Method and apparatus for using reference cell configuration when supporting LTM between cus in next generation mobile communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The method comprises the steps of: transmitting, to a central unit (CU) of at least one candidate base station, a handover request message for requesting configuration of a layer 1 (L1) / layer 2 (L2) triggered mobility (LTM) candidate cell; receiving, from the CU of the at least one candidate base station, a handover request response message in response to the handover request message, wherein the handover request response message includes configuration information of an LTM candidate cell related to the CU of each candidate base station; generating LTM configuration information on the basis of the configuration information of the LTM candidate cell related to the CU of each candidate base station; and transmitting, to a terminal, a radio resource control (RRC) message including the LTM configuration information.

Description

Method and device for using reference cell setting when supporting LTM between CUs in next-generation mobile communication systems

[0001] The present invention relates to operations of a terminal and a base station in a mobile communication system. More specifically, the present invention relates to a method and device for using a reference cell configuration when a terminal supports L1 / L2 triggered mobility (LTM) between Central Units (CUs).

[0002] 5G mobile communication technology defines a wide frequency band to enable fast transmission speeds and new services, and can be implemented not only in the sub-6GHz frequency band, such as 3.5 gigahertz (3.5GHz), but also in the ultra-high frequency band called millimeter wave (mmWave), such as 28GHz and 39GHz ('Above 6GHz'). In addition, for 6G mobile communication technology, which is called the system after 5G communication (Beyond 5G), implementation in the terahertz band (for example, the 3 terahertz (3THz) band at 95GHz) is being considered to achieve a transmission speed that is 50 times faster than 5G mobile communication technology and an ultra-low latency time that is reduced to one-tenth.

[0003] In the early stages of 5G mobile communication technology, the goal is to support services and meet performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC). These include beamforming and massive MIMO to mitigate path loss of radio waves in ultra-high frequency bands and increase the transmission distance of radio waves, support for various numerologies (such as operation of multiple subcarrier intervals) and dynamic operation of slot formats for efficient use of ultra-high frequency resources, initial access technology to support multi-beam transmission and wideband, definition and operation of BWP (Bidth Part), new channel coding methods such as LDPC (Low Density Parity Check) codes for large-capacity data transmission and Polar Code for reliable transmission of control information, and L2 pre-processing (L2). Standardization has been made for network slicing, which provides dedicated networks specialized for specific services, and pre-processing.

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

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

[0006] Once these 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, necessitating enhanced functionality and performance of 5G mobile communication systems and integrated operation of these connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, supporting AI services, supporting metaverse services, and drone communications by utilizing eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

[0007] In addition, the development of these 5G mobile communication systems includes new waveforms to ensure coverage in the terahertz band of 6G mobile communication technology, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), Array Antenna, and Large Scale Antenna, metamaterial-based lenses and antennas to improve the coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve the frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design stage and AI-based communication technology that realizes system optimization by internalizing end-to-end AI support functions, and ultra-high-performance communication and computing resources to provide services with complexity that goes beyond the limits of terminal computing capabilities. It could serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing this technology.

[0008] The present disclosure proposes a method for applying pre-configuration and reference cell configuration for LTM candidate cell configuration when a terminal supports L1 / L2 triggered mobility (LTM) for another base station (inter-CU).

[0009] The technical problems to be achieved in the embodiments of the present disclosure are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by a person having ordinary skill in the technical field to which the present disclosure belongs from the description below.

[0010] To solve the above problems, the present invention proposes a method performed by a central unit (CU) of a source base station in a communication system. More specifically, the method comprises the steps of: transmitting a handover request message to request configuration of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell to a CU of at least one candidate base station; receiving a handover request response message from the CU of the at least one candidate base station in response to the handover request message, the handover request response message including configuration information of an LTM candidate cell associated with each CU of the candidate base station; generating LTM configuration information based on the configuration information of the LTM candidate cell associated with each CU of the candidate base station; and transmitting a Radio Resource Control (RRC) message including the LTM configuration information to a terminal.

[0011] In order to solve the above problems, the present invention proposes a method performed by a central unit (CU) of a candidate base station in a communication system. More specifically, the method is characterized by the steps of: receiving, from a CU of a source base station, a handover request message requesting configuration of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell; the handover request message for requesting configuration of the LTM candidate cell including reference cell configuration information commonly applied to at least one or more candidate base station CUs; ​​transmitting the reference cell configuration information to at least one or more LTM candidate cells; obtaining, from the at least one LTM candidate cell, delta configuration information of each LTM candidate cell generated based on the reference cell configuration information; and transmitting, to the CU of the source base station, a handover request response message including configuration information of the LTM candidate cells generated based on the delta configuration information of each LTM candidate cell.

[0012] In order to solve the above problems, the present invention proposes a central unit (CU) of a source base station in a communication system. More specifically, the CU of the source base station includes a transceiver for transmitting and receiving signals; and a control unit connected to the transceiver, wherein the control unit transmits a handover request message to request the configuration of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell to CUs of at least one candidate base station, and receives a handover request response message from the CUs of the at least one candidate base station in response to the handover request message, wherein the handover request response message includes configuration information of an LTM candidate cell associated with each CU of the candidate base station, and generates LTM configuration information based on the configuration information of the LTM candidate cell associated with each CU of the candidate base station, and transmits a Radio Resource Control (RRC) message including the LTM configuration information to a terminal.

[0013] In order to solve the above problems, the present invention proposes a central unit (CU) of a candidate base station in a communication system. More specifically, the CU of the candidate base station includes a transceiver for transmitting and receiving a signal; and a control unit connected to the transceiver, wherein the control unit transmits a handover request message to request the configuration of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell to at least one CU of the candidate base station, and receives a handover request response message from the CU of the at least one candidate base station in response to the handover request message, wherein the handover request response message includes configuration information of an LTM candidate cell associated with each CU of the candidate base station, and generates LTM configuration information based on the configuration information of the LTM candidate cell associated with each CU of the candidate base station, and transmits a Radio Resource Control (RRC) message including the LTM configuration information to a terminal.

[0014] According to a method of applying an LTM candidate cell configuration and a reference cell configuration when supporting inter-CU LTM according to an embodiment of the present disclosure, the signaling overhead of pre-configuration for LTM can be reduced by making the reference cell configuration available.

[0015] The effects that can be obtained from the present disclosure are not limited to the effects mentioned in the various embodiments, and other effects that are not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure belongs from the description below.

[0016] FIG. 1a is a diagram illustrating the structure of a mobile communication system according to one embodiment of the present disclosure.

[0017] FIG. 1b is a diagram illustrating a wireless protocol structure of a next-generation mobile communication system according to an embodiment of the present disclosure.

[0018] FIG. 1c is a diagram illustrating the structure of another next-generation mobile communication system according to one embodiment of the present disclosure.

[0019] FIG. 1D is a diagram illustrating a scenario for inter-cell beam management according to one embodiment of the present disclosure, in which a terminal transmits and receives data through a beam of a TRP (transmission / reception point) of a neighboring cell that supports beam change on an L1 / L2 basis while maintaining a connection state with a serving cell.

[0020] FIG. 1ea is a diagram illustrating a scenario in which a terminal transmits and receives data by changing a serving cell and beam to a transmission / reception point (TRP) of a cell that supports L1 / L2-based beam changing according to an embodiment of the present disclosure.

[0021] FIG. 1eb is a diagram illustrating a scenario in which a terminal transmits and receives data by changing a serving cell and beam to a transmission / reception point (TRP) of a cell that supports L1 / L2-based beam changing according to an embodiment of the present disclosure.

[0022] FIG. 1f is a diagram illustrating a continuous L1 / L2 triggered mobility (LTM) operation based on a reference cell configuration in an intra-CU according to an embodiment of the present disclosure.

[0023] FIG. 1ga is a diagram illustrating the overall operation for explaining a reference cell setting method for supporting continuous L1 / L2-based Master cell group (MCG) handover (L1 / L2 triggered mobility, LTM) operation in cells within different CUs according to one embodiment of the present disclosure.

[0024] FIG. 1GB is a diagram illustrating the overall operation for explaining a reference cell setting method for supporting continuous L1 / L2-based Master cell group (MCG) handover (L1 / L2 triggered mobility, LTM) operation in cells within different CUs according to one embodiment of the present disclosure.

[0025] FIG. 1 is a diagram illustrating the overall operation for explaining a reference cell setting method for supporting continuous L1 / L2 based Secondary cell group (SCG) PSCell change (l1 / l2 triggered mobility, LTM) operation in cells within different CUs according to one embodiment of the present disclosure.

[0026] FIG. 1hb is a diagram illustrating the overall operation for explaining a reference cell setting method for supporting continuous L1 / L2 based Secondary cell group (SCG) PSCell change (l1 / l2 triggered mobility, LTM) operation in cells within different CUs according to one embodiment of the present disclosure.

[0027] FIG. 1i is a diagram illustrating the overall terminal operation for performing L1 / L2-based beam change and handover according to one embodiment of the present disclosure.

[0028] FIG. 1J is a diagram illustrating the operation of a base station according to an embodiment of the present disclosure.

[0029] FIG. 1k is a block diagram illustrating the internal structure of a terminal according to one embodiment of the present disclosure.

[0030] FIG. 1l is a block diagram illustrating the structure of a base station according to one embodiment of the present disclosure.

[0031] Hereinafter, the operating principles of the present invention will be described in detail with reference to the attached drawings. In the following description of the present invention, if a detailed description of a related known function or configuration is judged to unnecessarily obscure the gist of the present invention, such detailed description will be omitted. In addition, the terms described below are terms defined in consideration of the functions of the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. Terms used in the following description, such as terms for identifying connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, and terms referring to various identification information, are examples for the convenience of explanation. Therefore, the present invention is not limited to the terms described below, and other terms referring to objects with equivalent technical meanings may be used.

[0032] In the following description of the present invention, detailed descriptions of known functions or configurations will be omitted if they are deemed to unnecessarily obscure the gist of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

[0033] The terms used in the following description to identify connection nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, and terms referring to various identification information are provided for convenience of explanation. Therefore, the present invention is not limited to the terms described below, and other terms referring to objects with equivalent technical meanings may be used.

[0034] Hereinafter, the base station is an entity that performs resource allocation of the terminal, and may be at least one of a gNode B, an eNode B, a Node B, a BS (Base Station), a wireless access unit, a base station controller, or a node on a network. The terminal may include a UE (User Equipment), an MS (Mobile Station), a cellular phone, a smartphone, a computer, or a multimedia system capable of performing a communication function. In the present disclosure, downlink (DL) refers to a wireless transmission path of a signal transmitted from a base station to a terminal, and uplink (UL) refers to a wireless transmission path of a signal transmitted from a terminal to a base station. In addition, although the LTE or LTE-A system may be described below as an example, the embodiments of the present disclosure may also be applied to other communication systems having similar technical backgrounds or channel types. For example, the 5th generation mobile communication technology (5G, new radio, NR) developed after LTE-A may be included in a system to which the embodiments of the present disclosure may be applied, and 5G below may also be a concept that includes existing LTE, LTE-A, and other similar services. Furthermore, the present disclosure may be applied to other communication systems with some modifications, as determined by a person skilled in the art, without significantly departing from the scope of the present disclosure. It will be appreciated that each block of the processing flow diagrams and combinations of the flow diagrams can be executed by computer program instructions.

[0035] These computer program instructions may be installed in a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus, so that the instructions executed by the processor of the computer or other programmable data processing apparatus create means for performing the functions described in the flowchart block(s). These computer program instructions may also be stored in a computer-available or computer-readable memory that can be directed to a computer or other programmable data processing apparatus to implement functions in a particular manner, so that the instructions stored in the computer-available or computer-readable memory can produce an article of manufacture that includes instruction means for performing the functions described in the flowchart block(s). The computer program instructions may also be installed on a computer or other programmable data processing apparatus, so that a series of operational steps are performed on the computer or other programmable data processing apparatus to create a computer-implemented process, so that the instructions executing on the computer or other programmable data processing apparatus can provide steps for performing the functions described in the flowchart block(s).

