KR20220164408A - Method and apparatus of beam failure recovery in communication system - Google Patents

Abstract

Disclosed is a technology for beam failure recovery in a communication system. An operation of a terminal of the communication system can be provided, comprising: a step of detecting a beam failure of one or more of a plurality of transmission and reception points (TRPs); a step of searching a plurality of candidate beams for the one or more TRPs; a step of transmitting a beam failure recovery request signal to the one or more TRPs by using one of the plurality of candidate beams; and a step of receiving a beam failure recovery response signal which is a response to the beam failure recovery request signal from the one or more TRPs through the candidate beam. Therefore, the rapid beam failure recovery can be conducted.

Description

Beam failure recovery method and apparatus in communication system

The present invention relates to a beam failure recovery technique in a communication system, and more particularly, to a beam failure recovery technique in a communication system for recovering when a radio link related to a beam fails in multiple transmission and reception point (TRP) transmissions. will be.

Along with the development of information and communication technology, various wireless communication technologies may be developed. Representative wireless communication technologies may include long term evolution (LTE) and new radio (NR), which are defined in the 3rd generation partnership project (3GPP) standard. LTE may be one wireless communication technology among 4th generation (4G) wireless communication technologies, and NR may be one wireless communication technology among 5th generation (5G) wireless communication technologies.

For the processing of rapidly increasing wireless data after the commercialization of 4G communication systems (eg, communication systems supporting LTE), the frequency band (eg, frequency bands below 6 GHz) of the 4G communication system as well as the 4G communication system A 5G communication system (eg, a communication system supporting NR) using a frequency band higher than the frequency band of (eg, a frequency band of 6 GHz or higher) may be considered. The 5G communication system may support eMBB (enhanced Mobile BroadBand), URLLC (Ultra-Reliable and Low Latency Communication), and mMTC (massive machine type communication).

On the other hand, the recent NR communication system has been standardized for multiple transmission and reception point (TRP) transmission. To this end, the NR communication system may consider transmission of multiple control channels by multiple TRP transmission systems. Accordingly, the NR communication system may require a provision for a multi-TRP beam failure recovery procedure in addition to the basic beam failure recovery procedure.

An object of the present invention to solve the above problems is to provide a beam failure recovery method and apparatus in a communication system for recovering when a radio link related to any one TRP fails in multiple TRP transmission.

To achieve the above object, a beam failure recovery method in a communication system according to a first embodiment of the present invention is an operating method performed in a terminal of a communication system, and includes at least one TRP among a plurality of transmission and reception points (TRPs). Detecting a beam failure of ; Searching for a plurality of candidate beams for the at least one TRP; Transmitting a beam failure recovery request signal to the at least one TRP using one candidate beam from among the plurality of candidate beams; and receiving a beam failure recovery response signal, which is a response to the beam failure recovery request signal, from the at least one TRP through the one candidate beam.

According to the present application, when a beam failure instance occurs in some TRPs among a plurality of TRPs, the physical entity of the terminal transmits information indicating the TRP in which the beam failure instance occurred to the MAC of the terminal. (medium access control) can be transmitted to entities. In this case, the terminal can accurately detect beam failure for any one TRP among a plurality of TRPs.

In addition, according to the present application, when a beam failure is detected in one TRP in a multiple TRP transmission system, a UE may perform a beam failure recovery procedure through another TRP. Accordingly, the terminal may have flexibility in proceeding with the beam failure recovery procedure, and thus, rapid beam failure recovery may be possible.

1 is a conceptual diagram illustrating a first embodiment of a communication system.
2 is a block diagram showing a first embodiment of a communication node constituting a communication system.
3 is a timing diagram illustrating a first embodiment of a beam failure recovery procedure.
4 is a conceptual diagram illustrating a first embodiment of a multi-TRP transmission system.
5 is a conceptual diagram illustrating a second embodiment of a multi-TRP transmission system.
6 is a flowchart illustrating a first embodiment of a beam failure recovery method in a communication system.
FIG. 7 is a timing diagram illustrating a first embodiment of a TRP specific beam failure detection process of FIG. 6 .
8 is a conceptual diagram illustrating a first embodiment of a multi-TRP transmission system using carrier aggregation.
9 is a timing diagram illustrating a first embodiment of a process of receiving a beam failure recovery request and a beam failure recovery response.
10 is a timing diagram illustrating a first embodiment of a process of receiving a beam failure recovery request and a beam failure recovery response.

Since the present invention can make various changes and have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. The terms and/or include any combination of a plurality of related recited items or any of a plurality of related recited items.

In embodiments of the present application, “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”. Also, in the embodiments of the present application, “one or more of A and B” may mean “one or more of A or B” or “one or more of combinations of one or more of A and B”.

It is understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. It should be. On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

Terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in this application, they should not be interpreted in an ideal or excessively formal meaning. don't

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. In order to facilitate overall understanding in the description of the present invention, the same reference numerals are used for the same components in the drawings, and redundant descriptions of the same components are omitted.

1 is a conceptual diagram illustrating a first embodiment of a communication system.

Referring to FIG. 1, a communication system 100 includes 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 is a communication protocol based on code division multiple access (CDMA), a communication protocol based on wideband CDMA (WCDMA), a communication protocol based on time division multiple access (TDMA), and a frequency division multiple (FDMA) access) based communication protocol, OFDM (orthogonal frequency division multiplexing) based communication protocol, OFDMA (orthogonal frequency division multiple access) based communication protocol, SC (single carrier)-FDMA based communication protocol, NOMA (non-orthogonal multiple access) access)-based communication protocol, space division multiple access (SDMA)-based communication protocol, and the like may be supported. Each of the plurality of communication nodes may have the following structure.

2 is a block diagram showing a first embodiment of a communication node constituting a communication system.

