAC CE indicates only one beam), or it may indicate a specific plurality of beams of an LTM target cell through the MAC CE, and then select one of the plurality of beams of the activated surrounding cell through the subsequently transmitted MAC CE to instruct a handover. According to various embodiments, with reference to FIG. 9, when a cell change to an LTM candidate cell belonging to an inter-CU is instructed by MAC CE, the NCC value used for the cell change to the LTM candidate cell is described as being transmitted in advance via a separate RRC setting rather than the MAC CE, or transmitted after the MAC CE.

[0280] In step 920, the terminal can detect RLF based on the cause of the wireless link failure. The cause of the RLF is described in detail in FIG. 7. The terminal can start the T311 timer and enter the connection re-establishment procedure.

[0281] In step 925, the terminal can perform a cell selection operation by finding a suitable cell based on the measurement results of surrounding cells while the T311 timer is operating. The measurement used for the cell selection may include an operation to find a cell with a high signal strength among surrounding cells.

[0282] In step 930, the terminal can check the type of the selected cell. The terminal can check whether there is a new parameter (e.g., attemptLTM-Switch-InterCU-r19) indicating whether LTM fast recovery in inter-CU is supported in the LTM setting of the RRC setting received in step 910. This operation can be performed in the same way if the existing attemptLTM-Switch-r18 is defined and used to apply to the case of Inter-CU as well, or if it is indicated by the new field attemptLTM-Switch-InterCU-r19. For example, the terminal can determine whether the cell is capable of fast recovery through the CU identifier (Rel-19 CU ID) to which the candidate cell belongs within the LTM candidate cell setting of the RRC setting received in step 910.

[0283] According to one embodiment, if the CU identifier (Rel-19 CU ID) of the LTM candidate cell selected by cell selection is the same as the CU identifier (Rel-19 CU ID) of the source cell (e.g., a cell within the same CU), the terminal can apply the settings for the LTM target cell stored in step 935 and perform a cell change to that cell because it has a security key for that CU. That is, the terminal can perform fast recovery to that cell. In step 940, the terminal is connected to the designated LTM target cell and can transmit and receive data using the designated beam, perform channel measurement reporting according to the LTM settings, and continue to perform continuous LTM operations.

[0284] According to one embodiment, in step 930, if the cell selected by the terminal in cell selection is not an LTM candidate cell, or if it is an LTM candidate cell but the CU identifier (Rel-19 CU ID) of the cell is different from the CU identifier (Rel-19 CU ID) of the source cell (e.g., a cell within a different CU), and if the NCC value for the cell has not been received (e.g., if the terminal has not received the NCC value for the LTM candidate cell in RRC setting), the terminal may not perform a fast recovery operation for the selected cell. In step 945, the terminal may set and transmit an RRC re-establishment request message to the cell. In step 950, after completing the RRC re-establishment procedure (e.g., completing the reception of the RRC re-establishment message and the transmission of the RRC re-establishment complete message) and restoring the connection to the cell, the terminal may perform data transmission and reception. In this case, the terminal can clear all LTM settings in the cell (e.g., release, discard, etc.).

[0285] According to one embodiment, if the cell found through cell re-selection after the RRC Re-Establishment procedure is a cell other than an LTM candidate cell, or if it is an LTM candidate cell but the CU identifier (Rel-19 CU ID) of the cell is different from the CU identifier (Rel-19 CU ID) of the source cell (e.g., a cell within a different CU), the terminal may retain the LTM configuration information and reference cell configuration information that were stored in that cell as well. Alternatively, in such a case, the terminal may release the stored LTM-related configuration information and reference cell configuration information. Alternatively, the base station may explicitly specify an operation to the terminal through a setting.

[0286] FIG. 10 illustrates the flow of base station operation according to embodiments of the present disclosure.

[0287] In step 1005, the base station receives L3 measurement reports from the terminal and, based on the terminal's measurements regarding surrounding frequencies and cells, can determine whether the terminal requires a handover and which cells are handover candidate cells.

