Method and apparatus for acquiring uplink synchronization of user equipment in wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method performed by a user equipment in a wireless communication system, according to an embodiment of the present disclosure, comprises the steps of: receiving, from a base station, a radio resource control (RRC) reconfiguration message comprising first configuration information, wherein the first configuration information is related to early time advance (TA) acquisition for random access channel (RACH)-less conditional L1 / L2 triggered mobility (LTM); performing L1 measurement on at least one candidate cell, and reporting a result of the L1 measurement to the base station; determining, on the basis of the L1 measurement and the first configuration information, at least one candidate cell that satisfies a first condition for the early TA acquisition; and transmitting a RACH preamble for early TA to the at least one candidate cell that satisfies the first condition.

Description

Method and device for acquiring uplink synchronization of a terminal in a wireless communication system

[0001] The present disclosure relates to the operation of a terminal and a base station in a wireless communication system, and to a method for acquiring uplink synchronization of a terminal and an apparatus capable of performing the same.

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in frequency bands below 6 GHz ('Sub 6 GHz'), such as 3.5 gigahertz (3.5 GHz), but also in ultra-high frequency bands called millimeter waves (mmWave), such as 28 GHz and 39 GHz ('Above 6 GHz'). In addition, for 6G mobile communication technology, which is referred to as a system beyond 5G, implementation in the terahertz 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 to guarantee coverage in the terahertz band of 6G mobile communication technology, Full Dimensional MIMO (FD-MIMO), array antennas, and large-scale antennas; metamaterial-based lenses and antennas to improve terahertz band signal coverage; high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM); and Reconfigurable Intelligent Surface (RIS) technology; 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 considers a method for supporting a conditional LTM (RACH (random access channel)-less conditional LTM) to reduce the interruption time with the source cell caused by an additional operation of pre-synchronizing uplink with a candidate target cell when conditional L1 / L2 triggered mobility (LTM (lower layer triggered mobility); L1 / L2-based mobility) of a terminal is performed.

[0009] A method performed by a terminal in a wireless communication system according to one embodiment of the present disclosure comprises: receiving a radio resource control (RRC) reconfiguration message from a base station that includes first configuration information—the first configuration information being related to obtaining an early time advance (TA) for a random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—; performing an L1 measurement for at least one candidate cell and reporting the result of the L1 measurement to the base station; determining at least one candidate cell that satisfies a first condition for obtaining the early TA based on the L1 measurement and the first configuration information; and transmitting a RACH preamble for the early TA to at least one candidate cell that satisfies the first condition.

[0010] A method performed by a base station in a wireless communication system comprises the steps of: transmitting a radio resource control (RRC) reconfiguration message containing first configuration information to a terminal—the first configuration information being related to the acquisition of an early time advance (TA) for a random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—; receiving from the terminal a result of an L1 measurement for at least one candidate cell; and receiving a RACH preamble for the early TA through at least one candidate cell satisfying a first condition for the acquisition of the early TA based on the L1 measurement and the first configuration information.

[0011] In a wireless communication system, a terminal comprises: a transceiver; and at least one processor connected to the transceiver, wherein the at least one processor receives a radio resource control (RRC) reconfiguration message from a base station that includes first configuration information—the first configuration information is related to obtaining an early time advance (TA) for a random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—performs an L1 measurement for at least one candidate cell, reports the result of the L1 measurement to the base station, determines at least one candidate cell that satisfies a first condition for obtaining the early TA based on the L1 measurement and the first configuration information, and is configured to transmit a RACH preamble for the early TA to at least one candidate cell that satisfies the first condition.

[0012] In a wireless communication system, a base station comprises: a transceiver; and at least one processor connected to the transceiver, wherein the at least one processor transmits a radio resource control (RRC) reconfiguration message containing first configuration information to a terminal—the first configuration information is related to the acquisition of an early time advance (TA) for a random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—; receives from the terminal a result of an L1 measurement for at least one candidate cell, and is configured to receive a RACH preamble for the early TA through at least one candidate cell that satisfies a first condition for the acquisition of the early TA based on the L1 measurement and the first configuration information.

[0013] In the terminal triggering uplink synchronization acquisition method for supporting RACH-less conditional LTM proposed in the present disclosure, when a terminal performs conditional LTM, a random access operation to synchronize uplink with a target cell can be omitted, thereby reducing the interruption time during cell change.

[0014] FIG. 1 is a drawing illustrating the structure of a next-generation mobile communication system according to one embodiment of the present disclosure.

[0015] FIG. 2 is a diagram showing the wireless protocol structure of a next-generation mobile communication system according to one embodiment of the present disclosure.

[0016] FIG. 3 is a drawing illustrating the structure of a next-generation mobile communication system according to one embodiment of the present disclosure.

[0017] FIG. 4 illustrates an example of an operation 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, and is related to inter-cell beam management according to one embodiment of the present disclosure.

[0018] FIGS. 5A and 5B are drawings illustrating an example of an operation in which a terminal according to one embodiment of the present disclosure changes a serving cell and a beam to a TRP of a cell that supports L1 / L2-based beam changing to transmit and receive data.

[0019] FIG. 6 is a diagram illustrating an example of overall operation for supporting conditional LTM operation in cells within the same CU according to one embodiment of the present disclosure.

[0020] FIGS. 7a and 7b illustrate an example of an overall operation in which a terminal itself performs an uplink TA acquisition procedure for an LTM candidate cell to support a conditional LTM operation without random access according to one embodiment of the present disclosure.

[0021] FIG. 8 is a diagram illustrating an example of a full terminal operation performing a conditional LTM without random access according to one embodiment of the present disclosure.

[0022] FIG. 9 is a drawing illustrating an example of base station operation according to one embodiment of the present disclosure.

[0023] FIG. 10 is a block diagram illustrating the internal structure of a terminal according to one embodiment of the present disclosure.

[0024] FIG. 11 is a block diagram showing the configuration of a base station according to one embodiment of the present disclosure.

[0025] The operating principle of the present invention will be explained in detail below with reference to the attached drawings.

[0026] In describing the present invention below, if it is determined that a detailed description of related known functions or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted.

[0027] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the size of each component does not entirely reflect its actual size. Identical or corresponding components in each drawing have been assigned the same reference number. Additionally, the terms described below are defined in consideration of their functions within the present invention, 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, and terms referring to various identification information are examples provided for the convenience of explanation. Accordingly, the present invention is not limited to the terms described below, and other terms referring to objects having equivalent technical meanings may be used.

[0028] For convenience of explanation below, the present invention uses terms and names defined in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard. However, the present invention is not limited by the above terms and names and can be applied in the same way to systems conforming to other standards.

[0029] Hereinafter, the base station is an entity that performs resource allocation for terminals and may be at least one of a gNode B, eNode B, Node B, BS (Base Station), wireless access unit, base station controller, or a node on a network. The terminal may include a UE (User Equipment), MS (Mobile Station), cellular phone, smartphone, computer, or a multimedia system capable of performing communication functions. In this disclosure, the Downlink (DL) refers to the wireless transmission path of a signal transmitted by a base station to a terminal, and the Uplink (UL) refers to the wireless transmission path of a signal transmitted by a terminal to a base station. Furthermore, while LTE, LTE-A systems, and 5th generation mobile communication technologies (5G, new radio, NR) may be described as examples below, embodiments of this disclosure may be applied to other communication systems having similar technical backgrounds or channel types. Additionally, this disclosure may be applied to other communication systems with some modifications made at the discretion of a person with skilled technical knowledge, provided that it does not deviate significantly from the scope of this disclosure.

[0030] At this point, it will be understood that each block of the process flow diagrams and combinations of the flow diagrams can be executed by computer program instructions. Since these computer program instructions can be loaded into the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, the instructions executed through the processor of the computer or other programmable data processing equipment create means to perform the functions described in the flow diagram block(s). Since these computer program instructions can also be stored in computer-available or computer-readable memory that can be directed toward the computer or other programmable data processing equipment to implement the function in a specific way, the instructions stored in computer-available or computer-readable memory can also produce a manufactured item containing instruction means to perform the function described in the flow diagram block(s). Since computer program instructions can be loaded onto a computer or other programmable data processing equipment, instructions that perform a series of operation steps on the computer or other programmable data processing equipment to create a process executed by the computer can also provide steps for executing the functions described in the flowchart block(s).

[0031] Additionally, each block may represent a module, segment, or part of code containing one or more executable instructions for executing a specific logical function(s). It should also be noted that in some alternative execution examples, the functions mentioned in the blocks may occur out of order. For example, two blocks described in succession may actually be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order according to their corresponding functions.

[0032] In this embodiment, the term "part" refers to a software or hardware component such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit), and the "part" performs certain roles. However, the meaning of "part" is not limited to software or hardware. The "part" may be configured to reside in an addressable storage medium or configured to run one or more processors. Thus, as an example, the "part" includes components such as software components, object-oriented software components, class components, and task components, as well as processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and "parts" may be combined into a smaller number of components and "parts" or further separated into additional components and "parts." In addition, the components and 'parts' may be implemented to utilize one or more CPUs within the device or secure multimedia card. Also, in the embodiments, 'parts' may include one or more processors.

[0033] Hereinafter, a / b may be understood as at least one of a or b.

[0034] FIG. 1 is a drawing illustrating the structure of a next-generation mobile communication system according to one embodiment of the present disclosure.

[0035] Referring to FIG. 1, as illustrated, the wireless access network of a next-generation mobile communication system may include a next-generation base station (New Radio Node B, hereinafter NR NB, 110) and an NR CN (New Radio Core Network, or NG CN: Next Generation Core Network, 105). A user terminal (New Radio User Equipment, hereinafter NR UE or terminal, 115) can connect to an external network through the NR NB (110) and the NR CN (105).

[0036] In FIG. 1, the NR NB (110) can correspond to the eNB (Evolved Node B) of the existing LTE system. The NR NB (110) is connected to the NR UE (115) via a radio channel (radio access, 120) and can provide a superior service compared to the existing Node B. In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device is required to collect status information such as the buffer status, available transmission power status, and channel status of the UEs and perform scheduling, and the NR NB (110) can handle this.

[0037] A single NR NB can typically control multiple cells. Additionally, to achieve ultra-high-speed data transmission compared to existing LTE, the NR NB can have a bandwidth greater than the existing maximum bandwidth, and beamforming technology can be additionally incorporated into the NR NB by using Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM) as a wireless access technology. Furthermore, the NR NB can apply an Adaptive Modulation and Coding (hereinafter referred to as AMC) method to determine the modulation scheme and channel coding rate according to the channel conditions of the terminal. The NR CN (105) can perform 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 next-generation mobile communication system can be interoperable with the existing LTE system, and the NR CN can be connected to the MME (125) via a network interface. The MME (120) can be connected to the existing base station eNB (130).