Referring to FIG. 2 , a communication node 200 may include at least one processor 210, a memory 220, and a transceiver 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240, an output interface device 250, a storage device 260, and the like. Each component included in the communication node 200 may be connected by a bus 270 to communicate with each other. However, each component included in the communication node 200 may be connected through an individual interface or an individual bus centered on the processor 210 instead of the common bus 270 . For example, the processor 210 may be connected to at least one of the memory 220, the transmission/reception device 230, the input interface device 240, the output interface device 250, and the storage device 260 through a dedicated interface. .

The processor 210 may execute a program command 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 on which methods according to embodiments of the present invention are performed. Each of the memory 220 and the storage device 260 may include at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may include at least one of a read only memory (ROM) and a random access memory (RAM).

Referring back to FIG. 1, the communication system 100 includes a plurality of base stations (110-1, 110-2, 110-3, 120-1, 120-2), 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 belong to 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 belong 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 belong within the coverage of the third base station 110-3. . The first UE 130-1 may belong within the coverage of the fourth base station 120-1. The sixth UE 130-6 may belong within the coverage of the fifth base station 120-2.

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

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) Each may support cellular communication (eg, long term evolution (LTE), advanced (LTE-A), etc. specified in the 3rd generation partnership project (3GPP) standard). Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may operate in different frequency bands or may operate in the same frequency band. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to each other through ideal backhaul or non-ideal backhaul, and ideal backhaul Alternatively, information can be exchanged with each other through non-ideal backhaul. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to a core network (not shown) through an ideal backhaul or a non-ideal backhaul. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits a signal received from the core network to a corresponding UE 130-1, 130-2, 130-3, and 130. -4, 130-5, 130-6), and the signal received from the corresponding UE (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) to the core network can be sent to

Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may support OFDMA-based downlink transmission, and may support SC-FDMA-based uplink transmission. ) can support transmission. In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits multiple input multiple output (MIMO) (eg, single user (SU)-MIMO, MU (multi user)-MIMO, massive MIMO, etc.), CoMP (coordinated multipoint) transmission, carrier aggregation transmission, transmission in unlicensed band, device to device (D2D) ) communication (or proximity services (ProSe)), etc. Here, each of the plurality of UEs 130-1, 130-2, 130-3, 130-4, 130-5, and 130-6 is a base station Operations corresponding to (110-1, 110-2, 110-3, 120-1, 120-2) supported by base stations 110-1, 110-2, 110-3, 120-1, 120-2 action can be performed.

Meanwhile, in new radio (NR), a base station and a terminal may use beams to communicate with each other. At this time, beam directions of the base station and the terminal may be misaligned due to rotation or movement of the terminal in communication. Also, beams of the base station and the terminal may be blocked due to obstacles. In this situation, the quality of the wireless communication link between the base station and the terminal may rapidly deteriorate. In this case, in particular, the quality of a wireless communication link of a physical data shared channel (PDSCH), which is a data channel, may rapidly deteriorate. In this situation, the base station and the terminal may perform a beam management procedure through a physical downlink control channel (PDCCH), which is a control channel, to reselect a beam of a good wireless communication link. Alternatively, the quality of the wireless communication link in the control channel may be rapidly degraded. In this situation, since the terminal cannot properly receive a control signal, normal communication may be impossible. Such a situation may be defined as a beam failure.

When a beam failure occurs in this way, the communication link between the base station and the terminal may be disconnected. A long term evolution (LTE) communication system may have a procedure for recovering a disconnected communication link. Similarly, the NR communication system may also require a procedure for restoring a disconnected beam link. Accordingly, the NR communication system introduces a mechanism to recover from beam failure or a beam failure recovery procedure for convenience. Accordingly, the NR communication system can recover from beam failure through the introduced beam failure recovery mechanism or beam failure recovery procedure, and can perform normal communication.

3 is a timing diagram illustrating a first embodiment of a beam failure recovery procedure.

Referring to FIG. 3 , in the beam failure recovery procedure, the terminal may perform a beam failure detection (BFD) process (S310) and a new candidate beam identification (NBI) process (S320). And, the terminal may transmit a beam failure recovery request (BFRQ) signal to the base station (S330). Then, the base station may receive a beam failure recovery request signal from the terminal. And, the base station may transmit a beam failure recovery response (BFRR) signal to the terminal in response to this (S340). Accordingly, the terminal may receive a beam failure recovery response signal from the base station. A detailed procedure and method of such a beam failure recovery procedure may vary slightly depending on a beam failure recovery request transmission method.

In this way, in the beam failure detection process of the beam failure recovery procedure, the terminal may periodically check whether beam failure occurs through a reference signal. The UE receives a reference signal (eg, channel state information-reference signal (CSI-RS), demodulation-reference signal (DMRS), phase tracking (PT)-RS, cell-specific reference signal (CRS)) or SS from the base station. A /PBCH (synchronization signal/physical broadcast channel) block may be received, and whether beam failure occurs may be periodically checked based on a reference signal or SS/PBCH block. Also, the terminal may search for a new candidate beam when a beam failure is detected. The new candidate beam identification process may be performed after or before the beam failure detection process. Alternatively, the new candidate beam identification process may be performed together with the beam failure detection process. Thereafter, the terminal may transmit a beam failure recovery request signal to the base station, and may wait for a beam failure recovery response signal from the base station after a predetermined time. Meanwhile, the base station may receive a beam failure recovery request signal from the terminal. And, the base station may transmit a beam failure recovery response signal to the terminal in a beam failure recovery response process. Then, the terminal may receive a beam failure response signal from the base station.

The terminal may transmit a beam failure recovery request signal to the base station using the candidate beam (eg, the searched beam) identified in the new candidate beam identification process, and the beam failure through the candidate beam identified in the new candidate beam identification process. A beam failure recovery response signal, which is a response to the recovery request signal, may be received from the base station. In addition, the candidate beam identified in the process of identifying a new candidate beam may be used for transmission and reception of a control channel and/or a data channel until an optimal beam is set. In this way, upon receiving the beam failure recovery response signal from the base station, the terminal may receive a control channel or a data channel as a previously found candidate beam. In this way, if the terminal succeeds in receiving the beam failure recovery response signal from the base station, it may be recovered from the beam failure state. Accordingly, the terminal can newly configure a beam for receiving control information or data later.

