Method and terminal for triggering beam failure recovery procedure in multi-beam system

Abstract

Provided are a method and a terminal for triggering a beamfailurerecovery (BFR) procedure of a multi-beam system.SOLUTION: The method includes communicating with a first 1RRH connected to a first 1BBU using one or more beams, performing a BFR procedure for maintaining a radio link instead of performing a handover procedure when the UE moves from coverage of the first 1RRH to coverage of a second 2RRH connected to the first 1BBU, and communicating with the first 2RRH.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present description relates to a method and terminal for triggering a BFR procedure in a multi-beam system. [Background technology]

[0002] The 3GPP (registered trademark) NR work item (WI) is for designing an NR system that meets 5G requirements. 3GPP NR adopts multi-beam operation based on hybrid beamforming to improve system performance. To enable multi-beam operation, the RA procedure, including the physical random access channel (PRACH) and message design, must be considered. Summary of the Invention [Problem to be solved by the invention]

[0003] One embodiment provides a method for a terminal in a multiple beam system to trigger a BFR procedure.

[0004] Another embodiment provides a terminal of a multi-beam system that triggers a BFR procedure.

[0005] Yet another embodiment provides a method for a base station in a multiple beam system to trigger a BFR procedure. [Means for solving the problem]

[0006] According to one embodiment, a method for a terminal in a multi-beam system to trigger a beam failure recovery (BFR) procedure is provided, the BFR procedure triggering method including the steps of: monitoring a radio link with a base station to detect a beam failure; identifying a candidate transmission beam of the base station; and, when the candidate transmission beam of the base station is identified, transmitting a BFR request to the base station.

[0007] In the BFR procedure trigger method, the step of monitoring the radio link with the base station to detect beam failure may include the step of comparing the magnitude of the received power of a reference signal received from the base station with a predetermined threshold, and determining that the beam failure has occurred if the magnitude of the received power of the reference signal is always less than the predetermined threshold for a predetermined time.

[0008] In the BFR procedure trigger method, the reference signal may include at least one reference signal or channel state information-reference signal (CSI-RS) in a synchronization signal block including a synchronization signal and a demodulation reference signal of a physical broadcast channel.

[0009] In the BFR procedure trigger method, the step of identifying a candidate transmission beam of the base station may include identifying the candidate transmission beam based on a reference signal received power (RSRP) of a channel state information-reference signal (CSI-RS) received from the base station, and the step of transmitting a BFR request to the base station when the candidate transmission beam of the base station is identified may include transmitting the BFR request to the base station over a physical random access channel (PRACH) associated with the CSI-RS when the candidate transmission beam is identified based on the RSRP of the CSI-RS.

[0010] The BFR procedure trigger method may further include a step of identifying the candidate transmission beam based on a reference signal received power (RSRP) of a reference signal in a synchronization signal block (SSB) received from the base station when a candidate transmission beam of the base station is not identified by the RSRP of the CSI-RS, and a step of transmitting a BFR request to the base station when the candidate transmission beam is identified based on the RSRP of the reference signal in the SSB.

[0011] In the BFR procedure trigger method, when the candidate transmission beam is identified based on the RSRP of the reference signal in the SSB, the step of sending a BFR request to the base station may include the step of sending the BFR request via a physical random access channel (PRACH) associated with the SSB in which the candidate transmission beam is identified.

[0012] The BFR procedure triggering method may further include a step of triggering the RLF procedure after a timer set to measure radio link failure (RLF) out of synchronization (OOS) for a radio link with the base station expires if a candidate transmission beam of the base station is not identified by the RSRP of the CSI-RS and the RSRP of the reference signal in the SSB.

[0013] In the BFR procedure trigger method, the BFR request includes the ID of the terminal and information about the candidate transmission beam, and the ID of the terminal may correspond to an index of the sequence used when the BFR request is generated.

[0014] The BFR procedure trigger method may further include, after transmitting the BFR request, retransmitting the BFR request based on a preconfigured maximum number of retransmissions.

[0015] According to another embodiment, a terminal for a multi-beam system that triggers a beam failure recovery (BFR) procedure is provided, the terminal including a processor, a memory, and a wireless communication unit, the processor executing a program stored in the memory to perform the steps of monitoring a wireless link with a base station to detect beam failure, identifying candidate transmission beams of the base station, and, when the candidate transmission beams of the base station are identified, transmitting a BFR request to the base station using the wireless communication unit.