[0038] FIG. 2 is a diagram showing the wireless protocol structure of a next-generation mobile communication system according to one embodiment of the present disclosure.

[0039] Referring to FIG. 2, the wireless protocol of the next-generation mobile communication system consists of NR SDAP (service data adaptation protocol) (201, 245), NR PDCP (packet data convergence protocol) (205, 240), NR RLC (radio link control) (210, 235), and NR MAC (medium access control) (215, 230) at the terminal and the NR base station, respectively.

[0040] The main functions of NR SDAP (201, 245) may include at least one of the following functions.

[0041] - User data transfer function (transfer of user plane data)

[0042] - Mapping function between a QoS flow and a DRB for both DL and UL for uplink and downlink

[0043] - Marking QoS flow ID for uplink and downlink (marking QoS flow ID in both DL and UL packets)

[0044] - Function to map reflective QoS flow to data bearers for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

[0045] Regarding the above SDAP layer device, the terminal may receive a setting via an RRC message indicating whether to use the header of the SDAP layer device or the functions of the SDAP layer device for each PDCP layer device, bearer, or logical channel. Additionally, if the SDAP header is configured, 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 above SDAP header may include QoS flow ID information indicating QoS. The above QoS information may be used for data processing priority, scheduling information, etc., to support smooth service.

[0046] The main functions of NR PDCP (205, 240) may include at least one of the following functions.

[0047] - Header compression and decompression features (ROHC only)

[0048] - User data transfer function (Transfer of user data)

[0049] - Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0050] - Out-of-sequence delivery of upper layer PDUs

[0051] - Reordering function (PDCP PDU reordering for reception)

[0052] - Duplicate detection function (Duplicate detection of lower layer SDUs)

[0053] - Retransmission of PDCP SDUs

[0054] - Encryption and decryption functions (Ciphering and deciphering)

[0055] - Timer-based SDU discard in uplink.

[0056] The reordering function of the NR PDCP device may refer to a function that reorders PDCP PDUs received from a lower layer in order based on a PDCP SN (sequence number). The reordering function of the NR PDCP device may include a function that transmits data to an upper layer in the reordered order. Alternatively, the reordering function of the NR PDCP device may include at least one of a function that transmits immediately without considering the order, a function that records lost PDCP PDUs by reordering the order, a function that reports the status of lost PDCP PDUs to the transmitting side, and a function that requests retransmission of lost PDCP PDUs.

[0057] The main functions of NR RLC (210, 235) may include some of the following functions.

[0058] - Data transfer function (Transfer of upper layer PDUs)

[0059] - Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0060] - Out-of-sequence delivery of upper layer PDUs

[0061] - ARQ function (Error Correction through ARQ)

[0062] - Concatenation, segmentation, and reassembly functions of RLC SDUs

[0063] - Re-segmentation function (Re-segmentation of RLC data PDUs)

[0064] - Reordering function (Reordering of RLC data PDUs)

[0065] - Duplicate detection

[0066] - Error detection function (Protocol error detection)

[0067] - RLC SDU discard function

[0068] RLC re-establishment function

[0069] In the above, the in-sequence delivery function of the NR RLC device may refer to a function of delivering RLC SDUs received from a lower layer to an upper layer in order. The in-sequence delivery function of the NR RLC device may include at least one of the following: a function of reassembling and delivering the RLC SDUs when the original RLC SDU is received divided into multiple RLC SDUs; a function of rearranging the received RLC PDUs based on an RLC SN (sequence number) or PDCP SN (sequence number); and a function of recording lost RLC PDUs by rearranging the order.

[0070] The in-sequence delivery function of the above NR RLC device may include at least one of the following: a function of reporting the status of lost RLC PDUs to the transmitting side; a function of requesting retransmission of lost RLC PDUs; a function of delivering only the RLC SDUs prior to the lost RLC SDU in order to the upper layer if there is a lost RLC SDU; a function of delivering all RLC SDUs received before the timer started in order to the upper layer if a predetermined timer has expired even if there is a lost RLC SDU; or a function of delivering all RLC SDUs received up to now in order to the upper layer if a predetermined timer has expired even if there is a lost RLC SDU.

[0071] In addition, the RLC PDUs described above may be processed in the order they are received (regardless of the order of sequence numbers, in the order of arrival) and delivered to the PDCP device out of order (out-of-sequence delivery). In the case of segments, segments stored in a buffer or to be received later may be received, reconstructed into a single complete RLC PDU, processed, and delivered to the PDCP device. The NR RLC layer may not include a concatenation function, and this function may be performed by the NR MAC layer or replaced by the multiplexing function of the NR MAC layer.

[0072] The out-of-sequence delivery function of the above NR RLC device may refer to a function of delivering RLC SDUs received from a lower layer directly to an upper layer regardless of order. The out-of-sequence delivery function of the above NR RLC device may include at least one of the following: a function of reassembling and delivering RLC SDUs when a single RLC SDU is originally received divided into multiple RLC SDUs, and 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.

[0073] The NR MAC (215, 230) can be connected to multiple NR RLC layer devices configured in one terminal, and the main function of the NR MAC may include at least one of the following functions.

[0074] - Mapping function (Mapping between logical channels and transport channels)

[0075] - Multiplexing and demultiplexing functions (Multiplexing / demultiplexing of MAC SDUs)

[0076] - Scheduling information reporting function

[0077] - HARQ function (Error correction through HARQ)

[0078] - Priority handling between logical channels of one UE

[0079] - Priority handling between UEs by means of dynamic scheduling

[0080] - MBMS service identification function

[0081] - Transport format selection function

[0082] - Padding

[0083] The NR PHY layer (220, 225) can perform the operation of channel coding and modulating upper layer data, creating OFDM symbols and transmitting them to the wireless channel, or demodulating OFDM symbols received through the wireless channel and channel decoding them to transmit them to the upper layer.

[0084] FIG. 3 is a drawing illustrating the structure of another next-generation mobile communication system according to one embodiment of the present disclosure.

[0085] Referring to FIG. 3, a cell serviced by a beam-based NR gNB (305) may be composed of at least one TRP (transmission reception point, 310, 315, 320, 325, 330, 335, and 340). The TRP (310 to 340) represents a block that separates some functions of transmitting and receiving physical signals from an existing NR base station (eNB) and may be composed of multiple antennas.

[0086] The above NR gNB (305) can be represented as a CU (central unit) and the TRP as a DU (distributed unit). The functions of the above NR gNB (305) and TRP can be configured by separating each layer from the PDCP / RLC / MAC / PHY layers, such as 345. For example, the above TRP can perform the functions of the corresponding layer using only the PHY layer (e.g., 315, 325). For example, the above TRP can perform the functions of the corresponding layers using only the PHY layer and the MAC layer (310, 335, 340). For example, the above TRP can perform the functions of the corresponding layers using only the PHY layer, the MAC layer, and the RLC layer (320, 330). In particular, the TRP (310~340) can use beamforming technology to transmit and receive data by generating narrow beams in multiple directions using multiple transmitting and receiving antennas.

[0087] The user terminal (350) can connect to the NR gNB (305) and the external network through the TRP (310~340). The NR gNB (305) can support the connection between the terminals and the core network (CN), particularly the AMF / SMF (350), by collecting and scheduling status information such as the buffer status, available transmission power status, and channel status of the terminals to provide services to the users.

[0088] The TRP in the present disclosure is based on a structure (315, 325) that has only a PHY layer and can perform the functions of that layer.

[0089] FIG. 4 illustrates an example of an operation 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, and is related to inter-cell beam management according to one embodiment of the present disclosure.

[0090] FIG. 4 describes a case where multiple cells (TRP1-Cell1 (410), TRP2-Cell2 (415)) exist within a single DU (Distributed unit, 405), but the general content of the present disclosure is also applicable to inter-DU cases (each DU constitutes a single TRP-Cell).

[0091] Additionally, throughout the present disclosure, a non-serving cell (TRP 2- Cell 2) (415) that supports L1 / L2-based mobility (beam change and serving cell change) may be referred to interchangeably as a neighbor cell, a non-serving cell, an additional cell with the PCI different from the serving cell, etc.

[0092] In the legacy operation terminal beam change procedure (445), the terminal (420) is transmitting and receiving data in a connected state through the TRP 1 (410) of serving cell 1 and may be set to the optimal beam, TCI state 1 (425, 430). At this stage, the terminal may receive instructions for setting information for L3 channel measurement (RRM; radio resource management) for an additional cell (TRP 2-Cell 2 (415)) that has a different PCI from the serving cell through RRC setting information from the serving cell (410), and may perform an L3 measurement operation (446) for the corresponding frequency and cell.

[0093] Subsequently, the serving cell (TRP 1 - Cell 1 (410)) may direct a handover to the corresponding cell (TRP 2 - Cell 2 (415)) based on the reported measurement value (447), and once the handover is completed, additional RRC configuration information may be transmitted to the terminal (420) via TRP 2 - Cell 2 (415) (448). The RRC configuration information may include UL / DL configuration information and / or L1 measurement-related settings (CSI-RS measurement and reporting) in the corresponding cell, and in particular, may include TCI state configuration information for PDCCH and PDSCH channels. The terminal performs an L1 measurement according to the configuration (449), and the base station may update the TCI state via L1 / L2 signaling according to the measurement report (450). Here, the optimal beam TCI state 2 (440) may be directed. At this stage, the serving cell is Cell 1 until the handover, and Cell 2 serves after the handover. It becomes a cell. In other words, many procedures and time are required even after the handover until the optimal beam is indicated.

[0094] The improved beam changing technique (inter-cell beam management method) (455) proposed in the present disclosure is as follows. The terminal can transmit a beam setting associated with an additional cell (TRP 2-Cell 2 (415)) with a different PCI from the serving cell by referencing the serving cell through RRC setting information (456) from the serving cell (410). The part that associates the beam setting associated with the additional cell (TRP 2-Cell 2 (415)) with a different PCI from the serving cell, i.e., the TCI state corresponding to TRP2, may be applied by associating a new cell ID (Physical cell ID, PCI; additionalPCI-r17) as shown in Table 1.

[0095]

[0096] In addition, a unified TCI state framework can be applied for beam management between the cells as shown in Table 2. 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 set to either Joint UL / DL mode or separate UL / DL mode.

