Structure for supporting inter-cell mobility based on layer 1 / layer 2 in next generation mobile communication system, and signaling method and apparatus therefor

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. According to the present disclosure, a method performed by a terminal in a wireless communication system comprises the steps of: receiving, from a base station, a radio resource control (RRC) message including a configuration of a candidate of a target cell for handover; receiving a media access control, MAC, control element, CE, from the base station, the MAC CE including information indicating one of the candidates of the target cell; performing handover to a target cell indicated by the MAC CE; and transmitting a message indicating completion of the handover to the base station.

Description

Technical Field

[0001] The present disclosure relates to a mobile communication system, and more particularly, to a structure, a signaling method and a device for supporting inter-cell mobility in a mobile communication system. Background Art

[0002] The fifth generation (5G) mobile communication technology defines a wide frequency band that enables high transmission rates and new services, and can be implemented not only in "below 6 GHz" frequency bands such as 3.5 GHz, but also in ultra-high frequency ("above 6 GHz") frequency bands called millimeter waves such as 28 GHz or 39 GHz. In addition, the implementation of 6G mobile communication technology called "super 5G system" in the terahertz (THz) frequency band (e.g., 95 GHz to 3 THz frequency band) is being considered in order to achieve a transmission rate fifty times faster than that of 5G mobile communication technology and ultra-low latency reduced to one-tenth of that of 5G mobile communication technology.

[0003] At the beginning of the development of 5G mobile communication technology, in order to support services and meet performance requirements for enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC) and massive machine-type communication (mMTC), standardization has been carried out on the following technologies: beamforming and massive MIMO for reducing radio wave path loss and increasing radio wave transmission distance in millimeter waves, supporting parameters for dynamic operation of efficient utilization of millimeter wave resources and time slot formats (for example, operating multiple subcarrier spacings), initial access schemes for supporting multi-beam transmission and wide frequency bands, definition and operation of bandwidth parts (BWPs), new channel coding schemes such as low-density parity-check (LDPC) codes for large-scale data transmission and polar codes for highly reliable transmission of control information, L2 preprocessing, and network slicing for providing dedicated networks dedicated to specific services.

[0004] Currently, with respect to the services that 5G mobile communication technology is initially intended to support, the industry is continuously discussing the improvement of 5G mobile communication technology and the enhancement of its performance, and physical layer standardization is underway on technologies such as vehicle-to-everything (V2X) for helping autonomous vehicles make driving decisions based on information about the location and status of vehicles sent by vehicles and for improving user convenience, new radio unlicensed (NR-U) for system operations that comply with various regulatory-related requirements in unlicensed frequency bands, a low power consumption scheme for NR terminals (UE energy saving), a non-terrestrial network (NTN) as a terminal satellite direct communication for providing coverage in areas where communication with terrestrial networks is not possible, and positioning.

[0005] In addition, the standardization of air interface architecture / protocols for technologies such as smart factories (Industrial Internet of Things, IIOT) for supporting new services by interworking and integrating with other industries, Integrated Access and Backhaul (IAB) for providing nodes for network service area extension by integrating and supporting wireless backhaul links and access links, mobility enhancement including conditional handover and dual active protocol stack (DAPS) handover, two-step random access for simplifying the random access process (2-step RACH for NR), and system architecture / service standardization for technologies such as 5G baseline architecture (e.g., service-based architecture, service-based interface) for integrating network function virtualization (NFV) and software defined network (SDN) technologies, and mobile edge computing (MEC) for terminals to receive services based on their locations is also advancing.

[0006] When such 5G mobile communication systems are commercialized, a dramatically increasing number of connected devices will be connected to the communication network, and therefore enhancements in the functions and performance of the 5G mobile communication systems and integrated operations of the connected devices are expected to be required. To this end, new research will be conducted involving technologies such as 5G performance improvement and complexity reduction by utilizing extended reality (XR) for efficient support of augmented reality (AR), virtual reality (VR) and mixed reality (MR), artificial intelligence (AI) and machine learning (ML), AI service support, metaverse service support, and drone communications.

[0007] In addition, such developments in 5G mobile communication systems will lay the foundation for the development of new waveforms for securing coverage in the terahertz band of 6G mobile communication technology, full-dimensional MIMO (FD-MIMO), multi-antenna transmission technologies such as array antennas and massive antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional spatial multiplexing technology using orbital angular momentum (OAM), reconfigurable smart surface (RIS) technology, full-duplex technology for improving frequency efficiency and system networks in 6G mobile communication technology, satellites, AI-based communications that utilize artificial intelligence (AI) from the design stage and internalize end-to-end AI support functions to achieve system optimization, and next-generation distributed computing technologies that enable services whose complexity exceeds the computing power limits of terminals by utilizing ultra-high-performance communications and computing resources. Summary of the invention

[0008] [Technical issues]

[0009] The present disclosure enables a terminal to measure and report beams belonging to other cells while receiving services from a current serving cell through a specific beam, and if the beam of the adjacent cell is better, perform cell switching to the adjacent cell. The purpose of the present disclosure is to solve the inefficient part of the traditional cell switching process that requires a long delay time, and specifically, in order to reduce the delay time of handing over to the adjacent cell, the present disclosure solves the overall operation by pre-transmitting relevant configuration information and indicating this situation through L1 / L2 signaling.

[0010] [Technical solution]

[0011] In order to solve the above problem, the present disclosure provides a method performed by a terminal in a wireless communication system. The method may include: receiving a radio resource control (RRC) message including a configuration of a candidate target cell for handover from a base station; receiving a media access control (MAC) control element (CE) including information indicating one of the candidate target cells from the base station; performing handover to the target cell indicated by the MAC CE; and sending an RRC completion message indicating completion of the handover to the base station.

[0012] In addition, in order to solve the above problem, the present disclosure provides a method performed by a base station in a wireless communication system. The method may include: sending a radio resource control (RRC) message including a configuration of a candidate target cell for handover to a terminal; sending a media access control (MAC) control element (CE) including information indicating one of the candidate target cells to the terminal; and receiving an RRC completion message indicating handover completion from the terminal when the terminal hands over to the target cell indicated by the MAC CE.

[0013] In addition, in order to solve the above problems, the present disclosure provides a terminal in a wireless communication system. The terminal may include: a transceiver; and a controller connected to the transceiver, wherein the controller may be configured to: receive a radio resource control (RRC) message including a configuration of a candidate target cell for handover from a base station; receive a media access control (MAC) control element (CE) including information indicating one of the candidate target cells from the base station; perform handover to the target cell indicated by the MAC CE; and send an RRC completion message indicating completion of the handover to the base station.

[0014] In addition, in order to solve the above problems, the present disclosure provides a base station in a wireless communication system. The base station may include: a transceiver; and a controller connected to the transceiver, wherein the controller may be configured to: send a radio resource control (RRC) message including a configuration of a candidate target cell for handover to a terminal; send a media access control (MAC) control element (CE) including information indicating one of the candidate target cells to the terminal; and receive an RRC completion message indicating handover completion from the terminal when the terminal hands over to the target cell indicated by the MAC CE.

[0015] [Beneficial Effects]

[0016] By using the layer 1 measurement and reporting method for beam switching and handover based on layer 1 and layer 2 (L1 / L2) proposed in the present disclosure, the terminal can determine the handover operation by beam measurement on a cell other than the serving cell. In addition, according to the present disclosure, the terminal can support beam switching and handover operations to neighboring cells through beam measurement based on layer 1, and the delay time is reduced compared to the traditional process, so that the terminal can send and receive data after changing the beam and handing over to another cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a diagram showing the architecture of a next-generation mobile communication system to which the present disclosure is applied.

[0018] Figure 2 is a diagram showing a structure of a radio protocol in a next-generation mobile communication system to which the present disclosure can be applied.

[0019] Figure 3 is a diagram showing the architecture of another next-generation mobile communication system to which the present disclosure can be applied.

[0020] Figure 4 is a diagram showing a scenario for inter-cell beam management mentioned in the present disclosure, in which the UE sends and receives data through the beam of the transmit / receive point (TRP) of a neighboring cell that supports L1 / L2-based beam switching while maintaining a connection with the serving cell.

[0021] Figure 5A is a diagram illustrating a scenario as an embodiment considered in the present disclosure, in which the UE sends and receives data after performing a serving cell and beam change to a TRP of a cell supporting L1 / L2-based beam switching.

[0022] Figure 5Bis a diagram illustrating a scenario as an embodiment considered in the present disclosure, in which the UE sends and receives data after performing a serving cell and beam change to a TRP of a cell supporting L1 / L2-based beam switching.

[0023] Figure 6 It shows that the Figure 4 Diagram of the overall operation of inter-cell beam management.

[0024] Fig. 7A is a diagram illustrating a method for configuring candidate neighbor cells supporting L1 / L2 inter-cell handover proposed in the present disclosure.

[0025] Figure 7B is a diagram illustrating a method for configuring candidate neighbor cells supporting L1 / L2 inter-cell handover proposed in the present disclosure.

[0026] Fig. 8A It is the MAC CE and DCI format proposed in this disclosure for L1 / L2 based beam switching and handover.

[0027] Figure 8B It is the MAC CE and DCI format proposed in this disclosure for L1 / L2 based beam switching and handover.

[0028] Fig. 9 1 is a diagram showing an overall operation of performing handover after applying L1 / L2 inter-cell beam management as Embodiment 1 applied to the present disclosure.