[0016] In the terminal, when the processor performs the step of monitoring the radio link with the base station and detecting beam failure, it can perform the step of comparing the magnitude of the received power of a reference signal received from the base station with a predetermined threshold, and if the magnitude of the received power of the reference signal is always less than the predetermined threshold for a predetermined time, the step of determining that the beam failure has occurred.

[0017] In the terminal, the reference signal may include at least one reference signal or channel state information-reference signal (CSI-RS) in a synchronization signal block including a synchronization signal and a demodulation reference signal of a physical broadcast channel.

[0018] In the terminal, when the processor performs the step of identifying a candidate transmission beam of the base station, it may perform the step of identifying the candidate transmission beam based on a reference signal received power (RSRP) of a channel state information-reference signal (CSI-RS) received from the base station, and when the processor performs the step of transmitting a BFR request to the base station when the candidate transmission beam of the base station is identified, it may perform the step of transmitting the BFR request to the base station through a physical random access channel (PRACH) associated with the CSI-RS when the candidate transmission beam is identified based on the RSRP of the CSI-RS.

[0019] In the terminal, the processor executes the program to further perform the steps of: identifying the candidate transmission beam of the base station based on the reference signal received power (RSRP) of a reference signal in a synchronization signal block (SSB) received from the base station when the candidate transmission beam of the base station is not identified by the RSRP of the CSI-RS; and transmitting a BFR request to the base station using the wireless communication unit when the candidate transmission beam is identified based on the RSRP of the reference signal in the SSB.

[0020] In the terminal, when the processor performs a step of transmitting a BFR request to the base station using the wireless communication unit when the candidate transmission beam is identified based on the RSRP of the reference signal in the SSB, the processor may perform a step of transmitting the BFR request using the wireless communication unit through a physical random access channel (PRACH) associated with the SSB in which the candidate transmission beam is identified.

[0021] In the terminal, the processor executes the program to further perform a step of triggering the RLF procedure after a timer set to measure radio link failure (RLF) out of synchronization (OOS) for a radio link with the base station expires if a candidate transmission beam of the base station is not identified by the RSRP of the CSI-RS and the RSRP of the reference signal in the SSB.

[0022] The BFR request includes the ID of the terminal and information about the candidate transmission beam, and the ID of the terminal may correspond to an index of the sequence used when the BFR request is generated.

[0023] The BFR method may further include, after transmitting the BFR request, retransmitting the BFR request based on a preconfigured maximum number of retransmissions.

[0024] According to yet another embodiment, a method for a base station in a multi-beam system to trigger a beam failure recovery (BFR) procedure is provided, the BFR method including the steps of receiving a BFR request transmitted by a terminal after the terminal detects a beam failure, and transmitting a BFR request response to the terminal based on information about candidate transmission beams reported through the BFR request.

[0025] In the BFR procedure trigger method, the step of sending the BFR request may include, when the information regarding the candidate transmission beams includes information regarding a plurality of candidate transmission beams and beam quality information of the plurality of candidate transmission beams, selecting one candidate transmission beam from the information regarding the plurality of candidate transmission beams based on the beam quality information, and transmitting the BFR request response to the terminal using the wireless communication unit through the selected candidate transmission beam. [Effects of the Invention]

[0026] A method for triggering a BFR procedure suitable for a 3GPP NR multiple beam system is provided, and a method for triggering a BFR procedure suitable for a future fifth generation communication system including a high speed train (HST) scenario is also provided. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flowchart illustrating a BFR procedure based on CSI-RS according to one embodiment. [Figure 2] 1 is a flowchart illustrating a BFR procedure based on CSI-RS and SSB according to one embodiment. [Figure 3] 1 is a conceptual diagram illustrating a multi-beam operation of a high-speed train communication system according to an embodiment. [Figure 4] FIG. 2 is a conceptual diagram illustrating the timing difference between predicted and detected SSB timing from a TE perspective according to one embodiment. [Figure 5] 3 is a conceptual diagram illustrating SSB timing of a serving BBU and SSB timing of a target BBU according to an embodiment. [Figure 6] 1 is a block diagram illustrating a wireless communication system according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028]

[0033] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not relevant to the description are omitted, and similar parts are designated by similar reference numerals throughout the specification.

[0029] Throughout the specification, terminal equipment (TE) may refer to a terminal, mobile station (MS), mobile terminal (MT), advanced mobile station (AMS), high reliability mobile station (HR-MS), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), user equipment (UE), machine type communication device (MTC device), etc., and may include all or some of the functionality of an MT, MS, AMS, HR-MS, SS, PSS, AT, UE, etc.