[0097]

[0098] Table 3 shows an example of a setting for the Joint UL / DL mode that is configured so that the UL and DL share the same TCI setting (in PDSCH-Config).

[0099]

[0100] Table 4 illustrates an example of a configuration for the Separate UL / DL mode, where 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).

[0101]

[0102] After the setting for TRP 2-Cell 2 is provided in the RRC connection state to serving cell 1, the terminal can perform an L1 measurement for the TRP 2-Cell 2 according to the setting and report the result to the serving cell (Cell 1 (410)) (457). If the serving cell determines, based on measurement results, that a change is necessary from the serving cell beam (TCI state 1 (425 and 430)) to a specific beam (TCI state 2 (435 and 440)) of TRP 2 (Cell 2 (415)), it may trigger a beam change and instruct the terminal via L1 / L2 signaling (458). Through this instruction, the terminal changes the beam to the specific beam (TCI state 2 (440)) of TRP 2 (Cell 2 (415)) and performs physical channel configuration and upper layer configuration operations associated with the configured beam. From this stage, the terminal remains connected to the serving cell (Cell 1 (410)), but can perform data transmission and reception using the channel link of TRP 2 (Cell 2 (415)) (e.g., receiving PDCCH / PDSCH and transmitting PUCCH / PUSCH). That is, transmission and reception on the common control channel is performed on the serving cell (Cell This is performed through 1(410)). Afterwards, the terminal performs an L3 measurement operation according to the measurement settings set in an independent serving cell (459), receives a handover command message from the serving base station (Cell 1), and can perform a serving cell change to Cell 2 (460).

[0103] Through the above cell-to-cell beam management method (455), the terminal performs data transmission and reception with a specific TRP 2 of Cell2 that supports L1 / L2-based mobility while connected to a serving cell, and can continue to use the beam even after handover.

[0104] Examples of RRC settings for the settings and operations related to the L1 measurement and report in step 457 above are shown in Table 5 below. These contents can be basically applied to the following embodiments of the present disclosure, and enhancement techniques may be added in future embodiments.

[0105] 1. L1 measurement settings (configured within CSI-ResourceConfig and ServingCellConfig in IE)

[0106] - At least one of the CSI-RS / SSB resources and resource pools (nzp-CSI-RS, csi-IM, csi-SSB) requiring measurement

[0107] - At least one of the CSI-RS / SSB resource settings requiring measurement (aperiodic, semi-persistent) and triggering settings

[0108] - When a CSI-RS resource references an SSB resource, it provides additional PCI information to enable L1 measurements from neighboring cells (up to 7 additional neighboring cells (PCI) can be added from a single serving cell).

[0109]

[0110] 2. L1 report settings (configured within the serving cell, ServingCellConfig, configured within IE)

[0111] - Report Type: Periodic Report, Semi-periodic Report with PUCCH, Semi-periodic Report with PUSCH, Aperiodic Report with PUSCH

[0112] - Report quantity

[0113] - Other settings required for reporting

[0114] FIGS. 5A and 5B are drawings illustrating an example of an operation in which a terminal according to one embodiment of the present disclosure changes a serving cell and a beam to a TRP of a cell that supports L1 / L2-based beam changing to transmit and receive data.

[0115] FIGS. 5a and 5b illustrate a case where multiple cells (TRP1-Cell1 (510, 550), TRP2-Cell2 (515, 555)) exist within a single DU (Distributed unit (505, 545)), but the general content of the present disclosure is also applicable to inter-DU within an intra-CU (each DU constitutes a single TRP-Cell).

[0116] Unlike the terminal beam changing procedure (445, 455) described in FIG. 4, the enhanced beam changing technique (530, 575) considered in the embodiments of FIG. 5 is as follows.

[0117] 1. Case 1 (530): After performing inter-cell beam management (change) operation, perform L1 / L2 handover

[0118] 2. Case 2 (575): Perform L1 / L2 handover immediately

[0119] FIG. 5a is a diagram illustrating the operation of case 1 above.

[0120] Referring to FIG. 5a, the terminal can receive common configuration and dedicated configuration information for additional cells (TRP 2-Cell 2, 515) with different serving cell PCIs from the serving cell (510) through RRC configuration information (531). That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon, and ServingCellConfig can be provided in advance. The configuration information can be provided in the form of pre-configuration in the RRC configuration and may include configuration information for multiple cells.

[0121] In addition, the above settings may be characterized by including at least one of the setting information (cell settings, bearer settings, security key settings, etc.) applied when the terminal moves to the corresponding cell (handover). Furthermore, the settings may include enhanced settings by referring to the unified TCI state settings and L1 measurement and report settings described in step 456. More specifically, the above setting information may include enhanced unified TCI state settings and L1 measurement and report settings for continuous LTM, and a detailed description will be provided later.

[0122] After the setting for TRP 2-Cell 2 (515) is provided to the serving cell 1 (510) in an RRC connection state, the terminal can perform an L1 measurement for the TRP 2-Cell 2 (515) according to the setting received in step 533 and report the result to the serving cell (Cell 1, 510). If the serving cell determines that a beam change is necessary from the serving cell beam (TCI state 1 (513 and 525)) to a specific beam (TCE state 2 (517 and 527)) of TRP 2 (Cell 2 (515)) based on the measurement result, it can trigger a beam change in step 535 and instruct the terminal via L1 / L2 signaling.

[0123] The terminal can change the beam to TRP 2 (Cell 2 (515)) through the corresponding instruction and transmit and receive data through TRP 2 (Cell 2 (515)). At this time, no serving cell change occurs, and the terminal remains connected to the serving cell (Cell 1 (510)) via RRC.

[0124] Afterward, the terminal can still perform an L1 measurement for TRP 2-Cell 2 (515) and report the result to the serving cell (Cell 1 (510)). If the L1 measurement reported by the terminal satisfies a triggering condition for a handover to TRP 2-Cell 2 (515) (detailed operation is described later), the serving cell (Cell 1 (510)) can instruct the terminal to perform a handover. The instruction may be an L1 / L2 message. That is, the MAC CE may contain an indicator instructing a handover.

[0125] FIG. 5b is a diagram illustrating the operation of case 2. The terminal can receive common and dedicated configuration information for an additional cell (TRP 2-Cell 2 (555)) that has a different PCI from the serving cell (550) through RRC configuration information from the serving cell (550) (576). That is, at least one of the ServingCellID or candidateCellID (cell ID associated with PCI) and configuration information corresponding to the candidate LTM cell may be provided in advance. The configuration information may be provided in the form of pre-configuration in the RRC configuration and may include configuration information for multiple cells. In addition, the configuration information may be characterized by including at least one of configuration information (cell configuration, bearer configuration, channel measurement configuration, etc.) that is applied when the terminal moves to the corresponding cell (handover). Furthermore, in the configuration, the unified TCI state configuration and settings related to L1 measurement and report described in step 456 may be modified and included to support consecutive LTMs. The L1 measurement and report and TCI state settings applicable to the present disclosure are described in detail below.

[0126] After the setting for TRP 2-Cell 2 (555) is provided to the serving cell 1 (550) in an RRC connection state, the terminal can perform an L1 measurement for the TRP 2-Cell 2 (555) according to the setting received in step 577 and report the result to the serving cell (Cell 1 (550)). If the serving cell (550) determines that a handover is required simultaneously with a beam change from the serving cell beam (TCI state 1 (553 and 565)) to a specific beam of TRP 2 (Cell 2 (555)) (TCI state 2 (557 and 567)) based on the measurement result, it can trigger the beam change and handover in step 578 and instruct the terminal via L1 / L2 signaling.

[0127] The terminal (560) can perform a handover simultaneously with changing the beam to TRP 2 (Cell 2 (555)) through the corresponding instruction and transmit and receive data through the TRP 2 (Cell 2, 555). At this time, the terminal can apply the configuration information for the target cell where the handover is performed, which was pre-configured in step 576. Depending on whether uplink synchronization is required in that step, the terminal may perform random access, or random access to the target cell may be omitted. Detailed operation will be described later.

[0128] In particular, as explained above, the present disclosure proposes a detailed method for setting the unified TCI state and L1 measurement and report for candidate cells surrounding an LTM to support continuous LTM. As explained in Fig. 4, in the existing ICBM, L1 measurement resource settings for cells requiring measurement can be provided in the CSI-ResourceConfig within the ServingCellConfig IE within the serving cell configuration. 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.

[0129] Detailed settings for L1 measurement settings and reporting settings for LTM can be provided as L1 measurement resource settings applied to LTM candidate cells as follows. To this end, during the preprocessing stage, it is necessary to share and determine L1 measurement resources and reporting settings for LTM among LTM candidate cells, and examples of setting information for this are shown in Tables 6, 7, 8, and 9.

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137] The present disclosure proposes 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), in particular a method for performing uplink synchronization in advance for LTM candidate cells. In particular, key features of the RACH-less conditional LTM in the present disclosure include a method for obtaining a TA (timing advance) in advance for LTM candidate cells, a method for performing the first transmission after RACH-less conditional LTM, and a method for managing stored TA values. FIG. 6 is a diagram illustrating the overall operation for supporting conditional LTM operations in cells within the same CU according to an embodiment of the present disclosure.

[0138] Although the conditional LTM operation within the same CU is described in Fig. 6, the operation can be extended and applied to the conditional LTM in the inter-CU as well.

[0139] Referring to FIG. 6, a terminal (601) in an RRC connection state performs data transmission and reception with source cell 1 (602) and can transmit Layer 3 measurement values ​​for serving cells and surrounding cells to the source base station (603) according to the Layer 3 measurement and report set in step 610. At this time, the actual measurement values ​​can be transmitted to the base station CU (603). This is because the base station CU (603) is responsible for processing RRC messages and determining mobility. Based on the measurement report received from the terminal (601), the base station CU (603) can generate a message (UE Context Setup Request or UE Context Modification Request) requesting configuration information for LTM from LTM candidate surrounding cells (604, 605) in step 615 and transmit it to the F1 interface.

[0140] Although candidate cells are indicated in association with DUs in Fig. 6, 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 a request for a conditional LTM and a request for 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 summarized as follows. At least one of the following message contents may be used as the composition of the message in step 615.

[0141] 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.)

[0142] - LTM candidate ID

[0143] - Mapping information between the LTM candidate ID and the corresponding cell ID

[0144] - Beam information to be used for each candidate (TCI state)

[0145] ■ 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 provided to perform a cell switch.

[0146] - RACH preamble index

[0147] - 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.