[0288] In step 1010, the base station may request configuration information for L1 / L2-based handover from surrounding cells and receive responses from those cells. Here, LTM candidate cells may include cells within the same CU and cells within different CUs. In the preprocessing procedure for LTM candidate cell configuration, the source base station may additionally perform a procedure to request CSI resources and reference cell configuration for LTM surrounding cells, and through this procedure, it may obtain CSI resource requests and reference cell configurations for LTM surrounding cells per CU. Subsequently, the base station may transmit configuration information for the current source cell and the acquired reference cell configuration information together to the surrounding cells, and may receive RRC configuration information from the surrounding cells and LTM candidate cells, to which delta configuration based on the reference cell configuration information is applied. Additionally, in this step, inter-node coordination per CU may be performed to obtain reference cell configuration information. The procedure described in detail in Fig. 7 may be included in this step, and in particular, it may include determining the reference cell configuration and LTM candidate cell configuration within the inter-CU. Although omitted in Fig. 10, settings related to L3 measurement settings and basic RRC settings may be provided prior to that step.

[0289] In step 1015, the base station may transmit an RRC configuration message to a connected terminal, including the reference cell configuration, surrounding cell configuration information, and L1 measurement resource / reporting configuration received in step 1010. For example, the base station may transmit configuration information from surrounding cells that is applied after L1 / L2-based movement is instructed via an RRC reset message from the serving cell. Additionally, the transmitted information may include CU ID and fast recovery-related configurations in LTM. Detailed configuration methods and details are described in detail in Figure 7.

[0290] In step 1020, the base station may direct L1 measurement reports in various ways via RRC or L1 / L2 signaling, depending on the L1 measurements and reports for which configuration and triggering are desired. The base station may receive reports regarding L1 and L3 measurement values ​​from the terminal, wherein the L1 measurement value may be for a non-serving cell that supports L1 / L2-based mobility. The serving cell may determine whether to change the terminal's beam and perform a handover based on the received measurement results, and if it is determined that a change to a specific beam of a non-serving cell is necessary rather than a specific beam of the serving cell, it may direct the terminal's LTM handover via L1 / L2 signaling. The aforementioned L1 / L2 signaling may be MAC CE and may include information directing a change to a specific beam of a non-serving cell. Additionally, instructions for existing handovers via RRC messages may also be performed independently in that step. This may occur because the base station and the serving cell independently perform the determination of LTM and L3 handovers.

[0291] In step 1025, the terminal that experienced RLF may perform a fast recovery or RRC re-establishment operation for a specific cell, and the base station may complete the RRC connection re-establishment procedure in accordance with the terminal's fast recovery or RRC re-establishment procedure in step 1030. For example, the base station may perform a corresponding operation in response to the request of the terminal. More specific operations are described in detail in FIGS. 8 and 9. Subsequently, in step 1035, the base station may resume data transmission and reception for the terminal on a new cell.

[0292] FIG. 11 illustrates the structure of a terminal according to embodiments of the present disclosure.

[0293] Referring to FIG. 11, the terminal includes an RF (Radio Frequency) processing unit (1110), a baseband processing unit (1120), a storage unit (1130), and a control unit (1140).

[0294] The RF processing unit (1110) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1110) up-converts a baseband signal provided by the baseband processing unit (1120) into an RF band signal, transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1110) may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC (digital to analog converter), an ADC (analog to digital converter), etc. Although only one antenna is shown in FIG. 11, the terminal may be equipped with multiple antennas. Additionally, the RF processing unit (1110) may include multiple RF chains. Furthermore, the RF processing unit (1110) may perform beamforming. For beamforming, the RF processing unit (1110) can adjust the phase and magnitude of each of the signals transmitted and received through multiple antennas or antenna elements. Additionally, the RF processing unit (1110) can perform MIMO and can receive multiple layers when performing MIMO operation.