[0030] In addition, the term base station (BS) can be divided into advanced base station (ABS), high reliability base station (HR-BS), node B, evolved node B (eNodeB), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR)-BS, relay station (RS) playing the role of a base station, relay node (RN) playing the role of a base station, advanced relay station (ARS) playing the role of a base station, high reliability relay station (HR-RS) playing the role of a base station, small base station (femto BS), home node B (HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station (macro BS), micro base station (micro BS), etc. It may refer to a base station, such as an ABS, Node B, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc., and may include all or some of the functions of an ABS, Node B, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc.

[0031] The terminology used in this description follows the terminology defined in 3GPP NR (New Radio) and the terminology described in NR-related reports and standards published by 3GPP. Single-beam operation can be considered a special case of multiple-beam operation, and this description can also be applied to single-beam systems. This description will be explained with an emphasis on multiple-beam operation using a 3GPP NR system as an example.

[0032] Unlike the conventional PRACH use cases for handover when the UE is in radio resource control (RRC) CONNECTED mode and for initial access (IA) or paging when the UE is in RRC IDLE mode in 3GPP NR PRACH, a new use case for transmitting a beam failure recovery (BFR) request is adopted for the NR-PRACH. The new channel for transmitting the BFR request is a contention-free based channel based on the PRACH, whose resources are orthogonal to the different PRACH transmission resources. The BFR request can be transmitted by a UE in RRC CONNECTED mode when a beam failure is detected.

[0033] FIG. 1 is a flowchart showing a BFR procedure based on CSI-RS according to one embodiment, and FIG. 2 is a flowchart showing a BFR procedure based on CSI-RS and SSB according to one embodiment.

[0034] The BFR procedure according to the described embodiment includes beam failure detection and BFR trigger conditions, and the illustrated BFR procedure includes candidate transmission beam identification at the base station, BFR request transmission and retransmission, and BFR request response monitoring by the UE.

[0035] The beam failure detection and BFR trigger conditions are described below with reference to Figures 1 and 2.

[0036] Referring to FIG. 1, for beam failure detection, the UE monitors the radio link to determine whether the BFR trigger condition is met (S110). The UE can use a reference signal (RS) to monitor the radio link. The RS for beam failure detection may be all or some of the RSs in a synchronization signal block (SSB), which includes a synchronization signal (SS) and a demodulation reference signal (DMRS) of a physical broadcast channel (PBCH). The RS for beam failure detection may also be a channel state information RS (CSI-RS) configured in the UE for beam management purposes. In this description, the RS for beam failure detection may be an RS in an SSB, a CSI-RS, or both an RS in an SSB and a CSI-RS. Two conditions for triggering a BFR procedure are described below.

[0037] Condition 1: The UE determines whether the state in which the magnitude of the received power of the RS for beam failure detection measured by the UE is less than a predetermined threshold persists for a predetermined time (S120).

[0038] Condition 1 is equivalent to the case where some performance metric is related to the calculated error rate of some specific channel. For example, the PBCH error rate can be simply estimated based on the received power of the PBCH-DMRS. If the UE determines that the estimated PBCH error rate is unacceptable, the UE can determine that Condition 1 is met. Similar estimations or calculations for equivalent performance metrics of other physical channels can also be applied to Condition 1. In this description, the received power for the RS is used as an example for explanation.

[0039] Condition 2: The UE determines whether the candidate transmission beams of the base station are identified (S130).

[0040] Condition 1 is for the UE to detect beam failure, and Condition 2 is a necessary condition for the UE to trigger a BFR procedure. That is, beam failure is detected when Condition 1 is met, but the UE can transmit a BFR request to the base station to request triggering of the BFR procedure only when Conditions 1 and 2 are simultaneously met (S140). Conversely, if beam failure is detected but a candidate transmission beam is not identified by the UE, the BFR procedure is not triggered. In this case, out of synchronization (OOS) will be detected by the UE. The UE will then continue to monitor the radio link quality and can trigger radio link failure (RLF) if the RLF trigger condition is met. Once the two conditions for triggering the BFR procedure are met, the UE can perform a BFR procedure to restore the radio link even if timer N310 or T310 is still running. This operation causes the UE to stop timers related to RLF, thereby reducing UE interruption time due to radio link problems.