[0148] 2. Pre-configuration procedures for LTM and conditional LTM

[0149] - CSI resource request information for each candidate cell (requests for CSI-RS resources or SSB resources)

[0150] ■ It may be requested during the pre-configuration preprocessing section for LTM candidate cells.

[0151] ◆ Indicator for whether the request is for initial preparation, e.g., initiation, or for a modification request after the initial one

[0152] ■ 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.

[0153] ■ 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 2 steps.

[0154] In addition, it is possible to decide whether to request CSI-RS resources or SSB resources for each target candidate cell.

[0155] - 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, may use the same CSI resources as conditional LTM, but may also be transmitted with explicit distinction for conditional LTM.

[0156] ■ Based on the above CSI resource request information, provide L1 measurement settings for LTM transmitted from the corresponding candidate cell.

[0157] ■ 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.

[0158] - CSI report configuration considering the CSI resources of each of the above candidate cells

[0159] 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).

[0160] ■ 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. It is intended to be included in the target cell configuration for Subsequent LTM without providing separate L1 settings.

[0161] ■ Event-based L1 measurement reporting

[0162] You can define and use Best beam's L1-RSRP-based events.

[0163] ◆ For example, the following events may be introduced. That is, events are defined by comparing the serving cell beam and the surrounding cell beam, and L1 filtering values ​​such as threshold, beam offset, hysteresis, and time to trigger (TTT) may be introduced.

[0164] - Event A1beam: Beam of serving cell becomes better than absolute threshold;

[0165] - Event A2beam: Beam of serving cell becomes worse than absolute threshold;

[0166] - Event A3beam: Beam of candidate cell becomes amount of offset better than beam of serving cell;

[0167] - Event A4beam: Beam of candidate cell becomes better than absolute threshold;

[0168] - Event A5beam: Beam of serving cell becomes worse than absolute threshold1 AND Beam of candidate cell becomes better than another absolute threshold2.

[0169] The above event may also be used in 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.

[0170] ● For example, in the case of MCG LTM, the threshold used in Event A3beam can be provided as the execution condition of the conditional LTM.

[0171] Additionally, in the case of SCG LTM, the threshold used in Event A4beam can be provided as the execution condition of the conditional LTM.

[0172] The above conditions are determined by the coordination (F1 message) between the serving CU and the LTM candidate DU in step 615, 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.

[0173] - RACH configuration and lower layer setting information to be used in the concerned cell

[0174] ■ This 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.

[0175] ■ 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.

[0176] ■ Settings may be applied simultaneously to both LTM and Conditional LTM, but resources dedicated to Conditional LTM may also be configured separately.

[0177] That is, the request for the L1 measurement resource and reporting settings can be performed for each candidate cell (604, ..., 605), and although it is indicated as a single procedure at step 615 in FIG. 6, 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.

[0178] 1. Step 1: Request L1 measurement resource configuration from LTM candidate cells (604, ..., 605) (request SSB or CSI-RS resources)

[0179] 2. Step 2: LTM candidate cells (604, ..., 605) respond by setting up L1 measurement resources and transmit them to the source base station CU (603) (SSB or CSI-RS resource request). This procedure can be transmitted to the source base station via the F1 interface as a UE Context Setup Response message.

[0180] 3. Step 3: The source base station CU (603) transmits L1 measurement resource settings for continuous LTM and conditional LTM support to each candidate cell (604, ..., 605) through L1 measurement resource settings for each collected candidate cell (604, ..., 605). This procedure can be transmitted to the source base station via the F1 interface as a UE Context Modification Request message.

[0181] 4. Step 4: The source base station CU (603) requests and receives L1 measurement report setup from LTM candidate cells (604, ..., 605). This procedure can be transmitted to the source base station via the F1 interface as a UE Context Modification Response message.

[0182] 5. Step 5 (620): Transmit LTM and conditional LTM related settings to the terminal (601). The source base station may collect all LTM related settings received from LTM candidate cells (604, ..., 605) and store them in an RRCReconfiguration message transmitted to the terminal (601), and transmit the corresponding RRC setting information to the terminal (601). That is, pre-configuration information for the LTM candidate cells (604, ..., 605) may be transmitted to the terminal (601). 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.

[0183] At this time, the source base station CU (603) may include and transmit the source cell configuration information and separate reference cell configuration information. The reference cell configuration information transmitted by the source base station CU (603) to each candidate cell (604, ..., 605) may be a common configuration that can be applied to multiple target candidate cells in order to reduce signaling overhead when target candidate cells provide configuration information for LTM, and may include measurement configuration, bearer configuration, or, if the cells belong to the same CellGroup, configurations set at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.).

[0184] Alternatively, if the source base station CU (603) has a procedure to roughly know or know the configuration information for each candidate cell (604, ..., 605), the reference cell configuration may be determined through a separate procedure to obtain reference cell configuration information.

[0185] The purpose of the source base station CU (603) transmitting the reference cell settings to each candidate cell (604, ..., 605) is to allow each candidate cell (604, ..., 605) to transmit only the additional setting information based on the reference cell settings to the source base station CU (603) so that a delta configuration (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) can be applied. This is subsequently transmitted to the terminal (601) as is, thereby reducing the signaling of RRC messages transmitted to the terminal (601). Additionally, when the source base station CU (603) transmits the reference cell settings to each candidate cell (604, 605), this can be omitted, and in this case, the candidate cell settings can be provided as complete RRC settings.

[0186] In step 620, the source cell (602) can receive and transmit to the terminal (601) an RRC message generated by the base station CU (603) based on configuration information received from each candidate cell (604, ..., 605). 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 executed. Detailed configuration information can be referenced from the information received from each LTM candidate cell in step 615.

[0187] A terminal (601) that receives the RRC message may perform a procedure to decode and process the RRC message. The processing may include ASN.1 decoding of the received message, validation, and a method for storing and managing the configuration details. Additionally, the terminal (601) may store the LTM configuration information for each candidate cell decoded at this stage as complete configuration information in the terminal's (601) buffer (memory), and at the same time, store the received reference cell configuration information in the terminal's (601) buffer (memory) as well, and manage it for future use.

[0188] In step 625, the base station CU (603) may transmit a MAC CE that enables semi-persistent L1 reporting or a DCI that enables aperiodic L1 reporting to the terminal (601), and the terminal (601) receives this and performs L1 (Layer 1) measurement and reporting for each candidate surrounding cell in step 630, and may perform semi-persistent / aperiodic L1 measurement reporting depending on the setting. Subsequently, when a MAC CE that disables semi-persistent L1 reporting is received, semi-persistent L1 measurement and reporting may be terminated.

[0189] In step 620, the terminal (601) that receives the conditional LTM setting from the base station CU (603) can evaluate the L1 measurement for the conditional LTM in step 635. That is, it checks the execution conditions for the set conditional LTM, and if the conditions are satisfied (if the event-based L1 measurement reporting conditions are satisfied), the terminal (601) can determine the conditional LTM to the LTM candidate cell that satisfies the conditions. FIG. 6 describes the operation of a conditional LTM that performs random access.

[0190] In step 640, the terminal (601) applies the RRC configuration information of the LTM candidate cell (target cell where the conditional LTM is determined) configured in step 620, and can perform a random access procedure on the target cell (604) through the random access resources provided by the configuration. Through the random access, uplink and downlink synchronization can be achieved, and the handover procedure for the cell can be completed. This may be the conditional LTM completion procedure. The 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 the procedure. If the handover is successful, data transmission and reception with the cell is performed, and the RRC connection procedure service can be performed.

[0191] Additionally, the embodiment of the present disclosure may 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 (601) in step 620 is stored in the terminal (601) as is, and the terminal (601) continues to perform the conditional 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 can be transmitted to the terminal (601) to perform this. That is, the procedure described in FIG. 6 can be triggered again to be performed.

[0192] That is, if the terminal (601) receives reference cell setting information in step 620, it stores it in the terminal (601) buffer so that, unless there is an update to a separate setting, the setting can continue to be used as reference cell setting information even after LTM execution (step 640) (i.e., the reference cell setting and conditional LTM candidate setting values ​​stored in the continuous conditional LTM can be applied).

[0193] In step 645, if the conditional LTM procedure fails (e.g., RLF, random access failure, T304 timer completion, etc.), the terminal (601) may maintain the LTM settings configured in step 650 and fall back to the source cell. If the fallback to the source cell fails, the terminal (601) may perform an RRC re-establishment procedure, and if cell selection occurs, and the selected cell is an LTM candidate cell, the terminal may apply the LTM settings and perform a connection procedure. In this case, only random access-based LTM operation may be supported.

[0194] FIGS. 7a and 7b illustrate an example of an overall operation in which a terminal itself performs an uplink TA acquisition procedure for an LTM candidate cell to support a conditional LTM operation without random access according to one embodiment of the present disclosure.

[0195] Although Figures 7a and 7b illustrate conditional LTM operation within the same CU, the operation can be extended and applied to conditional LTM between CUs. In this case, a procedure for exchanging LTM setting information through an interface (Xn) between base stations may be added.

[0196] The features of the embodiments illustrated in FIGS. 7a and 7b allow for the consideration of the following three options for supporting a conditional LTM (RACH-less conditional LTM) without random access.

[0197] - How to obtain the 1st TA

[0198] ■ The source cell instructs the terminal to transmit a RACH preamble for an early TA via a PDCCH order

[0199] ■ The terminal sends a RACH prompt for the pre-configured early TA transmission to the designated LTM candidate cell.

[0200] ■ Receive the Random Access Response (RAR) to the RACH preamble of the Early TA procedure, acquire the TA for the corresponding cell, and start the TA timer.

[0201] ■ If conditional LTM is triggered while the TA timer is running, apply TA to the corresponding cell and perform RACH-less CLTM.

[0202] - How to obtain the 2nd TA

[0203] ■ Through RRC settings, determine whether to apply UE-based TA to each LTM candidate cell and share same-group information (apply UE-based TA operation when performing LTM with cells within the same group ID)

[0204] ■ When conditional LTM is triggered and the terminal changes to the corresponding target cell, it determines whether to apply UE-based TA; if the cell is eligible for UE-based TA, it applies TA to that cell and performs RACH-less CLTM.

[0205] - How to obtain the 3rd TA:

[0206] ■ Through RRC settings, provide activation indicators and related settings (thresholds) regarding how the terminal itself triggers the procedure for early TA during conditional LTM for each LTM candidate cell.

