Method and device pertaining to inter-CU l1 / l2 layer-based mobility in next generation mobile communication system

Abstract

Disclosed are a device and method for: transmitting a first message for requesting information for an LTM configuration to a CU of a candidate base station associated with a candidate cell for inter-CU LTM; receiving configuration information about the candidate cell from the CU of the candidate base station; on the basis of the configuration information about the candidate cell, generating configuration information about a resource for L1 measurement for the candidate cell; and transmitting, to a terminal, a second message including the configuration information about the resource for L1 measurement for the candidate cell.

Description

Method and device for L1 / L2 layer-based mobility between CUs in next-generation mobile communication systems

[0001] This technology relates to the operation of terminals in mobile communication systems. Specifically, it relates to technology for terminal mobility.

[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 satisfy 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 exceeds the limits of terminal computing capabilities. It can serve as a basis for the development of next-generation distributed computing technologies that can be realized by utilizing them.

[0008] As described above and with the development of mobile communication systems, various services have become available, and methods for effectively providing these services are required.

[0009] As a terminal moves, it performs a handover operation from the source cell to the target cell. At this time, the network can instruct the terminal to use a preferred beam in the target cell based on a specific beam. This L1 / L2 triggered cell switching operation is structured so that the DU (distributed unit) issues the command from the network perspective. This ensures that the terminal can only move between DUs connected to a single CU.

[0010] An embodiment of the present invention aims to provide a method and device for exchanging information necessary for movement of a terminal between a source CU, a target CU, and a DU linked to each CU.

[0011] In addition, one embodiment of the present invention aims to provide a method and device that enables a terminal to perform cell switch even between cells of an inter CU.

[0012] The technical problems to be achieved in the present invention 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 invention belongs from the description below.

[0013] In order to solve the above problem, information necessary for movement of a terminal can be exchanged between a source CU, a target CU, and a DU linked to each CU, and as a result, the terminal can perform a cell switch to a cell of an inter CU.

[0014] In order to solve the above-described problem, a method performed by a CU (central unit) of a source base station of a wireless communication system according to an embodiment of the present invention may include the steps of: transmitting a first message requesting information for LTM configuration to a CU of at least one candidate base station associated with at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs; ​​receiving configuration information for the at least one candidate cell from a CU of the at least one candidate base station; generating configuration information for resources for L1 measurement for the at least one candidate cell based on the configuration information for the at least one candidate cell; and transmitting a second message including the configuration information for resources for L1 measurement for the at least one candidate cell to a terminal.

[0015] According to an embodiment, the method may further include transmitting a third message including the configuration information of the resources for the L1 measurement for the at least one candidate cell to a CU of the at least one candidate base station.

[0016] According to an embodiment, the configuration information for the at least one candidate cell may include at least one of configuration information of the at least one candidate cell, an indicator indicating whether the configuration information of the at least one candidate cell is a complete configuration, transmission configuration indication (TCI) state configuration information, channel state information (CSI) resource configuration information, and CSI reporting configuration information.

[0017] According to an embodiment, the resource configuration information for the L1 measurement may include resource configuration information for CSI (channel state information) measurement of the at least one candidate cell.

[0018] In order to solve the above-described problem, according to an embodiment of the present invention, a method performed by a CU (central unit) of a candidate base station of a wireless communication system includes the steps of: receiving, from a CU of a source base station, a first message requesting information for LTM configuration for at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs; ​​requesting configuration information for the at least one candidate cell from at least one DU (distributed unit) of the candidate base station associated with the at least one candidate cell; receiving the configuration information for the at least one candidate cell from the at least one DU of the candidate base station; and transmitting the configuration information for the at least one candidate cell to the CU of the source base station, wherein configuration information for resources for L1 measurement for the at least one candidate cell can be generated based on the configuration information for the at least one candidate cell.

[0019] According to an embodiment, the method may further include receiving, from a CU of the source base station, a second message including the configuration information of resources for the L1 measurement for the at least one candidate cell.

[0020] In order to solve the above-described problem, according to an embodiment of the present invention, a CU (central unit) of a source base station of a wireless communication system may include a transceiver; and a control unit connected to the transceiver and configured to transmit a first message requesting information for LTM configuration to a CU of at least one candidate base station associated with at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs, receive configuration information for the at least one candidate cell from the CU of the at least one candidate base station, generate configuration information for resources for L1 measurement for the at least one candidate cell based on the configuration information for the at least one candidate cell, and transmit a second message including the configuration information for resources for L1 measurement for the at least one candidate cell to a terminal.

[0021] In order to solve the above-described problem, according to an embodiment of the present invention, a CU (central unit) of a candidate base station of a wireless communication system includes a transceiver; and a control unit connected to the transceiver, the control unit receiving a first message requesting information for LTM configuration for at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs from a CU of a source base station, requesting configuration information for the at least one candidate cell from at least one DU (distributed unit) of the candidate base station associated with the at least one candidate cell, receiving the configuration information for the at least one candidate cell from the at least one DU of the candidate base station, and transmitting the configuration information for the at least one candidate cell to the CU of the source base station, wherein configuration information for resources for L1 measurement for the at least one candidate cell can be generated based on the configuration information for the at least one candidate cell.

[0022] According to an embodiment of the present invention, any terminal may not experience communication interruption when moving to a different cell.

[0023] In addition, according to an embodiment of the present invention, a method and device for exchanging information necessary for movement of a terminal between a source CU, a target CU, and a DU linked to each CU can be provided.

[0024] In addition, according to an embodiment of the present invention, a method and device can be provided that enable a terminal to perform cell switch to a cell of an inter CU.

[0025] The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by a person having ordinary skill in the art to which the present disclosure pertains from the description below.

[0026] FIG. 1 is a diagram illustrating the structure of an LTE system according to one embodiment of the present invention.

[0027] FIG. 2 is a diagram illustrating a wireless protocol structure of an LTE system according to an embodiment of the present invention.

[0028] FIG. 3 is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present invention.

[0029] FIG. 4 is a diagram showing a wireless protocol structure of a next-generation mobile communication system according to an embodiment of the present invention.

[0030] FIG. 5 is a block diagram illustrating the structure of a terminal according to an embodiment of the present invention.

[0031] Figure 6 is a block diagram showing the configuration of a base station according to one embodiment of the present invention.

[0032] FIG. 7a and FIG. 7b are diagrams illustrating an example of an operation for an inter CU MCG LTM according to an embodiment of the present invention.

[0033] FIG. 8a and FIG. 8b are diagrams illustrating an example of a case where a source setting is changed in an inter-CU MCG LTM according to an embodiment of the present invention.

[0034] FIG. 9a and FIG. 9b are diagrams illustrating an example of an operation when a setting change occurs in a target DU according to an embodiment of the present invention.

[0035] FIG. 10a and FIG. 10b are diagrams illustrating an example of an operation when LTM preparation is canceled according to an embodiment of the invention.

[0036] FIG. 11a and FIG. 11b are diagrams illustrating an example of an operation when a cell switch execution and a cancel command conflict according to one embodiment of the invention.

[0037] The operating principles of the present invention will be described in detail below with reference to the attached drawings. In the following description of the present invention, detailed descriptions of known functions or components will be omitted if they are deemed to unnecessarily obscure the gist of the invention. Furthermore, the terms described below are defined based on their functions in the present invention and may vary depending on the intentions or practices of the user or operator. Therefore, their definitions should be based on the overall content of this specification.

[0038] 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.

[0039] The operating principles of the present invention are described in detail with reference to the attached diagram. The terms described below are defined based on their functions within the present invention. These terms may vary depending on the intent or custom of the user or operator, and therefore their definitions should be determined based on the overall content of this specification.

[0040] For the same reason, some components in the attached drawings are exaggerated, omitted, or schematically depicted. Furthermore, the dimensions of each component do not entirely reflect its actual size.

[0041] The advantages and features of the present disclosure, and methods for achieving them, will become clearer with reference to the embodiments described below in detail with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms. These embodiments are provided solely to ensure that the disclosure is complete and to fully inform those skilled in the art of the scope of the disclosure, and the present disclosure is defined only by the scope of the claims. Like reference numerals designate like elements throughout the disclosure.

[0042] Certain terms used in the following description are provided to aid in understanding the present disclosure, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present disclosure.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] 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.

[0047] For convenience of explanation, the present invention uses terms and names defined in the 5GS and NR standards, which are standards defined by the 3rd Generation Partnership Project (3GPP), among the existing communication standards. However, the present invention is not limited to the above terms and names and can be equally applied to wireless communication networks that follow other standards. For example, the present invention can be applied to the 3GPP 5GS / NR (5th generation mobile communication standard).

[0048] FIG. 1 is a diagram illustrating the structure of an LTE system according to one embodiment of the present invention.

[0049] Referring to FIG. 1, as illustrated, a wireless access network of an LTE system may be composed of next-generation base stations (Evolved Node Bs, hereinafter referred to as ENBs, eNBs, Node Bs or base stations) (1-05, 1-10, 1-15, 1-20), a mobility management entity (MME) (1-25) and an S-GW (1-30, Serving-Gateway). A user equipment (UE or terminal) (1-35) may access an external network through the ENBs (1-05 to 1-20) and the S-GW (1-30).

[0050] In Fig. 1, ENBs (1-05 to 1-20) may correspond to existing Node Bs of a UMTS system. ENBs (1-05 to 1-20) are connected to UEs (1-35) via a wireless channel and may perform a more complex role than existing Node Bs. In an LTE system, all user traffic, including real-time services such as VoIP (Voice over IP) via the Internet Protocol, can be serviced through a shared channel. Therefore, a device that collects status information such as buffer status, available transmission power status, and channel status of UEs (1-35) and performs scheduling is required, and ENBs (1-05 to 1-20) may be responsible for this. One ENB (1-05 to 1-20) can typically control multiple cells. For example, in order to achieve a transmission rate of 100 Mbps, an LTE system may use, for example, Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology in a 20 MHz bandwidth. In addition, the LTE system can apply an adaptive modulation and coding (AMC) method that determines a modulation scheme and a channel coding rate according to the channel condition of the terminal (1-35). The S-GW (1-30) is a device that provides a data bearer and can create or remove a data bearer according to the control of the MME (1-25). The MME (1-25) is a device that is responsible for various control functions as well as mobility management functions for the terminal (1-35) and can be connected to multiple base stations (1-05 to 1-20).

