Method and apparatus for lower-layer triggered mobility based on candidate transmission and reception point recognition

Abstract

The present disclosure relates to a technology for lower-layer triggered mobility based on candidate transmission and reception point recognition. According to the present disclosure, a method of a terminal comprises the steps of: receiving, by a terminal, service from a first base station; receiving SSBs from TRPs of a second base station; transmitting a first measurement report to the first base station; receiving, from the first base station, information about beam identifiers for candidate TRPs; receiving, from the first base station, information about resources for transmitting CSI-RS to the candidate TRPs; receiving the CSI-RS from the candidate TRPs via the resources; transmitting, to the first base station, a second measurement report for the CSI-RS; receiving, from the first base station, information about a target TRP selected from the candidate TRPs; and carrying out cell switching to the target TRP.

Description

Method and device for lower layer trigger mobility based on recognition of candidate transmitting and receiving points

[0001] The present disclosure relates to a lower layer triggered mobility technology based on candidate transceiver point recognition, and more particularly, to a lower layer triggered mobility technology based on candidate transceiver point recognition that enables seamless switching from a serving cell to candidate non-serving cell(s).

[0002] Advances in information and communication technology (ICT) can lead to the development of various wireless communication technologies. Representative wireless communication technologies include LTE (long term evolution), NR (new radio), and 6G (6th Generation), all of which are defined by the 3rd Generation Partnership Project (3GPP) standards. LTE can be one of the 4th Generation (4G) wireless communication technologies, and NR can be one of the 5th Generation (5G) wireless communication technologies.

[0003] In order to process the rapidly increasing amount of wireless data following the commercialization of 4G communication systems (e.g., communication systems supporting LTE), 5G communication systems (e.g., communication systems supporting NR) that use a higher frequency band (e.g., a frequency band higher than 6 GHz) than the frequency band of the 4G communication system (e.g., a frequency band below 6 GHz) may be considered. 5G communication systems may support enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communication (URLLC), and massive Machine Type Communication (mMTC).

[0004] In a communication system, a terminal can move from a serving cell to a non-serving cell, and for example, it can use the lower-layer triggered mobility (LTM) method introduced in 3GPP Release 18 (Rel-18). The LTM method introduced in 3GPP Release 18 can support the movement of a terminal between transmission reception points (TRPs) with different physical cell identities (PCIs) within the same central unit (CU). However, the LTM method introduced in 3GPP Release 18 cannot support the movement of a terminal between TRPs with different PCIs within different CUs. The LTM method introduced in 3GPP Release 18 can reduce handover delay and interruption time compared to the layer 3 (L3)-based mobility method, but it may still have considerable delay and interruption time.

[0005] The purpose of the present disclosure to solve the above problems is to provide a method and device for lower layer triggered mobility based on candidate transceiver point recognition that enables seamless switching from a serving cell to candidate non-serving cell(s).

[0006] In order to achieve the above object, a method for lower layer triggered mobility based on recognition of candidate transmission and reception points according to a first embodiment of the present disclosure is provided, as a method of a terminal, comprising: receiving a service from a transmission and reception point (TRP) of a first base station; receiving synchronization signal blocks (SSBs) from TRPs controlled by a second base station; transmitting a first measurement report for the SSBs to the first base station; receiving, from the first base station, information on a beam identifier for at least one candidate TRP selected from among the TRPs based on the first measurement report; receiving, from the first base station, information on a resource allocated to transmit a channel state information-reference signal (CSI-RS) to the at least one candidate TRP; receiving, through the resource, the CSI-RS transmitted using a beam having the beam identifier from the at least one candidate TRP; transmitting a second measurement report for the CSI-RS to the first base station; The method may include receiving information about a target TRP selected from the at least one candidate TRP based on the second measurement report from the first base station; and switching cells to the target TRP.

[0007] Here, the at least one candidate TRP may be a TRP located at the boundary of the first base station among the TRPs.

[0008] Here, the step of receiving a terminal capability report request from the first base station; and the step of transmitting the terminal capability report to the first base station may be further included.

[0009] Here, the terminal capability report may include at least one of the terminal's RF (radio frequency) capability, physical layer control capability, medium access control capability, radio link control capability, PDCP (packet data convergence protocol) capability, DC (dual connectivity) capability, CA (carrier aggregation) capability, NSA / SA (non-standalone / standalone) operation capability, NR bandwidth class, transmission class capability, LCS (location services) capability, reduced capability, or VoNR (voice over new radio) capability.

[0010] Here, the step of performing a SSB-based downlink synchronization process with the at least one candidate TRP; and the step of performing a PDCCH (physical downlink control channel) order-based uplink TA acquisition synchronization process with the at least one candidate TRP are further included, wherein the at least one candidate TRP can be determined as a TRP among the TRPs through the PDCCH order-based uplink TA acquisition synchronization process.

[0011] Here, the step of performing the at least one candidate TRP and PDCCH order-based uplink TA acquisition synchronization process may include the steps of: receiving a PDCCH order indicating connection with the at least one candidate TRP from the first base station; transmitting an RA (random access) preamble to the at least one candidate TRP using a second beam in a second beam direction having a quasi-colocation (QCL) relationship with a first beam direction of the first beam of the beam identifier according to the PDCCH order; and receiving a TA value from the second base station via the first base station.

[0012] Here, the step of receiving mapping information of the TRPs and SSB groups from the first base station; the step of confirming SSB indexes of the SSBs; and the step of determining a TRP mapped to each of the confirmed SSB indices based on the mapping information are further included, wherein the first measurement information may include information on the mapped TRP for each of the SSBs.

[0013] Meanwhile, a lower layer trigger mobility method based on candidate transmission and reception point recognition according to a second embodiment of the present disclosure for achieving the above object comprises the steps of: providing a service to a terminal through a transmission and reception point (TRP); receiving, from the terminal, a first measurement report for synchronization signal blocks (SSBs) transmitted from transmission and reception points (TRPs) controlled by a second base station; selecting at least one candidate TRP from the TRPs based on the first measurement report; transmitting information on a beam identifier of the at least one candidate TRP to the terminal; requesting the second base station to transmit a channel state information-reference signal (CSI-RS) in at least one TRP of the at least one candidate TRP using a second beam in a second beam direction having a quasi-colocation (QCL) relationship with a first beam direction of a first beam of the beam identifier; receiving, from the second base station, information on a resource allocated to transmit the CSI-RS in the at least one TRP; The method may include: transmitting information about the resource to the terminal; receiving a second measurement report for the CSI-RS transmitted from the at least one TRP from the terminal; selecting a target TRP from the at least one TRP based on the second measurement report; and performing a cell switching operation with the target TRP.

[0014] Here, the at least one TRP may be a TRP located at the boundary of the first base station.

[0015] Here, the method may further include: transmitting a physical downlink control channel (PDCCH) order instructing the terminal to perform uplink synchronization for the at least one candidate TRP; receiving information about signal quality of a random access (RA) preamble received from the terminal in the at least one candidate TRP from the second base station; and selecting the at least one TRP from the at least one candidate TRP based on the signal quality.

[0016] Here, the method further includes a step of transmitting mapping information of the TRPs and SSB groups to the terminal, wherein the first measurement information includes information on the signal quality of each of the SSBs and the TRP mapped to each of the SSBs, and based on the information on the signal quality of each of the SSBs and the TRP mapped to each of the SSBs, the at least one TRP can be selected from the at least one candidate TRP.

[0017] Meanwhile, a lower layer trigger mobility device based on candidate transmission and reception point recognition according to a third embodiment of the present disclosure for achieving the above object comprises a terminal, and at least one processor, wherein the terminal receives a service from a transmission and reception point (TRP) of a first base station; receives synchronization signal blocks (SSBs) from TRPs controlled by a second base station; transmits a first measurement report for the SSBs to the first base station; receives information on a beam identifier for at least one candidate TRP selected from the TRPs based on the first measurement report from the first base station; receives information on a resource allocated to transmit a channel state information-reference signal (CSI-RS) to the at least one candidate TRP from the first base station; receives the CSI-RS transmitted using a beam having the beam identifier from the at least one candidate TRP through the resource; and transmits a second measurement report for the CSI-RS to the first base station. Receive information about a target TRP selected from the at least one candidate TRP based on the second measurement report from the first base station; and cause cell switching to the target TRP.

[0018] Here, the at least one candidate TRP may be a TRP located at the boundary of the first base station among the TRPs.

[0019] Here, the at least one processor further causes the terminal to perform an SSB-based downlink synchronization process with the at least one candidate TRP; and to perform an uplink TA acquisition synchronization process based on a PDCCH (physical downlink control channel) order with the at least one candidate TRP, wherein the at least one candidate TRP can be determined to be a TRP among the TRPs through the PDCCH order-based uplink TA acquisition synchronization process.

[0020] Here, in the step of performing the at least one candidate TRP and the PDCCH order-based uplink TA acquisition synchronization process, the at least one processor may cause the terminal to receive a PDCCH order indicating connection with the at least one candidate TRP from the first base station; transmit an RA (random access) preamble to the at least one candidate TRP using a second beam in a second beam direction having a QCL (quasi-colocation) relationship with a first beam direction of the first beam of the beam identifier according to the PDCCH order; and receive a TA value from the second base station via the first base station.

[0021] Here, the at least one processor further causes the terminal to receive mapping information of the TRPs and SSB groups from the first base station; verify SSB indices of the SSBs; and determine a TRP mapped to each of the verified SSB indices based on the mapping information, wherein the first measurement information may include information about the mapped TRP for each of the SSBs.

[0022] According to the present disclosure, when a terminal moves from a serving cell to a non-serving cell area, a transmission / reception point transmitting an SSB with the best signal quality among candidate transmission / reception points transmitting SSBs containing the same cell identifier can be identified based on a physical downlink control channel (PDCCH) order. Accordingly, ambiguity that occurs when a transmission / reception point controlling a terminal transmits a CSI-RS (channel state information-reference signal) in an inter-CU (central unit) / intra-CU deployment scenario can be resolved.

[0023] Additionally, the Tx / Rx point controlling the terminal can request that the Tx / Rx point transmitting the SSB with the best signal quality transmit the CSI-RS toward the terminal. The terminal can receive the CSI-RS from the Tx / Rx point transmitting the SSB with the best signal quality to determine the channel status, enabling seamless cell switching when moving from a serving cell to a non-serving cell.

[0024] Figure 1 is a conceptual diagram illustrating a first embodiment of a communication system.

[0025] Figure 2 is a block diagram illustrating a first embodiment of a communication node constituting a communication system.

[0026] Figure 3a is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0027] FIG. 3b is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0028] FIG. 4 is a conceptual diagram illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0029] Figure 5 is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0030] FIG. 6 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0031] FIG. 7 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0032] Figure 8 is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0033] FIG. 9 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0034] FIG. 10 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0035] FIG. 11 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0036] FIG. 12 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0037] This disclosure may be subject to various modifications and various embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the disclosure to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the disclosure.

[0038] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present disclosure, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component." The term "and / or" includes a combination of multiple related items described herein or any of multiple related items described herein.

[0039] In embodiments of the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B.” Furthermore, in embodiments of the present disclosure, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B.”

[0040] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components intervening. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components intervening.

[0041] In the present disclosure, a phrase including “if (e.g., when ~)” can be expressed as a phrase including “based on (e.g., based on ~)” or a phrase including “in response to (e.g., in response to ~)”. In other words, a phrase including “if ~)” can be interpreted as being identical or similar to a phrase including “based on” or a phrase including “in response to”.

[0042] The terminology used in this disclosure is only used to describe specific embodiments and is not intended to limit the present disclosure. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this disclosure, it should be understood that the terms "comprises" or "has" indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0043] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and shall not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0044] A communication system to which embodiments according to the present disclosure are applied will be described. The communication system to which embodiments according to the present disclosure are applied is not limited to the scope described below, and embodiments according to the present disclosure can be applied to various communication systems. Here, the term "communication system" may be used interchangeably with "communication network."

[0045] Throughout the specification, the network may include, for example, wireless internet such as WiFi (wireless fidelity), mobile internet such as WiBro (wireless broadband internet) or WiMax (world interoperability for microwave access), 2G mobile communication networks such as GSM (global system for mobile communication) or CDMA (code division multiple access), 3G mobile communication networks such as WCDMA (wideband code division multiple access) or CDMA2000, 3.5G mobile communication networks such as HSDPA (high speed downlink packet access) or HSUPA (high speed uplink packet access), 4G mobile communication networks such as LTE (long term evolution) or LTE-Advanced, and 5G mobile communication networks.

[0046] Throughout the specification, a terminal may refer to a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, an access terminal, etc., and may include all or part of the functions of a terminal, a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, an access terminal, etc.

[0047] Here, a desktop computer, laptop computer, tablet PC, wireless phone, mobile phone, smart phone, smart watch, smart glass, e-book reader, portable multimedia player (PMP), portable game console, navigation device, digital camera, digital multimedia broadcasting (DMB) player, digital audio recorder, digital audio player, digital picture recorder, digital picture player, digital video recorder, digital video player, etc. capable of communicating with the terminal can be used.

[0048] Throughout the specification, a base station may also refer to an access point, a radio access station, a node B, an evolved node B, a base transceiver station, a mobile multihop relay (MMR)-BS, etc., and may include all or part of the functions of a base station, an access point, a radio access station, a node B, an eNodeB, a base transceiver station, an MMR-BS, etc.

[0049] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In order to facilitate an overall understanding in describing the present disclosure, identical reference numerals will be used for identical components in the drawings, and redundant descriptions of identical components will be omitted.

[0050] Figure 1 is a conceptual diagram illustrating a first embodiment of a communication system.

[0051] Referring to FIG. 1, a communication system (100) may include a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Here, the communication system may be referred to as a "communication network." Each of the plurality of communication nodes may support at least one communication protocol. For example, each of the plurality of communication nodes may support a communication protocol based on CDMA (code division multiple access), a communication protocol based on WCDMA (wideband CDMA), a communication protocol based on TDMA (time division multiple access), a communication protocol based on FDMA (frequency division multiple access), a communication protocol based on OFDM (orthogonal frequency division multiplexing), a communication protocol based on OFDMA (orthogonal frequency division multiple access), a communication protocol based on SC (single carrier)-FDMA, a communication protocol based on NOMA (non-orthogonal multiple access), a communication protocol based on SDMA (space division multiple access), etc. Each of the plurality of communication nodes may have the following structure.

[0052] Figure 2 is a block diagram illustrating a first embodiment of a communication node constituting a communication system.

[0053] Referring to FIG. 2, a communication node (200) may include at least one processor (210), a memory (220), and a transceiver (230) that is connected to a network and performs communication. In addition, the communication node (200) may further include an input interface device (240), an output interface device (250), a storage device (260), etc. Each component included in the communication node (200) may be connected by a bus (270) to perform communication with each other. However, each component included in the communication node (200) may be connected through an individual interface or an individual bus centered around the processor (210), rather than a common bus (270). For example, the processor (210) may be connected to at least one of the memory (220), the transceiver (230), the input interface device (240), the output interface device (250), and the storage device (260) through a dedicated interface.

[0054] The processor (210) can execute program commands stored in at least one of the memory (220) and the storage device (260). The processor (210) may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which methods according to embodiments of the present invention are performed. Each of the memory (220) and the storage device (260) may be configured with at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory (220) may be configured with at least one of a read-only memory (ROM) and a random access memory (RAM).

[0055] Referring again to FIG. 1, the communication system (100) may include a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) and a plurality of user equipment (UEs) (130-1, 130-2, 130-3, 130-4, 130-5, 130-6). Each of the first base station (110-1), the second base station (110-2), and the third base station (110-3) may form a macro cell. Each of the fourth base station (120-1) and the fifth base station (120-2) may form a small cell. The fourth base station (120-1), the third UE (130-3), and the fourth UE (130-4) may be within the coverage of the first base station (110-1). The second UE (130-2), the fourth UE (130-4), and the fifth UE (130-5) may be within the coverage of the second base station (110-2). The fifth base station (120-2), the fourth UE (130-4), the fifth UE (130-5), and the sixth UE (130-6) may be within the coverage of the third base station (110-3). The first UE (130-1) may be within the coverage of the fourth base station (120-1). The sixth UE (130-6) may be within the coverage of the fifth base station (120-2).

[0056] Here, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) may be referred to as a NodeB, an evolved NodeB, a BTS (base transceiver station), a radio base station, a radio transceiver, an access point, an access node, a road side unit (RSU), a DU (digital unit), a CDU (cloud digital unit), a RRH (radio remote head), a RU (radio unit), a TP (transmission point), a TRP (transmission and reception point), a relay node, etc. Each of the plurality of UEs (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) may be referred to as a terminal, an access terminal, a mobile terminal, a station, a subscriber station, a mobile station, a portable subscriber station, a node, a device, etc.

[0057] Each of the plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6) can support cellular communication (e.g., long term evolution (LTE), LTE-A (advanced) as defined in the 3rd generation partnership project (3GPP) standard). Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can operate in a different frequency band or can operate in the same frequency band. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can be connected to each other via an ideal backhaul or a non-ideal backhaul, and can exchange information with each other via the ideal backhaul or the non-ideal backhaul. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can be connected to a core network (not shown) via an ideal backhaul or a non-ideal backhaul. Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can transmit a signal received from the core network to the corresponding UE (130-1, 130-2, 130-3, 130-4, 130-5, 130-6), and can transmit a signal received from the corresponding UE (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) to the core network.

[0058] Each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can support OFDMA-based downlink transmission and SC-FDMA-based uplink transmission. In addition, each of the plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2) can support MIMO (multiple input multiple output) transmission (e.g., single user (SU)-MIMO, multi user (MU)-MIMO, massive MIMO, etc.), CoMP (coordinated multipoint) transmission, carrier aggregation transmission, transmission in an unlicensed band, device to device (D2D) communication (or, ProSe (proximity services), etc.). Here, each of the plurality of UEs (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) can support the base station (110-1, 110-2, 110-3, 120-1, 120-2) and can perform operations supported by base stations (110-1, 110-2, 110-3, 120-1, 120-2).

[0059] Meanwhile, in a communication system, a base station can perform all functions of a communication protocol (e.g., remote wireless transmission / reception functions, baseband processing functions). Among all functions of a communication protocol, the remote wireless transmission / reception function can be performed by a transmission reception point (TRP) (e.g., f(flexible)-TRP), and among all functions of a communication protocol, the baseband processing function can be performed by a baseband unit (BBU) block. A TRP can be a remote radio head (RRH), a radio unit (RU), a transmission point (TP), etc. A BBU block can include at least one BBU or at least one digital unit (DU). A BBU block can be referred to as a "BBU pool," a "centralized BBU," etc. A TRP can be connected to a BBU block via a wired fronthaul link or a wireless fronthaul link. A communication system consisting of a backhaul link and a fronthaul link can be as follows. When the function split method of the communication protocol is applied, the TRP can selectively perform some functions of the BBU or some functions of the MAC (medium access control) / RLC (radio link control).

[0060] In the present disclosure, a node communicating with a base station or transmission / reception point (TRP) may be referred to as a user equipment (UE) (i.e., a terminal). The TRP may be controlled by a base station (BS). The UE, BS, and / or TRP may include at least some of the configurations of FIG. 2 described above, and may further include additional configurations. For example, the UE may include various interfaces and / or sensors for user convenience. The BS may include an interface (e.g., a backhaul interface and / or a fronthaul interface) for communicating with the TRP, other BSs, and / or a specific network function (NF) of the core network. The TRP may include an interface for communicating with the BS. However, it should be noted that this is for convenience of description and is not limited thereto. All possible configurations read by the concepts of the methods, procedures, and devices according to the present disclosure may be included within the scope of the present disclosure. A plurality of TRPs and the UE may transmit signals isochronously or sequentially.

[0061] A UE can move from a serving cell to a non-serving cell. For example, the UE can use the lower-layer triggered mobility (LTM) method introduced in 3GPP (3rd generation partnership project) Release 18 (Rel-18). The LTM method introduced in 3GPP Release 18 can improve handover latency and interruption time compared to Layer 3 (L3)-based mobility methods. However, the LTM method introduced in 3GPP Release 18 may still have significant latency and interruption time. The LTM method introduced in 3GPP Release 18 may have several limitations.

[0062] FIG. 3a is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0063] Referring to FIG. 3A, a first terminal (330) may exist within a serving cell of a first base station (321) having a physical cell identity (PCI) PCI G. Two TRPs (TRP 1-1, TRP 1-2) having the same PCI may exist within the serving cell. The first terminal may exist outside a non-serving cell of a second base station (322) having a physical cell identity PCI Z. Two TRPs (TRP 2-1, TRP 2-2) having the same PCI may exist within the non-serving cell. The first terminal may move from the serving cell to the non-serving cell.

[0064] The first base station and the second base station may be connected to the same first CU (central unit) (310). Such a communication system may be called an intra-cell multi-TRP (M-TRP or MTRP) communication system. The serving cell may have two TRPs, but may include a larger number of TRPs. The non-serving cell may have two TRPs, but may include a larger number of TRPs. The LTM method introduced in 3GPP Release 18 can support the movement of a terminal between TRPs (e.g., radio units (RUs)) of base stations (e.g., distributed units (DUs)) with different PCIs within the same CU, i.e., within an intra-CU.

