WO2024167378A1 - Method and apparatus for efficiently transmitting configuration information of candidate cells for l1/l2-based mobility support in next-generation mobile communication system - Google Patents

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting higher data transmission rates. The present disclosure discloses a method and apparatus for providing configuration information for mobility support of terminal.

Description

Method and device for efficiently transmitting configuration information of candidate cells for supporting L1/L2-based mobility in a next-generation mobile communication system

The present disclosure relates to a method and device for providing configuration information for supporting mobility of a terminal.

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 (㎜Wave), 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 delay time that is reduced by one-tenth.

In the early stages of 5G mobile communication technology, the goal was to support services and satisfy performance requirements for enhanced Mobile Broadband (eMBB), Ultra-Reliable Low-Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), including 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.

Currently, discussions are underway on improving and enhancing the initial 5G mobile communication technology, taking into account the services that the 5G mobile communication technology was intended to support, and physical layer standardization is in progress for technologies such as V2X (Vehicle-to-Everything) to assist in driving decisions of autonomous vehicles and increase user convenience based on the vehicle's own location and status information transmitted by the vehicle, 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.

In addition, standardization of wireless interface architecture/protocols for technologies such as the Industrial Internet of Things (IIoT) to support new services through linkage and convergence with other industries, Integrated Access and Backhaul (IAB) to provide nodes for expanding network service areas by integrating wireless backhaul links and access links, Mobility Enhancement including Conditional Handover and Dual Active Protocol Stack (DAPS) handover, and 2-step RACH for NR to simplify random access procedures is also in progress, and standardization of system architecture/services for 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 is also in progress.

When such 5G mobile communication systems are commercialized, an explosive increase in connected devices will be connected to the communication network, which will require enhanced functions and performance of 5G mobile communication systems and integrated operation of connected devices. To this end, new research will be conducted on improving 5G performance and reducing complexity, AI service support, metaverse service support, drone communications, etc. using eXtended Reality (XR), Artificial Intelligence (AI), and Machine Learning (ML) to efficiently support Augmented Reality (AR), Virtual Reality (VR), and Mixed Reality (MR).

In addition, the development of these 5G mobile communication systems will require 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 coverage of terahertz band signals, high-dimensional spatial multiplexing technology using Orbital Angular Momentum (OAM), and Reconfigurable Intelligent Surface (RIS) technology, as well as full duplex technology to improve frequency efficiency and system network of 6G mobile communication technology, satellite, AI (Artificial Intelligence) from the design stage and AI-based communication technology that implements end-to-end AI support functions to realize system optimization, and ultra-high-performance communication and computing resources to provide services with complexity that goes beyond the limits of terminal computing capabilities. It could serve as a basis for the development of next-generation distributed computing technologies that utilize this technology.

Meanwhile, when a terminal is currently receiving a service from a specific beam from a serving cell, the terminal can measure a beam belonging to another cell and report it to the base station of the current serving cell, and if the base station determines that a beam of a neighboring cell is better, the base station can instruct the terminal to perform a cell change to the corresponding cell through L1/L2 signaling. At this time, when transmitting RRC configuration information, particularly, cell physical configuration, radio bearer configuration, and measurement configuration, to the terminal to perform a handover to neighboring cells, an effective message structure is required that can transmit only changes in specific RRC configuration information for candidate cells.

Accordingly, one purpose of the present disclosure is to propose an effective message structure that can transmit only changes in specific RRC configuration information for candidate cells when transmitting information or settings applied when performing handover to neighboring cells to a terminal.

In order to solve the above problem, according to an example of the present disclosure, in a communication system, a method of a terminal comprises the steps of: receiving, from a base station, a first radio resource control (RRC) message including first information on LTM (layer 1/layer 2 triggered mobility) candidate setting; receiving, from the base station, a second RRC message including second information on the LTM candidate setting; and reporting, to the base station, L1 (layer 1) measurement performed on candidate cells based on the second information.

The second information includes an RRC configuration for updating the LTM candidate configuration, and the RRC configuration including cell group configuration information for the candidate cells may further include updated information of at least one of a radio bearer configuration or a measurement configuration included in the first RRC message.

In addition, in a method of a base station in a communication system according to an example of the present disclosure, the method includes: transmitting, to a terminal, a first radio resource control (RRC) message including first information on LTM (layer 1/layer 2 triggered mobility) candidate configuration; acquiring an RRC configuration for updating the LTM candidate configuration; transmitting, to the terminal, a second RRC message including second information on the LTM candidate configuration, the second RRC message including the RRC configuration; and receiving, from the terminal, an L1 (layer 1) measurement report for candidate cells based on the second information, wherein the RRC configuration including cell group configuration information for the candidate cells may further include updated information on at least one of a radio bearer configuration or a measurement configuration included in the first RRC message.

In addition, in a communication system according to an example of the present disclosure, a terminal, comprising: a transceiver; and a control unit configured to control the transceiver to receive, from a base station, a first radio resource control (RRC) message including first information about LTM (layer 1/layer 2 triggered mobility) candidate configuration, and to control the transceiver to receive, from the base station, a second RRC message including second information about the LTM candidate configuration, and to control the transceiver to report, to the base station, L1 (layer 1) measurement performed on candidate cells based on the second information, wherein the second information includes an RRC configuration that updates the LTM candidate configuration, and the RRC configuration including cell group configuration information for the candidate cells may further include updated information on at least one of a radio bearer configuration or a measurement configuration included in the first RRC message.

In addition, in a communication system according to an example of the present disclosure, a base station, a transceiver; and a control unit configured to control the transceiver to transmit, to a terminal, a first radio resource control (RRC) message including first information on LTM (layer 1/layer 2 triggered mobility) candidate configuration, obtain an RRC configuration that updates the LTM candidate configuration, control the transceiver to transmit, to the terminal, a second RRC message including second information on the LTM candidate configuration, the RRC configuration, and receive, from the terminal, an L1 (layer 1) measurement report for candidate cells based on the second information, wherein the RRC configuration including cell group configuration information for the candidate cells may further include updated information on at least one of a radio bearer configuration or a measurement configuration included in the first RRC message.

According to one embodiment of the present disclosure, when transmitting RRC configuration information for LTM (L1/L2 triggered mobility) candidate cells, particularly, physical configuration of the cell, radio bearer configuration, and measurement configuration to a terminal, only changes in specific RRC configuration information can be transmitted, so that the overhead of RRC configuration information actually transmitted to the terminal can be significantly reduced.

FIG. 1 is a diagram illustrating the structure of a next-generation mobile communication system to which the present disclosure is applied.

FIG. 2 is a diagram showing a wireless protocol structure of a next-generation mobile communication system to which the present disclosure can be applied.

FIG. 3 is a diagram illustrating the structure of another next-generation mobile communication system to which the present disclosure can be applied.

FIG. 4 is a diagram illustrating a scenario for inter-cell beam management referred to in the present disclosure, in which a terminal transmits and receives data through a beam of a TRP (transmission/reception point) of a neighboring cell that supports beam changing based on L1/L2 while maintaining a connection state with a serving cell.

FIG. 5a is a diagram illustrating a scenario in which a terminal transmits and receives data by changing a serving cell and beam to a TRP of a cell that supports L1/L2-based beam changing.

FIG. 5b is a diagram illustrating a scenario in which a terminal transmits and receives data by changing a serving cell and beam to a TRP of a cell that supports L1/L2-based beam changing.

FIG. 6 is a diagram illustrating a first LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of surrounding cells for L1/L2-based handover in an intra-CU scenario, as an example 1 applied to the present disclosure.

FIG. 7 is a diagram illustrating a second LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of surrounding cells for L1/L2 based handover in an intra-CU scenario, as Example 2 applied to the present disclosure.

FIG. 8 is a diagram illustrating a first LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of surrounding cells for L1/L2 based handover in an inter-CU scenario, as an example 3 applied to the present disclosure.

FIG. 9 is a diagram illustrating a second LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of neighboring cells for L1/L2 based handover in an inter-CU scenario, as Example 4 applied to the present disclosure.

FIG. 10 is a diagram illustrating the overall terminal operation for performing L1/L2-based beam changing and handover, applied to examples of the present disclosure.

FIG. 11 is a diagram illustrating base station operation applied to examples of the present disclosure.

Fig. 12 is a block diagram illustrating the internal structure of a terminal to which the present disclosure is applied.

Figure 13 is a block diagram showing the configuration of a base station according to the present disclosure.

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

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

Figure 1 is a drawing illustrating the structure of a next-generation mobile communication system to which the present invention is applied.

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

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

NR CN (1a-05) performs functions such as mobility support, bearer setup, and QoS setup. NR CN is a device that handles various control functions as well as mobility management functions for terminals and is connected to multiple base stations. In addition, the next-generation mobile communication system can be linked with the existing LTE system, and NR CN is connected to MME (1a-25) through a network interface. MME is connected to the existing base station, eNB (1a-30).

FIG. 2 is a diagram showing a wireless protocol structure of a next-generation mobile communication system to which the present disclosure can be applied.

Referring to FIG. 2, the wireless protocol of the next-generation mobile communication system consists of NR SDAP (1b-01, 1b-45), NR PDCP (1b-05, 1b-40), NR RLC (1b-10, 1b-35), and NR MAC (1b-15, 1b-30) in the terminal and NR base station, respectively.

Key features of NR SDAP (1b-01, 1b-45) may include some of the following:

- Transfer of user plane data

- Mapping between a QoS flow and a DRB for both DL and UL

- Marking QoS flow ID in both DL and UL packets

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

For the above SDAP layer device, the terminal can be configured by an RRC message for each PDCP layer device, by bearer, or by logical channel, whether to use the header of the SDAP layer device or whether to use the function of the SDAP layer device, and if the SDAP header is configured, the terminal can be instructed to update or reset the QoS flow of the uplink and downlink and the mapping information for the data bearer by using a 1-bit indicator for reflecting NAS QoS (NAS reflective QoS) and a 1-bit indicator for reflecting AS QoS (AS reflective QoS) of 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 desired service.

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

● Header compression and decompression (ROHC only)

● Transfer of user data function

● In-sequence delivery of upper layer PDUs

● Out-of-sequence delivery of upper layer PDUs

● Reordering function (PDCP PDU reordering for reception)

● Duplicate detection of lower layer SDUs

● Retransmission function (Retransmission of PDCP SDUs)

● Encryption and deciphering functions (Ciphering and deciphering)

● Timer-based SDU discard in uplink

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

The main functions of NR RLC (1b-10, 1b-35) may include some of the following functions:

● Data transfer function (Transfer of upper layer PDUs)

● In-sequence delivery of upper layer PDUs

● Out-of-sequence delivery of upper layer PDUs

● Function (Error Correction through ARQ)

● Concatenation, segmentation and reassembly of RLC SDUs

● Re-segmentation of RLC data PDUs

● Reordering of RLC data PDUs

● Duplicate detection function

● Error detection function (Protocol error detection)

● DU discard function (RLC SDU discard)

● RLC re-establishment function

The in-sequence delivery function of the NR RLC device above refers to the function of sequentially transmitting RLC SDUs received from a lower layer to an upper layer, and may include a function of reassembling and transmitting RLC SDUs when an RLC SDU is originally divided into multiple RLC SDUs and received, a function of rearranging received RLC PDUs based on RLC SN (sequence number) or PDCP SN (sequence number), a function of recording lost RLC PDUs by rearranging the sequence, a function of reporting the status of lost RLC PDUs to the transmitting side, a function of requesting retransmission of lost RLC PDUs, a function of sequentially transmitting only RLC SDUs up to the lost RLC SDU to an upper layer in case of a lost RLC SDU, or a function of sequentially transmitting all RLC SDUs received before the timer starts if a predetermined timer expires even when a lost RLC SDU is present to an upper layer. Or, even if there are lost RLC SDUs, if a predetermined timer has expired, it may include a function to sequentially deliver all RLC SDUs received up to the present to the upper layer. In addition, the RLC PDUs may be processed in the order they are received (in the order of arrival, regardless of the order of the sequence number) and delivered to the PDCP device regardless of the order (Out-of sequence delivery). In case of segments, the segments stored in the buffer or to be received later may be received, reconstructed into a single complete RLC PDU, processed, and delivered to the PDCP device. The NR RLC layer may not include a concatenation function, and the function may be performed in the NR MAC layer or replaced with a multiplexing function of the NR MAC layer.

