Method and device for supporting continuous conditional LTM in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting higher data transmission rates. A user equipment (UE) according to one embodiment of the present disclosure can: receive radio resource control (RRC) configuration information from a distributed unit (DU) associated with a source cell; perform a random access procedure to an L1 / L2 triggered mobility (LTM) candidate cell on the basis of an execution condition of initial conditional LTM for the source cell included in the RRC configuration information; and, when handover to the LTM candidate cell is completed by performing the random access procedure, perform continuous conditional LTM on the basis of the execution condition of the continuous conditional LTM related to the LTM candidate cell included in the RRC configuration information.

Description

Method and apparatus for supporting continuous conditional LTM in a wireless communication system

[0001] The present disclosure relates to the operation of a base station and a terminal in a wireless communication system, and more specifically, to a method and apparatus for supporting continuous conditional LTM of a base station and a terminal.

[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 band (e.g., the 3 terahertz (3 THz) 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) for supporting new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) which provides nodes for expanding 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) for incorporating 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 disclosure provides overall configuration methods and procedures necessary for a terminal to perform continuous conditional L1 / L2 triggered mobility (LTM; L1 / L2-based mobility), and in particular considers the overall procedures and detailed terminal operations for supporting continuous conditional LTM.

[0009] According to one embodiment of the present disclosure, a UE (user equipment) receives radio resource control (RRC) configuration information from a distributed unit (DU) associated with a source cell, performs a random access procedure to an LTM candidate cell based on the execution conditions of an initial conditional LTM (L1 / L2 triggered mobility) regarding the source cell included in the RRC configuration information, and when a handover to an LTM candidate cell is completed according to the execution of the random access procedure, performs a continuous conditional LTM based on the execution conditions of a continuous conditional LTM regarding the LTM candidate cell included in the RRC configuration information.

[0010] Through the method for supporting continuous conditional LTM proposed in this disclosure, procedures between base stations and between CU-DUs and terminal operations are specified for base station settings required when a terminal performs continuous conditional LTM, thereby enabling support for continuous conditional LTM.

[0011] FIG. 1a is a drawing illustrating the structure of a wireless communication system to which the present disclosure applies.

[0012] FIG. 1b is a diagram showing the structure of a wireless protocol of a wireless communication system to which the present disclosure can be applied.

[0013] FIG. 1c is a drawing illustrating the structure of another wireless communication system to which the present disclosure may be applied.

[0014] FIG. 1d is a diagram illustrating a scenario for inter-cell beam management referenced in the present disclosure, in which a terminal transmits and receives data through the beam of a TRP (transmission / reception point) of a neighboring cell that supports beam changing based on L1 / L2 while maintaining a connection state with a serving cell.

[0015] FIG. 1e is a diagram illustrating 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, as an embodiment considered in the present disclosure, to transmit and receive data.

[0016] FIG. 1f is a diagram illustrating the overall operation for supporting conditional LTM operation in cells within the same CU, which is referenced in the present disclosure.

[0017] FIG. 1ga is a diagram illustrating the overall operation for supporting continuous conditional MCG LTM operation in cells belonging to different base stations as Embodiment 1 proposed in the present disclosure.

[0018] FIG. 1gb is a diagram illustrating a method for generating and configuring conditional LTM execution conditions for each LTM candidate cell as Embodiment 1 proposed in the present disclosure.

[0019] FIG. 1h is a diagram illustrating the overall operation for supporting continuous conditional SCG LTM operation in cells belonging to different base stations as Embodiment 2 proposed in the present disclosure.

[0020] FIG. 1i is a drawing illustrating the entire terminal operation that performs a continuous conditional LTM, applied to an embodiment of the present disclosure.

[0021] FIG. 1j is a drawing illustrating base station operation applied to embodiments of the present disclosure.

[0022] FIG. 1k is a block diagram illustrating the internal structure of a terminal to which the present disclosure is applied.

[0023] FIG. 11 is a block diagram showing the configuration of a base station according to the present disclosure.

[0024] A method performed by a DU (distributed unit) in a wireless communication system according to one embodiment of the present disclosure may include: receiving a message requesting execution conditions for a conditional LTM (L1 / L2 triggered mobility) from a CU (central unit); generating execution conditions for an initial conditional LTM when the DU is associated with a source cell; transmitting the generated execution conditions for the initial conditional LTM to the CU; generating execution conditions for a successor conditional LTM when the DU is associated with an LTM candidate cell; and transmitting the generated execution conditions for the successor conditional LTM to the CU.

[0025] A method performed by a UE (user equipment) in a wireless communication system according to one embodiment of the present disclosure may include: receiving RRC (radio resource control) setting information from a DU (distributed unit) associated with a source cell; performing a random access procedure to an LTM candidate cell based on the execution conditions of an initial conditional LTM (L1 / L2 triggered mobility) regarding the source cell included in the RRC setting information; and, when a handover to the LTM candidate cell is completed according to the execution of the random access procedure, performing a successive conditional LTM based on the execution conditions of a successive conditional LTM regarding the LTM candidate cell included in the RRC setting information.

[0026] A distributed unit (DU) of a wireless communication system according to one embodiment of the present disclosure comprises: a transceiver; and at least one processor connected to the transceiver, wherein the at least one processor receives a message requesting execution conditions for a conditional LTM (L1 / L2 triggered mobility) from a central unit (CU), and if the DU is associated with a source cell, generates execution conditions for an initial conditional LTM and transmits the generated execution conditions for the initial conditional LTM to the CU, and if the DU is associated with an LTM candidate cell, generates execution conditions for a successive conditional LTM and transmits the generated execution conditions for the successive conditional LTM to the CU.

[0027] In a user equipment (UE) of a wireless communication system according to one embodiment of the present disclosure, the device comprises: a transceiver; and at least one processor connected to the transceiver, wherein the at least one processor receives radio resource control (RRC) setting information from a distributed unit (DU) associated with a source cell, performs a random access procedure to an LTM candidate cell based on the execution conditions of an initial conditional LTM (L1 / L2 triggered mobility) regarding the source cell included in the RRC setting information, and when a handover to the LTM candidate cell is completed according to the execution of the random access procedure, performs a continuous conditional LTM based on the execution conditions of a continuous conditional LTM regarding the LTM candidate cell included in the RRC setting information.

[0028] The operating principles of the present disclosure will be described in detail below with reference to the attached drawings. In describing the present disclosure below, if it is determined that a detailed description of related known functions or configurations might unnecessarily obscure the essence of the present disclosure, such detailed description will be omitted. Furthermore, the terms described below are defined in consideration of their functions in the present disclosure, and these may vary depending on the intentions or conventions of the user or operator. Therefore, their 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 disclosure is not limited to the terms described below, and other terms referring to objects having equivalent technical meanings may be used.

[0029] For convenience of explanation, the present disclosure uses terms and names defined in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard. However, the present disclosure is not limited to the above terms and names and may be applied equally to systems conforming to other standards.

[0030] In this specification, a hierarchy (or hierarchy device) may also be described as an entity.

[0031] FIG. 1a is a drawing illustrating the structure of a wireless communication system to which the present disclosure applies.

[0032] Referring to FIG. 1a, as illustrated, the wireless access network of the wireless communication system consists of a next-generation base station (New Radio Node B, hereinafter NR NB, 1a-10) and an NR CN (New Radio Core Network, or NG CN: Next Generation Core Network, 1a-05). A user terminal (New Radio User Equipment, hereinafter NR UE or terminal, 1a-15) connects to an external network through the NR NB (1a-10) and the NR CN (1a-05).

[0033] In FIG. 1a, the NR NB (1a-10) corresponds to the eNB (Evolved Node B) of the existing LTE system. The NR NB is connected to the NR UE (1a-15) via a wireless channel and can provide superior service compared to the existing Node B. In a wireless 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 to perform scheduling, and this is handled by the NR NB (1a-10). A single NR NB typically controls multiple cells. To achieve ultra-high-speed data transmission compared to existing LTE, it can have a maximum bandwidth greater than the existing maximum bandwidth, and can additionally incorporate beamforming technology by using Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM) as the wireless access technology. In addition, an Adaptive Modulation & Coding (AMC) method is applied to determine the modulation scheme and channel coding rate according to the channel conditions of the terminal. The NR CN (1a-05) 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. Additionally, the wireless communication system can be interoperable with the existing LTE system, and the NR CN is connected to the MME (1a-25) via a network interface. The MME is connected to the existing base station eNB (1a-30).

[0034] FIG. 1b is a diagram showing the structure of a wireless protocol of a wireless communication system to which the present disclosure can be applied.

[0035] Referring to FIG. 1b, the wireless protocol of the wireless communication system consists of an NR SDAP layer (1b-01, 1b-45), an NR PDCP layer (1b-05, 1b-40), an NR RLC layer (1b-10, 1b-35), an NR MAC layer (1b-15, 1b-30), and an NR PHY layer (1b-20, 1b-25) at the terminal and the NR base station, respectively.

[0036] The main functions of the NR SDAP layer (1b-01, 1b-45) may include some of the following functions.

[0037] - User data transfer function (transfer of user plane data)

[0038] - Mapping function between a QoS flow and a DRB for both DL and UL for uplink and downlink

[0039] - Marking QoS flow ID for uplink and downlink (marking QoS flow ID in both DL and UL packets)

[0040] - Function to map reflective QoS flow to data bearers for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

[0041] For NR SDAP layer devices, the terminal may receive a setting via an RRC message regarding whether to use the header of the NR SDAP layer device or the functions of the NR SDAP layer device 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 the NAS reflective QoS and AS reflective QoS 1-bit indicators of 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 smooth service.

[0042] The main functions of the NR PDCP layer (1b-05, 1b-40) may include some of the following functions.

[0043] Header compression and decompression (ROHC only)

[0044] User data transfer function (Transfer of user data)

[0045] Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0046] Out-of-sequence delivery of upper layer PDUs

[0047] Reordering function (PDCP PDU reordering for reception)

[0048] Duplicate detection function (Duplicate detection of lower layer SDUs)

[0049] Retransmission of PDCP SDUs

[0050] Encryption and decryption functions (Ciphering and deciphering)

[0051] Timer-based SDU discard in uplink.

[0052] The reordering function of the NR PDCP layer device refers to a function of reordering PDCP PDUs received from the lower layer in order based on the PDCP SN (sequence number), and may include a function of transmitting data to the upper layer in the reordered order, or a function of transmitting immediately without considering the order, may include a function of recording lost PDCP PDUs by reordering, may include a function of reporting the status of lost PDCP PDUs to the transmitting side, and may include a function of requesting retransmission of lost PDCP PDUs.

[0053] The main functions of the NR RLC layer (1b-10, 1b-35) may include some of the following functions.