[0065] FIG. 3b is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0066] Referring to FIG. 3B, a second terminal (370) may exist within a serving cell of a third base station (361) having a physical cell identifier PCI G. Two TRPs (TRP 3-1, TRP 3-2) having the same PCI may exist within the serving cell. The second terminal may exist outside a non-serving cell of a fourth base station (362) having a physical cell identifier PCI Z. Two TRPs (TRP 4-1, TRP 4-2) having the same PCI may exist within the non-serving cell. The second terminal may move from the serving cell to the non-serving cell.

[0067] The third base station may be connected to the second CU (351), and the fourth base station may be connected to the third CU (352). The second CU and the third CU may be different. Such a communication system may be called an inter-cell multiple transmission / reception point communication system. The serving cell may have two TRPs, but may include a larger number of TRPs. The non-serving cell may have two TRPs, but may include a larger number of TRPs. The LTM method introduced in 3GPP Release 18 cannot support the movement of a terminal between TRPs (e.g., RUs) of base stations (e.g., DUs) with different PCIs within different CUs, i.e., within an inter-CU. The LTM method introduced in 3GPP Release 18 may require L1 (layer 1) measurement using SSB (synchronization signal block). L1 measurements using SSB can have difficulties with fast cell transitions. Therefore, the LTM method introduced in 3GPP Release 18 cannot support UE movement within different CUs.

[0068] If the LTM method introduced in 3GPP Release 18 is improved to support UE movement between TRPs of base stations with different PCIs within different CUs, it can enable seamless zero-latency handovers. If the LTM method introduced in 3GPP Release 18 is improved to support UE movement between TRPs of base stations with different PCIs within different CUs, it can improve network (NW) efficiency.

[0069] The LTM method introduced in 3GPP Release 18 can reduce downtime during cell switching compared to L3-based mobility methods. However, the LTM method introduced in 3GPP Release 18 cannot provide the high robustness offered by L3-based mobility methods. Therefore, the LTM method introduced in 3GPP Release 18 needs to be improved to support both high robustness and short downtime.

[0070] The improved LTM method can transmit a CSI-RS (channel state information-reference signal) from the TRP (TRP 4-1, TRP 4-2) of the fourth base station (362) of the third CU (352) before and / or during cell switching. The improved LTM method can enable the terminal to receive the CSI-RS from the TRP (TRP 4-1, TRP 4-2) and perform L1 measurement on the received CSI-RS, thereby solving various problems of the LTM method introduced in 3GPP Release 18.

[0071] In other words, in the improved LTM method, the TRP 4-1 (i.e., corresponding to a candidate cell) controlled by the fourth base station (362) of the third CU (352) can transmit CSI-RS to the terminal in the downlink. In the improved LTM method, the terminal can receive the CSI-RS from the TRP 4-1 and perform L1 measurement on the received CSI-RS. In this way, the improved LTM method can perform CSI-RS-based beam management and / or other necessary physical layer operations for the candidate cell before and / or during cell switching, thereby enabling the terminal to switch to the candidate cell while maintaining uninterrupted communication.

[0072] Figure 4 is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0073] Referring to FIG. 4, a terminal (430) may exist within a serving cell of a first base station (421) having a physical cell identifier PCI G. Two TRPs (TRP 1-1, TRP 1-2) having the same PCI may exist within the serving cell. The terminal may exist outside a non-serving cell of a second base station (422) having a physical cell identifier PCI Z. Two TRPs (TRP 2-1, TRP 2-2) having the same PCI may exist within the non-serving cell.

[0074] A first base station may be connected to a first CU (411), and a second base station may be connected to a second CU (412). The first CU and the second CU may be different. A serving cell may have two TRPs, but may include a larger number of TRPs. A non-serving cell may have two TRPs, but may include a larger number of TRPs.

[0075] A terminal may move from a serving cell to a non-serving cell. The terminal may be before cell switching to a candidate cell controlled by a second base station of a second CU, i.e., TRP 2-1. TRP 2-1 may transmit an SSB to the terminal. The terminal may receive an SSB from TRP 2-1 and perform measurement on the received SSB. The terminal may report the measurement result for the SSB received from TRP 2-1 to TRP 1-1. TRP 1-1 may receive the measurement result for the SSB of TRP 2-1 from the terminal. TRP 2-2 may transmit an SSB to the terminal. The terminal may receive an SSB from TRP 2-2 and perform measurement on the received SSB. The terminal may report the measurement result for the SSB received from TRP 2-2 to TRP 1-1. TRP 1-1 can receive measurement results for SSB of TRP 2-2 from the terminal.

[0076] Since TRP 2-1 is closer to the terminal than TRP 2-2, the signal quality for SSB of TRP 2-1 may be better than that of SSB of TRP 2-2. The network may instruct the TRP associated with the SSB with better signal quality to transmit the CSI-RS. However, the measurement result for SSB of TRP 2-1 may not include identification information for TRP 2-1, and the measurement result for SSB of TRP 2-2 may not include identification information for TRP 2-2. Therefore, TRP 1-1 cannot identify the TRP associated with SSB with better signal quality based solely on the measurement result for SSB.

[0077] In other words, it may be difficult for TRP 1-1 to determine whether TRP 2-1 or TRP 2-2 transmits SSB with better signal quality based only on the measurement results of SSB received from the terminal. Since the network cannot specify the TRP associated with the SSB with better signal quality, it cannot specify the TRP to transmit CSI-RS to the terminal. In other words, the network may have ambiguity in determining whether to specifically transmit CSI-RS to the terminal using TRP 2-1 or TRP 2-2. The network may instruct TRP 2-1 to transmit CSI-RS. The terminal may receive CSI-RS from TRP 2-1. Alternatively, the network may instruct TRP 2-2 to transmit CSI-RS. The terminal may receive CSI-RS from TRP 2-2.

[0078] To address the aforementioned ambiguity, an improved LTM method may require a procedural method that avoids the ambiguity. The improved LTM method may enable the terminal to estimate the best SSB(s) from the SSB(s) received from the TRPs, and may require a method that allows the terminal to recognize the TRP that transmitted the estimated best SSB(s).

[0079] A terminal that wishes to switch cells to one of the candidate cells can perform downlink communication. In an improved LTM method, the terminal can utilize measurements based on the CSI-RS mentioned above during downlink communication. The terminal may be performing uplink (UL) communication with a TRP at the terminal. The improved LTM method utilizes measurements based on a sounding reference signal (SRS) rather than CSI-RS during uplink communication to perform beam measurement and beam management for the candidate cell before and / or during cell switching, thereby performing seamless cell switching and communication. The improved LTM method may require methods, procedures, and devices utilizing SRS.

[0080] The present disclosure may aim to provide a procedural method for transmitting CSI-RS in downlink by minimizing resource waste in TRP and allowing a terminal to receive CSI-RS from TRP and perform L1 measurement on the received CSI-RS in order to solve the problems of the prior art described above. The present disclosure may aim to provide a method and device for performing downlink CSI-RS measurement and management before and / or during cell switching, in which a serving cell can recognize a TRP that transmitted the best SSB by estimating a best SSB from SSBs swept from an initial system access in a terminal in order to solve the problems of the prior art described above.

[0081] In this disclosure, the central device of the network may be referred to as a CU, and the wireless device may be referred to as a user equipment (or UE). The present disclosure may refer to a device that transmits a downlink signal to the UE and receives an uplink signal from the UE as a TRP or RU. The present disclosure may refer to a device that controls the TRP as a base station or gNB, and the area controlled by the base station as a cell. The present disclosure may describe specific methods, procedures, and devices of the present disclosure based on the configuration of the user equipment, TRP, gNB, and cell.

[0082] However, this is for convenience of explanation and is not limited thereto, and all possible configurations that can be read within the concept of the method, procedure, and device of the present disclosure may be included in the scope of the present disclosure, and it should be noted that the terminal is referred to as a mobile station (MS). The contents described below may assume an inter-CU situation. However, it should be noted that deployment scenarios that configure gNB / DU and RU with different PCI(s) and / or identical PCI(s) in an intra-CU situation are also included in the scope of the present disclosure. It should be noted that the CU and / or gNB and / or TRP may be collectively expressed as NW.

[0083] The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS toward a terminal before cell switching as shown in FIG. 4, and can propose several transmission methods, procedures, and communication devices for performing measurements in the reverse direction depending on the communication situation of the terminal, as follows. The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS in an inter-CU / intra-CU deployment scenario, and can propose the first simple method and procedure for performing uplink measurements depending on the situation based on FIGS. 5 and 6.

[0084] Figure 5 is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0085] Referring to FIG. 5, a terminal (530) may exist within a serving cell of a first base station (521) having a physical cell identifier PCI G. Two TRPs (TRP 1-1, TRP 1-2) having the same PCI may exist within the serving cell. The terminal may exist outside a non-serving cell of a second base station (522) having a physical cell identifier PCI Z. Three TRPs (TRP 2-1, TRP 2-2, TRP 2-3) having the same PCI may exist within the non-serving cell of the second base station. The terminal may exist outside a non-serving cell of a third base station (523) having a physical cell identifier PCI Q. One TRP (TRP 3-1) may exist within the non-serving cell of the third base station.

[0086] A first base station may be connected to a first CU (511), a second base station may be connected to a second CU (512), and a third base station may be connected to a third CU (513). The first CU, the second CU, and the third CU may be different. A serving cell may have two TRPs, but may include more TRPs. A non-serving cell of the second base station may have three TRPs, but may include more TRPs. A non-serving cell of the third base station may have one TRP, but may include more TRPs. A terminal may move from a first base station to a second base station, and may be in a situation where cell switching is required from TRP 1-1 of the first base station to TRP 2-1 of the second base station.

[0087] Each of TRP 2-1 and TRP 3-1 can transmit an SSB to the terminal. The terminal can receive an SSB from TRP 2-1. The terminal can receive an SSB from TRP 3-1. The terminal can select an SSB received from TRP 2-1, which is close to the terminal, as a best SSB among the SSBs received from TRP 2-1 and TRP 3-1. The best SSB may be the first SSB. The terminal can select an SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, as a second-best SSB among the SSBs received from TRP 2-1 and TRP 3-1. The second-best SSB may be the second SSB. The best SSB may be an SSB having the largest maximum correlation value. The second-best SSB may have the second maximum correlation value. The best SSB may be the one with the highest signal-to-interference-plus-noise ratio (SINR). The next best SSB may have the second-highest SINR.

[0088] The best SSB can have, for example, PCI, for example, PCI Z, a beam ID (identifier), for example, beam 5, etc. The second best SSB can have, for example, PCI Q, a beam ID, for example, beam 2, etc. The terminal can transmit information about the best SSB and information about the second best SSB in TRP 1-1. The information about the best SSB can include PCI Z, beam 5, etc. The information about the second best SSB can include PCI Q, beam 2, etc.

[0089] TRP 1-1 can receive information about the best SSB and information about the next best SSB from the terminal. TRP 1-1 can transmit information about the best SSB and information about the next best SSB to the first base station. The first base station can receive information about the best SSB and information about the next best SSB from TRP 1-1. The first base station can know the PCI Z from the information about the best SSB. The first base station can know the PCI of the second base station as PCI Z.

[0090] Before and / or during the cell switching operation at the terminal, the first base station may request the second base station to transmit a CSI-RS toward the terminal while transmitting the beam ID of beam 5 to the second base station. The second base station may receive a request for transmitting a CSI-RS including the beam ID of beam 5 from the first base station. If the second base station can identify TRP 2-1 as the TRP that transmitted the best SSB, the second base station may request TRP 2-1 to transmit the CSI-RS. TRP 2-1 may receive the request for transmitting the CSI-RS from the second base station and transmit the CSI-RS to the terminal. However, the second base station cannot distinguish the TRP that transmitted the best SSB from the request for transmitting the CSI-RS including the beam ID information of beam 5 received from the first base station. In other words, the second base station cannot know which TRP, TRP 2-1 or TRP 2-2, transmitted the best SSB.

[0091] A method and procedure for enabling a second base station to determine which TRP among TRP 2-1 and TRP 2-2 transmitted the best SSB can be described as follows based on FIG. 6. In the method and procedure described based on FIG. 6, it can be assumed that a terminal performs cell switching to TRP 2-1 of the second base station, which has the best channel quality among candidate cells, while communicating by establishing a connection with TRP 1-1 of the first base station. The method and procedure described based on FIG. 6 can be assumed that some and / or all of the SSBs swept in all TRPs are shared and used redundantly.

[0092] FIG. 6 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0093] Referring to FIG. 6, a first base station can control TRP 1-1. A second base station can control TRP 2-1 and TRP 2-2 (not shown). A third base station can control TRP 3-1. A terminal can be connected to TRP 1-1 and transmit and receive data through TRP 1-1. The cell formed by TRP 1-1 can be a serving cell. The cells formed by TRP 2-1, TRP 2-2, and TRP 3-1 can be non-serving cells.

[0094] TRP 2-1, TRP 2-2, and TRP 3-1 can transmit SSBs to the terminal (S611, S612). The terminal can receive SSBs from TRP 2-1. The terminal can receive SSBs from TRP 2-2. The terminal can receive SSBs from TRP 3-1. The terminal can measure the signal quality of each of the received SSBs. Based on the signal qualities of the SSBs, the terminal can select the SSB received from TRP 2-1, which is close to the terminal, among the SSBs received from TRP 2-1, TRP 2-2, and TRP 3-1. The best SSB may be the first SSB. The terminal may select, among the SSBs received from TRP 2-1, TRP 2-2, and TRP 3-1, the SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, as the next SSB. The next SSB may be the second SSB.

[0095] The best SSB may have a first PCI (e.g., PCI Z), a first beam ID (e.g., beam 5), etc. The next best SSB may have a second PCI (e.g., PCI Q), a second beam ID (e.g., beam 2), etc. The terminal may select candidate cell(s) through SSB estimation. For example, the terminal may select TRP 2-1, which transmitted an SSB having a PCI of PCI Z and a beam ID of beam 5, as the first candidate cell, TRP 3-1, which transmitted an SSB having a PCI of PCI Q and a beam ID of beam 2, as the second candidate cell, and so on. In addition, the terminal may sequentially select a third candidate cell, a fourth candidate cell, etc. The signal quality may be RSRP (reference signal received power), RSRQ (reference signal received quality), SINR, etc.

[0096] The terminal may perform a random access process for TRP 1-1. After the random access process, the terminal may perform a link connection process for TRP 1-1. The link connection process may be, for example, an RRC reconfiguration (radio resource control) process. During the link connection process, before or after the terminal's SSB estimation, TRP 1-1 may request the terminal to report its capabilities (S613).

[0097] A terminal can receive a request for a terminal capability report from TRP 1-1. In response to the request for a terminal capability report, the terminal can transmit a terminal capability report containing information on functions that the terminal can support to TRP 1-1 (S614). TRP 1-1 can receive a terminal capability report from the terminal. The terminal can transmit the terminal capability report to TRP 1-1 via an RRC message, and TRP 1-1 can receive the terminal capability report via an RRC message. TRP 1-1 can verify the capability of the terminal through the received terminal capability report, and can efficiently allocate network resources and establish an optimal connection based on the verified terminal capability.

[0098] The terminal capability report may include the terminal's radio frequency (RF) capability, physical layer (PHY) capability, medium access control (MAC) capability, radio link control (RLC) capability, packet data convergence protocol (PDCP) capability, dual connectivity (DC) capability, carrier aggregation (CA) capability, non-standalone / standalone (NSA / SA) operation capability, NR bandwidth class, transport class capability, location services (LCS) capability, reduced capability (RedCap), and voice over NR (VoNR) capability.

[0099] The RF capability of the terminal may include information on the frequency band and frequency bandwidth supported by the terminal, whether multi-band or CA is supported, and information related to the Tx (transmission) / Rx (reception) antenna configuration. The PHY capability may include information on whether MIMO (multiple input multiple output) is supported and the number of MIMO streams, information on modulation and coding scheme support, and information on whether beamforming is supported. The MAC capability may include information related to scheduling functions in the MAC layer and hybrid automatic repeat request (HARQ). The RLC capability may include information on RLC modes for data transmission (e.g., whether transparent mode, acknowledged mode, and unacknowledged mode are supported).

[0100] PDCP capabilities may include data compression / decompression functions, functions related to security processing, etc. DC capabilities may include information related to whether dual connectivity of LTE (long-term evolution) and NR (new radio) is supported, and data processing in DC. CA capabilities may include information related to the ability of a terminal to simultaneously combine multiple frequency bands and combination information thereof. NSA / SA operation capabilities may include whether a terminal can operate in 5G SA or NSA mode, etc. NR bandwidth classes may refer to bandwidth classes supported by the terminal for each frequency band (e.g., bandwidth classes NR-A, NR-B, etc.). Transmission class capabilities may include transmission power classes supported by the terminal, etc.

[0101] LCS capabilities may include whether the terminal supports location-based services, such as the global positioning system (GPS) or advanced global positioning system (A-GPS). RedCap capabilities may include information about terminals with reduced capabilities (e.g., lightweight 5G devices, Internet-of-Things (IoT) devices, etc.). VoNR capabilities may include whether the terminal supports Voice over 5G (Vo5G).

[0102] The terminal may transmit measurement information including signal quality information of SSB for each of the candidate cell(s) selected by the terminal to TRP 1-1 (S615). TRP 1-1 may receive measurement information including signal quality information of SSB for each of the candidate cells selected by the terminal from the terminal. Based on the measurement information of SSBs of the candidate cells received from the terminal, TRP 1-1 may select candidate cells to be transmitted to the terminal based on, for example, signal quality and / or terminal capability and / or status of the candidate cells (S616). For example, TRP 1-1 may select up to 8 candidate cells.

[0103] TRP 1-1 can transmit information about candidate cells selected by TRP 1-1 to the terminal (S617). TRP 1-1 can transmit information about candidate cells to the terminal and a command to perform an early synchronization process. The terminal can receive information about candidate cells from TRP 1-1. The terminal can receive information about candidate cells and a command to perform an early synchronization process from TRP 1-1.

[0104] The early synchronization process can be composed of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB, and a terminal-based TA synchronization process that acquires TA (time advance / adjustment) based on the terminal and performs uplink synchronization. TRP 1-1 can transmit a command to perform the early synchronization process to the terminal through RRC signaling and / or MAC-CE (medium access control-control element). The terminal can receive the command to perform the early synchronization process from TRP 1-1 through RRC signaling and / or MAC-CE.

[0105] In the SSB-based downlink synchronization process, the terminal can perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected in TRP 1-1 (e.g., SSB corresponding to beam 5 with PCI Z, SSB corresponding to beam 2 with PCI Q). In the terminal-based TA synchronization process, the terminal may not transmit preamble(s) toward each candidate cell through PRACH (physical random access channel) resource(s) from TRP 1-1 via RRC / MAC-CE.

[0106] In the terminal-based TA synchronization process, the terminal can estimate the TA corresponding to the transmission timing information to be sent to each candidate cell based on the SSBs it has received. In the terminal-based TA synchronization process, the terminal can use the estimated TA for uplink synchronization. It should be noted that in the terminal-based TA synchronization, the candidate cell(s) may have different, unique transmission timing errors. In the terminal-based TA synchronization process, the serving cell and the candidate cell(s) may not be synchronized with each other by the NW, which may result in significantly worse uplink synchronization performance compared to the PRACH preamble-based TA synchronization. It should also be noted that the early synchronization process may not be performed at the NW's discretion. In this case, the early synchronization process may be omitted. The terminal may perform the early synchronization process for each candidate cell(s) received from TRP 1-1 (S618). It should be noted that the early synchronization process may not be performed at the NW's discretion.

[0107] TRP 1-1 may select a target cell based on the results of the early synchronization process and / or based on previous results of the early synchronization process (S619). For example, TRP 1-1 may select a TRP that transmitted an SSB having PCI Z and beam 5 as a target cell. TRP 1-1 may know that the candidate cell that transmitted the SSB having PCI Z and beam 5 is a TRP belonging to the second base station. TRP 1-1 cannot determine which TRP transmitted the SSB having PCI Z and beam 5 is among TRP 2-1, TRP 2-2, or TRP 2-3 controlled by the second base station. This may be because all TRPs of the second base station share SSBs when performing SSB sweeping.

[0108] Since the TRP(s) corresponding to the target cell(s) cannot be specified as described above, TRP 1-1 may send a CSI-RS request to the second base station through the first base station to request the second base station to transmit CSI-RSs toward the terminal using TRPs belonging to the second base station (S620). Specifically, TRP 1-1 may request the second base station to transmit CSI-RSs for CSI-RS measurement toward the terminal using TRPs located at the boundary of the first base station belonging to the second base station. The second base station may receive a CSI-RS request from the first base station requesting transmission of CSI-RSs using TRPs located at the boundary of the first base station.

[0109] The second base station can identify TRPs at the boundary of the first base station based on location information about TRPs controlled by the second base station and location information about the first base station. For example, the second base station can identify TRP 2-1 and TRP 2-2 of the second base station as TRPs at the boundary of the first base station. The second base station can configure / allocate CSI-RS resource(s) capable of transmitting CSI-RS to the TRPs located at the boundary of the first base station (e.g., TRP 2-1 and TRP 2-2 as shown in FIG. 5). The second base station can transmit information about the configured / allocated CSI-RS resource(s) to the TRPs located at the boundary of the first base station (e.g., TRP 2-1 and TRP 2-2 as shown in FIG. 5). TRPs located at the boundary of the first base station can receive information about CSI-RS resource(s) configured / allocated from the second base station.

[0110] The second base station may transmit information about CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station (e.g., TRP 2-1 and TRP 2-2 in FIG. 5) to the first base station (S621). The first base station may receive information about CSI-RS resource(s) configured / allocated to TRPs of the second base station located at the boundary of the first base station from the second base station.