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

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

● Mapping function (Mapping between logical channels and transport channels)

● Multiplexing/demultiplexing of MAC SDUs

● Scheduling information reporting function

● HARQ function (Error correction through HARQ)

● Priority handling between logical channels of one UE

● Priority handling between UEs by means of dynamic scheduling

● MBMS service identification function

● Transport format selection function

● Padding function

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

FIG. 3 is a diagram illustrating the structure of another next-generation mobile communication system to which the present disclosure can be applied.

Referring to FIG. 3, a cell served by an NR gNB (1c-05) operating on a beam basis may be composed of multiple TRPs (Transmission Reception Points, 1c-10, 1c-15, 1c-20, 1c-25, 1c-30, 1c-35, 1c-40). TRPs (1c-10 to 1c-40) represent blocks that separate some of the functions of transmitting and receiving physical signals from an existing NR base station (eNB), and are composed of multiple antennas. The NR gNB (1c-05) may be expressed as a CU (Central Unit), and the TRP may also be expressed as a DU (Distributed Unit).

The functions of the above NR gNB (1c-05) and TRP can be configured by separating each layer in the PDCP/RLC/MAC/PHY layers such as 1c-45. For example, the TRP can perform the function of the corresponding layer with only the PHY layer (1c-15, 1c-25), can perform the functions of the corresponding layers with only the PHY layer and the MAC layer (1c-10, 1c-35, 1c-40), or can perform the functions of the corresponding layers with only the PHY layer, the MAC layer, and the RLC layer (1c-20, 1c-30). In particular, the TRP (1c-10 to 1c-40) can use beamforming technology that generates narrow beams in various directions using multiple transmit/receive antennas to transmit and receive data.

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

The TRP in this disclosure will be explained on the premise that the structure (1c-15, 1c-25) can perform the function of the corresponding layer with only the PHY layer.

FIG. 4 is a diagram illustrating a scenario for inter-cell beam management referred to in the present disclosure, in which a terminal transmits and receives data through a beam of a TRP (transmission/reception point) of a neighboring cell that supports L1/L2-based beam change while maintaining a connection state with a serving cell.

Although this drawing describes a case where multiple cells (TRP1-Cell1, TRP2-Cell2; 1d-10, 1d-15) exist within one DU (Distributed unit, 1d-05), the overall content of the present disclosure is also applicable to the inter-DU case (where each DU constitutes one TRP-Cell). In addition, in the present disclosure, a non-serving cell (TRP 2, Cell 2) supporting L1/L2 based mobility (beam change and serving cell change) will be described interchangeably as a neighbor cell, a non-serving cell, an additional cell with the PCI different from the serving cell, etc.

The existing terminal beam change procedure (1d-45) is such that the terminal (1d-20) is transmitting and receiving data in a connected state through TRP 1 (1d-10) of serving cell 1, and may be set to the optimal beam, TCI (transmission configuration indicator) state 1 (1d-25, 1d-30). At this stage, the terminal can receive configuration information for L3 channel measurement (RRM; radio resource management) for an additional cell (TRP 2-Cell 2, 1d-15) having a different PCI from the serving cell through RRC configuration information from the serving cell (1d-10), and perform the L3 measurement operation (1d-46) for the corresponding frequency and cell based on this. Thereafter, the serving cell (TRP 1-Cell 1, 1d-10) can instruct (1d-47) a handover to the cell (TRP 2-Cell 2, 1d-15) based on the measurement value reported from the terminal (1d-20), and when the handover is completed accordingly, additional RRC configuration information can be transmitted (1d-48) to the terminal (1d-20) through TRP 2-Cell 2 (1d-15). The additional RRC configuration information may include UL/DL configuration information in the corresponding cell, L1 measurement related settings (CSI-RS measurement and reporting), and in particular, TCI state configuration information for PDCCH (physical downlink control channel) and PDSCH (physical downlink shared channel) channels. The terminal performs L1 measurement according to the settings (1d-49), and the base station updates the TCI state through L1/L2 signaling according to the measurement report from the terminal (1d-50). Here, the optimal beam, TCI state 2 (1d-40), can be indicated to the terminal. The serving cell is Cell 1 before the handover, but becomes Cell 2 after the handover. However, even after the handover is completed, many procedures and time are required until the optimal beam is indicated to the terminal.

Unlike the above existing terminal beam changing procedure (1d-45), the improved beam changing technique (1d-55) considered in the present disclosure is as follows.

The terminal (1d-20) can receive beam settings associated with an additional cell (TRP 2-Cell 2, 1d-15) having a different PCI from the serving cell (1d-10) through RRC configuration information (1d-56) from the serving cell. The beam settings associated with the additional cell (TRP 2-Cell 2, 1d-15) having a different PCI from the serving cell, i.e., the part that associates the TCI state corresponding to TRP2, can be applied by associating a new cell ID (Physical cell ID, PCI; additionalPCI-r17) as shown in Table 1 below.

In addition, a unified TCI state framework is applied for beam management between the cells. The unified TCI state framework applies a common TCI state framework to uplink and downlink, and to common channels and dedicated channels, and can be set to either a Joint UL/DL mode as shown in Table 2 below or a separate UL/DL mode as shown in Tables 3-1 and 3-2 below.

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

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

When the terminal (1d-20) is connected to the serving cell 1 via RRC (radio resource control), after the configuration for TRP 2-Cell 2 is provided, the terminal performs L1 measurement for the corresponding TRP 2-Cell 2 according to the configuration and reports the result to the serving cell (Cell 1, 1d-10) (1d-57). If the serving cell determines that a change from the serving cell beam (TCI state 1, 1d-25, 1d-30) to a specific beam (TCI state 2, 1d-35, 1d-40) of TRP 2 (Cell 2, 1d-15) is necessary based on the measurement result, the serving cell triggers the beam change and instructs the terminal to change the beam through L1/L2 signaling (1d-58). The terminal (1d-20) changes the beam to a specific beam (TCI state 2, 1d-40) of TRP 2 (Cell 2, 1d-15) through the instruction, and performs physical channel setting and upper layer setting operations related to the set beam. From this step, the terminal (1d-20) remains connected to the serving cell (Cell 1, 1d-10), but performs data transmission and reception (PDCCH/PDSCH reception, PUCCH (physical uplink control channel)/PUSCH (physical uplink shared channel) transmission) using the channel link of TRP 2 (Cell 2, 1d-15). However, transmission and reception for the common control channel are performed through the serving cell (Cell 1, 1d-10).

Thereafter, the terminal (1d-20) performs L3 measurement operation according to the measurement settings set in the independent serving cell (1d-59), receives a handover command message from the serving base station (Cell 1), and can perform a serving cell change to Cell 2 (1d-60). Through this technique (1d-55), the terminal (1d-20) performs data transmission and reception with a specific TRP 2 of Cell 2 supporting L1/L2-based mobility while connected to the serving cell, and can continuously use the corresponding beam even after the handover.

For reference, the settings related to L1 measurement and report in step 1d-57 above and the RRC settings for operation are described below. The contents are also basically applied to the following embodiments of the present disclosure, and improved techniques may be added in future embodiments.

1. CSI measurement settings

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

　　　- Setting up CSI-RS resources that require measurement (aperiodic, semi-persistent) and triggering settings

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

2. CSI report settings

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

　　　- Report quantity

　　　- Settings required for other reports

FIG. 5A and FIG. 5B are examples referred to in the present disclosure, illustrating a scenario in which a terminal transmits and receives data by changing a serving cell and beam to a TRP of a cell that supports L1/L2-based beam switching. In the present disclosure, a case in which multiple cells (TRP1-Cell1, TRP2-Cell2; 1e-10, 1e-15, 1e-40, 1e-45) exist within one DU (Distributed unit, 1e-05, 1e-35) is illustrated, but the overall content of the present disclosure can also be applied to an inter-DU (each DU constitutes one TRP-Cell) case.

Unlike the existing terminal beam changing procedure (1d-45, 1d-55) described in Fig. 4, the improved beam changing technique (1e-25, 1e-75) considered in these examples is as follows.

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

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

First, referring to FIG. 5a to explain the entire operation of Example 1, the terminal (1e-20) can receive common configuration information and dedicated configuration information for an additional cell (TRP 2-Cell 2, 1e-15) having a different PCI from the serving cell (1e-10) through RRC configuration information (1e-26). That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon and ServingCellConfig can be provided to the terminal (1e-20) in advance. The corresponding configuration information can be provided in the form of pre-configuration in the RRC configuration and can include configuration information for multiple cells. In addition, the corresponding configuration is characterized in that it includes all configuration information (cell configuration, bearer configuration, measurement-related configuration, security key configuration, etc.) applied when the terminal moves (handovers) to the corresponding cell. And, the setting includes the unified TCI state setting described in step 1d-56 and the settings related to L1 measurement and report.

In the example in this drawing, a structure for providing configurations in advance for candidate neighboring cells where L1/L2 handover can be performed, particularly a method for configuring cell group configurations (CellGroupConfig) including cell configurations, radio bearer configurations (RadioBearerConfig), and L3 measurement-related configurations (MeasConfig), is described in detail. When delivering the above configuration information to a terminal, a method for delivering it more efficiently than when only specific configuration information of specific LTM candidate cells is updated is considered. In addition, a method for reducing signaling overhead by effectively setting RLC bearer configurations, logical channel configurations, MAC configurations, etc. that can be generally applied within the cell group configuration is also proposed. In addition, the following examples in the present disclosure specify the above solutions by considering not only intra-CU but also inter-CU scenarios.

The terminal (1e-20) performs L1 measurement on the corresponding TRP 2-Cell 2 (1e-15) according to the settings received in step 1e-27 after the configuration for TRP 2-Cell 2 (1e-15) is provided while in an RRC-connected state to the serving cell 1 (1e-10) and reports the result to the serving cell (Cell 1, 1e-10). If the serving cell determines that a change from the serving cell beam (TCI state 1, 1e-25) to a specific beam (TCI state 2, 1e-40) of TRP 2 (Cell 2, 1e-15) is necessary based on the measurement result, it triggers a beam change in step 1e-28 and instructs the terminal (1e-20) to change the beam through L1/L2 signaling. The terminal (1e-20) performs a beam change to TRP 2 (Cell 2, 1e-15) through the instruction, and performs data transmission and reception through the TRP 2 (Cell 2, 1e-15). At this time, the serving cell change does not occur, and the terminal (1e-20) is still RRC connected to the serving cell (Cell 1, 1e-10).

