Method and apparatus for performing UE-based uplink timing adjustment for mobility of layer 1 / 2 trigger in next generation communication system

Abstract

A method performed by a user equipment (UE) in a wireless communication system is provided. The method includes receiving mobility (LTM) configuration information including layer 1 / layer 2 triggers for a configuration for at least one candidate cell from a base station via a radio resource control (RRC) message, where the configuration includes information associated with a UE-based timing advance (TA) measurement configured for the candidate cell; identifying, based on the information, that the UE-based TA measurement is configured for a candidate cell of the at least one candidate cell; receiving, from the base station, a medium access control (MAC) control element (CE) indicating LTM cell handover, the MAC CE including first information indicating a configuration identity (ID) of a candidate cell for LTM cell handover and second information about a timing advance command; identifying whether a valid timing advance (TA) value is indicated based on the timing advance command; and applying the TA value to the LTM cell handover to the candidate cell if the valid TA value is indicated based on the timing advance command.

Description

Technical Field

[0001] This disclosure relates to methods and apparatus for adjusting uplink timing in Layer 1 / Layer 2 triggered mobility (LTM). Background Technology

[0002] Typically, fifth-generation (5G) mobile communication technology defines a wide frequency band, enabling high transmission rates and new services. This can be achieved not only in the "sub-6 GHz" band, such as 3.5 GHz, but also in the "above 6 GHz" band, including 28 GHz and 39 GHz, known as millimeter wave (mmWave). Furthermore, sixth-generation (6G) mobile communication technology, known as super 5G systems, has been considered for implementation in terahertz (THz) bands (e.g., the 95 GHz to 3 THz band), aiming to achieve transmission rates fifty times faster than 5G and ultra-low latency one-tenth that of 5G.

[0003] At the outset of the development of 5G mobile communication technology, in order to support services and meet the performance requirements associated with enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine-type communication (mMTC), there were ongoing standardization efforts regarding the following aspects: beamforming and massive multiple-input multiple-output (MIMO) in mmWave to mitigate radio wave path loss and increase radio wave transmission distance; dynamic operation to support parameter sets (e.g., operating multiple subcarrier spacings) and time slot formats for efficient utilization of mmWave resources; initial access technologies to support multi-beam transmission and broadband; definition and operation of bandwidth portions (BWP); new channel coding methods such as low-density parity-check (LDPC) codes for large-scale data transmission and polar codes for highly reliable transmission of control information; layer 2 (L2) preprocessing; and network slicing for providing dedicated networks for specific services.

[0004] Currently, given the services that 5G mobile communication technology needs to support, there is ongoing discussion about improvements and performance enhancements to the initial 5G mobile communication technology, and there is already physical layer standardization for technologies such as: Vehicle-to-Everything (V2X) for assisting autonomous vehicles in making driving decisions based on information about the location and status of vehicles transmitted by vehicles and for enhancing user convenience; New Radio Unlicensed (NR-U) for system operation aimed at complying with various regulatory requirements in unlicensed frequency bands; NR User Equipment (UE) power saving; Non-Terrestrial Networks (NTN) for providing coverage in areas where communication with terrestrial networks is not possible, as well as positioning.

[0005] In addition, standardization is underway in air interface architecture / protocols for technologies such as the Industrial Internet of Things (IIoT) supporting new services through interconnection and convergence with other industries; Integrated Access and Backhaul (IAB) providing nodes for network service area extension by supporting wireless backhaul and access links in an integrated manner; mobility enhancements including conditional handover and Dual Active Protocol Stack (DAPS) handover; and two-step random access (RACH for NR) to simplify the random access process. Standardization is also underway in system architecture / services for 5G baseline architectures (e.g., service-based architectures or service-based interfaces) that combine Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving UE location-based services.

[0006] With the commercialization of 5G mobile communication systems, the already exponentially growing number of connected devices will connect to the communication network. Therefore, enhanced functionality and performance of 5G mobile communication systems, as well as the integrated operation of connected devices, are expected to be necessary. To this end, new research is planned related to: Extended Reality (XR) for effectively supporting Augmented Reality (AR), Virtual Reality (VR), Mixed Reality (MR), etc.; 5G performance improvements and complexity reduction through the utilization of Artificial Intelligence (AI) and Machine Learning (ML); AI service support; Metaverse service support; and drone communication.

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

[0008] Technical issues

[0009] The cell serving the UE can instruct the corresponding UE to handover to another cell based on the UE's measurement report. In this case, the UE performs a separate random access procedure, etc., to synchronize the uplink with the new cell, which may cause interruptions and thus delay the handover process.

[0010] The above information is presented as background information only to aid in understanding this disclosure. No determination or assertion is made regarding whether any of the above content can be used as prior art with respect to this disclosure.

[0011] Solution to the problem

[0012] The aspects of this disclosure will at least address the aforementioned problems and / or disadvantages, and provide at least the following advantages. Therefore, one aspect of this disclosure is to provide a method and apparatus capable of mitigating uplink transmission disruptions to the target cell during an L1 / L2 triggered mobility (LTM) handover by a UE.

[0013] Additional aspects will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the embodiments presented.

[0014] According to an aspect of this disclosure, a method performed by a user equipment (UE) in a wireless communication system is provided. The method includes: receiving from a base station via a radio resource control (RRC) message layer 1 / layer 2 triggered mobility (LTM) configuration information including configuration for at least one candidate cell, wherein the configuration includes information associated with a UE-based timing advance (TA) measurement configured for the candidate cell; identifying, based on the information, that the UE-based TA measurement is configured for a candidate cell among the at least one candidate cell; receiving from the base station a media access control (MAC) control element (CE) indicating an LTM cell switch, the MAC CE including first information indicating a configuration identifier (ID) of the candidate cell for the LTM cell switch and second information regarding a timing advance command; identifying whether a valid timing advance (TA) value is indicated based on a timing advance command; and, if a valid TA value is indicated based on a timing advance command, applying the TA value to the LTM cell switch to the candidate cell.

[0015] According to another aspect of this disclosure, a method performed by a base station in a wireless communication system is provided. The method includes: sending Layer 1 / Layer 2 Triggered Mobility (LTM) configuration information, including a configuration of at least one candidate cell, to a user equipment (UE) via a Radio Resource Control (RRC) message, wherein the configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cells; and sending a Media Access Control (MAC) control element (CE) to the UE indicating LTM cell handover, the MAC CE including first information indicating a configuration identifier (ID) of a candidate cell for LTM cell handover and second information regarding a timing advance command, wherein, based on the information, UE-based TA measurements are configured using the UE for the candidate cell among at least one candidate cell, and wherein, if a valid timing advance (TA) value is indicated based on a timing advance command, the valid TA value is applied by the UE to the LTM cell handover to the candidate cell.

[0016] According to another aspect of this disclosure, a user equipment (UE) in a wireless communication system is provided. The UE includes a transceiver and a controller, the controller being configured to: control the transceiver to receive, via a radio resource control (RRC) message, from a base station Layer 1 / Layer 2 triggered mobility (LTM) configuration information including configuration for at least one candidate cell, wherein the configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cell; based on the information, identify that the UE-based TA measurements are configured for a candidate cell among the at least one candidate cell; control the transceiver to receive from the base station a media access control (MAC) control element (CE) indicating LTM cell handover, the MAC CE including first information indicating a configuration identifier (ID) of the candidate cell for LTM cell handover and second information regarding a timing advance command; identify whether a valid timing advance (TA) value is indicated based on a timing advance command; and, if a valid TA value is indicated based on a timing advance command, apply the TA value to the LTM cell handover of the candidate cell.

[0017] According to another aspect of this disclosure, a base station in a wireless communication system is provided. The base station includes a transceiver and a controller, the controller being configured to: control the transceiver to send, via Radio Resource Control (RRC) messages, Layer 1 / Layer 2 triggered Mobility Detection (LTM) configuration information including configuration for at least one candidate cell, wherein the configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cell; and control the transceiver to send to the UE a Media Access Control (MAC) control element (CE) indicating LTM cell handover, the MAC CE including first information indicating a configuration identifier (ID) of the candidate cell for LTM cell handover and second information regarding a timing advance command, wherein, based on the information, UE-based TA measurements are configured using the UE for the candidate cell among at least one candidate cell, and wherein, if a valid timing advance (TA) value is indicated based on a timing advance command, the valid TA value is applied by the UE to the LTM cell handover to the candidate cell.

[0018] Beneficial effects of the invention

[0019] According to embodiments of this disclosure, the UE obtains the TA of the target cell based on the timing advance (TA) of the current serving cell by using the received signal time difference of the downlink reference signals of the source cell and the target cell. This allows the UE to avoid performing random access during handover to the target cell, thereby reducing uplink interruption time.

[0020] Other aspects, advantages, and salient features of this disclosure will become apparent to those skilled in the art from the following detailed description of various embodiments disclosed in conjunction with the accompanying drawings. Attached Figure Description

[0021] The above and other aspects, features and advantages of certain embodiments of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, wherein:

[0022] Figure 1 This is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure;

[0023] Figure 2 This is a diagram illustrating the structure of a wireless protocol for a next-generation mobile communication system according to an embodiment of the present disclosure;

[0024] Figure 3 This is a diagram illustrating the structure of another next-generation mobile communication system according to an embodiment of the present disclosure;

[0025] Figure 4This is a diagram illustrating the operation of an L1 / L2 triggered mobility (LTM) scenario according to an embodiment of the present disclosure, wherein the UE changes the serving cell and beam to the TRP of the target cell that supports L1 / L2-based cell change, and transmits and receives data.

[0026] Figure 5 This is a diagram illustrating a scenario in which a UE proactively updates its TA based on the TA value of the source cell using the received signal time difference of the downlink reference signals of the source cell and the target cell, according to an embodiment of the present disclosure.

[0027] Figure 6 This is a diagram illustrating an embodiment of the present disclosure in which a UE is instructed to perform an LTM cell handover and a UE-based uplink TA acquisition for a target cell.

[0028] Figure 7 This is a diagram illustrating an embodiment of the present disclosure in which the UE is instructed to perform a UE-based uplink TA acquisition for a target cell before being instructed to perform an LTM cell handover;

[0029] Figure 8 This is a diagram illustrating an embodiment of the present disclosure in which the UE is instructed to perform a UE-based uplink TA acquisition for a target cell according to previously configured conditions before being instructed to perform an LTM cell handover.

[0030] Figure 9 This is a diagram illustrating UE operation according to an embodiment of the present disclosure;

[0031] Figure 10 This is a diagram illustrating base station operation according to an embodiment of the present disclosure;

[0032] Figure 11 This is a block diagram illustrating the internal structure of a UE according to an embodiment of the present disclosure; and

[0033] Figure 12 This is a block diagram illustrating the configuration of a base station according to an embodiment of the present disclosure.

[0034] Throughout the accompanying drawings, it should be noted that the same reference numerals are used to depict the same or similar elements, features, and structures. Detailed Implementation

[0035] The following description with reference to the accompanying drawings is provided to aid in a full understanding of the various embodiments of this disclosure as defined by the claims and their equivalents. It includes various specific details to aid understanding, but these are considered exemplary only. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the various embodiments described herein without departing from the scope and spirit of this disclosure. Furthermore, for clarity and brevity, descriptions of well-known functions and structures may be omitted.

[0036] The terms and words used in the following description and claims are not limited to their literal meaning, but are used by the inventors only to enable a clear and consistent understanding of this disclosure. Therefore, those skilled in the art should understand that the following description of various embodiments of this disclosure is provided for illustrative purposes only and is not intended to limit the scope of this disclosure as defined by the appended claims and their equivalents.