[0036] Additionally, each block may represent a module, segment, or portion of code that contains one or more executable instructions for executing a specific logical function(s). It should also be noted that in some alternative implementation examples, the functions mentioned in the blocks may occur out of order. For example, two blocks shown in succession may in fact be executed substantially simultaneously, or the blocks may sometimes be executed in reverse order depending on the corresponding function. In this case, the term '~unit' used in the present embodiment means software or a hardware component such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit), and the '~unit' may perform certain roles. However, the '~unit' is not limited to software or hardware. The '~unit' may be configured to be on an addressable storage medium and may be configured to execute one or more processors. Thus, as an example, the '~ unit' includes components such as software components, object-oriented software components, class components, and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functionality provided within the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. In addition, the components and '~ units' may be implemented to reproduce one or more CPUs within a device or a secure multimedia card. Also, in an embodiment, the '~ unit' may include one or more processors.

[0037] For convenience of explanation, the present invention uses terms and names defined in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard. However, the present invention is not limited to these terms and names and can be equally applied to systems conforming to other standards.

[0038] FIG. 1a is a diagram illustrating the structure of a mobile communication system according to one embodiment of the present disclosure.

[0039] Referring to FIG. 1a, a wireless access network of a next-generation mobile communication system may be composed of a next-generation base station (New Radio Node B, hereinafter referred to as NR NB, 1a-10) and a NR CN (New Radio Core Network, or NG CN: Next Generation Core Network, 1a-05). A user terminal (New Radio User Equipment, hereinafter referred to as NR UE or terminal, 1a-15) may access an external network through the NR NB (1a-10) and the NR CN (1a-05).

[0040] In Fig. 1a, NR NB (1a-10) corresponds to eNB (Evolved Node B) of the existing long term evolution (LTE) system. NR NB is connected to NR UE (1a-15) via a wireless channel and can provide superior service than the existing Node B. In the next-generation mobile communication system, all user traffic is serviced through a shared channel, so a device that collects status information such as buffer status, available transmission power status, and channel status of UEs and performs scheduling is required, and this is handled by NR NB (1a-10). One NR NB can typically control multiple cells. In order to implement ultra-high-speed data transmission compared to the existing long term evolution (LTE), it can have a bandwidth exceeding the existing maximum bandwidth, and beamforming technology can be additionally grafted using orthogonal frequency division multiplexing (OFDM) as a wireless access technology. In addition, an adaptive modulation and coding (AMC) method is applied, which determines the modulation scheme and channel coding rate according to the channel status of the terminal.

[0041] NR CN (1a-05) can perform functions such as mobility support, bearer setup, and QoS (quality of service) setup. NR CN is a device that handles various control functions as well as mobility management for terminals and can be connected to multiple base stations. Furthermore, the next-generation mobile communication system can be interoperable with the existing LTE system, and NR CN can be connected to the mobility management entity (MME, 1a-25) via a network interface. The MME can be connected to the existing base station, eNB (1a-30).

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

[0043] Referring to FIG. 1b, the wireless protocol of the next-generation mobile communication system is composed of NR SDAP (NR service data adaptation protocol, 1b-01, 1b-45), NR PDCP (NR packet data convergence protocol, 1b-05, 1b-40), NR RLC (NR radio link control, 1b-10, 1b-35), and NR MAC (NR medium access control, 1b-15, 1b-30) in the terminal and the new radio (NR) base station, respectively.

[0044] The main functions of NR SDAP (1b-01, 1b-45) may include some of the following functions.

[0045] - Transfer of user plane data

[0046] - Mapping function between QoS flow and data bearer for both DL and UL

[0047] - Marking function of QoS flow ID for both uplink and downlink (marking QoS flow ID in both DL and UL packets)

[0048] - Ability to map relective QoS flow to data bearer for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

[0049] For the above SDAP layer device, the terminal can be configured by a radio resource control (RRC) message for each PDCP layer device, each bearer, or each logical channel, whether to use the header of the SDAP layer device or whether to use the function of the SDAP layer device, and when the SDAP header is configured, the terminal can be instructed to update or reset the mapping information for the QoS flow and data bearer of the uplink and downlink with a 1-bit indicator for NAS QoS reflection configuration (NAS reflective QoS) and a 1-bit indicator for AS QoS reflection configuration (AS reflective QoS) of the SDAP header. The SDAP header can include QoS flow ID information indicating quality of service (QoS). The QoS information can be used as data processing priority, scheduling information, etc. to support a smooth service.

[0050] The main functions of NR PDCP (1b-05, 1b-40) may include some of the following functions:

[0051] ● Header compression and decompression (ROHC only)

[0052] ● User data transfer function

[0053] ● In-sequence delivery of upper layer PDUs

[0054] ● Out-of-sequence delivery of upper layer PDUs

[0055] ● Reordering function (PDCP PDU reordering for reception)

[0056] ● Duplicate detection of lower layer SDUs

[0057] ● Retransmission function (Retransmission of PDCP SDUs)

[0058] ● Encryption and decryption functions (Ciphering and deciphering)

[0059] ● Timer-based SDU discard in uplink

[0060] The reordering function of the NR PDCP device above refers to the function of reordering PDCP PDUs received from the lower layer in order based on the PDCP SN (sequence number), and may include a function of transmitting data to the upper layer in the reordered order. Alternatively, it may include a function of transmitting data directly without considering the order, a function of recording lost PDCP PDUs by reordering the order, a function of reporting the status of lost PDCP PDUs to the transmitting side, and a function of requesting retransmission of lost PDCP PDUs.

[0061] The main functions of NR RLC (1b-10, 1b-35) may include some of the following functions.

[0062] Data transfer function (Transfer of upper layer PDUs)

[0063] ● In-sequence delivery of upper layer PDUs

[0064] ● Out-of-sequence delivery of upper layer PDUs

[0065] ● ARQ function (Error Correction through ARQ)

[0066] ● Concatenation, segmentation and reassembly of RLC SDUs

[0067] ● Re-segmentation of RLC data PDUs

[0068] ● Reordering of RLC data PDUs

[0069] ● Duplicate detection function

[0070] ● Error detection function (Protocol error detection)

[0071] ● RLC SDU discard function

[0072] ● RLC re-establishment function

[0073] The in-sequence delivery function of the NR RLC device mentioned above refers to the function of sequentially delivering RLC SDUs received from a lower layer to an upper layer, and may include a function of reassembling and delivering a case where an original RLC SDU is received divided into multiple RLC SDUs. Or, it may include a function to reorder received RLC PDUs based on the RLC SN (sequence number) or PDCP SN (sequence number), it may include a function to record lost RLC PDUs by reordering the order, it may include a function to report the status of lost RLC PDUs to the transmitter, it may include a function to request retransmission of lost RLC PDUs, it may include a function to sequentially deliver only RLC SDUs up to the lost RLC SDU to the upper layer when there is a lost RLC SDU, or it may include a function to sequentially deliver all RLC SDUs received before the timer starts if a predetermined timer has expired even when there is a lost RLC SDU, or it may include a function to sequentially deliver all RLC SDUs received up to the timer has expired even when there is a lost RLC SDU to the upper layer. In addition, the RLC PDUs can be processed in the order in which they are received (in the order of arrival, regardless of the order of the sequence number) and delivered to the PDCP device out of order (out-of-sequence delivery). In the case of segments, the segments stored in the buffer or to be received later can be received, reconstructed into a complete RLC PDU, processed, and delivered to the PDCP device.The above NR RLC layer may not include a concatenation function, and the function may be performed in the NR MAC layer or replaced with a multiplexing function of the NR MAC layer.

[0074] The out-of-sequence delivery function of the NR RLC device above refers to the function of directly delivering RLC SDUs received from a lower layer to an upper layer regardless of the order, and may include a function of reassembling and delivering RLC SDUs when an original RLC SDU is received divided into multiple RLC SDUs, and may include a function of storing the RLC SN or PDCP SN of received RLC PDUs and arranging the order to record lost RLC PDUs.

[0075] NR MAC (1b-15, 1b-30) can be connected to multiple NR RLC layer devices configured in one terminal, and the main functions of NR MAC can include some of the following functions.

[0076] ● Mapping function (Mapping between logical channels and transport channels)

[0077] ● Multiplexing / demultiplexing of MAC SDUs

[0078] ● Scheduling information reporting function

[0079] ● HARQ function (Error correction through HARQ)

[0080] ● Priority handling between logical channels of one UE

[0081] ● Priority handling between UEs by means of dynamic scheduling

[0082] ● MBMS service identification function

[0083] ● Transport format selection function

[0084] ● Padding function

[0085] The NR PHY layer (1b-20, 1b-25) can perform operations such as channel coding and modulating upper layer data, converting it into OFDM symbols and transmitting it over a wireless channel, or demodulating and channel decoding OFDM symbols received over a wireless channel and transmitting them to a higher layer.

[0086] FIG. 1c is a diagram illustrating the structure of another next-generation mobile communication system according to one embodiment of the present disclosure.

[0087] Referring to FIG. 1c, a cell served by a beam-based NR gNB (1c-05) may be composed of multiple TRPs (Transmission Reception Points, 1c-10, 1c-15, 1c-20, 1c-25, 1c-30, 1c-35, 1c-40).

[0088] TRP (1c-10~1c-40) represents a block that separates some of the functions of transmitting and receiving physical signals from an existing NR base station (eNB), and is composed of multiple antennas. The NR gNB (1c-05) can also be expressed as a CU (Central Unit), and the TRP can be expressed as a DU (Distributed Unit). The functions of the NR gNB (1c-05) and TRP can be configured by separating each layer in the PDCP / RLC / MAC / PHY layers, such as 1c-45. That is, the TRP can perform the function of the corresponding layer with only the PHY layer (1c-15, 1c-25), the TRP can perform the functions of the corresponding layers with only the PHY layer and the MAC layer (1c-10, 1c-35, 1c-40), and the TRP can perform the functions of the corresponding layers with only the PHY layer, the MAC layer, and the RLC layer (1c-20, 1c-30). In particular, the TRP (1c-10 to 1c-40) can use beamforming technology that transmits and receives data by generating narrow beams in multiple directions using multiple transmit / receive antennas.

[0089] User terminals (1c-50) can connect to NR gNBs (1c-05) and external networks via TRPs (1c-10 to 1c-40). The NR gNBs (1c-05) collect and schedule status information, such as buffer status, available transmission power status, and channel status, of terminals to provide services to users, thereby supporting connections between the terminals and the core network (CN), particularly the AMF / SMF (1c-50).

[0090] The TRP in the present invention is based on a structure (1c-15, 1c-25) that can perform the function of the corresponding layer with only the PHY layer.

[0091] FIG. 1D is a diagram illustrating a scenario for inter-cell beam management according to one embodiment of the present disclosure, in which a terminal transmits and receives data through a beam of a TRP (transmission / reception point) of a neighboring cell that supports beam change on an L1 / L2 basis while maintaining a connection state with a serving cell.

[0092] Although this drawing describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2; 1d-10, 1d-15) exist within one DU (Distributed unit, 1d-05), the scope of the present invention is not limited thereto, and the overall content of the present invention can also be applied to the case of inter-DU (each DU constitutes one TRP-Cell). In addition, throughout the present invention, a cell (TRP 2, Cell 2) that is not a serving cell supporting L1 / L2-based mobility (beam change and serving cell change) is referred to as a neighbor cell, a non-serving cell, an additional cell with the PCI (physical cell identifier) ​​different from the serving cell, etc.

[0093] The existing terminal beam change procedure (1d-45) is such that the terminal (user equipment, UE, 1d-20) is transmitting and receiving data in a connected state through TRP 1 (1d-10) of serving cell 1, and may be set to the optimal beam, TCI state 1 (1d-25, 1d-30). In this step, the terminal may be instructed to configure information for L3 channel measurement (RRM; radio resource management) for an additional cell (TRP 2-Cell 2, 1d-15) having a different PCI from the serving cell through RRC configuration information (RRC configuration) from the serving cell (1d-10), and in step 1d-46, the terminal (1d-20) may perform an L3 measurement operation (1d-46) for the corresponding frequency and cell.

[0094] Thereafter, in step 1d-47, the serving cell (TRP 1-Cell 1, 1d-10) may instruct (1d-47) a handover to the corresponding cell (TRP 2-Cell 2, 1d-15) based on the reported measurement value, and the handover may be completed. In step 1d-48, additional RRC configuration information may be transmitted (1d-48) to the terminal (1d-20) via TRP 2-Cell 2 (1d-15). The RRC configuration information may include uplink (UL) / downlink (DL) configuration information in the corresponding cell, L1 measurement-related settings (e.g., channel state information - referece signal (CSI-RS) measurement and reporting), and in particular, TCI state configuration information for a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) channel.