After that, the terminal (1e-20) still performs L1 measurement for TRP 2-Cell 2 (1e-15) and reports the result to the serving cell (Cell 1, 1e-10). If the serving cell (Cell 1, 1e-10) determines that the L1 measurement reported by the terminal (1e-20) satisfies the triggering condition for handover to TRP 2-Cell 2 (1e-15) (the detailed operation is described in detail below), it instructs the terminal (1e-20) to perform a handover. The instruction may be an L1/L2 message. That is, an instruction for instructing a handover may be included in the MAC (medium access control) CE (control element) or DCI (downlink control information).

Referring to FIG. 5b to explain the entire operation of Example 2, the terminal (1e-50) can receive common configuration information and dedicated configuration information for an additional cell (TRP 2-Cell 2, 1e-45) having a different PCI from the serving cell (1e-40) through RRC configuration information (1e-76). That is, the configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon and ServingCellConfig can be provided to the terminal (1e-50) in advance. Here, the configuration information for the corresponding cell may be a configuration at the Cell group level (CellGroupConfig) rather than a cell-level configuration, or may be delivered as a configuration in the unit of an RRC configuration message (RRCReconfiguration).

The corresponding configuration information can be provided in the form of pre-configuration in the RRC configuration, and can include configuration information for multiple cells. In addition, the corresponding configuration is characterized by including all configuration information (cell configuration, bearer configuration, security key configuration, etc.) that is applied when the terminal (1e-50) moves (handovers) to the corresponding cell. In addition, the corresponding configuration includes the unified TCI state configuration described above in step 1d-56 of FIG. 1 and the configuration related to L1 measurement and report. In the example in this drawing, a structure for providing configurations for candidate neighboring cells where L1/L2 handover can be performed in advance, and in particular, a method for applying configuration information for a reference cell and delta configuration to the configurations for candidate neighboring cells is described in detail.

The terminal (1e-50), while in an RRC-connected state to the serving cell 1 (1e-40), performs L1 measurement on the corresponding TRP 2-Cell 2 (1e-45) according to the settings received in step 1e-77 after the settings for TRP 2-Cell 2 (1e-45) are provided, and reports the results to the serving cell (Cell 1, 1e-40). If the serving cell determines that a handover is necessary simultaneously with a beam change from the serving cell beam (TCI state 1, 1e-45) to a specific beam (TCI state 2, 1e-70) of TRP 2 (Cell 2, 1e-45) based on the measurement results, it triggers the beam change and handover in step 1e-78 and instructs the terminal (1e-50) to perform the beam change and handover through L1/L2 signaling. The terminal (1e-50) performs a handover to TRP 2 (Cell 2, 1e-15) at the same time as changing the beam through the instruction, and performs data transmission and reception through the TRP 2 (Cell 2, 1e-15). At this time, the terminal (1e-50) applies the configuration information for the target cell where the handover is performed, which was previously set in step 1e-76. Depending on whether uplink synchronization is required in the step, the terminal may perform random access or may omit random access to the target cell. The detailed operation is described in the drawings below.

In the following examples of the present disclosure, the RRC configuration information for LTM candidate cells includes cell and cell group configuration, radio bearer configuration, and measurement-related configuration, and the entire operation in which at least one of the configuration information is changed is considered. To this end, the following examples describe the entire procedure when applying an RRC configuration structure to provide effective RRC configuration updates for intra-CU scenarios and inter-CU scenarios, respectively. In particular, the following two methods are proposed for the RRC configuration structure.

1. Method for setting up the 1st LTM candidate cell RRC

- Cell group settings received from each LTM candidate cell (DU), wireless carrier settings generated by the CU, and measurement-related settings are generated as a single LTM candidate cell setting in the CU and transmitted to the terminal - Wireless carrier settings and measurement-related settings are optionally included.

2. Method for setting up the 2nd LTM candidate cell RRC

- Cell group settings received from each LTM candidate cell (DU), wireless carrier settings generated by the CU, and measurement-related settings are separately created/managed by the CU and delivered to the terminal.

- Wireless carrier settings and measurement-related settings are optionally managed as a separate list.

In particular, cell and cell group configurations include major cell-related configurations generated by the DU, which can be directly received by the base station through each LTM candidate cell, while radio bearer and layer 3 measurement-related configurations are generated by the CU. For LTM, radio bearer configuration may require split bearer configuration in LTM candidate cells, or may require an operation to set and change SRB 3 in the SCG of the LTM candidate cell when DC configuration is applied to the LTM candidate cells. In this case, an operation to update the radio bearer configuration for the LTM candidate cell is required. In addition, a very large area is basically covered by one CU, and the frequencies included in the CU are diverse. Therefore, for L3 measurement-related configurations, it is effective to distinguish measurement configurations by frequency band for efficient measurement management by frequency band. Since inter frequency operation is also supported for LTM, an operation to distinguish or update L3 measurement-related configurations by LTM candidate cells is required. That is, the changed configuration for specific LTM candidate cells can be effectively supported through the RRC configuration changeable structure for LTM candidate cells proposed in the present disclosure. In the present disclosure, the intra-CU scenario is considered in Examples 1 and 2, and the inter-CU scenario is considered in Examples 3 and 4.

In addition, a specific description of the above LTM candidate cell RRC configuration method is explained in detail in the following examples. For reference, this corresponds to a case where the RRC configuration message of the LTM candidate cell that the CU receives from the DU is CellGroupConfig, and when it is transmitted as an RRCReconfiguration message, a method that is a modification of the first LTM candidate cell RRC configuration method can be applied. That is, after the DU transmits the CellGroupConfig configuration to the CU through the F1AP interface, the DU receives the related radio carrier configuration and the measurement-related configuration from the CU again, generates one LTM candidate cell configuration in the DU, and then transmits an RRCReconfiguration message including the configuration to the CU through the F1AP interface. In the present disclosure, a detailed description of the case is omitted due to the similarity with Examples 1 and 3, but it is proposed that the method described above can also be applied to Examples 1 and 3. That is, the difference exists in whether an additional procedure for generating RRC configurations for LTM candidate cells by the CU and the DU through the F1AP is added compared to Examples 1 and 3.

FIG. 6 is a diagram illustrating a first LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of surrounding cells for L1/L2 based handover in an intra-CU scenario, as an example 1 applied to the present disclosure.

The terminal (1f-01) in the RRC connection state performs data transmission and reception with the source cell 1 (DU 1, 1f-02), and transmits the measurement values for the serving cell and surrounding cells to the source cell 1 (DU 1, 1f-02) according to the layer 3 measurement and reporting set in step 1f-10. At this time, the actual measurement values are transmitted to the CU (1f-03) of the base station. This is because the base station CU (1f-03) is responsible for RRC message processing and determines mobility.

The base station CU (1f-03) generates a message (L1/L2 config request message) requesting configuration information for L1/L2-based handover to the surrounding cells (DU 2, 1f-04; DU M, 1f-05) at step 1f-15 based on the measurement value report transmitted from the terminal (1f-01) and transmits the message to the F1 interface. In the drawing, the candidate cell is shown in connection with the DU, but in reality, the candidate cell and the DU may be mapped 1:1 or multiple candidate cells may be included in one DU. In addition, the message requesting configuration information for the above L1/L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, etc., or a new F1 or Xn message. The message requesting configuration information for the above L1/L2-based handover requests neighboring cells to be determined as candidate cells for L1/L2-based handover, and at the same time requests RRC configuration information that is applied when L1/L2-based handover is performed to the corresponding cell.

As described above, the RRC configuration information applied when L1/L2-based handover is performed can have one of the structures of cell level, cell group level, and RRC message level. In addition, a message requesting configuration information for the L1/L2-based handover can simultaneously transmit information and configuration for a reference cell. The configuration information for the reference cell can be transmitted together with the message requesting configuration information for L1/L2-based handover. In addition, the message may include an instruction requesting that the configuration information for L1/L2-based handover be transmitted to candidate neighboring cells (1f-04, 1f-05) by applying delta configuration. The instruction may be requested for each cell or may be commonly requested for all cells.

In step 1f-20, the candidate neighboring cells (1f-04, 1f-05) that have received a message requesting configuration information for L1/L2-based handover generate configuration information of each candidate neighboring cell based on delta configuration when L1/L2-based handover is applied based on the configuration information of the transmitted reference cell. Thereafter, in step 1f-25, each candidate neighboring cell (1f-04, 1f-05) stores the generated L1/L2-based handover configuration information in an L1/L2-based handover configuration information response message (L1/L2 config response message) and transfers it to the base station CU (1f-03). In the above step, the configuration information for the LTM candidate cells corresponds to cell configuration and cell group configuration (CellGroupConfig). Additionally, in the above step, each LTM candidate cell (1f-04, 1f-05) may reject the delta configuration request from the CU, in which case, it may apply the full configuration and transmit it to the CU (1f-03) including an instruction indicating it.

At step 1f-30, the source cell (1f-02) receives the RRC message generated by the base station CU (1f-03) and transmits it to the terminal (1f-01). The RRC message is a message that contains configuration information (Pre-Config1, 쪋Pre-ConfigN, 1f-31) for surrounding candidate cells to which L1/L2-based handover is applied, and the configuration information for each LTM candidate cell may be a message generated by including the radio bearer configuration (RadioBearerConfig) and L3 measurement related configuration (MeasConfig) generated by the CU in the cell group configuration (CellGroupConfig) received from the DU. This means that the DU generates the cell group configuration, which is a lower layer configuration, and transfers it to the CU, but the radio bearer and L3 measurement related configurations are generated by the CU. Therefore, the CU finally generates and manages the configuration information for each LTM candidate cell as a container (Pre-Config) and transfers it to the terminal (1f-01) through an RRC message. Accordingly, the configuration information (Pre-Config) for each LTM candidate cell has an index that can designate the LTM candidate cells. The index may be an actual cell index or an index that logically designates the configuration of a newly created LTM candidate cell.

In step 1f-35, the terminal (1f-01) that receives the RRC message performs a procedure for decoding and processing the RRC message. The processing includes ASN.1 decoding and validity determination of the received message and a method for storing and managing the configuration contents.

The base station and each LTM candidate cell perform a procedure for updating the LTM candidate cell configuration information transmitted in the above step, if it has changed. The examples of the present disclosure are characterized by proposing a structure of an LTM candidate cell RRC configuration for effectively updating the LTM candidate cell configuration information in such a case and proposing an overall procedure. That is, among the detailed settings of the LTM candidate cell RRC configuration, at least one of the serving cell and cell group configuration (CellGroupConfig), the radio bearer configuration (RadioBearerConfig), or the layer 3 measurement related configuration (MeasConfig) can be changed.

In step 1f-40, if a change in radio bearer configuration (RadioBearerConfig) is required in LTM candidate cell 1, the CU (1f-03) of the base station generates a change in radio bearer configuration (RadioBearerConfig1, 1f-42) for the corresponding cell, includes it in the corresponding LTM candidate cell configuration container (Pre-Config1, 1f-41), and transmits an RRC message to the terminal (1f-01). Here, Pre-Config1 (1f-41) includes updated RadioBearerConfig configuration information (1f-42) and an index indicating the configuration for the LTM candidate cell, and other information (CellGroupConfig, MeasConfig) of the LTM candidate cell configuration information may be omitted. In addition, the RadioBearerConfig may have a delta configuration applied.