[0037] It should be understood that, unless the context clearly specifies otherwise, the singular forms “a,” “an,” and “the” include plural indicators. Thus, for example, a reference to “component surface” includes a reference to one or more such surfaces.

[0038] For ease of description, the terms and names defined in the 3GPP LTE standard are used in this disclosure. However, this disclosure is not limited to the terms and names and can be applied equally to systems conforming to other standards.

[0039] Furthermore, for ease of description, in this disclosure, layer 1 / layer 2 (L1 / L2) based mobility support will be described interchangeably with terms such as L1 / L2 handover, L1 / L2 triggered mobility (LTM), or L1 / L2 triggered mobility.

[0040] It should be understood that the boxes in each flowchart and the combination of flowcharts can be executed by one or more computer programs including instructions. The entirety of one or more computer programs can be stored in a single memory device, or one or more computer programs can be divided into different parts stored in multiple different memory devices.

[0041] Any function or operation described herein may be processed by a processor or a combination of processors. A processor or combination of processors is circuitry that performs processing and includes circuitry such as an application processor (AP, e.g., a central processing unit (CPU)), a communication processor (CP, e.g., a modem), a graphics processing unit (GPU), a neural processing unit (NPU) (e.g., an artificial intelligence (AI) chip), a Wi-Fi chip, a Bluetooth chip, a global positioning system (GPS) chip, a near field communication (NFC) chip, a connectivity chip, a sensor controller, a touch controller, a fingerprint sensor controller, a display driver integrated circuit (IC), an audio codec (CODEC) chip, a universal serial bus (USB) controller, a camera controller, an image processing IC, a microprocessor unit (MPU), a system-on-a-chip (SoC), an IC, etc.

[0042] Figure 1 This is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0043] refer to Figure 1 As shown in the figure, the radio access network of the next-generation mobile communication system is configured to include new radio nodes (hereinafter referred to as NR NB) 1a-10 and a new radio core network (NR CN: next-generation core network) 1a-05. New radio user equipment (hereinafter referred to as NR UE or terminal) 1a-15 accesses the external network through NR gNB 1a-10 and NR CN 1a-05.

[0044] refer to Figure 1 The NR gNB 1a-10 corresponds to the evolved Node B (eNB) of the existing LTE system. The NR gNB 1a-10 can connect to the NR UE 1a-15 via a radio channel and can provide services superior to those of the existing Node B. In next-generation mobile communication systems, since all user services are served through a shared channel, equipment is needed to collect state information (such as the UE's buffer state, available transmission power state, and channel state) and perform scheduling. The NR gNB 1a-10 serves as such equipment. An NR gNB typically controls multiple cells. To achieve ultra-high data rates compared to existing LTE, the NR gNB can have a bandwidth equal to or greater than the maximum bandwidth of the existing system, can employ Orthogonal Frequency Division Multiplexing (OFDM) as the radio access technology, and can also employ beamforming technology. Furthermore, an adaptive modulation and coding scheme (hereinafter referred to as AMC) is applied to determine the modulation scheme and channel coding rate based on the UE's channel state.

[0045] The NR CN 1a-05 performs functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. The NR CN1a-05 is a device that performs various control functions and UE mobility management functions, and it connects to multiple base stations. Furthermore, the next-generation mobile communication system can interoperate with existing LTE systems, and the NR CN 1a-05 connects to the Mobility Management Entity (MME) 1a-25 via a network interface. The MME 1a-25 connects to the eNB 1a-30, which serves as an existing base station.

[0046] Figure 2 This is a diagram illustrating the structure of a wireless protocol for a next-generation mobile communication system according to an embodiment of the present disclosure.

[0047] refer to Figure 2 The wireless protocols of next-generation mobile communication systems include NR Service Data Adaptation Protocol (SDAP) 1b-01 and 1b-45, NR Packet Data Convergence Protocol (PDCP) 1b-05 and 1b-40, NR Radio Link Control (RLC) 1b-10 and 1b-35, and NR Media Access Control (MAC) 1b-15 and 1b-30 in UE and NR base station.

[0048] The main functions of NR SDAP 1b-01 and 1b-45 may include some of the following functions.

[0049] - User data delivery function (transmission of user plane data)

[0050] - The function of mapping QoS flows and data bearers for uplink and downlink (mapping between QoS flows and DRBs for both downlink (DL) and uplink (UL)).

[0051] - The function of marking QoS flow IDs for both uplink and downlink (marking QoS flow IDs in both DL and UL packets).

[0052] - The function of mapping reflected QoS flows to data bearers used for uplink SDAP PDUs (reflected QoS flows to DRB mapping for UL SDAPPDUs).

[0053] Regarding SDAP layer entities, the UE can be configured via Radio Resource Control (RRC) messages to use the SDAP layer entity header or functionality for each PDCP layer entity, each bearer, or each logical channel. When the SDAP header is configured, the 1-bit Non-Access Stratum (NAS) reflected QoS indicator and the 1-bit Access Stratum (AS) reflected QoS indicator in the SDAP header can instruct the UE to update or reconfigure the mapping of QoS flows and data bearers in the uplink and downlink. The SDAP header may include QoS flow identifier (ID) information indicating QoS. QoS information can be used for data processing priority, scheduling information, etc., to support seamless service.

[0054] The main functions of NR PDCP 1b-05 and 1b-40 may include some of the following functions.

[0055] ● Header compression and decompression function (Header compression and decompression: ROHC only)

[0056] ● User data transmission function (transmission of user data)

[0057] ● Sequential delivery function (in-sequence delivery of upper-layer PDUs)

[0058] ● Non-sequential delivery function (out-of-order delivery of upper-layer PDUs)

[0059] ● Reordering function (for reordering received PDCP PDUs)

[0060] ● Duplicate detection function (duplicate detection of lower-level SDUs)

[0061] ●Retransmission function (PDCP SDU retransmission)

[0062] ● Encryption and decryption functions (encryption and decryption)

[0063] ● Timer-based SDU discarding function (timer-based SDU discarding in uplink)

[0064] The reordering function of the NR PDCP layer entity is the function of reordering PDCP protocol data units (PDUs) received by the lower layer according to the PDCP sequence number (SN), and may include the function of delivering the reordered data to the higher layer in order, the function of directly delivering recorded data regardless of the order, the function of recording PDCP PDUs lost due to reordering, the function of reporting the status of lost PDCP PDUs to the sending side, and the function of requesting the retransmission of lost PDCP PDUs.

[0065] The main functions of NR RLC 1b-10 and 1b-35 may include some of the following functions.

[0066] ● Data transmission function (transmission of upper-layer PDUs)

[0067] ● Sequential delivery function (ordered delivery of upper-layer PDUs)

[0068] ● Non-sequential delivery function (out-of-order delivery of upper-layer PDUs)

[0069] ●ARQ function (error correction via ARQ)

[0070] ● Cascading, segmentation, and reassembly functions (cascading, segmentation, and reassembly of RLC SDU)

[0071] ● Re-segmentation function (re-segmentation of RLC data PDUs)

[0072] ● Reordering function (reordering RLC data PDUs)

[0073] ● Duplicate Detection Function (Duplicate Detection)

[0074] ● Error detection function (protocol error detection)

[0075] ●RLC SDU Disposal Function (RLC SDU Disposal)

[0076] ●RLC Reconstruction Function (RLC Reconstruction)

[0077] The sequential delivery function (in-order delivery) of NR RLC layer entities is the function of sequentially delivering RLC Service Data Units (SDUs) received from lower layers to higher layers, and may include: the function of reassembling and delivering RLC SDUs when an original RLC SDU is divided into multiple RLC SDUs and then received; the function of reordering received RLC SDUs based on RLC sequence number (SN) or PDCP sequence number (SN); the function of recording RLC SDUs lost due to reordering; the function of reporting the status of lost RLC SDUs to the sender; the function of requesting retransmission of lost RLC SDUs; the function of sequentially delivering only RLC SDUs preceding the lost RLC SDU to higher layers when a lost RLC SDU exists; the function of sequentially delivering all RLC SDUs received before the timer starts, even if a lost RLC SDU exists, if a predetermined timer expires; or the function of sequentially delivering all RLC SDUs received up to that time, even if a lost RLC SDU exists, if a predetermined timer expires. Furthermore, the NR RLC layer entity can process RLC PDUs in the order they are received (based on arrival order, regardless of serial number or sequence number) and can deliver RLC PDUs to the PDCP layer entity regardless of their order (out-of-order delivery). In the case of fragmentation, the NR RLC layer entity can receive segments stored in a buffer or those to be received in the future, reconstruct the segments into an RLC PDU, process the RLC PDU, and then deliver it to the PDCP layer entity. The NR RLC layer may not include concatenation functionality, and this functionality can be performed by the NR MAC layer, or it can be replaced by the multiplexing functionality of the NR MAC layer.

[0078] The out-of-order delivery function of NR RLC layer entities is the function of directly delivering RLC SDUs received from lower layers to higher layers regardless of the order of the RLC SDUs. It may include functions such as reassembling and delivering RLC PDUs when a raw RLC SDU is divided into multiple RLC SDUs and then received, as well as storing the RLCSN or PDCP SN of the received RLC PDUs, reordering RLC PDUs, and recording lost RLC PDUs.

[0079] NR MAC 1b-15 and 1b-30 can be connected to multiple NR RLC layer entities formed in a UE, and the main functions of NR MAC can include some of the following functions.

[0080] ● Mapping function (mapping between logical channels and transport channels)

[0081] ● Multiplexing and demultiplexing functions (multiplexing / demultiplexing of MAC SDU)

[0082] ● Scheduling information reporting function (Scheduling information report)

[0083] ● HARQ function (error correction via HARQ)

[0084] ● Priority processing function between logical channels (priority processing between logical channels of a UE)

[0085] ● Priority handling function between UEs (with the help of dynamic scheduling of priority handling between UEs)

[0086] ●MBMS Service Identification Function (MBMS Service Identification)

[0087] ●Transmission format selection function (Transmission format selection)

[0088] ● Fill function (Fill)

[0089] NR PHY layers 1b-20 and 1b-25 can perform operations such as channel coding and modulation of higher-layer data to generate orthogonal frequency division multiplexing (OFDM) symbols and transmit the OFDM symbols via radio channels, or demodulate and channel decode OFDM symbols received via radio channels and deliver the demodulated and channel decoded OFDM symbols to higher layers.

[0090] Figure 3 This is a diagram illustrating the structure of another next-generation mobile communication system according to an embodiment of the present disclosure.

[0091] refer to Figure 3A cell served by a beam-operated NR gNB 1c-05 can be configured as a group comprising multiple Transmit / Receive Points (TRPs) 1c-10, 1c-15, 1c-20, 1c-25, 1c-30, 1c-35, and 1c-40. TRPs 1c-10 to 1c-40 refer to blocks constructed by separating some functions used for transmitting / receiving physical signals from an existing NR base station (eNB) and include multiple antennas. An NR gNB 1c-05 can be represented as a Central Unit (CU), and a TRP can be represented as a Distributed Unit (DU). The functionality of the NR gNB 1c-05 and TRPs can be configured by separating the various layers from the PDCP / RLC / MAC / PHY layers into 1c-45. In other words, TRP can perform the functions of its corresponding layer using only the PHY layer (1c-15 and 1c-25), TRP can perform the functions of its corresponding layer using only the PHY layer and MAC layer (1c-10, 1c-35 and 1c-40), and TRP can perform the functions of its corresponding layer using only the PHY layer, MAC layer and RLC layer (1c-20 and 1c-30). Specifically, TRP 1c-10 to 1c-40 can use beamforming technology to transmit / receive data by generating narrow beams in multiple directions using multiple transmit / receive antennas.