[0054] Data transfer function (Transfer of upper layer PDUs)

[0055] Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0056] Out-of-sequence delivery of upper layer PDUs

[0057] ARQ function (Error Correction through ARQ)

[0058] Concatenation, segmentation and reassembly of RLC SDUs

[0059] Re-segmentation of RLC data PDUs

[0060] Reordering function (Reordering of RLC data PDUs)

[0061] Duplicate detection

[0062] Error detection function (Protocol error detection)

[0063] RLC SDU discard function

[0064] RLC re-establishment function

[0065] The in-sequence delivery function of an NR RLC layer 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 RLC SDUs when a single RLC SDU is received split into multiple RLC SDUs; a function to reorder received RLC PDUs based on an RLC SN (sequence number) or PDCP SN (sequence number); a function to record lost RLC PDUs after reordering; a function to report the status of lost RLC PDUs to the transmitting side; a function to request retransmission of lost RLC PDUs; a function to deliver only the RLC SDUs prior to the lost RLC SDU to the upper layer in sequence if there is a lost RLC SDU; or a function to deliver all RLC SDUs received before the timer started to the upper layer in sequence if a predetermined timer has expired even if there is a lost RLC SDU; 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 up to that point to the upper layer in order. Additionally, the NR RLC layer device may process RLC PDUs in the order they are received (regardless of the order of sequence numbers, in the order of arrival) and deliver them to the PDCP layer device out of order (out-of-sequence delivery), and in the case of segments, it may receive segments stored in a buffer or to be received later, reconstruct them into a single complete RLC PDU, process them, and deliver them to the PDCP layer device.The NR RLC layer (1b-10, 1b-35) may not include a concatenation function and may perform the function in the NR MAC layer (1b-15, 1b-30) or replace it with the multiplexing function of the NR MAC layer (1b-15, 1b-30).

[0066] In the above, the out-of-sequence delivery function of the NR RLC layer device refers to a function of delivering RLC SDUs received from a lower layer directly to an upper layer regardless of order, and may include a function of reassembling and delivering them 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.

[0067] The NR MAC layer (1b-15, 1b-30) can be connected to multiple NR RLC layer devices configured in one terminal, and the main functions of the NR MAC layer (1b-15, 1b-30) may include some of the following functions.

[0068] Mapping function (Mapping between logical channels and transport channels)

[0069] Multiplexing and demultiplexing functions of MAC SDUs

[0070] Scheduling information reporting function

[0071] HARQ function (Error correction through HARQ)

[0072] Priority handling between logical channels of one UE

[0073] Priority handling between UEs by means of dynamic scheduling

[0074] MBMS service identification function

[0075] Transport format selection function

[0076] Padding

[0077] The NR PHY layer (1b-20, 1b-25) 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.

[0078] FIG. 1c is a drawing illustrating the structure of another next-generation mobile communication system to which the present disclosure may be applied.

[0079] Referring to FIG. 1c, a cell serviced by a beam-based NR gNB (1c-05) can be composed of multiple TRPs (Transmission Reception Points, 1c-10, 1c-15, 1c-20, 1c-25, 1c-30, 1c-35, 1c-40). The TRPs (1c-10 to 1c-40) represent blocks from which some functions of transmitting and receiving physical signals from an existing NR base station (gNB) have been separated, and they are composed of multiple antennas. The NR gNB (1c-05) can also be represented as a CU (Central Unit), and the TRP as a DU (Distributed Unit). The functions of the NR gNB (1c-05) and the TRP can be configured by separating each layer from the PDCP / RLC / MAC / PHY layer, such as 1c-45. That is, the above TRP can perform the functions of the corresponding layer using only the PHY layer (1c-15, 1c-25), the above TRP can perform the functions of the corresponding layers using only the PHY layer and the MAC layer (1c-10, 1c-35, 1c-40), and the above TRP can perform the functions of the corresponding layers using only the PHY layer, the MAC layer, and the RLC layer (1c-20, 1c-30). In particular, the TRP (1c-10~1c-40) 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 (1c-50) connects to the NR gNB (1c-05) and the external network through the TRP (1c-10~1c-40). The above NR gNB (1c-05) collects status information such as the buffer status, available transmission power status, and channel status of terminals to provide services to users, and schedules them to support the connection between the terminals and the core network (CN), particularly the AMF / SMF (1c-50).

[0080] The TRP in the present disclosure is based on a structure (1c-15, 1c-25) that has only a PHY layer and can perform the functions of that layer.

[0081] FIG. 1d is a diagram illustrating a scenario for inter-cell beam management referenced in the present disclosure, in which a terminal transmits and receives data through the beam of a TRP (transmission / reception point) of a neighboring cell that supports beam changing based on L1 / L2 while maintaining a connection state with a serving cell.

[0082] Although this drawing describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2; 1d-10, 1d-15) exist within a single DU (Distributed unit, 1d-05), the general content of this disclosure is also applicable to inter-DU cases (each DU constitutes a single TRP-Cell). Furthermore, throughout this disclosure, non-serving cells (TRP 2, Cell 2) that support L1 / L2-based mobility (beam change and serving cell change) are referred to interchangeably as neighbor cells, non-serving cells, and additional cells with the PCI different from the serving cell.

[0083] In the existing terminal beam change procedure (1d-45), the terminal (1d-20) is transmitting and receiving data in a connected state through the TRP 1 (1d-10) of serving cell 1, and may be set to the optimal beam, TCI state 1 (1d-25, 1d-30). At this stage, the terminal (1d-20) may receive instructions for setting information for L3 channel measurement (RRM; radio resource management) for an additional cell (TRP 2-Cell 2, 1d-15) that has a different PCI from the serving cell through RRC setting information from the serving cell (1d-10), and performs an L3 measurement operation (1d-46) for the corresponding frequency and cell. Subsequently, the serving cell (TRP 1-Cell 1, 1d-10) may direct a handover to the corresponding cell (TRP 2-Cell 2, 1d-15) based on the reported measurement value (1d-47), and once the handover is completed, additional RRC configuration information may be transmitted to the terminal (1d-20) via TRP 2-Cell 2 (1d-15) (1d-48). The RRC configuration information may include UL / DL configuration information in the corresponding cell, L1 measurement related settings (CSI-RS measurement and reporting), and in particular, TCI state configuration information for PDCCH and PDSCH channels. The terminal (1d-20) performs an L1 measurement according to the configuration (1d-49), and the base station updates the TCI state through L1 / L2 signaling according to the measurement report (1d-50). Here, the optimal beam TCI state 2 (1d-40) may be directed. At this stage, Cell 1 is the serving cell until the handover, and Cell 2 becomes the serving cell after the handover. In other words, many procedures and time are required even after the handover to indicate the optimal beam.

[0084] Unlike the existing terminal beam change procedure (1d-45) described above, the improved beam change technique (1d-55) considered in this disclosure is as follows. The terminal (1d-20) can refer to and transmit the beam setting associated with an additional cell (TRP 2-Cell 2, 1d-15) with a different PCI from the serving cell through RRC setting information (1d-56) from the serving cell (1d-10). A method of associating a new cell ID (Physical cell ID, PCI; additionalPCI-r17) as follows may be applied to the part that associates the beam setting associated with the additional cell (TRP 2-Cell 2, 1d-15) with a different PCI from the serving cell (1d-10), i.e., the TCI state corresponding to TRP2.

[0085]

[0086] 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.

[0087]

[0088] 1. Joint UL / DL Mode: Configures UL and DL to share the same TCI settings (in PDSCH-Config)

[0089]

[0090] 2. Separate UL / DL Mode: The UL and DL each provide their own TCI settings. The TCI state for the DL follows the settings in dl-OrJoint-TCIStateList-r17 (in PDSCH-Config), and the TCI state for the UL follows ul-TCI-StateList-r17 (in BWP-UplinkDedicated).

[0091]

[0092] After the settings for TRP 2-Cell 2 are provided in the RRC connection state to serving cell 1, the terminal (1d-20) performs an L1 measurement for the corresponding TRP 2-Cell 2 according to the settings and reports the result to the serving cell (Cell 1, 1d-10) (1d-57). If the serving cell determines that a change to a specific beam (TCI state 2, 1d-35, 1d-40) of TRP 2 (Cell 2, 1d-15) is necessary from the serving cell beam (TCI state 1, 1d-25, 1d-30) based on the measurement result, it triggers a beam change and instructs the terminal (1d-20) via L1 / L2 signaling (1d-58). The terminal (1d-20) changes the beam to a specific beam (TCI state 2, 1d-40) of TRP 2 (Cell 2, 1d-15) through the corresponding instruction, and performs physical channel setup and upper layer setup operations associated with the set beam. From this stage, the terminal (1d-20) remains connected to the serving cell (Cell 1, 1d-10), but performs data transmission and reception using the channel link of TRP 2 (Cell 2, 1d-15) (receiving PDCCH / PDSCH, transmitting PUCCH / PUSCH). That is, transmission and reception for the common control channel are performed through the serving cell (Cell 1, 1d-10). Subsequently, the terminal (1d-20) performs an L3 measurement operation according to the measurement settings set in an independent serving cell (1d-59), receives a handover command message from the serving base station (Cell 1), and can perform a serving cell change to Cell 2 (1d-60). Through this technique (1d-55), the terminal (1d-20) performs data transmission and reception with a specific TRP 2 of Cell 2, which supports L1 / L2-based mobility, while connected to the serving cell (Cell 1, 1d-10), and can continue to use the beam even after the handover.

[0093] For reference, the RRC settings regarding the settings and operations related to the L1 measurement and report in step 1d-57 above are described as follows. These details are basically applicable to the embodiments below of the present disclosure, and enhancement techniques may be added in future embodiments.

[0094] 1. L1 measurement settings (configured within CSI-ResourceConfig and ServingCellConfig in IE)

[0095] - CSI-RS / SSB resources and resource pools requiring measurement (nzp-CSI-RS, csi-IM, csi-SSB)

[0096] - Configuration of CSI-RS / SSB resources requiring measurement (aperiodic, semi-persistent) and triggering settings

[0097] - When a CSI-RS (channel state information-reference signal) resource refers to an SSB (synchronization signal block) 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).

[0098]

[0099]

[0100] 2. L1 report configuration (configured within the serving cell, ServingCellConfig, configured within IE)

[0101] - Report Type: Periodic Report, Semi-periodic Report with PUCCH, Semi-periodic Report with PUSCH, Aperiodic Report with PUSCH

[0102] - Report quantity

[0103] - Other settings required for reporting

[0104] FIG. 1e is a diagram illustrating a scenario in which a terminal changes the serving cell and beam to a TRP of a cell that supports L1 / L2-based beam changing, as an embodiment considered in the present disclosure. Although the present figure describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2; 1e-10, 1e-15, 1e-40, 1e-45) exist within a single DU (Distributed unit, 1e-05, 1e-35), the overall content of the present disclosure is also applicable to inter-DU within an intra-CU (each DU constitutes a single TRP-Cell).

[0105] Unlike the conventional terminal beam changing procedure (1d-45, 1d-55) described in FIG. 1d, the improved beam changing technique (1e-25, 1e-75) considered in the present embodiments is as follows.