In step 1f-45, if a change in L3 measurement-related configuration (MeasConfig) is required in LTM candidate cell 1, the CU (1f-03) of the base station generates a change in L3 measurement-related configuration (MeasConfig1, 1f-47) for the corresponding cell, includes it in the corresponding LTM candidate cell configuration container (Pre-Config1, 1f-46), and transmits it to the terminal through an RRC message. Here, Pre-Config1 (1f-46) includes information on the L3 measurement-related configuration (MeasConfig1, 1f-47) to be updated and an index indicating the configuration for the LTM candidate cell, and other information (CellGroupConfig, RadioBearerConfig) of the LTM candidate cell configuration information may be omitted. In addition, the MeasConfig may have a delta configuration applied.

Unlike the procedure for changing RadioBearerConfig and MeasConfig for the above LTM candidate cells (performing a configuration change operation in the CU (1f-03) of the base station), when a configuration change for CellGroupConfig is required, an operation is required to request a configuration change in each LTM candidate cell (DU 2, 1f-04; DU M, 1f-05) and transmit the changed configuration to the CU (1f-03) of the base station. That is, in step 1f-50, LTM candidate cell 1 transmits a message requesting a configuration change for CellGroupConfig1 to the CU (1f-03) of the base station through the F1 interface.

In step 1f-55, the CU (1f-03) of the base station applies CellGroupConfig1 (1f-57) transmitted from LTM candidate cell 1 (DU 2, 1f-04), includes it in the corresponding LTM candidate cell configuration container (Pre-Config1, 1f-56), and transmits an RRC message to the terminal. Here, Pre-Config1 (1f-56) includes updated CellGroupConfig1 configuration information and an index indicating configuration for the LTM candidate cell, and other information (RadioBearerConfig, MeasConfig) of the LTM candidate cell configuration information may be omitted. In addition, delta configuration may be applied to the CellGroupConfig1.

In step 1f-60, the terminal (1f-01) performs L1 measurement and reporting for each candidate surrounding cell, and the source cell that receives the measurement and reports makes a handover decision and instructs the terminal (1f-01) to perform L1/L2 handover in step 1f-65. In the above step, MAC CE and DCI can be used as L1/L2 signaling including a handover indicator. The source cell (DU, 1f-02) or the source base station (CU, 1f-03) can receive the L1 measurement values for determining the L1/L2 handover in steps 1f-60 and 1f-65 and determine the handover. If the base station (CU, 1f-03) makes all decisions, the source cell (DU, 1f-02) transfers the L1 measurement value received from the terminal (1f-01) to the base station (CU, 1f-03) and transfers L1/L2 signaling to the terminal (1f-01) according to the handover decision instruction of the base station (CU, 1f-03). However, if the source cell (DU, 1f-02) makes the final decision, it does not transfer the L1 measurement value to the base station (CU, 1f-03), but decides the handover on its own according to the measurement value criteria (threshold value and measurement value range) for making the handover decision for each candidate neighboring cell received from the previous base station, and transfers L1/L2 signaling to the terminal (1f-01) accordingly.

When the L1/L2 handover instruction is transmitted to the terminal, the terminal (1f-01) starts a handover procedure in step 1f-70 and starts a timer for L1/L2 handover. The timer may be a newly set timer for LTM, or may reuse a T304 timer used for an existing handover. In addition, the terminal (1f-01) applies a setting for a target cell to which L1/L2 handover is applied. This is one of the neighboring cell settings received in advance in steps 1f-30/1f-40/1f-45/1f-55.

Depending on the settings applied in step 1f-75, the terminal (1f-01) performs random access when random access is required for the target cell, and skips the random access procedure when random access is not indicated or required (when uplink synchronization has already been performed or aligned).

In step 1f-80, the terminal (1f-01) performs a handover completion procedure with the target cell. The procedure may vary depending on the method of indicating the handover completion, and may be a process of transmitting an RRCReconfiugrationComplete message if the target cell configuration is received at the RRC message level, but if the cell level or cell group level configuration is received, a new handover completion indication message (new RRC message or MAC CE) may replace the procedure.

After LTM is completed at step 1f-85, the target cell (DU2, 1f-04) informs the base station (CU, 1f-03) that the LTM procedure is completed and the terminal (1f-01) has successfully performed RRC connection to the corresponding cell. Thereafter, the base station (CU, 1f-03) instructs the source cell (1f-02) to terminate the connection to the terminal (1f-01) and to release the UE context.

Although omitted in the drawing, when a change in a reference cell and its configuration is required, configuration-related operations may be updated with F1 interface messages between the base station CU and neighboring cells. In particular, when the configuration of the reference cell is changed, the LTM candidate cell configuration procedure described above is repeated to perform the reference cell configuration change and LTM candidate cell configuration change procedures, and the changed configuration information is transmitted to the terminal. In addition, although omitted in the drawing, new MAC CE and DCI may be introduced to dynamically indicate neighboring candidate cells to which L1/L2-based handover is applied, so that dynamically valid configurations may be indicated or released (previously transmitted L1/L2-based handover configurations may be released). Alternatively, the above-described related operations may be performed internally by the base station without transmitting separate signaling to the terminal.

FIG. 7 is a diagram illustrating a second LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of surrounding cells for L1/L2 based handover in an intra-CU scenario, as Example 2 applied to the present disclosure.

The terminal (1g-01) in the RRC connection state performs data transmission and reception with the source cell 1 (DU 1, 1g-02), and transmits the measurement values for the serving cell and surrounding cells to the source cell 1 (DU 1, 1g-02) according to the layer 3 measurement and reporting set in step 1g-10. At this time, the actual measurement values are transmitted to the CU (1g-03) of the base station. This is because the base station CU (1g-03) is responsible for RRC message processing and determines mobility.

The base station CU (1g-03) generates a message (L1/L2 config request message) requesting configuration information for L1/L2-based handover at step 1g-15 to surrounding cells (DU 2, 1g-04; DU M, 1g-05) based on the measurement value report transmitted from the terminal (1g-01) and transmits the message to the F1 interface. In the drawing, the candidate cell is shown in connection with the DU, but in reality, the candidate cell and the DU may be mapped 1:1 or multiple candidate cells may be included in one DU. In addition, the message requesting configuration information for the above L1/L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, etc., or a new F1 or Xn message. The message requesting the configuration information for the L1/L2-based handover requests neighboring cells to be determined as candidate cells for the L1/L2-based handover, and at the same time requests RRC configuration information to be applied when the L1/L2-based handover is performed to the corresponding cell. As described above, the RRC configuration information to be applied when the L1/L2-based handover is performed may have one of the structures of a cell level, a cell group level, and an RRC message level. In addition, the message requesting the configuration information for the L1/L2-based handover may simultaneously transmit information and configuration for a reference cell. The configuration information for the reference cell may be transmitted together with the message requesting the configuration information for the L1/L2-based handover. In addition, the message may include an instruction to transmit the configuration information for the L1/L2-based handover to the candidate neighboring cells (1g-04, 1g-05) by applying a delta configuration. The instruction may be requested for each cell or may be commonly requested for all cells.

In step 1g-20, the candidate neighboring cells (1g-04, 1g-05) that have received a message requesting configuration information for L1/L2-based handover generate configuration information of each candidate neighboring cell based on delta configuration when L1/L2-based handover is applied based on the configuration information of the transmitted reference cell. Thereafter, in step 1g-25, each candidate neighboring cell (1g-04, 1g-05) stores the generated L1/L2-based handover configuration information in an L1/L2-based handover configuration information response message (L1/L2 config response message) and transfers it to the base station CU (1g-03). In the above step, the configuration information for the LTM candidate cells corresponds to cell configuration and cell group configuration (CellGroupConfig). Additionally, in the above step, each LTM candidate cell (1g-04, 1g-05) may reject a delta configuration request from the CU, in which case, it may apply the full configuration and transmit it to the CU along with an instruction indicating the same.

In step 1g-30, the source cell (1g-02) receives an RRC message generated by the base station CU (1g-03) and transmits it to the terminal (1g-01). The RRC message is configuration information for surrounding candidate cells to which L1/L2-based handover is applied, and may be a message generated by including a list (List of CellGroupConfig, 1g-31) containing cell group configurations (CellGroupConfig) received from each candidate cell (DU), a list (List of RadioBearerConfig, 1g-32) of radio bearer configurations (RadioBearerConfig) generated by the CU applied to the candidate cells, and a list (List of MeasConfig, 1g-33) of L3 measurement-related configurations (MeasConfig) generated by the CU applied to the candidate cells. This is because, although the DU creates the cell group configuration, which is a lower layer configuration, and transfers it to the CU, the radio bearer and L3 measurement-related configurations are created in the CU. Therefore, when creating and managing configuration information for each LTM candidate cell, it may be more efficient for the CU to ultimately manage each piece of information separately. Accordingly, in the configuration information list (1g-31, 1g-32, 1g-33) for each LTM candidate cell, there is an index that can designate the LTM candidate cells. The index may be an actual cell index or an index that logically designates the configuration of a newly created LTM candidate cell.

In step 1g-35, the terminal (1g-01) that receives the RRC message performs a procedure for decoding and processing the RRC message. The processing includes ASN.1 decoding and validity determination of the received message, and a method for storing and managing configuration contents. A list including cell group configurations (CellGroupConfig) for LTM candidate cells includes an index that can designate LTM candidate cells. In addition, the list of radio bearer configurations (RadioBearerConfig) and the list of L3 measurement related configurations (MeasConfig) can include candidate cell indication index or bitmap information that can designate which LTM candidate cells each configuration in the list is applied to. This has an advantage of reducing signaling overhead compared to the structure in Example 1 because the radio bearer configuration and L3 measurement related configuration generated by the CU can be applied to a plurality of LTM candidate cells.

The base station and each LTM candidate cell perform a procedure for updating the LTM candidate cell configuration information transmitted in the above step, if it has changed. In the examples of the present disclosure, in such a case, a structure of an LTM candidate cell RRC configuration for effectively updating the LTM candidate cell configuration information is proposed, and the overall procedure is proposed. That is, among the detailed settings of the LTM candidate cell RRC configuration, at least one of the serving cell and cell group configuration (CellGroupConfig), the radio bearer configuration (RadioBearerConfig), or the layer 3 measurement related configuration (MeasConfig) may be changed.

In step 1g-40, if a change in radio bearer configuration (RadioBearerConfig) is required in LTM candidate cell 1, the CU (1g-03) of the base station generates a change in radio bearer configuration (RadioBearerConfig1, 1g-41) for the corresponding cell, includes it in the candidate LTM configuration information, and transmits it to the terminal via an RRC message. Here, the RadioBearerConfig1 configuration information (1g-41) includes an index indicating which LTM candidate cell the corresponding configuration information indicates the configuration for. In addition, the RadioBearerConfig can have a delta configuration applied. As an example, a change in one RadioBearerConfig1 is described as an example, but a list including multiple RadioBearerConfigs can be generated and transmitted to the terminal in the corresponding step.

In step 1g-45, if a change in L3 measurement-related settings (MeasConfig) is required in LTM candidate cell 1, the CU (1g-03) of the base station generates a change in L3 measurement-related settings (MeasConfig1, 1g-46) for the corresponding cell, includes it in the LTM configuration information, and transmits it to the terminal (1g-01) via an RRC message. Here, the MeasConfig1 configuration information (1g-46) includes an index indicating which LTM candidate cell the corresponding configuration information indicates the configuration for. In addition, the MeasConfig can have delta configuration applied. As an example, a single MeasConfig1 change is described as an example, but a list including multiple MeasConfigs can be generated and transmitted to the terminal in the corresponding step.