[0041] The UE can identify whether the base station has a candidate transmission beam in the following manner: In a multi-beam system such as NR, the SSB is transmitted from the base station through all transmission beam directions, and the CSI-RS is a UE-specific RS that can be transmitted only within a subset of the transmission beams. Therefore, in this description, the UE-specific CSI-RS configured at the network stage can be used as the primary RS for candidate transmission beam identification, and the RSs in the SSB can be used as auxiliary (supplementary) RSs for candidate transmission beam identification.

[0042] Referring to FIG. 2, a UE monitors a radio link (S210). If a beam failure is detected (condition 1 is met) (S220), the UE can first identify a candidate transmission beam of the base station by monitoring the reference signal received power (RSRP) of the CSI-RS (candidate beam identification) (S230). For example, the UE can complete candidate beam identification if the RSRP of the CSI-RS received through a specific transmission beam is greater than a predetermined threshold. If a candidate transmission beam is detected by the UE based on the CSI-RS, the UE sends a BFR request to the base station to trigger a BFR procedure (S250). However, the UE may not be able to find a candidate transmission beam based on the CSI-RS. For example, a configured subset of transmission beams with the CSI-RS may be blocked. In this case, the UE has two options:

[0043] Option 1: The UE can continue to monitor the quality of the radio link without triggering the BFR procedure, since BFR trigger condition 1 is not met.

[0044] Option 2: The UE can attempt to detect candidate transmission beams based on RSRP measurements of the RSs in the SSB instead of the CSI-RS, since the SSB is transmitted in all transmission beam directions.

[0045] The UE's behavior in Option 1 can trigger RLF, while the UE's behavior in Option 2 can trigger BFR procedures. This is because even if all beam directions in the subset of transmit beams with configured CSI-RS are blocked, some other beam directions may still be valid for the UE. If a candidate transmit beam is not detected based on CSI-RS, the UE may attempt to detect the candidate transmit beam again based on SSB (S240). Therefore, according to Figure 2, the probability of RLF being triggered may be reduced compared to Figure 1.

[0046] According to one embodiment, a BFR request may be retransmitted after being transmitted. The BFR request may include information for identifying the UE (e.g., UE ID) and information related to the base station's candidate transmission beams. The BFR request may be transmitted on a channel similar to a physical random access channel (PRACH), and the preamble format on the conventional PRACH may be reused as the BFR request format. For simplicity, the channel for transmitting the BFR request is referred to as a new PRACH. The conventional preamble format and preamble sequence may be reused for the BFR request. To convey UE ID information, the index of the sequence used to generate the BFR request may be used (i.e., the index of the sequence used to generate the BFR request corresponds to the UE ID). That is, the base station can identify the UE based on the index of the sequence used when the BFR request is generated. There are two options for the information on the candidate transmission beams:

[0047] Option 1: The UE can report whether there are candidate transmission beams through a BFR request.

[0048] Option 2: The UE can report one or more candidate transmission beams to the base station through a BFR request.

[0049] In option 1, one-bit information indicating whether a candidate transmission beam exists can be conveyed by partitioning the new PRACH resources, including frequency / time / sequence resources. For example, different frequency / time groups of the new PRACH or different groups of sequences for the BFR request can be used as information indicating whether a candidate transmission beam exists. In option 2, the association between the SSB and the new PRACH resources can be used to convey the candidate transmission beam information. For example, one or more SSBs can be associated with a subset of the new PRACH resources, including frequency / time / sequence resources. Based on the association, the UE can select a new PRACH resource (or a subset of the new PRACH resources) corresponding to the SSB detected as a candidate transmission beam and transmit a BFR request using the selected new PRACH resource. As a result, the base station can recognize the candidate transmission beam reported by the UE from the new PRACH resource on which the UE's BFR request is transmitted. A similar scheme can also be applied when the UE reports candidate transmission beam information based on the association between the CSI-RS and the new PRACH resource. In this case, the SSB can be quasi-colocated with the CSI-RS. To reduce interruption time due to beam failure, the UE can transmit multiple BFR requests on different UE transmission beams before receiving a response to the BFR request from the base station. When a BFR request is retransmitted, the network can pre-configure the maximum number of retransmissions allowed for a specific UE.

[0050] Meanwhile, the BFR request response monitored by the UE is as follows:

[0051] 1. When the UE reports to the base station that there is a candidate transmission beam of the base station, the base station transmits a BFR request response to the UE through all beam directions (or through all beam directions configured for the UE) or through Tx beam sweeping to ensure that the UE receives the BFR request response.