[0106] 1. Example 1 (1e-25): After performing inter-cell beam management (change) operation, perform L1 / L2 handover

[0107] 2. Example 2 (1e-75): Perform L1 / L2 handover immediately

[0108] First, to explain the overall operation of Embodiment 1, the terminal (1e-20) can receive common configuration and dedicated configuration information for an additional cell (TRP 2-Cell 2, 1e-15) that has a different PCI from the serving cell (1e-10) through RRC configuration information (1e-26). 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. Furthermore, the configuration is characterized by including all configuration information (cell configuration, bearer configuration, security key configuration, etc.) that is applied when the terminal (1e-20) moves to the corresponding cell (handover). Additionally, the configuration includes enhanced configurations by referring to the unified TCI state configuration and L1 measurement and report-related configurations described in step 1d-56. Specifically, for continuous LTM, it includes an enhanced unified TCI state setting and L1 measurement and report settings, which are described in detail in the drawings below of the present disclosure.

[0109] After the setting for TRP 2-Cell 2 (1e-15) is provided while the serving cell 1 is connected via RRC, the terminal (1e-20) performs an L1 measurement for the TRP 2-Cell 2 (1e-15) according to the setting received in step 1e-27 and reports the result to the serving cell (Cell 1, 1e-10). If the serving cell determines, based on the measurement result, that a change to a specific beam (TCI state 2, 1e-40) of TRP 2 (Cell 2, 1e-15) is necessary from the serving cell beam (TCI state 1, 1e-25), it triggers a beam change in step 1e-28 and instructs the terminal (1e-20) via L1 / L2 signaling. The terminal (1e-20) performs a beam change to TRP 2 (Cell 2, 1e-15) through the corresponding instruction and transmits and receives data through the TRP 2 (Cell 2, 1e-15). At this time, no serving cell change occurs, and the terminal (1e-20) remains connected to the serving cell (Cell 1, 1e-10) via RRC. Subsequently, the terminal (1e-20) performs an L1 measurement for TRP 2-Cell 2 (1e-15) and reports the result to the serving cell (Cell 1, 1e-10). If the L1 measurement reported by the terminal (1e-20) satisfies the triggering condition for a handover to TRP 2-Cell 2 (1e-15) (detailed operation is described in detail below), the serving cell (Cell 1, 1e-10) instructs the terminal (1e-20) to perform a handover. The instruction in question can be an L1 / L2 message. That is, the MAC CE may contain an instruction directive for a handover.

[0110] To describe the overall operation of Embodiment 2, the terminal (1e-50) can receive common and dedicated configuration information for an additional cell (TRP 2-Cell 2, 1e-45) that has a different PCI from the serving cell (1e-40) through RRC configuration information (1e-76). That is, ServingCellID or candidateCellID (cell ID associated with PCI), and configuration information corresponding to the corresponding 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. Furthermore, the configuration is characterized by including all configuration information (cell configuration, bearer configuration, channel measurement configuration, etc.) that is applied when the terminal (1e-50) moves to the corresponding cell (handover). In addition, the configuration includes the unified TCI state configuration and settings related to L1 measurement and report described in step 1d-56, modified to support consecutive LTMs. The L1 measurement, report, and TCI state settings applicable to the present disclosure are described in detail below.

[0111] After the setting for TRP 2-Cell 2 (1e-45) is provided while the terminal (1e-50) is connected to the serving cell 1 via RRC, the terminal (1e-50) performs an L1 measurement of the TRP 2-Cell 2 (1e-45) according to the setting received in step 1e-77 and reports the result to the serving cell (Cell 1, 1e-40). If the serving cell determines that a handover is required simultaneously with a beam change from the serving cell beam (TCI state 1, 1e-45) to a specific beam (TCI state 2, 1e-70) of TRP 2 (Cell 2, 1e-45) based on the measurement result, it triggers the beam change and handover in step 1e-78 and instructs the terminal (1e-50) via L1 / L2 signaling. The terminal (1e-50) performs a handover simultaneously with changing the beam to TRP 2 (Cell 2, 1e-15) via the corresponding instruction, and transmits and receives data through the TRP 2 (Cell 2, 1e-15). At this time, the terminal (1e-50) applies the configuration information for the target cell where the handover is performed, which was pre-configured in step 1e-76. Depending on whether uplink synchronization is required in this step, the terminal (1e-50) may perform random access, or random access to the target cell may be omitted. Detailed operation is described in the drawings below.

[0112] In particular, as explained above, this disclosure proposes a detailed method for setting the unified TCI state and L1 measurement and report for candidate cells surrounding the LTM to support the continuous LTM proposed in this disclosure. As described in Figure 1d, in the existing ICBM, L1 measurement resource settings for cells requiring measurement are provided in the CSI-ResourceConfig within 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.

[0113] Detailed settings for L1 measurement and reporting settings for LTM are provided as L1 measurement resource settings applied to LTM candidate cells as follows. To this end, it is necessary to share and determine the L1 measurement resources and reporting settings for LTM among LTM candidate cells during the preprocessing stage. The entire procedure is described together in the following example.

[0114] -LTM-Config

[0115] The IELTM-Configis used to provide LTM candidate configurations.

[0116] LTM-Configinformation element

[0117]

[0118] -LTM-CSI-ResourceConfig

[0119] The IELTM-CSI-ResourceConfigdefines a group of one or more CSI resources for one or more LTM candidate configurations.

[0120] LTM-CSI-ResourceConfiginformation element

[0121]

[0122] -CSI-MeasConfig

[0123] The IECSI-MeasConfigis used to configure CSI-RS (reference signals) belonging to the serving cell in whichCSI-MeasConfigis included, channel state information reports to be transmitted on PUCCH on the serving cell in whichCSI-MeasConfigis included and channel state information reports on PUSCH triggered by DCI received on the serving cell in whichCSI-MeasConfigis included. See also TS 38.214

[0019] , clause 5.2.

[0124] CSI-MeasConfiginformation element

[0125]

[0126] -LTM-CSI-ReportConfig

[0127] The IELTM-CSI-ReportConfigis used to configure report on the cell in which theLTM-CSI-ReportConfigis included.

[0128] LTM-CSI-ReportConfiginformation element

[0129]

[0130] In this disclosure, detailed operations for performing RACH-less cell changes instead of uplink synchronization operations during LTM execution to support RACH-less conditional LTM (conditional LTM without random access), and detailed operations for RACH-less operations for performing conditional LTM are proposed. In particular, key features of the RACH-less conditional LTM in this disclosure include a method for obtaining a TA (timing advance) for LTM candidate cells in advance, a method for performing the first transmission after RACH-less conditional LTM, and a method for managing stored TA values.

[0131] FIG. 1f is a diagram illustrating the overall operation for supporting conditional LTM operation in cells within the same CU, which is referenced in the present disclosure.

[0132] A terminal (1f-01) in an RRC connection state performs data transmission and reception with source cell 1 (1f-02) and transmits Layer 3 measurements for the serving cell and surrounding cells to the source base station CU (1f-03) according to the Layer 3 measurements and reports set in step 1f-10. At this time, the actual measurements are transmitted to the source base station CU (1f-03). This is because the source base station CU (1f-03) is responsible for processing RRC messages and determining mobility. Based on the measurement reports received from the terminal (1f-01), the source base station CU (1f-03) generates a message (UE Context Setup Request or UE Context Modification Request) requesting configuration information for LTM from LTM candidate surrounding cells (1f-04, 1f-05) in step 1f-15 and transmits it to the F1 interface. Although candidate cells are indicated in association with DUs in the diagram, in reality, candidate cells and DUs may have a 1:1 mapping, or multiple candidate cells may be included in a single DU. The message requesting the LTM configuration information may include a request to neighboring cells that the cell has been determined as an LTM candidate cell, as well as requests for conditional LTMs and configuration information. That is, it may include a procedure to request RRC configuration information that is applied when an L1 / L2-based handover is performed to the cell. The information that may be included in the message is summarized as follows. The following message content may be used as the composition of the messages in steps 1f-15 and 1f-35.

[0133] 1. Configuration information applicable to LTM and conditional LTM (Information to be displayed when issuing the cell switch command MAC CE instruction to the candidate cell that made the LTM decision.)

[0134] - LTM candidate ID

[0135] - Mapping information between the LTM candidate ID and the corresponding cell ID

[0136] - Beam information to be used for each candidate (TCI state)

[0137] In this case, the meaning of use may include a beam linked to the RACH occasion during DL and / or UL synchronization and / or RACH execution, and / or a beam to be used for the first UL data transmission. If necessary, an indicator corresponding to each case may be accompanied to perform a cell switch.

[0138] - RACH preamble index

[0139] - 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.

[0140] 2. Pre-configuration procedures for LTM and conditional LTM

[0141] - CSI resource request information for each candidate cell (requests for CSI-RS resources or SSB resources)

[0142] It may be requested during the pre-configuration preprocessing part for LTM candidate cells.

[0143] An indicator of whether the request is for initial preparation, e.g., initiation, or for a modification request after the initial one.

[0144] In particular, when the relevant request information is included, lower layer configuration information and CSI report configuration information in this message may not be transmitted.

[0145] If CSI resource information is received from candidate cells using the corresponding request information, the CSI resource settings of each of the following candidate cells may be transmitted instead of the request. In other words, a CSI resource setting preprocessing procedure is required in at least two steps.

[0146] In addition, it is possible to decide whether to request CSI-RS resources or SSB resources for each target candidate cell.

[0147] - CSI resource settings for each candidate cell (necessary when transmitting L1 measurement settings as source DU to the terminal), individual resource settings per cell and setting IDs, CSI resource settings for LTM, and may use the same CSI resources as the conditional LTM, but may also be transmitted by explicitly distinguishing the conditional LTM.

[0148] Based on the above CSI resource request information, provide L1 measurement settings for LTM transmitted from the corresponding candidate cell.

[0149] Depending on the request for CSI-RS or SSB resources from each target cell, one of the two resource configurations or both resource configurations can be delivered.

[0150] - CSI report configuration considering the CSI resources of each of the above candidate cells

[0151] The purpose of this is that when a candidate DU creates the above information and transmits it to a CU, this information can be used as the CSI report configuration within the target cell configuration (RRCReconfiguration) of the relevant concerned cell (i.e., target cell) created by the CU. Additionally, the information may not be transmitted separately but may be included and transmitted within the target cell configuration (RRCReconfiguration).

[0152] In other words, if the terminal moves from another cell to this cell (concerned cell), it can be used as a CSI report configuration with that cell as the serving cell. Its purpose is to include it in the target cell configuration for Subsequent LTM without providing separate L1 settings.

[0153] Event-based L1 measurement reporting

[0154] You can define and use Best beam's L1-RSRP-based events.

[0155] For example, the following events can be introduced. That is, events are defined by comparing the serving cell beam with the surrounding cell beam, and L1 filtering values ​​such as threshold, beam offset, hysteresis, and time to trigger (TTT) can be introduced.

[0156] - Event A1beam: Beam of serving cell becomes better than absolute threshold;

[0157] - Event A2beam: Beam of serving cell becomes worse than absolute threshold;

[0158] - Event A3beam: Beam of candidate cell becomes amount of offset better than beam of serving cell;

[0159] - Event A4beam: Beam of candidate cell becomes better than absolute threshold;

[0160] - Event A5beam: Beam of serving cell becomes worse than absolute threshold1 AND Beam of candidate cell becomes better than another absolute threshold2.