On the other hand, the recent NR communication system has been standardized for multiple transmission and reception point (TRP) transmission. To this end, the NR communication system may consider transmission of multiple control channels by multiple TRP transmission systems. Accordingly, the NR communication system may require a provision for a multi-TRP beam failure recovery procedure in addition to the basic beam failure recovery procedure.

4 is a conceptual diagram illustrating a first embodiment of a multi-TRP transmission system.

Referring to FIG. 4, in a multiple TRP transmission system, TRP 1 and TRP 2 may be connected through an ideal backhaul, and a base station may control TRP 1 and TRP 2. TRP 1 may transmit one downlink control information (DCI) to the UE through PDCCH 1 to schedule PDSCH 1 to be transmitted from TRP 1 to the UE and PDSCH 2 to be transmitted from TRP 2 to the UE. As such, in a multiple TRP transmission system, TRP 1 may schedule two PDSCHs using one DCI.

5 is a conceptual diagram illustrating a second embodiment of a multi-TRP transmission system.

Referring to FIG. 5, in a multiple TRP transmission system, TRP 1 and TRP 2 may be connected by non-ideal backhaul or ideal backhaul, and the base station may control TRP 1 and TRP 2. can TRP 1 may schedule PDSCH 1 to be transmitted from TRP 1 to the UE by transmitting DCI 1 through PDCCH 1 to the UE. In addition, TRP 2 may schedule PDSCH 2 to be transmitted by transmitting DCI 2 through PDCCH 2 to the terminal. As such, in a multi-TRP transmission system, TRP 1 may schedule PDSCH 1 using DCI 1. And, TRP 2 may schedule PDSCH 2 using DCI 2. Here, the multi-TRP transmission system may involve dual connectivity and carrier aggregation operations.

Meanwhile, in the basic beam failure recovery procedure, the terminal may define a beam failure when all beam links in a cell are disconnected, and may perform a beam failure recovery procedure accordingly. However, the multiple TRP beam failure recovery procedure proposed in this application may define a TRP-specific beam failure recovery procedure (or a beam failure recovery procedure for each TRP) for more advanced performance. That is, when beam links of some TRPs in a cell are disconnected, in the basic beam failure recovery procedure, the UE may not perform any recovery procedure because it is not defined as a beam failure. However, in the multiple TRP beam failure recovery procedure proposed in this application, the terminal may define a TRP specific beam failure (or a beam failure for each TRP) in this case. And, the terminal may immediately perform a beam failure recovery procedure for the disconnected TRP beam link.

6 is a flowchart illustrating a first embodiment of a beam failure recovery method in a communication system.

Referring to FIG. 6, the beam failure recovery method in the communication system includes a TRP-specific beam failure detection (or beam failure detection for each TRP) process (S610), a TRP-specific new candidate beam identification (or TRP-specific new candidate beam identification) process (S620). ), TRP specific beam failure recovery request (or beam failure recovery request per TRP) process (S630), and TRP specific beam failure recovery response reception (or beam failure recovery response per TRP reception) process (S640). A beam failure recovery method in such a communication system may be as follows.

(1) TRP specific beam failure detection process

In a general beam failure detection process, the terminal may define a reference signal (RS) to be used to detect beam failure, a quality to be measured, and a determination condition for determining beam failure. Here, the reference signal for beam failure detection may be defined as a beam failure detection RS (BFD-RS) for beam failure detection. One or more reference signals among CSI-RS, DM-RS, PT-RS, and CRS may be used as BFD-RS. Alternatively, the SS/PBCH block may be used as BFD-RS.

When the CSI-RS is used as the BFD-RS, the base station may transmit a radio resource control (RRC) message including information indicating that the CSI-RS resource(s) is used for the BFD-RS to the terminal. The terminal may receive the RRC message from the base station, and based on the information included in the RRC message, it may be determined that the CSI-RS resource(s) configured by the base station is used for BFD-RS. In this case, the base station uses the same beam as the beam used for transmission of the control channel (eg, DM-RS for the control channel) in the CSI-RS resource(s) used for the BFD-RS. RS can be transmitted. The terminal receives the CSI-RS in the CSI-RS resource(s) used for the BFD-RS using the same beam as the beam used for reception of the control channel (eg, DM-RS for the control channel) For this, monitoring operations can be performed.

Here, the CSI-RS resource(s) may have a spatial quasi co-location (QCL) relationship with the DM-RS for the control channel. The base station may transmit downlink control information (DCI) including a transmission configuration indication (TCI) indicating information on CSI-RS resource(s) having a spatial QCL relationship with the DM-RS for a control channel to the terminal. The UE may receive the DCI from the base station, and based on the TCI included in the DCI, it may check the CSI-RS resource(s) having a spatial QCL relationship with the DM-RS for the control channel. That is, the CSI-RS resource(s) having a spatial QCL relationship with the DM-RS for the control channel may be configured through one or more of the RRC message and DCI. If the RRC message indicating the CSI-RS resource(s) having a spatial QCL relationship with the DM-RS for the control channel is not received, the UE receives the CSI-RS or SS/PBCH block indicated by the TCI included in the DCI. can be used as BFD-RS.

As such, the base station may explicitly set the CSI-RS resource (s) to the terminal as a BFD-RS set through an RRC message. Here, the CSI-RS resource(s) configured from the base station may use the same beam as the beam used for the control channel to meet the purpose of detecting a beam failure. If the UE has not explicitly configured the BFD-RS set from the base station, the CSI-RS resources having the same index as the RS index indicated by the TCI state of the CORESET (control resource set) used for monitoring the PDCCH are implicitly It can be regarded as a BFD-RS set. Here, if there are two RS indexes in the TCI state, the QCL type among them may refer to the RS index corresponding to the type D.