[0207] ◆ Method for setting the first threshold

[0208] ● Provide a threshold value, and if the L1 measurement result (measurement value, or signal strength) for an LTM candidate cell is better than the L1 resource signal strength of the source cell by the threshold value (or better than the threshold value of a set L1-based LTM condition), the terminal transmits a RACH pre-set early TA transmission to the candidate cell. In one embodiment, after transmitting the RACH pre-set early TA transmission, the terminal may then perform a RACH-less conditional LTM cell change.

[0209] ◆ Method for setting the second threshold

[0210] ● Provides two thresholds

[0211] ▶ Threshold for Terminal Triggering Early TA Transmission: If the threshold is satisfied (if the L1 measurement result for the LTM candidate cell is better than the L1 resource signal strength of the source cell by the threshold (or better than the threshold of the configured L1-based LTM condition)), the terminal transmits a pre-configured RACH preamble for early TA transmission to the corresponding candidate cell.

[0212] ▶ Threshold for conditional LTM triggering: If the threshold is satisfied, and the L1 measurement result for the LTM candidate cell is better than the L1 resource signal strength of the source cell by the threshold amount (or better than the threshold of the configured L1-based LTM condition), the terminal performs conditional LTM to that cell (performs a cell change).

[0213] ■ Receive the Random Access Response (RAR) to the RACH preamble of the Early TA procedure, acquire the TA for the corresponding cell, and start the TA timer.

[0214] ◆ A new RAR monitoring window may be introduced at this stage

[0215] ◆ This is a method for a terminal to regulate data communication interruption with the current source cell for receiving RAR from a specific LTM candidate cell.

[0216] ◆ If a RAR is not received within the RAR monitoring window, the terminal considers the early TA procedure for the corresponding cell to have failed and stops RAR monitoring.

[0217] ■ When a RAR is received within the RAR monitoring window, apply the TA value specified by the RAR and perform RACH-less CLTM to the corresponding cell.

[0218] ■ RAR Monitoring: When receiving RAR outside the window, perform random access-based CLTM

[0219] ■ If the terminal is in the process of obtaining an early TA for one LTM candidate cell, that is, waiting for RAR reception from the LTM candidate cell, it does not simultaneously obtain an early TA for another LTM candidate cell.

[0220] That is, if there is an early TA acquisition procedure for a RACH-less conditional LTM in progress at the terminal, the terminal does not send a RACH preamble to that cell even if the early TA condition for another LTM candidate cell is satisfied. If conditional LTM triggering occurs, a random access-based CLTM can be performed on that cell.

[0221] ■ In addition, if RAR monitoring of an LTM candidate cell is possible without interruption of the source cell due to the terminal's capability, and such capability is reported as the terminal's RF capability, the terminal can perform RAR monitoring of the LTM candidate cell without interruption of the source cell. Additionally, depending on the terminal's capability, simultaneous execution of early TA procedures for multiple LTM candidate cells may also be possible. In this case, the terminal may report the number of early TA candidate cells that can be executed simultaneously or provide band and frequency information where the relevant operation is possible.

[0222] ■ Since the above early TA procedure, RACH preamble transmission, and RAR reception may cause interruption in the source cell, the base station may set a separate gap to perform these procedures during that period. This may involve reusing an existing measurement gap or providing a new gap for LTM candidate cells or per frequency / band. If such a gap is provided, the terminal may trigger the relevant procedure after waiting until the period during which the gap is valid, even if the early TA condition for conditional LTM is satisfied.

[0223] Figures 7a and 7b propose a detailed operation and procedure for a terminal to initiate a procedure for obtaining an early TA (third TA acquisition method) to an LTM candidate cell in order to obtain an uplink TA (timing advance) on its own.

[0224] A terminal (701) in an RRC connection state can transmit and receive data with source cell 1 (702) and, according to the Layer 3 measurement and report set in step 710, transmit Layer 3 measurement values ​​for the serving cell and surrounding cells to the source base station (703). In one embodiment, the actual measurement values ​​can be transmitted to the base station CU (703). This is because the base station CU (703) is responsible for processing RRC messages and determining mobility. In one embodiment, the base station CU (703) can generate a message (UE Context Setup Request or UE Context Modification Request) requesting configuration information for LTM from LTM candidate surrounding cells (704, 705) in step 715 according to the measurement report received from the terminal (701), and transmit it to the F1 interface.

[0225] Although candidate cells are indicated in association with DUs in FIGS. 7a and 7b, in one embodiment, a candidate cell and a DU may have a 1:1 mapping, or multiple candidate cells may be included in a single DU. In one embodiment, the message requesting the LTM configuration information may include a request to surrounding cells to confirm that they have been determined as LTM candidate cells, as well as a request for a conditional LTM and a request for configuration information. That is, a procedure (step 715) for requesting RRC configuration information applied when an L1 / L2-based handover is performed to the cell may be included. In one embodiment, the information that may be included in the message is the same as that described in step 615 of FIG. 6, and FIGS. 7a and 7b describe additional information required in step 715 to support a RACH-less conditional LTM, in addition to what is described in step 615 of FIG. 6.

[0226] - Information on early TA acquisition (for conditional LTM), application of UE-based TA, and related configuration settings for each candidate cell

[0227] ■ Preamble Resource Information for Early TA

[0228] ■ Indicator to distinguish whether early TA is supported in RACH-less conditional LTM

[0229] ■ Threshold for early TA in RACH-less conditional LTM (one or two threshold values ​​depending on the threshold setting method above)

[0230] ■ RAR Window Settings (Time or symbol / slot level settings)

[0231] ■ TA Timer Information (TA timer information exclusive to Conditional LTM: A timer that determines the validity of a TA after it is acquired; if this timer expires, the acquired TA is no longer valid)

[0232] - Event-based L1 measurement reporting

[0233] You can define and use Best beam's L1-RSRP-based events.

[0234] ■ As an 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.

[0235] -Event LTM2: Beam of serving cell becomes worse than absolute threshold;

[0236] -Event LTM3: Beam of candidate cell becomes amount of offset better than beam of serving cell;

[0237] -Event LTM4: Beam of candidate cell becomes better than absolute threshold;

[0238] -Event LTM5: Beam of serving cell becomes worse than absolute threshold1 AND Beam of candidate cell becomes better than another absolute threshold2.

[0239] ■ The above event may also be used for conditions that trigger 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.

[0240] ■ The above conditions are determined by coordination between the serving CU (703) and the LTM candidate DU in step 715, and the serving CU (703) can determine the event conditions for triggering the LTM provided by the LTM candidate cell and the L1 filtering value and transmit them to the terminal (701).

[0241] That is, the request for the corresponding L1 measurement resource and reporting settings can be performed for each candidate cell (704, ..., 705), and although it is illustrated as a single procedure of step 715 in FIGS. 7a and 7b, the step can be applied to multiple procedures. The multiple procedures that can be performed for L1 measurement resources and reporting, and RACH-less conditional LTM settings are as follows.

[0242] 1. Step 1: Request L1 measurement resource configuration from LTM candidate cells (704, ..., 705) (Request SSB or CSI-RS resources)

[0243] 2. Step 2: LTM candidate cells (704, ..., 705) respond by setting up L1 measurement resources and transmit them to the source base station CU (703) (SSB or CSI-RS resource request). This procedure can be transmitted to the source base station via the F1 interface as a UE Context Setup Response message.

[0244] 3. Step 3: The source base station CU (703) transmits L1 measurement resource settings for continuous LTM and RACH-less conditional LTM support to each candidate cell through L1 measurement resource settings for each collected candidate cell (704, ..., 705). This procedure may be transmitted to the source base station via the F1 interface as a UE Context Modification Request message. This step includes a request for configuration information related to early TA and UE-based TA for RACH-less conditional LTM.

[0245] 4. Step 4: The source base station CU (703) requests and receives L1 measurement report settings from LTM candidate cells (704, ..., 705). The procedure, including early TA and UE-based TA setting information for RACH-less conditional LTM, can be transmitted to the source base station via the F1 interface as a UE Context Modification Response message.

[0246] 5. Step 5 (720): Transmit LTM and conditional LTM related settings to the terminal (701). The source base station may collect all LTM related settings received from LTM candidate cells (704, ..., 705) and store them in an RRCReconfiguration message transmitted to the terminal (701), and transmit the corresponding RRC setting information to the terminal (701). That is, pre-configuration information for the LTM candidate cells (704, ..., 705) may be transmitted to the terminal (701). 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 applied when executed. In addition, the present drawing is characterized by including early TA and UE-based TA related setting information for RACH-less conditional LTM.

[0247] In one embodiment, the source base station CU (703) may include and transmit the source cell configuration information and separate reference cell configuration information. In one embodiment, the reference cell configuration information transmitted by the source base station CU (703) to each candidate cell (704, ..., 705) 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, and may include at least one of a measurement configuration, a bearer configuration, or a configuration configured at the CellGroup level if the cells belong to the same CellGroup (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.). In one embodiment, if the source base station CU (703) has a procedure to roughly know or know the configuration information for each candidate cell (704, 705), the reference cell configuration may be determined through a separate procedure to obtain the reference cell configuration information.

[0248] The purpose of the source base station CU (703) transmitting the reference cell settings to each candidate cell (704, ..., 705) is to ensure that each candidate cell transmits only the additional setting information based on the reference cell settings to the source base station CU (703), 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 (701) as is, thereby reducing the signaling of RRC messages transmitted to the terminal (701). Additionally, when the source base station CU (703) transmits the reference cell settings to each candidate cell (704, ..., 705), this can be omitted, in which case the candidate cell settings can be provided as complete RRC settings.

[0249] In step 720, the source cell (702) can receive and transmit to the terminal (701) an RRC message generated by the base station CU (703) based on configuration information received from each candidate cell (704, ..., 705). In one embodiment, the terminal (701) that receives the RRC message can perform a procedure to decode and process the RRC message. The processing may include ASN.1 decoding of the received message, validity determination, and a method for storing and managing configuration content. Additionally, the terminal (701) can store the LTM configuration information for each candidate cell (704, ..., 705) decoded in this step as complete configuration information in the terminal (701)'s buffer (memory), and at the same time, store the received reference cell configuration information together in the terminal (701)'s buffer (memory) and manage it for future use. Additionally, the present disclosure is characterized by including detailed settings for a RACH-less conditional LTM, and the relevant settings may be transmitted to the terminal (701) in step 720. The relevant settings transmitted to the terminal (701) in step 720 may include at least one of the following settings.

[0250] 1. RRC settings when RACH-less conditional LTM is applied

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

[0252] 3. Configuration for Securing Early TA for RACH-less Conditional LTM and CG Configuration

[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 settings per LTM candidate cell for Early TA. That is, resource settings for preamble transmission and information on resource settings that must be monitored to receive the corresponding preamble response (RAR window related settings (provided as time, or number of symbols / slots)

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

[0261] iii. For detailed operation, check the contents of this drawing above.