[0092] UE 1c-50 accesses NR gNB 1c-05 and external networks via TRPs 1c-10 to 1c-40. To provide services to the user, NR gNB 1c-05 aggregates and schedules state information, such as the UE's buffer state, available transmit power state, and channel state, thereby supporting the connection between the UE and the core network (CN) (specifically, Access and Mobility Management Function (AMF) / Session Management Function (SMF) 1c-50).

[0093] The TRP in this disclosure is based on a structure (1c-15 and 1c-25) that can perform the functions of the corresponding layer using only the PHY layer.

[0094] Figure 4 This is a diagram illustrating a scenario of L1 / L2 triggered mobility (LTM) according to an embodiment of the present disclosure, wherein the UE changes the serving cell and beam to the TRP of the target cell that supports L1 / L2-based cell change, and transmits and receives data.

[0095] The figure illustrates, as an example, the case where there are multiple cells (TRP1-cell 1, TRP2-cell 2) 1d-15 and 1d-20 in a distributed unit (DU) 1d-10, but the entire content of this disclosure can also be applied to the case between DUs (each DU constitutes a TRP cell).

[0096] refer to Figure 4 The UE can receive common and private configuration information for LTM candidate cells (TRP 2 - Cell 2) 1d-20 from serving cell 1d-15 (1d-50) via RRC configuration information. That is, overall RRC configuration information, such as cell group configuration (including ServingCellConfigCommon and ServingCellConfig, etc.), bearer configuration, and measurement configuration associated with ServingCellID or candidateCellID (the cell ID associated with the Physical Cell Identifier (PCI)), can be provided in advance. The corresponding configuration information can be provided in a pre-configured form within the RRC configuration, and configuration information for multiple candidate cells can be transmitted via the RRC configuration. Furthermore, the corresponding configuration is characterized by including all configuration information (cell configuration, bearer configuration, security key configuration, etc.) applied when the UE moves (handovers) to the corresponding cell. In addition, the Unified Transport Configuration Indicator (TCI) status configuration for candidate cells and the configuration related to L1 measurement and reporting are transmitted along with the corresponding configuration. In the following embodiments of this disclosure, particularly in the above-described scenario, when the UE performs a handover by receiving a handover message from the target cell via L1 / L2 triggered mobility (LTM), the UE performs an operation to automatically synchronize the uplink of the target cell. A more detailed method will be described in the following embodiments.

[0097] After UE 1d-25, which is in the RRC connection state to serving cell 1 1d-15, is provided with the configuration of TRP 2-cell 2 1d-20, the UE performs L1 measurement (1d-55) on the corresponding TRP 2-cell 2 1d-20 according to the received configuration and reports the corresponding result to serving cell (cell 1) 1d-15.

[0098] If the serving cell 1d-15 determines based on the measurement results that a handover is required at the same time as a specific beam change (TCI state 2) 1d-40 from the serving cell beam (TCI state 1) 1d-30 to TRP 2 (cell 2) 1d-20, the serving cell triggers the beam change and handover, and instructs UE 1d-25 to perform the beam change and handover (1d-60) via L1 / L2 signaling.

[0099] UE 1d-25 performs a handover simultaneously with the beam change to TRP 2 (cell 2) 1d-20 via the corresponding indication, and transmits and receives data through the corresponding TRP 2 (cell 2) 1d-20. In this case, UE 1d-25 applies the configuration information of the target cell for the handover, which was previously configured in operation 1d-50. In this case, UE 1d-25 may perform random access to the target cell depending on whether uplink synchronization is required, or the random access procedure may be omitted. Detailed operations related to this will be described below with reference to the accompanying drawings.

[0100] Figure 5 This is a diagram illustrating a scenario in which a UE proactively updates its TA based on the TA value of the source cell using the received signal time difference of the downlink reference signals of the source cell and the target cell, according to an embodiment of the present disclosure.

[0101] refer to Figure 5 UE 1e-01 can receive the LTM configuration (target cell configuration and L1 measurement / reporting configuration) from serving cell 1e-05 in RRC connected state. Then, UE 1e-01 can perform L1 measurement reporting according to the configuration while moving. Afterward, UE 1e-01 can be instructed to perform LTM from serving cell 1e-05 to target cell 1e-07. When UE 1e-01 is instructed to perform LTM against one of the LTM candidate cells, the UE can be instructed to perform UE-based TA acquisition for the corresponding cell. Here, UE-based TA acquisition refers to the operation where the UE autonomously updates the TA of target cell 1e-07 based on the TA value of serving cell 1e-05 using the received signal time difference (RSTD) of the downlink reference signals (e.g., synchronization signal block (SSB)) of serving cell 1e-05 and target cell 1e-07. The corresponding operation can be instructed by serving cell 1e-05 before or with the cell handover command, or the UE can autonomously perform the operation based on the conditions of the operation according to the RRC configuration.

[0102] The operation of UE 1e-01 to automatically update the TA value to be applied in the new cell 1e-07 after cell handover can be performed as follows.

[0103] UE 1e-01 in RRC connection state can perform uplink data transmission at TA1 (1e-25), which is a time point earlier than the reception timing of the downlink signal (e.g., SSB1) 1e-11 of cell 1e-05 within the existing cell 1e-05. This is to match the time when the uplink data sent by UE 1e-01 arrives at the base station of operating cell 1e-05 with the base station's timing (1e-10). In this case, the TA1 (1e-25) value can be twice the delay time Tp1 (1e-25) of the actual signal sent from the base station to the UE. For reference, UE 1e-01 can ensure the TA value for uplink data transmission by receiving a timing advance command (TAC) media access control (MAC) control element (CE) provided by the base station within the existing cell through a random access procedure. In addition, the base station can estimate the signal delay time TP1 (1e-25) between UE 1e-01 and the base station based on the reception time of the preamble signal sent by UE 1e-01 during random access or the reception time of the uplink data previously sent by UE 1e-01, and calculate the TA1 value based on the estimated TP1.

[0104] When UE 1e-01 receives a TA acquisition instruction for a new cell 1e-07 from cell 1e-05, the UE can update the TA value based on the downlink signal reception timing of the new cell 1e-07. For reference, if UE 1e-01 uses the TA value used in the existing serving cell 1e-05 to transmit uplink data within the coverage area of ​​the newly selected cell 1e-07, significant interruptions may occur in the reception of the uplink signal in the newly selected cell 1e-07. In this case, interruptions may occur and the handover process time may be prolonged when UE 1e-01 performs a separate random access procedure and TAC MAC CE reception to obtain the TA value to be used within the coverage area of ​​the new cell 1e-07. To reduce the additional interruption time for TA update in such LTM cell handover scenarios, the UE can update the TA value autonomously without the assistance of the base station. In other words, the UE can perform a UE-autonomous TA update operation.

[0105] For the aforementioned UE-initiated TA update, UE 1e-01 can calculate TP_diff (1e-21), which is the difference between the downlink signal reception timing of the existing cell 1e-05 and the downlink signal reception timing of the new cell 1e-07. If the actual distance between UE 1e-01 and the new cell 1e-07 differs from the distance between UE 1e-01 and the existing cell 1e-05, a signal delay time difference Tp_diff (1e-21) may occur. UE 1e-01 can use the Tp_diff value and the TA value (TA1, 1e-25) used for uplink transmission (1e-13) in the existing cell 1e-05 to calculate the TA value (TA2, 1e-27) to be used for uplink transmission (1e-17) in the new cell 1e-07, and the UE can update the TA value used for uplink transmission autonomously. For example, if UE 1e-01 receives the downlink signal (1e-15) of the new cell 1e-07 earlier by Tp_diff (1e-21) than the downlink signal (1e-11) of the existing cell 1e-05, this means that the transmission delay time (Tp2, 1e-20) with the new cell 1e-07 is shorter by Tp_diff (1e-21) than the transmission delay time (Tp1, 1e-22) with the existing cell 1e-05, because UE 1e-01 is closer to the new cell 1e-07 than the existing cell 1e-05. Therefore, UE 1e-01 can calculate the Tp_2 value as (TP1 - TP_diff), and the TA value (TA2, 1e-27) to be used in the actual coverage area of ​​the new cell 1e-07 can be calculated as 2. Tp2 (=2) TP1-2 Tp_diff=TA1-2 Tp_diff).

[0106] For reference, it can be assumed that the time synchronization of existing cell 1e-05 and new cell 1e-07 is matched to perform the above-described UE-initiated TA update operation. In other words, only under the assumption that existing cell 1e-05 and new cell 1e-07 transmit downlink signals (1e-11 and 1e-15) at the same timing, can UE 1e-01 correctly calculate the Tp_diff (1e-21) value and correctly update the TA value with the new TA value (TA2, 1e-27). If the time synchronization of existing cell 1e-05 and new cell 1e-07 exists between distributed units (DUs), an additional process is required to correct this.

[0107] In the embodiments of this disclosure below, the following can be made regarding such Figure 5 The method described herein for obtaining the TA from LTM to the target cell based on the UE reflects the following considerations.

[0108] 1. First consideration: When UE-based TA acquisition is executed.

[0109] 2. Second consideration: How to trigger TA acquisition based on UE

[0110] 3. Third consideration: How to compensate for the time mismatch between the source cell and the target cell.

[0111] 4. Fourth consideration: How to handle the simultaneous configuration of early TA acquisition and UE-based TA acquisition?

[0112] This disclosure presents examples 1, 2 and 3 that differ from those given the foregoing considerations.

[0113] Figure 6 This is a diagram illustrating a process for performing UE-based uplink TA acquisition for a target cell when a UE is instructed to perform an LTM cell handover, according to an embodiment of the present disclosure.

[0114] In particular, this embodiment is characterized in that, by providing an LTM handover indicator and executing a UE-based TA acquisition command for the target cell together, the UE is instructed to perform an operation to autonomously synchronize the uplink to the target cell, rather than random access.

[0115] refer to Figure 6 UE 1f-01 receives (1f-15) system information from cell 1 1f-02 in camp-on state (1f-10) and performs the transition process to connected state (1f-20).

[0116] Subsequently, the serving cell 1f-02 requests UE capabilities from UE 1f-01 (UE capability query message), and UE 1f-01 stores the UE capabilities according to the base station request and transmits them to base station 1f-02 (UE capability information message) (1f-25). The corresponding UE capabilities may include information about whether it supports L1 / L2 based inter-cell beam changing / management and handover, and the UE capabilities may also include capability information related to whether it can support operations matching UE-based uplink synchronization for the target cell during LTM handover. UE 1f-01 transmits information about at least one of UE-specific capabilities, frequency band-specific capabilities, and frequency band combination-specific capabilities to the serving cell 1f-02 via signaling.

[0117] In the event that the corresponding UE 1f-01 performs beam changes and handovers to neighboring cells 1f-03 and 1f-04 that support L1 / L2-triggered mobility based on L1 / L2, the serving cell 1f-02 can request (1f-30) the necessary configuration information, and neighboring cells 1f-03 and 1f-04 will include the relevant configuration information in their response messages to the corresponding request and transmit it to the serving cell 1f-02 (1f-35). Furthermore, in the corresponding operation, the source cell 1f-02 and neighboring cells 1f-03 and 1f-04 share information regarding whether to indicate matching uplink synchronization based on the UE, as well as information for correcting situations where the source cell 1f-02 and target candidate cells 1f-03 and 1f-04 lack downlink reference signal time synchronization due to different DUs. For example, cell identifier (ID), downlink (DL) synchronization offset information, synchronization signal block (SSB) measurement timing, etc., can be included in the shared information. Furthermore, the corresponding information can exist in the LTM candidate cell configuration information. However, since the UE must receive and apply the corresponding information in advance, it can exist outside the configuration for candidate cells and be transmitted to the UE as a separate configuration for each target cell, such as LTM L1 measurement configuration (LTM Channel State Information (CSI) resource configuration). The aforementioned 1f-30 and 1f-35 procedures can be applied to request and transmit pre-configuration related configurations of cells related to L1 / L2 inter-cell beam change and handover (LTM) via inter-node RRC messages, Xn, F1 interfaces, etc. In terms of network implementation, when cell 1 1f-02 and neighboring cells 1f-03 and 1f-04 exist in one DU (intra-DU scenario), the corresponding procedures can be omitted.