[0161] The above event may also be used for conditions that trigger a conditional LTM. Alternatively, in addition to a single beam, events through multiple beams or events through cell-level measurements estimated through multiple beams may be added.

[0162] The above conditions are determined by coordination between the serving CU and the LTM candidate DU in step 1f-15, and the serving CU can determine the event conditions that trigger the LTM provided by the LTM candidate cell and the L1 filtering values ​​and transmit them to the terminal.

[0163] - RACH configuration and lower layer setting information to be used in the relevant concerned cell

[0164] These information can be transmitted from the above candidate DU to the CU, written as settings required for RACH execution within the target cell configuration of the concerned cell, lower layer settings to be applied when moving to the cell, and / or reference settings including them, and later transmitted to the terminal.

[0165] In particular, some of the RACH settings can be used to include information on determining the Rach preamble index, Mask, and occasion in the cell switch command MAC CE described above.

[0166] It may be a setting that applies to both LTM and conditional LTM simultaneously, but resources dedicated to conditional LTM may also be configured separately.

[0167] In summary, the request for the L1 measurement resource and reporting settings can be performed for each candidate cell, and although it is indicated as a single procedure in step 1f-15 in the diagram, this step can be applied to multiple procedures. The multiple procedures that can be performed for the L1 measurement resource and reporting settings are as follows.

[0168] 1. Step 1: Request L1 measurement resource configuration from LTM candidate cells (request SSB or CSI-RS resources)

[0169] 2. Step 2: LTM candidate cells respond by setting up L1 measurement resources and transmit them to the source base station CU (1f-03) (SSB or CSI-RS resource request). This procedure can be transmitted to the source base station CU (1f-03) via the F1 interface as a UE Context Setup Response message.

[0170] 3. Step 3: The source base station CU (1f-03) transmits L1 measurement resource settings for continuous LTM and conditional LTM support to each candidate cell through L1 measurement resource settings for each collected candidate cell. This procedure can be transmitted to the source base station CU (1f-03) via the F1 interface as a UE Context Modification Request message.

[0171] 4. Step 4: The source base station CU (1f-03) requests and receives L1 measurement report setup from LTM candidate cells. This procedure can be transmitted to the source base station CU (1f-03) via the F1 interface as a UE Context Modification Response message.

[0172] 5. Step 5 (1f-20): Transmit LTM and conditional LTM related settings to the terminal (1f-01). The source base station CU (1f-03) collects all LTM related settings received from LTM candidate cells and stores them in an RRCReconfiguration message transmitted to the terminal, and transmits the corresponding RRC setting information to the terminal (1f-01). That is, pre-configuration information for LTM candidate cells is transmitted to the terminal (1f-01). In particular, regarding conditional LTM, it is characterized by matching and transmitting the execution condition (event-based L1 measurement report setting) with the RRC setting information of the target cell that is applied when executed.

[0173] At this time, the source base station CU (1f-03) may transmit the RRC configuration information including the configuration information of the source cell and separate reference cell configuration information. The reference cell configuration information transmitted by the source base station CU (1f-03) to each candidate cell (1f-04, 1f-05) may be a common configuration that can be applied to multiple target candidate cells to reduce signaling overhead when target candidate cells provide configuration information for LTM. This may be a measurement configuration, a bearer configuration, or, if the cells belong to the same CellGroup, configurations configured at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.). Alternatively, if the source base station CU (1f-03) has a procedure to roughly know or know the configuration information for each candidate cell (1f-04, 1f-05), the reference cell configuration may be determined through a separate procedure to obtain the reference cell configuration information. The purpose of the source base station CU (1f-03) transmitting the reference cell settings to each candidate cell (1f-04, 1f-05) is to ensure that only the setting information added based on the reference cell settings is transmitted to the source base station CU (1f-03), thereby enabling the application of delta configuration (a method of configuring a complete setting by applying settings added on top of the reference cell settings, or a method of configuring a complete setting by applying settings over the reference cell settings in the target cell). This is subsequently transmitted to the terminal (1f-01) as is, thereby reducing the signaling of RRC messages transmitted to the terminal (1f-01). Additionally, when the source base station CU (1f-03) transmits the reference cell settings to each candidate cell (1f-04, 1f-05), this information may be omitted; in this case, the candidate cell settings are provided as complete RRC settings.

[0174] In step 1f-20, the source cell (1f-02) receives an RRC message generated by the base station CU (1f-03) based on configuration information received from each candidate cell and transmits it to the terminal (1f-01). In particular, regarding conditional LTM, it is characterized by matching and transmitting the execution condition (event-based L1 measurement report setting) with the RRC configuration information of the target cell applied when execution occurs. The terminal (1f-01) that receives the RRC message performs a procedure to decode and process the RRC message. The processing includes ASN.1 decoding of the received message, validity determination, and a method for storing and managing the configuration content. Additionally, the terminal (1f-01) stores the LTM configuration information for each candidate cell decoded in this step as complete configuration information in the terminal (1f-01)'s buffer (memory), and simultaneously stores the received reference cell configuration information in the terminal (1f-01)'s buffer (memory) as well, and manages it for the future.

[0175] In step 1f-25, the source base station CU (1f-03) may transmit a MAC CE that enables semi-persistent L1 reporting or a DCI that enables aperiodic L1 reporting to the terminal (1f-01). The terminal (1f-01) receives this and performs L1 (Layer 1) measurements and reporting for each candidate surrounding cell in step 1f-30, and performs semi-persistent / aperiodic L1 measurement reporting according to the setting. Subsequently, when the terminal (1f-01) receives a MAC CE that disables semi-persistent L1 reporting, it terminates semi-persistent L1 measurements and reporting. The terminal (1f-01), having received a conditional LTM setting from the base station in step 1f-20, evaluates L1 measurements for conditional LTM in step 1f-35. That is, the execution conditions for the configured conditional LTM are checked, and if the conditions are satisfied (if the event-based L1 measurement reporting conditions are satisfied), the terminal (1f-01) determines the conditional LTM to the LTM candidate cell that satisfies the conditions. In this drawing, the operation of the conditional LTM that performs random access is described.

[0176] In step 1f-40, the terminal (1f-01) applies the RRC configuration information of the LTM candidate cell (target cell where the conditional LTM is determined) configured in step 1f-20, and performs a random access procedure on the target cell (1f-04) using the random access resources provided by the configuration. Through the random access, the terminal (1f-01) synchronizes the uplink and downlink and completes the handover procedure for the cell. This procedure may be a conditional LTM completion procedure. This procedure may vary depending on the method of giving the handover completion instruction; if the configuration of the target cell is received at the RRC message level, it may be a process of transmitting an RRCReconfigrationComplete message and receiving an ACK for it, but if the configuration at the cell level or cell group level is received, a new handover completion instruction message (a new RRC message or MAC CE) may replace this procedure. When the handover is successful, data transmission and reception with the cell is performed, and an RRC connection procedure service is performed.

[0177] Furthermore, the embodiments of the present disclosure support a subsequent conditional LTM operation. This means that the LTM setting information (settings for target candidate cells and reference cell setting information, etc.) received by the terminal (1f-01) in step 1f-20 is stored in the terminal (1f-01) as is, and the terminal (1f-01) continues to perform the conditional LTM procedure unless the LTM setting information is changed, released, or added through a separate RRC setting. If it is necessary to update the reference cell setting information, new RRC setting information is transmitted to the terminal (1f-01), and the update of the reference cell setting information can be performed based on the new RRC setting information. That is, the procedure described in the drawings can be triggered again and performed. Further details regarding the subsequent conditional LTM are described in the following embodiments.

[0178] In summary, when the terminal (1f-01) receives reference cell setting information in step 1f-20, it stores it in the terminal buffer and, unless there is an update to a separate setting, continues to use the setting as reference cell setting information even after LTM execution (step 1f-40) (i.e., applies the reference cell setting and conditional LTM candidate setting values ​​stored in the consecutive conditional LTM).

[0179] In step 1f-45, if the conditional LTM procedure fails (RLF, random access failure, T304 timer completion, etc.), the terminal (1f-01) maintains the LTM settings configured in step 1f-50 and falls back to the source cell. If the fallback to the source cell fails, the terminal (1f-01) performs the RRC re-establishment procedure, and if cell selection occurs, if the selected cell is an LTM candidate cell, it applies the LTM settings and performs the connection procedure. In this case, only random access-based LTM operation may be supported.

[0180] FIG. 1ga is a diagram illustrating the overall operation for supporting continuous conditional MCG LTM operation in cells belonging to different base stations as Embodiment 1 proposed in the present disclosure.

[0181] A terminal (1g-01) in an RRC connection state performs data transmission and reception with source cell 1 (1g-02) and transmits Layer 3 measurements for the serving cell and surrounding cells to the source base station CU (1g-03) according to the Layer 3 measurements and reports set in step 1g-10. At this time, the actual measurements are transmitted to the source base station CU (1g-03). This is because the source base station CU (1g-03) is responsible for processing RRC messages and determining mobility. Based on the measurement reports received from the terminal, the source base station CU (1g-03) generates a message (UE Context Setup Request or UE Context Modification Request) requesting configuration information for continuous conditional LTM in step 1g-15 from LTM candidate surrounding cells (1g-04, 1g-05) and transmits it to the F1 interface. Although candidate cells are indicated in association with DUs in the drawings, in reality, candidate cells and DUs may have a 1:1 mapping, or multiple candidate cells may be included in a single DU. The message requesting the LTM configuration information may include a request to surrounding cells to determine that a cell has been selected as an LTM candidate cell, as well as a request for conditional LTM and configuration information. That is, it may include a procedure for requesting RRC configuration information that is applied when an L1 / L2-based handover is performed to the cell. The information that may be included in the message is the same as that described in Figure 1f-15 above; however, in this drawing, in addition to the content described in 1f-15, the information required in step 1g-15 is explained in more detail to support continuous conditional LTMs. That is, the information in step 1f-15 is applied as is to the detailed procedure of step 1g-15 illustrated in Figure 1gb, and is omitted below to avoid repetition of the same sentences.If the conditional LTM is to be completed as a single execution rather than a continuous conditional LTM, a single node can decide and execute the creation of the execution condition for the conditional LTM and its delivery to the terminal. However, to support continuous conditional LTM, the conditional LTM execution conditions for each candidate cell must be maintained even when the candidate cell becomes a serving cell, and the terminal continues to evaluate the measurement value and the corresponding condition to perform the conditional LTM. To achieve this, instead of creating and delivering a single conditional LTM execution condition to the terminal, each candidate cell may need to deliver multiple execution conditions.

[0182] Figure 1gb illustrates the method of generating and configuring conditional LTM execution conditions for each LTM candidate cell within the intra-CU during stages 1g-16 to 1g-18. For reference, stages 1g-20 to 1g-25 described below focus on the exchange of new information to support continuous conditional LTM between different base stations via the inter-base station interface (Xn). Specifically, it explains the method of generating and sharing execution conditions necessary for inter-CU subsequent conditional LTM support.

[0183] First, the procedure of Fig. 1gb (including the detailed procedures of 1g-16 to 1g-18) is a procedure for generating execution conditions for a continuous conditional LTM within the intra-CU, and the following methods may be considered.