[0051] FIG. 2 is a diagram illustrating a wireless protocol structure of an LTE system according to an embodiment of the present invention.

[0052] Referring to FIG. 2, the wireless protocol of the LTE system may be composed of Packet Data Convergence Protocol (PDCP) (2-05, 2-40), Radio Link Control (RLC) (2-10, 2-35), and Medium Access Control (MAC) (2-15, 2-30) in the terminal and ENB, respectively. PDCP (2-05, 2-40) may be responsible for operations such as IP header compression / reconstruction. The main functions of PDCP (2-05, 2-40) can be summarized as follows.

[0053] - Header compression and decompression (ROHC only)

[0054] - User data transfer function

[0055] - In-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM

[0056] - Order reordering function (For split bearers in DC (only support for RLC AM): PDCP PDU routing for transmission and PDCP PDU reordering for reception)

[0057] - Duplicate detection function (Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM)

[0058] - Retransmission function (Retransmission of PDCP SDUs at handover and, for split bearers in DC, of ​​PDCP PDUs at PDCP data-recovery procedure, for RLC AM)

[0059] - Encryption and decryption functions (Ciphering and deciphering)

[0060] - Timer-based SDU discard in uplink.

[0061] Radio Link Control (RLC) (2-10, 2-35) can perform ARQ operations, etc. by reconfiguring PDCP packet data units (PDUs) to an appropriate size. The main functions of RLC (2-10, 2-35) can be summarized as follows.

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

[0063] - ARQ function (Error Correction through ARQ (only for AM data transfer))

[0064] - Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer)

[0065] - Re-segmentation of RLC data PDUs (only for AM data transfer)

[0066] - Reordering of RLC data PDUs (only for UM and AM data transfer)

[0067] - Duplicate detection (only for UM and AM data transfer)

[0068] - Error detection function (Protocol error detection (only for AM data transfer))

[0069] - RLC SDU discard function (RLC SDU discard (only for UM and AM data transfer))

[0070] - RLC re-establishment function

[0071] MAC(2-15, 2-30) is connected to multiple RLC layer devices configured in a single terminal, and can perform operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC(2-15, 2-30) can be summarized as follows.

[0072] - Mapping function (Mapping between logical channels and transport channels)

[0073] - Multiplexing and demultiplexing function (Multiplexing / demultiplexing of MAC SDUs belonging to one or different logical channels into / from transport blocks (TB) delivered to / from the physical layer on transport channels)

[0074] - Scheduling information reporting function

[0075] - HARQ function (Error correction through HARQ)

[0076] - Priority handling between logical channels of one UE

[0077] - Priority handling between UEs by means of dynamic scheduling

[0078] - MBMS service identification function

[0079] - Transport format selection function

[0080] - Padding function

[0081] The physical layer (2-20, 2-25) can perform the operation of channel coding and modulating upper layer data, converting it into OFDM symbols and transmitting it through a wireless channel, or demodulating and channel decoding OFDM symbols received through a wireless channel and transmitting them to a higher layer.

[0082] FIG. 3 is a diagram illustrating the structure of a next-generation mobile communication system according to an embodiment of the present invention.

[0083] Referring to FIG. 3, a wireless access network of a next-generation mobile communication system (hereinafter referred to as NR or 5g) may be composed of a next-generation base station (New Radio Node B, hereinafter referred to as NR gNB, gNB, or NR base station) (3-10) and a next-generation radio core network (New Radio Core Network, NR CN) (3-05). A next-generation radio user equipment (New Radio User Equipment, NR UE or terminal) (3-15) may access an external network through the NR gNB (3-10) and the NR CN (3-05).

[0084] In Fig. 3, the NR gNB (3-10) may correspond to the eNB (Evolved Node B) of the existing LTE system. The NR gNB (3-10) is connected to the NR UE (3-15) via a wireless channel and may provide a service superior to that of the existing Node B. In the next-generation mobile communication system, all user traffic may be serviced through a shared channel. Therefore, a device that collects status information such as buffer status, available transmission power status, and channel status of the UEs (3-15) and performs scheduling is required, and the NR NB (3-10) may be responsible for the scheduling. One NR gNB (3-10) may control multiple cells. In the next-generation mobile communication system, in order to implement ultra-high-speed data transmission compared to the general LTE, a bandwidth exceeding the general maximum bandwidth may be applied. In addition, in the next-generation mobile communication system, beamforming technology can be additionally incorporated with orthogonal frequency division multiplexing (OFDM) as a wireless access technology. In addition, adaptive modulation and coding (AMC) that determines the modulation scheme and channel coding rate according to the channel condition of the terminal can be applied. NR CN (3-05) can perform functions such as mobility support, bearer setup, and QoS setup. NR CN (3-05) is a device that is responsible for various control functions as well as mobility management for the terminal (3-15), and can be connected to multiple base stations (3-10). In addition, the next-generation mobile communication system can also be linked with the LTE system, and NR CN (3-05) can be connected to MME (3-25) through a network interface. MME (3-25) can be connected to eNB (3-30), which is an LTE base station.

[0085] FIG. 4 is a diagram showing a wireless protocol structure of a next-generation mobile communication system according to an embodiment of the present invention.

[0086] Referring to FIG. 4, the wireless protocol of the next-generation mobile communication system may be composed of NR Service Data Adaptation Protocol (SDAP) (4-01, 4-45), NR PDCP (4-05, 4-40), NR RLC (4-10, 4-35), NR MAC (4-15, 4-30), and NR PHY (4-20, 4-25) in the terminal and NR base station, respectively.

[0087] Key features of NR SDAP (4-01, 4-45) may include some of the following:

[0088] - Transfer of user plane data

[0089] - Mapping function between QoS flow and data bearer for both DL and UL

[0090] - QoS flow ID marking function for uplink and downlink (marking QoS flow ID in both DL and UL packets)

[0091] - Ability to map relective QoS flow to data bearer for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

[0092] For an SDAP layer device, a terminal can be configured by a Radio Resource Control (RRC) message for each PDCP layer device, per bearer, or per logical channel, whether to use the header of the SDAP layer device or whether to use the function of the SDAP layer device. When the SDAP header is configured, the terminal can instruct the terminal to update or reset the mapping information for the QoS flow and data bearer of the uplink and downlink by using a 1-bit indicator for reflecting the Non-Access Stratum (NAS) Quality of Service (QoS) in the SDAP header (NAS reflective QoS) and a 1-bit indicator for reflecting the Access Stratum (AS) QoS in the SDAP header. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority, scheduling information, etc. to support a smooth service.

[0093] The main functions of NR PDCP (4-05, 4-40) may include some of the following functions:

[0094] - Header compression and decompression (ROHC only)

[0095] - User data transfer function

[0096] - In-sequence delivery of upper layer PDUs

[0097] - Out-of-sequence delivery of upper layer PDUs

[0098] - PDCP PDU reordering for reception

[0099] - Duplicate detection of lower layer SDUs

[0100] - Retransmission function (Retransmission of PDCP SDUs)

[0101] - Encryption and decryption functions (Ciphering and deciphering)

[0102] - Timer-based SDU discard in uplink.

[0103] In the above, the reordering function of the NR PDCP device may refer to a function of reordering PDCP PDUs received from a lower layer in order based on a PDCP SN (sequence number). The reordering function of the NR PDCP device may include a function of transmitting data to an upper layer in the reordered order, or 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 a status of lost PDCP PDUs to the transmitting side, and a function of requesting retransmission of lost PDCP PDUs.

[0104] The main functions of NR RLC(4-10, 4-35) may include some of the following functions:

[0105] - Data transfer function (Transfer of upper layer PDUs)

[0106] - In-sequence delivery of upper layer PDUs

[0107] - Out-of-sequence delivery of upper layer PDUs

[0108] - ARQ function (Error Correction through ARQ)

[0109] - Concatenation, segmentation and reassembly of RLC SDUs

[0110] - Re-segmentation of RLC data PDUs

[0111] - Reordering of RLC data PDUs

[0112] - Duplicate detection function

[0113] - Protocol error detection

[0114] - RLC SDU discard function

[0115] - RLC re-establishment function

[0116] In the above, the in-sequence delivery function of the NR RLC device may refer to the function of sequentially delivering RLC SDUs received from the lower layer to the upper layer. If a single RLC SDU is originally received divided into multiple RLC SDUs, the in-sequence delivery function of the NR RLC device may include the function of reassembling and delivering them.

[0117] The in-sequence delivery function of the NR RLC device may include a function to reorder received RLC PDUs based on the RLC SN (sequence number) or PDCP SN (sequence number), a function to record lost RLC PDUs by reordering them, a function to report status of lost RLC PDUs to the transmitter, and a function to request retransmission of lost RLC PDUs.

[0118] The in-sequence delivery function of the NR RLC device may include a function to sequentially deliver only the RLC SDUs up to the lost RLC SDU to the upper layer when there is a lost RLC SDU.

[0119] The in-sequence delivery function of the NR RLC device may include a function to deliver all RLC SDUs received before a predetermined timer starts to the upper layer in sequence, even if there are lost RLC SDUs, if the timer has expired.

[0120] The in-sequence delivery function of the NR RLC device may include a function to deliver all RLC SDUs received up to now to the upper layer in sequence if a predetermined timer has expired, even if there are lost RLC SDUs.

[0121] An NR RLC device can process RLC PDUs in the order they are received and deliver them to an NR PDCP device, regardless of the order of the sequence number (out-of-sequence delivery).

[0122] When an NR RLC device receives a segment, it can receive segments that are stored in a buffer or will be received later, reconstruct them into a complete RLC PDU, and then transmit them to the NR PDCP device.

[0123] The NR RLC layer may not include concatenation functionality, and the functionality may be performed by the NR MAC layer or replaced by the multiplexing functionality of the NR MAC layer.

[0124] In the above, the out-of-sequence delivery function of the NR RLC device may refer to the function of directly delivering RLC SDUs received from a lower layer to an upper layer regardless of the order. The out-of-sequence delivery function of the NR RLC device may include the function of reassembling and delivering the RLC SDUs when an original RLC SDU is received fragmented into multiple RLC SDUs. The out-of-sequence delivery function of the NR RLC device may include the function of storing and arranging the RLC SN or PDCP SN of the received RLC PDUs to record the lost RLC PDUs.