[0262] C. Detailed Settings for RACH-less Conditional LTM Execution

[0263] i. Configured Grant (CG) Settings

[0264] 1) Allow the common use of resources used by the existing RACH-less LTM, or;

[0265] 2) Introduce CG resource settings dedicated to RACH-less conditional LTM

[0266] 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.

[0267] ii. TA Timer Settings

[0268] 1) A TA timer setting applied when the terminal acquires TA after transmitting a preamble according to the PDCCH order in the Early TA procedure and receiving a RAR in response to that transmission; this can be provided for each LTM candidate cell (or a common TA timer applicable to all candidate cells may be provided).

[0269] 2) Existing TA timer values ​​set for handover can be used commonly.

[0270] 3) If a conditional LTM is triggered within the valid time period of the corresponding TA timer, the terminal can perform a RACH-less LTM operation by applying a valid TA to the cell.

[0271] In step 725, the base station may transmit to the terminal (701) a MAC CE that enables semi-persistent L1 reporting or a DCI that enables aperiodic L1 reporting, and the terminal (701) receives this and performs L1 (Layer 1) measurement and reporting for each candidate surrounding cell (704, ..., 705) in step 730, and may perform semi-persistent / aperiodic L1 measurement reporting according to the settings. Subsequently, upon receiving a MAC CE that disables semi-persistent L1 reporting, the semi-persistent L1 measurement and reporting may be terminated. In step 730, the terminal (701) may perform event-based LTM L1 measurement according to the RRC settings received in step 720 and evaluate the measurement results. Additionally, in step 735, the terminal (701) may report the measured L1 / L3 measurement values ​​to the base station according to the settings.

[0272] In step 740, the terminal (701) compares the L1 measurement value for conditional LTM with a preset conditional LTM execution condition, and if the condition is satisfied, it can operate according to the threshold setting method.

[0273] That is, in the case of the first threshold setting method, when the first threshold is satisfied, the terminal (701) can perform an early TA acquisition procedure on the corresponding LTM candidate cell and then perform a RACH-less conditional LTM cell change as soon as the TA is acquired. If the TA acquisition fails during the period, a random access-based conditional LTM cell change operation can be performed.

[0274] On the other hand, in the case of the second threshold setting method, if the terminal (701) satisfies the condition for the first threshold, it can perform an early TA acquisition procedure on the corresponding LTM candidate cell and then wait for a conditional LTM procedure while checking the condition for the second threshold. The entire operation is described in detail as follows.

[0275] If the terminal (701) satisfies the first threshold condition for RACH-less conditional LTM, in step 745, it may transmit a preset RACH preamble to the LTM candidate cell that satisfies the condition to obtain an early TA. After transmitting the said preamble, the terminal (701) activates a preset RAR window related timer (747) and waits for the reception of a RAR containing TA information for the cell within the RAR window (747), and in step 750, receives a RAR containing TA information for the cell.

[0276] When a TA is obtained via RAR in step 755, the terminal (701) can run a TA timer for the corresponding LTM candidate cell. When a conditional LTM is triggered within the valid time of the TA timer (760), the terminal (701) can perform a RACH-less LTM operation by applying a valid TA to the cell. Performing a RACH-less conditional LTM cell change may mean the transmission of the first MAC PDU to the target cell in step 765. Here, the first MAC PDU may include an RRCReconfigurationComplete message regarding RRC configuration information (RRCReconfiguration message) previously received from the target cell.

[0277] In particular, a feature of the present disclosure is that the early TA acquisition procedure is not a method in which the base station directs it via a PDCCH order, but rather one in which the terminal can trigger it itself when specific conditions are satisfied. Furthermore, in the early TA of the existing LTM, the procedure from the terminal's perspective is completed when the terminal transmits the preamble, and subsequently, it is determined whether the TA value is included in the LTM cell change MAC CE, and subsequent RACH-less LTM operations are performed. However, in the conditional LTM, particularly the RACH-less conditional LTM operation, the terminal cannot receive the TA value from the base station through the LTM cell change MAC CE because the terminal triggers the LTM. Therefore, as shown in step 750 of FIG. 7b, the LTM target cell can calculate the TA through the preamble received from the terminal (701) in step 745, and include the calculated TA value in the RAR and transmit it to the terminal.

[0278] In one embodiment, the RAR may reuse the RAR format used in existing random access, but may be newly introduced for early TA in conditional LTM. In one embodiment, in addition to TA information, the RAR may include uplink grant information to be used for initial data transmission when the terminal performs RACH-less conditional LTM.

[0279] In one embodiment, since the uplink grant information cannot be held continuously for a long time, it may include limited grant resources and period and offset information referencing CG resources, or it may include temporary resource information referencing dynamic grants. In this case, since it is unknown when RACH-less LTM will be performed, it may be necessary to set a minimum valid resource range. For example, after the terminal receives the TA as a RAR, it may use the resource only within a set time (maximum UL resource validity time), and after that time has elapsed, the terminal determines that the resource is invalid and may use a pre-configured CG resource or perform a conditional LTM operation based on random access. The above maximum UL resource validity time may be set as a fixed value in the standard, or it may be set for each LTM candidate cell or commonly in the RRC settings.

[0280] The terminal may obtain a TA through UE-based TA operation and perform RACH-less conditional LTM to the corresponding target cell. This means that if an LTM candidate cell, for which the event-based conditional LTM execution conditions are satisfied according to base station settings, is a cell where UE-based TA can be performed, the terminal can obtain an uplink TA via a downlink signal (e.g., DL RS) and perform RACH-less conditional LTM by applying that value. Here, the cell where UE-based TA can be performed may be a cell co-located with the serving cell, and cell configurations that are possible in association with the serving cell may be provided via RRC settings. The description of the previously described configuration may be applied to this configuration.

[0281] In step 765, a first MAC PDU transmission containing an RRCReconfigurationComplete message for a pre-configured RRCReconfiguration for the target cell (LTM candidate cell) can be performed through an initial transmission resource to the target cell (a CG resource configured with RRC or a UL grant resource included in the RAR). In one embodiment, the terminal (701) may receive an ACK for the transmission, and the ACK may include a DCI containing uplink or downlink scheduling information.

[0282] In one embodiment, the terminal (701) may stop the TA timer that was running when the handover procedure to the target cell is completed (when the first MAC PDU is transmitted to the target cell and an ACK is received). However, if the TA timer that was running expires at a set value, the terminal (701) may consider the RACH-less handover operation to have failed and perform subsequent operations as follows.

[0283] 1. Method 1: The terminal (701) determines that there is a RACH-less conditional LTM failure and can perform an LTM operation based on random access on the cell. If the operation also fails, the conditional LTM failure procedure described below can be performed.

[0284] 2. Method 2: The terminal (701) can determine that there is a RACH-less conditional LTM failure and immediately perform the following conditional LTM failure procedure.

[0285] In step 770, if the conditional LTM procedure fails (RLF, random access failure, T304 timer completion, etc.), the terminal (701) may maintain the LTM settings configured in step 775 and fall back to the source cell. If the fallback to the source cell fails, the terminal may perform an RRC re-establishment procedure, and if cell selection occurs, and the selected cell is an LTM candidate cell, the terminal may apply the LTM settings and perform a connection procedure. In this case, only random access-based LTM operation may be supported.

[0286] In addition, the procedure for exchanging settings and information for the early TA applied to the RACH-less conditional LTM in step 715 above is described in detail. In particular, the operation may be different depending on whether RACH-less requests for the existing LTM and the conditional LTM are provided simultaneously or if only one is requested separately.

[0287] - Case 1: The source cell simultaneously provides RACH-less requests for the existing LTM and the conditional LTM.

[0288] ■ The LTM candidate cell selects a TA method (existing RACH-less LTM method or conditional RACH-less LTM method), responds while providing relevant settings to the source cell, and applies the selected method to the terminal.

[0289] - Case 2: The source cell provides only one of the RACH-less requests for the existing LTM and the conditional LTM.

[0290] ■ Apply the requested TA method (existing RACH-less LTM method or conditional RACH-less LTM method) to the terminal.

[0291] In addition, when applying the above-mentioned conditional RACH-less LTM, if a TA is received via the early TA procedure, particularly through RAR, and the corresponding TA value is valid, a conditional RACH-less LTM operation via a UE-based TA may be possible. That is, the early TA procedure and the UE-based TA procedure can be set on the terminal simultaneously, and in this case, a clear action regarding which operation to perform is required. In both of the above cases, the terminal has a valid TA value, and operation is possible regardless of which value is applied to perform the RACH-less conditional LTM.

[0292] - Prioritize and execute TAs acquired through UE-based TA and Early TA procedures

[0293] ■ Increase the priority of UE-based TAs for application; or

[0294] ■ Apply the TA obtained through the Early TA process with higher priority.

[0295] - The above priority may also be transmitted to the base station settings via RRC configuration.

[0296] - Or, if you have TA through two methods, the terminal can take the average value and apply it.

[0297] - Or, if there are two methods to have TA, the terminal can select and apply one of them in terms of implementation.

[0298] - Example of priority action (when the Early TA procedure has high priority)

[0299] ■ When the terminal has TAs using two TA methods, apply the TA obtained through the Early TA.

[0300] ■ If you do not have a TA through Early TA but have a TA through UE-based TA, apply the TA through the UE-based TA.

[0301] ■ If the TA of the target cell obtained through both methods is not available, perform random access (conditional LTM)

[0302] FIG. 8 is a diagram illustrating an example of a full terminal operation performing a conditional LTM without random access according to one embodiment of the present disclosure.

[0303] In step 805, 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. The detailed configuration method and content may be applied as described in FIGS. 6a / 6b and FIGS. 7a / 7b. Additionally, although omitted prior to the RRC configuration information in FIG. 8, the terminal has received basic RRC configuration from the base station and can perform an operation to report 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 805, is characterized by being transmitted with a delta configuration applied based on the configuration of a single reference cell.

[0304] The terminal can determine what the reference cell and configuration information for the reference cell are, which are known in advance or instructed by the RRC configuration, and the configurations for surrounding cells other than the reference cell share the reference cell configuration, and since configurations that may be added thereto are transmitted, the signaling overhead is low. In the configuration of the above step, the terminal can receive configuration information related to resources and reporting for L1 measurement for LTM candidate cells. In particular, in the present disclosure, configuration information for RACH-less conditional LTM can be determined through coordination between the source cell and LTM candidate cells in that step. In particular, the configuration information received in that step includes at least one of the following: configuration information related to whether early TA and UE-based TA are applied for RACH-less conditional LTM; event-based conditional settings for conditional LTM; RAR window and TA timer settings for RACH-less conditional LTM; and UL grant related settings when RACH-less conditional LTM is performed.