[0029] Fig.10 1 is a diagram showing the overall operation of performing L1 / L2 inter-cell handover as embodiment 2 applied to the present disclosure.

[0030] Fig.11 is a diagram illustrating UE operation of indicating L1 / L2 inter-cell beam switching and handover using only MAC CE in overall UE operation for performing L1 / L2-based beam switching and handover, which is applied to an embodiment of the present disclosure.

[0031] Fig.12 is a diagram illustrating UE operation of indicating L1 / L2 inter-cell beam switching and handover using MAC CE and DCI in overall UE operation for performing L1 / L2-based beam switching and handover, which is applied to an embodiment of the present disclosure.

[0032] Fig.13 is a diagram illustrating the operation of a base station applied to an embodiment of the present disclosure.

[0033] Fig.14 is a block diagram showing the internal structure of a UE to which the present disclosure is applied.

[0034] Fig.15 is a block diagram showing the structure of a base station according to the present disclosure. DETAILED DESCRIPTION

[0035] Hereinafter, the working principle of the present disclosure will be described in detail with reference to the accompanying drawings. When explaining the present disclosure below, the description of the well-known functions and structures incorporated herein may be omitted to avoid blurring the subject matter of the present disclosure. The terms described below are defined in consideration of their functions in the present disclosure, and these terms may vary according to the intention or habit of the user or operator. Therefore, their meanings should be determined based on the full content of this specification. Those terms used in the following description for identifying access nodes, indicating network entities, indicating messages, indicating interfaces between network entities, and indicating various identification information are used as illustrations for ease of description. Therefore, the present disclosure is not limited by the terms to be described later, and other terms relating to objects with equivalent technical meanings may be used.

[0036] For ease of description, the present disclosure uses terms and names defined in the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) standard. However, the present disclosure is not limited by the above terms and names and can be equally applied to systems conforming to other standards.

[0037] Figure 1 is a diagram showing the architecture of a next-generation mobile communication system to which the present disclosure is applied.

[0038] refer to Figure 1 As shown in the figure, the radio access network of the next generation mobile communication system may be composed of a new radio node B (NR NB or next generation base station) 1-10 and a new radio core network (NR CN or next generation core network (NG CN)) 1-05. A new radio user equipment (hereinafter referred to as NR UE or terminal) 1-15 may be connected to an external network through the NR NB 1-10 and the NR CN 1-05.

[0039] exist Figure 1In the present invention, the NR NB 1-10 may correspond to an evolved Node B (eNB) of a conventional LTE system. The NR NB 1-10 may be connected to the NR UE 1-15 through a radio channel, and it may provide services superior to those of the conventional Node B. In the next generation mobile communication system, all user services may be served through a shared channel. Therefore, an entity that performs scheduling by collecting status information such as a buffer status, an available transmission power status, and a channel status of each UE may be required, and the NR NB 1-10 may be responsible for this. In a typical case, one NR NB 1-10 controls multiple cells. In order to achieve ultra-high-speed data transmission compared to the current LTE, a bandwidth exceeding the conventional maximum bandwidth may be utilized. In addition, beamforming technology may be additionally used with orthogonal frequency division multiplexing (OFDM) used as a radio access technology. In addition, an adaptive modulation and coding (AMC) scheme that determines a modulation scheme and a channel coding rate to match the channel status of the UE may be applied. The NRCN 1-05 may perform functions such as mobility support, bearer configuration, and quality of service (QoS) configuration. NR CN 1-05 is an entity responsible not only for mobility management of UE 1-15 but also for various control functions of UE 1-15, and can be connected to multiple base stations. In addition, the next generation mobile communication system can interwork with the traditional LTE system, and NR CN can be connected to MME 1-25 through a network interface. MME is connected to eNB 1-30 which is a traditional base station.

[0040] Figure 2 is a diagram showing a structure of a radio protocol in a next-generation mobile communication system to which the present disclosure can be applied.

[0041] refer to Figure 2 In the UE or NR gNB, the radio protocol of the next generation mobile communication system may include NR SDAP2-01 or 2-45, NR PDCP 2-05 or 2-40, NR RLC 2-10 or 2-35, and NR MAC 2-15 or 2-30.

[0042] The main functions of NR SDAP 2-01 or 2-45 may include some of the following functions.

[0043] -User data transmission function (transmission of user plane data)

[0044] - Mapping function between QoS flows and data bearers for uplink and downlink (mapping between QoS flows and DRBs for both DL and UL)

[0045] -QoS flow ID marking function for uplink and downlink (QoS flow ID is marked in both DL and UL packets)

[0046] - Functionality for mapping Reflective QoS flows to data bearers for uplink SDAP PDUs (Mapping of Reflective QoS flows to DRBs for UL SDAPPDUs)

[0047] For the SDAP entity, the UE can be configured with the function of whether to use the header of the SDAP entity or whether to use the SDAP entity for each PDCP entity, bearer or logical channel through an RRC message. In addition, if the SDAP header is configured, the NAS reflection QoS 1-bit indication and AS reflection QoS 1-bit indication of the SDAP header can command the UE to update or reconfigure the mapping information between the QoS flow and data bearer for uplink and downlink. The SDAP header may include QoS flow ID information indicating QoS. QoS information can be used as data processing priority and scheduling information for supporting smooth services.

[0048] The main functions of NR PDCP 2-05 or 2-40 may include some of the following functions.

[0049] - Header compression and decompression function (Header compression and decompression: ROHC only)

[0050] -User data transmission function (transmission of user data)

[0051] - Sequential delivery function (sequential delivery of upper layer PDU)

[0052] - Out-of-order delivery function (out-of-order delivery of upper layer PDU)

[0053] - Reordering function (for reordering of received PDCP PDUs)

[0054] - Duplicate detection function (duplicate detection of lower layer SDU)

[0055] -Retransmission function (retransmission of PDCP SDU)

[0056] - Encryption and decryption functions (encryption and decryption)

[0057] -Timer-based SDU discard function (Timer-based SDU discard in uplink)

[0058] In the above description, the reordering function of the NR PDCP entity may indicate reordering of PDCP PDUs received from a lower layer in sequence based on a PDCP sequence number (SN), and may include transmitting data to a higher layer in a reordered order, directly transmitting data without considering the order, recording lost PDCP PDUs by reordering, reporting the status of lost PDCP PDUs to the transmitting side, or requesting retransmission of lost PDCP PDUs.

[0059] The main functions of NR RLC 2-10 or 2-35 may include some of the following functions.

[0060] -Data transmission function (transmission of upper layer PDU)

[0061] - Sequential delivery function (sequential delivery of upper layer PDU)

[0062] - Out-of-order delivery function (out-of-order delivery of upper layer PDU)

[0063] -ARQ function (error correction through ARQ)

[0064] - Concatenation, segmentation and reassembly functions (concatenation, segmentation and reassembly of RLC SDU)

[0065] -Re-segmentation function (resegmentation of RLC data PDU)

[0066] - Reordering function (reordering of RLC data PDUs)

[0067] - Duplicate detection function (duplicate detection)

[0068] - Error detection function (protocol error detection)

[0069] -RLC SDU discard function (RLC SDU discard)

[0070] -RLC re-establishment function (RLC re-establishment)

[0071] In the above description, the sequential delivery of the NR RLC entity may indicate that the RLC SDU received from the lower layer is sequentially delivered to the upper layer, and may include: when multiple RLC SDUs belonging to one original RLC SDU are received after segmentation, reassembling and delivering the RLC SDU; reordering the received RLC PDU based on the RLC sequence number SN or the PDCP SN; recording the lost RLC PDU by reordering; reporting the status of the lost RLC PDU to the transmitting side; and requesting retransmission of the lost RLC PDU. If there is a lost RLC SDU, the sequential delivery of the NR RLC entity may include sequentially delivering only the RLC SDU before the lost RLC SDU to the upper layer; or, although there is a lost RLC SDU, if a designated timer has expired, its sequential delivery may include sequentially delivering all RLC SDUs received before the timer is started to the upper layer; or, although there is a lost RLC SDU, if a designated timer has expired, its sequential delivery may include sequentially delivering all RLC SDUs received so far to the upper layer. In addition, the NR RLC entity may process the RLC PDUs in the order of reception, regardless of the order of the sequence numbers, and deliver them to the NR PDCP entity in an out-of-order delivery manner. In the case of receiving segmentation, the NR RLC entity may reconstruct a complete RLC PDU from the segments stored in the buffer or received later, and deliver it to the NR PDCP entity. The NR RLC layer may not include the cascading function, which may be performed by the NR MAC layer or may be replaced by the multiplexing function of the NR MAC layer.

[0072] In the above description, the out-of-order delivery of the NR RLC entity may indicate a function of directly transmitting the RLC SDUs received from the lower layer to the higher layer regardless of their order. If a plurality of RLC SDUs belonging to one original RLC SDU are received after segmentation, the out-of-order delivery of the NR RLC entity may include reassembly and delivery of the RLC SDUs. The out-of-order delivery of the NR RLC entity may include storing the RLC SN or PDCP SN of the received RLC PDUs and sorting them to record the lost RLC PDUs.

[0073] NR MAC 2-15 or 2-30 can be connected to several NR RLC entities configured in one UE, and the main functions of NR MAC may include some of the following functions.