[0125] NR MAC (4-15, 4-30) 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.

[0126] - Mapping function (Mapping between logical channels and transport channels)

[0127] - Multiplexing / demultiplexing of MAC SDUs

[0128] - Scheduling information reporting function

[0129] - HARQ function (Error correction through HARQ)

[0130] - Priority handling between logical channels of one UE

[0131] - Priority handling between UEs by means of dynamic scheduling

[0132] - MBMS service identification function

[0133] - Transport format selection function

[0134] - Padding function

[0135] The NR PHY layer (4-20, 4-25) can perform operations such as channel coding and modulating upper layer data, converting it into OFDM symbols and transmitting it through a wireless channel, or demodulating and channel decoding OFDM symbols received through a wireless channel and transmitting them to a higher layer.

[0136] FIG. 5 is a block diagram illustrating the structure of a terminal according to an embodiment of the present invention.

[0137] Referring to FIG. 5, the terminal may include an RF (Radio Frequency) processing unit (5-10), a baseband processing unit (5-20), a storage unit (5-30), a control unit (5-40), etc.

[0138] The RF processing unit (5-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. The RF processing unit (5-10) up-converts the baseband signal provided from the baseband processing unit (5-20) into an RF band signal and transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (5-10) 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 Fig. 5, only one antenna is illustrated, but the terminal may be equipped with multiple antennas. In addition, the RF processing unit (5-10) may include multiple RF chains. Furthermore, the RF processing unit (5-10) may perform beamforming. For the above beamforming, the RF processing unit (5-10) 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 can receive multiple layers when performing the MIMO operation.

[0139] The baseband processing unit (5-20) above performs 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 (5-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (5-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (5-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (5-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures 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 (5-20) divides the baseband signal provided from the RF processing unit (5-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT (fast Fourier transform), and then restores the received bit string through demodulation and decoding.

[0140] The baseband processing unit (5-20) and the RF processing unit (5-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (5-20) and the RF processing unit (5-10) may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. Furthermore, at least one of the baseband processing unit (5-20) and the RF processing unit (5-10) 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 (5-20) and the RF processing unit (5-10) may include different communication modules to process signals of different frequency bands. For example, the different wireless access technologies may include wireless LAN (e.g., IEEE 802.11), 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.

[0141] The storage unit (5-30) stores data such as basic programs, application programs, and setting information for the operation of the terminal. In particular, the storage unit (5-30) can store information related to a second access node that performs wireless communication using a second wireless access technology. In addition, the storage unit (5-30) provides the stored data at the request of the control unit (5-40).

[0142] The above control unit (5-40) controls the overall operations of the terminal. For example, the control unit (5-40) transmits and receives signals through the baseband processing unit (5-20) and the RF processing unit (5-10). In addition, the control unit (5-40) records and reads data in the storage unit (5-40). For this purpose, the control unit (5-40) may include at least one processor. For example, the control unit (5-40) may include a communication processor (CP) that performs control for communication and an application processor (AP) that controls upper layers such as application programs.

[0143] Figure 6 is a block diagram showing the configuration of a base station according to one embodiment of the present invention.

[0144] Referring to FIG. 6, the base station may be configured to include an RF processing unit (6-10), a baseband processing unit (6-20), a backhaul communication unit (6-30), a storage unit (6-40), a control unit (6-50), etc.

[0145] The RF processing unit (6-10) performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. The RF processing unit (6-10) up-converts the baseband signal provided from the baseband processing unit (6-20) into an RF band signal and transmits it through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (6-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. Although only one antenna is illustrated in FIG. 6, the base station may have multiple antennas. In addition, the RF processing unit (6-10) may include multiple RF chains. Furthermore, the RF processing unit (6-10) may perform beamforming. For the beamforming, the RF processing unit (6-10) may adjust the phase and magnitude of each signal transmitted and received through multiple antennas or antenna elements. The above RF processing unit can perform a downlink MIMO operation by transmitting one or more layers.

[0146] The baseband processing unit (6-20) above performs a conversion function between a baseband signal and a bit stream according to the physical layer specifications of the first wireless access technology. For example, when transmitting data, the baseband processing unit (6-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (6-20) restores the reception bit stream by demodulating and decoding the baseband signal provided from the RF processing unit (6-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (6-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols through IFFT operation and CP insertion. In addition, when receiving data, the baseband processing unit (6-20) divides the baseband signal provided from the RF processing unit (6-10) into OFDM symbol units, restores the signals mapped to subcarriers through FFT operation, and then restores the received bit string through demodulation and decoding. The baseband processing unit (6-20) and the RF processing unit (6-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (6-20) and the RF processing unit (6-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0147] The above backhaul communication unit (6-30) provides an interface for communicating with other nodes within the network. The above backhaul communication unit (6-30) converts a bit string transmitted from the base station to other nodes, such as auxiliary base stations and core networks, into a physical signal, and converts a physical signal received from the other nodes into a bit string.

[0148] The storage unit (6-40) stores data such as basic programs, application programs, and configuration information for the operation of the base station. In particular, the storage unit (6-40) can store information on bearers assigned to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (6-40) 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 (6-40) provides the stored data at the request of the control unit (6-50).

[0149] The control unit (6-50) controls the overall operations of the base station. For example, the control unit (6-50) transmits and receives signals through the baseband processing unit (6-20) and the RF processing unit (6-10) or through the backhaul communication unit (6-30). In addition, the control unit (6-50) records and reads data in the storage unit (6-40). For this purpose, the control unit (6-50) may include at least one processor.

[0150] Hereinafter, the following abbreviations may be used in this specification.

[0151] LTM: L1 / L2 triggered mobility

[0152] CU: central unit

[0153] DU: distributed unit

[0154] MCG: master cell group

[0155] MN: master node

[0156] This specification focuses on the operations necessary for preparing and performing LTM on inter-CU cells when a terminal performs LTM. In particular, it proposes operations for LTM on MCGs, i.e., movement of pcells (primary cells). Existing LTMs assume only intra-CU operation, thus lacking inter-node signaling.

[0157] As a basic prerequisite, since the execution command of LTM is issued by the DU, a DU ready for LTM (candidate DU) must have at least one of the following as information about all candidate cells:

[0158] - LTM candidate ID

[0159] - Mapping information between LTM candidate ID and corresponding cell ID

[0160] - Beam information to be used by each candidate (TCI (transmission configuration indication) state)

[0161] ■ In this case, the meaning of use can mean a beam that is linked to a RACH occasion when performing DL (downlink) and / or UL (uplink) synchronization and / or RACH (random access channel, random access), 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.

[0162] - RACH preamble index

[0163] - SSB index: This is the index of the SSB used to determine the RACH occasion in each candidate cell, and can mean the occasion for transmitting the RACH preamble of CFRA (contention free random access).

[0164] The above information is information that must be displayed when issuing a cell switch command MAC (medium access control) CE (control element) instruction to a candidate cell that has made an LTM decision.

[0165] As a preparatory step prior to cell switching, each candidate cell may transmit channel state information (CSI) for LTM, and each DU must also possess reference signal (RS) information for the corresponding CSI. Before instructing the LTM cell switch, the source DU transmits CSI information for specific candidate cells to the UE, and the UE can measure and report the corresponding CSI RS. Upon receiving this measurement result report, the source DU can determine whether it needs to move to the corresponding cell and which beam to use. To this end, each DU may require at least one of the following pieces of information for its concerned cell.

[0166] - CSI resource settings for each candidate cell (required when transmitting L1 measurement settings to the terminal as a source DU), individual resource settings and / or setting ID for each cell, CSI resource settings for LTM, etc.

[0167] - CSI report configuration considering the CSI resources of each candidate cell above

[0168] ■ The purpose of this is that when a candidate DU creates the above information and passes 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.

[0169] ■ That is, when a terminal moves from another cell to this cell (concerned cell), it can be used as a CSI report configuration with that cell as the serving cell. This can be used to include it in the target cell config (configuration) without providing a separate L1 setting for subsequent LTM.

[0170] - RACH configuration and lower layer setting information to be used in the concerned cell

[0171] ■ 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.

[0172] ■ 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.

[0173] Based on the above information, the inter CU signaling system is described.

[0174] FIG. 7a and FIG. 7b are diagrams illustrating an example of an operation for an inter CU MCG LTM according to an embodiment of the present invention.

[0175] The operation at each step of FIG. 7a and FIG. 7b can be as follows.

[0176] At step 710, the terminal (701) is connected to the source CU (704) and is also connected to the source DU (702) that operates the serving cell of the source CU (704). After receiving the L3 measurement configuration through the source CU (704), the terminal (701) can transmit the corresponding measurement result report to the source CU (704) through the source DU (702).

[0177] At step 715, the source CU (704) can determine a candidate cell of LTM based on the measurement result from the terminal (701) and determine LTM preparation.

[0178] At step 720, the source CU (704) may request resource allocation for the terminal (701) to the candidate CU (706) operating the determined candidate cell through a handover request message or a separate message (e.g., a new Xn message). At this time, the information that may be included in the message may be at least one of the following.

[0179] A. Instructions for performing LTM

[0180] i. Additionally, an indicator may be included indicating whether the request is for initial preparation, eg, initiation, or subsequent modification.

[0181] B. Terminal ID

[0182] C. ID of the source CU (704) and / or ID of the source DU (702), and / or TNL (transport network layer) address (e.g., IP address, etc.) of the source DU (704).

[0183] D. ID of the requesting candidate cell (PCI (physical cell identity) or NR CGI (cell global identity) with NR ARFCN (absolute radio frequency channel number))

[0184] E. LTM configuration ID of this candidate cell (if accepted, the source DU (702) can use the LTM config ID when switching cells to the target cell)

[0185] F. LTM configuration ID mapping list: When transmitted to a candidate DU (705), information for informing the candidate DU (705) of the mapping relationship between the currently operable LTM settings and its cells.

[0186] i. Opt 1. The above candidate cell list may be a list of candidate cells operated by all candidate CUs (706, 707) for the corresponding terminal (701),

[0187] ii. Opt 2. It may be a list that includes only candidate cells operated by the source CU (704) transmitting the HO request message.

[0188] G. Configuration information of CSI resources being transmitted by all currently configured candidate cells

[0189] H. An indicator requesting PRACH resource information for a target candidate cell.