[0305] In step 810, the terminal can decode the settings for the received LTM candidate cells based on the settings of the reference cell and store and manage the complete settings that are actually applied (i.e., the operation of storing the delta-configured settings based on the reference cell as a complete configuration by referring to the reference cell settings) in a separate buffer and list. In one embodiment, the terminal may not decode the received settings based on the reference cell and store and manage the settings that are actually applied, but may store and manage the received RRC settings as they are in the buffer.

[0306] In step 815, the terminal maintains a connection with the serving cell and performs an L1 measurement configured with an SSB or CSI-RS resource associated with a candidate surrounding cell, and can report the measurement result to the serving cell according to a pre-configured L1 measurement reporting setting method. In one embodiment, 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 the measurement reporting setting, event-based triggering conditions may be used for conditional LTM, and these may be transmitted to the terminal in conjunction with the L1 measurement settings.

[0307] At this stage, L1 / L2-based semi-persistent / aperiodic L1 channel measurements may be instructed. At this stage, the base station may control L1 measurement resource reporting for LTM surrounding cells requiring measurement through RRC settings and L1 / L2 signaling. The terminal may perform L1 measurement resource reporting according to the base station settings and instructions. Additionally, independently of this operation, it may measure surrounding cells according to L3 measurement settings and report the measurement results to the base station according to L3 measurement reporting settings.

[0308] In step 820, if the terminal determines that a RACH-less conditional LTM is required for a terminal that supports a RACH-less conditional LTM based on the received measurement results, that is, when the early TA procedure condition is satisfied and the transmission of a RACH preamble to the corresponding LTM candidate cell is triggered, the terminal can transmit a pre-configured preamble to the corresponding candidate cell and receive a RAR in response to the transmission of the preamble.

[0309] In one embodiment, the RAR includes the TA values ​​of the corresponding target cell and the terminal, and additionally may include UL grant information to be used when the terminal performs a RACH-less conditional LTM for the corresponding target cell. Furthermore, the RAR monitoring operation may be performed within a preset RAR monitoring timer, and within the corresponding RAR window, the terminal may stop transmitting and receiving data with the source cell. For this reason, the procedure may be performed at only one LTM candidate cell at a time, but if the terminal capability supports it, it may be performed simultaneously at multiple LTM candidate cells and may also be performed without interruption with the source cell. For a detailed description, refer to FIGS. 7a and 7b above. If the RAR is not received while passing through the RAR window, the terminal considers the early TA procedure for the corresponding LTM candidate cell as a failure.

[0310] In step 825, the terminal can start the TA timer the moment it obtains a valid TA through RAR in the above step. That is, while the timer is running, it is determined that the received TA value is valid, and in step 830, if a conditional LTM is triggered according to the L1 measurement value for the LTM candidate cell while the timer is running, a RACH-less conditional LTM can be performed.

[0311] That is, in step 835, the first MAC PDU containing the RRCReconfigurationComplete message can be transmitted to the target cell through the pre-configured UL grant resources (UL grant including CG and RAR). When an ACK for the transmission is received (received DCI including UL or DL ​​scheduling), it can be determined that the RACH-less conditional LTM operation is completed (840). Subsequently, data transmission and reception with the target cell can be performed.

[0312] In step 845, if a conditional LTM is triggered based on the L1 measurement value after the timer expires, a RACH-based conditional LTM can be performed.

[0313] FIG. 9 is a drawing illustrating an example of base station operation according to one embodiment of the present disclosure.

[0314] In step 905, the base station receives L3 measurement reports from the terminal and, based on the terminal's measurements regarding surrounding frequencies and cells, can determine whether the terminal requires a handover and which cells are handover candidate cells.

[0315] In step 910, the base station may request configuration information for RACH-less conditional LTM from surrounding cells and receive responses from those cells. In one embodiment, in this step, the base station transmits configuration information for the current source cell and reference cell configuration information together to the surrounding cells, and may receive RRC configuration information in which delta configuration is applied based on the reference cell configuration information from the surrounding cells and LTM candidate cells. The procedure described in detail in FIGS. 6a / 6b and FIGS. 7a / 7b may be applied to this step, and in particular, may include determining L1 measurement resources and reporting settings, securing early TA and UE-based TA for RACH-less conditional LTM, TA timers, and UL grant settings. Although omitted in FIG. 9, settings related to L3 measurement settings and basic RRC settings are provided prior to this step.

[0316] In step 915, an RRC setting message generated including the surrounding cell setting information and L1 measurement resource / reporting settings received in step 910 can be transmitted to the terminal in a connected state. That is, setting information from the surrounding cell that is applied after L1 / L2-based movement is instructed via an RRC reset message from the serving cell can be transmitted. The detailed setting method and configuration may be the configuration described in FIGS. 6a / 6b and FIGS. 7a / 7b.

[0317] Subsequently, in step 920, the base station may direct L1 measurement reporting in various ways via RRC or L1 / L2 signaling according to the L1 measurement and reporting that it wishes to configure and trigger. For detailed methods, refer to the disclosure above. In one embodiment, a report on L1 and L3 measurement values ​​is received from a terminal, wherein the L1 measurement value may be a non-serving cell that supports L1 / L2-based mobility.

[0318] In one embodiment, the terminal determines whether a RACH-less conditional LTM is applied based on the received measurement results, performs an early TA procedure for the RACH-less conditional LTM in step 925, and can transmit a RACH preamble to an LTM candidate cell that satisfies the conditions. The LTM candidate cell that receives this calculates an uplink TA value through the RACH preamble received from the terminal and can transmit the corresponding TA value to the terminal by including it in a RAR. Subsequently, the target cell and the terminal can perform a conditional LTM cell change procedure based on random access or without random access.

[0319] Subsequently, in step 930, when the base station receives a handover completion message from the target cell, it confirms that the LTM operation has been successfully completed and can release the terminal context accordingly. Additionally, if the base station receives a handover failure report message containing information that the handover failed, it can be determined that the terminal attempted to reconnect to the serving cell after the handover failure. The handover failure report message may include at least one of a UEInformationResponse or another uplink RRC message. In one embodiment, the terminal may report the handover failure report message via a new MAC CE or uplink control signal (UCI; uplink control information). The information included in the handover failure report message may include at least one of the following information.

[0320] - An indicator that the handover failed due to an LTM failure

[0321] - Target cell information where LTM attempt failed: LTM cell configuration index or actual cell index (PCI; Physical Cell Index) information

[0322] The source base station can know that the LTM attempt failed and fell back to the cell through the handover failure message report.

[0323] FIG. 10 is a block diagram illustrating the internal structure of a terminal according to one embodiment of the present disclosure.

[0324] Referring to FIG. 10, the terminal may include at least one of an RF (Radio Frequency) processing unit (1010), a baseband processing unit (1020), a storage unit (1030), and a control unit (1040).

[0325] The RF processing unit (1010) can perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1010) can up-convert a baseband signal provided by the baseband processing unit (1020) into an RF band signal and transmit it through an antenna, and down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1010) may include at least one of a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC (digital to analog converter), and an ADC (analog to digital converter).

[0326] In FIG. 10, only one antenna is shown, but the terminal may be equipped with multiple antennas. Additionally, the RF processing unit (1010) may include multiple RF chains. Furthermore, the RF processing unit (1010) may perform beamforming. For beamforming, the RF processing unit (1010) may adjust the phase and magnitude of each of the signals transmitted and received through multiple antennas or antenna elements. Additionally, the RF processing unit may perform MIMO and may receive multiple layers when performing MIMO operation.

[0327] The baseband processing unit (1020) can perform 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 (1020) can generate complex symbols by encoding and modulating the transmitted bit sequence. Additionally, when receiving data, the baseband processing unit (1020) can restore the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (1010). For example, in the case of following the orthogonal frequency division multiplexing (OFDM) method, when transmitting data, the baseband processing unit (1020) can generate complex symbols by encoding and modulating the transmitted bit sequence, map the complex symbols to subcarriers, and then construct OFDM symbols through inverse fast Fourier transform (IFFT) operations and cyclic prefix (CP) insertion. Additionally, upon receiving data, the baseband processing unit (1020) can divide the baseband signal provided from the RF processing unit (1010) into OFDM symbol units, restore the signals mapped to subcarriers through a fast Fourier transform (FFT) operation, and then restore the received bit sequence through demodulation and decoding.

[0328] The baseband processing unit (1020) and the RF processing unit (1010) can transmit and receive signals as described above. Accordingly, the baseband processing unit (1020) and the RF processing unit (1010) 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 (1020) and the RF processing unit (1010) may include a plurality of communication modules to support a plurality of different wireless access technologies. In addition, at least one of the baseband processing unit (1020) and the RF processing unit (1010) 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.

[0329] The storage unit (1030) can store data such as a basic program, an application program, and setting information for the operation of the terminal. In particular, the storage unit (1030) can store information related to a second connection node that performs wireless communication using a second wireless connection technology. Additionally, the storage unit (1030) can provide the stored data upon a request from the control unit (1040).

[0330] The control unit (1040) can control the overall operations of the terminal. For example, the control unit (1040) can transmit and receive signals through the baseband processing unit (1020) and the RF processing unit (1010). In addition, the control unit (1040) writes and reads data to and from the storage unit (1040). To this end, the control unit (1040) may include at least one processor. For example, the control unit (1040) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as applications.

[0331] FIG. 11 is a block diagram showing the configuration of a base station according to one embodiment of the present disclosure.

[0332] As illustrated in FIG. 11, the base station may be configured to include at least one of an RF processing unit (1110), a baseband processing unit (1120), a backhaul communication unit (1130), a storage unit (1140), and a control unit (1150).

[0333] The RF processing unit (1110) can perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1110) can up-convert a baseband signal provided by the baseband processing unit (1120) into an RF band signal and transmit it through an antenna, and down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1110) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is shown in FIG. 11, the first connection node may be equipped with multiple antennas. Additionally, the RF processing unit (1110) may include multiple RF chains. Furthermore, the RF processing unit (1110) may perform beamforming. For the above beamforming, the RF processing unit (1110) 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.