[0118] In the case of an indicated LTM handover, UE 1f-01 can apply pre-provided configurations to the cell indicating the handover. More specifically, the RRC structure for supporting L1 / L2 inter-cell beam change (management) and handover operations, particularly the pre-configuration for candidate neighboring cells, is provided to the UE (1f-40). In operation 1f-40, serving cell 1f-02 can transmit to UE 1f-01 the common / private configuration information applied after L1 / L2-triggered mobility (beam change and handover) to neighboring cells 1f-03 and 1f-04 is indicated. That is, since all configurations related to the corresponding cell applied after the handover must be pre-transmitted to UE 1f-01, ServingCellID or candidateCellID (the cell ID associated with PCI), configuration information corresponding to ServingCellConfigCommon and ServingCellConfig, and configurations for cell groups (MAC, RLC, etc.) can also be pre-provided to UE 1f-01. The corresponding configuration information can be provided in a pre-configured form in the RRC configuration, and may include configuration information for multiple cells and cell groups. Furthermore, the corresponding configuration is characterized by including all configuration information (cell configuration, bearer configuration, security key, measurement configuration, etc.) applied when UE 1f-01 moves (handovers) to the corresponding cell. In addition, along with the corresponding configuration, a unified TCI state configuration, configuration related to L1 measurement and reporting for LTM candidate cells, and configuration information associated with UE-based TA are transmitted. As described above in operations 1f-30 and 1f-35, information associated with UE-based TA is transmitted to UE 1f-01, which may include indicators indicating matching uplink synchronization operations based on the UE and information for correcting downlink reference signal time synchronization mismatches caused by differences in DU between the source cell and the target candidate cell. For example, correction information may include cell ID, DL synchronization offset information, SSB measurement timing, etc. Information associated with UE-based TA can exist in LTM candidate cell configuration information, but since the UE must receive and apply the corresponding information in advance, it can exist as a separate configuration for each target cell outside the candidate cell configuration, such as LTM L1 measurement configuration (LTM CSI resource configuration), and be transmitted to the UE.

[0119] UE 1f-01 performs measurements on L1 measurement resources for LTM according to the RRC configuration received in operation 1f-40, and reports the measurement results to the base station (serving cell 1f-02) (1f-45). The aforementioned L1 measurement report may be a measurement value for an LTM candidate cell, and is performed according to a scheme configured by the base station (periodic reporting, non-periodic reporting, one-time reporting).

[0120] Serving cell 1f-02 can determine the UE's cell change (handover) based on the L1 measurement results received from UE 1f-01, and instruct UE 1f-01 to hand over to the target cell (TRP 2 - Cell 2) 1f-03 (1f-50) via the LTM MAC (control element) CE. The aforementioned LTM MAC CE includes the following information:

[0121] - Where LTM is performed on the target cell index (candidate cell ID; candidate cell configuration ID).

[0122] -Active Bandwidth Part (BWP) ID in the target cell

[0123] - An indicator (1 bit or information about the activated SCell) indicating whether SCell activation (carrier aggregation) will be performed simultaneously during LTM execution.

[0124] - Uplink (UL) grant information (resources for data transmission after LTM in the target cell, e.g., resources for sending the RRCReconfigurationComplete message)

[0125] - Beam information used when transmitting in the target cell (TCI status; Unified TCI status information)

[0126] -The temporary cell radio network identifier (C-RNTI) used in the target cell.

[0127] - Related to RACH-less handover and uplink TA information (the case where the base station has the TA value of the target cell due to early TA operation).

[0128] ■Pre-time command information: The source cell can transmit a valid TA value to the LTM MAC CE to instruct the UE to perform a RACH-free handover to the target cell.

[0129] ■ TA value presence indicator (or RACH / no RACH indicator): The corresponding information can be transmitted as 1 bit, or it can be implicitly indicated through another field. In other words, it can be omitted.

[0130] ◆Example 1: When the TA value is provided in the MAC CE, the UE performs a RACH-less handover to the target cell by applying the corresponding TA value, even without a separate RACH / no-RACH indicator. In this case, the presence or absence of the TA value, or the indicator indicating the presence or absence of the TA value, serves as the RACH / no-RACH indicator.

[0131] ● When indicating a TA value, if the TA value is 0 compared to the current reference cell and timing advance group (TAG), the TA value of the corresponding TAG (e.g., the primary TAG (PTAG)) is applied as is.

[0132] ● When indicating a TA value, if an absolute TA value is used, the TA value of the current TAG (e.g., PTAG) is indicated and transmitted again.

[0133] ◆Example 2: You can specify both the TA value presence indicator and the RACH / no RACH indicator separately. This can be used when indicating the TA value but also indicating RACH, etc.

[0134] - Indicates information obtained based on the UE's TA.

[0135] ■ 1-bit indicator

[0136] ■DL synchronization offset information (source cell and target cell) can be omitted.

[0137] When an LTM MAC CE is received in operation 1f-50, UE 1f-01 decodes the corresponding MAC CE and performs operations according to the configured content. When early TA-related information and UE-based TA information are received together, UE 1f-01 prioritizes the early TA-related operation (or can arbitrarily choose a value in terms of UE implementation). Alternatively, when base station 1f-02 sends the LTM MAC CE, priority can be managed so that neither is included in the corresponding content. That is, base station 1f-02 can indicate an early TA operation that takes precedence over UE-based TA operations. In this case, the MAC CE can only indicate the valid TA value based on the early TA operation.

[0138] Specifically, when the MAC CE includes information indicating UE-based TA acquisition, UE 1f-01 performs a UE-based TA acquisition operation (1f-55). That is, UE 1f-01 can acquire the TA value of target cell 1f-03 by applying the reception time difference between the downlink reference signals of source cell 1f-02 and target cell 1f-03 based on the TA of source cell 1f-02. The detailed operation is as described above. Figure 5 As described in [the text].

[0139] Upon obtaining the TA values ​​for target cells 1f-03 and 1f-04, UE 1f-01 restarts the TA timer (1f-60). Here, the TA timer can be an existing TA timer, or it can be a newly introduced TA timer for UE-based TA. When applying the new TA timer (TAT), its value is configured to be less than or equal to the existing TA timer value, and UE-based TA acquisition can be performed when the new TA timer expires. If UE-based TA acquisition is successful, both the traditional TAT and the new TAT are (re)started, and if UE-based TA acquisition fails (due to the absence of a suitable cell for measurement or the impossibility of accurate UE-based TA acquisition), no additional operations are performed, or a report can be made to base station 1f-02 via the UL MAC CE or Physical Uplink Control Channel (PUCCH). When the traditional TAT expires, the traditional TAT expiration operation is performed. Furthermore, this disclosure proposes a method for applying priority rather than having the UE independently perform traditional TA and UE-based TA measurements. For example, in the presence of both a valid traditional TA (before the traditional TAT expires) and a valid new TA (before the new TAT expires), the following options are possible regarding priority.

[0140] Option 1. Traditional TA application

[0141] Option 2. New TA application

[0142] - Option 3. Latest TA application

[0143] On the other hand, when only the traditional TA is valid, the UE operates to apply the traditional TA, and when only the UE-based TA is valid, the UE applies the UE-based TA. Furthermore, when neither the traditional TA nor the UE-based TA is valid (both the new TAT and the traditional TAT have expired), the UE performs the traditional TAT expiration operation. For reference, existing operations for uplink synchronization mismatches, such as PUCCH / SRS release and Hybrid Automatic Repeat Request (HARQ) buffer refresh, can be performed. Refer to Table 1 below for details.

[0144] Table 1

[0145]

[0146] UE 1f-01 performs a handover to target cell 1f-03 based on information included in the configuration from the base station, changing its beam to the indicated beam and performing data transmission and reception through the corresponding beam. Whether random access is performed on target cell (TRP 2 - Cell 2) 1f-03 in this operation depends on whether the UE-based TA acquisition is successful. That is, if the UE-based TA acquisition is successful, UE 1f-01 skips the random access operation and obtains the application TA value based on the UE-based TA to match the uplink synchronization of the target cell during the handover. Conversely, if the UE-based TA acquisition fails, UE 1f-01 performs random access during the handover to the target cell.

[0147] Here, upon completion of the LTM handover, UE 1f-01 performs the first uplink transmission (RRCReconfigurationComplete message and TA information report) to the LTM target cell (1f-65) and receives a response to the corresponding message (1f-70). The response can be based on one of the following methods:

[0148] Option 1: Receive RLC ACK for the RRCReconfigurationComplete message

[0149] Option 2: Receive PDCCH addressed by C-RNTI

[0150] Option 3: UE contention resolution identifier MAC CE reception

[0151] Furthermore, in operation 1f-65, UE 1f-01 can report the TA value of the target cell obtained based on the UE's TA for the first uplink transmission, and the target cell can drive the TA timer in this operation. Here, UE 1f-01 can report the obtained TA value using the TA Report MAC CE, or it can use the newly introduced MAC CE to perform such reporting. For reference, the aforementioned first uplink transmission is transmitted through the configuration grant resources previously configured in the target cell.

[0152] UE 1f-01 completes the handover to the target cell and can perform data transmission and reception with the corresponding cell (1f-75). If the TA timer that has been running during data communication with the target cell expires (1f-80), UE 1f-01 determines that there is an uplink synchronization mismatch with the target cell and performs operations such as releasing the Physical Uplink Control Channel (PUCCH) / Sound Reference Signal (SRS) and refreshing the HARQ buffer (1f-85). These operations are performed when there is an existing uplink synchronization mismatch. For related operations, refer to Table 1 above.

[0153] Figure 7 This is a diagram illustrating an embodiment of the present disclosure in which the UE is instructed to perform a UE-based uplink TA acquisition for a target cell before being instructed to perform an LTM cell handover.

[0154] In particular, this embodiment is characterized by instructing the UE to perform an operation of autonomously synchronizing the uplink to the target cell, rather than random access, by providing the UE with a command to perform UE-based TA acquisition for the target cell before sending the MAC CE indicating LTM handover.

[0155] refer to Figure 7 In the camped state, UE 1g-01 receives (1g-15) system information (1g-10) from cell 1 1g-02 and performs the transition process to the connected state (1g-20).

[0156] Subsequently, serving cell 1g-02 requests UE capabilities from UE 1g-01 (UE capability query message), and UE 1g-01 stores the UE capabilities according to the request from base station 1g-02 and transmits them to base station 1g-02 (UE capability information message) (1g-25). The corresponding UE capabilities may include information about whether L1 / L2 based inter-cell beamforming / management and handover are supported, and the UE capabilities may also include capability information related to whether it can support operation matching UE-based uplink synchronization for the target cell during LTM handover. UE 1g-01 transmits information about at least one of UE-specific capabilities, frequency band-specific capabilities, and frequency band combination-specific capabilities as UE capabilities to base station 1g-02 via signaling.