[0111] The first base station can request the terminal to perform measurements on CSI-RSs in the CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station (for example, TRP 2-1 and TRP 2-2 in FIG. 5) (S622). The terminal can receive a request for measuring CSI-RSs in the CSI-RS resource(s) configured / allocated to TRPs of the second base station located at the boundary of the first base station. The first base station can transmit information about the CSI-RS resource(s) configured / allocated to the TRPs of the second base station located at the boundary of the first base station to the terminal. The terminal can receive information about the CSI-RS resource(s) configured / allocated to the TRPs of the second base station located at the boundary of the first base station.

[0112] The TRPs of the second base station located at the boundary of the first base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) (i.e., CSI-RS resource(s)) configured / allocated for transmission of the CSI-RSs (S623). The beam direction of the CSI-RS(es) transmitted in the TRPs of the second base station (e.g., TRP 2-1 and TRP 2-2 in FIG. 5) can have a QCL (quasi-colocation) relationship with the beam direction of the beam when transmitting the best SSB having the beam ID of beam 5.

[0113] The terminal can receive and measure CSI-RS(es) according to a measurement request for CSI-RS for CSI-RS resource(s) configured / allocated to TRPs of a second base station located at the boundary of a first base station. The terminal can report the measurement results of the CSI-RS(es) to TRP 1-1 periodically and / or aperiodically through the allocated reporting resource(s) (S624). TRP 1-1 can receive the measurement results of the CSI-RS(es) from the terminal periodically and / or aperiodically through the reporting resource(s). The measurement results of the CSI-RS can include information on the signal quality of the CSI-RS and the TRP that transmitted the CSI-RS. For example, the measurement result of CSI-RS may include information about a channel quality indicator (CQI), a precoding matrix indicator (PMI), a CSI-RS resource indicator (CRI), an SS / PBCH block resource indicator (SS / PBCH block resource indicator (DDBRI), a layer indicator (LI), a rank indicator (RI), a first layer reference signal reception power (L1-RSRP), and a TRP.

[0114] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of the serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0115] A terminal, a first base station, a second base station, TRP 1-1, and TRP 2-1 can perform an LTM execution process. During the LTM execution process, TRP 1-1 can transmit measurement results for candidate cells received from the terminal to the first base station. The first base station can receive measurement results for candidate cells from TRP 1-1. Based on the measurement results for candidate cells of the terminal received, the first base station can determine a candidate cell to be changed to a target cell. The candidate cell can be, for example, TRP 2-1 of the second base station.

[0116] The first base station can transmit a cell switch command to the terminal via MAC CE. The terminal can disconnect from TRP 1-1 and apply preset candidate cell configuration information. The terminal can attempt to connect to TRP 2-1 as a target cell. If the uplink synchronization is invalid, the terminal can perform a random access procedure to establish uplink synchronization. The TA value included in the cell switch command may be invalid, such as 'FFF'. The cell switch command may not include a contention-free random access resources field. The terminal can use a TA value measured by itself. The cell switch command may specify a TA value. The terminal can use the specified TA value.

[0117] A TA value may be specified in the cell switch command. In this case, the terminal may not perform the RACH procedure for cell switching. The TA value may be specified as an invalid value in the cell switch command, and a non-contention random access resource field may exist. In this case, the terminal may perform the RACH procedure to obtain a TA value for a candidate cell. Cell switching may be successfully completed (S625). During the LTM completion process of the LTM procedure, the terminal may notify the target base station (e.g., the second base station) that the target cell access has been successfully completed. The second base station may initiate data transmission to the terminal via TRP 2-1. During and after the above cell switching procedure, the terminal may perform zero-delay switching to the target cell without interruption to perform DL and UL communications (S626).

[0118] For example, target cell TRP 2-1 may request RRC reconfiguration from the terminal (S627). The terminal may receive a request for RRC reconfiguration from TRP 2-1. The terminal may complete the reconfiguration according to the RRC request. The terminal may transmit an RRC reconfiguration completion message to TRP 2-1 to report that the reconfiguration has been completed (S628). TRP 2-1 may receive the RRC reconfiguration completion message from the terminal. TRP 2-1 may complete the LTM cell switch and / or complete the system connection to maintain the connection state with the target cell as the new serving cell.

[0119] Meanwhile, the present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS toward a terminal before cell switching, and can propose several transmission methods, procedures, and communication devices for performing measurements in the reverse direction depending on the communication situation of the terminal, as follows. The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS in an inter-CU / intra-CU deployment scenario, and can propose a second simple method and procedure for performing uplink measurements depending on the situation, as follows, based on FIGS. 5 and 7.

[0120] Referring back to FIG. 5, before and / or during a cell switching operation at a terminal, a first base station may request a second base station to transmit a CSI-RS toward the terminal while transmitting the beam ID of beam 5 to the second base station. The second base station may receive a request for transmission of a CSI-RS including the beam ID of beam 5 from the first base station. If the second base station can specify TRP 2-1 as the TRP that transmitted the best SSB, it may request transmission of the CSI-RS to TRP 2-1. TRP 2-1 may receive the request for transmission of the CSI-RS from the second base station and transmit the CSI-RS to the terminal. However, the second base station cannot distinguish the TRP that transmitted the best SSB from the request for transmission of the CSI-RS including the beam ID information of beam 5 received from the first base station. In other words, the second base station cannot know which TRP, TRP 2-1 or TRP 2-2, transmitted the best SSB.

[0121] A method and procedure for enabling a second base station to determine which TRP among TRP 2-1 and TRP 2-2 transmitted the best SSB can be described as follows based on FIG. 7. In the method and procedure described based on FIG. 7, it can be assumed that a terminal performs cell switching to TRP 2-1 of the second base station, which has the best channel quality among candidate cells, while communicating by establishing a connection with TRP 1-1 of the first base station. The method and procedure described based on FIG. 7 can be assumed that some and / or all of the SSBs swept in all TRPs are shared and used redundantly.

[0122] FIG. 7 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0123] Referring to FIG. 7, a first base station can control TRP 1-1. A second base station can control TRP 2-1 and TRP 2-2 (not shown). A third base station can control TRP 3-1. A terminal can be connected to TRP 1-1 and transmit and receive data through TRP 1-1. The cell formed by TRP 1-1 can be a serving cell. The cells formed by TRP 2-1, TRP 2-2, and TRP 3-1 can be non-serving cells.

[0124] TRP 2-1, TRP 2-2, and TRP 3-1 can transmit SSBs to the terminal (S711, S712). The terminal can receive SSBs from TRP 2-1. The terminal can receive SSBs from TRP 2-2. The terminal can receive SSBs from TRP 3-1. The terminal can measure the signal quality of each of the received SSBs. Based on the signal qualities of the SSBs, the terminal can select the SSB received from TRP 2-1, which is close to the terminal, among the SSBs received from TRP 2-1, TRP 2-2, and TRP 3-1. The best SSB may be the first SSB. The terminal may select, among the SSBs received from TRP 2-1, TRP 2-2, and TRP 3-1, the SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, as the next SSB. The next SSB may be the second SSB.

[0125] The best SSB may have a first PCI (e.g., PCI Z), a first beam ID (e.g., beam 5), etc. The next best SSB may have a second PCI (e.g., PCI Q), a second beam ID (e.g., beam 2), etc. The terminal may select candidate cell(s) through SSB estimation. For example, the terminal may select TRP 2-1, which transmits an SSB having a PCI of PCI Z and a beam ID of beam 5, as the first candidate cell, TRP 3-1, which transmits an SSB having a PCI of PCI Q and a beam ID of beam 2, as the second candidate cell, and so on. The terminal may then select a third candidate cell, a fourth candidate cell, etc. The signal quality may be RSRP, RSRQ, or SINR.

[0126] The terminal may perform a random access process for TRP 1-1. After the random access process, the terminal may perform a link connection process for TRP 1-1. The link connection process may be, for example, an RRC reconfiguration process. During the link connection process, before or after the terminal's SSB estimation, TRP 1-1 may request the terminal to report its capabilities (S713).

[0127] A terminal can receive a request for a terminal capability report from TRP 1-1. Upon receiving the request for a terminal capability report, the terminal can transmit a terminal capability report containing information about functions that the terminal can support to TRP 1-1 (S714). TRP 1-1 can receive a terminal capability report from the terminal. The terminal can transmit the terminal capability report to TRP 1-1 via an RRC message, and TRP 1-1 can receive the terminal capability report via an RRC message. TRP 1-1 can verify the capabilities of the terminal through the received terminal capability report, and based on the verified terminal capabilities, can efficiently allocate network resources and establish an optimal connection.

[0128] The terminal capability report may include the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, VoNR capability, etc. Each of the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, and VoNR capability may be the same as described above with respect to FIG. 6.

[0129] The terminal may transmit measurement information including signal quality information of SSB for each of the candidate cell(s) selected by the terminal to TRP 1-1 (S715). TRP 1-1 may receive measurement information including signal quality information of SSB for each of the candidate cells selected by the terminal from the terminal. Based on the measurement information of SSBs of the candidate cells received from the terminal, TRP 1-1 may select candidate cells to be transmitted to the terminal based on, for example, signal quality and / or capability of the terminal and / or status of the candidate cells (S716). For example, TRP 1-1 may select up to 8 candidate cells.

[0130] TRP 1-1 can transmit information about candidate cells selected by TRP 1-1 to the UE (S717). TRP 1-1 can transmit a command to perform an early synchronization process while transmitting information about the candidate cells to the UE. The UE can receive information about the candidate cells from TRP 1-1. The UE can receive information about the candidate cells from TRP 1-1 and a command to perform an early synchronization process.

[0131] The early synchronization process can be comprised of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB, and a terminal-based TA synchronization process that acquires a TA based on the terminal and performs uplink synchronization. TRP 1-1 can transmit a command to perform the early synchronization process to the terminal via RRC signaling and / or MAC-CE. The terminal can receive the command to perform the early synchronization process from TRP 1-1 via RRC signaling and / or MAC-CE.

[0132] In the SSB-based downlink synchronization process, the terminal can perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected in TRP 1-1 (for example, the SSB corresponding to beam 5 with PCI Z, the SSB corresponding to beam 2 with PCI Q). In the terminal-based TA synchronization process, the terminal may not transmit the preamble(s) toward each candidate cell through the PRACH resource(s) from TRP 1-1 via RRC / MAC-CE. In the terminal-based TA synchronization process, the terminal can estimate the TA corresponding to the transmission timing information to be sent to each candidate cell based on the SSBs it has received. In the terminal-based TA synchronization process, the terminal can use the estimated TA as uplink synchronization. It should be noted here that in the terminal-based TA synchronization, the candidate cell(s) may have different, unique transmission timing errors.

[0133] During the terminal-based TA synchronization process, the serving cell and candidate cell(s) may not be synchronized with each other by the NW, which may result in significantly worse uplink synchronization performance compared to PRACH preamble-based TA synchronization. It should also be noted that the early synchronization process may not be performed at the NW's discretion. In such a case, the early synchronization process may be omitted. The terminal may perform the early synchronization process for each candidate cell(s) received from TRP 1-1 (S718). It should be noted that the early synchronization process may not be performed at the NW's discretion.

[0134] TRP 1-1 may request the candidate cells to transmit CSI-RSs through the first base station based on the results of the early synchronization process and / or based on the previous results of the early synchronization process. For example, TRP 1-1 may send a CSI-RS request to the second base station through the first base station to request the second base station to transmit CSI-RSs toward the terminal using TRPs belonging to the second base station (S719-1). Specifically, TRP 1-1 may request the second base station to transmit CSI-RSs for CSI-RS measurement toward the terminal using TRPs located at the boundary of the first base station belonging to the second base station. The second base station may receive a CSI-RS request from the first base station requesting transmission of CSI-RSs using TRPs located at the boundary of the first base station.

[0135] The second base station can identify TRPs at the boundary of the first base station based on location information about TRPs controlled by the second base station and location information about the first base station. For example, the second base station can identify TRP 2-1 and TRP 2-2 of the second base station as TRPs at the boundary of the first base station. The second base station can configure / allocate CSI-RS resource(s) capable of transmitting CSI-RS to the TRPs located at the boundary of the first base station (e.g., TRP 2-1 and TRP 2-2 as shown in FIG. 5). The second base station can transmit information about the CSI-RS resource(s) configured / allocated to the TRPs located at the boundary of the first base station (e.g., TRP 2-1 and TRP 2-2 as shown in FIG. 5) to the TRPs of the second base station located at the boundary of the first base station. The TRPs of the second base station located at the boundary of the first base station can receive information about the CSI-RS resource(s) configured / allocated from the second base station.

[0136] The second base station may transmit information about CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station (e.g., TRP 2-1 and TRP 2-2 in FIG. 5) to the first base station (S720-1). The first base station may receive information about CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station from the second base station.

[0137] TRP 1-1 may send a CSI-RS request to the third base station via the first base station to request the third base station to transmit CSI-RSs toward the terminal using TRPs belonging to the third base station (S719-2). Specifically, TRP 1-1 may request the third base station to transmit CSI-RSs for CSI-RS measurement toward the terminal using TRPs located at the boundary of the first base station belonging to the third base station. The third base station may receive a CSI-RS request from the first base station requesting transmission of CSI-RSs using TRPs located at the boundary of the first base station.

[0138] The third base station can identify TRPs at the boundary of the first base station based on location information about TRPs controlled by the third base station and location information of the first base station. For example, the third base station can identify TRP 3-1 of the third base station as a TRP at the boundary of the first base station. The third base station can configure / allocate CSI-RS resource(s) capable of transmitting CSI-RS to the TRPs located at the boundary of the first base station (e.g., TRP 3-1 as shown in FIG. 5). The third base station can transmit information about the configured / allocated CSI-RS resource(s) to the TRPs of the third base station located at the boundary of the first base station (e.g., TRP 3-1 as shown in FIG. 5). The TRPs of the third base stations located at the boundary of the first base station can receive information about the configured / allocated CSI-RS resource(s) from the third base station.

[0139] The third base station may transmit information about CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station (e.g., TRP 3-1 in FIG. 5) to the first base station (S720-2). The first base station may receive information about CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station from the third base station.

[0140] The first base station may request the terminal to perform measurements on CSI-RSs in the CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station (for example, TRP 2-1, TRP 2-2, and TRP 3-1 as shown in FIG. 5) (S721). The terminal may receive a request for CSI-RS measurement for the CSI-RS resource(s) configured / allocated to the TRPs located at the boundary of the first base station. The first base station may transmit information about the CSI-RS resource(s) configured / allocated to the TRPs located at the boundary of the first base station (for example, TRP 2-1, TRP 2-2, and TRP 3-1 as shown in FIG. 5) to the terminal. The terminal may receive information about the CSI-RS resource(s) configured / allocated to the TRPs located at the boundary of the first base station.

[0141] TRPs located at the boundary of the first base station (e.g., TRP 2-1, TRP 2-2, TRP 3-1 in FIG. 5) can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) configured / allocated for transmission of the CSI-RSs (S722-1, S722-2). For example, TRPs of the second base station (e.g., TRP 2-1, TRP 2-2 in FIG. 5) located at the boundary of the first base station can transmit CSI-RS(es) as instructed in the configured / allocated resource(s). The beam direction of the CSI-RS(es) transmitted by the TRPs of the second base station (e.g., TRP 2-1, TRP 2-2 in FIG. 5) can have a QCL relationship with the beam direction of the beam when transmitting the best SSB having the beam ID of beam 5. The TRPs of the third base station (e.g., TRP 3-1 in FIG. 5) located at the boundary of the first base station can transmit CSI-RS(es) as instructed from the configured / allocated resource(s). The beam direction of the CSI-RS(es) transmitted from the TRPs of the third base station (e.g., TRP 3-1 in FIG. 5) can have a QCL relationship with the beam direction of the beam when transmitting the next-best SSB having the beam ID of beam 2.

[0142] The terminal can measure CSI-RS(es) according to a request for CSI-RS measurement for CSI-RS resource(s) configured / allocated to TRPs located at the boundary of the first base station. The terminal can report the measurement results for the CSI-RS(es) to TRP 1-1 periodically and / or aperiodically using the allocated reporting resource(s) (S723). TRP 1-1 can receive the measurement results for the CSI-RS(es) from the terminal periodically and / or aperiodically through the reporting resource(s). The measurement results for the CSI-RS can include information about the signal quality of the CSI-RS and the TRP that transmitted the CSI-RS.

[0143] For example, the measurement result of CSI-RS may include information about channel quality indicator, precoding matrix indicator, CSI-RS resource indicator, SS / PBCH block resource indicator, layer indicator, rank indicator, first layer reference signal reception power, TRP, etc.

[0144] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of a serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0145] The first base station may select a target cell based on the CSI-RS measurement results received from the terminal (S724). For example, the signal quality of the CSI-RS transmitted in TRP 2-1 may be the best among the CSI-RS measurement results. The first base station may refer to the CSI-RS measurement results and confirm that TRP 2-1 is the TRP that transmitted the CSI-RS with the best signal quality. The first base station may select TRP 2-1 as the target cell.

[0146] The first base station can transmit a cell switch command to the terminal via MAC CE. The terminal can disconnect from TRP 1-1 and apply preset candidate cell configuration information. The terminal can attempt to connect to TRP 2-1 as a target cell. If UL synchronization is invalid, the terminal can establish UL synchronization by performing a random access procedure. The TA value included in the cell switch command may be invalid, such as 'FFF'. The cell switch command may not include a contention-free random access resource field. The terminal can use a TA value measured by itself. The cell switch command may specify a TA value. The terminal can use the specified TA value.

[0147] A TA value may be specified in the cell switch command. In this case, the terminal may not perform the RACH procedure for cell switching. The TA value may be specified as an invalid value in the cell switch command, and a non-contention random access resource field may exist. In this case, the terminal may perform the RACH procedure to obtain a TA value for a candidate cell. Cell switching may be successfully completed (S725). During the LTM completion process of the LTM procedure, the terminal may notify the target base station (e.g., the second base station) that the target cell access has been successfully completed. The second base station may initiate data transmission to the terminal via TRP 2-1. During and after the above cell switching procedure, the terminal may perform zero-delay switching to the target cell without interruption and perform DL and UL communications (S726).

[0148] For example, target cell TRP 2-1 may request RRC reconfiguration from the terminal (S727). The terminal may receive a request for RRC reconfiguration from TRP 2-1. The terminal may complete the reconfiguration according to the RRC request. The terminal may transmit an RRC reconfiguration completion message to TRP 2-1 to report that the reconfiguration has been completed (S728). TRP 2-1 may receive the RRC reconfiguration completion message from the terminal. TRP 2-1 may complete the LTM cell switch and / or complete the system connection to maintain the connection state with the target cell as the new serving cell.

[0149] The first simple method and procedure mentioned above may not cause a heavy load on CSI-RS resources and CSI-RS measurements on the UE, since the CSI-RS(es) for one target cell are transmitted to the UE. On the other hand, the second method may cause a much heavier load, as it requires allocation of CSI-RS resources for all candidate cell(s) selected by the NW and CSI-RS measurements on the UE. To reduce these loads, the number of candidate cells can be reduced when the NW selects the candidate cell(s). However, reducing the number of candidate cells for this reason may adversely affect the fast LTM performance before or during cell switching due to evaluation events and / or CSI-RS measurement(s) triggered by the evaluation events.

[0150] Meanwhile, the present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS toward a terminal before cell switching, and can propose several transmission methods, procedures, and communication devices for performing measurements in the reverse direction depending on the communication situation of the terminal, as follows. The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS in an inter-CU / intra-CU deployment scenario, and can propose a third simple method and procedure for performing uplink measurements depending on the situation, as follows, based on FIGS. 8 and 9.

[0151] Figure 8 is a conceptual diagram illustrating embodiments of a communication system having multiple transmitting and receiving points.

[0152] Referring to FIG. 8, a terminal (830) may exist within a serving cell of a first base station (821) having a physical cell identifier PCI G. Two TRPs (TRP 1-1, TRP 1-2) having the same PCI may exist within the serving cell. The terminal may exist outside a non-serving cell of a second base station (822) having a physical cell identifier PCI Z. Three TRPs (TRP 2-1, TRP 2-2, TRP 2-3) having the same PCI may exist within the non-serving cell of the second base station. The terminal may exist outside a non-serving cell of a third base station (823) having a physical cell identifier PCI Q. One TRP (TRP 3-1) may exist within the non-serving cell of the third base station.

[0153] A first base station may be connected to a first CU (811), a second base station may be connected to a second CU (812), and a third base station may be connected to a third CU (813). The first CU, the second CU, and the third CU may be different. A serving cell may have two TRPs, but may include more TRPs. A non-serving cell of the second base station may have three TRPs, but may include more TRPs. A non-serving cell of the third base station may have one TRP, but may include more TRPs. A terminal may move from a first base station to a second base station, and may be in a situation where cell switching is required from TRP 1-1 of the first base station to TRP 2-1 of the second base station.

[0154] Each of TRP 2-1 and TRP 3-1 can transmit an SSB to the terminal. The terminal can receive an SSB from TRP 2-1. The terminal can receive an SSB from TRP 3-1. The terminal can select an SSB received from TRP 2-1, which is close to the terminal, as an optimal SSB among the SSBs received from TRP 2-1 and TRP 3-1. The optimal SSB may be the first SSB. The terminal can select an SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, as a second optimal SSB among the SSBs received from TRP 2-1 and TRP 3-1. The second optimal SSB may be the second SSB. The optimal SSB may be an SSB having the largest maximum correlation value. The second optimal SSB may have the second maximum correlation value. The optimal SSB may be an SSB having the largest SINR. The second SSB can have a second SINR.