[0052] 2. When the UE reports the correct candidate transmission beam to the base station, the base station transmits a BFR request response to the UE through the candidate transmission beam reported by the UE. For example, the UE can report one best candidate transmission beam to the base station in the BFR request, and the base station can transmit a BFR request response to the UE through the transmission beam reported by the UE.

[0053] 3. When the UE reports multiple candidate transmission beams to the base station, the base station transmits a BFR request response to the UE through beam sweeping of the reported beams. Alternatively, the base station can use the best beam among the candidate transmission beams reported by the UE to transmit the BFR request response to the UE. In this case, the base station may further require beam quality information of the multiple candidate transmission beams to select the best beam.

[0054] FIG. 3 is a conceptual diagram showing a multi-beam operation of a high-speed train communication system according to an embodiment.

[0055] Referring to FIG. 3, a plurality of remote radio heads (RRH) (1101 to 1102) are installed along the railway line. m ) are arranged, and m RRHs (1101 to 110 m ) is the i-th baseband unit (BBU) 100 iThe train 10 moves along the tracks from left to right on the page, communicating with each remote radio head (RRH) using multiple beams. The train 10 includes onboard terminal equipment (TE) that operates as a mobile relay. The onboard TE can transmit data between the onboard TE and a terrestrial base station (BS) and can be treated as a single UE. The terrestrial BS can include a BBU and multiple remote radio heads connected to the BBU. Directional antennas can also be used in the TE and the remote radio heads. n beams can be generated in each remote radio head through beamforming using a directional antenna such as a panel antenna. In this description, the beam widths can become increasingly wider as the beam index increases. For example, the beam width of beam 1 is narrower than the beam width of beam 2, and the beam width of the nth beam is the widest. Different beam indices are assigned beams with different widths to reduce the need for frequent beam switching. Also, it is a reasonable allocation to consider that the path loss is lower when the train 10 is moving towards the serving RRH, at which time a wider beamwidth may be more important than a higher beamforming gain.

[0056] In FIG. 3, when a TE attempts to connect to a network by performing initial access, the TE can receive synchronization signal blocks (SSBs) transmitted on the transmit beams (Tx beams) of different remote radio heads (RRHs). At this time, one or more SSBs can be transmitted for each transmit beam of the RRHs. Because all RRHs in FIG. 3 are connected to the same BBU, SSBs within the same SSB period can be assigned to different transmit beams of multiple RRHs. The TE of the train 10 can assume that all RRHs are spatially quasi-colocated (QCL'ed) and that all transmit beams from different RRHs are transmitted from the same location. When the train 10 moves from the coverage area of ​​one RRH connected to the same BBU to the coverage area of ​​another RRH, a BFR procedure can be triggered to maintain the radio link instead of the existing handover procedure. Furthermore, due to the distance between the remote radio heads, the train 10's TE may discover that there is a timing difference between the predicted SSB timing and the actual searched SSB timing, which can be used to estimate the timing advance (TA) when the train 10 moves into the coverage of a new remote radio head.

[0057] FIG. 4 is a conceptual diagram illustrating the timing difference between the predicted SSB timing and the detected SSB timing from the TE perspective in one embodiment, and FIG. 5 is a conceptual diagram illustrating the SSB timing of the serving BBU and the SSB timing of the target BBU in one embodiment.

[0058] Referring to Figure 4, a train 10 travels from RRH 1 to RRH m, all connected to the same BBU. One SSB is transmitted to the TE of the train 10 on the transmit beam of each RRH. Because the train 10 is served by the transmit beam of RRH 1 and then by the transmit beam of RRH 2, there may be a timing difference between SSB n and SSB (n+1). However, because the TE predicts that it will receive SSBs consecutively from each RRH, there is a timing difference between the predicted SSB timing and the detected SSB timing.

[0059] When a train moves from the coverage area of ​​one BBU to the coverage area of ​​the next BBU, a handover procedure is performed without a BFR procedure. As shown in FIG. 3, when a TE is receiving service through transmit beam n of RRH m, the TE performs a handover to the next BBU. In this case, even if BBU i transmits SSBs on all transmit beams of RRH m, the TE can only detect the nth SSB transmitted through beam n of RRH m. If BBU (i+1) is synchronized with BBU i, the TE can detect SSB 1 from BBU (i+1) at the timing shown in FIG. 5. In this case, the timing of SSB 1 of BBU (i+1) does not overlap with the timing of the SSB of the serving BBU i. In other words, the TE can detect the SSB of the serving cell and the SSB of the target cell without interference. Therefore, the handover procedure of the 3GPP LTE system can be applied when the train 10 in FIG. 3 hands over from BBU i to BBU (i+1).