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

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

[0076] -Scheduling information reporting function (Scheduling information reporting)

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

[0078] - Priority handling between logical channels (priority handling between logical channels of a UE)

[0079] - Priority handling function between UEs (priority handling between UEs through dynamic scheduling)

[0080] -MBMS service identification function (MBMS service identification)

[0081] -Transmission format selection function (Transmission format selection)

[0082] - Fill function (fill)

[0083] The NR PHY 2-20 or 2-25 may synthesize OFDM symbols from higher layer data through channel coding and modulation and transmit them through a radio channel, or may demodulate and channel decode OFDM symbols received through a radio channel and forward the result to a higher layer.

[0084] Figure 3 is a diagram showing the architecture of another next-generation mobile communication system to which the present disclosure can be applied.

[0085] refer to Figure 3, a cell served by a beam-based NR gNB 3-05 may consist of a plurality of transmit receive points (TRPs) 3-10, 3-15, 3-20, 3-25, 3-30, 3-35, 3-40. TRPs 3-10 to 3-40 represent blocks separated from a conventional NR base station (eNB) having some functions for transmitting and receiving physical signals, and are composed of a plurality of antennas. The NR gNB 3-05 may also be referred to as a central unit (CU), and the TRP may also be referred to as a distributed unit (DU). The functions of the NR gNB 3-05 and the TRP may be configured by extracting some layers from the PDCP / RLC / MAC / PHY layers, as shown in 3-45. That is, TRP 3-15 or 3-25 may include only the PHY layer to perform the functions of the corresponding layer, TRP 3-10, 3-35 or 3-40 may include only the PHY layer and the MAC layer to perform the functions of the corresponding layer, and TRP 3-20 or 3-30 may include only the PHY layer, the MAC layer and the RLC layer to perform the functions of the corresponding layer. In particular, TRPs 3-10 to 3-40 may use beamforming technology to send and receive data by generating narrow beams in various directions using multiple transmit / receive antennas. UE 3-50 is connected to NR gNB 3-05 and an external network through TRPs 3-10 to 3-40. NR gNB 3-05 collects status information of UE such as buffer status, available transmission power status and channel status to provide services to users, and schedules them to support the connection between UE and the core network (CN), especially AMF / SMF 3-50.

[0086] The TRP in the present disclosure may be assumed to have a structure 3-15 or 3-25 that includes only a PHY layer and performs the functions of the corresponding layers.

[0087] Figure 4 : is a diagram showing the scenario of inter-cell beam management mentioned in the present disclosure, in which the UE sends and receives data through the beam of the transmit / receive point (TRP) of the neighboring cell that supports L1 / L2-based beam switching while maintaining a connection with the serving cell.

[0088] Although the figure describes a case where multiple cells (TRP 1-cell 1 4-10, TRP 2-cell 2 4-15) exist within one distributed unit (DU) 4-05, the entire content of the present disclosure can also be applied to the case between DUs (each DU constitutes a TRP-cell). In addition, throughout the disclosure, a cell (TRP 2, cell 2) that is not a serving cell supporting L1 / L2-based mobility (beam switching and serving cell change) may be interchangeably referred to as a neighboring cell, a non-serving cell, an additional cell having a PCI different from that of the serving cell, etc.

[0089] In the conventional UE beam switching process (4-45), the UE 4-20 may transmit and receive data through the TRP 1 (4-10) of the serving cell 1 in a connected state, and the beam of the UE may be aligned with the TCI state 1 as the best beam (4-25, 4-30). At this stage, the UE may receive configuration information for L3 channel measurement (radio resource management (RRM)) related to an additional cell having a different PCI from the serving cell (TRP2-cell 2, 4-15) from the serving cell 1 (4-10) through RRC configuration information, and may perform an L3 measurement operation on the corresponding frequency and cell (4-46).

[0090] Thereafter, serving cell 1 (TRP 1-cell 1, 4-10) may command handover to cell 2 (TRP 2-cell 2, 4-15) based on the reported measurement value (4-47), and after the handover is completed, additional RRC configuration information may be sent to UE 4-20 through TRP 2-cell 2 (4-15) (4-48). The RRC configuration information may include at least one of UL / DL configuration information or L1 measurement related configuration (CSI-RS measurement and reporting) in cell 2, and may specifically include TCI state configuration information for PDCCH and PDSCH channels. The UE may perform L1 measurement according to the configuration (4-49), and the base station may update the TCI state through L1 / L2 signaling according to the measurement report (4-50). Here, TCI state 2 (4-40) may be indicated as the best beam. In this case, the serving cell is cell 1 before the handover, and cell 2 becomes the serving cell after the handover. That is, even after the handover, many processes and time may be required until the best beam is indicated.

[0091] Different from the above-mentioned conventional UE beam switching process (4-45), the improved beam switching technique (4-55) considered in the present disclosure is as follows.

[0092] Serving cell 1 (4-10) may transmit a beam configuration associated with an additional cell having a different PCI from the serving cell (TRP 2-cell 2, 4-15) to the UE through RRC configuration information (4-56). As a method of setting a beam configuration associated with an additional cell having a PCI different from that of the serving cell (TRP2-cell 2, 4-15), that is, associating a TCI state corresponding to TRP 2, the following method of associating and indicating a new cell ID (physical cell ID (PCI), additional PCI-r17) may be applied.

[0093]

[0094] In addition, the unified TCI state framework can be applied to inter-cell beam management. The unified TCI state framework applies the common TCI state framework to uplink and downlink as well as common and dedicated channels, and can be set to joint UL / DL mode or separate UL / DL mode.

[0095]

[0096] 1. Joint UL / DL mode: Set UL and DL to share the same TCI configuration (in PDSCH-Config)

[0097] 2. Separate UL / DL mode: UL and DL provide their own TCI configurations. The TCI state for DL ​​follows the settings in dl-OrJoint-TCIStateList-r17 (in PDSCH-Config), and the TCI state for UL follows ul-TCI-StateList-r17 (in BWP-UplinkDedicated).

[0098]

[0099] After the UE is provided with a configuration for TRP 2-cell 2 while being in an RRC connected state with serving cell 1, the UE may perform L1 measurements on the corresponding TRP 2-cell 2 according to the configuration and report the results to the serving cell (cell 1, 4-10) (4-57). When it is determined based on the measurement results that it is necessary to switch from the serving cell beam (TCI state 1, 4-25, 4-30) to a specific beam (TCI state 2, 4-35, 4-40) of TRP 2 (cell 2, 4-15), the serving cell may trigger beam switching and indicate it to the UE through L1 / L2 signaling (4-58). The UE may switch the beam to the specific beam (TCI state 2, 4-40) of TRP 2 (cell 2, 4-15) based on the indication, and perform physical channel establishment and high layer establishment associated with the configured beam. While connected to the serving cell (cell 1, 4-10), the UE can perform data transmission and reception (PDCCH / PDSCH reception, PUCCH / PUSCH transmission) by using the channel link of TRP 2 (cell 2, 4-15). That is, transmission and reception on the common control channel are performed through the serving cell (cell 1, 4-10).

[0100] Thereafter, the UE may perform L3 measurement according to the measurement configuration set in the independent serving cell (4-59). In addition, the UE may receive a handover command message from the serving base station (cell 1) and perform handover from the serving cell to cell 2 (4-60). Through this method (4-55), the UE may perform data transmission to a specific TRP 2 of cell 2 supporting L1 / L2-based mobility and data reception from a specific TRP 2 of cell 2 supporting L1 / L2-based mobility in a state connected to the serving cell, and may continue to use the corresponding beam even after the handover.

[0101] The following describes the RRC configuration for settings and operations related to L1 measurement and reporting at step 4-57. These contents are basically applied to the following embodiments of the present disclosure, and improved techniques may be added in future embodiments.

[0102] 1. CSI measurement configuration

[0103] -CSI-RS resources and resource pools to be measured (nzp-CSI-RS, csi-IM, csi-SSB)

[0104] - Configuration of CSI-RS resources to be measured (aperiodic, semi-persistent) and configuration of triggers

[0105] - When CSI-RS resources refer to SSB resources, additional PCI information is provided to enable L1 measurement in neighboring cells (up to 7 neighboring cells (PCIs) can be added for one serving cell).

[0106]

[0107] 2. CSI report configuration

[0108] - Report type: periodic reporting, semi-periodic reporting on PUCCH, semi-periodic reporting on PUSCH, aperiodic reporting on PUSCH (periodic, semi-persistent for PUCCH, semi-persistent for PUSCH, aperiodic)

[0109] - Report quantity

[0110] - Other settings required for reporting

[0111] Figure 5A and Figure 5Bis a diagram showing a scenario as an embodiment considered in the present disclosure, in which the UE sends and receives data after performing a serving cell and beam change to a TRP of a cell supporting L1 / L2-based beam switching. Although these figures describe a scenario in which multiple cells (TRP 1-cell 1, TRP2-cell 2; 5-10, 5-15, 5-40, 5-45) exist within one distributed unit (DU) 5-05 or 5-35, the entire contents of the present disclosure can also be applied to the inter-DU scenario (each DU constitutes a TRP-cell).

[0112] The improved beam switching techniques (5-25 and 5-75) considered in these embodiments are as follows.