[0184] - Method to create the first execution condition

[0185] The source base station CU (hereinafter, CU) generates execution conditions for successive conditional LTM for all LTM candidate cells.

[0186] The above execution condition may be a threshold for L1-RSRP (or L1-SINR) and may have a different value for each LTM event. An LTM event may be one of the events described in step 1f-15. If multiple thresholds are required for an event, the threshold includes multiple thresholds.

[0187] To do this, CSI resource settings (L1 measurement resource settings) that can be set for source cells (DU) and LTM candidate cells within the corresponding CU must first be collected, and the CU generates a threshold for LTM events between the source cells and LTM candidate cells based on this information.

[0188] Considering consecutive conditional LTMs, the threshold setting must also generate execution conditions when each LTM candidate cell becomes a source cell. The CU repeats the above procedure for the case where each LTM candidate cell is a source cell to generate execution conditions and generates execution conditions consisting of a list of multiple thresholds. Alternatively, for each candidate cell, it generates and manages execution conditions (thresholds) when the cell is a source cell.

[0189] - Method for creating the second execution condition

[0190] Create execution conditions for the first conditional LTM for the current source cell and LTM candidate cells in the source CU

[0191] Subsequently, the execution conditions for subsequent consecutive conditional LTMs are determined in each LTM candidate cell, and the determined execution conditions (thresholds) are transmitted to the source CU. This information may be transmitted via a separate IE, or it may be transmitted by being included in the LTM candidate cell settings (RRCReconfiguration or CellGroupConfig).

[0192] The above execution condition may be a threshold for L1-RSRP (or L1-SINR) and may have a different value for each LTM event. An LTM event may be one of the events described in step 1f-15. If multiple thresholds are required for an event, the threshold includes multiple thresholds.

[0193] To this end, configurable CSI resource settings (L1 measurement resource settings) for source cells (DU) and LTM candidate cells within the corresponding CU must first be collected, and the CU must share this information with each LTM candidate cell. Based on this information, each LTM candidate cell generates a threshold for conditional LTM events with other LTM candidate cells when the LTM candidate cell becomes a source cell.

[0194] The conditional LTM execution condition (threshold) generated for each candidate cell is passed to the source CU.

[0195] - Method to create the third execution condition

[0196] Execution conditions for all consecutive conditional LTMs are determined by each LTM candidate cell, and the determined execution conditions (thresholds) are transmitted to the source CU. This information may be transmitted via a separate IE, or it may be included in the LTM candidate cell configuration (RRCReconfiguration or CellGroupConfig). Initial LTM execution conditions can be generated by the source cell (DU) and transmitted to the source CU.

[0197] The above execution condition may be a threshold for L1-RSRP (or L1-SINR) and may have a different value for each LTM event. An LTM event may be one of the events described in step 1f-15. If multiple thresholds are required for an event, the threshold includes multiple thresholds.

[0198] To this end, configurable CSI resource settings (L1 measurement resource settings) for source cells (DU) and LTM candidate cells within the corresponding CU must first be collected, and the CU must share this information with each LTM candidate cell. Based on this information, each LTM candidate cell generates a threshold for conditional LTM events with other LTM candidate cells when the LTM candidate cell becomes a source cell.

[0199] Steps 1g-16 through 1g-18 represent the procedure of the method for generating conditional LTM execution conditions described above. The details have already been explained above, and the signaling flow is explained once more as follows. In step 1g-16, the source base station CU (1g-03) can generate conditional LTM execution conditions. The exact operation may vary depending on which of the methods described above is performed. That is, the source base station CU (1g-03) may generate all consecutive conditional LTM execution conditions, generate only some of them, or generate none at all. In the existing conditional handover, the source base station CU (1g-03) generated all execution conditions, but since the corresponding measurement value is based on Layer 3 measurement values, whereas in the case of LTM, it is based on Layer 1 measurement values, there may be a difference in the entity performing the operation. Furthermore, since LTM may also operate based on Layer 3 measurement values, the method for generating conditional LTM execution conditions described above may not be a single solution, but rather multiple methods may be applied simultaneously. In step 1g-17, the source base station CU (1g-03) transmits a message to each LTM candidate cell (1g-04, 1g-05) requesting a successive conditional LTM execution condition. This message is a message within the F1 interface and may be an existing UE Context Setup / UE Context Modification message, and the request may be executed together with a request for LTM-related settings. As previously explained, the information included in these messages may differ depending on which method for generating successive conditional LTM execution conditions described above is used. Refer to the descriptions for each method for detailed information included in each method.

[0200] Since this disclosure considers the generation and configuration of conditional LTM execution conditions necessary to support continuous conditional LTM in inter-CU, it additionally considers cases where LTM candidate cells exist within different CUs, in addition to the intra-CU operations of step 1g-15. The following steps 1g-20 through 1g-35 describe in detail the preparation steps for supporting continuous conditional LTM between different base stations, focusing particularly on the generation and transmission of execution conditions for continuous conditional LTM.

[0201] In step 1g-20, the source base station CU (1g-03) generates a message (Handover Request or new message) requesting configuration information for L1 / L2-based handover to the target base station (CU2; 1g-06) for an LTM candidate cell configuration request for an LTM neighbor cell (1g-07) of the inter-CU based on the measurement report received from the terminal (1g-01), and transmits it to the X2 interface. Subsequently, in step 1g-25, the target base station (CU2; 1g-06) generates a message (UE Context Setup Request or UE Context Modification Request) requesting configuration information for an L1 / L2-based handover for an LTM candidate cell (1g-07) belonging to the CU, transmits it to the F1 interface, and receives a message (UE Context Setup Response or UE Context Modification Response) responding with configuration information for an L1 / L2-based handover. The procedure refers to the LTM configuration preprocessing procedure of steps 1f-15 and 1g-15. Subsequently, in step 1g-30, the target base station (CU2; 1g-06) generates a message (Handover Response or a new response message) to the source base station CU (1g-03), including the LTM candidate configuration information transmitted by the LTM candidate cell (1g-07) belonging to the CU, and transmits it via the X2 interface. The content that can be newly added to the LTM configuration request message through the X2 interface in step 1g-30 is summarized as follows.

[0202] - Indicator for LTM execution

[0203] Additionally, an indicator indicating whether the request is for initial preparation, e.g., initiation, or for a modification request after the initial one.

[0204] - Device ID

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

[0206] - ID of the requesting candidate cell (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 above candidate cell list may be a list of candidate cells operated by all candidate CUs for the terminal, and

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

[0211] - Information on CSI resource configuration for LTM L1 measurements

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

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

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

[0215] - Continuous delivery or request of conditional LTM-related settings (refer to details below)

[0216] Execution condition request for conditional LTM (event-specific threshold request)

[0217] If execution conditions for conditional LTM are passed from the source CU, include the relevant information (event-specific thresholds)

[0218] Request for Security key related parameters

[0219] Request for multiple NCC (Next Hop Chaining Counter) values ​​applied when consecutive conditional LTM is performed: When a CU change occurs, a master key update, i.e., a security parameter update, is required, and since the NCC values ​​used at this time are needed, a request for this is made. Since consecutive conditional LTM can cause a CU change again even after a key change occurs once due to a CU change, it is necessary to provide multiple security keys considering consecutive LTM. In this embodiment, since MCG LTM is considered, NCC values ​​related to master key updates are requested.

[0220] Naturally, in addition to the information above, information previously used in HO request messages may also be included. You can refer to the table below for this.

[0221]

[0222]

[0223] In the LTM setting response message through the X2 interface of the above 1g-30 step, LTM-related setting information of the LTM target cell within the corresponding CU may be added.

[0224] - Includes CSI resource configuration in response to the requested CSI resource

[0225] - CSI reporting configuration information

[0226] 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 configurations applied are delivered as is.

[0227] - RACH configuration and lower layer setting information to be used in the relevant concerned cell

[0228] These information can be transmitted from the LTM candidate DU within the CU to the CU, written as settings required for RACH execution within the target cell configuration of the concerned cell, lower layer settings to be applied when moving to the cell, and / or reference settings including them, and later transmitted to the terminal.

[0229] In particular, some of the RACH settings can be used to include information on determining the Rach preamble index, Mask, and occasion in the cell switch command MAC CE described above.

[0230] Beam information (TCI state) to be used for each candidate

[0231] In this case, the meaning of use may include a beam linked to the RACH occasion during DL and / or UL synchronization and / or RACH execution, and / or a beam to be used for the first UL data transmission. If necessary, an indicator corresponding to each case may be accompanied to perform a cell switch.

[0232] In addition, the configuration information transmitted by the DU can be configured as complete configuration information that is applied after the handover is completed.

[0233] - An indicator indicating reference cell setting information and whether the above candidate cell setting is complete

[0234] - Response to configuration request for continuous conditional LTM (see details below)

[0235] Execution conditions for conditional LTM (event-specific thresholds), multiple thresholds may be included when considering consecutive conditional LTMs. That is, thresholds that consider events with other LTM candidate cells when the corresponding LTM candidate cell becomes a source cell may be included.

[0236] If the source CU transmits execution conditions for a conditional LTM, ACK information regarding that information may also be included. (Per event)

[0237] Security key related parameters

[0238] Multiple NCC (Next Hop Chaining Counter) values ​​applied when consecutive conditional LTM is performed (provided in the form of a list): When a CU change occurs, a master key update, i.e., a security parameter update, is required, and the NCC values ​​used at this time are provided. Since consecutive conditional LTM can cause a CU change again even after a key change has occurred once due to a CU change, it is necessary to provide multiple security keys considering consecutive LTM. In this embodiment, since MCG LTM is considered, NCC values ​​related to master key updates are provided.

[0239] What is to be emphasized in the above 1g-20 and 1g-25 steps is the procedure for requesting and transmitting execution conditions for a continuous conditional LTM between CUs, as in 1g-15.

[0240] - Method for requesting conditional LTM execution conditions between 1st CUs

[0241] Generate all consecutive conditional LTM execution conditions in the source CU and pass the generated execution conditions to other CUs.

[0242] CUs that receive requests for LTM candidate cells forward them to the LTM candidate cells (DUs) within their respective CUs, and use them as a reference for application if the corresponding LTM candidate cell later becomes a source cell. A procedure to request changes or rejections from the source CU can also be added if necessary.

[0243] The CU containing the LTM candidate cell transmits the aggregated information to the source CU (performed together when providing LTM-related settings)

[0244] - Method for requesting conditional LTM execution conditions between 2nd CUs

[0245] Generate the first conditional LTM execution condition in the source CU and request the next execution condition of the consecutive conditional LTM from other CUs.

[0246] CUs that receive requests for LTM candidate cells perform operations in 1g-20 on the DUs containing the LTM candidate cells within each CU to generate the next execution conditions for a successive conditional LTM, aggregate the relevant information, and transmit it to the source CU.

[0247] In other words, at that stage, the next execution condition procedure of the successive conditional LTM in the intra-CU is applied, and additionally, security information updates are performed.

[0248] Subsequently, in step 1g-35, source cell 1 (1g-02) can trigger the 1g-15 and 1g-20 procedures again based on the information of LTM-related candidate cells received from the target base station (1g-06). In addition, the 1g-30 procedure can be performed in response to this. The detailed procedures are summarized above, categorized by option.