[0157] In the event that UE 1g-01 performs beam changes and handovers to neighboring cells 1g-03 and 1g-04 that support L1 / L2-triggered mobility based on L1 / L2, serving cell 1g-02 can request (1g-30) the configuration information required for the beam change and handover. Neighboring cells 1g-03 and 1g-04 include the requested configuration information in their response messages to the corresponding requests and transmit them to serving cell 1g-02 (1g-35). Furthermore, in the operations of 1g-30 and 1g-35, source cell 1g-02 and neighboring cells 1g-03 and 1g-04 share information regarding whether to indicate matching uplink synchronization based on the UE, as well as information for correcting downlink reference signal time synchronization mismatches caused by differences in the DU between source cell 1g-02 and the target candidate cell. For example, cell ID, DL synchronization offset information, and SSB measurement timing can be included in the shared information. Furthermore, the corresponding information can exist in the LTM candidate cell configuration information. However, since the UE must receive and apply the corresponding information in advance, it can exist outside the candidate cell configuration and be transmitted to the UE as a separate configuration for each target cell, such as LTM L1 measurement configuration (LTM CSI resource configuration), as a UE capability. The aforementioned processes 1g-30 and 1g-35 are used to request and transmit pre-configuration related configurations of cells related to L1 / L2 inter-cell beam changing and handover (LTM) via inter-node RRC messages, Xn, F1 interface, etc. In terms of network implementation, when cell 1 1g-02 and neighboring cells 1g-03 and 1g-04 exist in one DU (intra-DU scenario), processes 1g-30 and 1g-35 can be omitted.

[0158] In the case of an indicated LTM handover, UE 1g-01 can apply pre-provided configurations to the cell indicating the handover. More specifically, the RRC structure for supporting L1 / L2 inter-cell beam change (management) and handover operations, particularly the pre-configuration for candidate neighboring cells, is provided to UE 1g-01 (1g-40). In operation 1g-40, serving cell 1g-02 can transmit to UE 1g-01 the common / private configuration information applied after L1 / L2-triggered mobility (beam change and handover) to neighboring cells 1g-03 and 1g-04 is indicated. That is, since all configurations of the corresponding cell to be applied after the handover must be pre-transmitted to UE 1g-01, ServingCellID or candidateCellID (the cell ID associated with PCI), configuration information corresponding to ServingCellConfigCommon and ServingCellConfig, and configurations for cell groups (MAC, RLC, etc.) can also be pre-provided to UE 1g-01. The corresponding configuration information can be provided in a pre-configured form in the RRC configuration, and may include configuration information for multiple cells and cell groups. Furthermore, the corresponding configuration is characterized by including all configuration information (cell configuration, bearer configuration, security key, measurement configuration, etc.) applied when UE 1g-01 moves (handovers) to the corresponding cell. In addition, along with the corresponding configuration, a unified TCI state configuration, configuration related to L1 measurement and reporting for LTM candidate cells, and configuration information associated with UE-based TA are transmitted. As described above in operations 1g-30 and 1g-35, information associated with UE-based TA is transmitted to UE 1g-01, which may also include indicators indicating matching uplink synchronization operations based on the UE and information for correcting downlink reference signal time synchronization mismatches caused by differences in DU between the source cell and the target candidate cell. For example, correction information may include cell ID, DL synchronization offset information, SSB measurement timing, etc. In addition, the corresponding information can exist in the LTM candidate cell configuration information, but since the UE must receive and apply the corresponding information in advance, it can exist outside the candidate cell configuration as a separate configuration for each target cell, such as LTM L1 measurement configuration (LTM CSI resource configuration), and be transmitted to the UE.

[0159] UE 1g-01 performs measurements on L1 measurement resources for LTM according to the RRC configuration received in operation 1g-40, and reports the measurement results to the base station (serving cell 1g-02) (1g-45). The L1 measurement report may include measurement values ​​for each candidate cell in LTM, and is performed according to a scheme configured by the base station (periodic reporting, non-periodic reporting, one-time reporting).

[0160] Serving cell 1g-02 transmits a MAC CE (new MAC CE, extended logical channel ID (eLCID)) (1g-50) to UE 1g-01, indicating whether UE-based TA acquisition can be performed from a candidate target cell. The corresponding signaling can be sent via PDCCH commands. The MAC CE includes the cell ID and related information indicating whether UE-based TA acquisition can be performed from a candidate target cell.

[0161] - Indicates information obtained based on the UE's TA.

[0162] ■Community Information (ID)

[0163] ■ 1-bit indicator

[0164] ■DL synchronization offset information (source cell and target cell) can be omitted.

[0165] ■SSB Measurement Resource Location Information

[0166] In operation 1g-50, UE 1g-01, having received the UE-based TA acquisition instruction MAC CE (or PDCCH command), decodes the corresponding MAC CE and performs operations according to the configured content. When early TA-related information and the UE-based TA request are received together, both requests can be executed, or UE 1f-01 can prioritize the early TA-related operation (or any value can be chosen in terms of UE implementation). Alternatively, when base station 1g-02 sends the LTM MAC CE, priority can be managed so that neither request is included in the corresponding content. That is, the base station can instruct an early TA operation that takes precedence over the UE-based TA operation.

[0167] UE 1g-01 performs a TA acquisition operation based on the UE (1g-55). That is, UE 1g-01 acquires the TA value of the target cell 1g-03 by applying the receive time difference between the downlink reference signals of source cell 1g-02 and target cell 1g-03, based on the TA of source cell 1g-02. Detailed operations are as described above. Figure 5 As described in [the text].

[0168] If UE 1g-01 later obtains the TA value of the target cell, UE 1g-01 restarts the TA timer (1g-60). Here, the TA timer can be an existing TA timer, or it can be a newly introduced TA timer for UE-based TA. If the new TA timer (TAT) is configured to be less than or equal to the existing TA timer, and when the new TA timer expires, UE 1g-01 can perform UE-based TA acquisition. If UE-based TA acquisition is successful, both the traditional TAT and the new TAT are (re)started, and if UE-based TA acquisition fails (in cases where there is no suitable cell to measure or accurate UE-based TA acquisition is impossible), no additional operations are performed, or the failure can be reported to the base station via UL MAC CE or PUCCH. When the traditional TAT expires, the traditional TAT expiration operation is performed. Furthermore, this example proposes a method for applying priority instead of having the UE perform traditional TA and UE-based TA measurements independently. Regarding priority, the following options are possible when both a valid traditional TA (before the traditional TAT expires) and a valid new TA (before the new TAT expires) exist.

[0169] Option 1. Traditional TA application

[0170] Option 2. New TA application

[0171] - Option 3. Latest TA application

[0172] On the other hand, if only the traditional TA is valid, the traditional TA is applied; and if only the UE-based TA is valid, the UE-based TA is applied. Furthermore, if both the traditional TA and the UE-based TA are invalid (both the new TAT and the traditional TAT have expired), the traditional TAT expiration operation is performed. For reference, existing operations for uplink synchronization mismatches, such as PUCCH / SRS release and HARQ buffer refresh, can be performed. For this, refer to Table 1 above.

[0173] Furthermore, if a TA value is obtained through UE-based TA acquisition in the above operations, UE 1g-01 can transmit the obtained TA value to the base station via the TA Report MAC CE. Here, UE 1g-01 can report the obtained TA value using the TA Report MAC CE, or a new MAC CE can be introduced for this purpose. The obtained TA value can be transmitted to the source cell 1g-02, or it can be transmitted to the target cell 1g-03 where the corresponding TA is applied. If the obtained TA value is transmitted to the target cell 1g-03, the target cell 1g-03 forwards the corresponding information to the source cell 1g-02 (1g-70). Additionally, if there are no resources available for forwarding this information, UE 1g-01 triggers a scheduling request (SR) to receive uplink grants. Alternatively, if there is a significant difference between the value obtained by UE 1g-01 through the UE-based TA procedure and the conventional TA (the value given in the TA command) and the UE-based TA, the UE can report this using the TA Report MAC CE. Alternatively, as mentioned above, the obtained TA value can always be reported after obtaining the corresponding TA value, or when switching to the target cell.

[0174] Serving cell 1g-02 can determine the cell change (handover) of UE 1g-01 based on the L1 measurement results received from UE 1g-01, and instruct the UE to hand over to the target cell (TRP 2 - Cell 2) 1g-03 (1g-75) via the LTM MAC CE. The aforementioned LTM MAC CE includes the following information:

[0175] - Where LTM is performed on the target cell index (candidate cell ID; candidate cell configuration ID).

[0176] -Active BWP ID in the target cell

[0177] - An indicator (1 bit or information about the activated SCell) indicating whether SCell activation (carrier aggregation) will be performed simultaneously during LTM execution.

[0178] - Uplink (UL) grant information (resources for data transmission after LTM in the target cell, e.g., resources for sending the RRCReconfigurationComplete message)

[0179] - Beam information used when transmitting in the target cell (TCI status; Unified TCI status information)

[0180] -C-RNTI used in the target cell

[0181] - Related to no RACH handover and uplink TA information (the case where the base station has the TA value of the target cell due to early TA operation).

[0182] ■Pre-time command information: The source cell can transmit a valid TA value to the LTM MAC CE to instruct the UE to perform a RACH-free handover to the target cell.

[0183] ■ TA value presence indicator (or RACH / no RACH indicator): The corresponding information can be transmitted as 1 bit, or it can be implicitly indicated through another field. In other words, it can be omitted.

[0184] ◆Example 1: When the TA value is provided in the MAC CE, the UE performs a RACH-less handover to the target cell by applying the corresponding TA value, even without a separate RACH / no-RACH indicator. In this case, the presence or absence of the TA value, or the indicator indicating the presence or absence of the TA value, serves as the RACH / no-RACH indicator.

[0185] ● When indicating a TA value, if the TA value is 0 compared to the current reference cell and TAG, the TA value of the corresponding TAG (e.g., PTAG) is applied as is.

[0186] ● When indicating a TA value, if an absolute TA value is used, the TA value of the current corresponding TAG (e.g., PTAG) is indicated and transmitted again.

[0187] ◆Example 2: You can specify both the TA value presence indicator and the RACH / no RACH indicator separately. This can be used when indicating the TA value but also indicating RACH, etc.

[0188] - Instructs UE-based TA to obtain application information

[0189] ■ 1-bit indicator

[0190] ■DL synchronization offset information (source cell and target cell) can be omitted.

[0191] UE 1g-01 performs a handover to target cell 1g-03 based on information included in the LTM MAC CE, changing its beam to the indicated beam and performing data transmission and reception through the corresponding beam. Whether random access is performed on target cell (TRP 2 - Cell 2) 1g-03 in this operation depends on whether the LTM MAC CE indicates a TA value and whether it indicates no RACH handover. For example, if the LTM MAC CE indicates a TA value and no RACH handover, UE 1g-01 can skip the random access operation and apply the indicated TA value for uplink synchronization to the corresponding target cell when performing the handover to the target cell. Conversely, if the LTM MAC CE does not indicate a TA value and no RACH handover, UE 1g-01 performs random access when performing the handover to target cell 1g-03.

[0192] Here, upon completion of the LTM handover, UE 1g-01 transmits the first uplink transmission (RRCReconfigurationComplete message and TA information report) (1g-80) to the LTM target cell 1g-03 and receives (1g-85) a response to the corresponding message. The response method can be one of the following methods.

[0193] Option 1: Receive RLC ACK for the RRCReconfigurationComplete message

[0194] Option 2: Receive PDCCH addressed by C-RNTI

[0195] Option 3: UE contention resolution identifier MAC CE reception

[0196] Furthermore, in operation 1g-80, UE 1g-01 can report the TA value of the target cell obtained as a UE-based TA for the first uplink transmission, and target cell 1g-03 may have already received the TA value in the aforementioned process. Target cell 1g-03 can also start a TA timer in this operation. Here, UE 1g-01 can report the TA value using the TA report MAC CE, or a new MAC CE can be introduced for this purpose. For reference, the first uplink transmission is transmitted using the configuration grant resources previously configured in the target cell.