Meanwhile, the terminal may measure the radio link quality of the control channel using BFD-RS (eg, a CSI-RS or SS/PBCH block set to BFD-RS). The radio link quality may be a hypothetical block error rate (BLER). For example, when the virtual BLER measured based on the BFD-RS is greater than the preset first threshold value (Q _{out_LR} ), the terminal may determine that the radio link of the corresponding beam is disconnected. The first threshold may reuse an out-of synchronization threshold used in radio link monitoring (RLM). As for the control channel, beams can be set for each current CORESET, and if a plurality of CORESETs are set, the control channel can be transmitted with multiple beams. In this case of supporting multiple beams, the terminal may declare beam failure when radio link qualities of all beams are worse than the first threshold.

However, when a beam failure occurs, the terminal may have to go through a complicated recovery procedure. Accordingly, since the beam link may become bad for a while and then become good again, it may be inefficient for the terminal to declare a beam failure with one measurement. Therefore, similar to radio link failure in radio link management, the terminal may declare beam failure by measuring and determining a beam failure several times in succession. One beam failure determination made by the terminal may be referred to as a beam failure instance. That is, when the BFD-RS measurement result is greater than the first threshold, the UE may determine that one beam failure instance has occurred. The occurrence of a beam failure instance may be determined in a physical layer (eg, a physical layer entity performing a physical layer function) belonging to a terminal. A medium access control (MAC) layer (eg, a MAC entity performing a MAC function) may determine that a beam failure has occurred when a beam failure instance occurs more than a preset number of times.

As such, the physical layer of the terminal can recognize the beam failure instance through measurement so that the upper layer can detect the beam failure, and information related to the beam failure instance (eg, information indicating that a beam failure instance has occurred, radio Link quality measurement result, beam index) may be reported to the MAC layer. Information related to a beam failure instance may be referred to as “instance information”. Since beam-related procedures are usually defined as L1 (layer1)/L2 (layer2) processes, the upper layer may mean the MAC layer as such. In this case, the physical layer of the terminal may periodically report whether or not the beam failure instance is recognized to the upper layer. Of course, the physical layer of the terminal may report to a higher layer only when a beam failure instance occurs, and may not report to a higher layer otherwise. In this case, the reporting period may be a larger value among the shortest transmission period among transmission periods of BFD-RSs in the BFD-RS set and 2 msec.

The MAC layer may have a timer and counter to determine the occurrence of a beam failure. A timer may be used to reset a counter, and the counter may be used to count the number of consecutive beam failure instances. When the timer expires, the counter may be reset. In this case, the counter may be set to '0'. The MAC layer may reset the timer and increment the counter whenever a report of a beam failure instance is received from the physical layer. When the timer is reset, the timer may be set to an initial value. The MAC layer may determine that beam failure has occurred when the increased counter reaches a preset value. If the upper layer of the terminal may not receive a report on the beam failure instance during a certain period. At this time, the upper layer of the terminal may reset the counter when the timer expires. The base station may set values of a counter and a timer necessary for declaring beam failure to the terminal in an RRC message.

Meanwhile, in a TRP-specific beam failure detection process, the base station may configure BFD-RS sets as many as the number of TRPs transmitting PDCCHs in order to enable the UE to detect TRP-specific beam failure. In addition, the base station may set a timer and a counter corresponding to each TRP in the MAC layer of the terminal through an RRC message. In other words, the base station may configure a BFD-RS set for each TRP in the MAC layer of the terminal. In addition, the base station can independently perform the above-described beam failure detection process for one BFD-RS set for each BFD-RS set to detect beam failure for each TRP.

For example, in a TRP-specific beam failure detection operation, the base station may configure a first BFD-RS set for TRP 1 and a second BFD-RS set for TRP 2 in the UE. Here, the index for distinguishing the first BFD-RS set may be BFD-RS set index 1, and the index for distinguishing the second BFD-RS set may be BFD-RS set index 2. In this TRP-specific beam failure detection process, the physical layer of the UE may report the beam failure instance for each BFD-RS set to the MAC layer, and at this time, the BFD-RS set index may be reported together. This may be necessary to identify in which TRP the beam failure instance occurred because the MAC layer of the UE may operate a timer and counter for each TRP. At this time, the MAC layer of the terminal may perform identification of the TRP using the BFD-RS set index.

FIG. 7 is a timing diagram illustrating a first embodiment of a TRP specific beam failure detection process of FIG. 6 .

Referring to FIG. 7 , the control channel may be transmitted to the terminal using beam #1 in TRP 1 and may be transmitted to the terminal using beam #2 in TRP 2 . In this case, TRP 1 may transmit BFD-RS #1 included in the first BFD-RS set to the UE using beam #1, and TRP 2 may transmit BFD-RS #1 included in the second BFD-RS set using beam #2. BFD-RS #2 may be transmitted to the terminal. BFD-RS #1 may be a BFD-RS having a minimum transmission period among BFD-RSs of the first BFD-RS set. In this case, the transmission period of BFD-RS #1 may be less than 2 msec. Accordingly, the beam failure instance reporting period of the first BFD-RS set may be 2 msec. Meanwhile, BFD-RS #2 may be a BFD-RS having a minimum transmission period among BFD-RSs of the second BFD-RS set. At this time, the transmission period of BFD-RS #2 may be 2 msec or more. Accordingly, the beam failure instance reporting period of the second BFD-RS set may be the transmission period of BFD-RS #2.

In this situation, the physical layer of the UE can measure radio link qualities of beams used for transmission of the control channel in TRP 1 using BFD-RSs including BFD-RS #1 of the first BFD-RS set. have. In this case, when the physical layer of the UE is greater than the first threshold value, the measurement results (eg, error rates) of the BFD-RSs of the first BFD-RS set for all beams used for transmission of the control channel in TRP 1 are , it can be determined that a beam failure instance has occurred for TRP 1, and instance information can be reported to the MAC layer. Similarly, the physical layer of the UE can measure radio link qualities of beams used for transmission of a control channel in TRP 2 using BFD-RSs including BFD-RS #2 of the second BFD-RS set. At this time, when the physical layer of the UE measures the BFD-RSs of the second BFD-RS set for all beams used for transmission of the control channel in TRP 2 (eg, error rates) greater than the first threshold value. , it can be determined that a beam failure instance has occurred for TRP 2, and instance information can be reported to the MAC layer.