Unlike the procedure for changing RadioBearerConfig and MeasConfig for the above LTM candidate cells (performing a configuration change operation at the CU (1g-03) of the base station), when a configuration change is required for CellGroupConfig, an operation is required to request a configuration change at each LTM candidate cell (DU 2, 1g-04; DU M, 1g-05) and transmit the changed configuration to the CU (1g-03) of the base station. To this end, at step 1g-50, the LTM candidate cell 1 (1g-04) transmits a message requesting a configuration change for CellGroupConfig1 to the CU (1g-03) of the base station through the F1 interface. At step 1g-55, the CU (1g-03) of the base station transmits the LTM candidate cell configuration including CellGroupConfig1 (1g-56) transmitted from LTM candidate cell 1 (DU 2, 1g-04) to the terminal (1g-01) through an RRC message. Here, the CellGroupConfig1 configuration information (1g-56) includes an index indicating which LTM candidate cell the configuration information indicates. In addition, the CellGroupConfig can be applied with delta configuration. As an example, a single CellGroupConfig1 change is described, but a list including multiple CellGroupConfigs can be generated and transmitted to the terminal (1g-01) at the corresponding step.

In step 1g-60, the terminal (1g-01) performs L1 measurement and report for each candidate surrounding cell, and the source cell that receives the report makes a handover decision and instructs the terminal (1g-01) to perform L1/L2 handover in step 1g-65. In the above step, MAC CE and DCI can be used as L1/L2 signaling including a handover indicator. The source cell (DU, 1g-02) or the source base station (CU, 1g-03) can receive the L1 measurement values for determining the L1/L2 handover in steps 1g-60 and 1g-65 and determine the handover. If the base station (CU, 1g-03) makes all decisions, the source cell (DU, 1g-02) transmits the L1 measurement values received from the terminal (1g-01) and transmits L1/L2 signaling to the terminal (1g-01) according to the handover decision instruction of the base station (CU, 1g-03). However, if the source cell (DU, 1g-02) makes the final decision, it does not transmit the L1 measurement values to the base station, but decides the handover on its own according to the measurement value criteria (threshold value and measurement value range) for making the handover decision for each candidate neighboring cell received from the previous base station, and transmits L1/L2 signaling to the terminal (1g-01) accordingly.

When the L1/L2 handover instruction is transmitted to the terminal (1g-01), the terminal (1g-01) starts a handover procedure in step 1g-70 and starts a timer for L1/L2 handover. The timer may be a newly set timer for LTM, or may reuse a T304 timer used for an existing handover. In addition, the terminal (1g-01) applies a setting for a target cell to which the L1/L2 handover is applied. This is one of the neighboring cell settings previously received in steps 1g-30/1g-40/1g-45/1g-55. Depending on the setting applied in step 1g-75, the terminal (1g-01) performs a random access for the corresponding target cell if random access is required, and skips the random access procedure if random access is not indicated or is not required (if uplink synchronization has already been performed or aligned).

In step 1g-80, the terminal (1g-01) performs a handover completion procedure with the target cell. The procedure may vary depending on the method of indicating the handover completion, and may be a process of transmitting an RRCReconfiugrationComplete message if the target cell configuration is received at the RRC message level, but if the cell level or cell group level configuration is received, a new handover completion indication message (new RRC message or MAC CE) may replace the procedure.

After LTM is completed at step 1g-85, the target cell (DU2, 1g-04) informs the base station (CU, 1g-03) that the LTM procedure is completed and the terminal (1g-01) has successfully performed RRC connection to the cell. Thereafter, the base station (CU, 1g-03) instructs the source cell (1g-02) to terminate the connection to the terminal (1g-01) and to release the UE context.

Although omitted in the drawing, when a change in a reference cell and its configuration is required, configuration-related operations may be updated with F1 interface messages between the base station CU and neighboring cells. In particular, when the configuration of the reference cell is changed, the LTM candidate cell configuration procedure described above is repeated to perform the reference cell configuration change and LTM candidate cell configuration change procedures, and the changed configuration information is transmitted to the terminal. In addition, although omitted in the drawing, new MAC CE and DCI may be introduced to dynamically indicate neighboring candidate cells to which L1/L2-based handover is applied, so that dynamically valid configurations may be indicated or released (previously transmitted L1/L2-based handover configurations may be released). Alternatively, the above-described related operations may be performed internally by the base station without transmitting separate signaling to the terminal.

FIG. 8 is a diagram illustrating a first LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of neighboring cells for L1/L2 based handover in an inter-CU scenario, as an example 3 applied to the present disclosure.

The terminal (1h-01) in the RRC connection state performs data transmission and reception with the source cell 1 (DU 1, 1h-02), and transmits the measurement values for the serving cell and surrounding cells to the source cell 1 (DU 1, 1h-02) according to the layer 3 measurement and reporting set in step 1h-10. At this time, the actual measurement values are transmitted to the CU1 (1h-03) of the base station. This is because the base station CU1 (1h-03) is responsible for RRC message processing and determines mobility.

At step 1h-15, base station CU1 (1h-03) generates a message (L1/L2 config request message) requesting configuration information for L1/L2-based handover to neighboring cells (DU 2 - CU 2, 1h-04; DU M, 1h-05) based on the measurement value report transmitted from terminal (1h-01), and transmits the message to base station CU2 (1h-06) through Xn interface, and base station CU2 (1h-06) transmits the message to each neighboring cell (DU 2 - CU 2, 1h-04; DU M, 1h-05) through F1 interface. In the drawing, candidate cells are shown in connection with DUs, but in reality, candidate cells and DUs may be mapped 1:1, or multiple candidate cells may be included in one DU. In addition, the message requesting the configuration information for the above L1/L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, etc., or may be a new F1 or Xn message. The message requesting the configuration information for the L1/L2-based handover requests neighboring cells to be determined as candidate cells for the L1/L2-based handover, and at the same time requests RRC configuration information to be applied when the L1/L2-based handover is performed to the corresponding cell. As described above, the RRC configuration information applied when the L1/L2-based handover is performed may have one of the structures of a cell level, a cell group level, and an RRC message level. In addition, the message requesting the configuration information for the above L1/L2-based handover may simultaneously transmit information and configuration for a reference cell. In addition, the configuration information for the corresponding reference cell may be transmitted together through the message requesting the configuration information for the L1/L2-based handover. Additionally, the message may include an instruction to transfer the setup information for L1/L2-based handover to candidate neighboring cells (1h-04, 1h-05) by applying delta configuration. The instruction may be requested for each cell or may be requested commonly to all cells. In Example 3, a case where candidate neighboring cells (1h-04, 1h-05) exist in different DUs within inter CU is described as an example.

At step 1h-20, the candidate neighboring cells (1h-04, 1h-05) that have received a message requesting configuration information for L1/L2-based handover generate configuration information of each candidate neighboring cell based on delta configuration when L1/L2-based handover is applied based on the configuration information of the transmitted reference cell. Thereafter, at step 1h-25, each candidate neighboring cell (1h-04, 1h-05) stores the generated L1/L2-based handover configuration information in an L1/L2-based handover configuration information response message (L1/L2 config response message) and transfers it to base station CU 2 (1h-06). Base station CU 2 (1h-06) transfers the LTM configuration response message received from the neighboring cells (DU 2 - CU 2, 1h-04; DU M, 1h-05) to source base station CU1 (1h-03). In the above step, the configuration information for the LTM candidate cells corresponds to the cell configuration and cell group configuration (CellGroupConfig). In addition, in the above step, each LTM candidate cell (1h-04, 1h-05) may reject the delta configuration request from the CU (1h-02), in which case, the full configuration may be applied and transmitted to the CU (1h-03) including an instruction indicating this.

At step 1h-30, the source cell (1h-02) receives the RRC message generated by the base station CU (1h-03) and transmits it to the terminal (1h-01). The RRC message is a message that contains configuration information (Pre-Config1, 쪋, Pre-ConfigN, 1h-31) for surrounding candidate cells to which L1/L2-based handover is applied, and the configuration information for each LTM candidate cell may be a message generated by including the cell group configuration (CellGroupConfig) received from each candidate cell (radio bearer configuration (RadioBearerConfig) and L3 measurement-related configuration (MeasConfig) generated by the CU). This is because the DU generates the cell group configuration, which is a lower layer configuration, and transfers it to the CU, but the radio bearer and L3 measurement-related configuration are generated by the CU. Therefore, the configuration information for each LTM candidate cell is finally generated and managed as a container (Pre-Config) by the CU (1h-03) and transferred to the terminal (1h-01) through an RRC message. Accordingly, the configuration information (Pre-Config) for each LTM candidate cell has an index that can refer to the LTM candidate cells. The index may be an actual cell index or a logical index of a newly generated LTM candidate cell. It may be an index referring to a setting.

The terminal (1h-01) that receives the RRC message in step 1h-35 performs a procedure for decoding and processing the RRC message. The processing includes ASN.1 decoding and validity determination of the received message and a method for storing and managing the configuration contents.

The base station and each LTM candidate cell perform a procedure for updating the LTM candidate cell configuration information transmitted in the above step, if it has changed. In the examples of the present disclosure, in such a case, a structure of an LTM candidate cell RRC configuration for effectively updating the LTM candidate cell configuration information is proposed, and the overall procedure is proposed. That is, among the detailed settings of the LTM candidate cell RRC configuration, at least one of the serving cell and cell group configuration (CellGroupConfig), the radio bearer configuration (RadioBearerConfig), or the layer 3 measurement related configuration (MeasConfig) may be changed.

In step 1h-40, if a change in radio bearer configuration (RadioBearerConfig) is required in LTM candidate cell 1, CU2 (1h-06) of the base station generates a change in radio bearer configuration (RadioBearerConfig1, 1h-40) for the corresponding cell and transmits it to CU1 (1h-03) of the source base station.

At step 1h-45, CU1 (1h-03) of the source base station includes the received radio bearer configuration change contents in the corresponding LTM candidate cell configuration container (Pre-Config1, 1h-46) and transmits it to the terminal through an RRC message. Here, Pre-Config1 (1h-46) includes updated RadioBearerConfig configuration information (1h-47) and an index indicating the configuration for the LTM candidate cell, and other information (CellGroupConfig, MeasConfig) of the LTM candidate cell configuration information may be omitted. In addition, delta configuration may be applied to the RadioBearerConfig.

In step 1h-50, if a change in L3 measurement-related configuration (MeasConfig) is required in LTM candidate cell 1, CU2 (1h-06) of the base station generates a change in L3 measurement-related configuration (MeasConfig1, 1h-50) for the corresponding cell and transmits it to CU1 (1h-03) of the source base station. In step 1h-55, CU1 (1h-03) of the source base station includes the information received from LTM candidate cell 1 in the corresponding LTM candidate cell configuration container (Pre-Config1, 1h-56) and transmits it to the terminal (1h-01) through an RRC message. Here, Pre-Config1 (1h-56) includes updated L3 measurement-related configuration (MeasConfig1, 1h-57) information and an index indicating the configuration for the LTM candidate cell, and other information (CellGroupConfig, RadioBearerConfig) of the LTM candidate cell configuration information may be omitted. Additionally, the above MeasConfig can apply delta configuration.