[0190] I. A directive requesting lower layer settings for target candidate cells.

[0191] In addition to the above information, information previously used in the HO request message may also be included in the message. The information included in the HO request message can be referenced in [Table 1] below.

[0192] Source NG-RAN node UE XnAP ID referenceNG-RAN node UE XnAP ID9.2.3.16Allocated at the source NG-RAN nodeCause9.2.3.2Target Cell Global ID9.2.3.25Includes either an E-UTRA CGI or an NR CGIGUAMI9.2.3.24UE Context Information>NG-C UE associated Signalling referenceAMF UE NGAP ID 9.2.3.26Allocated at the AMF on the source NG-C connection.>Signalling TNL association address at source NG-C sideCP Transport Layer Information 9.2.3.31This IE indicates the AMF's IP address of the SCTP association used at the source NG-C interface instance.NOTE: If no UE TNLA binding exists at the source NG-RAN node, the source NG-RAN node indicates the TNL association address it would have selected if it would have had to create a UE TNLA binding.>UE Security Capabilities9.2.3.49>AS Security Information9.2.3.50>Index to RAT / Frequency Selection Priority9.2.3.23>UE Aggregate Maximum Bit Rate9.2.3.17>PDU Session Resources To Be Setup List9.2.1.1Similar to NG-C signalling, containing UL tunnel information per PDU Session Resource;and in addition, the source side QoS flow ⇔ DRB mapping>RRC ContextOCTET STRINGEither includes theHandoverPreparationInformationmessage as defined in subclause 10.2.2. of TS 36.331

[0014] , ortheHandoverPreparationInformation-NBmessage as defined in subclause 10.6.2 of TS 36.331

[0014] , if the target NG-RAN node is an ng-eNB,or theHandoverPreparationInformationmessage as defined in subclause 11.2.2 of TS 38.331

[0010] , if the target NG-RAN node is a gNB.>Location Reporting Information9.2.3.47Includes the necessary parameters for location reporting.>Mobility Restriction List9.2.3.53>5GC Mobility Restriction List Container9.2.3.100>NR UE Sidelink Aggregate Maximum Bit Rate9.2.3.107This IE applies only if the UE is authorized for NR V2X services.>LTE UE Sidelink Aggregate Maximum Bit Rate9.2.3.108This IE applies only if the UE is authorized for LTE V2X services.>ManagementBasedMDT PLMN ListMDT PLMN List 9.2.3.133>UE Radio Capability ID9.2.3.138>MBS Session Information List9.2.1.36>5G ProSe UE PC5 Aggregate Maximum Bit RateNR UE Sidelink Aggregate Maximum Bit Rate 9.2.3.107This IE applies only if the UE is authorized for 5G ProSe services.>UE Slice Maximum Bit Rate List9.2.3.167>NR A2X UE PC5 Aggregate Maximum Bit RateNR UE Sidelink Aggregate Maximum Bit Rate 9.2.3.107This IE applies only if the UE is authorized for NR A2X services.>LTE A2X UE PC5 Aggregate Maximum Bit RateLTE UE Sidelink Aggregate Maximum Bit Rate 9.2.3.108This IE applies only if the UE is authorized for LTE A2X services.Trace Activation9.2.3.55Masked IMEISV9.2.3.32UE History Information9.2.3.64UE Context Reference at the S-NG-RAN node>Global NG-RAN Node ID9.2.2.3>S-NG-RAN node UE XnAP IDNG-RAN node UE XnAP ID 9.2.3.16.

[0193] In step 723, the candidate CU (706) that received the request from the source CU (704) may transmit at least one of the following information to the candidate DU (705) corresponding to the candidate cell that received the request. This information may be transmitted in a UE context setup request message of the F1 interface or in a new F1 message.

[0194] A. Information received by candidate CU (706) from source CU (704)

[0195] i. Target candidate cell ID: An ID indicating a candidate target cell, which can be PCI or NR CGI.

[0196] ii. The configuration ID used in the LTM mapped to the candidate cell, i.e., the LTM configuration ID of the candidate cell,

[0197] iii. LTM configuration ID mapping list: Information on LTM candidate IDs and cell IDs allocated so far

[0198] 1. Opt 1. It may be information including candidate cells operated by all candidate CUs (706, 707).

[0199] 2. Opt 2. Only candidate cells operated by the source CU (704) may be included. In this case, the candidate CU (706) may separately transmit to the candidate DU (705) the LTM configuration ID and candidate cell mapping information in addition to the information on the candidate cells operated by the candidate CU (706).

[0200] iv. CSI resource configuration: CSI resource configuration information transmitted by candidate cells currently in operation can be transmitted. In this case, information can also be transmitted as classified information according to opt 1 and opt 2.

[0201] v. An indicator requesting PRACH resource information for the target candidate cell.

[0202] vi. A directive requesting lower layer settings for target candidate cells.

[0203] B. Additionally, the candidate CU (706) can transmit information it has. In the case of opt 2, information about LTM candidate cells operated by the candidate CU (706) can be transmitted.

[0204] i. Target candidate cell ID: An ID indicating a candidate target cell, which can be PCI or NR CGI.

[0205] ii. The configuration ID used in the LTM mapped to the candidate cell, i.e., the LTM configuration ID of the candidate cell,

[0206] iii. LTM configuration ID mapping list: Information on LTM candidate IDs and cell IDs allocated so far

[0207] 1. Opt 1. It may be information including candidate cells operated by all candidate CUs (706, 707).

[0208] 2. Opt 2. Only candidate cells operated by the source CU (704) may be included. In this case, the candidate CU (706) may separately transmit to the candidate DU (705) the LTM configuration ID and candidate cell mapping information in addition to the information on the candidate cells operated by the candidate CU (706).

[0209] iv. CSI resource configuration: CSI resource configuration information transmitted by candidate cells currently in operation can be transmitted. In this case, information can also be transmitted as classified information according to opt 1 and opt 2.

[0210] v. An indicator requesting PRACH resource information for the target candidate cell.

[0211] vi. A directive requesting lower layer settings for target candidate cells.

[0212] The candidate DU (705) that received the above information can accept or reject the LTM resource request for the corresponding terminal (701). If accepted, the candidate DU (705) can notify the candidate CU (706) of the acceptance result through a UE context setup response message or a corresponding F1 message at step 725. At this time, the message may additionally include the following information.

[0213] A. Generated lower layer RRC configuration

[0214] i. This information may be cellGroupConfiguration in RRC.

[0215] ii. If the above lower layer configuration is a complete configuration, the complete configuration directive may also be included.

[0216] B. It can convey SSB time / frequency information transmitted from the candidate cell.

[0217] i. This information is information collected from each DU (705) and candidate cells in the candidate CU (706) and transmitted to the terminal (701), and can be referenced as an element of the CSI resource referred to in the CSI report configuration of the LTM.

[0218] ii. Also, it can be referenced for DL ​​or UL or joint TCI state information.

[0219] C. DL or UL or joint TCI state configuration information operating in the candidate cell: The configuration information can be set by the CU to the terminal (701) via RRC, and then a specific TCI state can be activated / deactivated through the candidate cell TCI state activation / deactivation MAC CE. Through the activated TCI state, the terminal (701) can perform DL synchronization before the cell switch command. In addition, when one of the TCI states, DL or Joint and / or UL TCI state, is signaled in the cell switch command, the terminal (701) can activate the indicated TCI state of the candidate cell and instruct it to be used immediately during cell switch.

[0220] D. RACH configuration information: RACH configuration information used in the candidate cell.

[0221] E. CSI report configuration information: The candidate DU (705) can create a CSI report configuration by referring to the CSI resource configuration of all candidate cells provided by the candidate CU (706). This information may include instructions for measuring which CSI resource of which cell, and report settings such as periodic / semi-persistent / persistent. Thereafter, it may be included in the target cell configuration and used to automatically perform L1 measurement and reporting for LTM without separate settings when the terminal (701) moves to this cell.

[0222] The candidate CU (706) that has received the above information can create (generate) a HO command (Hocmd) message (e.g., RRCReconfiguration) for the corresponding candidate cell in step 727.

[0223] And the candidate CU (706) can transmit this information to the source CU (704) in step 729. At this time, the HO command message can be included in the HO request ACK (acknowledgement, response) message or a new / existing message of Xn corresponding thereto.

[0224] A. Opt 1. When a candidate CU (706) receives an HO request for one candidate target cell from a source CU (704), the candidate CU (706) can transmit information about one corresponding target cell to the source CU (704).

[0225] B. Opt 2. Even if the candidate CU (706) receives an HO request for one candidate target cell from the source CU (704), if there is a new message for another candidate cell that is allowed admission to LTM candidate cells for the same terminal (701) at the time when the candidate CU (706) sends the HO request ACK message, the HO request ACK message may include information on all newly allowed candidate cells and be delivered to the terminal (701) in batches (via the source CU (704)).

[0226] C. Opt 3. When a candidate CU (706) is requested by a source CU (704) to perform LTM preparation for multiple candidate target cells operated by the CU (candidate CU) (706), the candidate CU (706) may collect information on all other candidate cells allowed for admission and include it in the HO request ACK message to transmit it to the source CU (704).

[0227] D. For each admitted candidate cell, this message may include at least one of the following information: The candidate CU (706) may include the following information to distinguish each candidate cell: PCI or NR CGI with ARFCN or LTM configuration ID of each candidate cell assigned by the source CU (706).

[0228] i. Target cell configuration (e.g., RRCReconfiguration)

[0229] ii. An indicator of whether the above target cell setting is a complete setting or not.

[0230] iii. TCI state configuration (DL or Joint and / or UL TCI state)

[0231] iv. CSI report configuration

[0232] v. CSI resource configuration information transmitted from each cell

[0233] vi. RACH settings

[0234] E. Unlike the cell stars, the following information may be included for each candidate CU (706, 707).

[0235] i. LTM reference configuration for this candidate CU's candidate cells

[0236] 1. An ID (e.g., gNB ID, or integer ID assigned to the candidate CU by the source CU (704)) that distinguishes the above candidate CU (706, 707) can be transmitted to the terminal (701) in conjunction with each candidate cell configuration information.

[0237] 2. Afterwards, when the terminal (701) receives a cell switch command to a specific cell, the reference configuration linked to the specific cell can be applied.