Meanwhile, a method of configuring a BFD-RS set for each TRP in a UE may include an explicit method and an implicit method. An explicit method of configuring BFD-RS sets for each TRP may be a method of directly configuring BFD-RS sets in a UE through an RRC message from a base station. As such, the explicit method of configuring a BFD-RS set for each TRP may be applicable to both single DCI and multiple TRP data transmission scenarios by multiple DCIs. On the other hand, the implicit method may be a method in which the UE derives the BFD-RS set from the TCI state of the CORESET having the same CORESET pool index.

Here, the CORESET pool index is an RRC parameter introduced in multiple TRP transmissions by multiple DCI and may be a TRP specific index. Accordingly, the terminal can implicitly derive a BFD-RS set for each TRP without separately providing an index indicating the TRP. However, since there may not be a parameter such as a CORESET pool index in multiple TRP transmissions by a single DCI, the UE may configure a BFD-RS set using an explicit method. In addition, the maximum number of BFD-RS resources that can be configured for each BFD-RS set and the total number of BFD-RS resources that can be configured per DL (downlink) BWP (bandwidth part) may be determined according to the capability of the terminal. Therefore, the base station may set the maximum number of BFD-RS resources and the total number of BFD-RS resources that can be configured per DL BWP based on the capability of the terminal received from the terminal.

(2) TRP-specific new candidate beam identification process

A process performed simultaneously with the process of detecting a beam failure may be a process of identifying a new candidate beam. In general, after detecting a beam failure, the terminal may determine that a condition for requesting a beam failure recovery is satisfied when there is a new candidate beam. Therefore, the terminal may need to find in advance a candidate beam to be used newly when a beam failure occurs in a currently used beam through a synchronization signal block or CSI-RS periodically transmitted from the base station. Similar to the beam failure detection step, the terminal can determine a method for determining a new beam by measuring a quality of a signal transmitted from the base station and under a condition.

Like the beam failure detection procedure, the base station may define a new beam identification RS (NBI-RS) for beam identification. The base station may explicitly set the synchronization signal block and / or CSI-RS resources to the terminal as an NBI-RS set through an RRC message. Such an NBI-RS may be beamformed into candidate beams that can be used for data channel transmission until further control transmission and beam resetting. And, it can be said that the NBI-RS has a QCL-type D relationship with the DM-RS of the control channel or the data channel before beam resetting.

The UE can measure the quality of the beam link through the NBI-RSs in the NBI-RS set. In this case, the quality of the beam link may be RSRP (reference signal received power) measured in the physical layer, that is, L1-RSRP. That is, the UE determines that the L1-RSRP value measured in the physical layer at the request of the upper layer may be greater than or equal to the second threshold value (ie, Qin_LR) as new beam candidates, and the measured L1-RSRP It can be reported to the upper layer along with the value. Here, the terminal may receive the second threshold set through the RRC message from the base station. And, when there are several beams satisfying the condition, the upper layer of the terminal may finally determine one beam as a new candidate beam. If the serving cell is a secondary cell (SCell), the physical layer of the UE may additionally be greater than the second threshold value or may inform the higher layer whether there is at least one NBI-RS index equal to or greater than the second threshold value. At this time, the physical layer of the terminal may be greater than or equal to the second threshold if there is at least one NBI-RS index that may be greater than or equal to the second threshold, the upper layer together with the measured L1-RSRP value of NBI-RS indexes that may be greater than or equal to the second threshold can be reported as

Meanwhile, in the TRP-specific new candidate beam identification process, unlike the existing TRP new candidate beam identification process, the UE may also configure an NBI-RS set for each TRP. Accordingly, the NBI-RS set may have a one-to-one correspondence relationship with the BFD-RS set previously configured for each TRP. In this case, a new candidate beam may be found in the NBI-RS set associated with the BFD-RS set in which the beam failure is detected.

The base station may establish a one-to-one correspondence between the NBI-RS set and the BFD-RS set in the terminal using the RRC message. In this way, when the base station configures a one-to-one correspondence between the NBI-RS set and the BFD-RS set in the terminal using the RRC message, additional signaling may be required. In this way, if the base station sets a one-to-one relationship between the NBI-RS set and the BFD-RS set in the terminal, a more flexible configuration may be possible. However, there may be many cases where the purpose or advantage of having a flexible configuration in a TRP-specific new candidate beam identification procedure is not great. In addition, since only mapping is required in the TRP-specific new candidate beam identification procedure, the UE can make a one-to-one correspondence relationship in advance as much as the BFD-RS set and NBI-RS set are configured in the network. For example, the UE may use a method of implicitly mapping the first BFD-RS set to the first NBI-RS set in order between failure detection resources and a candidate beam RS list. there is.

This implicit mapping method may be possible in a state where a set index is not separately defined in the RRC parameters defining the BFD-RS set and the NBI-RS set. However, the number of BFD-RS sets configured at this time and the number of NBI-RS sets may be the same. In this way, the UE can naturally have a one-to-one correspondence between the NBI-RS set and the BFD-RS set without separate signaling.

(3) TRP specific beam failure recovery request process

In a general TRP beam failure detection process, the terminal may detect beam failure and may declare beam failure when a new candidate beam to be used is found after recovery. Alternatively, in a general TRP beam failure detection process, the terminal may detect beam failure, and may find a candidate beam to be newly used after recovery after declaring beam failure. After that, the terminal may request TRP beam failure recovery to the base station. At this time, the base station may set the beam failure recovery timer and the maximum number of beam failure recovery requests to the terminal through the RRC message. Accordingly, the terminal may operate a beam failure recovery timer upon declaring beam failure, and may transmit a beam failure recovery request signal to the base station. In case of primary cell (PCell) or primary-secondary cell (PSCell) beam failure, the UE transmits a beam failure recovery request signal to the base station through a random access (RA) procedure. there is. In contrast, in case of secondary cell (SCell) beam failure, the UE may transmit a beam failure recovery request signal to the base station through a physical uplink control channel (PUCCH). Each of the beam failure recovery request methods may be as follows.