[0095] In step 1d-49, the terminal (1d-20) can perform L1 measurement (1d-49) according to the settings, and in step 1d-50, the base station can update the TCI state through L1 / L2 signaling according to the measurement report. (1d-50) Here, the optimal beam, TCI state 2 (1d-40), can be indicated. In this step, before the handover, the serving cell is Cell 1, and after the handover, Cell 2 becomes the serving cell. In other words, many procedures and time are required even after the handover until the optimal beam is indicated.

[0096] Unlike the existing terminal beam change procedure (Legacy operation, 1d-45) described above, the improved beam change technique (1d-55) proposed in the present disclosure is as follows. In step 1d-56, the terminal (user equipment, UE, 1d-20) can receive beam settings associated with an additional cell (TRP 2-Cell 2, 1d-15) having a different PCI from the serving cell through RRC configuration information (1d-56) from the serving cell (1d-10).

[0097] The beam setting associated with the serving cell and the additional cell (TRP 2-Cell 2, 1d-15) with different PCI, i.e., the part that associates the TCI state corresponding to TRP2, can be applied by indicating by associating a new cell ID (Physical cell ID, PCI; additionalPCI-r17) as follows.

[0098]

[0099] Additionally, a unified TCI state framework can be applied to manage beams between the cells. The unified TCI state framework applies a common TCI state framework to uplink and downlink, common channels, and dedicated channels, and can be configured in either Joint UL / DL mode or Separate UL / DL mode.

[0100]

[0101] 1. Joint UL / DL mode: Set UL and DL to share the same TCI settings (in PDSCH-Config)

[0102]

[0103] 2. Separate UL / DL mode: The UL and DL each provide their own TCI configurations. The TCI state for the DL follows the configuration in dl-OrJoint-TCIStateList-r17 (in PDSCH-Config), and the TCI state for the UL follows ul-TCI-StateList-r17 (in BWP-UplinkDedicated).

[0104]

[0105] After the settings for TRP 2-Cell 2 are provided in the RRC connection state in serving cell 1, the terminal (1d-20) can perform L1 measurement for the corresponding TRP 2-Cell 2 according to the settings in step 1d-57 and report the results to the serving cell (Cell 1, 1d-10) (1d-57).

[0106] If the serving cell (Cell1, 1d-10) determines that a change to a specific beam (TCI state 2, 1d-35, 1d-40) of TRP 2 (Cell 2, 1d-15) is necessary from the serving cell beam (TCI state 1, 1d-25, 1d-30) based on the measurement results, the cell may trigger a beam change and instruct the terminal (1d-20) through L1 / L2 signaling (1d-58). The terminal (1d-20) may change the beam to the specific beam (TCI state 2, 1d-40) of TRP 2 (Cell 2, 1d-15) through the instruction, and may perform physical channel configuration and upper layer configuration operations associated with the configured beam. From this step onwards, the terminal (1d-20) remains connected to the serving cell (Cell 1, 1d-10), but can transmit and receive data using the channel link of TRP 2 (Cell 2, 1d-15). Data transmission and reception may include PDCCH reception and / or PDSCH reception, PUCCH transmission and / or PUSCH transmission. That is, transmission and reception for the common control channel is performed via the serving cell (Cell 1, 1d-10).

[0107] Thereafter, in step 1d-59, the terminal (1d-20) can perform L3 measurement operation according to the measurement settings set in the independent serving cell (1d-59), and in step 1d-60, the terminal (1d-20) can receive a handover command message from the serving base station (Cell 1) and perform a serving cell change to Cell 2 (1d-60).

[0108] Through this technique (1d-55), the terminal performs data transmission and reception with a specific TRP 2 of Cell2 that supports L1 / L2-based mobility while connected to the serving cell, and can continuously use the beam even after handover.

[0109] For reference, the RRC settings for the L1 measurement and report related settings and operations in step 1d-57 described above are described below. These contents are also fundamentally applicable to the following embodiments of the present invention, and enhanced techniques may be added in future embodiments.

[0110] 1. L1 measurement settings (CSI-ResourceConfig, set within the serving cell, set within the ServingCellConfig IE)

[0111] - CSI-RS / SSB resources and resource pools requiring measurement (nzp-CSI-RS, csi-IM, csi-SSB)

[0112] - CSI-RS / SSB resource settings (aperiodic, semi-persistent) and triggering settings that require measurement

[0113] - When CSI-RS resources reference SSB resources, additional PCI information is provided to enable L1 measurement from neighboring cells (up to 7 neighboring cells (PCI) can be added from one serving cell).

[0114]

[0115]

[0116] 2. L1 report configuration (configured within ServingCellConfig IE within the serving cell)

[0117] - Report type: periodic report, semi-periodic report on PUCCH, semi-periodic report on PUSCH, aperiodic report on PUSCH (periodic, semi-persistent for PUCCH, semi-persistent for PUSCH, aperiodic)

[0118] - Report quantity

[0119] - Settings required for other reports

[0120] FIG. 1ea and FIG. 1eb are diagrams illustrating a scenario in which a terminal transmits and receives data by changing a serving cell and beam to a transmission / reception point (TRP) of a cell that supports L1 / L2-based beam changing according to an embodiment of the present disclosure.

[0121] Although this drawing describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2; 1e-10, 1e-15, 1e-40, 1e-45) exist within one DU (Distributed unit, 1e-05, 1e-35), the scope of the present invention is not limited thereto, and the overall content of the present invention can also be applied to the case of inter-DU (each DU constitutes one TRP-Cell) within an intra CU.

[0122] Unlike the existing terminal beam changing procedure (1d-45, 1d-55) described in Fig. 1d, the improved beam changing technique (1e-25, 1e-75) considered in the present embodiments is as follows.

[0123] Example 1 (1e-25): After performing inter-cell beam management (change) operation, L1 / L2 handover is performed.

[0124] Example 2 (1e-75): Immediate L1 / L2 handover

[0125] First, to explain the entire operation of Example 1 (1e-25), in step 1e-26, the terminal (user equipment, 1e-20) can receive common configuration information and dedicated configuration information for an additional cell (TRP 2-Cell 2, 1e-15) with different PCI from the serving cell through RRC configuration information from the serving cell (1e-10) (1e-26). That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon, and ServingCellConfig can be provided in advance.

[0126] The configuration information may be provided in the form of pre-configuration in the RRC configuration, and may include configuration information for multiple cells. In addition, the configuration is characterized by including all configuration information (e.g., cell configuration, bearer configuration, security key configuration, etc.) applied when the terminal moves to the corresponding cell (handover). In addition, the configuration includes enhanced configurations with reference to the unified TCI state configuration and L1 measurement and report-related configurations described in step 1d-56 of FIG. More specifically, the enhanced unified TCI state configuration and L1 measurement and report configuration may be included for continuous LTM, which will be described in detail in the following drawings of the present invention.

[0127] After the terminal (1e-20) is provided with settings for TRP 2-Cell 2 (1e-15) in an RRC connection state with serving cell 1 (1e-20), the terminal (1e-20) can perform L1 measurement for the corresponding TRP 2-Cell 2 (1e-15) according to the settings received in step 1e-27 and report the results to the serving cell (Cell 1, 1e-10).

[0128] If the serving cell (1e-10) determines that a change to a specific beam (TCI state 2, 1e-40) of TRP 2 (Cell 2, 1e-15) is necessary from the serving cell beam (TCI state 1, 1e-25) based on the measurement results, the serving cell (1e-10) may trigger a beam change at step 1e-28 and instruct the terminal (1e-20) through L1 / L2 signaling. The terminal (1e-20) may perform a beam change to TRP 2 (Cell 2, 1e-15) through the instruction and transmit and receive data through the TRP 2 (Cell 2, 1e-15). At this time, the serving cell change does not occur and the terminal (1e-20) is still RRC connected to the serving cell (Cell 1, 1e-10). Afterwards, the terminal (1e-20) can still perform L1 measurement for TRP 2-Cell 2 (1e-15) and report the result to the serving cell (Cell 1, 1e-10).

[0129] The serving cell (Cell 1, 1e-10) can instruct the UE to perform a handover if the L1 measurement reported by the UE satisfies the triggering conditions for a handover to TRP 2-Cell 2 (1e-15). The specific operation of the triggering conditions for a handover will be described below. The handover indication can be an L1 / L2 message. That is, the Medium Access Control Control Element (MAC CE) can contain an indication for a handover.

[0130] To explain the entire operation of Embodiment 2 (1e-75), in step 1e-76, the terminal (1e-50) can receive common configuration information and dedicated configuration information for an additional cell (TRP 2-Cell 2, 1e-45) with a different PCI from the serving cell (1e-40) through RRC configuration information (1e-76). That is, the ServingCellID or candidateCellID (cell ID associated with PCI) and configuration information corresponding to the candidate L1 / L2 triggered mobility (LTM) cell can be provided in advance.

[0131] The configuration information may be provided in the form of pre-configuration in the RRC configuration, and may include configuration information for multiple cells. In addition, the configuration is characterized by including all configuration information (e.g., cell configuration, bearer configuration, channel measurement configuration, etc.) applied when the terminal moves to the corresponding cell (handover). In addition, the configuration includes the unified TCI state configuration described in step 1d-56 of FIG. 1 and the L1 measurement and report-related configurations modified to support continuous LTM. The L1 measurement and report and TCI state configurations applied to the present invention are described in detail below.

[0132] After the configuration for TRP 2-Cell 2 (1e-45) is provided in the RRC connection state to serving cell 1, the terminal (1e-50) can perform L1 measurement for the TRP 2-Cell 2 (1e-45) according to the configuration received in step 1e-77 and report the result to the serving cell (Cell 1, 1e-40).

[0133] If the serving cell determines that a handover is necessary simultaneously with a beam change to a specific beam (TCI state 2, 1e-70) of TRP 2 (Cell 2, 1e-45) rather than the serving cell beam (TCI state 1, 1e-45) based on the measurement results, the beam change and handover can be triggered in step 1e-78 and instructed to the terminal (1e-50) through L1 / L2 signaling. The terminal (1e-50) can perform a handover simultaneously with a beam change to TRP 2 (Cell 2, 1e-15) through the instruction and can transmit and receive data through the TRP 2 (Cell 2, 1e-15). At this time, the terminal can apply the configuration information for the target cell where the handover is performed, which was previously configured in step 1e-76. In this step, the terminal may perform a random access or may omit the random access to the target cell depending on whether uplink synchronization is required. Detailed operations are described in the drawings below.

[0134] FIG. 1f is a diagram illustrating a continuous L1 / L2 triggered mobility (LTM) operation based on a reference cell configuration in an intra-CU according to an embodiment of the present disclosure.

[0135] In step 1f-10, the terminal (user equipment, UE, 1f-01) can report L3 measurements to the source cell (1f-02).

[0136] More specifically, a terminal (1f-01) in an RRC connection state performs data transmission and reception with a source cell 1 (1f-02), and can transmit layer 3 measurement values ​​for the serving cell and surrounding cells to the source cell 1 (1f-02) according to the layer 3 measurement and reporting set in step 1f-10.

[0137] At this time, the actual measurement value is transmitted to the CU (1f-03) of the base station. This is because the base station CU (1f-03) is responsible for processing radio resource control (RRC) messages and determining mobility.

[0138] In step 1f-15, the base station CU (1f-03) can transmit an L1 / L2 configuration request message to at least one LTM candidate cell (1f-04, 1f-05, 쪋).

[0139] More specifically, the base station CU (1f-03) can generate a message requesting setup information for L1 / L2-based handover to LTM candidate surrounding cells (1f-04, 1f-05) in step 1f-15 based on the measurement value report received from the terminal, and transmit the message to the F1 interface. The message requesting setup information for the L1 / L2-based handover may include a UE Context Setup Request or a UE Context Modification Request. Although the candidate cell is shown in connection with the DU in the drawing, in reality, the candidate cell and the DU may be mapped 1:1, or multiple candidate cells may be included in one DU.

[0140] The message requesting configuration information for the above L1 / L2-based handover may request neighboring cells to be determined as candidate cells for L1 / L2-based handover, and at the same time, request RRC configuration information to be applied when L1 / L2-based handover is performed to the corresponding cell.