[0238] ii. LTM CSI-resource configuration information

[0239] 1. The LTM CSI-Resource configuration may include an LTM CSI resource config determined by the DU (705) of each candidate cell for each admitted candidate cell within the candidate CU (706).

[0240] A. When considering the above one candidate cell as a source cell, the CSI resources transmitted by all or some specific candidate cells excluding that cell can be indicated. At this time, a bit list in which the LTM config ID of each cell and the SSB index or CSI-RS resource ID considered as CSI in that cell are mapped can be included by linking them with the LTM config ID of the source cell.

[0241] Before or immediately after the candidate CU (706) transmits the HO Request ACK message in step 729, the candidate CU (706) may transmit at least one piece of information about newly admitted (permitted) candidate cells to the DUs of other candidate CUs (707) in step 730. Although the information is shown to be transmitted to the candidate DU (705) in the drawing, the information about the admitted candidate cells may be transmitted to the candidate DU (not shown) of candidate CU2 (707). The DUs (705) that receive this may store the information and, after the terminal (701) moves to its candidate cell, may execute a cell switch command using the given information. The information that the candidate CU (706) transmits to each DU through the UE context modification request or the corresponding F1 message may include all or part of the information that the candidate CU (706) transmits to the source CU (704) in step 279. And each DU that receives the above message can transmit a response message, for example, a UE context modification response message or a corresponding F1 message, to the candidate CU (706).

[0242] In step 733, the source CU (704) may use the information received in step 729 to transmit the information to the source DU (702) and other DUs (703) managed by its CU (704). This process may be possible via a UE context modification request message and a corresponding F1 message. The transmitted information may include all or part of the information contained in the message transmitted in step 729.

[0243] The DUs (702, 703) of the source CU (704) that have received the above information (including the source DU (702)) can modify the LTM-CSI-resource config for performing L1 measurement if their candidate cells are source cells by referring to the CSI resources of the candidate cells of the newly admitted candidate CU (706). (i.e., the SSB / CSI-RS index of the new candidate cell can be added as a measurement target). In this regard, the LTM-CSI-ReportConfig that refers to the modified LTM-CSI-resource config can also be updated. In addition, the lower layer configuration can also be updated as needed.

[0244] At step 735, the DUs (702, 703) of each source CU (704) can transmit updated CSI-related information and updated information on lower layer configuration to the source CU (704). This process can be made possible through a UE context modification response message and a corresponding F1 message.

[0245] The source CU (704) that has received the above information can transmit the received information to the candidate CU (706) at step 740. The transmission of the information can be performed using an HO request message or a new Xn message. Accordingly, the candidate CU (706) can transmit the updated LTM CSI resource config, LTM CSI-reportConfig, and lower layer settings to the DUs (705) of the candidate CU (706) in association with the ID (PCI, or CGI with ARFCN, or LTM config ID) of each candidate cell.

[0246] The candidate CU (706) that received the information in step 740 can transmit the received updated information to its DUs (705). Then, in step 743, the candidate CU (706) can transmit a response message to the source CU (704). The response message can include an HO response message or a new Xn message. And, the response message can include updated information.

[0247] At step 745, the source CU (704) may compile the above information to create an ltm-Config. This ltm-Config may include at least one of the following information for each candidate cell.

[0248] A. LTM configuration ID,

[0249] B. Candidate cell PCI and / or CGI with AFRCN

[0250] C. SSB config

[0251] D. Target cell configuration (RRCReconfig msg)

[0252] E. TCI state configuration

[0253] F. CSI-RS resource config

[0254] G. Using early TA indicator

[0255] H. RACH-less execution indicator

[0256] At step 750, the source CU (704) can transmit to the terminal (701) a list of LTM-CSI-ResourceConfigs in a common field, not per cell, in the MN RRCReconfiguration message (RRC reconfiguration message). In addition, a reference configuration can be given, and in this case, multiple reference configurations can exist, so the source CU (704) can transmit to the terminal (701) a reference configuration applicable to each candidate cell, and for this linkage, a specific ID can be assigned to each reference configuration, and one of these IDs can be assigned to each candidate cell so that the terminal (701) can distinguish them when applying them.

[0257] The current serving cell setting of the Pcell of the terminal (701) can be configured and transmitted by referencing some of the configuration IDs of the LTM-CSI-ResourceConfigs and configuring LTM-CSI-ReportConfig.

[0258] The RRC reconfiguration message is included in a DL RRC message at step 750 and transmitted from the source CU (704) to the source DU (702), and the source DU (702) can transmit the RRC reconfiguration message to the terminal (701) at step 753. Then, the terminal (701) can transmit an RRC reconfiguration complete message (RRC reconfiguration complete message) to the source DU (702) at step 755. The source DU (702) can transmit a UL RRC message including the received RRC reconfiguration complete message to the source CU (704) at step 757. Thereafter, in step 770, when the network instructs the terminal (701) to activate the TCI state ID of a specific candidate cell through the MAC CE, the terminal (701) can perform DL synchronization by referring to the corresponding TCI state, and based on this, the terminal (701) can measure the resources of the CSI resources indicated in the LTM-CSI-ResourceConfig referred to in the corresponding LTM-CSI-ReportConfig. In addition, the terminal can perform report transmission set in this LTM-CSI-ReportConfig.

[0259] Regardless of the above DL synchronization and CSI measurement, the source CU (704) may request early TA acquisition at step 760. In this case, the terminal (701) may transmit a RACH preamble to the candidate cell (candidate DU (705)) indicated in the request.

[0260] A candidate cell (candidate DU (705)) that detects the above RACH preamble transmission can notify the candidate CU (706) of the TA detection through a DU-CU TA info transfer message in step 761. The candidate CU (706) can estimate the TA value, and if it determines that it is valid, it can notify the source CU (704) of the measurement of the TA value through an Xn TA info Transfer message or an equivalent message in step 763. The information included at this time can include an estimated TA value, a probability value or an accuracy value indicating the accuracy of the TA value, an LTM config ID of the cell that detected the preamble, or at least one of a PCI or CGI.

[0261] The source CU (704), which has acquired the above information in step 765, can transmit the TA value to the source DU (702). The message used at this time may be a CU-DU TA info transfer message. The source DU (702), which has been maintaining this TA value, can include the corresponding TA value in an LTM cell switch command and transmit it to the terminal (701). In this case, the terminal (701) can perform a RACH less handover through an early TA using the TA value.

[0262] The source DU (702) can determine the LTM cell switch in step 773 based on the L1 measurement result report received from the terminal (701) in step 770. Then, the source DU (702) can transmit a cell switch command to the terminal (701) in step 775. The source DU (702) that transmitted the cell switch command can notify the source CU (704) that the cell switch has been performed in step 777 (e.g., a DU-CU cell switch notification message). The message can include a target cell ID, a TCI state ID, etc. The source CU (704) that received this can transmit an Xn message to the CU of the target candidate cell, i.e., the candidate CU (706), in step 779, notifying that the LTM cell switch has been performed. This message may include at least one of the Xn AP UE ID, the ID of the target cell that commanded the cell switch as PCI or CGI with AFRCN, and the TCI state ID value indicated at the time of the cell switch. The message may be an LTM cell switch notification message.

[0263] The candidate CU (706) that has received the above information can notify the candidate DU (705) that a cell switch command has been performed, for example, using a cell switch notification message, at step 780. If the candidate DU (705) successfully receives UL data transmission at step 783 and determines that access is successful, the candidate DU (705) can notify the candidate CU (706) of the result at step 785. Depending on the embodiment, the candidate DU (705) can also transmit a target cell ID, UE ID, etc. to the candidate CU (706).

[0264] At step 790, the terminal (701) can perform an LTM cell switch by transmitting an RRC reconfiguration complete message to the candidate DU (705), and at step 793, the candidate DU (705) can transmit a UL RRC MSG transfer message to the candidate CU (706) based on the received message. The UL RRC MSG transfer message may include the RRC reconfiguration complete message received from the terminal (701).

[0265] At step 795, the candidate CU (706) can inform the source CU (704) of the success of the HO.

[0266] And at step 797, the source CU (706) can transmit a cell switch complete message to another candidate CU, candidate CU2 (707), to inform that the cell switch of the terminal (701) has been completed. The message can include a UE ID, a target cell ID, etc.

[0267] FIG. 8a and FIG. 8b are diagrams illustrating an example of a case where a source setting is changed in an inter-CU MCG LTM according to an embodiment of the present invention.

[0268] The embodiment illustrated in FIGS. 8a and 8b relates to a case where, after the LTM preparation illustrated in FIGS. 7a and 7b is completed, when a setting change occurs in a source cell, the source CU (804) sends the changed source setting to the candidate CU (806) and transmits it including an instruction indicating a change in the LTM setting.

[0269] Referring to FIGS. 8A and 8B , at step 810, the terminal (801) is connected to the source CU (804) and is also connected to the source DU (802) that operates the serving cell of the source CU (804). After receiving the L3 measurement configuration through the source CU (804), the terminal (801) can transmit the corresponding measurement result report to the source CU (804) through the source DU (802).

[0270] At step 815, the source CU (804) can determine a candidate cell for LTM based on the measurement result from the terminal (801) and determine LTM preparation.

[0271] At step 820, the source CU (804) may request resource allocation for the terminal (801) to the candidate CU (806) operating the determined candidate cell through an existing HO request message or a separate message (e.g., a new Xn message). At this time, the information that may be included in the message may be at least one of the following.

[0272] A. Instructions for performing LTM

[0273] i. Additionally, an indicator may be included indicating whether this is for a subsequent modification request.

[0274] B. Terminal ID

[0275] C. ID of the source CU (804) and / or ID of the source DU (802), and / or TNL (transport network layer) address (e.g., IP address, etc.) of the source DU (802).

[0276] D. ID of the requesting candidate cell (PCI (physical cell identity) or NR CGI (cell global identity) with NR ARFCN (absolute radio frequency channel number))

[0277] E. LTM configuration ID of this candidate cell (if accepted, the source DU (802) can use the LTM config ID when switching cells to the target cell)

[0278] F. LTM configuration ID mapping list: When transmitted to a candidate DU (805), information for informing the candidate DU (805) of the mapping relationship between the currently operable LTM settings and its cells.