[0197] UE 1g-01 can complete the handover to the target cell 1g-03 and perform data transmission and reception with the corresponding cell (1g-90). During data communication with the target cell, if the already running TA timer expires (1g-95), UE 1g-01 determines that the uplink synchronization with the target cell is mismatched, and therefore, as is the existing operation when uplink synchronization is mismatched, performs operations such as PUCCH / SRS release and HARQ buffer refresh (1g-100). For related operations, refer to Table 1 above.

[0198] Figure 8 This is a diagram illustrating a process in which a UE performs a UE-based uplink TA acquisition for a target cell according to previously configured conditions before being instructed to perform an LTM cell handover, according to an embodiment of the present disclosure.

[0199] UE 1h-01 receives system information from cell 1 1h-02 (1h-15) in the camped state (1h-10) and performs a transition to the connected state (1h-20). Afterwards, the serving cell 1h-02 requests UE capabilities from UE 1h-01 (UE capability query message), and UE 1h-01 stores the UE capabilities according to the base station request and transmits them to base station 1h-02 (UE capability information message) (1h-25). The corresponding UE capabilities may include information about whether L1 / L2-based inter-cell beamforming / management and handover are supported, and may also include capability information related to whether it can support UE-based uplink synchronization for the target cell during LTM handover. UE 1h-01 transmits information about at least one of UE-specific capabilities, frequency band-specific capabilities, and frequency band combination-specific capabilities as UE capabilities to base station 1h-02 via signaling.

[0200] When the corresponding UE performs beam changes and handovers to neighboring cells 1h-03 and 1h-04 that support L1 / L2-triggered mobility based on L1 / L2, the serving cell 1h-02 can request (1h-30) the configuration information required for the beam change and handover, and neighboring cells 1h-03 and 1h-04 include the requested configuration information in their response messages to the corresponding requests and transmit them (1h-35). Furthermore, in the operations of 1h-30 and 1h-35, the source cell 1h-02 and neighboring cells 1h-03 and 1h-04 share information regarding whether to indicate matching operations based on UE uplink synchronization, as well as information for correcting downlink reference signal time synchronization mismatches caused by differences in the DU of the source cell and the target candidate cell. For example, cell ID, DL synchronization offset information, SSB measurement timing, etc., can be included in the shared information. Furthermore, the corresponding information can exist in the LTM candidate cell configuration information. However, since the UE must receive and apply the corresponding information in advance, it can exist outside the candidate cell configuration and be transmitted to UE 1h-01 as a separate configuration for each target cell, such as LTM L1 measurement configuration (LTM CSI resource configuration). The processes 1h-30 and 1h-35 described above can be used to request and transmit pre-configuration related configurations of cells associated with L1 / L2 inter-cell beam changing and handover (LTM) via inter-node RRC messages, Xn, F1 interface, etc. In terms of network implementation, when cell 1 1h-02 and neighboring cells 1h-03 and 1h-04 exist in one DU (intra-DU scenario), the processes 1h-30 and 1h-35 can be omitted.

[0201] In the case of an indicated LTM handover, UE 1h-01 can apply pre-provided configurations to the cell indicating the handover. More specifically, the RRC structure for supporting L1 / L2 inter-cell beam change (management) and handover operations, particularly the pre-configuration for candidate neighboring cells, is provided to UE 1g-01 (1h-40). In operation 1h-40, serving cell 1h-02 can transmit to UE 1h-01 the common / private configuration information applied after L1 / L2-triggered mobility (beam change and handover) to neighboring cells 1h-03 and 1h-04 is indicated. That is, since all configurations of the corresponding cell to be applied after the handover must be pre-transmitted to UE 1h-01, ServingCellID or candidateCellID (the cell ID associated with PCI), configuration information corresponding to ServingCellConfigCommon and ServingCellConfig, and configurations for cell groups (MAC, RLC, etc.) can also be pre-provided to UE 1h-01. The corresponding configuration information can be provided in a pre-configured form in the RRC configuration, and may include configuration information for multiple cells and cell groups. Furthermore, the corresponding configuration is characterized by including all configuration information (cell configuration, bearer configuration, security key, measurement configuration, etc.) applied when UE 1h-01 moves (handovers) to the corresponding cell. In addition, along with the corresponding configuration, a unified TCI state configuration, configuration related to L1 measurement and reporting for LTM candidate cells, and configuration information associated with UE-based TA are transmitted. As described above in operations 1h-30 and 1h-35, information associated with UE-based TA is transmitted to UE 1h-01, which may also include indicators indicating matching uplink synchronization operations based on the UE and information for correcting downlink reference signal time synchronization mismatches caused by differences in DU between the source cell and the target candidate cell. For example, correction information may include cell ID, DL synchronization offset information, SSB measurement timing, etc. In addition, the corresponding information can exist in the LTM candidate cell configuration information, but since the UE must receive and apply the corresponding information in advance, it can exist outside the candidate cell configuration as a separate configuration for each target cell, such as LTM L1 measurement configuration (LTM CSI resource configuration), and be transmitted to UE 1h-01.

[0202] UE 1h-01 performs measurements on the L1 measurement resources used for LTM according to the RRC configuration received in operation 1h-40, and reports the measurement results to the base station (serving cell 1h-02) (1h-45). The above L1 measurement report may include measurement values ​​for each candidate cell in LTM, and is performed according to a scheme configured by the base station (periodic reporting, non-periodic reporting, one-time reporting).

[0203] When specific conditions are met according to the UE-based TA acquisition configuration in operation 1h-40, UE 1h-01 performs a UE-based TA acquisition operation on the corresponding target cell (or immediately if a UE-based TA acquisition indicator for the target cell exists in the configuration) (1h-50). Specific conditions may be, for example, the Reference Signal Timing Difference (RSTD) between the downlink reference signal received from the target cell and the downlink reference signal of the source cell being within a pre-configured range. Alternatively, whether the specific conditions are met can be determined by comparing the RSTD with a pre-configured threshold. Here, performing UE-based TA acquisition based on an RSTD within a specific range according to the aforementioned pre-configured threshold means that if the RSTD is too small to be included in the specific range, the change in the TA value is small enough that the existing TA value can be applied as is, therefore, UE-based TA acquisition will not be performed; and if the RSTD is too large to be included in the specific range, the change in TA compared to the current source cell is too large, making the error in the TA value obtained through UE-based TA acquisition potentially large, and therefore, UE-based TA acquisition will not be performed. In addition to the RSTD-based triggering conditions mentioned above, UE-based TA acquisition operations can also be determined based on conditions regarding signal strength. This is because if the signal strength is less than a predetermined threshold, the error in UE-based TA estimation may be large; therefore, it would be appropriate not to perform UE-based TA acquisition.

[0204] - Signal strength triggering method 1: When the signal strength of at least one target cell is greater than or equal to a threshold (because if the target cell signal is too low, the accuracy of TA measurement may be reduced).

[0205] - Signal strength triggering method 2: When the signal strength of the source cell is greater than or equal to a threshold or less than or equal to a threshold...

[0206] - Signal strength triggering method 3: When the conditions of simultaneously considering the signal strength of the source cell and the signal strength of the target cell are met (e.g., the signal strength of the source cell is greater than or equal to the first threshold & the signal strength of the target cell is greater than or equal to the second threshold).

[0207] In the above operations, when UE 1h-01 performs UE-based TA acquisition and obtains TA values ​​from multiple target cells, the corresponding values ​​are maintained and managed for each candidate target cell. When UE 1h-01 obtains the TA value of a target cell, the TA timer (1h-55) is restarted. Here, the TA timer can be an existing TA timer, or it can be a newly introduced TA timer for UE-based TA. If the new TA timer (TAT) is configured to be less than or equal to the existing TA timer, and when the new TA timer expires, UE 1h-01 can perform UE-based TA acquisition. If UE-based TA acquisition is successful, both the traditional TAT and the new TAT are (re)started, and if UE-based TA acquisition fails (due to the lack of a suitable cell to measure or the impossibility of accurate UE-based TA acquisition), UE 1h-01 may not perform any further operations, or it may report the failure to the base station via UL MAC CE or PUCCH. When the traditional TAT expires, UE 1h-01 performs the traditional TAT expiration operation. Furthermore, this example proposes a method for applying priorities instead of independently performing traditional TA and UE-based TA measurement operations. Regarding priority, the following options are possible when both a valid traditional TA (before the traditional TAT expires) and a valid new TA (before the new TAT expires) exist.

[0208] Option 1. Traditional TA application

[0209] Option 2. New TA application

[0210] Option 3. Latest TA application

[0211] On the other hand, when only the traditional TA is valid, the traditional TA is applied, and when only the UE-based TA is valid, the UE-based TA is applied. Furthermore, when both the traditional TA and the UE-based TA are invalid (both the new TAT and the traditional TAT have expired), the traditional TAT expiration operation is performed. For reference, existing operations for uplink synchronization mismatches, such as PUCCH / SRS release and HARQ buffer refresh, can be performed. In this regard, refer to Table 1 above.

[0212] Furthermore, if a TA value is obtained through UE-based TA in the above operations, UE 1h-01 can transmit the obtained TA value to the base station via TA Report MAC CE (1h-60). Here, UE 1h-01 can report using TA Report MAC CE, or use the newly introduced MAC CE for this purpose. The obtained TA value can be transmitted to the source cell 1h-02, or it can be transmitted to the target cell 1h-03 where the corresponding TA is applied. If the obtained TA value is transmitted to the target cell 1h-03, the target cell 1h-03 forwards the corresponding information to the source cell 1h-02 (1h-65). Additionally, if UE 1h-01 does not have the resources to forward this information, the UE triggers SR to receive uplink grant. Alternatively, if the value obtained by UE 1h-01 through the UE-based TA procedure has a significant difference between the traditional TA (the value given in the TA command) and the UE-based TA, the UE can report this using TA Report MAC CE. Alternatively, as mentioned above, the obtained TA value can always be reported after obtaining the corresponding TA value, or when switching to the target cell.

[0213] Serving cell 1h-02 can determine the cell change (handover) of UE 1h-01 based on the L1 measurement results received from UE 1h-01, and instruct UE 1h-01 to hand over to the target cell (TRP 2 - Cell 2) 1h-03 (1h-70) via the LTM MAC CE. The aforementioned LTM MAC CE includes the following information:

[0214] - Where LTM is performed on the target cell index (candidate cell ID; candidate cell configuration ID).

[0215] -Active BWP ID in the target cell

[0216] - An indicator (1 bit or information about the activated SCell) indicating whether SCell activation (carrier aggregation) will be performed simultaneously during LTM execution.

[0217] -UL authorization information (resources for data transmission after LTM in the target cell, e.g., resources for sending the RRCReconfigurationComplete message)

[0218] - Beam information used when transmitting in the target cell (TCI status; Unified TCI status information)

[0219] -C-RNTI used in the target cell

[0220] - Related to no RACH handover and uplink TA information (the case where the base station has the TA value of the target cell due to early TA operation).

[0221] ■Pre-time command information: The source cell can transmit a valid TA value to the LTM MAC CE to instruct the UE to perform a RACH-free handover to the target cell.

[0222] ■ Value Presence Indicator (or RACH / No RACH Indicator): The corresponding information can be transmitted as 1 bit, or it can be implicitly indicated through another field. In other words, it can be omitted.