[0295] The baseband processing unit (1120) performs a conversion function between a baseband signal and a bit sequence according to the physical layer specifications of the system. For example, when transmitting data, the baseband processing unit (1120) generates complex symbols by encoding and modulating the transmitted bit sequence. Additionally, when receiving data, the baseband processing unit (1120) restores the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (1110). For example, in the case of following the orthogonal frequency division multiplexing (OFDM) method, when transmitting data, the baseband processing unit (1120) generates complex symbols by encoding and modulating the transmitted bit sequence, maps the complex symbols to subcarriers, and then constructs the OFDM symbols through inverse fast Fourier transform (IFFT) operations and cyclic prefix (CP) insertion. Additionally, upon receiving data, the baseband processing unit (1120) divides the baseband signal provided by the RF processing unit (1110) into OFDM symbol units, restores the signals mapped to subcarriers through a fast Fourier transform (FFT) operation, and then restores the received bit sequence through demodulation and decoding.

[0296] The baseband processing unit (1120) and the RF processing unit (1110) transmit and receive signals as described above. Accordingly, the baseband processing unit (1120) and the RF processing unit (1110) may be referred to as a transmitting unit, a receiving unit, a transmitting and receiving unit, or a communication unit. Furthermore, at least one of the baseband processing unit (1120) and the RF processing unit (1110) may include multiple communication modules to support multiple different wireless access technologies. Additionally, at least one of the baseband processing unit (1120) and the RF processing unit (1110) may include different communication modules to process signals of different frequency bands. For example, different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), cellular network (e.g., LTE), etc. In addition, different frequency bands may include super high frequency (SHF) bands (e.g., 2 NRHz, NRHz) and millimeter wave (e.g., 60 GHz) bands.

[0297] The storage unit (1130) stores data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (1130) can store information related to a second connection node that performs wireless communication using the second wireless connection technology. Additionally, the storage unit (1130) provides the stored data upon request from the control unit (1140). The storage unit (1130) may also be connected to a multiple connection processing unit (1142) within the control unit (1140) to provide multiple connections with a base station.

[0298] The control unit (1140) (or controller) controls the overall operations of the terminal. For example, the control unit (1140) transmits and receives signals through the baseband processing unit (1120) and the RF processing unit (1110). Additionally, the control unit (1140) writes and reads data to and from the storage unit (1140). To this end, the control unit (1140) may include at least one processor. For example, the control unit (1140) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as applications.

[0299] FIG. 12 illustrates the structure of a base station according to embodiments of the present disclosure.

[0300] Referring to FIG. 12, the base station is configured to include an RF processing unit (1210), a baseband processing unit (1220), a backhaul communication unit (1230), a storage unit (1240), and a control unit (1250).

[0301] The RF processing unit (1210) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1210) up-converts the baseband signal provided by the baseband processing unit (1220) into an RF band signal, transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1210) may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in FIG. 12, the first connection node may be equipped with multiple antennas. Additionally, the RF processing unit (1210) may include multiple RF chains. Furthermore, the RF processing unit (1210) may perform beamforming. For beamforming, the RF processing unit (1210) may adjust the phase and magnitude of each of the signals transmitted and received through multiple antennas or antenna elements. The RF processing unit (1210) can perform down-to-down MIMO operation by transmitting one or more layers.

[0302] The baseband processing unit (1220) performs a conversion function between a baseband signal and a bit sequence according to the physical layer specifications of the first wireless access technology. For example, when transmitting data, the baseband processing unit (1220) generates complex symbols by encoding and modulating the transmitted bit sequence. Also, when receiving data, the baseband processing unit (1220) restores the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (1210). For example, in the case of following the OFDM method, when transmitting data, the baseband processing unit (1220) generates complex symbols by encoding and modulating the transmitted bit sequence, maps the complex symbols to subcarriers, and then constructs OFDM symbols through IFFT operation and CP insertion. Additionally, upon receiving data, the baseband processing unit (1220) divides the baseband signal provided by the RF processing unit (1210) into OFDM symbol units, restores the signals mapped to subcarriers through FFT operations, and then restores the received bit sequence through demodulation and decoding. The baseband processing unit (1220) and the RF processing unit (1210) transmit and receive signals as described above. Accordingly, the baseband processing unit (1220) and the RF processing unit (1210) may be referred to as a transmitting unit, a receiving unit, a transmitting and receiving unit, a communication unit, or a wireless communication unit.