[0279] i. Opt 1. The above candidate cell list may be a list of candidate cells operated by all candidate CUs (806) for the corresponding terminal (801),

[0280] ii. Opt 2. It may be a list that includes only candidate cells operated by the source CU (804) transmitting the HO request message.

[0281] G. Configuration information of CSI resources being transmitted by all currently configured candidate cells

[0282] H. An indicator requesting PRACH resource information for a target candidate cell.

[0283] I. A directive requesting lower layer settings for target candidate cells.

[0284] In addition to the above information, information previously used in the HO request message may also be included in the message. Information included in the HO request message can be referenced in [Table 1] above.

[0285] At step 825, the candidate CU (806) may transmit at least one of the following information to the candidate DU (805) corresponding to the requested candidate cell. This information may be transmitted in a UE context setup request message of the F1 interface or in a new F1 message.

[0286] A. Information received by candidate CU (806) from source CU (804)

[0287] i. Target candidate cell ID: An ID indicating a candidate target cell, which can be PCI or NR CGI.

[0288] ii. The configuration ID used in the LTM mapped to the candidate cell, i.e., the LTM configuration ID of the candidate cell,

[0289] iii. LTM configuration ID mapping list: Information on LTM candidate IDs and cell IDs allocated so far

[0290] 1. Opt 1. It may be information including candidate cells operated by all candidate CUs (806).

[0291] 2. Opt 2. Only candidate cells operated by the source CU (804) may be included. In this case, the candidate CU (806) may separately transmit to the candidate DU (805) the LTM configuration ID and candidate cell mapping information in addition to the information on the candidate cells operated by the candidate CU (806).

[0292] iv. CSI resource configuration: CSI resource configuration information transmitted by candidate cells currently in operation can be transmitted. In this case, information can also be transmitted as classified information according to opt 1 and opt 2.

[0293] v. An indicator requesting PRACH resource information for the target candidate cell.

[0294] vi. A directive requesting lower layer settings for target candidate cells.

[0295] B. Additionally, the candidate CU (806) can transmit information it has. In the case of opt 2, information about LTM candidate cells operated by the candidate CU (806) can be transmitted.

[0296] i. Target candidate cell ID: An ID indicating a candidate target cell, which can be PCI or NR CGI.

[0297] ii. The configuration ID used in the LTM mapped to the candidate cell, i.e., the LTM configuration ID of the candidate cell,

[0298] iii. LTM configuration ID mapping list: Information on LTM candidate IDs and cell IDs allocated so far

[0299] 1. Opt 1. It may be information including candidate cells operated by all candidate CUs (806).

[0300] 2. Opt 2. Only candidate cells operated by the source CU (804) may be included. In this case, the candidate CU (806) may separately transmit to the candidate DU (805) the LTM configuration ID and candidate cell mapping information in addition to the information on the candidate cells operated by the candidate CU (806).

[0301] iv. CSI resource configuration: CSI resource configuration information transmitted by candidate cells currently in operation can be transmitted. In this case, information can also be transmitted as classified information according to opt 1 and opt 2.

[0302] v. An indicator requesting PRACH resource information for the target candidate cell.

[0303] vi. A directive requesting lower layer settings for target candidate cells.

[0304] The candidate DU (805) that received the above information can accept or reject the LTM resource request for the corresponding terminal (801). If accepted, the candidate DU (805) can notify the candidate CU (806) of the acceptance result through a UE context setup response message or a corresponding F1 message at step 827. At this time, the message may additionally include the following information.

[0305] A. Generated lower layer RRC configuration

[0306] i. This information may be cellGroupConfiguration in RRC.

[0307] ii. If the above lower layer configuration is a complete configuration, a complete configuration indicator may also be included.

[0308] B. It can convey SSB time / frequency information transmitted from the candidate cell.

[0309] i. This information is information collected from each DU (805) and candidate cells in the candidate CU (806) and transmitted to the terminal (801), and can be referenced as an element of the CSI resource referred to in the CSI report configuration of the LTM.

[0310] ii. Also, it can be referenced for DL ​​or UL or joint TCI state information.

[0311] C. DL or UL or joint TCI state configuration information operating in the candidate cell: The configuration information can be set by the CU to the terminal (801) via RRC, and then a specific TCI state can be activated / deactivated through the candidate cell TCI state activation / deactivation MAC CE. Through the activated TCI state, the terminal (801) can perform DL synchronization before the cell switch command. In addition, when one of the TCI states, DL or Joint and / or UL TCI state, is signaled in the cell switch command, the terminal (801) can activate the indicated TCI state of the candidate cell and instruct it to use it immediately during cell switch.

[0312] D. RACH configuration information: RACH configuration information used in the candidate cell.

[0313] E. CSI report configuration information: The candidate DU (805) can create a CSI report configuration by referring to the CSI resource configuration of all candidate cells provided by the candidate CU (806). This information may include instructions for measuring which CSI resource of which cell, and report configurations such as periodic / semi-persistent / persistent. Thereafter, it can be included in the target cell configuration and used to automatically perform L1 measurement and reporting for LTM without separate configuration when the terminal (801) moves to this cell.

[0314] The candidate CU (806) that has received the above information can create (generate) an HO command message (e.g., RRCReconfiguration) for the corresponding candidate cell in step 830.

[0315] And the candidate CU (806) can transmit this information to the source CU (804) in step 835. At this time, the HO command message can be included in the HO request ACK (acknowledgement) message or a new / existing message of Xn corresponding thereto.

[0316] A. Opt 1. When a candidate CU (806) receives an HO request for one candidate target cell from a source CU (804), the candidate CU (806) can transmit information about one corresponding target cell to the source CU (804).

[0317] B. Opt 2. Even if the candidate CU (806) receives a HO request for one candidate target cell from the source CU (804), if there is a new message for another candidate cell that is allowed admission to LTM candidate cells for the same terminal (801) at the time the candidate CU (806) sends the HO request ACK message, the HO request ACK message may include information on all newly allowed candidate cells and be delivered to the terminal (801) in batches (via the source CU (804)).

[0318] C. Opt 3. When a candidate CU (806) is requested by a source CU (804) to perform LTM preparation for multiple candidate target cells operated by the CU (candidate CU (806)), the candidate CU (806) may collect information on all other candidate cells allowed for admission and include it in the HO request ACK message to transmit it to the source CU (804).

[0319] D. For each admitted candidate cell, this message may include at least one of the following information: The candidate CU (806) may include the following information to distinguish each candidate cell: PCI or NR CGI with ARFCN or LTM configuration ID of each candidate cell assigned by the source CU (804).

[0320] i. Target cell configuration (e.g., RRCReconfiguration)

[0321] ii. An indicator of whether the above target cell setting is a complete setting or not.

[0322] iii. TCI state configuration (DL or Joint and / or UL TCI state)

[0323] iv. CSI report configuration

[0324] v. CSI resource configuration information transmitted from each cell

[0325] vi. RACH settings

[0326] E. Unlike the cell stars, the following information may be included for each candidate CU (806).

[0327] i. LTM reference configuration for this candidate CU's candidate cells

[0328] 1. An ID (e.g., gNB ID, or integer ID assigned to the candidate CU (806) by the source CU (804), etc.) that distinguishes the candidate CU (806) may be transmitted to the terminal (801) in conjunction with each candidate cell configuration information.

[0329] 2. Afterwards, when the terminal (801) receives a cell switch command to a specific cell, the reference configuration linked to the specific cell can be applied.

[0330] ii. LTM CSI-resource configuration information

[0331] 1. The LTM CSI-Resource configuration may include an LTM CSI resource config determined by the DU (805) of each candidate cell for each admitted candidate cell within the candidate CU (806).

[0332] A. When considering the above one candidate cell as a source cell, the CSI resources transmitted by all or some specific candidate cells excluding that cell can be indicated. At this time, a bit list in which the LTM config ID of each cell and the SSB index or CSI-RS resource ID considered as CSI in that cell are mapped can be included by linking them with the LTM config ID of the source cell.

[0333] Alternatively, the candidate CU (806) that received the information in step 820 may update the config or lower layer setting information of the LTM candidate that was previously defined as needed in step 835 and transmit it to the terminal (801) again through the source CU (804).

[0334] Although not shown, before or immediately after the candidate CU (806) transmits the HO Request ACK message, the candidate CU (806) may transmit at least one piece of information about newly admitted candidate cells to DUs (not shown) of other candidate CUs (not shown). The DUs that receive this may store the information and, after the terminal (801) moves to its candidate cell, may execute a cell switch command using the given information. The information that the candidate CU (806) transmits to each DU via the UE context modification request or the corresponding F1 message may include all or part of the information that the candidate CU (806) transmits to the source CU (804) in step 835.

[0335] In step 840, the source CU (804) may use the information received in step 835 to transmit the information to the source DU (802) and other DUs (803) managed by its CU (804). This process may be possible via a UE context modification request message and a corresponding F1 message. The transmitted information may include all or part of the information included in the message transmitted in step 835.

[0336] The DUs (802, 803) of the source CU (804) that have received the above information (including the source DU (802)) can modify the LTM-CSI-resource config for performing L1 measurement if their candidate cells are source cells by referring to the CSI resources of the candidate cells of the newly admitted candidate CU (806). (i.e., the SSB / CSI-RS index of the new candidate cell can be added as a measurement target). In this regard, the LTM-CSI-ReportConfig that refers to the modified LTM-CSI-resource config can also be updated. In addition, the lower layer configuration can also be updated as needed.

[0337] At step 845, the DUs (802, 803) of each source CU (804) can transmit updated CSI-related information and updated information on lower layer configuration to the source CU (804). This process can be made possible through a UE context modification response message and a corresponding F1 message.

[0338] Although not shown, the source CU (804) that received the above information can forward the received information to the candidate CU (806). The forwarding of the information can be done using an HO request message or a new Xn message. Accordingly, the candidate CU (806) can forward the updated LTM CSI resource config, LTM CSI-reportConfig and lower layer settings to the DUs (805) of the candidate CU (806) in association with the ID (PCI, or CGI with ARFCN, or LTM config ID) of each candidate cell.

[0339] A candidate CU (806) that has received the above information can transmit the received updated information to its DUs (805). Then, the candidate CU (806) can transmit a response message to the source CU (804). The response message can include an HO response message or a new Xn message. And, the response message can include updated information.