[0141] At this time, the source base station CU (1f-03) can transmit the source cell configuration information and separate reference cell configuration information. Although omitted in the drawing, if the source base station CU (1f-03) fails to generate the reference cell configuration from the LTM candidate surrounding cells (1f-04, 1f-05) at that stage, it can request an IE requesting the reference cell configuration. That is, two methods can be used for the setting of the following IE. (Using the CHOICE structure)

[0142] 1. Request to set the reference cell (request to set the lower layer of LTM candidate cells): i.e., used as a preprocessing procedure for LTM coordination.

[0143]

[0144] 2. Providing reference cell settings ((providing reference cell settings to LTM candidate cells; CellGroupConfig format): Used when requesting LTM settings

[0145] In response to this, lower layer settings that can be reference cell settings can be received from LTM candidate surrounding cells (1f-04, 1f-05).

[0146]

[0147] Step 1f-25, i.e., UE Context Setup / Modificatoin Response message, can be used as a preprocessing procedure for LTM coordination, in which case, as described above, the message transmitted from the LTM candidate cells (1f-04, 1f-05) of step 1f-25 to the source base station CU (1f-03) may include the lower layer configuration information of each LTM cell. When step 1f-25 (UE Context Setup / Modificatoin Response message) is used as an LTM configuration request, the UE can generate a candidate cell configuration to be applied to each LTM candidate cell in step 1f-20 based on the received reference cell configuration, and can check whether the candidate cell configuration is complete (LTM Complete Configuration Indicator) and transmit it as a response message.

[0148] Whether the candidate cell configuration is complete refers to whether the reference cell configuration is received from the source base station CU (1f-03) and the configuration information of the corresponding LTM candidate cell is generated based on the configuration information. In other words, if it is generated based on the delta configuration based on the reference cell configuration, the configuration of the corresponding cell is said to be incomplete, and only when the LTM candidate cell configuration information provided by the corresponding cell is completely generated regardless of the reference cell configuration can the LTM Complete Configuration Indicator be checked as complete and transmitted.

[0149] The reference cell configuration information transmitted by the above-described source base station CU (1f-03) to each candidate cell (1f-04, 1f-05) may be configuration information (common configuration) that can be commonly applied to multiple target candidate cells to reduce signaling overhead when the target candidate cells provide configuration information for LTM. The configuration information that can be commonly applied may include measurement configuration, bearer configuration, or, if the cells belong to the same CellGroup, configurations set at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.).

[0150] Alternatively, if the source base station CU (1f-03) roughly knows (or has a procedure for knowing) the configuration information for each candidate cell (1f-04, 1f-05), the reference cell configuration may be determined through a separate procedure for obtaining the reference cell configuration information.

[0151] For example, the purpose of the source base station CU (1f-03) transmitting the reference cell configuration to each candidate cell (1f-04, 1f-05) is to enable each candidate cell to transmit only the configuration information added based on the reference cell configuration to the source base station CU (1f-03) so that the delta configuration can be applied. Applying the delta configuration can mean a method of configuring a complete configuration by applying a configuration added on top of the reference cell configuration, or a method of configuring a complete configuration by overwriting the settings in the target cell based on the reference cell configuration. This method can be transmitted to the terminal as is thereafter, thereby reducing the signaling of the RRC message transmitted to the terminal.

[0152] That is, according to the method described above, the candidate neighboring cells (1f-04, 1f-05) that received a message requesting configuration information for L1 / L2-based handover in step 1f-20 generate configuration information of each candidate neighboring cell when L1 / L2-based handover is applied based on the configuration information of the transmitted reference cell, based on the delta configuration or without applying it.

[0153] In step 1f-25 thereafter, the base station CU (1f-03) can receive an L1 / L2 configuration response message from at least one LTM candidate cell (1f-04, 1f-05, 쪋).

[0154] More specifically, each candidate peripheral cell (1f-04, 1f-05) can store the configuration information for the generated L1 / L2-based handover in a configuration information response message for the L1 / L2-based handover (L1 / L2 config response message; UE Context Setup Response or UE Context Modification Response) and transmit it to the base station CU (1f-03).

[0155] In step 1f-30, the base station CU (1f-03) can transmit an RRC reset message including at least one candidate cell configuration information to the terminal (1f-01).

[0156] More specifically, the base station CU (1f-03) can receive an RRC message generated based on the configuration information received from each candidate cell, and the source cell (1f-02) can then transmit the message to the terminal (1f-01).

[0157] The above RRC message may include configuration information (Pre-Config1, 쪋, Pre-ConfigN) for surrounding candidate cells to which L1 / L2-based handover (LTM) is applied. The Pre-Config included in the above message is a message that includes CellGroupConfig configuration received from LTM candidate cells in step 1f-25, bearer configuration for LTM candidate cells generated by the base station, and Layer 3 (Layer 3, L3) measurement configuration.

[0158] The terminal (1f-01) that receives the RRC message in step 1f-35 performs a procedure for decoding and processing the RRC message.

[0159] The above processing may include methods for ASN.1 decoding and validating the received message and storing and managing the configuration contents. In addition, the terminal (1f-01) may store the LTM configuration information for each candidate cell decoded in this step as complete configuration information in the terminal's buffer (memory), and at the same time, store the received reference cell configuration information in the terminal's buffer (memory) and manage it for the future.

[0160] In the RRC message (or the configuration information for each LTM candidate cell) at step 1f-30, an indicator may be provided indicating whether the reference cell configuration information and the configuration information for each candidate cell are complete.

[0161]

[0162] In step 1f-40, the terminal (1f-01) can perform L1 (layer 1) measurement and reporting for each candidate surrounding cell, and at the same time, in step 1f-45, it can also perform L3 measurement and reporting according to the settings.

[0163] A source cell that receives an L1 measurement report can decide on a handover based on the measurement value, and can instruct the terminal (1f-01) to perform an L1 / L2 handover in step 1f-50.

[0164] In step 1f-50, a MAC CE indicating a handover can be used for L1 / L2 signaling. The L1 measurement value transmission and handover decision for determining the L1 / L2 handover in steps 1f-40 and 1f-50 above can be performed by the source cell (DU). That is, the source cell can independently determine the handover based on the measurement value criteria (threshold and measurement value range) for making the handover decision for each candidate neighboring cell received from the previous base station and accordingly transmit the L1 / L2 signaling to the terminal.

[0165] When the L1 / L2 handover instruction is transmitted to the terminal (1f-01), the terminal (1f-01) can start the handover procedure in step 1f-55 and start the timer for L1 / L2 handover.

[0166] At this time, the timer for L1 / L2 handover can reuse the T304 timer for LTM.

[0167] In step 1f-60, the terminal (1f-01) can apply settings for a target cell to which L1 / L2 handover is applied.

[0168] More specifically, the terminal (1f-01) can replace the current configuration with the complete configuration information of the designated LTM target cell previously stored in the terminal. This is one of the LTM candidate neighboring cell configurations previously received in step 1f-30 and is stored in the terminal.

[0169] At step 1f-65, if necessary, the terminal may perform a random access procedure.

[0170] More specifically, depending on the applicable settings, the terminal can perform random access to the target cell if random access is required. Conversely, if random access is not indicated or required, the random access procedure is omitted. Cases where random access is not indicated or required may include cases where uplink synchronization has already been performed or aligned.

[0171] In step 1f-70, the terminal (1f-01) can perform a handover completion procedure with the target cell.

[0172] The above handover completion procedure may be a handover completion procedure for LTM. This procedure may vary depending on the method of indicating the handover completion, and is a process of transmitting an RRCReconfigurationComplete message when the target cell's configuration is received at the RRC message level.

[0173] Additionally, since this scenario considers application to intra-CU, the target cell (DU, 1f-04) that receives the handover completion message in step 1f-75 can forward the received message to the base station CU (1f-03). At this time, the target cell (DU, 1f-04) can forward the handover completion message received via the F1 interface as is, or can reprocess the message based on the received information and forward it.

[0174] Thereafter, in step 1f-80, the base station CU (1f-03) can transmit information about the completion of the handover to the source cell (1f-02) and instruct it to release the terminal context.

[0175] Additionally, as described in step 1f-85, embodiments of the present invention support subsequent LTM operations.

[0176] Subsequent LTM operation means that the LTM configuration information (configuration of target candidate cells and reference cell configuration information, etc.) received by the terminal in step 1f-30 is stored in the terminal as is, and the terminal continues to perform the LTM procedure unless the corresponding LTM configuration information is changed / released / added through a separate RRC configuration. If it is necessary to update the reference cell configuration information, new RRC configuration information can be transmitted to the terminal to update the reference cell configuration information. That is, the procedure described in this drawing can be triggered again to perform this.

[0177] In summary, if the terminal (1f-01) receives reference cell setting information in step 1f-30, it stores it in the terminal buffer and, if there is no separate setting update, can continue to use the corresponding setting as reference cell setting information even after performing LTM (step 1f-50). In other words, the reference cell setting and LTM candidate setting values ​​stored in successive LTMs can be applied.

[0178] Also, in step 1f-30, if the terminal (1f-01) is not provided with reference cell configuration information in an RRC connection state, the reference cell configuration can be saved as empty according to the terminal operation option described above, or the configuration information for the corresponding source cell (PCell) from which the LTM configuration information was received can be saved as reference cell configuration information.

[0179] FIG. 1ga and FIG. 1gb are diagrams illustrating the overall operation for explaining a reference cell setting method for supporting continuous L1 / L2-based Master cell group (MCG) handover (L1 / L2 triggered mobility, LTM) operation in cells within different CUs according to one embodiment of the present disclosure.

[0180] In step 1g-10, the terminal (user equipment, UE, 1g-01) can report L3 measurements to the source cell (1g-02).

[0181] More specifically, a terminal (1g-01) in an RRC connection state performs data transmission and reception with a source cell 1 (1g-02), and can transmit layer 3 measurement values ​​for the serving cell and surrounding cells to the source base station (1g-03) according to the layer 3 measurement and reporting set in step 1g-10.

[0182] At this time, the actual measurement value is transmitted to the CU (1g-03) of the base station. This is because the base station CU (1g-03) is responsible for processing radio resource control (RRC) messages and determining mobility.

[0183] In step 1g-15, the CU (1g-03) of the base station can perform an Intra-CU MCG LTM candidate decision and configuration preparation procedure. (Intra-CU MCG LTM candidate decision and configuration preparation)

[0184] More specifically, the base station CU (1g-03) can generate a message requesting setup information for L1 / L2-based handover to the intra-CU's LTM candidate surrounding cells (1g-04, 1g-05) in step 1g-15 based on the measurement value report received from the terminal, and transmit the message to the F1 interface. The message requesting setup information for the L1 / L2-based handover can include a UE Context Setup Request or a UE Context Modification Request.

[0185] The information that can be included in requesting setup information for the above L1 / L2-based handover is summarized as follows. The following message content can be used as a component of messages in steps 1g-15 and 1g-35.

[0186] - LTM candidate ID

[0187] - Mapping information between LTM candidate ID and corresponding cell ID

[0188] - Beam information to be used for each candidate (TCI state)

[0189] ■ In this case, the meaning of “use” may mean a beam that is linked to a RACH occasion when performing downlink (DL) and / or uplink (UL) synchronization and / or random access channel (RACH), and / or a beam to be used for first UL data transmission. If necessary, an indicator for each case may be accompanied to perform a cell switch.

[0190] - RACH preamble index

[0191] - SSB index: This is the index of the synchronization signal block (SSB) used to determine the RACH occasion in each candidate cell, and can mean the occasion of the RACH preamble of contention-free random access (CFRA).

[0192] The above information is the information that must be displayed when issuing a cell switch command MAC CE instruction to a candidate cell that has made an LTM decision.

[0193] - Reference cell setting information (in a CHOICE structure, one of the two contents below can be included and transmitted. See Fig. 1f)

[0194] ■ Request for standard cell definition

[0195] ■ Provides reference cell settings

[0196] - CSI resource request information for each candidate cell

[0197] ■ It can be requested in the pre-configuration preprocessing part for LTM candidate cells.

[0198] ◆ Indicator of whether the request is for initial preparation, eg, initiation, or subsequent to the initial request for modification.

[0199] ■ In particular, when the request information is included, lower layer setting information in this message may not be transmitted.

[0200] ■ If CSI resource information is received from candidate cells with the corresponding request information, the CSI resource settings of each candidate cell below may be transmitted instead of the request. In other words, a CSI resource setting preprocessing procedure of at least 2 steps is required.