Unlike the procedure for changing RadioBearerConfig and MeasConfig for the above LTM candidate cells (performing a configuration change operation in CU2 (1h-03) of the base station), when a configuration change for CellGroupConfig is required, an operation is required to request a configuration change in each LTM candidate cell (DU 2, 1h-04; DU M, 1h-05) and transmit the changed configuration to CU2 (1h-06) of the base station. To this end, in step 1h-60, LTM candidate cell 1 transmits a message requesting a configuration change for CellGroupConfig1 to CU2 (1h-06) of the base station through the F1 interface. At step 1h-65, CU2 (1h-06) of the base station applies CellGroupConfig1 (1h-67) transmitted from LTM candidate cell 1 (DU 2, 1h-04), includes it in the corresponding LTM candidate cell configuration container (Pre-Config1, 1h-66), and transmits it to the terminal through an RRC message. Here, Pre-Config1 (1h-66) includes updated CellGroupConfig1 configuration information and an index indicating configuration for the LTM candidate cell, and other information (RadioBearerConfig, MeasConfig) of the LTM candidate cell configuration information may be omitted. In addition, delta configuration may be applied to the CellGroupConfig1.

In step 1h-70, the terminal (1h-01) performs L1 measurement and reporting for each candidate surrounding cell, and if the source cell receiving the measurement determines a handover, it instructs the terminal (1h-01) to perform L1/L2 handover in step 1h-65. In the above step, MAC CE and DCI can be used as L1/L2 signaling including a handover indicator. The source cell (DU, 1h-02) or the source base station (CU, 1h-03) can receive the L1 measurement values for determining the L1/L2 handover in steps 1h-70 and 1h-75 and determine the handover. If the base station (CU, 1h-03) makes all decisions, the source cell (DU, 1h-02) transmits the L1 measurement values received from the terminal (1h-01) and transmits L1/L2 signaling to the terminal (1h-01) according to the handover decision instruction of the base station (CU, 1h-03). However, if the source cell (DU, 1h-02) makes the final decision, it does not transmit the L1 measurement values to the base station, but decides the handover on its own according to the measurement value criteria (threshold value and measurement value range) for making the handover decision for each candidate neighboring cell received from the previous base station, and transmits L1/L2 signaling to the terminal accordingly.

When the L1/L2 handover instruction is transmitted to the terminal (1h-01), the terminal starts the handover procedure in step 1h-80 and starts a timer for L1/L2 handover. The timer may be a newly set timer for LTM, or may reuse a T304 timer used for an existing handover. In addition, the terminal (1h-01) applies a setting for a target cell to which L1/L2 handover is applied. This is one of the neighboring cell settings received in advance in steps 1h-30/1h-45/1h-55/1h-65.

Depending on the settings applied in step 1h-85, the terminal (1h-01) performs random access if random access is required for the target cell, and skips the random access procedure if random access is not indicated or required (uplink synchronization has already been performed or aligned).

At step 1h-90, the terminal (1h-01) performs a handover completion procedure with the target cell. The procedure may vary depending on the method of indicating the handover completion, and may be a process of transmitting an RRCReconfiugrationComplete message if the target cell configuration is received at the RRC message level, but if the cell level or cell group level configuration is received, a new handover completion indication message (new RRC message or MAC CE) may replace the procedure.

After LTM is completed at step 1h-95, the target cell (DU2, 1h-04) informs the base station (CU, 1h-03) that the LTM procedure is completed and the terminal (1h-01) has successfully performed RRC connection to the corresponding cell. Thereafter, the base station (CU, 1h-03) instructs the source cell (1h-02) to terminate the connection to the corresponding terminal and to release the UE context.

Although omitted in the drawing, when a change in a reference cell and its configuration is required, configuration-related operations may be updated by messages in the F1 interface between the base station CU and neighboring cells and in the Xn interface between the base station CU1 and base station CU2. In particular, when the configuration of the reference cell is changed, the LTM candidate cell configuration procedure described above is repeated to perform the reference cell configuration change and LTM candidate cell configuration change procedures, and the changed configuration information is transmitted to the terminal. In addition, although omitted in the drawing, new MAC CE and DCI may be introduced to dynamically indicate neighboring candidate cells to which L1/L2-based handover is applied, so that dynamically valid configurations may be indicated or released (previously transmitted L1/L2-based handover configurations may be released). Alternatively, the above-described related operations may be performed internally by the base station without transmitting separate signaling to the terminal.

FIG. 9 is a diagram illustrating a second LTM candidate cell RRC configuration method and procedure for providing effective RRC configuration update for configuration of neighboring cells for L1/L2 based handover in an inter-CU scenario, as Example 4 applied to the present disclosure.

The terminal (1i-01) in the RRC connection state performs data transmission and reception with the source cell 1 (DU 1, 1i-02), and transmits the measurement values for the serving cell and surrounding cells to the source cell 1 (DU 1, 1i-02) according to the layer 3 measurement and reporting set in step 1i-10. At this time, the actual measurement values are transmitted to the CU (1i-03) of the base station. This is because the base station CU (1i-03) is responsible for RRC message processing and determines mobility. The base station CU (1i-03) generates a message (L1/L2 config request message) requesting configuration information for L1/L2-based handover at step 1i-15 to neighboring cells (DU 2, 1i-04; DU M, 1i-05) based on the measurement value report transmitted from the terminal and transmits it to the base station CU2 (1i-06) through the Xn interface. The base station CU2 (1i-06) then transmits it to each neighboring cell (DU 2 - CU 2, 1i-04; DU M, 1i-05) through the F1 interface. In the drawing, the candidate cell is shown in connection with the DU, but in reality, the candidate cell and the DU may be mapped 1:1 or multiple candidate cells may be included in one DU. In addition, the message requesting configuration information for the above L1/L2-based handover may be an existing handover request message, a UE context request message, a UE context modification request message, etc., or may be a new F1 or Xn message. The message requesting the configuration information for the L1/L2-based handover requests neighboring cells to be determined as candidate cells for the L1/L2-based handover, and at the same time requests RRC configuration information to be applied when the L1/L2-based handover is performed to the corresponding cell. As described above, the RRC configuration information to be applied when the L1/L2-based handover is performed may have one of the structures of a cell level, a cell group level, and an RRC message level. In addition, the message requesting the configuration information for the L1/L2-based handover may simultaneously transmit information and configuration for a reference cell. In addition, the configuration information for the reference cell may be transmitted together with the message requesting the configuration information for the L1/L2-based handover. In addition, the message may include an instruction to transmit the configuration information for the L1/L2-based handover to the candidate neighboring cells (1i-04, 1i-05) by applying a delta configuration. The instruction may be requested for each cell or may be commonly requested for all cells.

At step 1i-20, the candidate neighboring cells (1i-04, 1i-05) that have received a message requesting configuration information for L1/L2-based handover generate configuration information of each candidate neighboring cell based on delta configuration when L1/L2-based handover is applied based on the configuration information of the transmitted reference cell. Thereafter, at step 1i-25, each candidate neighboring cell (1i-04, 1i-05) stores the generated L1/L2-based handover configuration information in an L1/L2-based handover configuration information response message (L1/L2 config response message) and transfers it to base station CU 2 (1i-06). Base station CU 2 (1i-06) transfers the LTM configuration response message received from the neighboring cells (DU 2 - CU 2, 1i-04; DU M, 1i-05) to source base station CU 1 (1i-03). In the above step, the configuration information for the LTM candidate cells corresponds to the cell configuration and cell group configuration (CellGroupConfig). In addition, in the above step, each LTM candidate cell (1i-04, 1i-05) may reject the delta configuration request from the CU, and in this case, may apply the full configuration and transmit it to the CU (1i-03) including an instruction indicating this.

At step 1i-30, the source cell (1i-02) receives the RRC message generated by the base station CU (1i-03) and transfers it to the terminal (1i-01). The RRC message is configuration information for surrounding candidate cells to which L1/L2-based handover is applied, and may be a message generated by including a list (List of CellGroupConfig, 1i-31) containing cell group configurations (CellGroupConfig) received from each candidate cell (DU), a list (List of RadioBearerConfig, 1i-32) of radio bearer configurations (RadioBearerConfig) generated by the CU applied to the candidate cells, and a list (List of MeasConfig, 1i-33) of L3 measurement-related configurations (MeasConfig) generated by the CU applied to the candidate cells. This is because, although the DU creates the cell group configuration, which is a lower layer configuration, and transfers it to the CU, the radio bearer and L3 measurement-related configurations are created in the CU, so when creating and managing configuration information for each LTM candidate cell, it may be more efficient for the CU to separately manage each piece of information. Accordingly, in the configuration information list (1i-31, 1i-32, 1i-33) for each LTM candidate cell, there is an index that can designate the LTM candidate cells. The index may be an actual cell index or an index that logically designates the configuration of a newly created LTM candidate cell.

In step 1i-35, the terminal (1i-01) that receives the RRC message performs a procedure for decoding and processing the RRC message. The processing includes ASN.1 decoding and validity determination of the received message, and a method for storing and managing configuration contents. A list including cell group configurations (CellGroupConfig) for LTM candidate cells includes an index that can designate LTM candidate cells. In addition, the list of radio bearer configurations (RadioBearerConfig) and the list of L3 measurement related configurations (MeasConfig) can include candidate cell indication index or bitmap information that can designate which LTM candidate cells each configuration in the list is applied to. This has an advantage of reducing signaling overhead compared to the structure in Example 1 because the radio bearer configuration and L3 measurement related configuration generated by the CU can be applied to a plurality of LTM candidate cells.

The base station and each LTM candidate cell perform a procedure for updating the LTM candidate cell configuration information transmitted in the above step, if it has changed. In the examples of the present disclosure, in such a case, a structure of an LTM candidate cell RRC configuration for effectively updating the LTM candidate cell configuration information is proposed, and the overall procedure is proposed. That is, among the detailed settings of the LTM candidate cell RRC configuration, at least one of the serving cell and cell group configuration (CellGroupConfig), the radio bearer configuration (RadioBearerConfig), or the layer 3 measurement related configuration (MeasConfig) may be changed.

In step 1i-40, if a change in radio bearer configuration (RadioBearerConfig) is required in LTM candidate cell 1, CU2 (1i-06) of the base station generates a radio bearer configuration change for the corresponding cell (RadioBearerConfig1, 1i-40) and transmits it to CU1 (1i-03) of the source base station. The change in configuration transmitted to CU1 (1i-03) of the source base station is included in the candidate LTM configuration information in step 1i-45 and transmitted to the terminal through an RRC message. Here, the RadioBearerConfig1 configuration information (1i-46) includes an index indicating which LTM candidate cell the corresponding configuration information indicates the configuration for. In addition, delta configuration can be applied to the RadioBearerConfig. As an example, a change in one RadioBearerConfig1 is described, but a list including multiple RadioBearerConfigs can be generated and transmitted to the terminal (1i-01) in the corresponding step.

In step 1i-45, if a change in L3 measurement-related settings (MeasConfig) is required in LTM candidate cell 1, CU2 (1i-06) of the base station generates a radio bearer setting change for the corresponding cell (MeasConfig1, 1i-50) and transmits it to CU1 (1i-03) of the source base station. The setting change transmitted to CU1 (1i-03) of the source base station is included in the candidate LTM setting information in step 1i-55 and transmitted to the terminal (1i-01) via an RRC message. Here, the MeasConfig1 setting information (1i-56) includes an index indicating which LTM candidate cell the setting information indicates. In addition, delta configuration can be applied to the MeasConfig. As an example, a single MeasConfig1 change is exemplified, but a list including multiple MeasConfigs can be generated and transmitted to the terminal (1i-01) in the corresponding step.