(3.1) Random access-based beam failure recovery request

In a general TRP beam failure recovery request process, when a serving cell is a PCell or a PSCell, after beam failure detection and a new beam identification procedure, the UE may request beam failure recovery from the base station through a random access procedure. At this time, the UE may receive a physical random access channel (PRACH) resource (time, frequency, preamble ID (identifier), etc.) designated by the RRC parameter PRACH-ResourceDedicatedBFR, and transmit the PRACH with the beam found in the new beam identification procedure. can be done The UE may use the PRACH resource associated with the selected new beam for a beam failure recovery request. The terminal may repeatedly transmit a beam failure recovery request to the base station within a predetermined maximum number of times until a beam failure recovery response from the base station is successfully received.

(3.2) PUCCH-based beam failure recovery request

In a general TRP beam failure recovery request process, when the serving cell is an SCell, after beam failure detection and a new beam search procedure, the terminal may request beam failure recovery to the base station through PUCCH. As such, the PUCCH-based beam failure recovery request method may include a link recovery request (LRR) and transmission of a PUSCH MAC control element (MAC-CE) accompanying beam failure related information. The link recovery request transmits a link recovery request to the base station using PUCCH-SR (scheduling request) resources set by the RRC parameter schedulingRequestID-BFR-SCell in order for the terminal to request uplink resources to transmit beam failure related information. can be a process. Further, PUSCH MAC-CE transmission may be a process in which a UE transmits a MAC-CE carrying information related to beam failure to a base station using PUSCH resources. Here, the information related to beam failure may be a SCell index in which beam failure is detected, an indication of whether a new beam exists in the corresponding SCell, and a new beam index to be used in the corresponding SCell if a new beam exists.

Meanwhile, the terminal may utilize both of the two beam failure recovery request methods for the TRP-specific beam failure recovery request. However, when a beam failure is detected in some TRPs among several TRPs, the UE can recover the beam failure through the TRPs in which the beam failure has not occurred. Therefore, the UE can utilize the PUCCH-based beam failure recovery request method to the TRP in which beam failure has not occurred. Since the PUCCH-based beam failure recovery request consists of a link recovery request and PUSCH MAC-CE transmission, the PUCCH-based TRP-specific beam failure recovery request can also be divided into two parts. In addition, there is a case where the terminal cannot recover from a TRP-specific beam failure in a specific situation. In this case, a random access based beam failure recovery request can be made to the base station.

(3.3) TRP Specific Beam Failure Recovery Request Process - Link Recovery Request

Unlike a general TRP beam failure recovery request, in a TRP specific beam failure recovery request process, the UE can receive up to two PUCCH-SR resources per cell group through an RRC message. A multiple TRP transmission system using carrier aggregation may use, for example, two TRPs and two component carriers as shown in FIG. 8 .

8 is a conceptual diagram illustrating a first embodiment of a multi-TRP transmission system using carrier aggregation.

Referring to FIG. 8, in a multi-TRP transmission system using carrier aggregation, TRP 1 and TRP 2 perform multi-TRP transmission using a component carrier (CC 1) and a component carrier 2 (CC 2). can CC 1 may be set to PCell/PSCell, and CC 2 may be set to SCell. Also, PUCCH-SR 1 may be set for link recovery request for TRP 1, and PUCCH-SR 2 may be set similarly for TRP 2. Here, the meaning that the TRP and the PUCCH-SR are associated may mean that the PUCCH-SR is associated with a BFD-RS set configured for each TRP.

A case in which beam failure occurs in the proposed multi-TRP transmission system may be as follows.

① When beam failure occurs in one of the two TRPs in CC 1 (PCell/PSCell)

② When beam failure occurs in all TRPs in CC 1 (PCell/PSCell)

③ When beam failure occurs in one of the two TRPs in CC 2 (SCell)

④ When beam failure occurs in all TRPs in CC 2 (SCell)

A description of how a link recovery request is made for each case may be as follows.

(3.3.1) In case of beam failure in one TRP in CC 1 (PCell/PSCell)

The UE may transmit a beam failure recovery request to a TRP (BFD-RS set) in which beam failure has not occurred by using a PUCCH-SR associated with a TRP (BFD-RS set) in which beam failure has not occurred. For example, if beam failure is detected for TRP 1, the UE may request beam failure recovery to TRP 2 using PUCCH-SR 2 associated with TRP 2. Then, TRP 2 may receive a beam failure recovery request for TRP 1 from the terminal. And, TRP 2 may transfer the received beam failure recovery request for TRP 1 to TRP 1 . Accordingly, TRP 1 may receive a beam failure recovery request from TRP 2 . And, TRP 1 may transmit an uplink grant to TRP2. Then, TRP 2 may transmit an uplink grant to the terminal. The UE may receive an uplink grant from TRP 2.

(3.3.2) When beam failure occurs in all TRPs in CC 1 (PCell/PSCell)

Since beam failure occurs over the entire PCell/PSCell, the UE may perform a random access based beam failure recovery request.

(3.3.3) In case of beam failure in one TRP in CC 2 (SCell)

Basically, similar to the case where beam failure occurs in one of the two TRPs in CC 1, the UE transmits a beam failure recovery request using a PUCCH-SR associated with a TRP (BFD-RS set) in which beam failure does not occur. It can be transmitted to a TRP that has not been For example, if beam failure is detected for the SCell of TRP 1, the UE may request beam failure recovery to TRP 2 using PUCCH-SR 2 associated with TRP 2. Then, TRP 2 may receive a beam failure recovery request for TRP 1 from the terminal. And, TRP 2 may transfer the received beam failure recovery request for TRP 1 to TRP 1 . Accordingly, TRP 1 may receive a beam failure recovery request from TRP 2 . And, TRP 1 may transmit an uplink grant to TRP2. Then, TRP 2 may transmit an uplink grant to the terminal. The UE may receive an uplink grant from TRP 2.