[0249] In step 1g-40, Source Cell 1 (1g-02) collects all LTM-related settings received from LTM candidate cells and stores them in an RRCReconfiguration message transmitted to the terminal (1g-01), and transmits the corresponding RRC setting information to the terminal (1g-01). That is, pre-configuration information for the LTM candidate cells is transmitted to the terminal (1g-01). At this time, the Source Base Station CU (1g-03) may include the source cell's setting information and separate reference cell configuration information in the RRCReconfiguration message and transmit them. Upon receiving the RRCReconfiguration message, the terminal (1g-01) performs a procedure to decode and process the RRCReconfiguration message. The processing includes ASN.1 decoding of the received message, validity determination, and a method for storing and managing the setting content. Additionally, the terminal (1g-01) stores LTM setting information for each candidate cell decoded at this stage as complete setting information in the buffer (memory) of the terminal (1g-01), and at the same time, stores the received reference cell setting information together in the buffer (memory) of the terminal (1g-01) and manages it for the future. Furthermore, the present disclosure is characterized by including detailed settings for consecutive conditional LTMs, and the relevant settings may be transmitted to the terminal (1g-01) at the corresponding stage.

[0250] 1. RRC settings when consecutive conditional LTMs are applied

[0251] 2. Execution condition triggering continuous conditional LTM (event-based L1 measurement reporting settings, Best beam's L1-RSRP-based events described above, L1 filtering parameters described above)

[0252] 3. Configuration for securing Early TA and CG settings when supporting continuous conditional LTM, especially RACH-less

[0253] A. UE-based TA related settings

[0254] i. Provides LTM candidate cell information applied based on the UE-based TA terminal capability reported by the terminal.

[0255] ii. For example, add an indicator to the LTM candidate cell settings to specify a RACH-less conditional LTM, or provide cell information where UE-based TA is applied in the RACH-less conditional LTM above the LTM settings.

[0256] 1. Provide LTM candidate cell index in association with serving cell information (i.e., provide LTM candidate cell index to which UE-based TA can be applied per serving cell)

[0257] 2. Provides a group index that groups identical candidate cells to which UE-based TA applies, and if the group index is identical to the serving cell, UE-based TA is applied.

[0258] B. Early TA Related Settings

[0259] i. Early TA msg1 (msg2) resource configuration per LTM candidate cell for Early TA. That is, resource configuration for preamble transmission and resource configuration information that must be monitored to receive the corresponding preamble response.

[0260] ii. In other words, since the PDCCH order with RAR operation for Early TA is supported, configuration information for this is required.

[0261] C. Detailed Settings for RACH-less Conditional LTM Execution

[0262] i. Configured Grant (CG) Settings

[0263] 1. Allow the common use of resources used by the existing RACH-less LTM, or;

[0264] 2. Introduction of CG resource settings dedicated to RACH-less conditional LTM

[0265] 3. Frequency / time resources of the CG resource, period of the CG resource, number of repetitions or hold time for semi-static setting (e.g., using only resources up to the set time after the first valid resource), etc.

[0266] ii. TA Timer Settings

[0267] 1. A TA timer setting applied when the terminal acquires TA after transmitting a preamble according to the PDCCH order and receiving a RAR in response to that transmission in the Early TA procedure; this can be provided for each LTM candidate cell.

[0268] 2. Existing TA timer values ​​set for handover can be used commonly.

[0269] In step 1g-45, the terminal (1g-01) applies the received RRC settings (including continuous conditional LTM settings) and performs Layer 1 channel measurements for LTM candidate cells according to the settings. The L1 measurement resource may be an SSB or CSI-RS resource, and the terminal (1g-01) determines the operation by comparing it with the execution conditions of the conditional LTM. If L1 resource reporting and L3 resource reporting settings are set together with the conditional LTM settings, the terminal (1g-01) can independently perform L1 measurement and L3 channel measurement reporting in steps 1g-50 and 1g-55, respectively. In step 1g-60, if the L1 resource set for a specific LTM candidate cell satisfies the conditional LTM execution conditions (for example, if the beam performance of the candidate cell is better than the offset of the source cell's beam performance), the terminal (1g-01) attempts to change the cell by applying the conditional LTM to the corresponding LTM candidate cell. That is, in step 1g-65, a random access procedure is performed to the corresponding target cell (an LTM candidate cell that satisfies the conditions). After the random access procedure, in step 1g-70, the terminal (1g-01) performs a handover completion procedure with the target cell. This completion procedure may be a handover completion procedure for the LTM. This procedure may vary depending on the method of giving the handover completion instruction, and is a process of transmitting an RRCReconfiugrationComplete message and an ACK in response when the configuration of the target cell (1g-07) within the inter-CU is received at the RRC message level. Here, if a RACH-less handover procedure is introduced, uplink or downlink scheduling may be included in the handover completion ACK.

[0270] In addition, since this scenario considers the application to inter-CU, the target cell (DU, 1g-07) that receives the handover completion message in step 1g-80 can transmit the received message to the target CU (1g-06). At this time, the target cell (DU, 1g-07) can transmit the handover completion message received through the F1 interface as is, or it can transmit a newly processed message based on the received information. Subsequently, in step 1g-85, the target base station CU (1g-06) transmits information regarding the handover completion to the source base station CU (1g-03), and the source base station CU (1g-03) can transmit this to the source cell (1g-02) to instruct it to release the terminal context.

[0271] In addition, as described in step 1g-90, the embodiment of the present disclosure supports a subsequent conditional LTM operation. This means that the LTM setting information (settings for target candidate cells and reference cell setting information, etc.) received by the terminal (1g-01) in step 1g-40 is stored in the terminal (1g-01) as is, and the terminal (1g-01) continues to perform the LTM procedure unless the LTM setting information is changed / released / added through a separate RRC setting. If it is necessary to update the reference cell setting information, new RRC setting information is transmitted to the terminal (1g-01) to perform this. That is, the update of the reference cell setting information can be performed by re-triggering the procedure described in this drawing.

[0272] FIG. 1h is a diagram illustrating the overall operation for supporting continuous conditional SCG LTM operation in cells belonging to different base stations, as Embodiment 2 proposed in the present disclosure. For reference, the overall procedure and operation of this embodiment follow the entire procedure of FIG. 1ga and FIG. 1gb exactly, the difference being that the LTM candidate cell is a cell corresponding to a PSCell change. Therefore, in the following description of the drawings, parts common to FIG. 1ga and FIG. 1gb are omitted as much as possible, and only parts that differentiate this embodiment are additionally described.

[0273] In step 1h-15, a procedure to determine LTM candidate cells and request related settings for intra-CU conditional SCG LTM may be added. Unlike step 1g-15, this step can be initiated in two main ways.

[0274] - MN-initiated intra-SN SCG LTM: A method in which the source MN requests LTM candidate cells from the PSCell, and the source PSCell determines and requests SCG LTM candidate cells within the SN.

[0275] - SN-initiated intra-SN SCG LTM: A method in which the source SN (PSCell) determines SCG LTM candidate cells within the SN and requests each candidate cell.

[0276] In this stage, UE context setup and UE context modification procedures for the F1 interface may be performed. The requests and content regarding successive conditional LTM configuration may be identical to those in steps 1f-15 and 1g-15, and at least some parts may be modified to fit the SCG LTM. In particular, regarding the generation and transmission of execution conditions (event-specific thresholds) in successive conditional LTMs, which are primarily considered in this disclosure, the methods described in step 1g-15 may be applied as is. That is, the following procedure may be introduced. As mentioned earlier, since the following method can be applied to both L1-based and L3-based LTMs, both methods may be introduced simultaneously for L1-based and L3-based LTMs, respectively.

[0277] - Method to create the first execution condition

[0278] Generate execution conditions for successive conditional LTM for all LTM candidate cells in the source SN.

[0279] The above execution condition may be a threshold for L1-RSRP (or L1-SINR) and may have a different value for each LTM event. An LTM event may be one of the events described in step 1f-15. If multiple thresholds are required for an event, the threshold includes multiple thresholds.

[0280] To do this, CSI resource settings (L1 measurement resource settings) that can be set for source cells (DU) and LTM candidate cells within the SN must first be collected, and the CU generates a threshold for LTM events between the source cells and LTM candidate cells based on this information.

[0281] Considering consecutive conditional LTMs, the threshold setting must also generate execution conditions when each LTM candidate cell becomes a source cell. The CU repeats the above procedure for the case where each LTM candidate cell is a source cell to generate execution conditions and generates execution conditions consisting of a list of multiple thresholds. Alternatively, for each candidate cell, it generates and manages execution conditions (thresholds) when the cell is a source cell.

[0282] - Method for creating the second execution condition

[0283] Generate execution conditions for the first conditional LTM for the current source cell and LTM candidate cells in the source SN

[0284] Subsequently, the execution conditions for subsequent consecutive conditional LTMs are determined by each LTM candidate cell, and the determined execution conditions (thresholds) are transmitted to the source SN. This information may be transmitted to a separate IE, or it may be transmitted included in the LTM candidate cell configuration (RRCReconfiguration or CellGroupConfig).

[0285] The above execution condition may be a threshold for L1-RSRP (or L1-SINR) and may have a different value for each LTM event. An LTM event may be one of the events described in step 1f-15. If multiple thresholds are required for an event, the threshold includes multiple thresholds.

[0286] To this end, configurable CSI resource settings (L1 measurement resource settings) for source cells (DU) and LTM candidate cells within the corresponding CU must first be collected, and the CU must share this information with each LTM candidate cell. Based on this information, each LTM candidate cell generates a threshold for conditional LTM events with other LTM candidate cells when the LTM candidate cell becomes a source cell.

[0287] The conditional LTM execution condition (threshold) generated for each candidate cell is passed to the source CU.

[0288] - Method to create the third execution condition

[0289] Execution conditions for all consecutive conditional LTMs are determined by each LTM candidate cell, and the determined execution conditions (thresholds) are transmitted to the source SN. This information may be transmitted via a separate IE, or it may be included in the LTM candidate cell configuration (RRCReconfiguration or CellGroupConfig). Initial LTM execution conditions can be generated by the source cell (DU) and transmitted to the source CU.

[0290] The above execution condition may be a threshold for L1-RSRP (or L1-SINR) and may have a different value for each LTM event. An LTM event may be one of the events described in step 1f-15. If multiple thresholds are required for an event, the threshold includes multiple thresholds.

[0291] To this end, configurable CSI resource settings (L1 measurement resource settings) for source cells (DU) and LTM candidate cells within the corresponding CU must first be collected, and the CU must share this information with each LTM candidate cell. Based on this information, each LTM candidate cell generates a threshold for conditional LTM events with other LTM candidate cells when the LTM candidate cell becomes a source cell.

[0292] The conditional LTM execution condition (threshold) generated for each candidate cell is passed to the source CU.