[0223] ◆Example 1: When the TA value is provided in the MAC CE, the UE performs a RACH-less handover to the target cell by applying the corresponding TA value, even without a separate RACH / no-RACH indicator. In this case, the presence or absence of the TA value, or the indicator indicating the presence or absence of the TA value, serves as the RACH / no-RACH indicator.

[0224] ● When indicating a TA value, if the TA value is 0 compared to the current reference cell and TAG, the TA value of the corresponding TAG (e.g., PTAG) is applied as is.

[0225] ● When indicating a TA value, if an absolute TA value is used, the TA value of the current corresponding TAG (e.g., PTAG) is indicated and transmitted again.

[0226] ◆Example 2: You can specify both the TA value presence indicator and the RACH / no RACH indicator separately. This can be used when indicating the TA value but also indicating RACH, etc.

[0227] - Instructs UE-based TA to obtain application information

[0228] ■ 1-bit indicator

[0229] ■DL synchronization offset information (source cell and target cell) can be omitted.

[0230] UE 1h-01 performs a handover to target cell 1h-03 based on the information included in the MAC CE indicating LTM, changing its beam to the indicated beam and performing data transmission and reception through the corresponding beam. Whether random access is performed on target cell (TRP 2 - Cell 2) 1h-03 in this operation varies depending on whether the LTM MAC CE indicates a TA value and whether it indicates no RACH handover. For example, if the LTM MAC CE indicates a TA value and no RACH handover, UE 1h-01 can skip the random access operation and apply the indicated TA value for uplink synchronization to the corresponding target cell 1h-03 when performing the handover to target cell 1h-03. Conversely, if the LTM MAC CE does not indicate a TA value and no RACH handover, UE 1h-01 performs random access when performing the handover to target cell 1h-03. Here, upon completion of the LTM handover, UE 1h-01 transmits the first uplink transmission (RRCReconfigurationComplete message and TA information report) to the LTM target cell (1h-75) and receives (1h-80) a response to the corresponding message. The response method can be one of the following methods.

[0231] Option 1: Receive RLC ACK for the RRCReconfigurationComplete message

[0232] Option 2: Receive PDCCH addressed by C-RNTI

[0233] Option 3: UE contention resolution identifier MAC CE reception

[0234] Furthermore, in operation 1h-75, UE 1h-01 can report the TA value of the target cell obtained based on the UE's TA for the first uplink transmission, and target cell 1h-03 may have already received the corresponding TA value in the aforementioned process. Target cell 1h-03 can also start a TA timer in this operation. Here, UE 1h-01 can use the TA report MAC CE to report the TA value of the target cell, or a new MAC CE can be introduced for this purpose. For reference, the first uplink transmission is transmitted using the configuration grant resources previously configured in the target cell.

[0235] UE 1h-01 can complete the handover with target cell 1h-03 and perform data transmission and reception with the corresponding cell (1h-85). During data communication with target cell 1h-03, if the already running TA timer expires (1h-90), UE 1h-01 determines that there is an uplink synchronization mismatch with target cell 1h-03 (1h-95). Therefore, as is the existing procedure when there is an uplink synchronization mismatch, operations such as PUCCH / SRS release and HARQ buffer refresh are performed. For related operations, please refer to Table 1 above.

[0236] Figure 9 This is a diagram illustrating UE operation according to an embodiment of the present disclosure.

[0237] In Operation 1i-05, a UE in a connected state can receive public / private configuration information of neighboring cells applied after mobility is triggered via an L1 / L2 indication through an RRC reconfiguration message from the serving cell. For detailed configuration methods and content, please refer to the above embodiments.

[0238] In operation 1i-10, the corresponding configured UE receive signaling indicating a TA acquisition operation based on the UE's TA (triggered autonomously by the UE according to MAC CE, PDCCH command, or RRC configuration) has been received. This signaling may include an indicator indicating that the TA-based operation should be performed, an index of the LTM candidate cell, DL synchronization offset information, etc. In this operation, if the UE obtains a TA value through the TA-based operation, the UE can report the obtained TA value to the base station (source cell or target cell). For reference, the corresponding operation corresponds to the operations in Examples 2 and 3 described in this disclosure, and as in Example 1, the related operation can be performed together with the operation indicated in the LTM MAC CE of operation 1i-20 in the accompanying drawings.

[0239] In Operation 1i-15, the UE performs L1 resource measurement and reporting according to the L1 measurement and reporting configuration for the configured LTM candidate cells.

[0240] In Operation 1i-20, the UE receives the LTM MAC CE and determines whether any value exists. The corresponding signaling indicates this. In particular, the operation differs depending on whether the LTM MAC CE includes an indicator indicating whether random access is performed (without RACH handover indication), a UE-based TA acquisition indicator, or a valid TA value (1i-25).

[0241] When the corresponding LTM MAC CE includes a UE-based TA acquisition indicator, the UE performs a UE-based TA acquisition operation on the target cell indicated in Operation 1i-30. If the corresponding operation is successful and a valid TA value is obtained, the UE performs a RACH-free handover operation to the target cell. If the corresponding operation fails and a valid TA value is not obtained, the UE performs random access to the target cell. Furthermore, when a valid TA value is indicated, the UE performs a RACH-free handover operation to the target cell by applying the corresponding value. In this case, a timer is driven and the corresponding cell configuration pre-configured via RRC is applied. In this case, the valid TA value of the target cell for which handover is performed is transmitted to the LTM MAC CE, and if the corresponding TA value is applied, the random access procedure can be omitted, thereby significantly reducing uplink downtime. Furthermore, for example, the current serving cell and the target cell may have the same uplink synchronization, and if they belong to the same DU, the base station can indicate the corresponding TA value as 0 or set the RACH-free handover indicator to true to indicate the same information to the UE. In other words, this operation can be indicated provided that the base station has the same synchronization with the target cell and the serving cell, and in this case, the UE applies the uplink synchronization in the serving cell as is. Alternatively, the specific serving cell and the timing advance group (TAG) index can be transmitted together, and this operation can be indicated by the reference cell and the TAG.

[0242] In operation 1i-35, when the uplink TA timer expires, the UE performs the timer expiration operation described in the above embodiments. For example, the UE performs operations such as PUCCH / SRS release, HARQ buffer refresh, etc. Alternatively, in this operation, random access can be triggered to obtain new uplink synchronization by receiving a PDCCH command from the base station before the uplink TA timer expires.

[0243] In Operation 1i-25, if the UE determines that the LTM MAC CE from the base station does not include a valid TA value, there is no RACH handover indicator, or the UE-based TA acquisition indicator, the UE performs a handover by performing a random access operation on the target cell indicated in Operation 1i-40. Furthermore, when handing over to the target cell, the configuration pre-configured by the base station for the corresponding cell is applied. Because random access is also performed in this operation, the UE can obtain a valid TA value after random access to the target cell (via RAR or TA command MAC CE) and perform an operation to maintain the corresponding value according to the TA timer pre-configured in the RRC.

[0244] Furthermore, in Operation 1i-45, when the uplink TA timer expires, the UE performs existing uplink TA timer expiration operations. For example, the UE performs operations such as PUCCH / SRS release, HARQ buffer refresh, etc. Alternatively, in this operation, random access can be triggered to obtain new uplink synchronization by receiving a PDCCH command from the base station before the uplink TA timer expires.

[0245] Figure 10 This is a diagram illustrating base station operation according to an embodiment of the present disclosure.

[0246] In Operation 1j-05, the base station provides system information to the UE, and in Operation 1j-10, the base station transmits to the connected UE the common / private configuration information of neighboring cells applied after the serving cell indicates L1 / L2-triggered mobility via an RRC reconfiguration message. For detailed configuration methods and content, please refer to the above. Figure 4 and Figure 6 The content of this disclosure. In particular, the feature of this disclosure is that the configuration information of the cell applying L1 / L2 handover includes early TA-related configuration and an indication for performing uplink synchronization for candidate cells in advance.

[0247] In the corresponding operation, the base station can coordinate with neighboring LTM candidate cells regarding UE-based TA acquisition and whether LTM configuration is supported. This can be performed via Xn, F1 interface, inter-node RRC messages (CG-ConfigInfo, CG-Config), etc. Subsequently, in operation 1j-15, the source base station (serving cell) transmits signaling to the UE to trigger the UE-based TA procedure for the LTM candidate cell requiring UE-based TA. The signaling can be included in the LTM MAC CE and transmitted to the UE.

[0248] Subsequently, in Operation 1j-25, L1 measurements are received from the UE, and the measurements may be reports about neighboring cells (non-serving cells) (i.e., LTM candidate cells) that support L1 / L2 triggered mobility.

[0249] Based on the measurement results received from the UE, the serving cell can determine whether to change the UE's beam and whether to perform a handover. If it is determined that a change and handover to a specific beam in a neighboring cell is needed instead of a specific beam in the serving cell, then in operation 1j-30, the base station instructs the UE to change the cell and beam via LTM MAC CE. In the corresponding operation, whether to perform random access, transmit valid TA values, and provide UE-based TA indication for the cell where the handover occurs can be indicated via L1 / L2 signaling.

[0250] In the case of indicated handover, the serving cell performs the handover procedure, and in operation 1j-35, when the handover with the target cell is completed, the UE context is deleted and the connection with the UE is released. The key feature is that the measurement used to determine whether to perform a handover is an L1 measurement. Furthermore, operations 1j-15 and 1j-20 can occur as needed. That is, if the base station determines that the TA value with the UE is invalid, the corresponding operation can be retried to regain the TA. Conversely, even if the TA value is determined to be invalid for a specific LTM candidate cell, the base station can omit the early TA procedure for the purpose of triggering random access. In this case, the base station can indicate LTM handover via signaling, such as by not including a valid TA value in the LTM MAC CE and indicating a false no-RACH handover indicator.

[0251] Figure 11 This is a block diagram of the internal structure of a UE according to an embodiment of the present disclosure.

[0252] refer to Figure 11 According to this disclosure, the UE includes a radio frequency (RF) processor 1k-10, a baseband processor 1k-20, a storage device 1k-30, and a controller 1k-40.

[0253] The RF processor 1k-10 performs functions for transmitting / receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processor 1k-10 up-converts the baseband signal provided by the baseband processor 1k-20 into an RF band signal, transmits this signal through an antenna, and down-converts the RF band signal received through the antenna back into a baseband signal. For example, the RF processor 1k-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, digital-to-analog converters (DACs), analog-to-digital converters (ADCs), etc. Although only one antenna is shown in the figure, the UE may include multiple antennas. Furthermore, the RF processor 1k-10 may include multiple RF chains. Additionally, the RF processor 1k-10 can perform beamforming. For beamforming, the RF processor 1k-10 can adjust the phase and amplitude of signals transmitted / received through multiple antennas or antenna elements. Furthermore, the RF processor can perform MIMO and can receive multiple layers when performing MIMO operation.

[0254] The baseband processor 1k-20 performs the conversion function between baseband signals and bit strings according to the system's physical layer specifications. For example, during data transmission, the baseband processor 1k-20 encodes and modulates the transmitted bit string to generate complex symbols. Furthermore, during data reception, the baseband processor 1k-20 demodulates and decodes the baseband signal provided from the RF processor 1k-10 to recover the received bit string. For example, following an Orthogonal Frequency Division Multiplexing (OFDM) scheme, during data transmission, the baseband processor 1k-20 encodes and modulates the transmitted bit string to generate complex symbols, maps these complex symbols to subcarriers, and then constructs OFDM symbols through inverse Fast Fourier Transform (IFFT) operations and cyclic prefix (CP) insertion. Furthermore, during data reception, the baseband processor 1k-20 divides the baseband signal provided from the RF processor 1k-10 into OFDM symbol units, recovers the signals mapped to subcarriers through Fast Fourier Transform (FFT) operations, and then recovers the received bit string through demodulation and decoding.