[0060] FIG. 6 is a block diagram illustrating a wireless communication system according to an embodiment.

[0061] Referring to FIG. 6, a wireless communication system according to one embodiment includes a base station 610 and a terminal 620.

[0062] The base station 610 includes a processor 611, a memory 612, and a radio frequency unit (RF unit) 613. The memory 612 is coupled to the processor 611 and can store various information for operating the processor 611 or at least one program executed by the processor 611. The radio unit 613 is coupled to the processor 611 and can transmit and receive radio signals. The processor 611 can implement the functions, processes, or methods proposed in the embodiments of the present disclosure. In this case, the radio interface protocol layer in the wireless communication system according to one embodiment of the present disclosure can be implemented by the processor 611. The operation of the base station 610 according to one embodiment can be implemented by the processor 611.

[0063] The terminal 620 includes a processor 621, a memory 622, and a wireless communication unit 623. The memory 622 is coupled to the processor 621 and can store various information for operating the processor 621 or at least one program executed by the processor 621. The wireless communication unit 623 is coupled to the processor 621 and can transmit and receive wireless signals. The processor 621 can implement functions, steps, or methods proposed in the embodiments of the present disclosure. In this case, the air interface protocol layer in the wireless communication system according to one embodiment of the present disclosure can be implemented by the processor 621. The operation of the terminal 620 according to one embodiment can be implemented by the processor 621.

[0064] In the described embodiments, the memory may be located internal or external to the processor and may be coupled to the processor through various known means. The memory may be any of a variety of forms of volatile or non-volatile storage media, including, for example, read-only memory (ROM) or random access memory (RAM).

[0065] Although the embodiments have been described in detail above, the scope of the invention is not limited to these examples, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the invention.

Claims

1. 1. A method of a terminal, comprising: communicating with a first remote radio head (RRH) connected to a first baseband unit (BBU) using one or more beams; When the terminal moves from the coverage of the first remote radio head to the coverage of a second remote radio head connected to the first beam block unit, performing a beam failure recovery (BFR) procedure to maintain a radio link instead of performing a handover procedure; and communicating with the second remote radio head; A terminal method, including:

2. the first remote control head (RRH) and the second remote control head (RRH) are located at a quasi-coincident position in space; The signals received from the first remote radio head (RRH) and the second remote radio head (RRH) are considered to have been transmitted via the same transmission beam. The method of claim 1.

3. A timing advance (TA) of the second remote radio head is estimated based on a timing difference between a predicted synchronization signal block (SSB) timing and an actual SSB timing. The method of claim 1.

4. Further comprising predicting that the SSBs from the first remote radio head and the second remote radio head are received in sequence; a predicted SSB timing is determined based on the prediction; The method of claim 3.

5. When the terminal moves from the coverage of the second BBU to the coverage of the third BBU, performing a handover procedure instead of a BFR procedure. The method of claim 1.

6. When the second BBU is synchronized with the first BBU, the SSB timing of the second BBU is determined based on the SSB timing of the first BBU. The method of claim 5.

7. A terminal comprising at least one processor, The at least one processor may include: communicating with a first remote radio head (RRH) connected to a first baseband unit (BBU) using one or more beams; When the terminal moves from the coverage of the first remote radio head to the coverage of the second remote radio head connected to the first beam block unit, instead of performing a handover procedure, perform a beam failure recovery (BFR) procedure to maintain a radio link; communicate with the second remote radio head; It is configured as follows: Terminal.

8. the first remote control head (RRH) and the second remote control head (RRH) are located at a quasi-coincident position in space; The signals received from the first remote radio head (RRH) and the second remote radio head (RRH) are considered to have been transmitted via the same transmission beam. The terminal according to claim 7.

9. A timing advance (TA) of the second remote radio head is estimated based on a timing difference between a predicted synchronization signal block (SSB) timing and an actual SSB timing. The terminal according to claim 7.

10. The at least one processor causes the terminal to predict that SSBs from the first remote radio head and the second remote radio head are received consecutively; the predicted SSB timing is determined based on the prediction. The terminal according to claim 9.

11. The at least one processor is further configured to, when the terminal moves from a coverage area of ​​the second BBU to a coverage area of ​​the third BBU, cause the terminal to perform the handover procedure instead of a BFR procedure. The terminal according to claim 7.

12. When the second BBU is synchronized with the first BBU, the SSB timing of the second BBU is determined based on the SSB timing of the first BBU. The terminal according to claim 11.

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