[0293] Since this embodiment considers the creation and configuration of conditional LTM execution conditions necessary to support continuous conditional SCG LTM in inter-CU, it also considers cases where SCG LTM candidate cells exist within different CUs in addition to the intra-CU operation in step 1h-15. The following steps 1h-20 through 1h-35 describe in detail the preparation steps for supporting continuous conditional LTM between different base stations, focusing particularly on the creation and transmission of execution conditions for continuous conditional LTM.

[0294] In step 1h-20, the source base station CU (1h-03) generates a message (Handover Request or new message) requesting configuration information for L1 / L2-based handover to the target base station (CU2; 1h-06) for an LTM candidate cell configuration request for an LTM neighbor cell (1h-07) of the inter-CU based on a measurement report received from the terminal, and transmits it to the X2 interface. Subsequently, in step 1h-25, the target base station (CU2; 1h-06) generates a message (UE Context Setup Request or UE Context Modification Request) requesting configuration information for an L1 / L2-based handover for an LTM candidate cell (1h-07) belonging to the CU, transmits it to the F1 interface, and receives a message (UE Context Setup Response or UE Context Modification Response) responding with configuration information for an L1 / L2-based handover. The procedure refers to the LTM configuration preprocessing procedure of steps 1f-15, 1g-15, and 1h-15. Subsequently, in step 1h-30, the target base station (CU2; 1h-06) generates a message (Handover Response or a new response message) to the source base station CU (1h-03), including the LTM candidate configuration information transmitted by the LTM candidate cell (1h-07) belonging to the CU, and transmits it via the X2 interface. The information included in the LTM configuration request message via the X2 interface in step 1h-30 is identical to that described in 1g-30. In particular, the inclusion of execution condition information for the conditional LTM considered in this disclosure is identical, and the overall procedure for obtaining this information also follows the procedure in Example 1. The distinguishing feature of Example 2 included in the message is security-related update information.Unlike Example 1, in Example 2, since it handles SCG LTM, a PSCell key update procedure may be performed instead of a master key update procedure, and for this purpose, sk-counter values ​​applied whenever an inter-SN change to each SN is performed may be provided in the form of a list of multiple values. That is, a request for security information is made at step 1h-20, and in response to this, multiple sk-counter values ​​may be provided at step 1h-30.

[0295] Subsequently, in step 1h-35, the source cell (1h-02) can trigger the 1h-15 and 1h-20 procedures again based on the information of LTM-related candidate cells received from the target base station (1h-06). Additionally, the 1h-30 procedure can be performed in response to this. The detailed procedures are summarized above, categorized by option.

[0296] In step 1h-40, the source cell (1h-02) collects all LTM-related settings received from LTM candidate cells and stores them in an RRCReconfiguration message transmitted to the terminal (1h-01), and transmits the corresponding RRC setting information to the terminal (1h-01). That is, pre-configuration information for the LTM candidate cells is transmitted to the terminal (1h-01). At this time, the source base station CU (1h-03) may transmit the source cell's setting information along with separate reference cell configuration information. The terminal (1h-01) that receives the RRC message performs a procedure to decode and process the RRC message. The processing includes ASN.1 decoding of the received message, validity determination, and a method for storing and managing the setting content. Additionally, the terminal (1h-01) stores LTM setting information for each candidate cell decoded at this stage as complete setting information in the buffer (memory) of the terminal (1h-01), and at the same time, also stores the received reference cell setting information in the buffer (memory) of the terminal (1h-01) and manages it for the future. Furthermore, this embodiment is characterized by including detailed settings for consecutive conditional SCG LTMs, and the relevant settings may be transmitted to the terminal (1h-01) at the corresponding stage. Refer to FIG. 1ga and FIG. 1gb for the detailed settings.

[0297] In step 1h-45, the terminal (1h-01) applies the received RRC settings (including continuous conditional LTM settings) and performs Layer 1 channel measurements for LTM candidate cells according to the settings. The L1 measurement resource can be an SSB or CSI-RS resource, and the operation is determined by comparing it with the execution conditions of the conditional LTM. If L1 resource reporting and L3 resource reporting settings are set together with the conditional LTM settings, the terminal (1h-01) can independently perform L1 measurement and L3 channel measurement reporting in steps 1h-50 and 1h-55, respectively. In step 1h-60, if the L1 resource set for a specific LTM candidate cell satisfies the conditional LTM execution conditions (for example, if the beam performance of the candidate cell is better than the offset of the source cell's beam performance), the terminal (1h-01) attempts to change the cell by applying the conditional LTM to the corresponding LTM candidate cell. That is, at step 1h-65, the terminal (1h-01) performs a random access procedure to the corresponding target cell (an LTM candidate cell that satisfies the conditions). After the random access procedure, at step 1h-70, the terminal (1h-01) performs a handover completion procedure with the target cell. The completion procedure may be a handover completion procedure for the LTM. The procedure may vary depending on the method of giving the handover completion instruction, and is a process of transmitting an RRCReconfiugrationComplete message and an ACK in response when the configuration of the target cell (1h-07) within the inter-CU is received at the RRC message level. Here, if a RACH-less handover procedure is introduced, uplink or downlink scheduling may be included in the handover completion ACK.

[0298] In addition, since this scenario considers the application to inter-CU, the target cell (DU, 1h-07) that receives the handover completion message in step 1h-80 can transmit the received message to the target CU (1h-06). At this time, the target cell (DU, 1h-07) can transmit the handover completion message received through the F1 interface as is, or it can transmit a newly processed message based on the received information. Subsequently, in step 1h-85, the target base station CU (1h-06) transmits information regarding the handover completion to the source base station CU (1h-03), and the source base station CU (1h-03) can transmit this to the source cell (1h-02) to instruct it to release the terminal context.

[0299] Additionally, as described in step 1h-90, the embodiment of the present disclosure supports a subsequent conditional LTM operation. This means that the LTM configuration information (settings for target candidate cells and reference cell configuration information, etc.) received by the terminal (1h-01) in step 1h-40 is stored in the terminal (1h-01) as is, and the terminal (1h-01) continues to perform the LTM procedure unless the LTM configuration information is changed / released / added through a separate RRC setting. If it is necessary to update the reference cell configuration information, new RRC configuration information can be transmitted to the terminal (1h-01) to perform the update. That is, the update of the reference cell configuration information can be performed by re-triggering the procedure described in this drawing.

[0300] FIG. 1i is a drawing illustrating the entire terminal operation that performs a continuous conditional LTM, applied to an embodiment of the present disclosure.

[0301] In step 1i-05, the connected terminal can receive configuration information from surrounding cells that is applied after L1 / L2-based movement is instructed via an RRC reset message from the serving cell. For detailed configuration methods and content, refer to Figures 1f, 1g, and 1h. Additionally, although omitted prior to the above RRC configuration information, the terminal has received basic RRC configuration from the base station and performs the operation of reporting layer 3 measurements for surrounding cells. In particular, the configuration information from LTM candidate cells that is applied after an LTM cell change is instructed or after a conditional LTM is triggered, received in step 1i-05, is characterized by being transmitted with a delta configuration applied based on the configuration of a single reference cell. The terminal can know what the reference cell and the configuration information for the reference cell are, whether known in advance or instructed by the RRC configuration. Since the configurations for surrounding cells other than the reference cell share the reference cell configuration and the configurations that can be added thereto are transmitted, the signaling overhead is low. In the configuration of the above step, the terminal may receive configuration information related to resources and reporting for L1 measurement for LTM candidate cells. In particular, the present disclosure is characterized in that the configuration information for a continuous conditional LTM is determined through coordination between the source cell and the LTM candidate cells in the said step. In particular, the configuration information received in the said step may include information for determining execution conditions and configuration for a continuous conditional LTM.

[0302] In step 1i-10, 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 (i.e., 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 and store and manage the settings that are actually applied, or store and manage the received RRC settings as they are in the buffer.

[0303] In steps 1i-15, the terminal maintains a connection with the serving cell, performs an L1 measurement configured with SSB or CSI-RS resources associated with candidate surrounding cells, and reports the measurement results to the serving cell according to a pre-configured L1 measurement reporting method. Target cells configured with CSI-RS resources may be provided with settings distinct from cells configured with SSB resources. Alternatively, L1 resource settings provided by LTM candidate cells may be listed without distinction. Furthermore, L1 measurement settings for existing LTM and conditional LTM are applied commonly without separate distinction. However, for conditional LTM, event-based triggering conditions may be used for measurement reporting settings, which are transmitted to the terminal in conjunction with the L1 measurement settings. In this step, L1 / L2-based semi-persistent / aperiodic L1 channel measurements may be instructed. In this step, the base station may control L1 measurement resource reporting for LTM surrounding cells requiring measurement through RRC settings and L1 / L2 signaling. The terminal performs L1 measurement resource reporting according to the base station settings and instructions. In addition, independently of the operation, surrounding cells are measured according to the L3 measurement settings, and the measurement results are reported to the base station according to the L3 measurement reporting settings.

[0304] In step 1i-20, the terminal performs a successive conditional LTM when the conditional LTM is triggered based on the L1 measurement value for the LTM candidate cell. That is, in step 1h-25, it triggers a random access procedure to the target cell to perform a cell change to that cell. After the random access procedure is completed, it performs data transmission and reception with the target cell.

[0305] If the conditional LTM is not triggered based on the L1 measurement value in step 1h-35, the terminal maintains the connection with the current source cell and continues to perform data transmission and reception and evaluation for the conditional LTM.

[0306] FIG. 1j is a drawing illustrating base station operation applied to embodiments of the present disclosure.

[0307] In step 1j-05, the base station receives L3 measurement reports from the terminal and, based on the terminal's measurements regarding surrounding frequencies and cells, determines whether the terminal requires a handover and which cells are handover candidate cells. In step 1j-10, the base station requests configuration information for a continuous conditional LTM from surrounding cells and receives responses from those cells. In this step, the base station transmits configuration information for the current source cell and reference cell configuration information to the surrounding cells, and receives RRC configuration information with delta configuration applied based on the reference cell configuration information from the surrounding cells and LTM candidate cells. The procedures described in detail in Figures 1f, 1g, and 1h are included in this step, specifically regarding L1 measurement resources and reporting settings, and determining and transmitting execution conditions for a continuous conditional LTM. Although omitted in this figure, settings related to L3 measurement settings and basic RRC settings are provided prior to this step.

[0308] In step 1j-15, an RRC configuration message is transmitted to the terminal in the connected state, including the surrounding cell configuration information and L1 measurement resource / reporting settings received in step 1j-10. That is, configuration information from the surrounding cell that is applied after L1 / L2-based movement is instructed via the RRC reset message from the serving cell is transmitted. Detailed configuration methods and contents are described in detail in Figures 1f, 1g, and 1h.

[0309] Subsequently, in the 1j-20 stage, the base station may instruct L1 measurement reports of various methods via RRC or L1 / L2 signaling according to the L1 measurements and reports that it wishes to configure and trigger. For detailed methods, refer to the invention described above. Reports regarding L1 and L3 measurement values ​​are received from the terminal, wherein the L1 measurement value may be a measurement value for a non-serving cell that supports L1 / L2-based mobility. The serving cell may instruct a cell change by triggering a conditional LTM based on the received measurement results, or it may wait for a pre-configured conditional LTM triggering.