[0303] The backhaul communication unit (1230) provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit (1230) converts a bit sequence transmitted from the main base station to other nodes, such as an auxiliary base station or a core network, into a physical signal, and converts a physical signal received from other nodes into a bit sequence.

[0304] The storage unit (1240) stores data such as basic programs, application programs, and configuration information for the operation of the main station. In particular, the storage unit (1240) can store information regarding bearers assigned to connected terminals, measurement results reported from connected terminals, etc. Additionally, the storage unit (1240) can store information that serves as a criterion for determining whether to provide or discontinue multiple connections to the terminal. Furthermore, the storage unit (1240) provides the stored data upon a request from the control unit (1250). The storage unit (1240) may also be connected to the multiple connection processing unit (1252) within the control unit (1250) to provide multiple connections with the terminal.

[0305] The control unit (1250) (or controller) controls the overall operations of the main station. For example, the control unit (1250) transmits and receives signals through the baseband processing unit (1220) and the RF processing unit (1210) or through the backhaul communication unit (1230). Additionally, the control unit (1250) writes and reads data to and from the storage unit (1240). To this end, the control unit (1250) may include at least one processor.

[0306] Methods according to the claims or embodiments described in the specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0307] When implemented in software, a computer-readable storage medium may be provided for storing one or more programs (software modules). One or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. One or more programs include instructions that cause the electronic device to execute methods according to the claims or embodiments described in the specification of this disclosure.

[0308] Such programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, ROM (Read Only Memory), Electrically Erasable Programmable Read Only Memory (EEPROM), magnetic disc storage devices, Compact Disc-ROM (CD-ROM), Digital Versatile Discs (DVDs), or other forms of optical storage devices, magnetic cassettes. Alternatively, they may be stored in memory composed of some or all of these. Additionally, each constituent memory may include multiple units.

[0309] Additionally, the program may be stored on an attachable storage device accessible via a communication network such as the Internet, Intranet, Local Area Network (LAN), Wide LAN (WLAN), or Storage Area Network (SAN), or a combination thereof. Such a storage device may be connected to a device performing an embodiment of the present disclosure through an external port. Additionally, a separate storage device on a communication network may be connected to a device performing an embodiment of the present disclosure.

[0310] In the specific embodiments of the present disclosure described above, the components included in the invention are expressed in a singular or plural form according to the specific embodiments presented. However, the singular or plural expression is selected to suit the situation presented for convenience of explanation, and the present disclosure is not limited to singular or plural components; even if a component is expressed in the plural form, it may be composed of a singular form, and even if a component is expressed in the singular form, it may be composed of a plural form.

[0311] Meanwhile, the embodiments of the present disclosure disclosed in this specification and drawings are merely specific examples provided to facilitate the explanation of the technical content of the present disclosure and to aid in understanding the present disclosure, and are not intended to limit the scope of the present disclosure. That is, it is obvious to those skilled in the art that other variations based on the technical concept of the present disclosure are possible. Furthermore, each of the above embodiments may be combined and operated as needed. For example, parts of one embodiment of the present disclosure and parts of another embodiment may be combined to operate a base station and a terminal. For example, parts of the first embodiment and the second embodiment of the present disclosure may be combined to operate a base station and a terminal. In addition, although the above embodiments are presented based on an FDD LTE system, other variations based on the technical concept of the above embodiments may be implemented in other systems such as a TDD LTE system, 5G, or NR system.

[0312] Meanwhile, the order of description in the drawings illustrating the method of the present invention does not necessarily correspond to the order of execution, and the order of execution may be changed or executed in parallel.