However, in this case, since the beam failure is in the SCell rather than the PCell/PSCell, the PUCCH-SR related to the TRP of the beam failure may also be transmitted. For example, if beam failure is detected for the SCell of TRP 1, the UE may request beam failure recovery to TRP 1 using PUCCH-SR 1 associated with TRP 1. Then, TRP 1 may receive a beam failure recovery request from the terminal. And, TRP 1 may transmit an uplink grant to the terminal. Then, the UE can receive the uplink grant from TRP 1.

As such, even if beam failure is detected in TRP 1, the UE cannot use only PUCCH-SR 2, and can transmit a beam failure recovery request signal to TRP 1 using PUCCH-SR 1. However, the UE may select a PUCCH-SR associated with a TRP in which no beam failure has occurred for consistency of specifications in relation to PUCCH-SR selection. Alternatively, the UE may select a better PUCCH-SR using information it knows (eg, spatial relation and uplink channel quality of the PUCCH-SR).

(3.3.4) When beam failure occurs for all TRPs in CC 2 (SCell)

The case where beam failure occurs for all TRPs in the SCell may be the same as the case where beam failure occurs in one of the two TRPs. Accordingly, a beam failure recovery request procedure may be the same as a case where beam failure occurs in one of the two TRPs. However, the UE may need to notify all new beams of all TRPs in which beam failure has occurred as information related to beam failure in the PUSCH MAC-CE transmitted later.

In this way, if the terminal considers all cases, the standard may be complicated. In addition, when the number of CCs increases in the multi-TRP transmission system, more cases may be considered by the UE. Therefore, the UE can simplify the link recovery condition to simplify the standard. Accordingly, when a beam failure occurs in one of the two TRPs, the UE may select a PUCCH-SR for transmitting a link recovery request to the TRP in which the beam failure occurs in order to stably transmit the link recovery request. At this time, if the UE always uses the UL spatial filter directed to the TRP in which the beam failure does not occur, the PUCCH-SR related to the BFD-RS set of the TRP in which the beam failure occurs can always be selected regardless of the CC in which the beam failure occurs.

For example, if a beam failure occurs in TRP 1, the UE may transmit a link recovery request by selecting PUCCH-SR 1 related thereto. At this time, the UE may transmit a link recovery request signal to TRP 2 using PUCCH-SR 1 using a UL spatial filter directed to TRP 2. At this time, TRP 2 may receive a beam failure recovery request for TRP 1 from the terminal. And, TRP 2 may transfer the received beam failure recovery request for TRP 1 to TRP 1 . Accordingly, TRP 1 may receive a beam failure recovery request from TRP 2 . And, TRP 1 may transmit an uplink grant to TRP2. Then, TRP 2 may transmit an uplink grant to the terminal. The UE may receive an uplink grant from TRP 2.

Similarly, when a beam failure occurs in TRP 2, the UE may request link recovery using PUCCH-SR 2. At this time, the UE may transmit a link recovery request signal using PUCCH-SR 1 using a UL spatial filter directed to TRP 2. At this time, TRP 1 may receive a beam failure recovery request for TRP 2 from the terminal. And, TRP 1 may transfer the received beam failure recovery request for TRP 2 to TRP 2 . Accordingly, TRP 2 may receive a beam failure recovery request from TRP 1. And, TRP 2 may transmit an uplink grant to TRP 1. Then, TRP 1 may transmit an uplink grant to the terminal. The UE may receive an uplink grant from TRP 1.

Meanwhile, when beam failure occurs in all TRPs, subsequent procedures may be different depending on whether the TRP is a special cell (SpCell) (ie PCell/PSCell) or an SCell. Here, in the case of SpCell, the UE may not be comfortable with PUCCH-SR transmission, so it may be better to perform a random access based beam failure recovery request. Unlike this, in the case of SCell, the UE can select the PUCCH-SR on its own using information known to it.

Meanwhile, since independent beam failure situations may occur simultaneously in a multiple TRP transmission system, TRP-specific beam failure occurrence situations may be different between cells. For example, beam failure may occur in TRP 1 of CC 1 (PCell/PSCell) and in TRP 2 of CC 2 (SCell). These beam failures can occur simultaneously. In this case, since uplink channels including PUCCH-SR exist in SpCell (PCell/PSCell), SpCell's beam failure situation is given priority to PUCCH-SR (PUCCH-SR 1) associated with TRP 1 where beam failure occurred in SpCell. can choose In addition, the UE may transmit a link recovery request to TRP 2 using PUCCH-SR 1 using a UL spatial filter directed to TRP 2. Meanwhile, when considering a multi-TRP transmission system using three CCs, beam failure may occur in CC 2 and CC 3, which are SCells, in addition to CC 1 (PCell/PSCell). At this time, beam failure may be detected in TRP 1 in CC 2 and in TRP 2 in CC 3, and the terminal may select one of several methods to proceed with subsequent procedures.

In this case, since TRP-specific beam failure occurs only in SCells, the UE can select one of the PUCCH-SRs and proceed with the beam failure recovery request. However, the UE may indicate the CC index and TRP index in which beam failure occurred in the PUSCH MAC-CE to be transmitted subsequently. In addition, the UE may perform beamforming using a spatial filter on PUCCH-SR resources. At this time, the UE may configure two spatial filters in one PUCCH-SR resource. In this way, if the UE sets two spatial filters, it can select one spatial filter out of the two and use it to transmit the PUCCH-SR and use it as a beam diversity scheme.