[0113] 1. Embodiment 1 (5-25): Performing L1 / L2 handover after inter-cell beam management (switching) operation

[0114] 2. Example 2 (5-75): Immediate L1 / L2 handover

[0115] First, in order to describe the overall operation of Example 1, the UE may receive public configuration and dedicated configuration information for an additional cell having a PCI different from the serving cell (TRP 2-cell 2, 5-15) from the serving cell 5-10 through RRC configuration information (5-26). That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon, and ServingCellConfig may be provided to the UE in advance. The configuration information may be provided in a pre-configured form through RRC configuration, and the configuration information may include configuration information for multiple cells. In addition, the corresponding configuration information may include all configuration information (cell configuration, bearer configuration, security key configuration, etc.) applied when the UE moves to the corresponding cell (handover). In addition, the corresponding configuration information may include the unified TCI state configuration described in step 4-56 and the configuration related to L1 measurement and reporting. The embodiment of the accompanying drawings is characterized by providing a structure for pre-providing settings for candidate neighboring cells that can perform L1 / L2 handover, an operation for selectively applying the settings through L1 / L2 signaling after the handover, and a specific method for L1 / L2 beam switching and cell switching (handover).

[0116] After serving cell 1 is provided with the configuration for TRP 2-cell 2 (5-15) in the RRC connected state, at step 5-27, the UE may perform L1 measurement on the corresponding TRP 2-cell 2 (5-15) according to the received configuration and report the result to the serving cell (cell 1, 5-10). When it is determined based on the measurement result that it is necessary to switch from the serving cell beam (TCI state 1, 5-25) to a specific beam (TCI state 2, 5-40) of TRP 2 (cell 2, 5-15), at step 5-28, the serving cell may trigger the beam switching and indicate it to the UE through L1 / L2 signaling.

[0117] The UE can perform beam switching to TRP 2 (cell 2, 5-15) through indication, and send and receive data through TRP 2 (cell 2, 5-15). At this time, the serving cell does not change, and the UE is still RRC connected to the serving cell (cell 1, 5-10). Thereafter, the UE can still perform L1 measurement on TRP 2-cell 2 (5-15) and report the corresponding results to the serving cell (cell 1, 5-10). If the L1 measurement reported by the UE meets the trigger condition for handover to TRP 2-cell 2 (5-15) (the detailed operation will be described below), the serving cell (cell 1, 5-10) can indicate handover to the UE. The indication can be an L1 / L2 message. That is, the indicator indicating the handover can be included in the MAC CE or DCI. The operation for the L1 / L2 message will be described in detail in the following embodiments of the present disclosure.

[0118] To describe the overall operation of Embodiment 2, the UE may receive, from the serving cell 5-40, through RRC configuration information (5-76), public configuration and dedicated configuration information for an additional cell having a PCI different from that of the serving cell (TRP 2-cell 2, 5-45). That is, configuration information corresponding to ServingCellID or candidateCellID (a cell ID associated with the PCI), ServingCellConfigCommon, and ServingCellConfig may be provided to the UE in advance. The configuration information may be provided in a pre-configured form through RRC configuration, and the configuration information may include configuration information for multiple cells. In addition, the corresponding configuration information may include all configuration information (cell configuration, bearer configuration, security key configuration, etc.) applied when the UE moves to the corresponding cell (handover). In addition, the corresponding configuration information may include the unified TCI state configuration described in step 4-56 and the configuration related to L1 measurement and reporting. The embodiment of the accompanying drawings is characterized by providing a structure for pre-providing settings for candidate neighboring cells that can perform L1 / L2 handover, an operation for selectively applying the settings through L1 / L2 signaling after the handover, and a specific method for L1 / L2 beam switching and cell switching (handover).

[0119] After serving cell 1 is provided with configuration for TRP 2-cell 2 (5-45) in the RRC connected state, in step 5-77, the UE may perform L1 measurement on the corresponding TRP 2-cell 2 (5-45) according to the received configuration, and report the corresponding result to the serving cell (cell 1, 5-40). When it is determined based on the measurement result that handover needs to be performed along with beam switching from the serving cell beam (TCI state 1, 5-45) to the specific beam (TCI state 2, 5-70) of TRP 2 (cell 2, 5-45), in step 5-78, the serving cell may trigger beam switching and handover, and indicate it to the UE through L1 / L2 signaling.

[0120] The UE may perform handover along with beam switching to TRP 2 (cell 2, 5-15) according to the corresponding indication, and may send and receive data through the corresponding TRP 2 (cell 2, 5-15). At this time, the UE may apply the configuration information that has been provided in advance in step 5-76 for the target cell for which the handover has been performed. Depending on whether uplink synchronization is required at this stage, the UE may perform random access to the target cell or may omit random access to the target cell. Detailed operations are described in the following figures.

[0121] Figure 6 It shows that the Figure 4Diagram of the overall operation of inter-cell beam management.

[0122] The UE 6-01 in the resident state (6-10) may receive system information (6-15) from the cell 1 (6-02) and may perform a transition process to the connected state (6-20). Thereafter, the serving cell 6-02 may make a UE capability request (UE capability query message) to the UE, and the UE may send its UE capabilities (UE capability information message) to the base station in response to the request of the base station (6-25). The UE capabilities may include whether L1 / L2-based inter-cell beam switching / management and handover are supported, and the UE reports its UE capabilities to the base station, including at least one of UE-specific capabilities, frequency band-specific capabilities, or frequency band combination-specific capabilities.

[0123] The serving cell 6-02 may send a request for configuration information required to perform L1 / L2-based beam switching and handover for the corresponding UE to the neighboring cell 2 (6-03) supporting L1 / L2-based mobility (6-25), and in response, the cell 2 (6-03) may send a response message including the requested configuration information to the serving cell 6-02 (6-30). When the cell 1 (6-02) and the cell 2 (6-03) exist within one DU (intra-DU scenario), the processes indicated by 6-30 and 6-35 may be omitted in the network implementation.

[0124] At step 6-40, the serving cell may send UE common / dedicated configuration information to be applied after indicating L1 / L2 based mobility (beam switching) to cell 2 (6-03). For detailed settings and contents, refer to Figure 4 For the TCI state configuration and L1 measurement and reporting configuration provided in step 6-40, refer to Figure 4 There may be multiple neighboring cells, and the serving cell may perform the same process with multiple neighboring cells. For example, a serving cell may be provided with configurations for up to 7 neighboring cells.

[0125] Thereafter, at step 6-45, the UE may perform L1 measurements related to TRP2-cell 2 while maintaining a connection state with the serving cell 6-02, and may report the corresponding measurement results to the serving cell 6-02 according to the pre-set L1 measurement report configuration (6-50). The serving cell 6-02 may determine to change the beam of the UE based on the received measurement results, and upon determining that it is necessary to switch from a specific beam of the serving cell (TRP 1-cell 1) to a specific beam of TRP 2-cell 2, at step 6-55, it may command the target cell (TRP 2-cell 2) to change the TCI state of the UE through L1 / L2 signaling. The L1 / L2 signaling at step 6-55 may be a MAC CE or a DCI, and the L1 / L2 signaling may include information indicating the handover to the specific beam of TRP 2-cell 2. For example, a MAC CE may be used when multiple TCI states are activated, and one of the activated TCI states may be indicated by the DCI. Alternatively, only one TCI state may be indicated by the MAC CE, in which case the DCI is omitted.

[0126] In step 6-60, the UE may perform beam switching to the beam indicated in TRP 2-cell 2 (6-03), and perform data transmission and reception through the corresponding beam. In this step, the UE may maintain the RRC connection with the serving cell.

[0127] Fig. 7A and Figure 7B is a diagram illustrating a method for configuring candidate neighbor cells supporting L1 / L2 inter-cell handover proposed in the present disclosure.

[0128] In the L1 / L2 inter-cell beam switching and handover applied to the embodiments proposed in the present disclosure, these figures describe the structure and method for the serving cell to provide the cell configuration to be applied after the UE hands over to the neighboring cell. The serving cell provides the UE with configuration information for the neighboring cell through pre-configuration, and when the handover and TCI status of the neighboring cell are indicated through L1 / L2 signaling, the UE performs a handover to the neighboring cell associated with the indicated TCI state. Therefore, the operation of the pre-stored configuration needs to be applied immediately. In addition, the number of candidate neighboring cells supporting L1 / L2 inter-cell beam switching and handover should match the number of neighboring cells that can be associated with the beam in the unified TCI state framework. For example, the unified TCI state beam currently set in one serving cell can be associated with up to 7 candidate neighboring cells. For details, see Figure 4 Next, the pre-configuration method for neighboring cells proposed in the present disclosure will be described.

[0129] 1. First pre-configuration method (7-05): Provide a configuration list at the cell group level for candidate neighbor cells to be applied after handover.

[0130] 1) Signaling Option 1

[0131] - Provide N candidate neighbor cell configurations (CandidateCellConfig, 7-30) that are commonly applied within a cell group. For example, N may be the maximum number (7) allowed in association with a unified TCI state.

[0132] - Includes neighboring cell ID and configuration information (7-35)

[0133] - Apply the same candidate neighbor cell configuration to all serving cells within the cell group (7-15, 7-20). Alternatively, N or fewer neighbor cell configurations may be indicated to be applied to each serving cell (7-25).

[0134] 2) Signaling Option 2

[0135] - Provide M candidate neighbor cell configurations (CandidateCellConfig, 7-30) that are commonly applied within the cell group. For example, M may be greater than the maximum number (7) allowed in association with the unified TCI state (M>7).

[0136] - In each serving cell (7-15, 7-20) within the cell group, N of the M candidate neighbor cell configurations set in the cell group may be selected and applied (7-25). For example, N may be less than or equal to the maximum number (7) allowed in association with the unified TCI state (N≤7).