[0155] The best SSB may include, for example, PCI Z as PCI, beam ID as for example, beam 5, etc. The next best SSB may include, for example, PCI Q as PCI, beam ID as for example, beam 2, etc. The terminal may transmit information about the best SSB and information about the next best SSB in TRP 1-1. Information about the best SSB may include, for example, PCI Z, beam 5, etc. Information about the next best SSB may include, for example, PCI Q, beam 2, etc.

[0156] TRP 1-1 can receive information about the best SSB and information about the next best SSB from the terminal. TRP 1-1 can transmit information about the best SSB and information about the next best SSB to the first base station. The first base station can receive information about the best SSB and information about the next best SSB from TRP 1-1. The first base station can know the PCI Z from the information about the best SSB. The first base station can know the PCI of the second base station as PCI Z.

[0157] Before and / or during the cell switching operation at the terminal, the first base station may request the second base station to transmit CSI-RS toward the terminal while transmitting the beam ID of beam 5 to the second base station. The second base station may receive a request for CSI-RS including the beam ID of beam 5 from the first base station. If the second base station can specify TRP 2-1 as the TRP that transmitted the best SSB, it may request transmission of CSI-RS to TRP 2-1. TRP 2-1 may receive the request for transmission of CSI-RS from the second base station and transmit the CSI-RS to the terminal. However, the second base station cannot distinguish the TRP that transmitted the best SSB from the request for transmission of CSI-RS including the beam ID information of beam 5 received from the first base station. In other words, the second base station cannot know in which TRP, TRP 2-1 or TRP 2-2, the best SSB was transmitted.

[0158] To solve this, the first base station can instruct the terminal to perform uplink TA acquisition synchronization based on a physical downlink control channel (PDCCH) order. The terminal can receive an instruction to perform PDCCH order-based uplink TA acquisition synchronization from the first base station. The terminal can perform PDCCH order-based uplink TA acquisition synchronization according to the instruction of the first base station. Due to the PDCCH order-based uplink TA acquisition synchronization, the second base station can determine to some extent, although not exactly, that TRP 2-1 is the TRP that transmitted the best SSB. The method and procedure for using the PDCCH order to enable the second base station to determine in which TRP among TRP 2-1 and TRP 2-2 the best SSB was transmitted can be described as follows based on FIG. 9. In the method and procedure described based on Fig. 9, it may be prerequisite that the terminal performs cell switching to TRP 2-1 of the second base station, which has the best channel quality among the candidate cells, while communicating by establishing a connection with TRP 1-1 of the first base station. The method and procedure described based on Fig. 9 may be prerequisite that some and / or all of the SSBs swept in all TRPs are shared and used redundantly.

[0159] FIG. 9 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0160] Referring to FIG. 9, the first base station can control TRP 1-1. The second base station can control TRP 2-1, TRP 2-2 (not shown), and TRP 2-3 (not shown). The third base station can control TRP 3-1. A terminal can be connected to TRP 1-1 and transmit and receive data through TRP 1-1. The cell formed by TRP 1-1 can be a serving cell. The cells formed by TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can be non-serving cells.

[0161] TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can transmit SSBs to the terminal (S911, S912). The terminal can receive SSBs from TRP 2-1. The terminal can receive SSBs from TRP 2-2. The terminal can receive SSBs from TRP 3-1. The terminal can measure the signal quality of each of the received SSBs. Based on the signal qualities of the SSBs, the terminal can select the SSB received from TRP 2-1, which is close to the terminal, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 as the best SSB. The best SSB may be the first SSB. The terminal may select, as a secondary SSB, the SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1. The secondary SSB may be the second SSB.

[0162] The best SSB may have a first PCI (e.g., PCI Z), a first beam ID (e.g., beam 5), etc. The next best SSB may have a second PCI (e.g., PCI Q), a second beam ID (e.g., beam 2), etc. The terminal may select candidate cell(s) through SSB estimation. For example, the terminal may select TRP 2-1, which transmitted an SSB having a PCI of PCI Z and a beam ID of beam 5, as the first candidate cell, TRP 3-1, which transmitted an SSB having a PCI of PCI Q and a beam ID of beam 2, as the second candidate cell, TRP 2-2, which transmitted an SSB having a PCI of PCI Z and a beam ID of beam 3, as the third candidate cell, and so on. In addition, the terminal may select a fourth candidate cell, a fifth candidate cell, etc. in succession. The signal quality may be RSRP, RSRQ, SINR, etc.

[0163] The terminal may perform a random access process for TRP 1-1. After the random access process, the terminal may perform a link connection process for TRP 1-1. The link connection process may be, for example, an RRC reconfiguration process. During the link connection process, before or after the terminal's SSB estimation, TRP 1-1 may request the terminal to report its capabilities (S913).

[0164] A terminal can receive a request for a terminal capability report from TRP 1-1. The terminal can transmit a terminal capability report containing information on functions that the terminal can support to TRP 1-1 according to the request for a terminal capability report (S914). TRP 1-1 can receive a terminal capability report from the terminal. The terminal can transmit the terminal capability report to TRP 1-1 via an RRC message, and TRP 1-1 can receive the terminal capability report via an RRC message. TRP 1-1 can confirm the capability of the terminal through the received terminal capability report, and can efficiently allocate network resources and establish an optimal connection based on the confirmed terminal capability.

[0165] The terminal capability report may include the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, VoNR capability, etc. Each of the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, and VoNR capability may be the same as described above with respect to FIG. 6.

[0166] The terminal may transmit measurement information including signal quality information of SSB for each of the candidate cell(s) selected by the terminal to TRP 1-1 (S915). TRP 1-1 may receive measurement information including signal quality information of SSB for each of the candidate cells selected by the terminal from the terminal. Based on the measurement information of SSBs of the candidate cells received from the terminal, TRP 1-1 may select candidate cells to be transmitted to the terminal based on, for example, signal quality and / or capability of the terminal and / or status of the candidate cells (S916). For example, TRP 1-1 may select up to 8 candidate cells.

[0167] TRP 1-1 can transmit information about candidate cells selected by TRP 1-1 to the UE (S917). TRP 1-1 can transmit a command to perform an early synchronization process while transmitting information about candidate cells to the UE. For example, TRP 1-1 can transmit a command to perform an SSB-based downlink synchronization process and a PDCCH order-based uplink TA acquisition synchronization process while transmitting information about candidate cells to the UE. The UE can receive information about candidate cells from TRP 1-1. The UE can receive a command to perform an early synchronization process along with information about candidate cells from TRP 1-1. For example, the UE can receive a command to perform an SSB-based downlink synchronization process and a PDCCH order-based uplink TA acquisition synchronization process while receiving information about candidate cells from TRP 1-1. The UE can perform an SSB-based downlink synchronization process and a PDCCH order-based uplink TA acquisition synchronization process (S918).

[0168] The early synchronization process may be composed of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB and an uplink TA acquisition synchronization process based on PDCCH order. TRP 1-1 may transmit a command to perform the early synchronization process to the terminal through RRC signaling and / or MAC-CE. The terminal may receive the command to perform the early synchronization process from TRP 1-1 through RRC signaling and / or MAC-CE. In the SSB-based downlink synchronization process, the terminal may perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected by TRP 1-1 (e.g., the SSB corresponding to beam 5 with PCI Z, the SSB corresponding to beam 2 with PCI Q).

[0169] In the PDCCH order-based uplink TA acquisition synchronization process, TRP 1-1 may transmit a PDCCH order to the UE to initiate a random access procedure for candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include control information instructing the UE to perform a random access procedure. The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to perform a setup procedure based on Contention-Free Random Access (CFRA) for link establishment.

[0170] The PDCCH order can provide resource information that allows a UE to perform a dedicated random access procedure without competition with other UEs when performing a random access procedure with TRP 2-1. The PDCCH order can include a preamble index for TRP 2-1, RO (RACH occasion) information, an SSB index corresponding to a link, PCI information, etc. The UE can receive a PDCCH order including the information described above from TRP 1-1. The UE can obtain setup resource information based on TRP 2-1 and CFRA. The UE can perform a setup procedure based on TRP 2-1 and CFRA based on the PDCCH order. The UE can transmit a designated preamble from a designated RO to TRP 2-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-1 can be set to have reciprocity with the reception beam direction of the downlink signal from TRP 2-1 (e.g., the SSB received from TRP 2-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted. TRP 2-1 can receive the random access preamble from the terminal.

[0171] TRP 2-1 can measure the signal quality of a random access preamble received from a terminal. TRP 2-1 can estimate a propagation delay time between TRP 2-1 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink receive sample timing offset value. The uplink receive sample timing offset value may be a time or sample-unit error value indicating how much the sampling timing of a signal received from the terminal in TRP 2-1 is ahead or behind a reference timing. TRP 2-1 can determine a TA value based on the estimated propagation delay time between TRP 2-1 and the terminal. TRP 2-1 can transmit a RAR (random access response) including the determined TA value to the terminal. In addition to the TA value, the RAR may include a preamble index, uplink grant information, a temporary C-RNTI (cell radio network temporary identifier) ​​value, identification information of TRP 2-1, propagation delay time between TRP 2-1 and the terminal, signal quality of the preamble, etc. TRP 2-1 may report identification information of TRP 2-1, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-1 may not transmit the RAR to the terminal. TRP 2-1 may forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 may receive the RAR from TRP 2-1 and transmit the received RAR to the terminal. The terminal may receive the RAR from TRP 1-1 and know the TA value.

[0172] The PDCCH order can provide resource information that allows a UE to perform a dedicated random access procedure without competition with other UEs when performing a random access procedure with TRP 2-2. The PDCCH order can include a preamble index for TRP 2-2, RO information, an SSB index corresponding to a link, PCI information, etc. The UE can receive a PDCCH order including the information described above from TRP 1-1. The UE can obtain setup resource information based on TRP 2-2 and CFRA. The UE can perform a setup procedure based on TRP 2-2 and CFRA based on the PDCCH order. The UE can transmit a designated preamble from a designated RO to TRP 2-2 via PRACH based on the information included in the PDCCH order received from TRP 1-1.

[0173] The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-2 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 2-2 (e.g., the SSB received from TRP 2-2 as described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted. TRP 2-2 can receive the random access preamble from the terminal.

[0174] TRP 2-2 can measure the signal quality of a random access preamble received from a terminal. TRP 2-2 can estimate a propagation delay time between TRP 2-2 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in units of time or samples indicating how much the sampling timing of a signal received from the terminal in TRP 2-2 is ahead or behind a reference timing. TRP 2-2 can determine a TA value based on the estimated propagation delay time between TRP 2-2 and the terminal. TRP 2-2 can transmit an RAR including the determined TA value to the terminal.

[0175] In addition to the TA value, the RAR may include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-2, propagation delay time between TRP 2-2 and the terminal, signal quality of the preamble, etc. TRP 2-2 may report identification information of TRP 2-2, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-2 may not transmit the RAR to the terminal. TRP 2-2 may forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 may receive the RAR from TRP 2-2 and transmit the received RAR to the terminal. The terminal may receive the RAR from TRP 1-1 and know the TA value.

[0176] Through the process described above, the second base station can receive from TRP 2-1 the identification information of TRP 2-1, the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated in TRP 2-1, the signal quality of the preamble measured in TRP 2-1, etc. The second base station can receive from TRP 2-2 the identification information of TRP 2-2, the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated in TRP 2-2, the signal quality of the preamble measured in TRP 2-2, etc. The second base station can determine that TRP 2-1 is the TRP that transmitted the best SSB based on the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 2-1, the TA value calculated from TRP 2-2, the signal quality of the preamble measured from TRP 2-1, the signal quality of the preamble measured from TRP 2-2, etc.

[0177] Through the process described above, the first base station or TRP 1-1 can receive, from the TRP 2-1 via the second base station, identification information of the TRP 2-1, propagation delay time between the TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), TA value calculated by the TRP 2-1, signal quality of the preamble measured by the TRP 2-1, etc. The first base station or TRP 1-1 can receive, from the TRP 2-2 via the second base station, identification information of the TRP 2-2, propagation delay time between the TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), TA value calculated by the TRP 2-2, signal quality of the preamble measured by the TRP 2-2, etc. The first base station or TRP 1-1 can be determined to be the TRP that transmitted the best SSB based on the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 2-1, the TA value calculated from TRP 2-2, the signal quality of the preamble measured from TRP 2-1, the signal quality of the preamble measured from TRP 2-2, etc.

[0178] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure with TRP 3-1. The PDCCH order can include a preamble index for TRP 3-1, RO information, an SSB index corresponding to a link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 3-1 and CFRA. The terminal can perform a setup procedure based on TRP 3-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble from a designated RO to TRP 3-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1.

[0179] The uplink beam direction in which the terminal transmits the random access preamble to TRP 3-1 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 3-1 (e.g., the SSB received from TRP 3-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted. TRP 3-1 can receive the random access preamble from the terminal. TRP 3-1 can measure the signal quality of the random access preamble received from the terminal. TRP 3-1 can estimate the propagation delay time between TRP 3-1 and the terminal using the random access preamble received from the terminal. The propagation delay time can be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in time or sample units indicating how much the sampling timing of a signal received from a terminal in TRP 3-1 is ahead or behind the reference timing.

[0180] TRP 3-1 can determine a TA value based on the estimated propagation delay time between TRP 3-1 and the terminal. TRP 3-1 can transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR can include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 3-1, propagation delay time between TRP 3-1 and the terminal, signal quality of the preamble, etc. TRP 3-1 can report the identification information of TRP 3-1, signal quality of the preamble, propagation delay time, etc. to a third base station. TRP 3-1 may not transmit the RAR to the terminal. TRP 3-1 can forward the RAR to TRP 1-1 via the third base station and the first base station. TRP 1-1 can receive the RAR from TRP 3-1 and transmit the received RAR to the terminal. The terminal can receive RAR from TRP 1-1 and know the TA value.

[0181] Through the process described above, the third base station can receive from TRP 3-1 the identification information of TRP 3-1, the propagation delay time between TRP 3-1 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 3-1, the signal quality of the preamble measured from TRP 3-1, etc. The third base station can confirm that TRP 3-1 is the TRP that transmitted the next-best SSB based on the propagation delay time between TRP 3-1 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 3-1, the signal quality of the preamble measured from TRP 3-1, etc.

[0182] Through the process described above, the first base station or TRP 1-1 can receive, from the TRP 3-1 via the third base station, the identification information of the TRP 3-1, the propagation delay time between the TRP 3-1 and the terminal (e.g., the uplink reception sample timing offset value), the TA value calculated in the TRP 3-1, the signal quality of the preamble measured in the TRP 3-1, etc. The first base station or TRP 1-1 can confirm that the TRP that transmitted the next-best SSB is the TRP 3-1 based on the propagation delay time between the TRP 3-1 and the terminal (e.g., the uplink reception sample timing offset value), the TA value calculated in the TRP 3-1, the signal quality of the preamble measured in the TRP 3-1, etc.

[0183] One thing to keep in mind here is that this third method and procedure for resolving the ambiguity that occurs when transmitting CSI-RS in inter-CU / intra-CU deployment scenarios may have the disadvantage of compromising the freedom to freely choose between UE-based TA acquisition and PDCCH order-based TA acquisition methods when performing the early synchronization process. It is also important to note that PRACH preamble-based TA synchronization can provide improved UL synchronization performance compared to UE-based TA synchronization, where candidate cell(s) may have different inherent transmission timing errors and the serving cell and candidate cell(s) may not be synchronized with each other by the NW. This PRACH preamble-based TA synchronization allows the NW to determine which BS's TRP(s) the candidate cell(s) reported by the UE belong to.

[0184] The reason for obtaining this advantage may be that when the terminal transmits a preamble in the spatially filtered direction in the downlink SSB beam direction of each candidate cell reported to TRP 1-1, the TRP that receives this with the best quality and estimates the uplink reception sample timing offset value is very likely to be the TRP to which the candidate cell belongs. The terminal can perform an early synchronization process for each candidate cell received from TRP 1-1. It should be noted that, as mentioned above, the NW may need to perform early synchronization processes for all selected candidate cells. The terminal may pursue low power. In such a case, the NW may reduce the number of candidate cells.

[0185] (Method 1)

[0186] TRP 1-1 may select a target cell based on the results of the early synchronization process and / or based on previous results of the early synchronization process (S919). For example, TRP 1-1 may select a TRP that transmitted an SSB having PCI Z and beam 5 as a target cell. TRP 1-1 may know that the candidate cell that transmitted the SSB having PCI Z and beam 5 is a TRP belonging to the second base station. TRP 1-1 cannot know whether the TRP that transmitted the SSB having PCI Z and beam 5 is TRP 2-1, TRP 2-2, or TRP 2-3 controlled by the second base station.

[0187] TRP 1-1 can send a CSI-RS request to the second base station via the first base station to request the second base station to transmit CSI-RSs toward the terminal using a TRP belonging to the second base station (S920). The second base station can receive the CSI-RS request requesting transmission of CSI-RSs using the TRP from the first base station. The second base station can estimate TRP 2-1 as the TRP that transmitted the best SSB, and can configure / allocate CSI-RS resource(s) so that the CSI-RS can be transmitted in TRP 2-1. The second base station can transmit information about the configured / allocated CSI-RS resource(s) of TRP 2-1 to the TRP 2-1 of the second base station. The TRP 2-1 of the second base station can receive information about the configured / allocated CSI-RS resource(s) from the second base station. The second base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the first base station (S921). The first base station may receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1 from the second base station. The first base station may request the terminal to perform measurement of CSI-RSs in the CSI-RS resource(s) configured / allocated to TRP 2-1 (S922). The terminal may receive a CSI-RS measurement request for the CSI-RS resource(s) configured / allocated to TRP 2-1. The first base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the terminal. The terminal may receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1.

[0188] (Method 2)

[0189] TRP 1-1 may select a target cell based on the results of the early synchronization process and / or based on the previous results of the early synchronization process (S919). For example, TRP 1-1 may select a TRP that has transmitted an SSB with PCI Z and beam 5 as the target cell. TRP 1-1 may recognize that the candidate cell that has transmitted an SSB with PCI Z and beam 5 is a TRP belonging to the second base station. TRP 1-1 is the TRP that transmits the best SSB based on the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value) acquired through the PDCCH order-based uplink TA acquisition synchronization process, the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 2-1, the TA value calculated from TRP 2-2, the signal quality of the preamble measured from TRP 2-1, and the signal quality of the preamble measured from TRP 2-2. It can be confirmed that TRP 2-1 is the TRP that transmits the best SSB.

[0190] TRP 1-1 may send a CSI-RS request to the second base station via the first base station to request the second base station to transmit CSI-RSs toward the terminal using TRP 2-1 belonging to the second base station (S920). The second base station may receive the CSI-RS request requesting transmission of CSI-RSs using TRP 2-1 from the first base station. The second base station may configure / allocate CSI-RS resource(s) to enable transmission of CSI-RSs in TRP 2-1. The second base station may transmit information about the configured / allocated CSI-RS resource(s) of TRP 2-1 to the TRP 2-1 of the second base station. The TRP 2-1 of the second base station may receive information about the configured / allocated CSI-RS resource(s) from the second base station.

[0191] The second base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the first base station (S921). The first base station may receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1 from the second base station. The first base station may request the terminal to perform measurement of CSI-RSs in the CSI-RS resource(s) configured / allocated to TRP 2-1 (S922). The terminal may receive a CSI-RS measurement request for the CSI-RS resource(s) configured / allocated to TRP 2-1. The first base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the terminal. The terminal may receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1.

[0192] The TRP 2-1 of the second base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) configured / allocated for transmission of the CSI-RSs (S923). It should be noted here that since the CSI-RS(es) specific to one target cell are transmitted to the terminal, the load on the CSI-RS resource and the CSI-RS measurement load of the terminal may not be severe. However, if the target cell is one, it may have a negative impact on the fast LTM performance before or during cell switching due to the evaluation event and / or CSI-RS measurement(s) triggered by the evaluation event mentioned below. The beam direction of the CSI-RS(es) transmitted by the TRP 2-1 of the second base station may have a QCL relationship with the beam direction of the beam when transmitting the best SSB having the beam ID of beam 5.

[0193] The terminal can measure CSI-RS(es) according to a measurement request of CSI-RS for CSI-RS resource(s) configured / allocated to TRP 2-1 of the second base station. The terminal can report the measurement result of CSI-RS(es) to TRP 1-1 periodically and / or aperiodically using the allocated reporting resource(s) (S924). TRP 1-1 can receive the measurement result of CSI-RS(es) from the terminal periodically and / or aperiodically through the reporting resource(s). The measurement result of CSI-RS can include information about signal quality of CSI-RS and TRP that transmitted CSI-RS. For example, the measurement result of CSI-RS can include a channel quality indicator, a precoding matrix indicator, a CSI-RS resource indicator, an SS / PBCH block resource indicator, a layer indicator, a rank indicator, first layer reference signal reception power, information about TRP, etc.

[0194] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of a serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0195] A terminal, a first base station, a second base station, TRP 1-1, and TRP 2-1 can perform an LTM execution process. During the LTM execution process, TRP 1-1 can transmit measurement results for candidate cells received from the terminal to the first base station. The first base station can receive measurement results for candidate cells from TRP 1-1. Based on the measurement results for candidate cells of the terminal received, the first base station can determine a candidate cell to be changed to a target cell. The candidate cell can be, for example, TRP 2-1 of the second base station.