[0310] Subsequently, upon receiving a handover completion message from the target cell in step 1j-25, it is confirmed that the corresponding LTM operation has been successfully completed, and the terminal context is released accordingly. Additionally, if a handover failure report message containing information that the handover failed is received in step 1j-30, it indicates that the terminal attempted to reconnect to the serving cell after the handover failure. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Furthermore, the handover failure report message may be reported via a new MAC CE or uplink control signal (UCI; uplink control information). The information included in the handover failure report message may include the following information.

[0311] - An indicator that the handover failed due to an LTM failure

[0312] - Target cell information where LTM was attempted but failed: LTM cell configuration index or actual cell index (PCI; Physical Cell Index) information

[0313] The source base station can know that the LTM attempt failed and fell back to the cell through the handover failure message report.

[0314] FIG. 1k is a block diagram illustrating the internal structure of a terminal to which the present disclosure is applied.

[0315] Referring to the drawing above, the terminal includes an RF (Radio Frequency) processing unit (1k-10), a baseband processing unit (1k-20), a storage unit (1k-30), and a control unit (1k-40).

[0316] The RF processing unit (1k-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1k-10) up-converts the baseband signal provided by the baseband processing unit (1k-20) into an RF band signal and 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 (1k-10) 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 the drawing, the terminal may be equipped with multiple antennas. In addition, the RF processing unit (1k-10) may include multiple RF chains. Furthermore, the RF processing unit (1k-10) may perform beamforming. For the above beamforming, the RF processing unit (1k-10) can adjust the phase and magnitude of each of the signals transmitted and received through a plurality of antennas or antenna elements. In addition, the RF processing unit can perform MIMO and can receive multiple layers when performing MIMO operation.

[0317] The baseband processing unit (1k-20) 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 (1k-20) generates complex symbols by encoding and modulating the transmitted bit sequence. Additionally, when receiving data, the baseband processing unit (1k-20) restores the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (1k-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (1k-20) generates complex symbols by encoding and modulating the transmitted bit sequence, maps the complex symbols to subcarriers, and then constructs OFDM symbols through IFFT (inverse fast Fourier transform) operation and CP (cyclic prefix) insertion. Additionally, upon receiving data, the baseband processing unit (1k-20) divides the baseband signal provided by the RF processing unit (1k-10) 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.

[0318] The baseband processing unit (1k-20) and the RF processing unit (1k-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1k-20) and the RF processing unit (1k-10) 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 (1k-20) and the RF processing unit (1k-10) may include a plurality of communication modules to support a plurality of different wireless access technologies. Additionally, at least one of the baseband processing unit (1k-20) and the RF processing unit (1k-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), cellular network (e.g., LTE), etc. In addition, the above different frequency bands may include super high frequency (SHF) bands (e.g., 2 NRHz, NRHz) and millimeter wave (e.g., 60 GHz) bands.

[0319] The storage unit (1k-30) stores data such as basic programs, application programs, and configuration information for the operation of the terminal. In particular, the storage unit (1k-30) can store information related to a second connection node that performs wireless communication using a second wireless connection technology. Additionally, the storage unit (1k-30) provides the stored data upon the request of the control unit (1k-40).

[0320] The control unit (1k-40) controls the overall operations of the terminal. For example, the control unit (1k-40) transmits and receives signals through the baseband processing unit (1k-20) and the RF processing unit (1k-10). Additionally, the control unit (1k-40) writes and reads data to and from the storage unit (1k-40). To this end, the control unit (1k-40) may include at least one processor. For example, the control unit (1k-40) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as applications.

[0321] FIG. 11 is a block diagram showing the configuration of a base station according to the present disclosure.

[0322] As illustrated in the drawing above, the base station is configured to include an RF processing unit (11-10), a baseband processing unit (11-20), a backhaul communication unit (11-30), a storage unit (11-40), and a control unit (11-50).

[0323] The RF processing unit (1l-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1l-10) upconverts the baseband signal provided by the baseband processing unit (1l-20) into an RF band signal and transmits it through an antenna, and downconverts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1l-10) may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in the drawing, the first connection node may be equipped with multiple antennas. Additionally, the RF processing unit (1l-10) may include multiple RF chains. Furthermore, the RF processing unit (1l-10) may perform beamforming. For the above beamforming, the RF processing unit (1l-10) can adjust the phase and magnitude of each of the signals transmitted and received through a plurality of antennas or antenna elements. The RF processing unit can perform down-to-down MIMO operation by transmitting one or more layers.

[0324] The baseband processing unit (1l-20) 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 (1l-20) generates complex symbols by encoding and modulating the transmitted bit sequence. Additionally, when receiving data, the baseband processing unit (1l-20) restores the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (1l-10). For example, in the case of following the OFDM method, when transmitting data, the baseband processing unit (1l-20) 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 (1l-20) divides the baseband signal provided by the RF processing unit (1l-10) 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 (1l-20) and the RF processing unit (1l-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1l-20) and the RF processing unit (1l-10) may be referred to as a transmitting unit, a receiving unit, a transmitting and receiving unit, a communication unit, or a wireless communication unit.

[0325] The backhaul communication unit (1l-30) provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit (1l-30) converts a bit sequence transmitted from the main base station to another node, e.g., an auxiliary base station, a core network, etc., into a physical signal, and converts a physical signal received from the other node into a bit sequence.

[0326] The storage unit (1l-40) stores data such as basic programs, application programs, and configuration information for the operation of the main station. In particular, the storage unit (1l-40) can store information regarding bearers assigned to connected terminals, measurement results reported from connected terminals, etc. Additionally, the storage unit (1l-40) can store information serving as a criterion for determining whether to provide multiple connections to the terminal or to disconnect them. Furthermore, the storage unit (1l-40) provides the stored data upon the request of the control unit (1l-50).

[0327] The control unit (1l-50) controls the overall operations of the main station. For example, the control unit (1l-50) transmits and receives signals through the baseband processing unit (1l-20) and the RF processing unit (1l-10) or through the backhaul communication unit (1l-30). Additionally, the control unit (1l-50) writes and reads data to and from the storage unit (1l-40). To this end, the control unit (1l-50) may include at least one processor.

[0328] It should be noted that the aforementioned configuration diagrams, exemplary diagrams of control / data signal transmission methods, exemplary diagrams of operation procedures, and configuration diagrams are not intended to limit the scope of the rights of the present disclosure. That is, all components, entities, or steps of operation described in the embodiments of the present disclosure should not be interpreted as essential components for the implementation of the disclosure, and may be implemented within a scope that does not impair the essence of the disclosure even if only some components are included. Furthermore, each embodiment may be combined with one another as needed. For example, parts of the methods proposed in the present disclosure may be combined with one another to operate a base station and a terminal.

Claims

1. In a method performed by a DU (distributed unit) in a wireless communication system, A step of receiving a message from a CU (central unit) requesting an execution condition for a conditional LTM (L1 / L2 triggered mobility); If the above DU is associated with a source cell, Step of generating execution conditions for an initial conditional LTM; and A step of transmitting the execution conditions of the generated initial conditional LTM to the CU; and If the above DU is associated with an LTM candidate cell, Step of generating execution conditions for a successive conditional LTM; and A method comprising the step of transmitting the execution conditions of the generated successive conditional LTM to the CU.

2. In Paragraph 1, The execution condition of the initial conditional LTM or the execution condition of the successive conditional LTM is, A method comprising a threshold for L1-RSRP for each of one or more LTM events.

3. In Paragraph 1, A method in which a message requesting an execution condition for the above conditional LTM is received through the F1 interface.

4. In the case of Paragraph 1, where the DU is associated with a source cell, A method further comprising the step of transmitting RRC (radio resource control) setting information, including the execution conditions of the initial conditional LTM and the execution conditions of the successive conditional LTM, to the UE (user equipment).

5. In a method performed by a UE (user equipment) in a wireless communication system, A step of receiving RRC (radio resource control) configuration information from a DU (distributed unit) associated with a source cell; A step of performing a random access procedure to an LTM candidate cell based on the execution condition of an initial conditional LTM (L1 / L2 triggered mobility) regarding the source cell included in the above RRC setting information; and A method comprising the step of performing a successive conditional LTM based on the execution conditions of a successive conditional LTM regarding the LTM candidate cell included in the RRC setting information, when a handover to the LTM candidate cell is completed according to the execution of the above random access procedure.

6. In Paragraph 5, The execution condition of the initial conditional LTM or the execution condition of the successive conditional LTM is, A method comprising a threshold for L1-RSRP for each of one or more LTM events.

7. In Paragraph 5, The execution condition of the above initial conditional LTM is generated in the DU associated with the source cell, and The execution conditions of the above-mentioned successive conditional LTM are generated in the DU associated with the above-mentioned LTM candidate cell, a method.

8. In paragraph 5, the above RRC setting information is, A method comprising at least one of a UE-based TA (timing advance) related setting, an Early TA related setting, or a RACH (random access channel)-less conditional LTM setting.

9. In a DU (distributed unit) in a wireless communication system, Transmitter / receiver; and It includes at least one processor connected to the above-mentioned transmitting and receiving unit, and the at least one processor is: Receive a message from the CU (central unit) requesting execution conditions for conditional LTM (L1 / L2 triggered mobility), and If the above DU is associated with a source cell, Generates the execution conditions of the initial conditional LTM, and Transmit the execution conditions of the initial conditional LTM generated above to the CU, and If the above DU is associated with an LTM candidate cell, Generate execution conditions for a continuous conditional LTM, and A DU that transmits the execution conditions of the generated successive conditional LTM to the CU.

10. In Paragraph 9, The execution condition of the initial conditional LTM or the execution condition of the successive conditional LTM is, DU including a threshold for L1-RSRP for each of one or more LTM events.

11. In Paragraph 9, The message requesting execution conditions for the above conditional LTM is a DU received through the F1 interface.

12. In paragraph 9, the above at least one processor, A DU that transmits RRC (radio resource control) configuration information, including the execution conditions of the initial conditional LTM and the execution conditions of the successive conditional LTM, to a UE (user equipment) when the DU is associated with a source cell.

13. In the case of UE (user equipment) in a wireless communication system, Transmitter / receiver; and It includes at least one processor connected to the above-mentioned transmitting and receiving unit, and the at least one processor is: Receive RRC (radio resource control) configuration information from the DU (distributed unit) associated with the source cell, and Based on the execution conditions of the initial conditional LTM (L1 / L2 triggered mobility) regarding the source cell included in the above RRC configuration information, a random access procedure is performed on the LTM candidate cell, and A UE that performs a successive conditional LTM based on the execution conditions of a successive conditional LTM regarding the LTM candidate cell included in the RRC setting information, when a handover to the LTM candidate cell is completed in accordance with the execution of the above random access procedure.

14. In Paragraph 13, The execution condition of the initial conditional LTM or the execution condition of the successive conditional LTM is, UE including a threshold for L1-RSRP for each of one or more LTM events.

15. In Paragraph 13, The execution condition of the above initial conditional LTM is generated in the DU associated with the source cell, and The execution conditions of the above-mentioned continuous conditional LTM are UEs generated from the DU associated with the above-mentioned LTM candidate cell.

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