[0137] 2. Second pre-configuration method (7-45): Provide a configuration list at the serving cell level for candidate neighbor cells to be applied after handover.

[0138] - Provide up to N candidate neighbor cell configurations from each serving cell (7-50, 7-65) (CandidateCellConfig, 7-60, 7-75). For example, N may be the maximum number (7) allowed in association with the unified TCI state.

[0139] - Providing configuration of neighbor cells associated with a serving cell at the serving cell level (7-55, 7-70) is consistent with indicating the TCI state for each serving cell in the unified TCI state framework and configuring N neighbor cells associated with the corresponding beam. For example, N can be the maximum number (7) allowed in association with the unified TCI state.

[0140] - Includes neighboring cell ID and configuration information (7-60, 7-75)

[0141] - This method provides a high degree of freedom for each serving cell, but the number of configurations for neighboring cells increases, which may lead to a high signaling load.

[0142] Figure 8B and Figure 8B Indicates the MAC CE and DCI formats for L1 / L2-based beam switching and handover proposed in the present disclosure. The method proposed in these figures is a MAC CE format and DCI for L1 / L2 inter-cell beam switching and handover applied to all embodiments proposed in the present disclosure. That is, the corresponding L1 / L2 signaling is used as a dynamic switching method, which commands the handover to be performed together with the beam switching to the candidate neighboring cell. The following two methods can be considered.

[0143] 1. The first L1 / L2 signaling method: traditional L1 / L2 inter-cell beam switching MAC CE and DCI process

[0144] 1) Activate multiple TCI states by using MAC CE, and indicate the TCI state for one neighboring cell by using DCI.

[0145] 2) Activate (indicate) the TCI state for a neighboring cell by using MAC CE.

[0146] 2. Second L1 / L2 signaling method: Activate (indicate) TCI state for a neighboring cell by using a new MAC CE

[0147] The MAC CE formats applicable to the above two signaling methods are as follows.

[0148] 1. MAC CE signaling option 1 for L1 / L2 inter-cell beam switching and handover (8-05)

[0149] - Reuse the legacy L1 / L2 inter-cell beam switching MAC CE without or with modification. This can be applied to the first L1 / L2 signaling method described above.

[0150] - That is, the DCI following the corresponding MAC CE indicates a handover and a TCI state.

[0151] - Use some of the reserved bits as new modified fields

[0152] a) "H" field (8-10): Indicator indicating whether to perform handover

[0153] b) Serving cell ID (8-15)

[0154] c) DL BWP ID (8-20)

[0155] d) RA field (8-25): An indicator indicating whether random access to the target cell is required when performing handover. This field can be set to "1" only when the H field is set to "1" to indicate handover. If the RA field is set to "1", random access can be indicated.

[0156] e) Type field (8-30): A field including information on whether to perform CBRA or CFRA and whether to perform 2-step RACH or 4-step RACH when a random access indication is received after handover is performed. For example, "00" may indicate that CBRA and 2-step RACH are performed to the target cell; "01" may indicate that CBRA and 4-step RACH are performed; "10" may indicate that CFRA and 2-step RACH are performed; and "11" may indicate that CFRA and 4-step RACH are performed. However, this is merely an example of how to set the type field, and the relationship between the type field and the information indicated by the type field may be changed.

[0157] f) "R" field (8-35): reserved field

[0158] g) UL BWP ID (8-40)

[0159] h) P i Field (8-45): A field indicating whether the following ith TCI Status field indicates beams in two TRPs. i field is set to "1", the corresponding i-th TCI state code point consists of two TCI states; if P i field is set to "0", the corresponding i-th TCI status code point consists of one TCI status.

[0160] i) D / U field (8-50, 8-60, 8-70): an indicator indicating whether the TCI state ID is set in UL or DL.

[0161] j) TCI State ID field (8-55, 8-65, 8-75): A field indicating the TCI state. The corresponding beam is set to a unified TCI state and is associated with a specific neighboring cell. The associated PCI setting is provided by the RRC configuration.

[0162] 2. MAC CE signaling option 2-1 (8-80) for L1 / L2 inter-cell beam switching and handover

[0163] -Use the newly introduced MAC CE

[0164] The -H field may be present but may be omitted since the handover is already indicated by the LCID / eLCID.

[0165] - A handover can be directly indicated without DCI by indicating only one TCI state. This can be applied to the second L1 / L2 signaling method described above.

[0166] a) "R" field (8-85): reserved field

[0167] b) Serving cell ID (8-90)

[0168] c) DL BWP ID (8-95)

[0169] d) RA field (8-100): An indicator indicating whether random access to the target cell is required when performing handover. If the RA field is set to "1", random access may be indicated.

[0170] e) Type field (8-105): A field including information on whether to perform CBRA or CFRA and whether to perform 2-step RACH or 4-step RACH when a random access indication is received after handover is performed. For example, "00" may indicate that CBRA and 2-step RACH are performed to the target cell; "01" may indicate that CBRA and 4-step RACH are performed; "10" may indicate that CFRA and 2-step RACH are performed; and "11" may indicate that CFRA and 4-step RACH are performed. However, this is merely an example of how to set the type field, and the relationship between the type field and the information indicated by the type field may be changed.

[0171] f) P field (8-105): A field indicating whether the following TCI status field indicates beams in two TRPs. If the P field is set to "1", the corresponding TCI status code point consists of two TCI statuses; if the P field is set to "0", the corresponding i-th TCI status code point consists of one TCI status.

[0172] g) UL BWP ID (8-110)

[0173] h) D / U field (8-190, 8-200, 8-210): an indicator indicating whether the TCI state ID is set in UL or DL.

[0174] i) TCI State ID field (8-195, 8-205, 8-215): A field indicating the TCI state. The corresponding beam is set to a unified TCI state and is associated with a specific neighboring cell. The associated PCI setting is provided by the RRC configuration.

[0175] 3. MAC CE signaling option 2-2 for L1 / L2 inter-cell beam switching and handover (8-140)

[0176] - Using the newly introduced MAC CE. It can be applied to the first L1 / L2 signaling method mentioned above.

[0177] - That is, the DCI following the corresponding MAC CE indicates a handover and a TCI state.

[0178] The -H field may be present but may be omitted since the handover is already indicated by the LCID / eLCID.

[0179] a) "R" field (8-145): reserved field

[0180] b) Serving cell ID (8-150)

[0181] c) DL BWP ID (8-155)

[0182] d) RA field (8-160): an indicator indicating whether random access to the target cell is required when performing handover. If the RA field is set to "1", random access may be indicated.

[0183] e) Type field (8-165): A field including information on whether to perform CBRA or CFRA and whether to perform 2-step RACH or 4-step RACH when a random access indication is received after handover is performed. For example, "00" may indicate that CBRA and 2-step RACH are performed to the target cell; "01" may indicate that CBRA and 4-step RACH are performed; "10" may indicate that CFRA and 2-step RACH are performed; and "11" may indicate that CFRA and 4-step RACH are performed. However, this is merely an example of how to set the type field, and the relationship between the type field and the information indicated by the type field may be changed.

[0184] f) UL BWP ID (8-180)

[0185] g) P i Field (8-185): A field indicating whether the following ith TCI Status field indicates beams in two TRPs. i field is set to "1", the corresponding i-th TCI state code point consists of two TCI states; if P i is set to "0", the corresponding i-th TCI state code point consists of one TCI state.

[0186] h) D / U field (8-190, 8-200, 8-210): an indicator indicating whether the TCI state ID is set in UL or DL.

[0187] i) TCI State ID field (8-195, 8-205, 8-215): A field indicating the TCI state. The corresponding beam is set to a unified TCI state and is associated with a specific neighboring cell. The associated PCI setting is provided by the RRC configuration.

[0188] In the above description, the situation where handover can be directly indicated without random access can correspond to the situation where the uplink timing advance between the serving cell and the target cell performing the handover is matched in the intra-DU situation, and it can be the situation where these cells know that the uplink synchronization is aligned through inter-cell information and exchange. The same applies to the ideal backhaul link.

[0189] In the operations in the above MAC CE, the following contents may also be provided by DCI as in MAC CE.

[0190] 1) Indicator indicating whether to perform handover

[0191] 2) Indicator indicating whether to perform random access during handover

[0192] - Indicator indicating CBRA or CFRA

[0193] -Indicator indicating 2-step RACH or 4-step RACH

[0194] In addition, in order for the UE to perform L1 / L2 inter-cell beam switching and handover, a process is required to notify the base station that the above-mentioned L1 / L2 signaling sent by the base station has been successfully received and the inter-cell beam switching and handover will be performed according to the corresponding operation. That is, the base station must recognize when the L1 / L2 inter-cell beam switching and handover is performed and when the corresponding process is completed. The present disclosure proposes the following two methods.

[0195] 1. First method for identifying L1 / L2 inter-cell beam switching and handover completion

[0196] -When the UE completes random access to the target cell, it is determined that the L1 / L2 inter-cell beam switching and handover operations are completed.

[0197] - Release the configuration for the previous serving cell and complete forwarding of data to the target cell.

[0198] 2. Second method for identifying L1 / L2 inter-cell beam switching and handover completion

[0199] -When the UE is instructed to perform handover through L1 / L2 signaling, the UE sends a confirmation MAC CE to the source serving cell.

[0200] -Introduction of new confirmation MAC CE and process (identified via LCID / eLCID and may include additional information)

[0201] a) Step 1: Instruct the UE to perform handover through L1 / L2 signaling.