[0196] The first base station can transmit a cell switch command to the terminal via MAC CE. The terminal can disconnect from TRP 1-1 and apply preset candidate cell configuration information. The terminal can attempt to connect to TRP 2-1 as a target cell. If UL synchronization is invalid, the terminal can establish UL synchronization by performing a random access procedure. The TA value included in the cell switch command may be invalid, such as 'FFF'. The cell switch command may not include a contention-free random access resource field. The terminal can use a TA value measured by itself. The cell switch command may specify a TA value. The terminal can use the specified TA value.

[0197] A TA value may be specified in the cell switch command. In this case, the terminal may not perform the RACH procedure for cell switching. The TA value may be specified as an invalid value in the cell switch command, and a non-contention random access resource field may exist. In this case, the terminal may perform the RACH procedure to obtain a TA value for a candidate cell. Cell switching may be successfully completed (S925). During the LTM completion process of the LTM procedure, the terminal may notify the target base station (e.g., the second base station) that the target cell access has been successfully completed. The second base station may initiate data transmission to the terminal via TRP 2-1. During and after the above cell switching procedure, the terminal may perform zero-delay switching to the target cell without interruption to perform DL and UL communications (S926).

[0198] For example, target cell TRP 2-1 may request RRC reconfiguration from the terminal (S927). The terminal may receive a request for RRC reconfiguration from TRP 2-1. The terminal may complete the reconfiguration according to the RRC request. The terminal may transmit an RRC reconfiguration completion message to TRP 2-1 to report that the reconfiguration has been completed (S928). TRP 2-1 may receive the RRC reconfiguration completion message from the terminal. TRP 2-1 may complete the LTM cell switch and / or complete the system connection to maintain the connection state by making the target cell the new serving cell.

[0199] Meanwhile, the present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS toward a terminal before cell switching, and can propose several transmission methods, procedures, and communication devices for performing measurements in the reverse direction depending on the communication situation of the terminal, as follows. The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS in an inter-CU / intra-CU deployment scenario, and can propose a fourth simple method and procedure for performing uplink measurements depending on the situation, as follows, based on FIGS. 8 and 10.

[0200] Referring back to FIG. 8, before and / or while performing a cell switching operation at the terminal, the first base station may request the second base station to transmit a CSI-RS toward the terminal while transmitting the beam ID of beam 5 to the second base station. The second base station may receive a request for transmission of a CSI-RS including the beam ID of beam 5 from the first base station. If the second base station can specify TRP 2-1 as the TRP that transmitted the best SSB, it may request transmission of the CSI-RS to TRP 2-1. TRP 2-1 may receive the request for transmission of the CSI-RS from the second base station and transmit the CSI-RS to the terminal. However, the second base station cannot distinguish the TRP that transmitted the best SSB from the request for transmission of the CSI-RS including the beam ID information of beam 5 received from the first base station. In other words, the second base station cannot know which TRP, TRP 2-1 or TRP 2-2, transmitted the best SSB.

[0201] To address this, the first base station can instruct the terminal to perform PDCCH order-based uplink TA acquisition synchronization. The terminal can receive an instruction from the first base station to perform PDCCH order-based uplink TA acquisition synchronization. The terminal can perform PDCCH order-based uplink TA acquisition synchronization according to the instruction from the first base station. Due to the PDCCH order-based uplink TA acquisition synchronization, the second base station can confirm to some extent, although it may not be exact, that the TRP that transmitted the best SSB is TRP 2-1.

[0202] A method and procedure for using a PDCCH order to enable a second base station to determine which TRP transmitted the best SSB among TRP 2-1 and TRP 2-2 can be described as follows based on FIG. 10. In the method and procedure described based on FIG. 10, it can be assumed that a terminal performs cell switching to TRP 2-1 of the second base station, which has the best channel quality among candidate cells, while communicating by establishing a connection with TRP 1-1 of the first base station. The method and procedure described based on FIG. 10 can be assumed that some and / or all of the SSBs swept in all TRPs are shared and used redundantly.

[0203] FIG. 10 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0204] Referring to FIG. 10, a first base station can control TRP 1-1. A second base station can control TRP 2-1, TRP 2-2 (not shown), and TRP 2-3 (not shown). A third base station can control TRP 3-1. A terminal can be connected to TRP 1-1 and transmit and receive data through TRP 1-1. The cell formed by TRP 1-1 can be a serving cell. The cells formed by TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can be non-serving cells.

[0205] TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can transmit SSBs to the terminal (S1011, S1012). The terminal can receive SSBs from TRP 2-1. The terminal can receive SSBs from TRP 2-2. The terminal can receive SSBs from TRP 3-1. The terminal can measure the signal quality of each of the received SSBs. Based on the signal qualities of the SSBs, the terminal can select the SSB received from TRP 2-1, which is close to the terminal, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 as the best SSB. The best SSB may be the first SSB. The terminal may select, as a secondary SSB, the SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1. The secondary SSB may be the second SSB.

[0206] The best SSB may have a first PCI (e.g., PCI Z), a first beam ID (e.g., beam 5), etc. The next best SSB may have a second PCI (e.g., PCI Q), a second beam ID (e.g., beam 2), etc. The terminal may select candidate cell(s) through SSB estimation. For example, the terminal may select TRP 2-1, which transmitted an SSB having a PCI of PCI Z and a beam ID of beam 5, as the first candidate cell, TRP 3-1, which transmitted an SSB having a PCI of PCI Q and a beam ID of beam 2, as the second candidate cell, TRP 2-2, which transmitted an SSB having a PCI of PCI Z and a beam ID of beam 3, as the third candidate cell, and so on. In addition, the terminal may select a fourth candidate cell, a fifth candidate cell, etc. in succession. The signal quality may be RSRP, RSRQ, SINR, etc.

[0207] The terminal may perform a random access process for TRP 1-1. After the random access process, the terminal may perform a link connection process for TRP 1-1. The link connection process may be, for example, an RRC reconfiguration process. During the link connection process, before or after the terminal's SSB estimation, TRP 1-1 may request the terminal to report its capabilities (S1013).

[0208] A terminal can receive a request for a terminal capability report from TRP 1-1. The terminal can transmit a terminal capability report containing information on functions that the terminal can support to TRP 1-1 according to the request for a terminal capability report (S1014). TRP 1-1 can receive a terminal capability report from the terminal. The terminal can transmit the terminal capability report to TRP 1-1 via an RRC message, and TRP 1-1 can receive the terminal capability report via an RRC message. TRP 1-1 can verify the capability of the terminal through the received terminal capability report, and can efficiently allocate network resources and establish an optimal connection based on the verified terminal capability.

[0209] The terminal capability report may include the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, VoNR capability, etc. Each of the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, and VoNR capability may be the same as described above with respect to FIG. 6.

[0210] The terminal may transmit measurement information including signal quality information of SSB for each of the candidate cell(s) selected by the terminal to TRP 1-1 (S1015). TRP 1-1 may receive measurement information including signal quality information of SSB for each of the candidate cells selected by the terminal from the terminal. Based on the measurement information of SSBs of the candidate cells received from the terminal, TRP 1-1 may select candidate cells to be transmitted to the terminal based on, for example, signal quality and / or capability of the terminal and / or status of the candidate cells (S1016). For example, TRP 1-1 may select up to 8 candidate cells.

[0211] TRP 1-1 can transmit information about candidate cells selected by TRP 1-1 to the UE (S1017). TRP 1-1 can transmit a command to perform an early synchronization process while transmitting information about candidate cells to the UE. For example, TRP 1-1 can transmit a command to perform an SSB-based downlink synchronization process and a PDCCH order-based uplink TA acquisition synchronization process while transmitting information about candidate cells to the UE. The UE can receive information about candidate cells from TRP 1-1. The UE can receive a command to perform an early synchronization process along with information about candidate cells from TRP 1-1. For example, the UE can receive a command to perform an SSB-based downlink synchronization process and a PDCCH order-based uplink TA acquisition synchronization process while receiving information about candidate cells from TRP 1-1. The UE can perform an SSB-based downlink synchronization process and a PDCCH order-based uplink TA acquisition synchronization process (S1018).

[0212] The early synchronization process may be composed of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB and an uplink TA acquisition synchronization process based on PDCCH order. TRP 1-1 may transmit a command to perform the early synchronization process to the terminal through RRC signaling and / or MAC-CE. The terminal may receive the command to perform the early synchronization process from TRP 1-1 through RRC signaling and / or MAC-CE. In the SSB-based downlink synchronization process, the terminal may perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected by TRP 1-1 (e.g., the SSB corresponding to beam 5 with PCI Z, the SSB corresponding to beam 2 with PCI Q).

[0213] During the PDCCH order-based uplink TA acquisition synchronization process, TRP 1-1 may transmit a PDCCH order to the UE to initiate a random access procedure for candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include control information instructing the UE to perform a random access procedure. The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to perform a setup procedure based on non-contention random access for link establishment.

[0214] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure with TRP 2-1. The PDCCH order can include a preamble index for TRP 2-1, RO information, an SSB index corresponding to a link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 2-1 and CFRA. The terminal can perform a setup procedure based on TRP 2-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble from a designated RO to TRP 2-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1.

[0215] The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-1 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 2-1 (e.g., the SSB received from TRP 2-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted. TRP 2-1 can receive the random access preamble from the terminal. TRP 2-1 can measure the signal quality of the random access preamble received from the terminal. TRP 2-1 can estimate the propagation delay time between TRP 2-1 and the terminal using the random access preamble received from the terminal. The propagation delay time can be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in time or sample units indicating how much the sampling timing of a signal received from a terminal in TRP 2-1 is ahead or behind the reference timing.

[0216] TRP 2-1 can determine a TA value based on the estimated propagation delay time between TRP 2-1 and the terminal. TRP 2-1 can transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR can include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-1, propagation delay time between TRP 2-1 and the terminal, signal quality of the preamble, etc. TRP 2-1 can report the identification information of TRP 2-1, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-1 may not transmit the RAR to the terminal. TRP 2-1 can forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 can receive the RAR from TRP 2-1 and transmit the received RAR to the terminal. The terminal can receive RAR from TRP 1-1 and know the TA value.

[0217] The PDCCH order can provide resource information that allows a UE to perform a dedicated random access procedure without competition with other UEs when performing a random access procedure using TRP 2-2. The PDCCH order can include a preamble index for TRP 2-2, RO information, an SSB index corresponding to the link, PCI information, etc. The UE can receive a PDCCH order including the information described above from TRP 1-1. The UE can obtain setup resource information based on TRP 2-2 and CFRA.

[0218] A terminal can perform a TRP 2-2 and CFRA-based setup procedure based on a PDCCH order. The terminal can transmit a designated preamble to TRP 2-2 through a PRACH in a designated RO based on information included in a PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits a random access preamble to TRP 2-2 can be configured to have reciprocity with the reception beam direction of a downlink signal from TRP 2-2 (e.g., an SSB received from TRP 2-2 as described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use a preamble sequence indicated in the PDCCH order for the preamble to be transmitted.

[0219] TRP 2-2 can receive a random access preamble from a terminal. TRP 2-2 can measure the signal quality of the random access preamble received from the terminal. TRP 2-2 can estimate the propagation delay time between TRP 2-2 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be a time or sample unit error value indicating how much the sampling timing of the signal received from the terminal in TRP 2-2 is ahead or behind the reference timing.

[0220] TRP 2-2 can determine a TA value based on the estimated propagation delay time between TRP 2-2 and the terminal. TRP 2-2 can transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR can include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-2, propagation delay time between TRP 2-2 and the terminal, signal quality of the preamble, etc. TRP 2-2 can report the identification information of TRP 2-2, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-2 may not transmit the RAR to the terminal. TRP 2-2 can forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 can receive the RAR from TRP 2-2 and transmit the received RAR to the terminal. The terminal can receive RAR from TRP 1-1 and know the TA value.

[0221] Through the process described above, the second base station can receive from TRP 2-1 the identification information of TRP 2-1, the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated in TRP 2-1, the signal quality of the preamble measured in TRP 2-1, etc. The second base station can receive from TRP 2-2 the identification information of TRP 2-2, the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated in TRP 2-2, the signal quality of the preamble measured in TRP 2-2, etc. The second base station can determine that TRP 2-1 is the TRP that transmitted the best SSB based on the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 2-1, the TA value calculated from TRP 2-2, the signal quality of the preamble measured from TRP 2-1, the signal quality of the preamble measured from TRP 2-2, etc.

[0222] Through the process described above, the first base station or TRP 1-1 can receive, from the TRP 2-1 via the second base station, identification information of the TRP 2-1, propagation delay time between the TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), TA value calculated by the TRP 2-1, signal quality of the preamble measured by the TRP 2-1, etc. The first base station or TRP 1-1 can receive, from the TRP 2-2 via the second base station, identification information of the TRP 2-2, propagation delay time between the TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), TA value calculated by the TRP 2-2, signal quality of the preamble measured by the TRP 2-2, etc. The first base station or TRP 1-1 can be determined to be the TRP that transmitted the best SSB based on the propagation delay time between TRP 2-1 and the terminal (e.g., uplink reception sample timing offset value), the propagation delay time between TRP 2-2 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 2-1, the TA value calculated from TRP 2-2, the signal quality of the preamble measured from TRP 2-1, the signal quality of the preamble measured from TRP 2-2, etc.

[0223] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure with TRP 3-1. The PDCCH order can include a preamble index for TRP 3-1, RO information, an SSB index corresponding to a link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 3-1 and CFRA. The terminal can perform a setup procedure based on TRP 3-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble from a designated RO to TRP 3-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 3-1 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 3-1 (e.g., the SSB received from TRP 3-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction.

[0224] For example, a terminal may use a preamble sequence indicated in the PDCCH order as a preamble to be transmitted. TRP 3-1 may receive a random access preamble from the terminal. TRP 3-1 may measure the signal quality of the random access preamble received from the terminal. TRP 3-1 may estimate the propagation delay time between TRP 3-1 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in time or sample units that indicates how much the sampling timing of the signal received from the terminal in TRP 3-1 is ahead or behind the reference timing. TRP 3-1 may determine a TA value based on the estimated propagation delay time between TRP 3-1 and the terminal.

[0225] TRP 3-1 can transmit an RAR including a determined TA value to the terminal. In addition to the TA value, the RAR can include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 3-1, propagation delay time between TRP 3-1 and the terminal, signal quality of the preamble, etc. TRP 3-1 can report the identification information of TRP 3-1, signal quality of the preamble, propagation delay time, etc. to a third base station. TRP 3-1 may not transmit the RAR to the terminal. TRP 3-1 can forward the RAR to TRP 1-1 via the third base station and the first base station. TRP 1-1 can receive the RAR from TRP 3-1 and transmit the received RAR to the terminal. The terminal can receive the RAR from TRP 1-1 and know the TA value.

[0226] Through the process described above, the third base station can receive from TRP 3-1 the identification information of TRP 3-1, the propagation delay time between TRP 3-1 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 3-1, the signal quality of the preamble measured from TRP 3-1, etc. The third base station can confirm that TRP 3-1 is the TRP that transmitted the next-best SSB based on the propagation delay time between TRP 3-1 and the terminal (e.g., uplink reception sample timing offset value), the TA value calculated from TRP 3-1, the signal quality of the preamble measured from TRP 3-1, etc.

[0227] Through the process described above, the first base station or TRP 1-1 can receive, from the TRP 3-1 via the third base station, the identification information of the TRP 3-1, the propagation delay time between the TRP 3-1 and the terminal (e.g., the uplink reception sample timing offset value), the TA value calculated in the TRP 3-1, the signal quality of the preamble measured in the TRP 3-1, etc. The first base station or TRP 1-1 can confirm that the TRP that transmitted the next-best SSB is the TRP 3-1 based on the propagation delay time between the TRP 3-1 and the terminal (e.g., the uplink reception sample timing offset value), the TA value calculated in the TRP 3-1, the signal quality of the preamble measured in the TRP 3-1, etc.

[0228] One thing to keep in mind here is that this fourth method and procedure for resolving the ambiguity that occurs when transmitting CSI-RS in inter-CU / intra-CU deployment scenarios may have the disadvantage of compromising the freedom to freely choose between UE-based TA acquisition and PDCCH order-based TA acquisition methods when performing the early synchronization process. It should be noted here that PRACH preamble-based TA synchronization may provide improved UL synchronization performance compared to UE-based TA synchronization, where candidate cell(s) may have different inherent transmission timing errors and the serving cell and candidate cell(s) may not be synchronized with each other by the NW.

[0229] This PRACH preamble-based TA synchronization allows the NW to determine which base station's TRP(s) the candidate cell(s) reported by the UE belong to. This advantage may be achieved because, when the UE transmits a preamble in a spatially filtered direction along the downlink SSB beam direction of each candidate cell reported to TRP 1-1, the TRP that receives the preamble with the best quality and estimates the uplink reception sample timing offset value is very likely to be the TRP to which the candidate cell belongs. The UE can perform an early synchronization process for each candidate cell received from TRP 1-1. It should be noted that, as mentioned above, the NW may need to perform early synchronization processes for all selected candidate cells. The UE may pursue low power. In this case, the NW may reduce the number of candidate cells.

[0230] (Method 1)

[0231] TRP 1-1 can know that the candidate cell that transmitted the SSB with PCI Z and beam 5 is a TRP belonging to the second base station. TRP 1-1 cannot know which TRP among TRP 2-1, TRP 2-2, or TRP 2-3 controlled by the second base station is the TRP that transmitted the SSB with PCI Z and beam 5. TRP 1-1 can send a CSI-RS request to the second base station via the first base station to request the second base station to transmit CSI-RSs toward the terminal using the TRP belonging to the second base station (S1019-1). The second base station can receive the CSI-RS request requesting transmission of CSI-RSs using the TRP from the first base station. The second base station can estimate TRP 2-1 as the TRP that transmitted the best SSB, and can configure / allocate CSI-RS resource(s) so that the CSI-RS can be transmitted in TRP 2-1. The second base station may transmit information about the configured / allocated CSI-RS resource(s) of TRP 2-1 to the TRP 2-1 of the second base station.

[0232] The TRP 2-1 of the second base station can receive information about CSI-RS resource(s) configured / allocated from the second base station. The second base station can transmit information about CSI-RS resource(s) configured / allocated to TRP 2-1 to the first base station (S1020-1). The first base station can receive information about CSI-RS resource(s) configured / allocated to TRP 2-1 from the second base station. The first base station can request the terminal to perform measurement of CSI-RSs on the CSI-RS resource(s) configured / allocated to TRP 2-1 (S1021). The terminal can receive a request for CSI-RS measurement on the CSI-RS resource(s) configured / allocated from TRP 2-1.

[0233] TRP 1-1 can know that the candidate cell that transmitted the SSB with PCI Q and beam 2 is a TRP belonging to the third base station. TRP 1-1 cannot know that the TRP that transmitted the SSB with PCI Q and beam 2 is TRP 3-1 controlled by the third base station. TRP 1-1 can send a CSI-RS request to the third base station through the first base station to request the third base station to transmit CSI-RSs toward the terminal using the TRP belonging to the third base station (S1019-2). The third base station can receive the CSI-RS request requesting the transmission of CSI-RSs using the TRP from the first base station.

[0234] The third base station can estimate TRP 3-1 as the TRP that transmitted the next SSB, and can configure / allocate CSI-RS resource(s) so that CSI-RS can be transmitted in TRP 3-1. The third base station can transmit information about the configured / allocated CSI-RS resource(s) of TRP 3-1 to TRP 3-1 of the third base station. TRP 3-1 of the third base station can receive information about the configured / allocated CSI-RS resource(s) from the third base station. The third base station can transmit information about the configured / allocated CSI-RS resource(s) of TRP 3-1 to the first base station (S1020-2). The first base station can receive information about the configured / allocated CSI-RS resource(s) for TRP 3-1 from the third base station. The first base station may request the terminal to perform measurements on CSI-RSs on the CSI-RS resource(s) configured / allocated to TRP 3-1 (S1021). The terminal may receive a request for CSI-RS measurement on the CSI-RS resource(s) configured / allocated to TRP 3-1.

[0235] (Method 2)

[0236] It can be seen that TRP 1-1 is a TRP belonging to the second base station, which is a candidate cell transmitting SSB with PCI Z and beam 5. TRP 1-1 is the TRP that transmits the best SSB based on the propagation delay time (e.g., uplink reception sample timing offset value) between TRP 2-1 and the terminal acquired through the PDCCH order-based uplink TA acquisition synchronization process, the propagation delay time (e.g., uplink reception sample timing offset value) between TRP 2-2 and the terminal, the propagation delay time (e.g., uplink reception sample timing offset value) between TRP 2-3 and the terminal, the TA value calculated in TRP 2-1, the TA value calculated in TRP 2-2, the TA value calculated in TRP 2-3, the signal quality of the preamble measured in TRP 2-1, the signal quality of the preamble measured in TRP 2-2, the signal quality of the preamble measured in TRP 2-3, etc., and it can be confirmed that TRP 2-1 is TRP 2-1.