[0201] - CSI report configuration considering the CSI resources of each candidate cell above

[0202] ■ The purpose is that when a candidate DU creates the above information and transmits it to the CU, this information can be used as the CSI report configuration within the target cell configuration (RRCReconfiguration) of the concerned cell (i.e., target cell) created by the CU. In addition, the information may not be transmitted separately, but may be included within the target cell configuration (RRCReconfiguration) and transmitted.

[0203] ■ That is, when a terminal moves from another cell to a concerned cell, it can be used as a CSI report configuration with that cell as the serving cell. It is used to include it in the target cell config without providing a separate L1 configuration for subsequent LTM.

[0204] - RACH configuration and lower layer setting information to be used in the concerned cell

[0205] ■ This information is transmitted from the candidate DU to the CU, and can be written as the settings required for performing RACH within the target cell configuration of the concerned cell, the lower layer settings to be applied when moving to the cell, and / or the reference settings including them, and can be transmitted to the terminal later.

[0206] ■ In particular, some of the RACH settings can be used to include RACH preamble index, mask, and occasion decision information in the cell switch command MAC CE described above.

[0207] In other words, a step is required to generate LTM pre-configuration while the base station CU and LTM candidate cells send and receive messages through the F1 interface to request application and setup for LTM candidate cells.

[0208] Although the drawing illustrates a single procedure of step 1g-15, the step can be applied to multiple procedures (procedures 1g-15 and 1g-35).

[0209] There are several procedures that can be performed to configure L1 measurement resources and reporting, namely, the 1g-15 and 1g-35 procedures are summarized below.

[0210] 1. Step 1: Request L1 measurement resources and reference cell settings to at least one LTM candidate cell.

[0211] 2. Step 2: At least one LTM candidate cell responds with lower layer configuration information for configuring L1 measurement resources and reference cells for the corresponding cell to the source base station CU (1g-03). This procedure can be transmitted to the source base station via the F1 interface as a UE Context Setup Response message.

[0212] 3. Step 3: The source base station CU (1g-03) transmits to each candidate cell the L1 measurement resource settings and reference cell settings for continuous LTM support based on the settings collected for each candidate cell. This procedure can be transmitted to the source base station via the F1 interface as a UE Context Modification Request message.

[0213] 4. Step 4: The source base station CU (1g-03) can receive the final L1 measurement report configuration and configuration information (CellGroupConfig) applied to the LTM candidate cells from the LTM candidate cells. This procedure can be delivered to the source base station through the F1 interface as a UE Context Modification Response message.

[0214] 5. Step 5: LTM-related settings can be delivered to the terminal. The source base station can collect all LTM-related settings received from LTM candidate cells and store them in an RRCReconfiguration message delivered to the terminal, and deliver the corresponding RRC configuration information to the terminal. In other words, pre-configuration information for LTM candidate cells can be delivered to the terminal.

[0215] At this time, the source base station CU (1g-03) can transmit source cell configuration information and separate reference cell configuration information.

[0216] The reference cell configuration information transmitted by the above-described source base station CU (1g-03) to each candidate cell (1g-04, 1g-05) may be configuration information (common configuration) that can be commonly applied to multiple target candidate cells to reduce signaling overhead when the target candidate cells provide configuration information for LTM. The configuration information that can be commonly applied may include measurement configuration, bearer configuration, or, if the cells belong to the same CellGroup, configurations set at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.).

[0217] Alternatively, if the source base station CU (1g-03) roughly knows (or has a procedure to know) the configuration information for each candidate cell (1g-04, 1g-05), the reference cell configuration may be determined through a separate procedure, such as obtaining the reference cell configuration information.

[0218] For example, the purpose of the source base station CU (1g-03) transmitting the reference cell configuration to each candidate cell (1g-04, 1g-05) is to enable each candidate cell to transmit only the configuration information added based on the reference cell configuration to the source base station CU (1g-03) so that the delta configuration can be applied.

[0219] Applying Delta configuration can mean configuring a complete configuration by applying additional configurations on top of the reference cell configuration or by overwriting the configurations in the target cell based on the reference cell configuration and then configuring a complete configuration. This method can be transmitted to the terminal as is, thereby reducing the signaling of RRC messages transmitted to the terminal. In addition, when the source base station CU (1g-03) transmits the reference cell configuration to each candidate cell (1g-04, 1g-05), it can be omitted, in which case the candidate cell configuration is provided as a complete RRC configuration.

[0220] In addition, the base station CU (1g-03) can generate a message (Handover Request or new message) requesting configuration information for L1 / L2-based handover to the target base station (CU2; 1g-06) in step 1g-20 to request LTM candidate cell configuration for the LTM surrounding cell (1g-07) of the inter-CU based on the measurement value report received from the terminal, and transmit the message to the X2 interface.

[0221] Afterwards, in step 1g-25, the target base station (CU2, 1g-06) can perform the Intra-CU MCG LTM candidate decision and configuration preparation procedure. (Intra-CU MCG LTM candidate decision and configuration preparation)

[0222] The target base station (CU2, 1g-06) can generate a message requesting setup information for L1 / L2-based handover for an LTM candidate cell (1g-07) belonging to the corresponding CU and transmit the message to the F1 interface. The message requesting setup information for L1 / L2-based handover may include a UE Context Setup Request or a UE Context Modification Request.

[0223] Afterwards, the target base station (CU2, 1g-06) can receive a message (UE Context Setup Response or UE Context Modification Response) responding with setup information for L1 / L2-based handover. The message responding with setup information for L1 / L2-based handover can include UE Context Setup Response or UE Context Modification Response.

[0224] The procedure refers to the LTM setup preprocessing procedure of Fig. 1g-15.

[0225] In the subsequent 1g-20 step, the target base station (CU2; 1g-06) can transmit a message including LTM candidate configuration information to the source base station (CU; 1g-03).

[0226] More specifically, the target base station (CU2; 1g-06) can generate a message to the source base station (CU; 1g-03) including the LTM candidate configuration information transmitted by the LTM candidate cell (1g-07) belonging to the CU and transmit the message through the X2 interface. At this time, the message may be a Handover Response message or a new response message.

[0227] The following new contents can be added to the LTM setup request message via the X2 interface of the above 1g-20 step:

[0228] - Instructions for performing LTM

[0229] ■ Additionally, an indicator of whether the request is for initial preparation, eg, initiation, or subsequent to the initial request for modification.

[0230] - Terminal ID

[0231] - Source CU and / or source DU ID, and / or TNL address (e.g., IP address) of the source DU

[0232] - ID of the requesting candidate cell (physical cell identity (PCI) or NR cell group identity (CGI) with NR absolute radio frequency channel number (ARFCN))

[0233] - LTM configuration ID of this candidate cell (if accepted, the source DU can use this LTM config ID when switching cells to the target cell)

[0234] - LTM configuration ID mapping list: When delivered to a candidate DU, information to inform the candidate DU of the mapping relationship between the currently operable LTM settings and its cells.

[0235] ■ Opt 1. The above candidate cell list may be a list of candidate cells operated by all candidate CUs for the corresponding terminal, or

[0236] ■ Opt 2. It may be a list that includes only candidate cells operated by the source CU that transmits the HO request message.

[0237] - Channel state information (CSI) resource setup request information for LTM L1 measurement

[0238] - An indicator requesting physical random access channel (PRACH) resource information for the target candidate cell.

[0239] - A directive requesting lower layer settings for target candidate cells.

[0240] - Request to set a reference cell or provide a reference cell setting (detailed explanation below)

[0241] In addition to the above information, information previously used in HO request messages may also be included. This can be referenced in the table below.

[0242]

[0243]

[0244] In particular, the present disclosure proposes the following methods (first to third methods) with respect to requesting and applying reference cell setting for LTM candidate cells existing within an inter-CU.

[0245] 1. Method 1: The reference cell settings applied to each CU are distinguished, and each CU manages them independently (Each CU handles the reference configuration within the CU).

[0246] ● Step 1: Request the reference cell settings applied to the target CU from the source CU (Xn interface; Handover request message or new message)

[0247] ● Step 2: Each target CU requests lower layer setup for reference cell setup to LTM candidate cells within the CU (F1 interface; UE Context Setup Request or UE Context Modification Request)

[0248] ● Step 3: Each target CU creates reference cell configuration information by referring to the lower layer configuration collected from LTM candidate cells and transmits the information to the source CU (Xn interface; handover response message or new message).

[0249] ● Step 4: The source CU stores the reference cell settings received from each target CU and transmits them to the terminal as LTM setting information.

[0250] - Reference cell settings may or may not be provided for each target CU.

[0251] - The source CU may signal the reference cell configuration and candidate cell configuration as a single set for each CU. Alternatively, the signaling may be performed without distinction, but explicit information about the LTM candidate cells (e.g., CU ID, cell ID, etc.) may be included. That is, the information related to the LTM candidate cells to which the reference cell configuration information applies may be included. (For example, by providing the LTM configuration ID, PCI, ARFCN, cell ID, etc., or by creating a separate list of LTM candidate cells applicable to each CU.)

[0252] - If a reference cell setting does not exist in the CU, the LTM candidate cell setting within the CU must be provided as a complete setting, and this can be indicated by a complete indicating indicator.

[0253] 2. Second method: The source CU manages the reference cell configuration of one master cell group (MCG) managed by the source base station CU (Source CU handles the reference configuration across all the CUs)

[0254] ● Step 1: The source CU transmits the reference cell settings that apply to all CUs to the target CU (Xn interface; Handover request message or new message)

[0255] - At this stage, the information can be omitted and transmitted for each target CU. In this case, the reference cell setting is not applied to the CU. In other words, the LTM candidate cell setting must be applied as a complete setting.

[0256] ● Step 2: Each target CU transmits the reference cell configuration received from the source CU to the LTM candidate cells within the CU (F1 interface; UE Context Setup Request or UE Context Modification Request). Requests the delta configuration that applies the reference cell configuration. In this case, the corresponding information can also be requested for each LTM candidate cell. In other words, complete configuration can be requested for a specific cell using the LTM candidate cell configuration.

[0257] ● Step 3: Additional reference cell configuration information is updated by referring to the LTM candidate cell configuration collected from the LTM candidate cells in each target CU, or the LTM candidate cell configuration generated based on the received reference cell configuration is transmitted to the source CU (Xn interface; Handover response message or new message).

[0258] ● Step 4: The source CU stores the reference cell settings received from each target CU and transmits them to the terminal as LTM setting information.

[0259] - Reference cell settings may or may not be provided for each target CU.

[0260] - The source CU may signal whether the reference cell configuration is applied to each CU and the candidate cell configuration as a single set. Alternatively, the signaling may be performed without distinction, but explicit information on LTM candidate cells (e.g., CU ID, cell ID, etc.) may be included. That is, the associated information of LTM candidate cells to which the reference cell configuration information is applied may be included (e.g., providing LTM configuration ID, PCI, ARFCN, cell ID, etc., or providing a separate list of LTM candidate cells to which the reference cell configuration information is applied).

[0261] - If a reference cell setting does not exist in the CU, the LTM candidate cell setting within the CU must be provided as a complete setting, and this can be indicated by a complete indicating indicator.

[0262] 3. Third method: No reference configuration for the candidate cell within other CUs: candidate configuration should always be complete.

[0263] - Or restrict the use of the reference cell settings to only specific CUs.

[0264] - If the reference cell setting does not exist in the CU, the LTM candidate cell setting within the CU must be provided as a complete setting, and this is indicated by a complete indication directive.

[0265] In particular, in the case of the first method, since the reference cell setting is used for each CU, the reference cell setting currently applied in the intra-CU is also applied to the target CU. In other words, the common settings included in the reference cell setting are at the same level as the reference cell setting in the intra-CU. For example, the common settings include common settings for bearer settings, channel measurement settings, and cell group settings.

[0266] Meanwhile, the second method may have limitations in common settings, as the reference cell settings applied to the source CU must be applied to all CUs. This is because each CU often has its own independent RRC and PDCP and is often deployed in different locations. Some common settings, such as limited bearer settings, channel measurement settings, and cell group settings, can be achieved through the reference cell settings.

[0267] Additionally, the LTM setup response message through the X2 interface of the above 1g-30 step may include LTM-related setup information of the LTM target cell within the corresponding CU.

[0268] - Includes CSI resource settings in response to requested CSI resources.

[0269] - CSI reporting settings information

[0270] ■ If the CSI resource request is omitted and the configuration information of the CSI resources being transmitted by all currently configured candidate cells is transmitted, the CSI reporting settings that apply the settings are transmitted as is.