[0340] At step 850, the source CU (804) can compile the above information and create an ltm-Config. This ltm-Config can include at least one of the following information for each candidate cell.

[0341] A. LTM configuration ID,

[0342] B. Candidate cell PCI and / or CGI with AFRCN

[0343] C. SSB config

[0344] D. Target cell configuration (RRCReconfig msg)

[0345] E. TCI state configuration

[0346] F. CSI-RS resource config

[0347] G. Using early TA indicator

[0348] H. RACH-less execution indicator

[0349] At step 853, the source CU (804) can transmit to the terminal (801) a list of LTM-CSI-ResourceConfigs in a common field, not per cell, in the MN RRCReconfiguration message. In addition, a reference configuration can be given, and in this case, multiple reference configurations can exist, so the source CU (804) can transmit to the terminal (801) a reference configuration applicable to each candidate cell, and for this linkage, a specific ID can be assigned to each reference configuration, and one of these IDs can be assigned to each candidate cell so that the terminal (801) can distinguish them when applying them.

[0350] The current serving cell setting of the Pcell of the terminal (801) can be configured and transmitted by referencing some of the configuration IDs of the LTM-CSI-ResourceConfigs and configuring LTM-CSI-ReportConfig.

[0351] The RRC reconfiguration message is included in a DL RRC message in step 853 and transmitted from the source CU (804) to the source DU (802), and the source DU (802) can transmit the RRC reconfiguration message to the terminal (801) in step 855. In addition, the terminal (801) can transmit an RRC reconfiguration complete message (RRC reconfiguration complete message) to the source DU (802) in step 857. The source DU (802) can transmit a UL RRC message including the received RRC reconfiguration complete message to the source CU (804) in step 859.

[0352] Thereafter, in step 870, when the network instructs the terminal (801) to activate the TCI state ID of a specific candidate cell through MAC CE, the terminal (801) can perform DL synchronization by referring to the corresponding TCI state, and based on this, the terminal (801) can measure the resources of the CSI resources indicated in the LTM-CSI-ResourceConfig referred to in the corresponding LTM-CSI-ReportConfig. In addition, the terminal can perform report transmission set in this LTM-CSI-ReportConfig.

[0353] Regardless of the above DL synchronization and CSI measurement, the source CU (804) may request early TA acquisition at step 860. In this case, the terminal (801) may transmit a RACH preamble to the candidate cell (candidate DU (805)) indicated in the request.

[0354] A candidate cell (candidate DU (805)) that detects the above RACH preamble transmission can notify the candidate CU (806) of the TA detection through a DU-CU TA info transfer message in step 863. The candidate CU (806) can estimate the TA value, and if it is determined to be valid, can notify the source CU (804) of the measurement of the TA value through an Xn TA info Transfer message or an equivalent message in step 865. The information included at this time can include an estimated TA value, a probability value or an accuracy value indicating the accuracy of the TA value, an LTM config ID of the cell that detected the preamble, or at least one of a PCI or CGI.

[0355] The source CU (804), which has acquired the above information in step 867, can transmit the TA value to the source DU (802). The message used at this time may be a CU-DU TA info transfer message. The source DU (802), which has been maintaining this TA value, can include the corresponding TA value in an LTM cell switch command and transmit it to the terminal (801). In this case, the terminal (801) can perform a RACH less handover through an early TA using the TA value.

[0356] The source DU (802) can determine an LTM cell switch in step 875 based on the L1 measurement result report received from the terminal (801) in step 870. Then, the source DU (802) can transmit a cell switch command to the terminal (801) in step 880. The source DU (802) that transmitted the cell switch command can notify the source CU (804) that the cell switch has been performed in step 885 (e.g., a DU-CU cell switch notification message). The message can include a target cell ID, a TCI state ID, etc. The source CU (804) that received this can transmit an Xn message that also notifies the CU of the target candidate cell, i.e., the candidate CU (806), that the LTM cell switch has been performed. This message can include at least one of an Xn AP UE ID, an ID of the target cell that commanded the cell switch, PCI or CGI with AFRCN, a TCI state ID value indicated at the time of the cell switch, etc. The above message may be an LTM cell switch notification message.

[0357] Although not shown, the candidate CU (806) that has received the above information can notify the candidate DU (805) that a cell switch command has been performed, for example, using a cell switch notification message. If the candidate DU (805) successfully receives the UL data transmission and determines that access is successful, the candidate DU (805) can notify the candidate CU (806) of the result. Depending on the embodiment, the candidate DU (805) can also transmit a target cell ID, UE ID, etc. to the candidate CU (806).

[0358] Although not shown, the terminal (801) can perform an LTM cell switch by transmitting an RRC reconfiguration complete message to the candidate DU (805), and the candidate DU (805) can transmit a UL RRC MSG transfer message to the candidate CU (806) based on the received message. The UL RRC MSG transfer message can include the RRC reconfiguration complete message received from the terminal (801).

[0359] Although not shown, the candidate CU (806) can inform the source CU (804) of the success of the HO.

[0360] Although not shown, the source CU (804) may notify another candidate CU, candidate CU2 (not shown), that the cell switch of the terminal (801) has been completed by sending a cell switch complete message. The message may include a UE ID, a target cell ID, etc.

[0361] FIG. 9a and FIG. 9b are diagrams illustrating an example of an operation when a setting change occurs in a target DU according to an embodiment of the present invention.

[0362] Referring to FIGS. 9A and 8B , at step 910, the terminal (901) is connected to the source CU (904) and is also connected to the source DU (902) that operates the serving cell of the source CU (904). After receiving the L3 measurement configuration through the source CU (904), the terminal (901) can transmit the corresponding measurement result report to the source CU (904) through the source DU (902).

[0363] According to the embodiments related to the above-described FIGS. 7a and 7b or 8a and 8b, LTM candidate determination and preparation may be completed at step 915.

[0364] If at least one of CSI report Config, RACH config, and TCI state changes in one of the candidate DUs (905), the candidate DU (905) can notify the candidate CU (906) of the change at step 920. This can be performed with a UE context change notification message or a new F1 message. The message can include at least one of a related UE ID (F1 AP UE ID or Xn AP UE ID) and changed configuration information. The candidate CU (906) can provide the changed information to its DUs so that each DU can change the LTM configuration when necessary, and if there is a changed configuration, each DU can convey the changed configuration to the candidate CU (906).

[0365] And at step 925, the candidate CU (906) can change the HO command based on the information received from the candidate DU (905). In addition, the candidate CU (906) can also change the CSI report Config, CSI resource config, RACH config, TCI state config, etc. based on the received information.

[0366] At step 930, the candidate CU (906) may transmit changed configuration information to the source CU (904). This information may be carried in an HO modification message, an HO request ACK message, or a separate Xn message. The information included in this message may be at least one of the indicated terminal ID, changed HO command, changed CSI report Config, CSI resource config, RACH config, and TCI state config.

[0367] At step 925, the source CU (904) can transmit the changed configuration information to the source DU (902) and other DUs (903) managed by its own CU (904). This process can be possible through a UE context modification request message and a corresponding F1 message. The transmitted information can include all or part of the information included in the message transmitted at step 930. The DUs (902, 903) of the source CU (904) that have received the configuration information to be changed (including the source DU (902)) can transmit a response (e.g., a UE context modification response message) to the source CU (904) at step 940.

[0368] At step 945, the source CU (904) can collect information and change the ltm-Config.

[0369] And the source CU (904) can generate an RRC reconfiguration message reflecting the changed ltm-Config and transmit it to the terminal (901) in step 950. The RRC reconfiguration message is included in a DL RRC message in step 950 and transmitted from the source CU (904) to the source DU (902), and the source DU (902) can transmit the RRC reconfiguration message to the terminal (901) in step 953. And the terminal (901) can transmit an RRC reconfiguration complete message (RRC reconfiguration complete message) to the source DU (902) in step 955. And the terminal (901) can change the L1 parameter based on the received RRC reconfiguration message in step 957. The terminal (901) can also change the L1 parameter in step 957 before transmitting the RRC reconfiguration complete message in step 955. The source DU (902) may transmit a UL RRC message including the received RRC reconfiguration complete message to the source CU (904) at step 959.

[0370] Since the operations in steps 960 to 985 are similar to the operations in FIGS. 7a and 7b and 8a and 8b described above, a detailed description thereof will be omitted.

[0371] FIG. 10a and FIG. 10b are diagrams illustrating an example of an operation when LTM preparation is canceled according to an embodiment of the invention.

[0372] Referring to FIGS. 10A and 10B , at step 1010, the terminal (1001) is connected to the source CU (1004) and is also connected to the source DU (1002) that operates the serving cell of the source CU (1004). After receiving the L3 measurement configuration through the source CU (1004), the terminal (1001) can transmit the corresponding measurement result report to the source CU (1004) through the source DU (1002).

[0373] According to the embodiments related to FIGS. 7A and 7B or 8A and 8B, LTM candidate determination and preparation may be completed in steps 1015 to 1067. A detailed description thereof has been described above, and thus will be omitted.

[0374] And, LTM cell switch cancel can be performed.

[0375] If the candidate DU (1005) or the candidate CU (1006) can no longer allocate resources, or if necessary, or if a preset time has expired, or other preset conditions exist, the candidate CU (1006) may decide to notify the cancellation of the prepared LTM cell switch at step 1070. To this end, the candidate CU (1006) may transmit, for example, an LTM cell switch cancel message to the source CU (1004) at step 1073. The message notifying the cancellation of the LTM cell switch may include the following information.

[0376] The above message may include at least one of S RAN node UE XnAP ID, target RAN node UE XnAP Id, cause value, target LTM candidate cell, related LTM config ID, etc. In an embodiment, if target candidate cell information is not included in the message, it may mean that all resources included in the candidate CU (1006) are targeted.

[0377] According to the above notification, the source CU (1004) may notify the source DU (1002) of the cancellation of the LTM cell switch at step 1075. The information notifying the LTM cell switch cancellation may be included and transmitted in a CU-DU LTM cell switch cancel notification message. Then, the source DU (1002) may cancel the target setting at step 1077, and the source CU (1004) may modify the LTM setting at step 1079. The modification may include releasing the target setting.