[0237] TRP 1-1 can send a CSI-RS transmission request to the second base station via the first base station to request the second base station to transmit CSI-RSs toward the terminal using TRP 2-1 belonging to the second base station (S1019-1). The second base station can receive a CSI-RS transmission request requesting transmission of CSI-RSs using TRP 2-1 from the first base station. The second base station can configure / allocate CSI-RS resource(s) to enable transmission of CSI-RSs in TRP 2-1. The second base station can transmit information about the configured / allocated CSI-RS resource(s) of TRP 2-1 to the TRP 2-1 of the second base station. The TRP 2-1 of the second base station can receive information about the configured / allocated CSI-RS resource(s) from the second base station. The second base station can transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the first base station (S1020-1). The first base station can receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1 from the second base station. The first base station can request the terminal to perform measurement of CSI-RSs on the CSI-RS resource(s) configured / allocated to TRP 2-1 (S1021). The terminal can receive a request for CSI-RS measurement for the CSI-RS resource(s) configured / allocated to TRP 2-1.

[0238] It can be seen that TRP 1-1 is a TRP belonging to the third base station, which is a candidate cell that transmitted SSB with PCI Q and beam 2. TRP 1-1 can be confirmed to be TRP 3-1, which transmitted the next-best SSB, based on the propagation delay time between TRP 3-1 and the terminal (e.g., uplink reception sample timing offset value) obtained through the PDCCH order-based uplink TA acquisition synchronization process, the TA value calculated in TRP 3-1, and the signal quality of the preamble measured in TRP 3-1.

[0239] TRP 1-1 can send a CSI-RS request to a third base station via the first base station to request the third base station to transmit CSI-RSs toward a terminal using TRP 3-1 belonging to the third base station (S1019-2). The third base station can receive a CSI-RS request requesting transmission of CSI-RSs using TRP 3-1 from the first base station. The third base station can configure / allocate CSI-RS resource(s) to enable transmission of CSI-RSs in TRP 3-1. The third base station can transmit information about the configured / allocated CSI-RS resource(s) of TRP 3-1 to the TRP 3-1 of the third base station. The TRP 3-1 of the third base station can receive information about the configured / allocated CSI-RS resource(s) from the third base station. The third base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 3-1 to the first base station (S1020-2). The first base station may receive information about the CSI-RS resource(s) configured / allocated to TRP 3-1 from the third base station. The first base station may request the terminal to perform measurement of CSI-RSs on the CSI-RS resource(s) configured / allocated to TRP 3-1 (S1021). The terminal may receive a request for CSI-RS measurement for the CSI-RS resource(s) configured / allocated to TRP 3-1.

[0240] The TRP 2-1 of the second base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) configured / allocated for transmission of the CSI-RSs (S1022-1). The TRP 3-1 of the third base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) configured / allocated for transmission of the CSI-RSs (S1022-2). It should be noted here that since allocation of CSI-RS resources for the entire selected candidate cell(s) and CSI-RS measurements of the terminal occur, the load of the CSI-RS resources and the load of the CSI-RS measurement of the terminal may be much more severe. For this reason, reducing the number of candidate cells may adversely affect the fast LTM performance before or during cell switching due to the evaluation events and / or CSI-RS measurement(s) triggering the evaluation events mentioned below.

[0241] The beam direction of the CSI-RS(es) transmitted in TRP 2-1 of the second base station may have a QCL relationship with the beam direction of the beam when transmitting the best SSB having the beam ID of beam 5. The terminal may measure the CSI-RS(es) in response to a request for measuring the CSI-RS for the CSI-RS resource(s) configured / allocated to TRP 2-1 of the second base station. The beam direction of the CSI-RS(es) transmitted in TRP 3-1 of the third base station may have a QCL relationship with the beam direction of the beam when transmitting the next best SSB having the beam ID of beam 2. The terminal may measure the CSI-RS(es) in response to a request for measuring the CSI-RS for the CSI-RS resource(s) configured / allocated to TRP 3-1 of the third base station. The terminal can periodically and / or aperiodically report the measurement results for CSI-RS(s) to TRP 1-1 using the allocated reporting resource(s) (S1023). TRP 1-1 can periodically and / or aperiodically receive the measurement results for CSI-RS(s) from the terminal through the reporting resource(s). The measurement results for CSI-RS can include information about the signal quality of the CSI-RS and the TRP that transmitted the CSI-RS. For example, the measurement results for CSI-RS can include a channel quality indicator, a precoding matrix indicator, a CSI-RS resource indicator, an SS / PBCH block resource indicator, a layer indicator, a rank indicator, a first layer reference signal reception power, information about the TRP, etc.

[0242] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of a serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0243] The first base station may select a target cell based on the CSI-RS measurement results received from the terminal (S1024). For example, the signal quality of the CSI-RS transmitted in TRP 2-1 may be the best among the CSI-RS measurement results. The first base station may refer to the CSI-RS measurement results and determine that TRP 2-1 is the TRP that transmitted the CSI-RS with the best signal quality. The first base station may select TRP 2-1 as the target cell. The terminal, the first base station, the second base station, TRP 1-1, and TRP 2-1 may perform an LTM execution process. During the LTM execution process, TRP 1-1 may transmit measurement results for candidate cells received from the terminal to the first base station. The first base station may receive measurement results for candidate cells from TRP 1-1. The first base station may determine a candidate cell to be changed to a target cell based on the measurement results for the candidate cells of the terminal that it has received. A candidate cell may be, for example, TRP 2-1 of the second base station.

[0244] The first base station can transmit a cell switch command to the terminal via MAC CE. The terminal can disconnect from TRP 1-1 and apply preset candidate cell configuration information. The terminal can attempt to connect to TRP 2-1 as a target cell. If UL synchronization is invalid, the terminal can establish UL synchronization by performing a random access procedure. The TA value included in the cell switch command may be invalid, such as 'FFF'. The cell switch command may not include a contention-free random access resource field. The terminal can use a TA value measured by itself. The cell switch command may specify a TA value. The terminal can use the specified TA value.

[0245] A TA value may be specified in the cell switch command. In this case, the terminal may not perform the RACH procedure for cell switching. The TA value may be specified as an invalid value in the cell switch command, and a non-contention random access resource field may exist. In this case, the terminal may perform the RACH procedure to obtain a TA value for a candidate cell. Cell switching may be successfully completed (S1025). During the LTM completion process of the LTM procedure, the terminal may notify the target base station (e.g., the second base station) that the target cell access has been successfully completed. The second base station may initiate data transmission to the terminal via TRP 2-1. During and after the above cell switching procedure, the terminal may perform zero-delay switching to the target cell without interruption to perform DL and UL communications (S1026).

[0246] For example, target cell TRP 2-1 may request RRC reconfiguration from the terminal (S1027). The terminal may receive a request for RRC reconfiguration from TRP 2-1. The terminal may complete the reconfiguration according to the RRC request. The terminal may transmit an RRC reconfiguration completion message to TRP 2-1 to report that the reconfiguration has been completed (S1028). TRP 2-1 may receive the RRC reconfiguration completion message from the terminal. TRP 2-1 may complete the LTM cell switch and / or complete the system connection to maintain the connection state with the target cell as the new serving cell.

[0247] Meanwhile, the present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS toward a terminal before cell switching, and can propose several transmission methods, procedures, and communication devices for performing measurements in the reverse direction depending on the communication situation of the terminal, as follows. The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS in an inter-CU / intra-CU deployment scenario, and can propose a fifth simple method and procedure for performing uplink measurements depending on the situation, based on FIGS. 8 and 11.

[0248] Referring back to FIG. 8, before and / or while performing a cell switching operation at the terminal, the first base station may request the second base station to transmit a CSI-RS toward the terminal while transmitting the beam ID of beam 5 to the second base station. The second base station may receive a request for transmission of a CSI-RS including the beam ID of beam 5 from the first base station. If the second base station can specify TRP 2-1 as the TRP that transmitted the best SSB, it may request transmission of the CSI-RS to TRP 2-1. TRP 2-1 may receive the request for transmission of the CSI-RS from the second base station and transmit the CSI-RS to the terminal. However, the second base station cannot distinguish the TRP that transmitted the best SSB from the request for transmission of the CSI-RS including the beam ID information of beam 5 received from the first base station. In other words, the second base station cannot know which TRP, TRP 2-1 or TRP 2-2, transmitted the best SSB.

[0249] To solve this, the first base station can instruct the terminal to perform terminal-based TA synchronization or PDCCH order-based uplink TA acquisition synchronization. The terminal can receive an instruction from the first base station to perform terminal-based TA synchronization or PDCCH order-based uplink TA acquisition synchronization. The terminal can perform terminal-based TA synchronization or PDCCH order-based uplink TA acquisition synchronization according to the instruction of the first base station. A method and procedure using terminal-based TA synchronization or PDCCH order can be described as follows based on FIG. 11. In the method and procedure described based on FIG. 11, it can be preconditioned that the terminal performs cell switching to TRP 2-1 of the second base station, which has the best channel quality among the candidate cells, while communicating by establishing a connection with TRP 1-1 of the first base station. The method and procedure described based on FIG. 11 can be preconditioned that some and / or all of the SSBs swept in all TRPs are shared and used redundantly.

[0250] FIG. 11 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0251] Referring to FIG. 11, a first base station can control TRP 1-1. A second base station can control TRP 2-1, TRP 2-2 (not shown), and TRP 2-3 (not shown). A third base station can control TRP 3-1. A terminal can be connected to TRP 1-1 and transmit and receive data through TRP 1-1. The cell formed by TRP 1-1 can be a serving cell. The cells formed by TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can be non-serving cells.

[0252] TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can transmit SSBs to the terminal (S1111, S1112). The terminal can receive SSBs from TRP 2-1. The terminal can receive SSBs from TRP 2-2. The terminal can receive SSBs from TRP 3-1. The terminal can measure the signal quality of each of the received SSBs. Based on the signal qualities of the SSBs, the terminal can select the SSB received from TRP 2-1, which is close to the terminal, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 as the best SSB. The best SSB may be the first SSB. The terminal may select, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1, the SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, as the next SSB. The next SSB may be the second SSB.

[0253] The best SSB may have a first PCI (e.g., PCI Z), a first beam ID (e.g., beam 5), etc. The next best SSB may have a second PCI (e.g., PCI Q), a second beam ID (e.g., beam 2), etc. The terminal may select candidate cell(s) through SSB estimation. For example, the terminal may select TRP 2-1, which transmits an SSB having a PCI of PCI Z and a beam ID of beam 5, as the first candidate cell, TRP 3-1, which transmits an SSB having a PCI of PCI Q and a beam ID of beam 2, as the second candidate cell, and so on. In addition, the terminal may sequentially select a third candidate cell, a fourth candidate cell, etc. The signal quality may be RSRP, RSRQ, SINR, etc.

[0254] The terminal may perform a random access process for TRP 1-1. After the random access process, the terminal may perform a link connection process for TRP 1-1. The link connection process may be, for example, an RRC reconfiguration process. During the link connection process, before or after the terminal's SSB estimation, TRP 1-1 may request the terminal to report its capabilities (S1113).

[0255] A terminal can receive a request for a terminal capability report from TRP 1-1. The terminal can transmit a terminal capability report containing information on functions that the terminal can support to TRP 1-1 according to the request for a terminal capability report (S1114). TRP 1-1 can receive a terminal capability report from the terminal. The terminal can transmit the terminal capability report to TRP 1-1 via an RRC message, and TRP 1-1 can receive the terminal capability report via an RRC message. TRP 1-1 can confirm the capability of the terminal through the received terminal capability report, and can efficiently allocate network resources and establish an optimal connection based on the confirmed terminal capability.

[0256] The terminal capability report may include the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, VoNR capability, etc. Each of the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, and VoNR capability may be the same as described above with respect to FIG. 6.

[0257] The second base station can classify the SSBs into SSB groups based on the indices of the SSBs. For example, the second base station can classify the even SSB indices including SSB index zero (e.g., SSB #0, SSB #2, SSB #4, etc.) into SSB group #0. The second base station can classify the odd SSB indices (e.g., SSB #1, SSB #3, SSB #5, etc.) into SSB group #1 based on the SSB index. The second base station can classify the TRPs under the control of the second base station to be included in one of the SSB groups. For example, the second base station can classify TRP 2-1, TRP 2-3, etc. to be included in SSB group #0. In other words, SSB group #0 can include TRP 2-1, TRP 2-3, etc. The second base station can classify TRP 2-2, etc. to be included in SSB group #1. In other words, SSB Group #1 may include TRP 2-2, etc.

[0258] TRP 2-1 may be a TRP included in SSB group #0 as described above. The SSB indexes of each of the SSBs transmitted in TRP 2-1 may be SSB index #0, SSB index #2, SSB index #6, etc. TRP 2-2 may be a TRP included in SSB group #1 as described above. The SSB indexes of each of the SSBs transmitted in TRP 2-2 may be SSB index #1, SSB index #3, SSB index #5, etc. The second base station may transmit mapping information of TRPs and SSB groups under the control of the second base station to the first base station. The first base station may receive mapping information of TRPs and SSB groups under the control of the second base station from the second base station. The mapping information of the TRP and SSB groups under the control of the second base station may include mapping information of TRP 2-1 and SSB group #0, mapping information of TRP 2-2 and SSB group #1, mapping information of TRP 2-3 and SSB group #0, etc.

[0259] The third base station can classify the SSBs into SSB groups based on the indices of the SSBs. For example, the third base station can classify the even SSB indices including SSB index zero (e.g., SSB #0, SSB #2, SSB #4, etc.) into SSB group #0. The third base station can classify the odd SSB indices (e.g., SSB #1, SSB #3, SSB #5, etc.) into SSB group #1 based on the SSB index. The third base station can classify the TRPs under the control of the third base station to be included in one of the SSB groups. For example, the third base station can classify TRP 3-1 to be included in SSB group #0. In other words, SSB group #0 can include TRP 3-1. TRP 3-1 can be a TRP included in SSB group #0 as described above. The SSB index of each SSB transmitted in TRP 3-1 may be SSB index #0, SSB index #2, SSB index #4, etc.

[0260] The third base station may transmit mapping information regarding TRPs and SSB groups under the control of the third base station to the first base station. The first base station may receive mapping information regarding TRPs and SSB groups under the control of the third base station from the third base station. The mapping information regarding TRPs and SSB groups under the control of the third base station may include mapping information regarding TRP 3-1 and SSB group #0, etc.

[0261] The first base station can transmit mapping information of TRPs and SSB groups under the control of neighboring base stations to the terminal (S1115). The terminal can receive mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station from the first base station. For example, the mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station can include mapping information of TRP 2-1 and SSB group #0, mapping information of TRP 2-2 and SSB group #1, mapping information of TRP 2-3 and SSB group #0, mapping information of TRP 3-1 and SSB group #0, etc.

[0262] TRP 1-1 may transmit mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station to the terminal before and / or after the terminal reports terminal capabilities. TRP 1-1 may transmit mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station to the terminal before and / or after the terminal reports SSB-based measurements to TRP 1-1.

[0263] The terminal may transmit measurement information including signal quality information of SSB for each of the candidate cell(s) selected by the terminal to TRP 1-1 (S1116). TRP 1-1 may receive measurement information including signal quality information of SSB for each of the candidate cells selected by the terminal from the terminal. Based on the measurement information of SSBs of the candidate cells received from the terminal, TRP 1-1 may select candidate cells to be transmitted to the terminal based on, for example, signal quality and / or capability of the terminal and / or status of the candidate cells (S1117). For example, TRP 1-1 may select up to 8 candidate cells.

[0264] TRP 1-1 can transmit information about candidate cells selected by TRP 1-1 to the UE (S1118). TRP 1-1 can transmit a command to perform an early synchronization process while transmitting information about candidate cells to the UE. For example, TRP 1-1 can transmit a command to perform at least one of an SSB-based downlink synchronization process, a UE-based TA acquisition synchronization process, or a PDCCH order-based uplink TA acquisition synchronization process while transmitting information about candidate cells to the UE. The UE can receive information about candidate cells from TRP 1-1. The UE can receive a command to perform an early synchronization process together with information about candidate cells from TRP 1-1.

[0265] For example, the terminal may receive a command to perform at least one of an SSB-based downlink synchronization process, a terminal-based TA acquisition synchronization process, or a PDCCH order-based uplink TA acquisition synchronization process while receiving information about candidate cells from TRP 1-1. The terminal may perform at least one of an SSB-based downlink synchronization process, a terminal-based TA acquisition synchronization process, or a PDCCH order-based uplink TA acquisition synchronization process (S1119). It should be noted here that this early synchronization process may not be performed due to the SSB group-based TRP indication relationship in which an SSB group can indicate a TRP due to the mapping relationship between TRPs and SSB groups. The SSB group-based TRP indication relationship may enable the second base station, which consists of two TRPs, to distinguish the TRP that transmitted the SSB through the SSB index of the SSB received by the terminal.

[0266] (Method 1)

[0267] The early synchronization process can be comprised of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB, and a terminal-based TA synchronization process that acquires a TA based on the terminal and performs uplink synchronization. TRP 1-1 can transmit a command to perform the early synchronization process to the terminal via RRC signaling and / or MAC-CE. The terminal can receive the command to perform the early synchronization process from TRP 1-1 via RRC signaling and / or MAC-CE.

[0268] In the SSB-based downlink synchronization process, the terminal can perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected in TRP 1-1 (e.g., SSB corresponding to beam 5 with PCI Z, SSB corresponding to beam 2 with PCI Q). In the terminal-based TA synchronization process, the terminal may not transmit preamble(s) toward each candidate cell through PRACH resource(s) from TRP 1-1 via RRC / MAC-CE. In the terminal-based TA synchronization process, the terminal can estimate the TA corresponding to the transmission timing information to be sent to each candidate cell based on the SSBs it has received.

[0269] In the terminal-based TA synchronization process, the terminal can use the estimated TA as uplink synchronization. It should be noted that in the terminal-based TA synchronization, the candidate cell(s) may have different, unique transmission timing errors. In the terminal-based TA synchronization process, the serving cell and the candidate cell(s) may not be synchronized with each other by the NW, which may result in significantly worse uplink synchronization performance compared to the PRACH preamble-based TA synchronization. It should also be noted that the early synchronization process may not be performed at the NW's discretion. In this case, the early synchronization process may be omitted. The terminal may perform the early synchronization process for each candidate cell(s) received from TRP 1-1 (S1119). It should be noted that the early synchronization process may not be performed at the NW's discretion.

[0270] (Method 2)

[0271] The early synchronization process may be composed of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB and an uplink TA acquisition synchronization process based on PDCCH order. TRP 1-1 may transmit a command to perform the early synchronization process to the terminal through RRC signaling and / or MAC-CE. The terminal may receive the command to perform the early synchronization process from TRP 1-1 through RRC signaling and / or MAC-CE. In the SSB-based downlink synchronization process, the terminal may perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected by TRP 1-1 (e.g., the SSB corresponding to beam 5 with PCI Z, the SSB corresponding to beam 2 with PCI Q).

[0272] During the PDCCH order-based uplink TA acquisition synchronization process, TRP 1-1 may transmit a PDCCH order to the UE to initiate a random access procedure for candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include control information instructing the UE to perform a random access procedure. The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to perform a setup procedure based on non-contention random access for link establishment.

[0273] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure with TRP 2-1. The PDCCH order can include a preamble index for TRP 2-1, RO information, an SSB index corresponding to a link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 2-1 and CFRA. The terminal can perform a setup procedure based on TRP 2-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble from a designated RO to TRP 2-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-1 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 2-1 (e.g., the SSB received from TRP 2-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted.

[0274] TRP 2-1 can receive a random access preamble from a terminal. TRP 2-1 can measure the signal quality of the random access preamble received from the terminal. TRP 2-1 can estimate a propagation delay time between TRP 2-1 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in units of time or samples that indicates how much the sampling timing of a signal received from the terminal in TRP 2-1 is ahead or behind a reference timing. TRP 2-1 can determine a TA value based on the estimated propagation delay time between TRP 2-1 and the terminal. TRP 2-1 can transmit an RAR including the determined TA value to the terminal.

[0275] In addition to the TA value, the RAR may include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-1, propagation delay time between TRP 2-1 and the terminal, signal quality of the preamble, etc. TRP 2-1 may report identification information of TRP 2-1, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-1 may not transmit the RAR to the terminal. TRP 2-1 may forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 may receive the RAR from TRP 2-1 and transmit the received RAR to the terminal. The terminal may receive the RAR from TRP 1-1 and know the TA value.

[0276] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure using TRP 2-2. The PDCCH order can include a preamble index for TRP 2-2, RO information, an SSB index corresponding to the link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 2-2 and CFRA. The terminal can perform a setup procedure based on TRP 2-2 and CFRA based on the PDCCH order.

[0277] The terminal can transmit a designated preamble in a designated RO to TRP 2-2 via PRACH based on information included in a PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-2 can be set to have reciprocity with the reception beam direction of a downlink signal from TRP 2-2 (e.g., an SSB received from TRP 2-2 as described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use a preamble sequence indicated in the PDCCH order as the preamble to be transmitted. TRP 2-2 can receive the random access preamble from the terminal. TRP 2-2 can measure the signal quality of the random access preamble received from the terminal. TRP 2-2 can estimate the propagation delay time between TRP 2-2 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in time or sample units indicating how much the sampling timing of the signal received from the terminal in TRP 2-2 is ahead or behind the reference timing.