[0255] As described above, the baseband processor 1k-20 and the RF processor 1k-10 transmit and receive signals. Therefore, the baseband processor 1k-20 and the RF processor 1k-10 can be referred to as transmitters, receivers, transceivers, or communication units. Furthermore, at least one of the baseband processor 1k-20 and the RF processor 1k-10 may include multiple communication modules to support various different radio access technologies. Additionally, at least one of the baseband processor 1k-20 and the RF processor 1k-10 may include different communication modules to process signals in different frequency bands. For example, different radio access technologies may include wireless LAN (e.g., IEEE 802.11), cellular networks (e.g., LTE), etc. Moreover, different frequency bands may include ultra-high frequency (SHF) bands (e.g., 2.0 NRHz, 0.0 NRHz) and millimeter wave (e.g., 60 GHz) bands.

[0256] Storage device 1k-30 stores data used for UE operation, such as basic procedures, application programs, and configuration information. Specifically, storage device 1k-30 can store information related to a second access node performing wireless communication using a second radio access technology. Additionally, storage device 1k-30 provides stored data upon request from controller 1k-40.

[0257] Controller 1k-40 controls the overall operation of the UE. For example, controller 1k-40 receives / transmits signals via baseband processor 1k-20 and RF processor 1k-10. Furthermore, controller 1k-40 records and retrieves data in storage device 1k-30. For this purpose, controller 1k-40 may include at least one processor. For example, controller 1k-40 may include a communication processor (CP) that performs control for communication, and an application processor (AP) that controls higher-level functions such as applications.

[0258] Figure 12 This is a block diagram illustrating the configuration of a base station according to an embodiment of the present disclosure.

[0259] refer to Figure 12 According to this disclosure, the base station is configured to include an RF processor 11-10, a baseband processor 11-20, a backhaul communication unit 11-30, a storage device 11-40, and a controller 11-50.

[0260] RF processor 1l-10 performs functions for transmitting / receiving signals via a wireless channel, such as signal band conversion and amplification. Specifically, RF processor 1l-10 up-converts the baseband signal provided by baseband processor 1l-20 into an RF band signal, transmits the signal through an antenna, and down-converts the RF band signal received through the antenna back into a baseband signal. For example, RF processor 1l-10 may include transmit filters, receive filters, amplifiers, mixers, oscillators, DACs, ADCs, etc. Although only one antenna is shown in the figure, the first access node may include multiple antennas. Furthermore, RF processor 1l-10 may include multiple RF chains. Additionally, RF processor 1l-10 can perform beamforming. For beamforming, RF processor 1l-10 can adjust the phase and amplitude of signals transmitted / received through multiple antennas or antenna elements. The RF processor can perform downlink MIMO operation by transmitting one or more layers.

[0261] Baseband processor 11-20 performs the conversion function between baseband signals and bit strings according to the physical layer specification of the first radio access technology. For example, during data transmission, baseband processor 11-20 encodes and modulates the transmitted bit string to generate complex symbols. Furthermore, during data reception, baseband processor 11-20 demodulates and decodes the baseband signal provided from RF processor 11-10 to recover the received bit string. For example, in the case of following an OFDM scheme, during data transmission, baseband processor 11-20 encodes and modulates the transmitted bit string to generate complex symbols, maps the complex symbols to subcarriers, and then constructs OFDM symbols through IFFT operations and CP insertion. Furthermore, during data reception, baseband processor 11-20 divides the baseband signal provided from RF processor 11-10 into OFDM symbol units, recovers the signal mapped to the subcarriers through FFT operations, and then recovers the received bit string through demodulation and decoding. As described above, baseband processor 11-20 and RF processor 11-10 transmit and receive signals. Therefore, the baseband processor 1l-20 and the RF processor 1l-10 can be referred to as a transmitter, receiver, transceiver, communication unit, and wireless communication unit.

[0262] The backhaul communication unit 1l-30 provides an interface for communicating with other nodes within the network. That is, the backhaul communication unit 1l-30 converts bit strings sent from the main base station to another node (e.g., an auxiliary base station or the core network) into physical signals, and converts physical signals received from another node into bit strings.

[0263] Storage device 11-40 stores data used for the operation of the main base station, such as basic procedures, application programs, and configuration information. Specifically, storage device 11-40 can store information about bearers assigned to accessing UEs, measurement results reported from accessing UEs, etc. Furthermore, storage device 11-40 can store information used as criteria for determining whether to provide multiple connections to a UE or interrupt multiple connections. In addition, storage device 11-40 provides the stored data upon request from controller 11-50.

[0264] The controller 1l-50 controls the overall operation of the main base station. For example, the controller 1l-50 receives / transmits signals via the baseband processor 1l-20 and the RF processor 1l-10, or via the backhaul communication unit 1l-30. Furthermore, the controller 1l-50 records and retrieves data in the storage device 1l-40. For this purpose, the controller 1l-50 may include at least one processor.

[0265] While this disclosure has been shown and described with reference to various embodiments thereof, those skilled in the art will understand that various changes in form and detail may be made therein without departing from the spirit and scope of this disclosure as defined by the appended claims and their equivalents.

Claims

1. A method performed by a user equipment (UE) in a wireless communication system, the method comprising: Receive from the base station via Radio Resource Control (RRC) messages Layer 1 / Layer 2 triggered mobility (LTM) configuration information, including configuration for at least one candidate cell, wherein the configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cell; Based on the information, UE-based TA measurements are identified and configured for use in the at least one candidate cell. The base station receives a Media Access Control (MAC) control element (CE) indicating LTM cell handover. The MAC CE includes first information indicating the configuration identifier (ID) of a candidate cell for LTM cell handover and second information regarding a timing advance command. Identify whether a valid timing advance (TA) value is indicated based on a timing advance command; and When an effective TA value is indicated based on a timed advance command, the TA value is applied to the LTM cell handover of the candidate cell.

2. The method according to claim 1, further comprising: UE-based TA measurement is configured to perform TA measurement for candidate cell identification; TA values ​​are obtained based on TA measurements; as well as If the effective TA value is not indicated by the timed advance command, the obtained TA value will be applied to the LTM cell handover of the candidate cell.

3. The method according to claim 2, further comprising: Start the time alignment timer associated with the candidate cell. Specifically, TA measurement is performed before the MAC CE receives the data. This information includes the ID of the cell to which the UE-based TA measurement is performed. Among them, the No Random Access Channel (RACH) procedure is performed for LTM cell handover to the candidate cell, and Specifically, if the first uplink data is successfully sent to the candidate cell, the LTM cell handover to the candidate cell is completed.

4. The method according to claim 1, further comprising: Receive UE capability query message from base station; as well as A UE capability information message is sent to the base station, the UE capability information message including information indicating that the UE supports UE-based TA measurement.

5. A method performed by a base station in a wireless communication system, the method comprising: A Layer 1 / Layer 2 triggered mobility (LTM) configuration information, including configuration for at least one candidate cell, is sent to the User Equipment (UE) via a Radio Resource Control (RRC) message. The configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cell. The UE is sent a Media Access Control (MAC) control element (CE) indicating LTM cell handover. The MAC CE includes first information indicating the configuration identifier (ID) of the candidate cell for LTM cell handover and second information regarding the timing advance command. Specifically, based on information, for each candidate cell among the at least one candidate cell, TA measurement based on the UE is configured using the UE, and In cases where the effective timing advance (TA) value is indicated based on the timing advance command, the effective TA value is applied by the UE to the LTM cell handover to the candidate cell.

6. The method according to claim 5, further comprising: A valid TA value is obtained based on an early TA acquisition process performed before the MAC CE transmission. Where a valid TA value is not indicated by a timing advance command, the TA value obtained in the UE based on TA measurement is applied to the LTM cell handover to the candidate cell, and The information includes the ID used to identify the cell to which the UE-based TA measurement is performed.

7. The method according to claim 5, further comprising: Send a first message to the at least one candidate cell, the first message being used to request the configuration of the at least one candidate cell for LTM cell handover; as well as A second message is received from the at least one candidate cell as a response to the first message, the second message including the configuration of the at least one candidate cell.

8. The method according to claim 5, further comprising: Send a UE capability query message to the UE; as well as Receive a UE capability information message from the UE, the UE capability information message including information indicating that the UE supports UE-based TA measurement.

9. A user equipment (UE) in a wireless communication system, the UE comprising: transceiver; and The controller is configured as follows: The control transceiver receives from the base station via Radio Resource Control (RRC) messages Layer 1 / Layer 2 triggered mobility (LTM) configuration information, including configuration for at least one candidate cell, wherein the configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cell. Based on the information, UE-based TA measurements are identified and configured for use in the at least one candidate cell. The control transceiver receives a Media Access Control (MAC) control element (CE) from the base station indicating LTM cell handover. The MAC CE includes first information indicating the configuration identifier (ID) of the candidate cell for LTM cell handover and second information regarding the timing advance command. Identify whether a valid timing advance (TA) value is indicated based on a timing advance command, and When a timed advance command based on a valid TA value is indicated, the TA value is applied to the LTM cell handover of the candidate cell.

10. The UE according to claim 9, wherein, The controller is also configured as follows: UE-based TA measurement is configured for candidate cell identification and TA measurement. The TA value is obtained based on TA measurement, and If the effective TA value is not indicated by the timed advance command, the obtained TA value will be applied to the LTM cell handover of the candidate cell.

11. The UE according to claim 9, in, The controller is also configured to initiate a time alignment timer associated with the candidate cells. Specifically, TA measurement is performed before the MAC CE receives the data. This information includes the ID of the cell to which the UE-based TA measurement is performed. Among them, the No Random Access Channel (RACH) procedure is performed for LTM cell handover to the candidate cell, and Specifically, if the first uplink data is successfully sent to the candidate cell, the LTM cell handover to the candidate cell is completed.

12. The UE according to claim 9, wherein, The controller is also configured as follows: The control transceiver receives UE capability query messages from the base station, and The control transceiver sends a UE capability information message to the base station, the UE capability information message including information indicating that the UE supports UE-based TA measurement.

13. A base station in a wireless communication system, the base station comprising: transceiver; and The controller is configured as follows: The control transceiver sends Layer 1 / Layer 2 triggered mobility (LTM) configuration information to the user equipment (UE) via Radio Resource Control (RRC) messages, including configuration for at least one candidate cell. The configuration includes information associated with UE-based timing advance (TA) measurements configured for the candidate cell, and... The control transceiver sends a Media Access Control (MAC) control element (CE) to the UE indicating LTM cell handover. The MAC CE includes first information indicating the configuration identifier (ID) of the candidate cell for LTM cell handover and second information regarding the timing advance command. Specifically, based on information, for each candidate cell among the at least one candidate cell, TA measurement based on the UE is configured using the UE, and In the case where a timing advance command based on a valid timing advance (TA) value is indicated, the valid TA value is applied by the UE to the LTM cell handover to the candidate cell.

14. The base station according to claim 13, in, The controller is also configured to obtain a valid TA value based on an early TA acquisition process performed before the MAC CE transmission. Where a valid TA value is not indicated by a timing advance command, the TA value obtained in the UE based on TA measurement is applied to the LTM cell handover to the candidate cell, and The information includes the ID used to identify the cell to which the UE-based TA measurement is performed.

15. The base station according to claim 13, wherein, The controller is also configured as follows: The control transceiver sends a UE capability query message to the UE, and The control transceiver receives a UE capability information message from the UE, the UE capability information message including information indicating that the UE supports UE-based TA measurements.

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