[0378] And, in step 1080, the source CU (1004) can instruct the terminal (1001) to release the configuration. The information instructing the configuration release can be included in a DL RRC message and transmitted from the source CU (1004) to the source DU (1002), and the DL RRC message can be included in an RRC reconfiguration message. And, in step 1083, the source DU (1002) can transmit an RRC reconfiguration message to the terminal (1001). When the terminal (1001) receives the message instructing the release of the configuration, the terminal (1001) can transmit a complete message to the source CU (1004) (via the source DU (1002)) in step 1085. The complete message can be an RRC reconfiguration complete message.

[0379] And in step 1090, the source CU (1004) can transmit a message such as cancel ACK to the candidate CU (1006). And, the candidate CU (1006) can remove (release) resources in step 1095. The terminal (1001) can release configuration information for the target cell in step 1087. Depending on the embodiment, step 1087 may be performed before the RRC reconfiguration complete message is transmitted in step 1085.

[0380] Depending on the embodiment, the source CU (1004) or the source DU (1002) may also cancel the LTM cell switch. In this case, a new message may be defined to indicate that the LTM cell switch has been canceled, or an existing CHO message may be reused. In steps 1075 to 1085, the source CU (1004) may notify the source DU (1002) of the cancellation of the LTM cell switch and instruct the terminal (1001) to release the configuration. Alternatively, if the source DU (1002) decides to cancel the LTM cell switch, the source DU (1002) may notify the source CU (1004) of the cancellation of the LTM cell switch (not shown), and accordingly, the source CU (1004) may instruct the terminal (1001) to release the configuration in steps 1080 to 1085. The source CU (1004) can then notify the candidate CU (1006) of the cancellation of the LTM cell switch (not shown). The candidate CU (1006) can then transmit a response to the source CU (1004) (not shown). The source CU (1004) can remove (release) resources (not shown), and the terminal (1001) can release the configuration information at step 1087.

[0381] FIG. 11a and FIG. 11b are diagrams illustrating an example of an operation when a cell switch execution and a cancel command conflict according to one embodiment of the invention.

[0382] Referring to FIGS. 11A and 11B , at step 1110, the terminal (1101) is connected to the source CU (1104) and is also connected to the source DU (1102) that operates the serving cell of the source CU (1104). After receiving the L3 measurement configuration through the source CU (1104), the terminal (1101) can transmit the corresponding measurement result report to the source CU (1104) through the source DU (1102).

[0383] According to the embodiments related to FIGS. 7A and 7B or 8A and 8B, LTM candidate determination and preparation may be completed in steps 1115 to 1167. A detailed description thereof has been described above, and thus will be omitted.

[0384] And cell switch cancel may occur as described in the examples in FIGS. 10a and 10b.

[0385] When the candidate DU (1105) or the candidate CU (1106) can no longer allocate resources, or when necessary, or when a preset time has expired, or other preset conditions, the candidate CU (1106) may decide to notify cancellation of the prepared LTM cell switch at step 1170. To this end, the candidate CU (1106) may transmit, for example, an LTM cell switch cancel message to the source CU (1104) at step 1173. The message notifying cancellation of the LTM cell switch may include at least one of an S RAN node UE XnAP ID, a target RAN node UE XnAP Id, a cause value, a target LTM candidate cell, and a related LTM config ID.

[0386] Meanwhile, in the case of the cell switch cancel, the source CU (1104) may receive a cell switch notification message from the source DU (1102) at step 1193 before receiving a message requesting / indicating the cancel from the candidate CU (1106). The description of the L1 measurement report of the terminal (1101) to the source DU (1102) at step 1180, the LTM cell switch decision of the source DU (1102) at step 1183, the transmission of the cell switch command of the source DU (1102) to the terminal (1101) at step 1185, and the reception of the cell switch notification message of the source CU (1104) from the source DU (1102) at step 1193 has been described in the embodiment related to FIG. 7 or FIG. 8, and thus, a detailed description thereof will be omitted.

[0387] In this case, a conflict may occur between the cell switch cancel and the cell switch notification, as in step 1190. Although step 1190 is depicted as occurring before step 1193, step 1190 may occur after step 1193. In this case, the source CU (1104) may ignore the received cell switch notification. In this case, the terminal (1101) may not receive a response to the RACH transmission or a response to the UL grant CG usage. As a result, a radio link failure (RLF) may occur, or the terminal (1101) may move to the RRC idle state.

[0388] Alternatively, if the source CU (1104) receives a cell switch cancel instruction from the candidate CU (1106) after receiving the cell switch notification message according to an embodiment, the source CU (1104) may transmit a cell switch happened instruction to the candidate CU (1106) at step 1195, and may cause the candidate CU (1106) to maintain resources for a certain period of time at step 1199.

[0389] It should be noted that the configuration diagrams, exemplary diagrams of control / data signal transmission methods, exemplary diagrams of operating procedures, and configuration diagrams illustrated in FIGS. 1 to 11b above are not intended to limit the scope of the present disclosure. That is, not all components, entities, or operational steps described in FIGS. 1 to 11 above should be construed as essential components for implementing the disclosure, and the disclosure may be implemented without detriment to its essence even if only some components are included.

[0390] 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.

[0391] 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.

[0392] 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.

[0393] 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.

[0394] 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.

[0395] 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. A method performed by a CU (central unit) of a source base station of a wireless communication system, A step of transmitting a first message requesting information for LTM setup to a CU of at least one candidate base station associated with at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs; A step of receiving configuration information for at least one candidate cell from a CU of at least one candidate base station; A step of generating configuration information of resources for L1 measurement for the at least one candidate cell based on the configuration information for the at least one candidate cell; and A method comprising the step of transmitting a second message to a terminal including the configuration information of resources for the L1 measurement for the at least one candidate cell.

2. In paragraph 1, A method characterized in that it further comprises the step of transmitting a third message including the configuration information of the resource for the L1 measurement for the at least one candidate cell to the CU of the at least one candidate base station.

3. In paragraph 1, A method characterized in that the configuration information for the at least one candidate cell includes at least one of configuration information of the at least one candidate cell, an indicator indicating whether the configuration information of the at least one candidate cell is a complete configuration, transmission configuration indication (TCI) state configuration information, channel state information (CSI) resource configuration information, and CSI reporting configuration information.

4. In paragraph 1, A method characterized in that the resource configuration information for the L1 measurement includes resource configuration information for CSI (channel state information) measurement of the at least one candidate cell.

5. In a method performed by a CU (central unit) of a candidate base station of a wireless communication system, A step of receiving a first message from a CU of a source base station requesting information for LTM setup for at least one candidate cell for CU-to-CU LTM (L1 / L2 (layer 1 / layer 2) triggered mobility); A step of requesting configuration information for at least one candidate cell to at least one DU (distributed unit) of the candidate base station associated with the at least one candidate cell; A step of receiving the configuration information for the at least one candidate cell from the at least one DU of the candidate base station; and comprising a step of transmitting the configuration information for the at least one candidate cell to the CU of the source base station, A method characterized in that, based on the configuration information for the at least one candidate cell, configuration information for resources for L1 measurement for the at least one candidate cell is generated.

6. In paragraph 5, A method further comprising the step of receiving a second message including the configuration information of the resources for the L1 measurement for the at least one candidate cell from the CU of the source base station.

7. In paragraph 5, A method characterized in that the configuration information for the at least one candidate cell includes at least one of configuration information of the at least one candidate cell, an indicator indicating whether the configuration information of the at least one candidate cell is a complete configuration, transmission configuration indication (TCI) state configuration information, channel state information (CSI) resource configuration information, and CSI reporting configuration information.

8. In paragraph 5, A method characterized in that the resource configuration information for the L1 measurement includes resource configuration information for CSI (channel state information) measurement of the at least one candidate cell.

9. In the CU (central unit) of the source base station of a wireless communication system, Transmitter and receiver; and A CU of a source base station, comprising a control unit that is connected to the transceiver and transmits a first message requesting information for LTM configuration to a CU of at least one candidate base station associated with at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs, receives configuration information for the at least one candidate cell from the CU of the at least one candidate base station, generates configuration information for resources for L1 measurement for the at least one candidate cell based on the configuration information for the at least one candidate cell, and transmits a second message including the configuration information for resources for L1 measurement for the at least one candidate cell to a terminal.

10. In the 9th paragraph, the control unit, A CU of a source base station, characterized in that it transmits a third message including the configuration information of the resource for the L1 measurement for the at least one candidate cell to the CU of the at least one candidate base station.

11. In paragraph 9, A CU of a source base station, characterized in that the configuration information for the at least one candidate cell includes at least one of configuration information of the at least one candidate cell, an indicator indicating whether the configuration information of the at least one candidate cell is a complete configuration, transmission configuration indication (TCI) state configuration information, channel state information (CSI) resource configuration information, and CSI reporting configuration information.

12. In paragraph 9, A CU of a source base station, characterized in that the above configuration information of resources for the above L1 measurement includes resource configuration information for CSI (channel state information) measurement of the at least one candidate cell.

13. In the CU (central unit) of a candidate base station of a wireless communication system, Transmitter and receiver; and A control unit connected to the transceiver, receiving a first message requesting information for LTM configuration for at least one candidate cell for LTM (L1 / L2 (layer 1 / layer 2) triggered mobility) between CUs from a CU of a source base station, requesting configuration information for the at least one candidate cell from at least one DU (distributed unit) of the candidate base station associated with the at least one candidate cell, receiving the configuration information for the at least one candidate cell from the at least one DU of the candidate base station, and transmitting the configuration information for the at least one candidate cell to the CU of the source base station, A CU of a candidate base station, characterized in that, based on the configuration information for the at least one candidate cell, configuration information of resources for L1 measurement for the at least one candidate cell is generated.

14. In the 13th paragraph, the control unit, A CU of a candidate base station, characterized in that it receives a second message including the configuration information of the resource for the L1 measurement for the at least one candidate cell from the CU of the source base station.

15. In paragraph 13, The configuration information for the at least one candidate cell includes at least one of configuration information of the at least one candidate cell, an indicator indicating whether the configuration information of the at least one candidate cell is a complete configuration, transmission configuration indication (TCI) state configuration information, channel state information (CSI) resource configuration information, and CSI reporting configuration information. A CU of a candidate base station, characterized in that the above configuration information of resources for the above L1 measurement includes resource configuration information for CSI measurement of the at least one candidate cell.

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