Unlike the procedure for changing RadioBearerConfig and MeasConfig for the above LTM candidate cells (performing a configuration change operation in CU2 (1i-06) of the base station), when a configuration change for CellGroupConfig is required, an operation is required to request a configuration change in each LTM candidate cell (DU 2, 1i-04; DU M, 1i-05) and transmit the changed configuration to CU2 (1i-03) of the base station. To this end, in step 1i-60, LTM candidate cell 1 transmits a message requesting a configuration change for CellGroupConfig1 to CU2 (1i-06) of the base station through the F1 interface. CU2 (1i-06) of the base station applies CellGroupConfig1 (1i-66) transmitted from LTM candidate cell 1 (DU 2, 1i-04) and transmits it to CU1 (1i-03) of the base station. In step 1i-65, an LTM candidate cell configuration including CellGroupConfig1 (1i-66) transmitted from LTM candidate cell 1 (DU 2, 1i-04) is transmitted to the terminal (1i-01) via an RRC message. Here, the CellGroupConfig1 configuration information (1i-66) includes an index indicating which LTM candidate cell the corresponding configuration information indicates configuration for. In addition, the CellGroupConfig can have a delta configuration applied. As an example, a single CellGroupConfig1 change is described as an example, but a list including multiple CellGroupConfigs may be generated and transmitted to the terminal (1i-01) in the corresponding step.

In step 1i-70, the terminal (1i-01) performs L1 measurement and reporting for each candidate surrounding cell, and if the source cell that receives the measurement and reports decides to perform a handover, it instructs the terminal (1i-01) to perform an L1/L2 handover in step 1i-75. In the step, MAC CE and DCI can be used as L1/L2 signaling including a handover indicator. The source cell (DU, 1i-02) or the source base station (CU, 1i-03) can receive the L1 measurement values for determining the L1/L2 handover in steps 1i-70 and 1i-75 and determine the handover. If the base station (CU, 1i-03) makes all decisions, the source cell (DU, 1i-02) transfers the L1 measurement values received from the terminal and transfers L1/L2 signaling to the terminal according to the handover decision instruction of the base station (CU, 1i-03). However, when the source cell (DU, 1i-02) makes the final decision, it does not transmit the L1 measurement value to the base station, but rather decides the handover on its own based on the measurement value criteria (threshold value and measurement value range) for making the handover decision for each candidate neighboring cell received from the previous base station, and transmits L1/L2 signaling to the terminal accordingly.

When the L1/L2 handover instruction is transmitted to the terminal, the terminal (1i-01) starts a handover procedure in step 1i-80 and starts a timer for L1/L2 handover. The timer may be a newly set timer for LTM, or may reuse a T304 timer used for an existing handover. In addition, the terminal (1i-01) applies a setting for a target cell to which L1/L2 handover is applied. This is one of the neighboring cell settings received in advance in steps 1i-30/1i-45/1i-55/1i-65.

Depending on the settings applied in step 1i-85, the terminal (1i-01) performs random access when random access is required for the target cell, and skips the random access procedure when random access is not indicated or required (when uplink synchronization has already been performed or aligned).

In step 1i-90, the terminal (1i-01) performs a handover completion procedure with the target cell. The procedure may vary depending on the method of indicating the handover completion, and may be a process of transmitting an RRCReconfiugrationComplete message if the target cell configuration is received at the RRC message level, but if the cell level or cell group level configuration is received, a new handover completion indication message (new RRC message or MAC CE) may replace the procedure.

After LTM is completed at step 1i-95, the target cell (DU2, 1i-04) informs the base station (CU, 1i-03) that the LTM procedure is completed and the terminal (1i-01) has successfully performed RRC connection to the corresponding cell. Thereafter, the base station (CU, 1i-03) instructs the source cell (1i-02) to terminate the connection to the corresponding terminal and instructs it to release the UE context.

Although omitted in the drawing, when a change in a reference cell and its configuration is required, configuration-related operations may be updated with messages in the F1 interface between the base station CU and neighboring cells and in the Xn interface between the base station CU1 and base station CU 2. In particular, when the configuration of the reference cell is changed, the LTM candidate cell configuration procedure described above is repeated to perform the reference cell configuration change and LTM candidate cell configuration change procedures, and the changed configuration information is transmitted to the terminal. In addition, although omitted in the drawing, new MAC CE and DCI may be introduced to dynamically indicate neighboring candidate cells to which L1/L2-based handover is applied, so that dynamically valid configurations may be indicated or released (previously transmitted L1/L2-based handover configurations may be released). Alternatively, the related operations may be performed internally by the base station without transmitting separate signaling to the terminal.

In addition to the above examples of the present disclosure, if there are multiple LTM candidate cells in one DU, the settings commonly applied to the cells may be duplicated, which may be inefficient. This leads to a signaling burden and a burden on the processing and buffer capacity of the terminal due to duplicate processing of the same settings. To this end, a reference setting is provided for the following settings existing in CellGroupConfig, and a reference index is indicated for LTM candidate cells and serving cells to which the same setting is applied, so that the same setting can be applied.

- Logical channel configuration

- RLC bearer configuration

- MAC cell group configuration

Refer to the settings corresponding to ASN.1 as shown in [Table 6] below.

If the reference configuration index (reference configuration ID) exists in the CellGroupConfig IE, the terminal applies the settings in the CellGroupConfig IE indicated by the reference configuration index. See the simple pseudo code below.

CellGroupConfig IE

{

ID A

RLC bearer config, LCH config, MAC config are present

SpCell X

}

CellGroupConfig IE

{

ID B

Reference ID A

RLC bearer config, LCH config, MAC config are absent

SpCell Y

}

That is, cells existing in CellGroupConfig ID B apply the RLC bearer config, LCH config, and MAC config settings existing in CellGroupConfig ID A because reference ID A was indicated.

FIG. 10 is a diagram illustrating the overall terminal operation for performing L1/L2-based beam change and handover, which is applied to examples of the present disclosure. In particular, the present disclosure features an operation when the terminal receives configuration information from a neighboring cell as a delta configuration after L1/L2-based movement is instructed through RRC configuration.

In step 1j-05, a terminal in a connected state can receive configuration information in a neighboring cell that is applied after L1/L2-based movement is instructed through an RRC reconfiguration message from a serving cell. For detailed configuration methods and contents, refer to the contents described above in drawings 6, 7, 8, and 9. In addition, although omitted, the terminal performs an operation of reporting layer 3 measurement values for neighboring cells to the base station before the RRC configuration information. In particular, the configuration information in a neighboring cell that is applied after L1/L2-based movement is instructed received in step 1j-05 is characterized in that a delta configuration is applied and transmitted based on the configuration for one reference cell.

The terminal can know what the reference cell and the configuration information for the reference cell are, which are known in advance or indicated in the RRC configuration, and since only the parts that are different (independent) from the reference cell are set for the settings for neighboring cells other than the reference cell, the signaling overhead is small. The terminal can decode the settings for the received neighboring cells based on the configuration of the reference cell at that stage, and store and manage the actually applied settings (i.e., the operation of saving the delta configured settings based on the reference cell as the full configuration by referring to the reference cell configuration) in a separate buffer and list. Alternatively, the terminal can store and manage the received RRC settings as they are in the buffer without decoding the received settings based on the reference cell and storing and managing the actually applied settings. The advantage of decoding the settings for the neighboring cells based on the reference cell at that stage and storing the actually applied settings is that when an actual L1/L2-based handover is indicated, the handover for the corresponding cell can be applied immediately, so there is no additional delay time.

The terminal may receive an RRC message including a change in RRC configuration information for specific LTM candidate cells from the base station in step 1j-10. The RRC message may include a configuration update including at least one of a cell group configuration, a radio bearer configuration, and an L3 measurement-related configuration that are applied to each LTM candidate cell. Upon receiving the message, the terminal updates the configuration for the LTM candidate cells by applying the corresponding configuration based on the delta configuration.

The terminal performs L1 measurement related to a candidate neighboring cell while maintaining a connection state with the serving cell in step 1j-15, and reports the measurement result to the serving cell according to a preset L1 measurement reporting setting method. The serving cell can determine whether to change the beam of the terminal and perform a handover based on the received measurement result, and if it is determined that a change from a specific beam of the serving cell to a specific beam of the neighboring cell is necessary, it instructs the handover and beam change of the terminal through L1/L2 signaling in step 1j-20. It is different from the existing operation in that the L1/L2 signaling can also trigger a handover. In this drawing, the L1/L2 signaling is a case where the MAC CE and DCI are used, and all information indicating a specific beam of the neighboring cell and a serving cell change are indicated in the MAC CE (when the MAC CE indicates only one beam), or specific multiple beams of the neighboring cell are indicated in the MAC CE, and in the DCI transmitted subsequent to step 1j-20, one of the multiple beams of the neighboring cell activated in the MAC CE can be selected to instruct a handover. That is, steps 1j-25 may be omitted.

In step 1j-30, the terminal checks whether a handover is indicated from the MAC CE and DCI signaling received in steps 1j-20 and 1j-25, and performs different operations thereafter. If the MAC CE and DCI received in step 1j-30 indicate a handover (if the MAC CE itself indicates a handover or if the MAC CE activates multiple beams and indicates a handover while indicating one of the corresponding beams in the DCI), the terminal performs a handover to a cell associated with the TCI state indicated in step 1j-35, and, according to the handover, also applies the settings for the corresponding target cell that were stored as pre-configuration for neighboring cells received in steps 1j-05 and 1j-10, and performs data transmission and reception using the indicated beam.

If the MAC CE and DCI received in step 1j-30 do not indicate a handover (if the MAC CE does not indicate whether to perform a handover or if the DCI does not indicate a handover), the terminal maintains the connection with the current serving cell in step 1j-40, changes the beam to the TCI state of the indicated cell, and then transmits and receives data through the corresponding beam. After the beam change, data is transmitted and received through the dedicated channels (PDCCH/PDSCH and PUCCH/PUSCH) of the corresponding beam.

In step 1j-45, L1 measurement and reporting for neighboring cells and RRM (Radio resource management) procedures, i.e. L3 measurement and channel reporting operations are performed. In this step, if the serving cell determines that a handover to a neighboring cell is necessary for the terminal based on the L1 measurement report or L3 measurement report of the terminal, it can instruct a handover for changing the serving cell.

In step 1j-50, a handover command can be received as L1/L2 signaling or an RRC message, and if the terminal receiving it is already performing beam changing to a neighboring cell and performing data transmission and reception to the cell, random access related operations can be omitted. The terminal changes the serving cell according to the handover instruction and releases the settings of the previous serving cell.

FIG. 11 is a diagram illustrating base station operations applied to examples of the present disclosure.

At step 1k-05, the base station receives an L3 measurement value report from the terminal, and based on the terminal's measurement values for surrounding frequencies and cells, determines whether the terminal requires handover and which cells are handover candidate cells.

In step 1k-10, the base station requests configuration information for L1/L2-based handover to neighboring cells and receives responses from the corresponding cells. The present disclosure is characterized in that RRC configuration information is received from neighboring cells based on delta configuration in the step, and examples are configured according to what a reference cell and reference cell configuration information are, and a message exchange method through a related F1 interface, etc. are described in detail in drawings 1f, 1g, 1h, and 1i. That is, the base station notifies neighboring cells of a reference cell and reference cell configuration, and receives configuration information for L1/L2-based handover for other neighboring cells based on the reference cell configuration.

In step 1k-15, the base station transmits to the terminal in the connected state an RRC configuration message generated including the neighboring cell configuration information received in step 1k-10. That is, the base station transmits to the terminal the configuration information in the neighboring cell applied after L1/L2-based movement is instructed from the serving cell through an RRC reconfiguration message. Detailed configuration methods and contents are described in detail in drawings 1f, 1g, 1h, and 1i. That is, the base station informs neighboring cells of the reference cell and the reference cell configuration, and receives configuration information for L1/L2-based handover to other neighboring cells based on the reference cell configuration. In addition, in the step, the base station transmits to the terminal the configuration for updating specific configuration information for LTM candidate cells when there is a change in the specific configuration information from another base station or a DU and LTM candidate serving cell within the base station.