[0202] b) Step 2: UE applies configuration to the target cell (applying configuration provided by pre-configuration)

[0203] c) Step 3: UE sends confirmation MAC CE

[0204] d) Step 4: (Optional) Perform random access to the target cell

[0205] NOTE: The order of step 3 and step 4 depends on the UE implementation.

[0206] - Release the configuration for the serving cell and complete forwarding data to the target cell

[0207] Fig. 9 1 is a diagram showing an overall operation of performing handover after applying L1 / L2 inter-cell beam management as Embodiment 1 applied to the present disclosure.

[0208] UE 9-01 in a resident state (9-10) may receive system information (9-15) from cell 1 (9-02) and may perform a transition process to a connected state (9-20). Thereafter, the serving cell 9-02 may make a UE capability request (UE capability query message) to the UE, and the UE may send its UE capabilities (UE capability information message) to the base station in response to the request of the base station (9-25). The UE capabilities may include whether L1 / L2-based inter-cell beam switching / management and handover are supported, and the UE reports its UE capabilities to the base station, including at least one of UE-specific capabilities, frequency band-specific capabilities, or frequency band combination-specific capabilities.

[0209] The serving cell 9-02 may send a request for configuration information required to perform L1 / L2-based beam switching and handover for the corresponding UE to the neighboring cell 2 (9-03) supporting L1 / L2-based mobility (9-25), and in response, the cell 2 (9-03) may send a response message including the requested configuration information to the serving cell 9-02 (9-30). The processes indicated by 9-30 and 9-35 may be performed through inter-node RRC messages or Xn, F1 interfaces, etc., and may be performed to exchange configurations related to the pre-configuration of cells participating in L1 / L2 inter-cell beam switching and handover. When the cell 1 (9-02) and the cell 2 (9-03) exist within one DU (intra-DU scenario), it may be omitted in the network implementation.

[0210] At step 9-40, the serving cell may send UE common / dedicated configuration information to be applied after indicating L1 / L2 based mobility (beam switching and handover) to cell 2 (9-03). Figure 6 The difference is that in step 9-40, public and dedicated configuration information for additional cells (TRP 2-cell 2, 9-03) having a PCI different from that of the serving cell is included. That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon and ServingCellConfig can be provided to the UE in advance. The corresponding configuration information can be provided in a pre-configured form through RRC configuration, and the above configuration information may include configuration information for multiple cells. In addition, the corresponding configuration information may include all configuration information (cell configuration, bearer configuration, security key configuration, etc.) applied when the UE moves to the corresponding cell (handover). In addition, the corresponding configuration information may include the unified TCI state configuration described in step 4-56 and the configuration related to L1 measurement and reporting. This embodiment proposes an RRC structure for supporting L1 / L2 inter-cell beam switching (management) and handover operations, especially a pre-configuration method for candidate neighboring cells, and proposes an L1 / L2 signaling method for a base station to indicate inter-cell beam switching and handover based on L1 measurement values. When inter-cell beam switching and handover are indicated by L1 / L2-based signaling, the configuration preset for the cell indicating the handover is applied. That is, in step 9-40, a pre-configured RRC structure for supporting L1 / L2 inter-cell beam switching (management) and handover operations, especially for candidate neighboring cells, is provided, and in this case, the content described in Figure 7 is applied.

[0211] Thereafter, in step 9-45, the UE may perform L1 measurements related to TRP2-cell 2 while maintaining a connection state with the serving cell 9-02, and may report corresponding measurement results to the serving cell 9-02 according to a pre-set L1 measurement report configuration (9-50). For L1 measurement value reporting, one of the above methods (L1 measurement improvement method) may be applied.

[0212] The serving cell 9-02 may determine to change the beam of the UE based on the received measurement result, and upon determining that a switch from a specific beam of the serving cell (TRP 1-cell 1) to a specific beam of TRP 2-cell 2 is required, in step 9-55, it may command the target cell (TRP 2-cell 2) to change the TCI state of the UE through L1 / L2 signaling. The L1 / L2 signaling in step 9-55 may be a MAC CE or a DCI, and the L1 / L2 signaling may include information indicating the handover to the specific beam of TRP 2-cell 2. For example, a MAC CE may be used when multiple TCI states are activated, and one of the activated TCI states may be indicated by the DCI. Alternatively, the MAC CE may indicate only one TCI state, in which case the DCI is omitted.

[0213] In step 9-60, the UE may perform beam switching to the beam indicated in TRP 2-cell 2 (9-03), and perform data transmission and reception through the corresponding beam. In this step, the UE may maintain the RRC connection with the serving cell. The above L1 / L2 signaling may be one of the methods described in FIG. 8.

[0214] Thereafter, the UE may perform L1 measurements related to TRP 2-cell 2 while maintaining a connection state with the serving cell 9-02, and may report the corresponding measurement results to the serving cell 9-02 according to the pre-set L1 measurement report configuration (9-65). The serving cell 9-02 may determine to perform cell switching (handover) of the UE based on the received measurement results, and may command the UE to perform the handover along with changing the TCI state to the target cell (TRP 2-cell 2) through L1 / L2 signaling at step 9-70. The L1 / L2 signaling at step 9-70 may be a MAC CE or a DCI, and the L1 / L2 signaling may include information indicating a specific beam and handover to TRP 2 cell 2 (indicated by a field in the LCID or MAC CE). For example, a MAC CE may be used when multiple TCI states are activated, and one of the activated TCI states may be indicated by the DCI. Alternatively, the MAC CE may indicate only one TCI state, in which case the DCI is omitted. The L1 / L2 signaling may be one of the methods described in FIG. 8. In step 9-75, the UE may perform handover to TRP 2-cell 2 (9-03), switch the beam to the indicated beam, and perform data transmission and reception through the corresponding beam.

[0215] Fig.10 1 is a diagram showing the overall operation of performing L1 / L2 inter-cell handover as embodiment 2 applied to the present disclosure.

[0216] The UE 10-01 in the camping state (10-10) may receive system information (10-15) from the cell 1 (10-02) and may perform a transition process to the connected state (10-20). Thereafter, the serving cell 10-02 may make a UE capability request (UE capability query message) to the UE, and the UE may send its UE capability (UE capability information message) to the base station in response to the request of the base station (10-25). The UE capability may include whether L1 / L2-based inter-cell beam switching / management and switching are supported, and the UE reports its UE capability to the base station, including at least one of UE-specific capability, frequency band-specific capability, or frequency band combination-specific capability.

[0217] The serving cell 10-02 may send a request for configuration information required for the corresponding UE to perform L1 / L2-based beam switching and handover to a neighboring cell 2 (10-03) supporting L1 / L2-based mobility (10-25), and in response, the cell 2 (10-03) may send a response message including the requested configuration information to the serving cell 1 (10-02) (10-30). The processes indicated by 9j30 and 10-35 may be performed through inter-node RRC messages or Xn, F1 interfaces, etc., and may be performed to exchange configurations related to pre-configuration of cells participating in L1 / L2 inter-cell beam switching and handover. When the cell 1 (10-02) and the cell 2 (10-03) exist within one DU (intra-DU scenario), it may be omitted in network implementation.

[0218] At step 10-40, the serving cell may send UE common / dedicated configuration information to be applied after indicating L1 / L2 based mobility (beam switching and handover) to cell 2 (10-03). Figure 6The difference is that in step 10-40, public and dedicated configuration information for additional cells (TRP 2-cell 2, 10-03) having a PCI different from that of the serving cell is included. That is, configuration information corresponding to ServingCellID or candidateCellID (cell ID associated with PCI), ServingCellConfigCommon and ServingCellConfig can be provided to the UE in advance. The corresponding configuration information can be provided in a pre-configured form through RRC configuration, and the above configuration information may include configuration information for multiple cells. In addition, the corresponding configuration information may include all configuration information (cell configuration, bearer configuration, security key configuration, etc.) applied when the UE moves to the corresponding cell (handover). In addition, the corresponding configuration information may include the unified TCI state configuration described in step 4-56 and the configuration related to L1 measurement and reporting. This embodiment proposes an RRC structure for supporting L1 / L2 inter-cell beam switching (management) and handover operations, especially a pre-configuration method for candidate neighboring cells, and proposes an L1 / L2 signaling method for a base station to indicate inter-cell beam switching and handover based on L1 measurement values. When inter-cell beam switching and handover are indicated by L1 / L2 based signaling, the configuration preset for the cell indicating the handover is applied. That is, in step 10-40, a pre-configured RRC structure for supporting L1 / L2 inter-cell beam switching (management) and handover operations, especially for candidate neighboring cells, is provided, and in this case, the content described in Figure 7 is applied.

[0219] Thereafter, in step 10-45, the UE may perform L1 measurements related to TRP2-cell 2 while maintaining a connection state with the serving cell 10-02, and may report corresponding measurement results to the serving cell 10-02 according to a pre-set L1 measurement report configuration (10-50). For L1 measurement value reporting, one of the above methods (L1 measurement improvement method) may be applied.