[0313] Alternatively, drawings describing the method of the present invention may omit some components and include only some components to the extent that the essence of the present invention is not impaired.

[0314] In addition, the method of the present invention may be executed by combining some or all of the contents included in each embodiment within a scope that does not impair the essence of the invention. The memory may store programs and data necessary for the operation of the base station. In addition, the memory may store control information or data included in signals transmitted and received by the base station. The memory may be composed of a storage medium or a combination of storage media such as ROM, RAM, hard disk, CD-ROM, and DVD. In addition, there may be multiple memories.

Claims

1. A method performed by a terminal (user equipment) in a wireless communication system is, A step of receiving information for setting LTM (L1 / L2 triggered mobility) from a first CU (central unit), wherein the information for setting LTM includes information regarding an ID (identifier) ​​associated with the first CU and an LTM candidate cell; A step of performing cell selection to select a first cell by detecting a radio link failure (RLF); If the first cell is the LTM candidate cell, a step of determining whether the ID associated with the first cell is the same as the ID associated with the first CU; and A method comprising the step of performing an LTM cell switch for the first cell when the ID associated with the first cell is the same as the ID associated with the first CU.

2. In claim 1, the above method is, A method comprising the step of transmitting a radio resource control (RRC) reestablishment message if the ID associated with the first cell is not the same as the ID associated with the first CU.

3. The method of claim 1, wherein the information for setting the LTM further includes an indicator for setting the attemptLTM-Switch.

4. In Paragraph 1, Information for setting the above LTM is included in the RRC reconfiguration message, and A method in which information regarding the above LTM candidate cell includes an ID associated with the above first cell.

5. A method according to claim 1, wherein the cell selection is performed while the T311 timer is in operation.

6. In claim 1, the above method is, A method further comprising the step of storing an ID associated with the first CU, which includes information for setting the LTM.

7. In claim 1, the above method is, The method further includes the step of receiving an LTM cell switching command MAC (medium access control) CE (control element) for a second cell of a second CU different from the first CU from the first CU, and The above LTM cell switching command MAC CE is the base station key (K) for the second cell. gNB A method including an NCC (next hop chaining counter) value used to update ).

8. In a wireless communication system, the terminal (user equipment) is, At least one transceiver; At least one processor communicatively coupled to the above at least one transceiver; and It includes at least one memory that is communicationally coupled to the above at least one processor and stores instructions, and The above instructions are executed individually or in any combination by the above at least one processor, so that the terminal: Information for setting LTM (L1 / L2 triggered mobility) is received from the first CU (central unit), and the information for setting the LTM includes information regarding an ID (identifier) ​​associated with the first CU and an LTM candidate cell. By detecting RLF (radio link failure), cell selection is performed to select the first cell, and If the first cell is the LTM candidate cell, determine whether the ID associated with the first cell is the same as the ID associated with the first CU, and A terminal that performs LTM cell switching for the first cell when the ID associated with the first cell is the same as the ID associated with the first CU.

9. In claim 1, the above commands are the terminal: A terminal that transmits a radio resource control (RRC) reestablishment message if the ID associated with the 8th cell is not the same as the ID associated with the 1st CU.

10. In claim 8, the information for setting the LTM further includes an indicator for setting the attemptLTM-Switch, a terminal.

11. In Paragraph 8, Information for setting the above LTM is included in the RRC reconfiguration message, and Information regarding the above LTM candidate cell includes an ID associated with the first cell, a terminal.

12. In claim 8, the cell selection is performed while the T311 timer is in operation, in a terminal.

13. In claim 8, the above commands are the terminal: A terminal that stores an ID associated with the first CU, which includes information for setting the above LTM.

14. In claim 8, the above commands are the terminal: From the first CU, receive an LTM cell switching command MAC (medium access control) CE (control element) for a second cell of a second CU different from the first CU, and The above LTM cell switching command MAC CE is the base station key (K) for the second cell. gNB A terminal containing an NCC (next hop chaining counter) value used to update ).

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