[0271] - RACH configuration and lower layer setting information to be used in the concerned cell

[0272] ■ This information is transmitted from the LTM candidate DU within the CU to the CU, and is written as the settings required for performing RACH within the target cell configuration of the concerned cell, the lower layer settings to be applied when moving to the cell, and / or the reference settings including them, and can be transmitted to the terminal later.

[0273] ■ In particular, some of the RACH settings can be used to include RACH preamble index, mask, and occasion decision information in the cell switch command MAC CE described above.

[0274] ■ Beam information to be used for each candidate (TCI state)

[0275] ■ In this case, the meaning of use can mean a beam that is linked to a RACH occasion when performing downlink (DL) and / or uplink (UL) synchronization and / or random access channel (RACH), and / or a beam to be used for the first UL data transmission. If necessary, an indicator for each case can be accompanied to perform a cell switch.

[0276] - In addition, the configuration information transmitted by DU can be configured as complete configuration information as configuration information applied after handover is completed.

[0277] - An indicator indicating whether the reference cell setting information and the candidate cell setting are complete.

[0278] Afterwards, in step 1g-35, the source base station (1g-02) can trigger the 1g-15 procedure and the 1g-20 procedure again based on the information on LTM-related candidate cells received from the target base station (1g-06).

[0279] In response, the 1g-30 procedure can be used. The detailed procedure is summarized by option above.

[0280] In step 1g-40, the source base station (1g-02) can collect all LTM-related settings received from at least one LTM candidate cell and store them in an RRCReconfiguration message to be transmitted to the terminal, and transmit the corresponding RRC configuration information to the terminal. That is, pre-configuration information for LTM candidate cells can be transmitted to the terminal. At this time, the source base station CU (1g-03) can transmit the configuration information of the source cell together with separate reference cell configuration information. The present invention features a method including the reference cell configuration information and LTM candidate cell configuration for each CU in an inter-CU situation, and has been described in detail above.

[0281] The reference cell configuration information transmitted by the above-described source base station CU (1g-03) to each candidate cell (1g-04, 1g-05) may be configuration information (common configuration) that can be commonly applied to multiple target candidate cells to reduce signaling overhead when the target candidate cells provide configuration information for LTM. The configuration information that can be commonly applied may include measurement configuration, bearer configuration, or, if the cells belong to the same CellGroup, configurations set at the CellGroup level (e.g., MAC-CellGroupConfig, RLC bearer configuration, SCell configuration, etc.).

[0282] Alternatively, if the source base station CU (1g-03) roughly knows (or has a procedure to know) the configuration information for each candidate cell (1g-04, 1g-05, 1g-07), the reference cell configuration may be determined through a separate procedure, such as obtaining the reference cell configuration information.

[0283] For example, the purpose of the source base station CU (1g-03) transmitting the reference cell configuration to each candidate cell (1g-04, 1g-05, 1g-07) is to enable each candidate cell to transmit only the configuration information added based on the reference cell configuration to the source base station CU (1g-03) so that the delta configuration can be applied.

[0284] Applying Delta configuration can mean a method of configuring a complete configuration by applying additional settings on top of the reference cell settings or a method of configuring a complete configuration by covering and applying settings in a target cell based on the reference cell settings. This method can reduce signaling of RRC messages transmitted to the terminal by transmitting the reference cell configuration to the terminal as is. In addition, when the source base station CU (1g-03) transmits the reference cell configuration to each candidate cell (1g-04, 1g-05, 1g-07), it can be omitted, and in this case, the candidate cell configuration is provided as a complete RRC configuration.

[0285] At step 1g-40, the source base station (1g-02) can transmit an RRC message containing LTM related configuration information to the terminal (1g-01).

[0286] More specifically, the source cell (1g-02) receives an RRC message generated by the base station CU (1g-03) based on the configuration information received from each candidate cell and transmits the message to the terminal. The RRC message may include configuration information (Pre-Config1, 쪋, Pre-ConfigN) for surrounding candidate cells to which L1 / L2-based handover (LTM) is applied.

[0287] The Pre-Config included in the above message is a message that includes CellGroupConfig settings received from LTM candidate cells in step 1g-35, bearer settings for LTM candidate cells generated by the base station, and Layer 3 (L3) measurement settings.

[0288] The terminal (1g-01) that receives the RRC message in step 1g-45 performs a procedure for decoding and processing the RRC message.

[0289] The above processing may include methods for ASN.1 decoding and validating the received message and storing and managing the configuration contents. In addition, the terminal (1f-01) may store the LTM configuration information for each candidate cell decoded in this step as complete configuration information in the buffer (memory) of the terminal, and at the same time, store the received reference cell configuration information in the buffer (memory) of the terminal and manage it for the future. The reference cell configuration information may be omitted from the RRC message (or configuration information for each LTM candidate cell) in step 1g-40.

[0290] In this case, the terminal recognizes that there is no reference cell configuration information and stores the configuration information for the received LTM target candidate cells as complete configuration information. At this time, the reference cell configuration information is not stored separately (i.e., it operates as empty). In other words, delta configuration is not applied. In addition, the message transmits L1 measurement resource and reporting configuration information for continuous LTM. For detailed configuration, refer to the above description of the present invention.

[0291] In step 1g-50, the terminal (1g-01) performs L1 (layer 1) measurement and reporting for each candidate surrounding cell, and can perform L1 measurement reporting according to the settings.

[0292] Additionally, in step 1g-55, the terminal (1g-01) can perform L3 channel measurement and reporting operations, if configured. Subsequently, in step 1g-60, the source cell that receives the L1 measurement report can make a handover decision based on the measurement value and instruct the terminal to perform L1 / L2 handover.

[0293] Although the present invention illustrates a handover to an LTM candidate cell (1g-07) within an inter-CU, the scope of the present invention is not limited thereto. A MAC CE containing a handover indicator can be used for L1 / L2 signaling.

[0294] LTM allows the source cell to make the final decision and, without transmitting L1 measurements to the base station, independently determine handover based on measurement criteria (thresholds and measurement ranges) received from the previous base station for making handover decisions for each candidate neighboring cell. The source cell can then transmit L1 / L2 signaling to the terminal. LTM decision information can then be transmitted to the CU.

[0295] When an L1 / L2 handover instruction is transmitted to the terminal, the terminal (1g-01) can start a handover procedure in step 1g-65 and start a timer for L1 / L2 handover.

[0296] The above timer may be a newly set timer for LTM, or an existing T304 timer may be reused.

[0297] In step 1g-70, the terminal (1g-01) can apply settings for a target cell to which L1 / L2 handover is applied.

[0298] In other words, the current configuration can be replaced with the complete configuration information of the designated LTM target cell previously stored in the terminal. This is one of the LTM candidate surrounding cell configurations previously received in step 1g-40 and is stored in the terminal.

[0299] At step 1g-75, the terminal may perform a random access procedure if necessary.

[0300] More specifically, depending on the applicable settings, the terminal can perform random access to the target cell if random access is required. Conversely, if random access is not indicated or required, the random access procedure is omitted. Cases where random access is not indicated or required may include cases where uplink synchronization has already been performed or aligned.

[0301] In step 1g-80, the terminal (1g-01) can perform a handover completion procedure with the target cell.

[0302] The above handover completion procedure may be a handover completion procedure for LTM. This procedure may vary depending on the method of indicating the handover completion, and may be a process of transmitting an RRCReconfigurationComplete message when the configuration of the target cell (1g-07) within the inter-CU is received at the RRC message level.

[0303] Furthermore, since this scenario considers application to inter-CU, the target cell (DU, 1g-07) that received the handover completion message in step 1g-85 can forward the received message to the target CU (1g-06). At this time, the handover completion message received via the F1 interface can be forwarded as is, or the message can be reprocessed and forwarded based on the received information.

[0304] Afterwards, in step 1g-90, the target base station CU (1g-06) can transmit information about the completion of the handover to the source base station (1g-03), and the source base station can transmit this to the source cell (1g-02) to instruct it to release the terminal context.

[0305] Additionally, as described in step 1g-95, embodiments of the present invention support subsequent LTM operations.

[0306] Subsequent LTM operation means that the LTM configuration information (configuration of target candidate cells and reference cell configuration information, etc.) received by the UE in step 1g-40 is stored in the UE as is, and the UE continues to perform the LTM procedure unless the LTM configuration information is changed / released / added through a separate RRC configuration. If it is necessary to update the reference cell configuration information, new RRC configuration information can be transmitted to the UE to update the reference cell configuration information. That is, the procedure described in this drawing can be triggered again to perform this.

[0307] In summary, if the terminal (1g-01) receives reference cell setting information in step 1g-40, it stores it in the terminal buffer and, if there is no separate setting update, can continue to use the corresponding setting as reference cell setting information even after performing LTM (step 1g-60). In other words, the reference cell setting and LTM candidate setting values ​​stored in successive LTMs can be applied.

[0308] Also, in step 1g-40, if the terminal (1g-01) is not provided with reference cell configuration information in the RRC connection state, the reference cell configuration can be saved as empty according to the terminal operation option described above, or the configuration information for the corresponding source cell (PCell) from which the LTM configuration information was received can be saved as reference cell configuration information.

[0309] FIG. 1ha and FIG. 1hb are diagrams illustrating the overall operation for explaining a reference cell setting method for supporting continuous L1 / L2 based Secondary cell group (SCG) PSCell change (l1 / l2 triggered mobility, LTM) operation in cells within different CUs according to one embodiment of the present disclosure.

[0310] Embodiment 2 follows the overall procedure of Embodiment 1, with the only difference being the scenario in which Embodiment 1 supports master cell group (MCG) L1 / L2 triggered mobility (LTM) in inter-CU.

[0311] That is, while Embodiment 1 describes a handover case, Embodiment 2 differs only in that it performs inter-CU PSCell change with LTM in a situation where dual connectivity (DC) is established.

[0312] In the following Example 2, only the differentiating parts will be described to reduce redundant explanations, and most of the procedures follow the contents of Fig. 1g.

[0313] This is a scenario in which a terminal (1h-01) is connected to a source cell (1h-02) within a source base station (1h-03) and supports data communication by being connected to a PSCell (1h-04) belonging to CU 1 with Dual Connectivity (hereinafter referred to as DC). Here, LTM candidate cells (1h-05) belonging to CU1 for secondary cell group (SCG) LTM and an LTM candidate cell (1h-07) belonging to CU2 (1h-06) may exist.

[0314] The terminal receives basic radio resource control (RRC) settings from the base station in step 1h-10 and performs an operation of reporting layer 3 measurements for surrounding cells.

[0315] Steps 1h-15 to 1h-35 thereafter are procedures for obtaining LTM settings between base stations and LTM candidate cells to set up SCG LTM between base stations, and are identical to the procedures in steps 1g-15 to 1g-35 of FIG.

[0316] The present invention proposes that the three methods for setting reference cells, similar to those used in MCG LTM, can be applied to SCG LTM as well. That is, the first, second, and third methods for setting reference cells in inter-CUs described above in FIG. 1g are the core concepts proposed in the present invention.

[0317] The overall procedure for triggering and performing LTM, as described in Figure 1g, is followed in the subsequent procedures. The only difference is that the cell where LTM is performed is a candidate cell (1h-07) within the inter-CU, and a PSCell change is performed rather than a handover to that cell.

[0318] FIG. 1i is a diagram illustrating the overall terminal operation for performing L1 / L2-based beam change and handover according to one embodiment of the present disclosure.

[0319] According to one embodiment of the present disclosure, the operation of the terminal is characterized by considering handover and PSCell change operations to an L1 / L2 triggered mobility (LTM) candidate cell existing within an inter-CU, and receiving and applying a reference cell configuration and an LTM candidate cell configuration in the inter-CU.

[0320] In step 1i-05, a connected UE may receive a radio resource control (RRC) message containing configuration information about at least one candidate cell.

[0321] More specifically, a connected terminal can receive configuration information from a neighboring cell that is applied after L1 / L2-based movement is instructed via a radio resource control (RRC) reset message from the serving cell. For detailed configuration methods and details, refer to the contents of the aforementioned drawing 1g.

[0322] In addition, although omitted before the above RRC configuration information, the terminal has received basic RRC configuration from the base station and can perform an operation of reporting layer 3 measurement values ​​for neighboring cells. In particular, the configuration information in the LTM candidate cell applied after the L1 / L2-based movement received in step 1i-05 is instructed is transmitted with a delta configuration applied based on the configuration for the reference cell applied to a specific CU or all CUs.