[0278] TRP 2-2 can determine a TA value based on the estimated propagation delay time between TRP 2-2 and the terminal. TRP 2-2 can transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR can include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-2, propagation delay time between TRP 2-2 and the terminal, signal quality of the preamble, etc. TRP 2-2 can report the identification information of TRP 2-2, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-2 may not transmit the RAR to the terminal. TRP 2-2 can forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 can receive the RAR from TRP 2-2 and transmit the received RAR to the terminal. The terminal can receive RAR from TRP 1-1 and know the TA value.

[0279] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure with TRP 3-1. The PDCCH order can include a preamble index for TRP 3-1, RO information, an SSB index corresponding to a link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 3-1 and CFRA. The terminal can perform a setup procedure based on TRP 3-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble from a designated RO to TRP 3-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 3-1 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 3-1 (e.g., the SSB received from TRP 3-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction.

[0280] For example, a terminal can use a preamble sequence indicated in the PDCCH order for a preamble to be transmitted. TRP 3-1 can receive a random access preamble from the terminal. TRP 3-1 can measure the signal quality of the random access preamble received from the terminal. TRP 3-1 can estimate the propagation delay time between TRP 3-1 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be a time or sample unit error value indicating how much the sampling timing of the signal received from the terminal in TRP 3-1 is ahead or behind the reference timing.

[0281] TRP 3-1 can determine a TA value based on the estimated propagation delay time between TRP 3-1 and the terminal. TRP 3-1 can transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR can include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 3-1, propagation delay time between TRP 3-1 and the terminal, signal quality of the preamble, etc. TRP 3-1 can report the identification information of TRP 3-1, signal quality of the preamble, propagation delay time, etc. to a third base station. TRP 3-1 may not transmit the RAR to the terminal. TRP 3-1 can forward the RAR to TRP 1-1 via the third base station and the first base station. TRP 1-1 can receive the RAR from TRP 3-1 and transmit the received RAR to the terminal. The terminal can receive RAR from TRP 1-1 and know the TA value.

[0282] It should be noted that PRACH preamble-based TA synchronization can improve UL synchronization performance compared to UE-based TA synchronization, where candidate cell(s) may have different inherent transmission timing errors and the serving cell and candidate cell(s) may not be synchronized with each other by the NW. The UE can perform an early synchronization process for each candidate cell received from TRP 1-1. It should be noted that, as mentioned above, the NW may need to perform early synchronization processes for all selected candidate cells. The UE may pursue low power. In such a case, the NW may reduce the number of candidate cells.

[0283] TRP 1-1 may select a target cell based on the results of the early synchronization process and / or based on the previous results of the early synchronization process (S1120). For example, TRP 1-1 may select a TRP that has transmitted a best SSB with PCI Z and beam 5 as a target cell. TRP 1-1 may know that the candidate cell that has transmitted the SSB with PCI Z and beam 5 is a TRP belonging to the second base station. The terminal may transmit an SSB index for the best SSB to TRP 1-1. TRP 1-1 may receive an SSB index corresponding to the best SSB from the terminal. The SSB index may be SSB #4. TRP 1-1 may use an SSB group-based TRP indication relationship to specify that the TRP that has transmitted the best SSB with PCI Z and beam 5 is TRP 2-1 controlled by the second base station. In other words, TRP 1-1 can select TRP 2-1, which has PCI Z and beam 5 and transmits the best SSB having SSB #4, which is an even-numbered SSB index, as a target cell based on the mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station.

[0284] Since the TRP(s) corresponding to the target cell(s) can be specified as described above, TRP 1-1 can send a CSI-RS request to the second base station through the first base station, requesting the second base station to transmit CSI-RSs toward the terminal using TRP 2-1 belonging to the second base station (S1121). The second base station can receive the CSI-RS request requesting transmission of CSI-RSs using TRP 2-1 from the first base station.

[0285] The second base station can configure / allocate CSI-RS resource(s) capable of transmitting the CSI-RS of TRP 2-1. The second base station can transmit information about the configured / allocated CSI-RS resource(s) to TRP 2-1. TRP 2-1 can receive information about the configured / allocated CSI-RS resource(s) from the second base station.

[0286] The second base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the first base station (S1122). The first base station may receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1 of the second base station from the second base station.

[0287] The first base station may request the terminal to perform measurements on CSI-RSs in the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station (S1123). The terminal may receive a request for CSI-RS measurement for the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station. The first base station may transmit information about the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station to the terminal. The terminal may receive information about the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station.

[0288] The TRP 2-1 of the second base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) (i.e., CSI-RS resource(s)) configured / allocated for transmission of the CSI-RSs (S1124). The beam direction of the CSI-RS(es) transmitted from the TRP 2-1 of the second base station can have a QCL relationship with the beam direction of the beam when transmitting the best SSB having the beam ID of beam 5. The terminal can measure the CSI-RS(es) according to a CSI-RS measurement request for the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station. The terminal can periodically and / or aperiodically report the measurement result for the CSI-RS(es) to the TRP 1-1 in the allocated reporting resource(s) (S1125). TRP 1-1 can receive measurement results for CSI-RS(s) from the terminal periodically and / or aperiodically from the reporting resource(s). The measurement results for the CSI-RS may include information about the signal quality of the CSI-RS and the TRP that transmitted the CSI-RS. For example, the measurement results for the CSI-RS may include a channel quality indicator, a precoding matrix indicator, a CSI-RS resource indicator, an SS / PBCH block resource indicator, a layer indicator, a rank indicator, information about the reception power of the first layer reference signal, and information about the TRP.

[0289] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of a serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0290] A terminal, a first base station, a second base station, TRP 1-1, and TRP 2-1 can perform an LTM execution process. During the LTM execution process, TRP 1-1 can transmit measurement results for candidate cells received from the terminal to the first base station. The first base station can receive measurement results for candidate cells from TRP 1-1. Based on the measurement results for candidate cells of the terminal received, the first base station can determine a candidate cell to be changed to a target cell. The candidate cell can be, for example, TRP 2-1 of the second base station.

[0291] The first base station can transmit a cell switch command to the terminal via MAC CE. The terminal can disconnect from TRP 1-1 and apply preset candidate cell configuration information. The terminal can attempt to connect to TRP 2-1 as a target cell. If UL synchronization is invalid, the terminal can establish UL synchronization by performing a random access procedure. The TA value included in the cell switch command may be invalid, such as 'FFF'. The cell switch command may not include a contention-free random access resource field. The terminal can use a TA value measured by itself. The cell switch command may specify a TA value. The terminal can use the specified TA value.

[0292] A TA value may be specified in the cell switch command. In this case, the terminal may not perform the RACH procedure for cell switching. The TA value may be specified as an invalid value in the cell switch command, and a non-contention random access resource field may exist. In this case, the terminal may perform the RACH procedure to obtain a TA value for a candidate cell. Cell switching may be successfully completed (S1126). During the LTM completion process of the LTM procedure, the terminal may notify the target base station (e.g., the second base station) that the target cell access has been successfully completed. The second base station may initiate data transmission to the terminal via TRP 2-1. During and after the above cell switching procedure, the terminal may perform zero-delay switching to the target cell without interruption to perform DL and UL communications (S1127).

[0293] For example, the target cell TRP 2-1 may request an RRC reconfiguration from the terminal (S1128). The terminal may receive a request for RRC reconfiguration from TRP 2-1. The terminal may complete the reconfiguration according to the RRC request. The terminal may transmit an RRC reconfiguration completion message to TRP 2-1 to report that the reconfiguration has been completed (S1129). TRP 2-1 may receive the RRC reconfiguration completion message from the terminal. TRP 2-1 may complete the LTM cell switch and / or complete the system connection to maintain the connection state with the target cell as the new serving cell.

[0294] Meanwhile, the present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS toward a terminal before cell switching, and can propose several transmission methods, procedures, and communication devices for performing measurements in the reverse direction depending on the communication situation of the terminal, as follows. The present disclosure can resolve the ambiguity that occurs when transmitting CSI-RS in an inter-CU / intra-CU deployment scenario, and can propose an eighth simple method and procedure for performing uplink measurements depending on the situation, as follows, based on FIGS. 8 and 12.

[0295] Referring back to FIG. 8, before and / or while performing a cell switching operation at the terminal, the first base station may request the second base station to transmit a CSI-RS toward the terminal while transmitting the beam ID of beam 5 to the second base station. The second base station may receive a request for transmission of a CSI-RS including the beam ID of beam 5 from the first base station. If the second base station can specify TRP 2-1 as the TRP that transmitted the best SSB, it may request transmission of the CSI-RS to TRP 2-1. TRP 2-1 may receive the request for transmission of the CSI-RS from the second base station and transmit the CSI-RS to the terminal. However, the second base station cannot distinguish the TRP that transmitted the best SSB from the request for transmission of the CSI-RS including the beam ID information of beam 5 received from the first base station. In other words, the second base station cannot know which TRP, TRP 2-1 or TRP 2-2, transmitted the best SSB.

[0296] To solve this, the first base station can instruct the terminal to perform terminal-based TA synchronization or PDCCH order-based uplink TA acquisition synchronization. The terminal can receive an instruction from the first base station to perform terminal-based TA synchronization or PDCCH order-based uplink TA acquisition synchronization. The terminal can perform terminal-based TA synchronization or PDCCH order-based uplink TA acquisition synchronization according to the instruction of the first base station. A method and procedure using terminal-based TA synchronization or PDCCH order can be described as follows based on FIG. 12. In the method and procedure described based on FIG. 12, it can be preconditioned that the terminal performs cell switching to TRP 2-1 of the second base station, which has the best channel quality among the candidate cells, while communicating by establishing a connection with TRP 1-1 of the first base station. The method and procedure described based on FIG. 12 can be preconditioned that some and / or all of the SSBs swept in all TRPs are shared and used redundantly.

[0297] FIG. 12 is a flowchart illustrating embodiments of a lower layer trigger mobility method based on candidate transceiver point recognition.

[0298] Referring to FIG. 12, the first base station can control TRP 1-1. The second base station can control TRP 2-1, TRP 2-2 (not shown), and TRP 2-3 (not shown). The third base station can control TRP 3-1. A terminal can be connected to TRP 1-1 and transmit and receive data through TRP 1-1. The cell formed by TRP 1-1 can be a serving cell. The cells formed by TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can be non-serving cells.

[0299] TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 can transmit SSBs to the terminal (S1211, S1212). The terminal can receive SSBs from TRP 2-1. The terminal can receive SSBs from TRP 2-2. The terminal can receive SSBs from TRP 3-1. The terminal can measure the signal quality of each of the received SSBs. Based on the signal qualities of the SSBs, the terminal can select the SSB received from TRP 2-1, which is close to the terminal, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1 as the best SSB. The best SSB may be the first SSB. The terminal may select, among the SSBs received from TRP 2-1, TRP 2-2, TRP 2-3, and TRP 3-1, the SSB received from TRP 3-1, which is further away from the terminal than TRP 2-1, as the next SSB. The next SSB may be the second SSB.

[0300] The best SSB may have a first PCI (e.g., PCI Z), a first beam ID (e.g., beam 5), etc. The next best SSB may have a second PCI (e.g., PCI Q), a second beam ID (e.g., beam 2), etc. The terminal may select candidate cell(s) through SSB estimation. For example, the terminal may select TRP 2-1, which transmits an SSB having a PCI of PCI Z and a beam ID of beam 5, as the first candidate cell, TRP 3-1, which transmits an SSB having a PCI of PCI Q and a beam ID of beam 2, as the second candidate cell, and so on. In addition, the terminal may sequentially select a third candidate cell, a fourth candidate cell, etc. The signal quality may be RSRP, RSRQ, SINR, etc.

[0301] The terminal may perform a random access process for TRP 1-1. After the random access process, the terminal may perform a link connection process for TRP 1-1. The link connection process may be, for example, an RRC reconfiguration process. During the link connection process, before or after the terminal's SSB estimation, TRP 1-1 may request the terminal to report its capabilities (S1213).

[0302] A terminal can receive a request for a terminal capability report from TRP 1-1. The terminal can transmit a terminal capability report containing information on functions that the terminal can support to TRP 1-1 according to the request for a terminal capability report (S1214). TRP 1-1 can receive a terminal capability report from the terminal. The terminal can transmit the terminal capability report to TRP 1-1 via an RRC message, and TRP 1-1 can receive the terminal capability report via an RRC message. TRP 1-1 can confirm the capability of the terminal through the received terminal capability report, and can efficiently allocate network resources and establish an optimal connection based on the confirmed terminal capability.

[0303] The terminal capability report may include the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, VoNR capability, etc. Each of the terminal's RF capability, physical layer control capability, medium access control capability, radio link control capability, PDCP capability, DC capability, CA capability, NSA / SA operation capability, NR bandwidth class, transport class capability, LCS capability, reduced capability, and VoNR capability may be the same as described above with respect to FIG. 6.

[0304] The second base station can classify the SSBs into SSB groups based on the indices of the SSBs. For example, the second base station can classify the even SSB indices including SSB index zero (e.g., SSB #0, SSB #2, SSB #4, etc.) into SSB group #0. The second base station can classify the odd SSB indices (e.g., SSB #1, SSB #3, SSB #5, etc.) into SSB group #1 based on the SSB index. The second base station can classify the TRPs under the control of the second base station to be included in one of the SSB groups. For example, the second base station can classify TRP 2-1, TRP 2-3, etc. to be included in SSB group #0. In other words, SSB group #0 can include TRP 2-1, TRP 2-3, etc. The second base station can classify TRP 2-2, etc. to be included in SSB group #1. In other words, SSB Group #1 may include TRP 2-2, etc.

[0305] TRP 2-1 may be a TRP included in SSB group #0 as described above. The respective SSB indexes of the SSBs transmitted in TRP 2-1 may be SSB index #0, SSB index #2, SSB index #4, etc. TRP 2-2 may be a TRP included in SSB group #1 as described above. The respective SSB indexes of the SSBs transmitted in TRP 2-2 may be SSB index #1, SSB index #3, SSB index #5, etc. The second base station may transmit mapping information of TRPs and SSB groups under the control of the second base station to the first base station. The first base station may receive mapping information of TRPs and SSB groups under the control of the second base station from the second base station. The mapping information of the TRP and SSB groups under the control of the second base station may include mapping information of TRP 2-1 and SSB group #0, mapping information of TRP 2-2 and SSB group #1, mapping information of TRP 2-3 and SSB group #0, etc.

[0306] The third base station can classify the SSBs into SSB groups based on the indices of the SSBs. For example, the third base station can classify the even SSB indices including SSB index zero (e.g., SSB #0, SSB #2, SSB #4, etc.) into SSB group #0. The third base station can classify the odd SSB indices (e.g., SSB #1, SSB #3, SSB #5, etc.) into SSB group #1 based on the SSB index. The third base station can classify the TRPs under the control of the third base station to be included in one of the SSB groups. For example, the third base station can classify TRP 3-1 to be included in SSB group #0. In other words, SSB group #0 can include TRP 3-1. TRP 3-1 can be a TRP included in SSB group #0 as described above. The SSB index of each SSB transmitted in TRP 3-1 may be SSB index #0, SSB index #2, SSB index #4, etc.

[0307] The third base station may transmit mapping information regarding TRPs and SSB groups under the control of the third base station to the first base station. The first base station may receive mapping information regarding TRPs and SSB groups under the control of the third base station from the third base station. The mapping information regarding TRPs and SSB groups under the control of the third base station may include mapping information regarding TRP 3-1 and SSB group #0, etc.

[0308] The first base station can transmit mapping relationship information of TRPs and SSB groups under the control of adjacent base stations to the terminal (S1215). The terminal can receive mapping information of TRPs and SSB groups under the control of adjacent base stations of the first base station from the first base station. For example, the mapping information of TRPs and SSB groups under the control of adjacent base stations of the first base station can include mapping information of TRP 2-1 and SSB group #0, mapping information of TRP 2-2 and SSB group #1, mapping information of TRP 2-3 and SSB group #0, mapping information of TRP 3-1 and SSB group #0, etc.

[0309] TRP 1-1 may transmit mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station to the terminal before and / or after the terminal reports terminal capabilities. TRP 1-1 may transmit mapping information of TRPs and SSB groups under the control of neighboring base stations of the first base station to the terminal before and / or after the terminal reports SSB-based measurements to TRP 1-1.

[0310] The terminal may transmit measurement information including signal quality information of SSB for each of the candidate cell(s) selected by the terminal to TRP 1-1 (S1216). TRP 1-1 may receive measurement information including signal quality information of SSB for each of the candidate cells selected by the terminal from the terminal. Based on the measurement information of SSBs of the candidate cells received from the terminal, TRP 1-1 may select candidate cells to be transmitted to the terminal based on, for example, signal quality and / or capability of the terminal and / or status of the candidate cells (S1217). For example, TRP 1-1 may select up to 8 candidate cells.

[0311] TRP 1-1 can transmit information about candidate cells selected by TRP 1-1 to the UE (S1218). TRP 1-1 can transmit a command to perform an early synchronization process while transmitting information about candidate cells to the UE. For example, TRP 1-1 can transmit a command to perform one of an SSB-based downlink synchronization process, a UE-based TA acquisition synchronization process, or a PDCCH order-based uplink TA acquisition synchronization process while transmitting information about candidate cells to the UE. The UE can receive information about candidate cells from TRP 1-1. The UE can receive a command to perform an early synchronization process together with information about candidate cells from TRP 1-1.

[0312] For example, the terminal may receive a command to perform one of the SSB-based downlink synchronization process, the terminal-based TA acquisition synchronization process, or the PDCCH order-based uplink TA acquisition synchronization process while receiving information about candidate cells from TRP 1-1. The terminal may perform one of the SSB-based downlink synchronization process, the terminal-based TA acquisition synchronization process, or the PDCCH order-based uplink TA acquisition synchronization process (S1219). It should be noted here that this early synchronization process may not be performed due to the SSB group-based TRP indication relationship that allows an SSB group to indicate a TRP due to the mapping relationship between TRPs and SSB groups. The SSB group-based TRP indication relationship can enable a second base station consisting of two TRPs to distinguish the TRP that transmitted the SSB through the SSB index of the SSB received by the terminal.

[0313] (Method 1)

[0314] The early synchronization process can be comprised of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB, and a terminal-based TA synchronization process that acquires a TA based on the terminal and performs uplink synchronization. TRP 1-1 can transmit a command to perform the early synchronization process to the terminal via RRC signaling and / or MAC-CE. The terminal can receive the command to perform the early synchronization process from TRP 1-1 via RRC signaling and / or MAC-CE.

[0315] In the SSB-based downlink synchronization process, the terminal can perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected in TRP 1-1 (for example, the SSB corresponding to beam 5 with PCI Z, the SSB corresponding to beam 2 with PCI Q). In the terminal-based TA synchronization process, the terminal may not transmit the preamble(s) toward each candidate cell through the PRACH resource(s) from TRP 1-1 via RRC / MAC-CE. In the terminal-based TA synchronization process, the terminal can estimate the TA corresponding to the transmission timing information to be sent to each candidate cell based on the SSBs it has received. In the terminal-based TA synchronization process, the terminal can use the estimated TA as uplink synchronization. It should be noted here that in the terminal-based TA synchronization, the candidate cell(s) may have different, unique transmission timing errors.

[0316] During the terminal-based TA synchronization process, the serving cell and candidate cell(s) may not be synchronized with each other by the NW, which may result in significantly worse uplink synchronization performance compared to PRACH preamble-based TA synchronization. It should also be noted that the early synchronization process may not be performed at the NW's discretion. In such a case, the early synchronization process may be omitted. The terminal may perform the early synchronization process for each candidate cell(s) received from TRP 1-1 (S1219). It should be noted that the early synchronization process may not be performed at the NW's discretion.

[0317] (Method 2)

[0318] The early synchronization process may be composed of an SSB-based downlink synchronization process that synchronizes the downlink based on SSB and an uplink TA acquisition synchronization process based on PDCCH order. TRP 1-1 may transmit a command to perform the early synchronization process to the terminal through RRC signaling and / or MAC-CE. The terminal may receive the command to perform the early synchronization process from TRP 1-1 through RRC signaling and / or MAC-CE. In the SSB-based downlink synchronization process, the terminal may perform DL synchronization by beamforming toward each candidate cell for the SSB of each candidate cell selected by TRP 1-1 (e.g., the SSB corresponding to beam 5 with PCI Z, the SSB corresponding to beam 2 with PCI Q).

[0319] During the PDCCH order-based uplink TA acquisition synchronization process, TRP 1-1 may transmit a PDCCH order to the UE to initiate a random access procedure for candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include control information instructing the UE to perform a random access procedure. The PDCCH order may include information instructing the UE to establish a link with the candidate cells (e.g., TRP 2-1, TRP 2-2, TRP 3-1). The PDCCH order may include information instructing the UE to perform a setup procedure based on non-contention random access for link establishment.

[0320] The PDCCH order can provide resource information that allows a terminal to perform a dedicated random access procedure without competition with other terminals when performing a random access procedure with TRP 2-1. The PDCCH order can include a preamble index for TRP 2-1, RO information, an SSB index corresponding to a link, PCI information, etc. The terminal can receive a PDCCH order including the information described above from TRP 1-1. The terminal can obtain setup resource information based on TRP 2-1 and CFRA. The terminal can perform a setup procedure based on TRP 2-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble from a designated RO to TRP 2-1 via PRACH based on the information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-1 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 2-1 (e.g., the SSB received from TRP 2-1 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted.