[0334] The baseband processing unit (1120) can perform 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 (1120) can generate complex symbols by encoding and modulating the transmitted bit sequence. In addition, when receiving data, the baseband processing unit (1120) can restore the received bit sequence by demodulating and decoding the baseband signal provided by the RF processing unit (1110). For example, in the case of following the OFDM method, when transmitting data, the baseband processing unit (1120) can generate complex symbols by encoding and modulating the transmitted bit sequence, map the complex symbols to subcarriers, and then construct OFDM symbols through IFFT operation and CP insertion. Additionally, upon receiving data, the baseband processing unit (1120) can divide the baseband signal provided by the RF processing unit (1110) into OFDM symbol units, restore the signals mapped to subcarriers through FFT operations, and then restore the received bit sequence through demodulation and decoding. The baseband processing unit (1120) and the RF processing unit (1110) can transmit and receive signals as described above. Accordingly, the baseband processing unit (1120) and the RF processing unit (1110) may be referred to as a transmitting unit, a receiving unit, a transmitting and receiving unit, a communication unit, or a wireless communication unit.

[0335] The backhaul communication unit (1130) can provide an interface for communicating with other nodes within the network. That is, the backhaul communication unit (1130) can convert a bit sequence transmitted from the main base station to other nodes, such as an auxiliary base station or a core network, into a physical signal, and can convert a physical signal received from the other nodes into a bit sequence. The storage unit (1140) can store data such as a basic program, an application program, and configuration information for the operation of the main base station. In particular, the storage unit (1140) can store information regarding a bearer assigned to a connected terminal, measurement results reported by the connected terminal, etc. Additionally, the storage unit (1140) can store information that serves as a criterion for determining whether to provide or disconnect multiple connections to the terminal. Furthermore, the storage unit (1140) can provide the stored data upon a request from the control unit (1150).

[0336] The control unit (1150) can control the overall operations of the main station. For example, the control unit (1150) can transmit and receive signals through the baseband processing unit (1120) and the RF processing unit (1110) or through the backhaul communication unit (1130). Additionally, the control unit (1150) can write and read data to and from the storage unit (1140). To this end, the control unit (950) may include at least one processor.

[0337] Methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0338] When implemented in software, a computer-readable storage medium may be provided for storing one or more programs (software modules). One or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. One or more programs include instructions that cause the electronic device to execute methods according to the embodiments described in the claims or specification of this disclosure.

[0339] Such programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, ROM (Read Only Memory), Electrically Erasable Programmable Read Only Memory (EEPROM), magnetic disc storage devices, Compact Disc-ROM (CD-ROM), Digital Versatile Discs (DVDs), or other forms of optical storage devices, magnetic cassettes. Alternatively, they may be stored in memory composed of some or all of these. Additionally, each constituent memory may include multiple units.

[0340] Additionally, the program may be stored on an attachable storage device accessible via a communication network such as the Internet, Intranet, Local Area Network (LAN), Wide LAN (WLAN), or Storage Area Network (SAN), or a combination thereof. Such a storage device may be connected to the device performing the embodiment of the present disclosure through an external port. Additionally, a separate storage device on the communication network may be connected to the device performing the embodiment of the present disclosure.

[0341] In the specific embodiments of the present disclosure described above, the components included in the invention are expressed in a singular or plural form according to the specific embodiments presented. However, the singular or plural expression is selected to suit the situation presented for convenience of explanation, and the present disclosure is not limited to singular or plural components; even if a component is expressed in the plural form, it may be composed of a singular form, or even if a component is expressed in the singular form, it may be composed of a plural form.

[0342] Meanwhile, the embodiments of the present disclosure disclosed in this specification and drawings are merely specific examples provided to facilitate the explanation of the technical content of the present disclosure and to aid in understanding the present disclosure, and are not intended to limit the scope of the present disclosure. That is, it is obvious to those skilled in the art that other variations based on the technical concept of the present disclosure are possible. Furthermore, each of the above embodiments may be combined and operated as needed. For example, parts of one embodiment of the present disclosure and parts of another embodiment may be combined to operate a base station and a terminal. For example, parts of the first embodiment and the second embodiment of the present disclosure may be combined to operate a base station and a terminal.

[0343] Meanwhile, the order of description in the drawings illustrating the method of the present invention does not necessarily correspond to the order of execution, and the order of execution may be changed or executed in parallel.

[0344] Alternatively, drawings describing the method of the present invention may omit some components and include only some components to the extent that the essence of the present invention is not compromised.

[0345] In addition, the method of the present invention may be implemented by combining some or all of the contents included in each embodiment within a scope that does not impair the essence of the invention.

[0346] Various embodiments of the present disclosure have been described above. The foregoing description of the present disclosure is for illustrative purposes only and the embodiments of the present disclosure are not limited to the disclosed embodiments. Those skilled in the art will understand that modifications can be easily made to other specific forms without altering the technical spirit or essential features of the present disclosure. The scope of the present disclosure is defined by the claims set forth below rather than by the foregoing detailed description, and all modifications or variations derived from the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of the present disclosure.

Claims

1. In a method performed by a terminal in a wireless communication system, A step of receiving a radio resource control (RRC) reconfiguration message from a base station containing first configuration information—the first configuration information relates to obtaining an early time advance (TA) for random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—; A step of performing an L1 measurement for at least one candidate cell, and reporting the result of the L1 measurement to the base station; A step of determining at least one candidate cell satisfying a first condition for early TA acquisition based on the above L1 measurement and the above first setting information; and A method characterized by including the step of transmitting a RACH preamble for early TA to at least one candidate cell satisfying the first condition above.

2. In Paragraph 1, A step of receiving at least one random access response (RAR) including first TA information for said cell from at least one candidate cell satisfying the above conditions; and A method characterized by including the step of performing a RACH-less LTM based on the first TA information by transmitting a MAC (medium access control) PDU (protocol data unit) to at least one candidate cell that transmitted the RAR.

3. In paragraph 1, the above first condition is, Comparing the L1 measurement value for at least one candidate cell and the L1 resource signal strength for the source cell based on a first threshold value, and A method characterized in that the above-mentioned first setting information includes the above-mentioned first threshold value.

4. In paragraph 2, the step of performing RACH-less LTM based on the first TA information is: A step of determining a first candidate cell satisfying a second condition for a conditional LTM among at least one candidate cell that transmitted the above RAR; and A method characterized by including the step of performing a RACH-less LTM based on the first TA information by transmitting a MAC PDU to the first candidate cell.

5. In Paragraph 4, the above second condition is, Comparing the L1 measurement value for at least one candidate cell and the L1 resource signal strength for the source cell based on a second threshold value, and A method characterized in that the first setting information includes the second threshold value.

6. In paragraph 1, the above-mentioned first setting information is, Resource information for RACH preamble transmission for early TA, Indicator for distinguishing whether early TA support is available in RACH-less conditional LTM, RAR window configuration information (configuration information in time or symbol / slot units), or A method characterized by including at least one of TA timer information for determining the validity of a TA dedicated to conditional LTM.

7. In Paragraph 1, A step of receiving a first message from at least one candidate cell satisfying the above conditions, the message including first TA information and TA timer-related information for the said cell, and initiating the TA timer; A step of determining a first candidate cell satisfying a second condition for a conditional LTM among at least one candidate cell that transmitted the RAR before the TA timer expires; and A method characterized by including the step of performing a RACH-less LTM based on the TA information by transmitting a MAC PDU to the first candidate cell.

8. In Paragraph 1, A step of receiving at least one random access response (RAR) containing first TA information for said cell from at least one candidate cell satisfying the above conditions; A step of receiving second TA information for at least one candidate cell from the base station—the second TA information is information related to the UE base TA—; When the first TA information and the second TA information are applied to the first candidate cell, a step of identifying the first priority of the first TA information and the second priority of the second TA information; and A method characterized by including the step of determining TA information to be applied to the first candidate cell based on the first priority and the second priority.

9. In a method performed by a base station in a wireless communication system, A step of transmitting a radio resource control (RRC) reconfiguration message containing first configuration information to a terminal—the first configuration information is related to obtaining an early time advance (TA) for random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—; A step of receiving a result for an L1 measurement for at least one candidate cell from the above terminal; and A method characterized by including the step of receiving a RACH preamble for early TA through at least one candidate cell satisfying a first condition for early TA acquisition based on the L1 measurement and the first setting information.

10. In Paragraph 9, A step of transmitting at least one random access response (RAR) containing first TA information for said cell through at least one candidate cell satisfying the above conditions; and A method characterized by including the step of receiving a MAC (medium access control) PDU (protocol data unit) through at least one candidate cell that transmitted the RAR.

11. In Paragraph 9, the above-mentioned first condition is, Comparing the L1 measurement value for at least one candidate cell and the L1 resource signal strength for the source cell based on a first threshold value, and A method characterized in that the above-mentioned first setting information includes the above-mentioned first threshold value.

12. In Clause 10, the step of performing RACH-less LTM based on the above-mentioned first TA information is, A step of determining a first candidate cell satisfying a second condition for a conditional LTM among at least one candidate cell that transmitted the above RAR; and The method includes the step of performing a RACH-less LTM based on the first TA information by transmitting a MAC PDU to the first candidate cell, and The second condition above includes comparing the L1 measurement value for the at least one candidate cell and the L1 resource signal strength for the source cell based on a second threshold value, and A method characterized in that the first setting information includes the second threshold value.

13. In paragraph 9, the above-mentioned first setting information is, Resource information for RACH preamble transmission for early TA, Indicator for distinguishing whether early TA support is available in RACH-less conditional LTM, RAR window configuration information (configuration information in time or symbol / slot units), or A method characterized by including at least one of TA timer information for determining the validity of a TA dedicated to conditional LTM.

14. In a terminal of 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, Receiving a radio resource control (RRC) reconfiguration message from a base station containing first configuration information—the first configuration information relates to obtaining an early time advance (TA) for random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—, Perform L1 measurements for at least one candidate cell, and report the results of the L1 measurements to the base station, Based on the above L1 measurement and the above first setting information, at least one candidate cell satisfying the first condition for the early TA acquisition is determined, and A terminal characterized by being configured to transmit a RACH preamble for early TA to at least one candidate cell satisfying the first condition above.

15. In a base station of 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, Transmitting a radio resource control (RRC) reconfiguration message containing first configuration information to a terminal—the first configuration information is related to obtaining an early time advance (TA) for random access channel (RACH)-less conditional LTM (L1 / L2 triggered mobility)—; From the above terminal, receive the result of an L1 measurement for at least one candidate cell, and A base station characterized by being configured to receive a RACH preamble for early TA through at least one candidate cell satisfying a first condition for early TA acquisition based on the above L1 measurement and the above first setting information.

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