[0220] The serving cell 10-02 may determine to change the cell of the UE (handover) based on the received measurement results, and may perform a handover negotiation process with the target cell by making a handover request (10-55) and receiving a configuration message (10-60). Then, in step 10-65, the serving cell 10-02 commands the UE to perform the handover along with changing the TCI state of the UE to the target cell (TRP 2-cell 2) through L1 / L2 signaling. The above-mentioned L1 / L2 signaling may be one of the methods described in FIG. 8. Note that steps 10-50 and 10-55 may be omitted in terms of network implementation in the case of intra-DU, or steps 10-50 and 10-55 may also be omitted if the relevant information has been shared in step 10-40. The L1 / L2 signaling in step 10-65 may be a MAC CE or a DCI, and the L1 / L2 signaling may include information indicating a specific beam and handover to TRP 2 cell 2. For example, MAC CE may be used when multiple TCI states are activated, and one of the activated TCI states may be indicated by DCI. Alternatively, MAC CE may indicate only one TCI state, in which case DCI is omitted.

[0221] In step 10-70, the UE may perform handover to TRP 2-cell 2 (10-03) and switch the beam to the indicated beam, and in step 7-75, the UE may perform data transmission and reception through the corresponding beam.

[0222] Fig.11 is a diagram illustrating UE operation of indicating L1 / L2 inter-cell beam switching and handover using only MAC CE in overall UE operation for performing L1 / L2-based beam switching and handover, which is applied to an embodiment of the present disclosure.

[0223] In step 11-05, the UE in the connected state may receive the public / dedicated configuration information of the neighboring cells to be applied after the L1 / L2-based mobility from the serving cell through the RRC reconfiguration message. For detailed configuration methods and contents, refer to Figure 4 5 and 7. Thereafter, in step 11-10, the UE may perform L1 measurement related to the candidate neighboring cell while maintaining a connection state with the serving cell, and may report the measurement result to the serving cell according to a preset L1 measurement report configuration.

[0224] The serving cell can determine whether to command the UE to perform beam switching and handover based on the received measurement results, and when it is determined that beam switching from a specific beam of the serving cell to a specific beam of a neighboring cell is required, in step 11-15, it can command the UE to change the TCI state through L1 / L2 signaling. The above-mentioned L1 / L2 signaling differs from traditional operations in that it can also trigger handover. In the figure, the above-mentioned L1 / L2 signaling is a MAC CE, and the MAC CE may include information indicating changes in a specific beam of a neighboring cell and a serving cell. In step 11-20, the UE may check whether there is a handover indication in the MAC CE signaling received in step 11-15, and then operate in a different manner. For the specific format of the MAC CE and related operations, refer to Figure 8.

[0225] If handover is indicated in the MAC CE received in step 11-20 (the new MAC CE directly indicates handover, or a specific field of the MAC CE indicates whether to perform handover), then in step 11-25, the UE can perform handover to the cell associated with the indicated TCI state, apply the configuration to the corresponding cell that has been stored as a pre-configuration according to the handover, and perform data transmission and reception by using the indicated beam.

[0226] If the MAC CE received in step 11-20 does not indicate handover (a conventional inter-cell beam switching MAC CE is received, or a specific field in the new MAC CE does not indicate whether to perform handover), then in step 11-30, the UE can maintain connection to the current serving cell, switch the beam to the TCI state of the indicated cell, and perform data transmission and reception through the corresponding beam. After beam switching, data transmission and reception are performed through the dedicated channels (PDCCH / PDSCH and PUCCH / PUSCH) of the corresponding beam.

[0227] In step 11-35, the UE may perform L1 measurement and reporting and RRM (Radio Resource Management) processes, i.e., L3 measurement and channel reporting operations, for neighboring cells. In this step, if the serving cell determines that a handover to a neighboring cell is required through an L1 measurement report or an L3 measurement report from the UE, the serving cell may command the UE to change the serving cell by issuing a handover instruction. In step 11-40, the UE may receive a handover instruction through L1 / L2 signaling or an RRC message, and if the UE that has received it has already performed beam switching to a neighboring cell and performed data transmission and reception with the corresponding cell, operations related to random access may be omitted. The UE may change the serving cell according to the handover instruction and release the configuration of the previous serving cell.

[0228] Fig.12is a diagram illustrating UE operation of indicating L1 / L2 inter-cell beam switching and handover using MAC CE and DCI in the overall UE operation for performing L1 / L2-based beam switching and handover, which is applied to an embodiment of the present disclosure.

[0229] In step 12-05, the UE in the connected state may receive the public / dedicated configuration information of the neighboring cells to be applied after the L1 / L2-based mobility from the serving cell through the RRC reconfiguration message. Figure 4 5 and 7. Thereafter, in step 12-10, the UE may perform L1 measurement related to the candidate neighboring cell while maintaining a connection state with the serving cell, and may report the measurement result to the serving cell according to a preset L1 measurement report configuration.

[0230] The serving cell can determine whether to command the UE to perform beam switching and handover based on the received measurement results, and when it is determined that a beam switching from a specific beam of the serving cell to a specific beam of a neighboring cell is required, in step 12-15, it can command the UE to change the TCI state through L1 / L2 signaling. The above-mentioned L1 / L2 signaling differs from conventional operations in that it can also trigger a handover. In the figure, the above-mentioned L1 / L2 signaling is a MAC CE and a DCI. Here, the MAC CE may include information indicating both a specific beam of a neighboring cell and a change in the serving cell (the MAC CE indicates only one beam). Alternatively, the MAC CE may indicate a specific plurality of beams of a neighboring cell, and the subsequent DCI transmitted in step 12-20 may select one of the multiple beams of the neighboring cell activated by the MAC CE. Thus, a handover can be indicated.

[0231] At step 12-25, the UE may check whether there is a handover indication in the MAC CE and DCI signaling received at steps 12-15 and 12-20, and then operate differently. For the specific format of the MAC CE and related operations, refer to FIG. 8.

[0232] If handover is indicated in the MAC CE and DCI received in step 12-25 (the MAC CE itself indicates handover, or the MAC CE activates multiple beams and the DCI indicates one of these beams, thereby indicating handover), then in step 12-30, the UE can perform handover to the cell associated with the indicated TCI state, apply the configuration to the corresponding cell that has been stored as a pre-configuration according to the handover, and perform data transmission and reception by using the indicated beam.

[0233] If handover is not indicated in the MAC CE and DCI received in step 12-25 (MAC CE does not indicate handover, or DCI does not indicate handover), then in step 12-35, the UE can maintain the connection to the current serving cell, switch the beam to the TCI state of the indicated cell, and perform data transmission and reception through the corresponding beam. After the beam switching, data transmission and reception are performed through the dedicated channels (PDCCH / PDSCH and PUCCH / PUSCH) of the corresponding beam. In step 12-40, the UE can perform L1 measurement and reporting and RRM (Radio Resource Management) processes for neighboring cells, that is, L3 measurement and channel reporting operations. In this step, if the serving cell determines that handover to the neighboring cell is required through the L1 measurement report or L3 measurement report from the UE, the serving cell can command the UE to change the serving cell by issuing a handover instruction. In step 12-45, the UE may receive a handover instruction through L1 / L2 signaling or an RRC message, and if the UE that has received it has performed beam switching to a neighboring cell and performed data transmission and reception with the corresponding cell, operations related to random access may be omitted. The UE may change the serving cell according to the handover instruction and release the configuration of the previous serving cell.

[0234] Fig.13 is a diagram illustrating the operation of a base station applied to an embodiment of the present disclosure.

[0235] In step 13-05, the base station may provide system information to the UE. In step 13-10, the serving cell may send the public / dedicated configuration information of the neighboring cells to be applied after the L1 / L2-based mobility to the UE in the connected state through an RRC reconfiguration message. For detailed configuration methods and contents, refer to Figure 4 Description related to Figure 5.

[0236] Thereafter, in step 13-15, the base station may receive an L1 measurement value from the UE, wherein the measurement value may be a measurement on a neighboring cell (non-service cell) that supports L1 / L2-based mobility. The serving cell may determine whether to change the beam of the UE based on the received measurement result, and upon determining that it is necessary to switch from a specific beam of the serving cell to a specific beam of the neighboring cell, in step 13-20, it may command the UE to change the TCI state through L1 / L2 signaling. The above-mentioned L1 / L2 signaling may be a MACCE or a DCI, and the above-mentioned L1 / L2 signaling may include information indicating switching to a specific beam of the neighboring cell. In addition, handover may also be indicated through L1 / L2 signaling in this step. If handover is also indicated, the serving cell may perform a handover process, and when the handover to the target cell is completed, the UE context may be deleted and the connection released. The above description is characterized in that the measurement value used to determine whether to perform handover is an L1 measurement. For the various proposed methods, refer to Fig. 9 and Fig.10 .

[0237] If the above L1 / L2 signaling does not include a handover process, the serving cell may maintain a connection state with the UE in steps 13-25. In this step, the UE may perform data transmission and reception through dedicated channels (PDCCH / PDSCH and PUCCH / PUSCH) by applying the preset configuration information for the neighboring cell. The UE may also return to the current serving cell from the link with the neighboring cell.

[0238] In step 13-25, the base station may receive additional L1 / L3 measurement reports while maintaining a connection state with the UE. If the serving cell determines that a handover to a neighboring cell is required, it may command the UE to change the serving cell by sending a handover message. In step 13-30, after the UE changes the serving cell according to the handover indication, it may release the configuration of the previous serving cell.

[0239] Fig.14 is a block diagram showing the internal structure of a UE to which the present disclosure is applied.

[0240] Referring to the drawing, the UE may include a Radio Frequency (RF) processor 14 - 10 , a baseband processor 14 - 20 , a memory 14 - 30 , and a controller 14 - 40 .