[0321] TRP 2-1 can receive a random access preamble from a terminal. TRP 2-1 can measure the signal quality of the random access preamble received from the terminal. TRP 2-1 can estimate a propagation delay time between TRP 2-1 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in units of time or samples that indicates how much the sampling timing of a signal received from the terminal in TRP 2-1 is ahead or behind a reference timing. TRP 2-1 can determine a TA value based on the estimated propagation delay time between TRP 2-1 and the terminal. TRP 2-1 can transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR may include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-1, propagation delay time between TRP 2-1 and the terminal, signal quality of the preamble, etc. TRP 2-1 may report identification information of TRP 2-1, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-1 may not transmit the RAR to the terminal. TRP 2-1 may forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 may receive the RAR from TRP 2-1 and transmit the received RAR to the terminal. The terminal may receive the RAR from TRP 1-1 and know the TA value.

[0322] The PDCCH order can provide resource information that allows a UE to perform a dedicated random access procedure without competition with other UEs when performing a random access procedure with TRP 2-2. The PDCCH order can include a preamble index for TRP 2-2, RO information, an SSB index corresponding to a link, PCI information, etc. The UE can receive a PDCCH order including the information described above from TRP 1-1. The UE can obtain setup resource information based on TRP 2-2 and CFRA. The UE can perform a setup procedure based on TRP 2-2 and CFRA based on the PDCCH order. The UE can transmit a designated preamble from a designated RO to TRP 2-2 via PRACH based on the information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 2-2 can be configured to have reciprocity with the reception beam direction of the downlink signal from TRP 2-2 (e.g., the SSB received from TRP 2-2 described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction. For example, the terminal can use the preamble sequence indicated in the PDCCH order for the preamble to be transmitted.

[0323] TRP 2-2 can receive a random access preamble from a terminal. TRP 2-2 can measure the signal quality of the random access preamble received from the terminal. TRP 2-2 can estimate a propagation delay time between TRP 2-2 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in units of time or samples that indicates how much the sampling timing of a signal received from the terminal in TRP 2-2 is ahead or behind a reference timing. TRP 2-2 can determine a TA value based on the estimated propagation delay time between TRP 2-2 and the terminal. TRP 2-2 can transmit an RAR including the determined TA value to the terminal.

[0324] In addition to the TA value, the RAR may include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 2-2, propagation delay time between TRP 2-2 and the terminal, signal quality of the preamble, etc. TRP 2-2 may report identification information of TRP 2-2, signal quality of the preamble, propagation delay time, etc. to the second base station. TRP 2-2 may not transmit the RAR to the terminal. TRP 2-2 may forward the RAR to TRP 1-1 via the second base station and the first base station. TRP 1-1 may receive the RAR from TRP 2-2 and transmit the received RAR to the terminal. The terminal may receive the RAR from TRP 1-1 and know the TA value.

[0325] The PDCCH order can provide resource information that allows a UE to perform a dedicated random access procedure without competition with other UEs when performing a random access procedure using TRP 3-1. The PDCCH order can include a preamble index for TRP 3-1, RO information, an SSB index corresponding to the link, PCI information, etc. The UE can receive a PDCCH order including the information described above from TRP 1-1. The UE can obtain setup resource information based on TRP 3-1 and CFRA.

[0326] The terminal can perform a setup procedure based on TRP 3-1 and CFRA based on the PDCCH order. The terminal can transmit a designated preamble to TRP 3-1 through PRACH in a designated RO based on information included in the PDCCH order received from TRP 1-1. The uplink beam direction in which the terminal transmits the random access preamble to TRP 3-1 can be configured to have reciprocity with the reception beam direction of a downlink signal from TRP 3-1 (e.g., SSB received from TRP 3-1 as described above). In other words, the terminal can transmit the preamble in a spatially filtered direction of the downlink SSB beam direction.

[0327] For example, a terminal may use a preamble sequence indicated in the PDCCH order as a preamble to be transmitted. TRP 3-1 may receive a random access preamble from the terminal. TRP 3-1 may measure the signal quality of the random access preamble received from the terminal. TRP 3-1 may estimate a propagation delay time between TRP 3-1 and the terminal using the random access preamble received from the terminal. The propagation delay time may be an uplink reception sample timing offset value. The uplink reception sample timing offset value may be an error value in time or sample units indicating how much the sampling timing of the signal received from the terminal in TRP 3-1 is ahead or behind the reference timing. TRP 3-1 may determine a TA value based on the estimated propagation delay time between TRP 3-1 and the terminal. TRP 3-1 may transmit an RAR including the determined TA value to the terminal. In addition to the TA value, the RAR may include a preamble index, uplink grant information, a temporary C-RNTI value, identification information of TRP 3-1, propagation delay time between TRP 3-1 and the terminal, signal quality of the preamble, etc. TRP 3-1 may report identification information of TRP 3-1, signal quality of the preamble, propagation delay time, etc. to a third base station. TRP 3-1 may not transmit the RAR to the terminal. TRP 3-1 may forward the RAR to TRP 1-1 via the third base station and the first base station. TRP 1-1 may receive the RAR from TRP 3-1 and transmit the received RAR to the terminal. The terminal may receive the RAR from TRP 1-1 and know the TA value.

[0328] It should be noted that PRACH preamble-based TA synchronization can improve UL synchronization performance compared to UE-based TA synchronization, where candidate cell(s) may have different inherent transmission timing errors and the serving cell and candidate cell(s) may not be synchronized with each other by the NW. The UE can perform an early synchronization process for each candidate cell received from TRP 1-1. It should be noted that, as mentioned above, the NW may need to perform early synchronization processes for all selected candidate cells. The UE may pursue low power. In such a case, the NW may reduce the number of candidate cells.

[0329] TRP 1-1 can know that the candidate cell that transmitted the best SSB with PCI Z and beam 5 is a TRP belonging to the second base station. The terminal can transmit the SSB index for the best SSB to TRP 1-1. The SSB index for the best SSB can be, for example, SSB #4. TRP 1-1 can receive the SSB index corresponding to the best SSB from the terminal. TRP 1-1 can use the SSB group-based TRP indication relationship to specify that the TRP that transmitted the best SSB with PCI Z and beam 5 is TRP 2-1 controlled by the second base station. TRP 1-1 can use the SSB group-based TRP indication relationship to select TRP 2-1 that transmitted the best SSB with PCI Z and beam 5 and an even-numbered SSB index as a candidate cell.

[0330] Since the TRP(s) corresponding to the candidate cell(s) can be specified as described above, TRP 1-1 can send a CSI-RS transmission request to the second base station through the first base station, requesting the second base station to transmit CSI-RSs toward the terminal using TRP 2-1 belonging to the second base station (S1220-1). The second base station can receive a CSI-RS request requesting transmission of CSI-RSs using TRP 2-1 from the first base station.

[0331] The second base station can configure / allocate CSI-RS resource(s) capable of transmitting the CSI-RS of TRP 2-1. The second base station can transmit information about the configured / allocated CSI-RS resource(s) to TRP 2-1. TRP 2-1 can receive information about the configured / allocated CSI-RS resource(s) from the second base station.

[0332] The second base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 2-1 to the first base station (S1221-1). The first base station may receive information about the CSI-RS resource(s) configured / allocated to TRP 2-1 of the second base station from the second base station.

[0333] The first base station may request the terminal to perform measurements on CSI-RSs in the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station (S1222-1). The terminal may receive a request for CSI-RS measurement for the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station. The first base station may transmit information about the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station to the terminal. The terminal may receive information about the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station.

[0334] The TRP 2-1 of the second base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) (i.e., CSI-RS resource(s)) configured / allocated for transmission of the CSI-RSs (S1223-1). The beam direction of the CSI-RS(es) transmitted from the TRP 2-1 of the second base station can have a QCL relationship with the beam direction of the beam when transmitting the best SSB having the beam ID of beam 5. The terminal can measure the CSI-RS(es) according to a CSI-RS measurement request for the CSI-RS resource(s) configured / allocated to the TRP 2-1 of the second base station. The terminal can periodically and / or aperiodically report the measurement result for the CSI-RS(es) to the TRP 1-1 in the allocated reporting resource(s) (S1224). TRP 1-1 can receive measurement results for CSI-RS(s) from the terminal periodically and / or aperiodically from the reporting resource(s). The measurement results for the CSI-RS may include information about the signal quality of the CSI-RS and the TRP that transmitted the CSI-RS. For example, the measurement results for the CSI-RS may include a channel quality indicator, a precoding matrix indicator, a CSI-RS resource indicator, an SS / PBCH block resource indicator, a layer indicator, a rank indicator, information about the reception power of the first layer reference signal, and information about the TRP.

[0335] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of a serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0336] TRP 1-1 can know that the candidate cell that transmitted the sub-SSB with PCI Q and beam 2 is TRP3-1 belonging to the third base station. Since the TRP(s) corresponding to the candidate cell(s) can be specified as above, TRP 1-1 can send a CSI-RS request to the third base station through the first base station to request the third base station to transmit CSI-RSs toward the terminal using TRP 3-1 belonging to the third base station (S1220-2). The third base station can receive the CSI-RS request requesting transmission of CSI-RSs using TRP 3-1 from the first base station.

[0337] The third base station can configure / allocate CSI-RS resource(s) capable of transmitting the CSI-RS of TRP 3-1. The third base station can transmit information about the configured / allocated CSI-RS resource(s) to TRP 3-1. TRP 3-1 can receive information about the configured / allocated CSI-RS resource(s) from the third base station.

[0338] The third base station may transmit information about the CSI-RS resource(s) configured / allocated to TRP 3-1 to the first base station (S1221-2). The first base station may receive information about the CSI-RS resource(s) configured / allocated to TRP 3-1 of the third base station from the third base station.

[0339] The first base station may request the terminal to perform measurements on CSI-RSs on the CSI-RS resource(s) configured / allocated to the TRP 3-1 of the third base station (S1222-2). The terminal may receive a request for CSI-RS measurement on the CSI-RS resource(s) configured / allocated to the TRP 3-1 of the third base station. The first base station may transmit information on the CSI-RS resource(s) configured / allocated to the TRP 3-1 of the third base station to the terminal. The terminal may receive information on the CSI-RS resource(s) configured / allocated to the TRP 3-1 of the third base station.

[0340] The TRP 3-1 of the third base station can generate CSI-RS(es) and transmit the generated CSI-RS(es) to the terminal in the time and frequency resource(s) (i.e., CSI-RS resource(s)) configured / allocated for transmission of the CSI-RSs (S1223-2). The beam direction of the CSI-RS(es) transmitted from the TRP 3-1 of the third base station can have a QCL relationship with the beam direction of the beam when transmitting the next-best SSB having the beam ID of beam 2. The terminal can measure the CSI-RS(es) according to a CSI-RS measurement request for the CSI-RS resource(s) configured / allocated to the TRP 3-1 of the third base station. The terminal can periodically and / or aperiodically report the measurement result for the CSI-RS(es) to the TRP 1-1 in the allocated reporting resource(s) (S1224). TRP 1-1 can receive measurement results for CSI-RS(s) from the terminal periodically and / or aperiodically from the reporting resource(s). The measurement results for the CSI-RS may include information about the signal quality of the CSI-RS and the TRP that transmitted the CSI-RS.

[0341] The terminal may report measurement result(s) to TRP 1-1 based on an evaluation event and / or based on the triggering of an evaluation event. For example, the evaluation event may be an LTM2 event or an LTM5 event. An LTM2 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold for a certain period of time. An LTM3 event may be an event indicating that a beam of a candidate cell is better than a beam of a serving cell by an offset for a certain period of time. An LTM4 event may be an event indicating that a beam of a candidate cell is better than an absolute threshold for a certain period of time. An LTM5 event may be an event indicating that a beam of a serving cell is worse than an absolute threshold 1 for a certain period of time, and at the same time, a beam of a candidate cell is better than another absolute threshold 2.

[0342] The first base station may select a target cell based on the CSI-RS measurement results received from the terminal (S1225). For example, the signal quality of the CSI-RS transmitted in TRP 2-1 may be the best among the CSI-RS measurement results. The first base station may refer to the CSI-RS measurement results and confirm that TRP 2-1 is the TRP that transmitted the CSI-RS with the best signal quality. The first base station may select TRP 2-1 as the target cell.

[0343] The first base station can transmit a cell switch command to the terminal via MAC CE. The terminal can disconnect from TRP 1-1 and apply preset candidate cell configuration information. The terminal can attempt to connect to TRP 2-1 as a target cell. If UL synchronization is invalid, the terminal can establish UL synchronization by performing a random access procedure. The TA value included in the cell switch command may be invalid, such as 'FFF'. The cell switch command may not include a contention-free random access resource field. The terminal can use a TA value measured by itself. The cell switch command may specify a TA value. The terminal can use the specified TA value.

[0344] A TA value may be specified in the cell switch command. In this case, the terminal may not perform the RACH procedure for cell switching. The TA value may be specified as an invalid value in the cell switch command, and a non-contention random access resource field may exist. In this case, the terminal may perform the RACH procedure to obtain a TA value for a candidate cell. Cell switching may be successfully completed (S1226). During the LTM completion process of the LTM procedure, the terminal may notify the target base station (e.g., the second base station) that the target cell access has been successfully completed. The second base station may initiate data transmission to the terminal via TRP 2-1. During and after the above cell switching procedure, the terminal may perform zero-delay switching to the target cell without interruption and perform DL and UL communications (S1227).

[0345] For example, target cell TRP 2-1 may request RRC reconfiguration from the terminal (S1228). The terminal may receive a request for RRC reconfiguration from TRP 2-1. The terminal may complete the reconfiguration according to the RRC request. The terminal may transmit an RRC reconfiguration completion message to TRP 2-1 to report that the reconfiguration has been completed (S1229). TRP 2-1 may receive the RRC reconfiguration completion message from the terminal. TRP 2-1 may complete the LTM cell switch and / or complete the system connection to maintain the connection state with the target cell as the new serving cell.

[0346] The operations of the method according to the embodiments of the present disclosure can be implemented as a computer-readable program or code on a computer-readable recording medium. A computer-readable recording medium includes any type of recording device that stores information readable by a computer system. Furthermore, a computer-readable recording medium can be distributed across network-connected computer systems, allowing the computer-readable program or code to be stored and executed in a distributed manner.

[0347] Additionally, the computer-readable recording medium may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. The program instructions may include not only machine language codes produced by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc.

[0348] While some aspects of the present disclosure have been described in the context of a device, they may also represent a description of a corresponding method, wherein a block or device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of a method may also be described as a corresponding block or item or a feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware device, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, at least one or more of the most important method steps may be performed by such a device.

[0349] In embodiments, a programmable logic device (e.g., a field-programmable gate array) may be used to perform some or all of the functions of the methods described herein. In embodiments, the field-programmable gate array may operate in conjunction with a microprocessor to perform one of the methods described herein. In general, the methods are preferably performed by some hardware device.

[0350] Although the present disclosure has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and changes may be made to the present disclosure without departing from the spirit and scope of the present disclosure as set forth in the claims below.

Claims

1. As a terminal method, A step of receiving service from the TRP (transmission and reception point) of the first base station; A step of receiving SSBs (synchronization signal blocks) from TRPs controlled by a second base station; A step of transmitting a first measurement report for the above SSBs to the first base station; A step of receiving information about a beam identifier for at least one candidate TRP selected from among the TRPs based on the first measurement report from the first base station; A step of receiving information about resources allocated to transmit a CSI-RS (channel state information-reference signal) to at least one candidate TRP from the first base station; A step of receiving the CSI-RS transmitted using a beam having the beam identifier from at least one candidate TRP through the resource; A step of transmitting a second measurement report for the CSI-RS to the first base station; A step of receiving information about a target TRP selected from the at least one candidate TRP based on the second measurement report from the first base station; and Comprising a step of switching cells to the target TRP, Terminal method.

2. In claim 1, The at least one candidate TRP is a TRP located at the boundary of the first base station among the TRPs, Terminal method.

3. In claim 1, A step of receiving a terminal capability report request from the first base station; and Further comprising the step of transmitting a terminal capability report to the first base station, Terminal method.

4. In claim 3, The terminal capability report includes at least one of the terminal's RF (radio frequency) capability, physical layer control capability, medium access control capability, radio link control capability, PDCP (packet data convergence protocol) capability, DC (dual connectivity) capability, CA (carrier aggregation) capability, NSA / SA (non-standalone / standalone) operation capability, NR bandwidth class, transmission class capability, LCS (location services) capability, reduced capability, or VoNR (voice over new radio) capability. Terminal method.

5. In claim 1, performing a SSB-based downlink synchronization process with at least one candidate TRP; and Further comprising a step of performing an uplink TA acquisition synchronization process based on at least one candidate TRP and a physical downlink control channel (PDCCH) order, Through the above PDCCH order-based uplink TA acquisition synchronization process, it is determined which TRP among the TRPs the at least one candidate TRP is. Terminal method.

6. In claim 5, The step of performing the above at least one candidate TRP and PDCCH order-based uplink TA acquisition synchronization process is: A step of receiving a PDCCH order indicating connection with at least one candidate TRP from the first base station; A step of transmitting a RA (random access) preamble to the at least one candidate TRP using a second beam in a second beam direction having a QCL (quasi-colocation) relationship with a first beam direction of the first beam of the beam identifier according to the PDCCH order; and A step of receiving a TA value from the second base station via the first base station, Terminal method.

7. In claim 1, A step of receiving mapping information of the TRPs and SSB groups from the first base station; A step of checking the SSB indexes of the above SSBs; Further comprising a step of determining a TRP mapped to each of the confirmed SSB indices based on the above mapping information, The first measurement information includes information about the mapped TRP for each of the SSBs. Terminal method.

8. As a method of the first base station, A step of providing a service to a terminal through a transmission and reception point (TRP); A step of receiving a first measurement report from the terminal for synchronization signal blocks (SSBs) transmitted from transmission and reception points (TRPs) controlled by the second base station; A step of selecting at least one candidate TRP from the TRPs based on the first measurement report; A step of transmitting information about a beam identifier of at least one candidate TRP to the terminal; A step of requesting the second base station to transmit a CSI-RS (channel state information-reference signal) in at least one TRP of the at least one candidate TRP using a second beam in a second beam direction having a QCL (quasi-colocation) relationship with the first beam direction of the first beam of the beam identifier; A step of receiving information about resources allocated to transmit the CSI-RS in the at least one TRP from the second base station; A step of transmitting information about the above resource to the terminal; A step of receiving a second measurement report for the CSI-RS transmitted from the at least one TRP from the terminal; A step of selecting a target TRP from the at least one TRP based on the second measurement report; and Comprising a step of performing the target TRP and cell switching operation, Method of the first base station.

9. In claim 8, wherein said at least one TRP is a TRP located at the boundary of said first base station, Method of the first base station.

10. In claim 8, A step of transmitting a physical downlink control channel (PDCCH) order to the terminal, the PDCCH order instructing the terminal to perform uplink synchronization for at least one candidate TRP; A step of receiving information about the signal quality of a RA (random access) preamble received from the terminal in the at least one candidate TRP from the second base station; and Further comprising the step of selecting the at least one TRP from the at least one candidate TRP based on the signal quality. Method of the first base station.

11. In claim 8, Further comprising a step of transmitting mapping information of the above TRPs and SSB groups to the terminal, The above first measurement information includes information about the signal quality of each of the SSBs and the TRP mapped to each of the SSBs, Selecting at least one TRP from the at least one candidate TRP based on information about the signal quality of each of the SSBs and the TRP mapped to each of the SSBs. Method of the first base station.

12. As a terminal, Contains at least one processor, At least one processor of the terminal, Receive service from the TRP (transmission and reception point) of the first base station; Receives SSBs (synchronization signal blocks) from TRPs controlled by the second base station; Transmitting a first measurement report for the above SSBs to the first base station; Receive information about a beam identifier for at least one candidate TRP selected from among the TRPs based on the first measurement report from the first base station; Receive information about resources allocated to transmit a CSI-RS (channel state information-reference signal) to at least one candidate TRP from the first base station; Receive the CSI-RS transmitted using a beam having the beam identifier from at least one candidate TRP through the resource; Transmitting a second measurement report for the CSI-RS to the first base station; Receive information about a target TRP selected from the at least one candidate TRP based on the second measurement report from the first base station; and causing the cell to switch to the above target TRP, Terminal.

13. In claim 12, The at least one candidate TRP is a TRP located at the boundary of the first base station among the TRPs, Terminal.

14. In claim 12, At least one processor of the terminal, Performing at least one candidate TRP and SSB-based downlink synchronization process; and Further causing at least one candidate TRP and PDCCH (physical downlink control channel) order-based uplink TA acquisition synchronization process to be performed, Through the above PDCCH order-based uplink TA acquisition synchronization process, it is determined which TRP among the TRPs the at least one candidate TRP is. Terminal.

15. In claim 14, In the step of performing the above at least one candidate TRP and PDCCH order-based uplink TA acquisition synchronization process, the at least one processor is configured such that the terminal, Receive a PDCCH order indicating connection with at least one candidate TRP from the first base station; Transmitting a random access (RA) preamble to the at least one candidate TRP using a second beam in a second beam direction having a quasi-colocation (QCL) relationship with a first beam direction of the first beam of the beam identifier according to the PDCCH order; and Causing the TA value to be received from the second base station via the first base station, Terminal.

16. In claim 12, At least one processor of the terminal, Receive mapping information of the above TRPs and SSB groups from the first base station; Check the SSB indexes of the above SSBs; Further causing a TRP to be mapped to each of the above-identified SSB indices based on the above mapping information to be determined, The first measurement information includes information about the mapped TRP for each of the SSBs. Terminal.

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