[0323] The terminal can know what the reference cell and configuration information for the reference cell are, which are known in advance or have been instructed in the RRC settings, and the settings for surrounding cells other than the reference cell are transmitted in common with the reference cell settings and settings that can be added thereto, so there is less signaling overhead.

[0324] In particular, as described in Embodiments 1 and 2 of the present disclosure, it is based on receiving settings for LTM candidate cells within an inter-CU, storing them, and applying them when an LTM cell change is instructed.

[0325] In step 1i-10, the terminal can configure and store candidate cell settings.

[0326] More specifically, the terminal decodes the settings for the received LTM candidate cells based on the settings of the reference cell that are transmitted separately for each CU, and stores and manages the complete settings that are actually applied (i.e., the operation of saving the settings that are delta-configured based on the reference cell as a complete configuration by referring to the reference cell settings) in a separate buffer and list. Alternatively, the terminal may store and manage the received RRC settings as they are in the buffer, without decoding the received settings based on the reference cell and storing and managing the settings that are actually applied.

[0327] As described above in Drawing 1g, if the terminal receives a data stream with the reference cell configuration omitted, the terminal can recognize that there is no reference cell configuration information, and can determine and store the configuration information for the received LTM target candidate cells as complete configuration information. In this case, the reference cell configuration information is not stored separately (i.e., it operates as empty). In other words, the delta configuration is not applied.

[0328] Whether or not the above reference cell is set may vary for each CU, and multiple reference cell setting information may be provided for each CU. The terminal may store the settings of complete target candidate cells based on the associated information about LTM candidate cells within the CU to which the reference cell setting is applied.

[0329] The advantage of decoding the settings for surrounding cells at that stage based on the reference cell and storing the settings to be actually applied is that when an actual L1 / L2-based handover is instructed, the handover for the corresponding cell can be applied immediately, so there is no additional delay time.

[0330] In step 1i-15, the terminal performs L1 measurement configured with synchronized sinal block (SSB) or channel state information - reference signal (CSI-RS) resources associated with candidate neighboring cells while maintaining a connection state with the serving cell, and reports the measurement results to the serving cell according to a preset L1 measurement reporting configuration method. In this step, the base station can control L1 measurement resource reporting for LTM neighboring cells requiring measurement through RRC configuration and L1 / L2 signaling.

[0331] The terminal performs L1 measurement resource reporting according to the base station settings and instructions. Additionally, independently of this operation, the terminal can measure neighboring cells according to the L3 measurement settings and report the measurement results to the base station according to the L3 measurement reporting settings. The serving cell can determine whether to change the beam and perform a handover for the terminal based on the received measurement results. If it determines that a change to a specific beam of a neighboring cell is necessary rather than a specific beam of the serving cell, the terminal can instruct the handover and beam change through L1 / L2 signaling.

[0332] At step 1i-20, the terminal can receive L1 / L2 signaling indicating a candidate beam.

[0333] The above L1 / L2 signaling may include a MAC CE, in which all information indicating a specific beam of a neighboring cell and a change of serving cell is indicated (if the MAC CE indicates only one beam), or in which multiple specific beams of the LTM target cell are indicated in the MAC CE, and then one of the multiple beams of the activated neighboring cell is selected in the transmitted MAC CE to indicate a handover.

[0334] In step 1i-25, the terminal can check whether a handover instruction is given from the MAC CE signaling received in step 1i-20 and perform an LTM handover operation.

[0335] More specifically, when a handover is indicated in the received MAC CE, the terminal can perform a handover to a cell associated with the indicated TCI state. The handover indication in the received MAC CE may include a case where the handover is indicated in the MAC CE itself, or a case where the handover is indicated by activating multiple beams in the MAC CE and indicating one of the beams in the DCI.

[0336] In step 1i-30, the terminal can determine whether the LTM handover was successful.

[0337] If random access is successfully performed in step 1i-30 and handover is successful, the settings for the corresponding LTM target cell stored in step 1i-10 may also be applied. In step 1i-35, the terminal maintains the previously stored LTM configuration information and reference cell configuration information. In step 1i-40, the terminal connects to the indicated LTM target cell, transmits and receives data using the indicated beam, performs channel measurement reporting according to the LTM configuration, and can continue to perform continuous LTM operations.

[0338] If the LTM handover of the terminal fails in step 1i-30, in step 1i-45, the terminal maintains the configuration for the LTM candidate cell and can perform an RRC re-establishment (RRC connection Reestbilishement, RRE) procedure.

[0339] More specifically, if the LTM handover fails, the terminal falls back to the previous source cell and attempts to connect. To achieve this, the terminal must maintain configuration information for the source cell even if LTM is triggered. Furthermore, even after falling back to the source cell, the terminal maintains LTM configuration information for the LTM target cell and reference cell configuration information. This is to ensure that LTM can be triggered again according to the previous configuration.

[0340] If fallback to the source cell fails, the UE initiates the RRC Re-Establishment procedure to reselect available cells. If the cell found through cell reselection is one of the LTM candidate cells, the UE attempts to establish a connection by applying the preset RRC settings for that cell.

[0341] Afterwards, in step 1i-50, the terminal can generate a handover failure report message in the cell where the connection was performed (source cell or target cell) and transmit it to the base station.

[0342] The above handover failure report message may include a UEInformationResponse or another uplink RRC message. Additionally, it may be reported via a new MAC CE or uplink control information (UCI). The information contained in the above handover failure report message may include the following:

[0343] - Indicator indicating that the handover failed due to LTM failure.

[0344] - Target cell information that failed when attempting LTM: LTM cell setup index or physical cell index (PCI) information

[0345] The source base station can inform the terminal that the LTM attempt failed and fell back to the corresponding cell through the handover failure message report. In addition, if the cell found through cell reselection after the RRC Re-Establishment procedure is not one of the LTM candidate cells, the terminal can maintain the LTM configuration information and reference cell configuration information stored in the corresponding cell in step 1i-55. Alternatively, in this case, the stored LTM-related configuration information and reference cell configuration information can be released. Alternatively, the base station can explicitly designate the operation through configuration.

[0346] FIG. 1J is a diagram illustrating the operation of a base station according to an embodiment of the present disclosure.

[0347] At step 1j-05, the base station can receive L3 measurements from the terminal.

[0348] More specifically, the base station receives L3 measurement value reports from the terminal, and based on the terminal's measurement values ​​for surrounding frequencies and cells, can determine whether the terminal requires handover and which cells are handover candidate cells.

[0349] In step 1j-10, the base station can request setup information for L1 / L2-based handover to neighboring cells and receive responses from those cells.

[0350] Here, L1 / L2 triggered measurement (LTM) candidate cells may be cells within the same CU and / or cells within different CUs. In the LTM candidate cell configuration preprocessing procedure, a procedure may be added in which the source base station requests channel state information (CSI) resources and reference cell configuration for LTM peripheral cells, and through this procedure, the source base station may obtain CSI resource requests and reference cell configuration for LTM peripheral cells for each central unit (CU). Thereafter, the base station may transmit configuration information for the current source cell and the obtained reference cell configuration information together to the peripheral cells, and receive RRC configuration information to which delta configuration is applied based on the reference cell configuration information from the peripheral cells and LTM candidate cells.

[0351] In addition, this step performs inter-node coordination for each CU to acquire reference cell configuration information proposed in the present invention. The procedure described above in Drawing 1g is included in this step, and in particular, it includes determining reference cell configuration and LTM candidate cell configuration within the inter-CU. Although omitted in this drawing, settings related to L3 measurement configuration and basic RRC settings are provided prior to this step.

[0352] In step 1j-15, the base station can provide LTM configuration information to the terminal.

[0353] More specifically, the base station can transmit to the terminal in the connected state an RRC configuration message generated including the reference cell configuration, neighboring cell configuration information, and L1 measurement resource / report configuration information received in step 1j-10. That is, the configuration information in the neighboring cell applied after L1 / L2-based movement is indicated by an RRC reconfiguration message from the serving cell can be transmitted. The detailed configuration method and contents are described above in drawing 1g.

[0354] In the subsequent step 1j-20, the base station can receive L1 / L3 measurement from the terminal.

[0355] More specifically, the base station can instruct L1 measurement reporting in various ways through RRC or L1 / L2 signaling depending on the L1 measurements and reports desired for configuration and triggering. The base station can receive reports on L1 and L3 measurement values ​​from the terminal, wherein the L1 measurement values ​​may be from a neighboring cell (non-serving cell) that supports L1 / L2-based mobility.

[0356] At step 1j-25, the base station (or serving cell) may indicate an LTM handover.

[0357] More specifically, the serving cell can determine whether to change the beam of the terminal and whether to perform a handover based on the measurement results received, and if it is determined that a change to a specific beam of a neighboring cell is necessary rather than a specific beam of the serving cell, it can instruct an LTM handover of the terminal through L1 / L2 signaling in step 1j-25.

[0358] The above L1 / L2 signaling can be MAC CE and contain information indicating a change to a specific beam in a neighboring cell. Furthermore, existing handovers via RRC messages can also be performed independently and indicated during this phase. This can occur because the base station and serving cell independently determine LTM and Layer 3 handovers.

[0359] At step 1j-35, the base station can perform handover completion and handover failure related actions.

[0360] More specifically, upon receiving a handover completion message from a terminal, it is confirmed that the corresponding LTM operation has been successfully completed, and accordingly, the handover completion can be notified to the previous source cell and a request for the terminal context to be released.

[0361] Additionally, when receiving a handover failure report message from a terminal that includes information that the handover failed, a message may be received indicating that the terminal has attempted to reconnect to the cell after the handover failure. The handover failure report message may be a UEInformationResponse or another uplink RRC message. Additionally, this may be reported via a new MAC CE or uplink control information (UCI).

[0362] The above handover failure report message may include the following information:

[0363] - Indicator indicating that the handover failed due to LTM failure.

[0364] - Target cell information that failed when attempting LTM: LTM cell setup index or physical cell index (PCI) information

[0365] The source base station can report a handover failure message to indicate that the LTM attempt failed and fell back to that cell.

[0366] FIG. 1k is a block diagram illustrating the internal structure of a terminal according to one embodiment of the present disclosure.

[0367] Referring to FIG. 1k, the terminal may include an RF (Radio Frequency) processing unit (1k-10), a baseband processing unit (1k-20), a storage unit (1k-30), and a control unit (1k-40).

[0368] The RF processing unit (1k-10) may perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1k-10) may up-convert a baseband signal provided from the baseband processing unit (1k-20) into an RF band signal and transmit the up-converted signal through an antenna, and may down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1k-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital to analog convertor (DAC), an analog to digital convertor (ADC), etc. In the drawing, only one antenna is illustrated, but the terminal may be equipped with multiple antennas. In addition, the RF processing unit (1k-10) may include multiple RF chains. Furthermore, the RF processing unit (1k-10) may perform beamforming. For the above beamforming, the RF processing unit (1k-10) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processing unit can perform MIMO and receive multiple layers when performing the MIMO operation.

[0369] The baseband processing unit (1k-20) above can perform a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the system. For example, when transmitting data, the baseband processing unit (1k-20) can generate complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1k-20) can restore a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (1k-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (1k-20) can generate complex symbols by encoding and modulating a transmission bit stream, map the complex symbols to subcarriers, and then configure OFDM symbols through an inverse fast Fourier transform (IFFT) operation and a cyclic prefix (CP) insertion. In addition, when receiving data, the baseband processing unit (1k-20) divides the baseband signal provided from the RF processing unit (1k-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform) operation, and then restores the received bit string through demodulation and decoding.

[0370] The baseband processing unit (1k-20) and the RF processing unit (1k-10) can transmit and receive signals as described above. Accordingly, the baseband processing unit (1k-20) and the RF processing unit (1k-10) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (1k-20) and the RF processing unit (1k-10) may include a plurality of communication modules to support a plurality of different wireless access technologies. In addition, at least one of the baseband processing unit (1k-20) and the RF processing unit (1k-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include a wireless LAN (e.g., IEEE 802.11), a cellular network (e.g., LTE), etc. Additionally, the different frequency bands may include a super high frequency (SHF) (e.g., 2.NRHz, NRhz) band, a millimeter wave (mm wave) (e.g., 60GHz) band.