(3.4) TRP specific beam failure recovery request - PUSCH MAC-CE transmission

The UE may receive the PDCCH, which is a UL grant, from the base station after requesting link recovery through the PUCCH-SR. Then, the UE may transmit the MAC-CE containing information related to beam failure to the BS through the PUSCH. Beam failure-related information that may be included in the MAC-CE includes TRP index information where beam failure occurred, CC index (when carrier aggregation is used), whether or not at least one new candidate beam was found, and new candidate beam index (at least one new candidate beam). when a candidate beam is found) and the like. Here, the TRP index information in which beam failure has occurred may be a BFD-RS set index or a CORESET pool index associated with TRP, since the TRP index is not separately specified in the standard. And if beam failure occurs for multiple TRPs in multiple CCs, if a new candidate beam is found or not found for each, whether a new beam is found for each TRP of each CC in which beam failure occurs, and if found, a new beam is found. All index information of candidate beams must be included in the MAC-CE. In the case of a TRP-specific beam failure, MAC-CEs accompanying beam failure-related information may be divided for each TRP. However, it is possible to do so because it is efficient for the terminal to send information all at once through one MAC-CE. Composing multiple TRP beam failure information of multiple CCs into one MAC-CE is all information to be included in the MAC-CE above, such as TRP index information in which beam failure occurred, CC index (when carrier aggregation is used), and a new candidate beam. It may be a method of performing aggregation by indicating whether at least one or more beams have been found and a new candidate beam index (when at least one or more new beams are found) in a bitmap form, respectively.

(4) TRP specific beam failure recovery response (BFRR)

The base station may receive a beam failure recovery request from the terminal. Then, the base station may transmit a beam failure response signal to the terminal. Responses to beam failure recovery are given differently depending on the type of beam failure recovery request, and each can be described as follows.

(4.1) Case of random access-based beam failure recovery request

In the case of a random access-based beam failure recovery request, a beam failure recovery response may be given as a CORESET connected to a search space provided by a recovery search space ID.

9 is a timing diagram illustrating a first embodiment of a process of receiving a beam failure recovery request and a beam failure recovery response.

Referring to FIG. 9 , a beam failure recovery timer may be driven after the terminal declares beam failure. And, the terminal may transmit a beam failure recovery request to the base station in the nth slot (S910). Thereafter, the terminal may observe whether a beam failure recovery response is received within a monitoring window set by beam failure recovery configuration from the n+4th slot (S920). At this time, the terminal may perform the search using the beam found and selected in the new beam search process. In this way, it can be seen that the beam found and selected in the new beam search process is connected to a beam transmitting a designated PRACH resource including a beam failure recovery request. Thereafter, the terminal may use the beam until a new beam is instructed by the base station. If there is no response from the base station within the monitoring window, the terminal may transmit a beam failure recovery request back to the base station (S930). If the terminal cannot continuously receive a beam failure recovery response while the beam failure recovery timer is running, the terminal may repeat this process up to the maximum number of beam failure recovery requests. Thereafter, the terminal may observe whether a beam failure recovery response is received within the set monitoring window (S940). At this time, the terminal may receive a beam failure recovery response from the base station (S950).

(4.2) In case of PUCCH-based beam failure recovery request

In the case of a PUCCH-based beam failure recovery request, the base station schedules PUSCH transmission having the same HARQ process number as the PUSCH transmission accompanying beam failure related information and beam failure recovery with a PDCCH including a DCI having a toggled NDI field value. A response may be transmitted to the terminal. Since the beam failure recovery request and beam failure recovery response procedures use PUCCH, they can be performed in PCell or PSCell.

10 is a timing diagram illustrating a second embodiment of a process of receiving a beam failure recovery request and a beam failure recovery response.

Referring to FIG. 10, a UE may request beam failure recovery using PUCCH-SR to a base station (S1010). Then, the base station may receive a beam failure recovery request from the terminal. And, the base station may transmit a PDCCH including an uplink grant to the terminal (S1020). Accordingly, the terminal can receive the PDCCH including the grant from the base station. Thereafter, the terminal may transmit a PUSCH including MAC-CE to the base station (S1030). A base station may receive a PUSCH including a MAC-CE from a terminal. And, the base station may transmit a beam failure recovery response to the terminal (S1040). Then, the terminal may receive a beam failure recovery response from the base station.

(4.3) TRP specific beam failure recovery response reception process

The TRP-specific beam failure recovery request may be based on a PUCCH-based beam failure recovery request method. Accordingly, the TRP-specific beam failure recovery response may also operate similarly to the beam failure recovery response method for the PUCCH-based beam failure recovery request of FIG. 10 . That is, when the TRP-specific beam failure recovery request is performed with PUCCH-SR and PUSCH MAC-CE transmission, the base station toggles while instructing PUSCH transmission having the same HARQ process number as PUSCH MAC-CE transmission accompanying information related to beam failure. A PDCCH including a DCI having an NDI field value may be transmitted as a TRP specific beam failure recovery response.

(5) Operation process of the base station and the terminal after the terminal receives the beam failure recovery response

In case of beam failure in one or some TRPs in a TRP-specific beam failure situation, the UE receives the beam failure recovery response (PDCCH) from the base station for the PUSCH MAC-CE 28 symbols after the TRP in which the beam failure occurred. The PDCCH may be monitored for and the PUCCH may be transmitted. At this time, the terminal may use a candidate beam selected from candidate beams identified in the new candidate beam identification procedure.

The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer readable medium. Computer readable media may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on a computer readable medium may be specially designed and configured for the present invention or may be known and usable to those skilled in computer software. Examples of computer readable media may include hardware devices specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions may include not only machine language codes generated by a compiler but also high-level language codes that can be executed by a computer using an interpreter and the like. The hardware device described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa. In addition, the above-described method or device may be implemented by combining all or some of its components or functions, or may be implemented separately.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention within the scope not departing from the spirit and scope of the present invention described in the claims below. You will understand that it can be done.

Claims (1)

As an operation method performed in a terminal of a communication system,
Detecting a beam failure of at least one TRP among a plurality of transmission and reception points (TRPs);
Searching for a plurality of candidate beams for the at least one TRP;
Transmitting a beam failure recovery request signal to the at least one TRP using one candidate beam from among the plurality of candidate beams; and
And receiving a beam failure recovery response signal that is a response to the beam failure recovery request signal from the at least one TRP through the one candidate beam.

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