Thereafter, in step 1k-20, the base station receives an L1 measurement value from the terminal, and the measurement value may be a measurement value for a neighboring cell (non-serving cell) supporting L1/L2-based mobility. The serving cell may determine whether to change the beam of the terminal based on the received measurement result, and if it is determined that a change from a specific beam of the serving cell to a specific beam of the neighboring cell is necessary, it instructs the terminal to change the beam through L1/L2 signaling in step 1k-25. The L1/L2 signaling may be MAC CE or DCI, and includes information instructing a change to a specific beam of the neighboring cell. In addition, a handover may also be simultaneously instructed through L1/L2 signaling in the corresponding step. When a handover is simultaneously instructed, the serving cell performs a handover procedure, and when the handover with the target cell is completed, deletes the terminal context and releases the connection. At this time, it is characterized in that the measurement value for determining whether to perform the handover is an L1 measurement.

If the above L1/L2 signaling does not include a handover procedure, the terminal maintains a connection state in step 1k-30. In this step, the terminal performs data transmission and reception through dedicated channels (PDCCH/PDSCH and PUCCH/PUSCH) by applying configuration information for preset neighboring cells. The terminal can also return to the current serving cell on the link with the neighboring cell. In step 1k-30, the terminal can receive additional L1/L3 measurement reports while in the connection state with the terminal, and if the serving cell determines that a handover to the neighboring cell is necessary, the terminal can instruct a handover message to instruct a change of serving cell.

At step 1k-35, when the terminal changes the serving cell according to the handover instruction, the terminal releases the settings of the previous serving cell.

Fig. 12 is a block diagram illustrating the internal structure of a terminal to which the present disclosure is applied.

Referring to FIG. 12, the terminal includes an RF (Radio Frequency) processing unit (1l-10), a baseband processing unit (1l-20), a storage unit (1l-30), and a control unit (1l-40).

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

The above baseband processing unit (1l-20) 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 (1l-20) generates complex symbols by encoding and modulating a transmission bit stream. In addition, when receiving data, the baseband processing unit (1l-20) restores a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (1l-10). For example, in the case of following the OFDM (orthogonal frequency division multiplexing) method, when transmitting data, the baseband processing unit (1l-20) generates complex symbols by encoding and modulating a transmission bit stream, maps the complex symbols to subcarriers, and then configures OFDM symbols by performing an IFFT (inverse fast Fourier transform) operation and CP (cyclic prefix) insertion. In addition, when receiving data, the baseband processing unit (1l-20) divides the baseband signal provided from the RF processing unit (1l-10) into OFDM symbol units, restores signals mapped to subcarriers through an FFT (fast Fourier transform) operation, and then restores the received bit string through demodulation and decoding.

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

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

The above control unit (1l-40) controls the overall operations of the terminal. For example, the control unit (1l-40) transmits and receives signals through the baseband processing unit (1l-20) and the RF processing unit (1l-10). In addition, the control unit (1l-40) records and reads data in the storage unit (1l-30). For this purpose, the control unit (1l-40) may include at least one processor. For example, the control unit (1l-40) may include a CP (communication processor) that performs control for communication and an AP (application processor) that controls upper layers such as application programs.

Figure 13 is a block diagram showing the configuration of a base station according to the present disclosure.

Referring to FIG. 12, the base station is configured to include an RF processing unit (1m-10), a baseband processing unit (1m-20), a backhaul communication unit (1m-30), a storage unit (1m-40), and a control unit (1m-50).

The RF processing unit (1m-10) above performs functions for transmitting and receiving signals through a wireless channel, such as signal band conversion and amplification. That is, the RF processing unit (1m-10) up-converts a baseband signal provided from the baseband processing unit (1m-20) into an RF band signal and transmits it through an antenna, and down-converts an RF band signal received through the antenna into a baseband signal. For example, the RF processing unit (1m-10) may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, etc. In the drawing, only one antenna is shown, but the first access node may have multiple antennas. In addition, the RF processing unit (1m-10) may include multiple RF chains. Furthermore, the RF processing unit (1m-10) may perform beamforming. For the above beamforming, the RF processing unit (1m-10) can adjust the phase and size of each signal transmitted and received through multiple antennas or antenna elements. The RF processing unit can perform a downward MIMO operation by transmitting one or more layers.

The above baseband processing unit (1m-20) 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 (1m-20) encodes and modulates a transmission bit stream to generate complex symbols. In addition, when receiving data, the baseband processing unit (1m-20) restores a reception bit stream by demodulating and decoding a baseband signal provided from the RF processing unit (1m-10). For example, in the case of OFDM, when transmitting data, the baseband processing unit (1m-20) encodes and modulates a transmission bit stream to generate complex symbols, 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 (1m-20) divides the baseband signal provided from the RF processing unit (1m-10) into OFDM symbol units, restores signals mapped to subcarriers through FFT operation, and then restores the received bit stream through demodulation and decoding. The baseband processing unit (1m-20) and the RF processing unit (1m-10) transmit and receive signals as described above. Accordingly, the baseband processing unit (1m-20) and the RF processing unit (1m-10) may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

The above backhaul communication unit (1m-30) provides an interface for performing communication with other nodes within the network. That is, the backhaul communication unit (1m-30) converts a bit string transmitted from the main base station to another node, such as an auxiliary base station or core network, into a physical signal, and converts a physical signal received from the other node into a bit string.

The above storage unit (1m-40) stores data such as basic programs, application programs, and setting information for the operation of the above base station. In particular, the storage unit (1m-40) can store information on bearers allocated to connected terminals, measurement results reported from connected terminals, and the like. In addition, the storage unit (1m-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 (1m-40) provides stored data according to a request from the control unit (1m-50).

The above control unit (1m-50) controls the overall operations of the above base station. For example, the control unit (1m-50) transmits and receives signals through the baseband processing unit (1m-20) and the RF processing unit (1m-10) or through the backhaul communication unit (1m-30). In addition, the control unit (1m-50) records and reads data in the storage unit (1m-40). For this purpose, the control unit (1m-50) may include at least one processor.

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

Meanwhile, the embodiments disclosed in the specification and drawings described above are only specific examples presented to easily explain and aid understanding of the contents of the present invention, and are not intended to limit the scope of the present invention. Therefore, the scope of the present invention should be interpreted as including all changes or modified forms derived based on the technical idea of the present invention in addition to the embodiments disclosed herein.

Claims (14)

In a terminal method in a communication system, A step of receiving, from a base station, a first radio resource control (RRC) message including first information on LTM (layer 1/layer 2 triggered mobility) candidate setting; A step of receiving a second RRC message including second information about the LTM candidate setting from the base station; and A step of reporting L1 (layer 1) measurements performed on candidate cells based on the second information to the base station, The second information includes an RRC setting for updating the LTM candidate setting, A method of a terminal, characterized in that the RRC configuration including cell group configuration information for the candidate cells further includes updated information of at least one of a radio bearer configuration or a measurement configuration included in the first RRC message. In the first paragraph, The second information includes information about each of the candidate cells and information about criteria settings that are commonly applied to the candidate cells. A terminal method, characterized in that the information for each of the above candidate cells includes an ID (identity) of the candidate cell and the RRC setting corresponding to the candidate cell. In the first paragraph, At least one of the updated information of the above radio bearer setup and the above measurement setup is determined by the CU (central unit) of the base station, A terminal method, characterized in that cell group setting information for the above candidate cells is generated by each of the above candidate cells. In a method of a base station in a communication system, A step of transmitting, to a terminal, a first radio resource control (RRC) message including first information on LTM (layer 1/layer 2 triggered mobility) candidate setting; A step of obtaining RRC settings for updating the above LTM candidate settings; A step of transmitting a second RRC message including second information about the LTM candidate settings, including the RRC settings, to the terminal; and A step of receiving an L1 (layer 1) measurement report for candidate cells based on the second information from the terminal, A method of a base station, characterized in that the RRC configuration including cell group configuration information for the candidate cells further includes updated information of at least one of a radio bearer configuration or a measurement configuration included in the first RRC message. In paragraph 4, The second information includes information about each of the candidate cells and information about criteria settings that are commonly applied to the candidate cells. A method of a base station, characterized in that the information for each of the above candidate cells includes an ID (identity) of the candidate cell and the RRC setting corresponding to the candidate cell. In the fourth paragraph, the step of obtaining the RRC settings comprises: A method of a base station, characterized by comprising a step of generating updated information of at least one of the radio bearer setup and the measurement setup. In the fourth paragraph, the step of obtaining the RRC settings comprises: A step in which the CU (central unit) of the above base station transmits a message requesting setup information for handover to each of the candidate cells through the F1 interface; and A method of a base station, characterized by comprising a step of receiving cell group configuration information generated by each of the candidate cells based on the message from each of the candidate cells through the F1 interface. In a terminal in a communication system, Transmitter and receiver; and A control unit configured to control the transceiver to receive, from a base station, a first radio resource control (RRC) message including first information about LTM (layer 1/layer 2 triggered mobility) candidate configuration, control the transceiver to receive, from the base station, a second RRC message including second information about the LTM candidate configuration, and control the transceiver to report, to the base station, L1 (layer 1) measurements performed on candidate cells based on the second information. The second information includes an RRC setting for updating the LTM candidate setting, A terminal characterized in that the RRC configuration including cell group configuration information for the candidate cells further includes updated information of at least one of a radio bearer configuration or a measurement configuration included in the first RRC message. In Article 8, The second information includes information about each of the candidate cells and information about criteria settings that are commonly applied to the candidate cells. A terminal characterized in that the information for each of the above candidate cells includes an ID (identity) of the candidate cell and the RRC setting corresponding to the candidate cell. In Article 8, At least one of the updated information of the above radio bearer setup and the above measurement setup is determined by the CU (central unit) of the base station, A terminal characterized in that cell group setting information for the above candidate cells is generated by each of the above candidate cells. In a base station in a communication system, Transmitter and receiver; and A control unit configured to control the transceiver to transmit, to a terminal, a first radio resource control (RRC) message including first information about LTM (layer 1/layer 2 triggered mobility) candidate settings, obtain an RRC setting for updating the LTM candidate settings, control the transceiver to transmit, to the terminal, a second RRC message including second information about the LTM candidate settings, including the RRC setting, and control the transceiver to receive, from the terminal, an L1 (layer 1) measurement report for candidate cells based on the second information. A base station, characterized in that the RRC configuration including cell group configuration information for the candidate cells further includes updated information of at least one of a radio bearer configuration or a measurement configuration included in the first RRC message. In Article 11, The second information includes information about each of the candidate cells and information about criteria settings that are commonly applied to the candidate cells. A base station, characterized in that the information for each of the candidate cells includes an ID (identity) of the candidate cell and the RRC settings corresponding to the candidate cell. In Article 11, A base station, characterized in that the control unit generates updated information of at least one of the radio bearer settings and the measurement settings. In Article 11, A base station, characterized in that the control unit controls the transceiver to transmit a message requesting setup information for handover to each of the candidate cells through the F1 interface from the CU (central unit) of the base station, and controls the transceiver to receive cell group setup information generated by each of the candidate cells based on the message from each of the candidate cells through the F1 interface.

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