[0371] The storage unit (1k-30) can store data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (1k-30) can store information related to a second access node that performs wireless communication using a second wireless access technology. In addition, the storage unit (1k-30) can provide the stored data upon request from the control unit (1k-40).

[0372] The control unit (1k-40) can control the overall operations of the terminal. For example, the control unit (1k-40) can transmit and receive signals through the baseband processing unit (1k-20) and the RF processing unit (1k-10). In addition, the control unit (1k-40) can record and read data in the storage unit (1k-40). For this purpose, the control unit (1k-40) can include at least one processor. For example, the control unit (1k-40) can include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs.

[0373] FIG. 1l is a block diagram illustrating the structure of a base station according to one embodiment of the present disclosure.

[0374] Referring to FIG. 1l, the base station is configured to include an RF processing unit (1l-10), a baseband processing unit (1l-20), a backhaul communication unit (1l-30), a storage unit (1l-40), and a control unit (1l-50).

[0375] The RF processing unit (11-10) may perform functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (11-10) may up-convert a baseband signal provided from the baseband processing unit (11-20) into an RF band signal and transmit the up-converted signal through an antenna, and may down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (11-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. In the drawing, only one antenna is illustrated, but the first access node may have multiple antennas. In addition, the RF processing unit (11-10) may include multiple RF chains. Furthermore, the RF processing unit (11-10) may perform beamforming. For the above beamforming, the RF processing unit (11-10) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform a downlink MIMO operation by transmitting one or more layers.

[0376] The baseband processing unit (11-20) above can perform a conversion function between a baseband signal and a bit stream according to the physical layer specification of the first wireless access technology. For example, when transmitting data, the baseband processing unit (11-20) can generate complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (11-20) can restore a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (11-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (11-20) can generate complex symbols by encoding and modulating a transmission bit stream, map the complex symbols to subcarriers, and then configure OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (11-20) divides the baseband signal provided from the RF processing unit (11-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT operation, and then restores the received bit string through demodulation and decoding. The baseband processing unit (11-20) and the RF processing unit (11-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (11-20) and the RF processing unit (11-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0377] The above backhaul communication unit (11-30) can provide an interface for performing communication with other nodes within the network. That is, the backhaul communication unit (11-30) can convert a bit string transmitted from the main base station to another node, such as an auxiliary base station or a core network, into a physical signal, and can convert a physical signal received from the other node into a bit string.

[0378] The storage unit (11-40) can store data such as basic programs, application programs, and setting information for the operation of the main base station. In particular, the storage unit (11-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (11-40) can store information that serves as a judgment criterion for whether to provide or terminate multiple connections to a terminal. In addition, the storage unit (11-40) can provide stored data upon request from the control unit (11-50).

[0379] The control unit (11-50) can control the overall operations of the base station. For example, the control unit (11-50) transmits and receives signals through the baseband processing unit (11-20) and the RF processing unit (11-10) or through the backhaul communication unit (11-30). In addition, the control unit (11-50) records and reads data in the storage unit (11-40). For this purpose, the control unit (11-50) can include at least one processor.

[0380] The methods according to the embodiments described in the claims or specification of the present invention may be implemented in the form of hardware, software, or a combination of hardware and software.

[0381] When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. The one or more programs include instructions that cause the electronic device to execute methods according to the embodiments described in the claims or specification of the present invention.

[0382] These programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage device, compact disc ROM (CD-ROM), digital versatile discs (DVDs) or other forms of optical storage device, magnetic cassette. Or, they may be stored in a memory configured as a combination of some or all of these. In addition, each configuration memory may be included in multiple numbers.

[0383] Additionally, the program may be stored in an attachable storage device that is accessible via a communication network such as the Internet, an intranet, a local area network (LAN), a wide local area network (WLAN), a storage area network (SAN), or a combination thereof. Such a storage device may be connected to a device implementing an embodiment of the present invention via an external port. Additionally, a separate storage device on the communication network may be connected to a device implementing an embodiment of the present invention.

[0384] In this disclosure, the term "computer program product" or "computer-readable medium" is used to collectively refer to media such as memory, a hard disk installed in a hard disk drive, and signals. These "computer program products" or "computer-readable mediums" are components provided in a method for reporting terminal capabilities in a wireless communication system according to the present disclosure.

[0385] A device-readable storage medium may be provided in the form of a non-transitory storage medium. Here, the term "non-transitory storage medium" simply means a tangible device that does not contain signals (e.g., electromagnetic waves). This term does not distinguish between cases where data is permanently stored in the storage medium and cases where data is temporarily stored. For example, a "non-transitory storage medium" may include a buffer in which data is temporarily stored.

[0386] According to one embodiment, the method according to the various embodiments disclosed in the present document may be provided as included in a computer program product. The computer program product may be traded as a product between a seller and a buyer. The computer program product may be distributed in the form of a machine-readable storage medium (e.g., compact disc read only memory (CD-ROM)), or may be distributed online (e.g., downloaded or uploaded) via an application store (e.g., Play Store™) or directly between two user devices (e.g., smartphones). In the case of online distribution, at least a portion of the computer program product (e.g., a downloadable app) may be temporarily stored or temporarily generated in a machine-readable storage medium, such as the memory of a manufacturer's server, an application store's server, or an intermediary server.

[0387] In the specific embodiments of the present invention described above, components included in the invention are expressed in the singular or plural form depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present invention is not limited to singular or plural components. Even components expressed in the plural form may be composed of singular elements, or even components expressed in the singular form may be composed of plural elements.

[0388] While the detailed description of the present invention has described specific embodiments, it is clear that various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims but also by equivalents thereof.

Claims

1. In a method performed by a central unit (CU) of a source base station in a communication system, A step of transmitting a handover request message to request establishment of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell to a CU of at least one candidate base station; In response to the handover request message, receiving a handover request response message from a CU of at least one candidate base station, the handover request response message including configuration information of an LTM candidate cell associated with the CU of each candidate base station; A step of generating LTM configuration information based on configuration information of an LTM candidate cell associated with a CU of each candidate base station; and A method characterized by comprising the step of transmitting a Radio Resource Control (RRC) message including the LTM setting information to a terminal.

2. In paragraph 1, A method characterized in that the handover request message for requesting the configuration of the above LTM candidate cell includes reference cell configuration information commonly applied to at least one candidate base station CU.

3. In paragraph 1, The handover request message for requesting the setup of the above LTM candidate cell includes at least one piece of information from among an LTM execution indicator, identification information of the requesting LTM candidate cell, channel state information (CSI) resource setup request information, or physical random access channel (PRACH) resource setup request information. A method characterized in that the configuration information of the LTM candidate cell includes at least one piece of information from among CSI resource configuration information, CSI report configuration information, Random Access Channel (RACH) resource configuration information, and an indicator indicating whether the configuration information of the LTM candidate cell is complete.

4. In paragraph 1, A method characterized in that the above LTM setting information is related to Master Cell Group (MCG) LTM operation between CUs (Inter-CU MCG LTM).

5. In a method performed by a central unit (CU) of a candidate base station in a communication system, A step of receiving a handover request message requesting the setup of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell from a CU of a source base station, wherein the handover request message for requesting the setup of the LTM candidate cell includes reference cell configuration information (Reference Cell Configuration) commonly applied to at least one or more candidate base station CUs; A step of transmitting the reference cell setting information to at least one LTM candidate cell; A step of obtaining delta configuration information of each LTM candidate cell generated based on the reference cell configuration information from at least one LTM candidate cell; and A method characterized by comprising the step of transmitting a handover request response message including configuration information of an LTM candidate cell generated based on delta configuration information of each LTM candidate cell to a CU of the source base station.

6. In paragraph 5, The handover request message requesting the setup of the above LTM candidate cell includes at least one piece of information from among an LTM execution indicator, identification information of the requesting LTM candidate cell, channel state information (CSI) resource setup request information, or physical random access channel (PRACH) resource setup request information. A method characterized in that the configuration information of the LTM candidate cell includes at least one of CSI resource configuration information, CSI report configuration information, or Random Access Channel (RACH) resource configuration information, and an indicator indicating whether the configuration information of the LTM candidate cell is complete.

7. In a method performed by a terminal in a communication system, A step of transmitting a Radio Resource Control (RRC) message including Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) configuration information from a Central Unit (CU) of a source base station, wherein the LTM configuration information is related to configuration information of an LTM candidate cell included in at least one candidate base station, A step of performing Layer 1 (L1) measurements on at least one candidate cell and reporting the results of the measurements; A step of receiving a Media Access Control Control Element (MAC CE) indicating a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) cell change from a CU of the source base station; and A method characterized in that a procedure for changing to a candidate LTM cell is performed based on the MAC CE and the LTM setting information.

8. In paragraph 7, A method characterized in that the above LTM setting information is related to Master Cell Group (MCG) LTM operation between CUs (Inter-CU MCG LTM).

9. In the central unit (CU) of the source base station in the communication system, A transceiver for transmitting and receiving signals; and It includes a control unit connected to the above transmitter and receiver, and the control unit, Transmitting a handover request message to request the establishment of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell to at least one CU of a candidate base station, In response to the handover request message, a handover request response message is received from a CU of at least one candidate base station, wherein the handover request response message includes configuration information of an LTM candidate cell associated with the CU of each candidate base station, Generate LTM configuration information based on the configuration information of the LTM candidate cell associated with the CU of each candidate base station, and A CU of a source base station, characterized in that it transmits a Radio Resource Control (RRC) message including the LTM setting information to the terminal.

10. In paragraph 9, A CU of a source base station, characterized in that the handover request message for requesting the configuration of the above LTM candidate cell includes reference cell configuration information commonly applied to at least one candidate base station CU.

11. In paragraph 9, The handover request message for requesting the setup of the above LTM candidate cell includes at least one piece of information from among an LTM execution indicator, identification information of the requesting LTM candidate cell, channel state information (CSI) resource setup request information, or physical random access channel (PRACH) resource setup request information. A CU of a source base station, characterized in that the configuration information of the LTM candidate cell includes at least one piece of information from among CSI resource configuration information, CSI report configuration information, Random Access Channel (RACH) resource configuration information, and an indicator indicating whether the configuration information of the LTM candidate cell is complete.

12. In paragraph 9, The above LTM configuration information is a CU of a source base station characterized in that it is related to Master Cell Group (MCG) LTM operation between CUs (Inter-CU MCG LTM).

13. In the central unit (CU) of a candidate base station in a communication system, A transceiver for transmitting and receiving signals; and It includes a control unit connected to the above transmitter and receiver, and the control unit, Receive a handover request message requesting the configuration of a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell from a CU of a source base station, wherein the handover request message for requesting the configuration of the LTM candidate cell includes reference cell configuration information (Reference Cell Configuration) commonly applied to at least one candidate base station CU, At least one LTM candidate cell is transmitted with the reference cell setting information, Obtaining delta configuration information of each LTM candidate cell generated based on the reference cell configuration information from at least one LTM candidate cell, A CU of a candidate base station, characterized in that it transmits a handover request response message including configuration information of an LTM candidate cell generated based on the delta configuration information of each LTM candidate cell to the CU of the source base station.

14. In paragraph 13, The handover request message requesting the setup of the above LTM candidate cell includes at least one piece of information from among an LTM execution indicator, identification information of the requesting LTM candidate cell, channel state information (CSI) resource setup request information, or physical random access channel (PRACH) resource setup request information. A CU of a candidate base station, characterized in that the configuration information of the LTM candidate cell includes at least one of CSI resource configuration information, CSI report configuration information, or Random Access Channel (RACH) resource configuration information, and an indicator indicating whether the configuration information of the LTM candidate cell is complete.

15. In a terminal in a communication system, A transceiver for transmitting and receiving signals; and It includes a control unit connected to the above transmitter and receiver, and the control unit, From a central unit (CU) of a source base station, a Radio Resource Control (RRC) message including Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) configuration information is transmitted, wherein the LTM configuration information is related to configuration information of an LTM candidate cell included in at least one candidate base station, Perform Layer 1 (L1) measurements on at least one candidate cell and report the results of said measurements; Receive a Media Access Control Control Element (MAC CE) from the CU of the above source base station, which indicates a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) cell change, Based on the above MAC CE and the above LTM setting information, change to a candidate LTM cell, A terminal characterized in that the above LTM configuration information is related to inter-CU master cell group (MCG) LTM operation (Inter-CU MCG LTM).

Images