[0241] The RF processor 14-10 performs functions such as signal band conversion and amplification for sending and receiving signals through a radio channel. That is, the RF processor 14-10 performs up-conversion from a baseband signal provided by the baseband processor 14-20 to an RF band signal, and transmits it through an antenna, and performs down-conversion of an RF band signal received by the antenna to a baseband signal. For example, the RF processor 14-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC). Although only one antenna is shown in the accompanying drawings, multiple antennas may be provided to the UE. Moreover, the RF processor 14-10 may include multiple RF chains. In addition, the RF processor 14-10 may perform beamforming. For beamforming, the RF processor 14-10 may adjust the phase and amplitude of each signal sent and received through multiple antennas or antenna elements. In addition, the RF processor may perform MIMO (multiple input multiple output) and may receive several layers during MIMO operation.

[0242] The baseband processor 14-20 performs conversion between baseband signals and bit streams according to the physical layer specification of the system. For example, during data transmission, the baseband processor 14-20 generates complex symbols by encoding and modulating the transmission bit stream. In addition, during data reception, the baseband processor 14-20 recovers the received bit stream by demodulating and decoding the baseband signal provided from the RF processor 14-10. For example, in the case of orthogonal frequency division multiplexing (OFDM), for data transmission, the baseband processor 14-20 generates complex symbols by encoding and modulating the transmission bit stream, maps the complex symbols to subcarriers, and synthesizes OFDM symbols by inverse fast Fourier transform (IFFT) operation and cyclic prefix (CP) insertion. In addition, for data reception, the baseband processor 14-20 divides the baseband signal provided from the RF processor 14-10 in units of OFDM symbols, recovers the signal mapped to the subcarrier by fast Fourier transform (FFT) operation, and recovers the received bit stream by demodulation and decoding.

[0243] The baseband processor 14-20 and the RF processor 14-10 send and receive signals as described above. The baseband processor 14-20 and the RF processor 14-10 may be referred to as a transmitter, a receiver, a transceiver, or a communication unit. In addition, in order to support different radio access technologies, at least one of the baseband processor 14-20 or the RF processor 14-10 may include multiple communication modules. In addition, in order to process signals of different frequency bands, at least one of the baseband processor 14-20 or the RF processor 14-10 may include different communication modules. For example, different radio access technologies may include wireless LAN (e.g., IEEE802.11), cellular networks (e.g., LTE), etc. In addition, different frequency bands may include ultra-high frequency (SHF) bands (e.g., 2.NRHz, NRHz) and millimeter wave (mmWave) bands (e.g., 60GHz).

[0244] The memory 14-30 stores data such as basic programs, applications, and configuration information for UE operation. In particular, the memory 14-30 may store information of a second access node for performing wireless communication using a second radio access technology. The memory 14-30 provides stored data in response to a request from the controller 14-40.

[0245] The controller 14-40 controls the overall operation of the UE. For example, the controller 14-40 sends and receives signals through the baseband processor 14-20 and the RF processor 14-10. In addition, the controller 14-40 writes data to the memory 14-30 or reads data from the memory 14-30. To this end, the controller 14-40 may include at least one processor. For example, the controller 14-40 may include a communication processor (CP) for controlling communication and an application processor (AP) for controlling high layers such as application programs.

[0246] Fig.15 is a block diagram showing the structure of a base station according to the present disclosure.

[0247] As shown, the base station includes an RF processor 15-10, a baseband processor 15-20, a backhaul communication unit 15-30, a memory 15-40, and a controller 15-50.

[0248] The RF processor 15-10 performs functions such as signal band conversion and amplification for sending and receiving signals through a radio channel. That is, the RF processor 15-10 performs up-conversion of the baseband signal provided by the baseband processor 15-20 to the RF band signal, and transmits the converted signal through the antenna, and performs down-conversion of the RF band signal received by the antenna to the baseband signal. For example, the RF processor 15-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC. Although only one antenna is shown in the accompanying drawings, the first access node may have multiple antennas. In addition, the RF processor 15-10 may include multiple RF chains. In addition, the RF processor 15-10 may perform beamforming. For beamforming, the RF processor 15-10 may adjust the phase and amplitude of each signal sent and received by multiple antennas or antenna elements. The RF processor may perform downlink MIMO operations by sending one or more layers.

[0249] The baseband processor 15-20 performs conversion between baseband signals and bit streams according to the physical layer specification of the first radio access technology. For example, for data transmission, the baseband processor 15-20 generates complex symbols by encoding and modulating the transmission bit stream. In addition, for data reception, the baseband processor 15-20 recovers the received bit stream by demodulating and decoding the baseband signal provided from the RF processor 15-10. For example, in the case of using OFDM, for data transmission, the baseband processor 15-20 generates complex symbols by encoding and modulating the transmission bit stream, maps the complex symbols to subcarriers, and synthesizes OFDM symbols by IFFT operation and CP insertion. In addition, for data reception, the baseband processor 15-20 divides the baseband signal provided from the RF processor 15-10 in units of OFDM symbols, recovers the signal mapped to the subcarrier by FFT operation, and recovers the received bit stream by demodulation and decoding. The baseband processor 15-20 and the RF processor 15-10 send and receive signals as described above. Therefore, the baseband processor 15-20 and the RF processor 15-10 may be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit.

[0250] The backhaul communication unit 15-30 provides an interface for communicating with other nodes in the network. That is, the backhaul communication unit 15-30 converts a bit stream to be sent from the base station to another node (eg, a second base station or a core network) into a physical signal, and converts a physical signal received from another node into a bit stream.

[0251] The memory 15-40 stores data such as basic programs, applications, and configuration information for base station operation. In particular, the memory 15-40 may store information about the bearer assigned to the connected UE and measurement results reported from the connected UE. In addition, the memory 15-40 may store information used as a criterion for determining whether to provide or suspend multiple connections to the UE. In addition, the memory 15-40 provides stored data in response to a request from the controller 15-50.

[0252] The controller 15-50 controls the overall operation of the base station. For example, the controller 15-50 sends and receives signals through the baseband processor 15-20 and the RF processor 15-10 or through the backhaul communication unit 15-30. In addition, the controller 15-50 writes data to the memory 15-40 or reads data from the memory 15-40. To this end, the controller 15-50 may include at least one processor.

Claims

1. A method performed by a terminal in a wireless communication system, the method comprising: receiving a radio resource control (RRC) message from a base station, the RRC message including a configuration of a candidate target cell for handover; receiving a media access control MAC control element CE from the base station, the MAC CE including information indicating a target cell among the candidate target cells; Performing handover to the target cell indicated by the MAC CE; as well as An RRC completion message indicating completion of the handover is sent to the base station.

2. The method according to claim 1, wherein: The MAC CE also includes a transmission configuration indicator TCI status for the target cell.

3. The method according to claim 1, wherein: The MAC CE further includes a field indicating whether to perform a random access channel RACH process on the target cell.

4. The method according to claim 3, wherein: In a case where uplink synchronization between the source cell of the terminal and the target cell matches, the field indicates that the RACH process is not performed.

5. A method performed by a base station in a wireless communication system, the method comprising: Sending a radio resource control (RRC) message to the terminal, wherein the RRC message includes a configuration of a candidate target cell for handover; Sending a media access control MAC control element CE to the terminal, where the MAC CE includes information indicating a target cell among the candidate target cells; as well as In a case where the terminal is handed over to the target cell indicated by the MAC CE, an RRC completion message indicating handover completion is received from the terminal.

6. The method according to claim 5, wherein: The MAC CE also includes a transmission configuration indicator TCI status for the target cell.

7. The method according to claim 5, wherein: The MAC CE further includes a field indicating whether to perform a random access channel RACH process on the target cell.

8. The method according to claim 7, wherein: In a case where uplink synchronization between the source cell of the terminal and the target cell matches, the field indicates that the RACH process is not performed.

9. A terminal in a wireless communication system, comprising: Transceiver; as well as A controller connected to the transceiver, Wherein, the controller is configured as: receiving a radio resource control (RRC) message from a base station, the RRC message including a configuration of a candidate target cell for handover; receiving a media access control MAC control element CE from the base station, the MAC CE including information indicating a target cell among the candidate target cells from the base station; performing a handover to a target cell indicated by the MAC CE; and An RRC completion message indicating completion of the handover is sent to the base station.

10. The terminal according to claim 9, wherein: The MAC CE also includes a transmission configuration indicator TCI status for the target cell.

11. The terminal according to claim 9, wherein: The MAC CE further includes a field indicating whether to perform a random access channel RACH process on the target cell.

12. The terminal according to claim 11, wherein: In a case where uplink synchronization between the source cell of the terminal and the target cell matches, the field indicates that the RACH process is not performed.

13. A base station in a wireless communication system, comprising: Transceiver; as well as A controller connected to the transceiver, Wherein, the controller is configured as: Sending a radio resource control (RRC) message to the terminal, wherein the RRC message includes a configuration of a candidate target cell for handover; Sending a media access control MAC control element CE to the terminal, where the MAC CE includes information indicating a target cell among the candidate target cells; as well as In a case where the terminal is handed over to the target cell indicated by the MAC CE, an RRC completion message indicating handover completion is received from the terminal.

14. The base station according to claim 13, wherein: The MAC CE also includes a transmission configuration indicator TCI status for the target cell.

15. The base station according to claim 13, wherein: The MAC CE further includes a field indicating whether to perform a random access channel RACH process on the target cell; as well as In a case where uplink synchronization between the source cell of the terminal and the target cell matches, the field indicates that the RACH process is not performed.

Images