Communication device, base station, and communication method

Abstract

To provide user equipment and a communication method that perform beam failure detection and recovery in units of TRPs (transmission / reception points) when a cell is operated with a plurality of TRPs.SOLUTION: UE 100 that performs wireless communication with a base station that manages a cell having N (N≥2) TRPs includes: a communication unit 110 that receives, from the base station, a radio resource control (RRC) message containing a beam failure detection setting list associated with a downlink bandwidth portion, which is part of bandwidth of the cell, for setting N beam failure detection resource sets; and a control unit 120 that individually detects a beam failure for each of the N beam failure detection resource sets based on the beam failure detection setting list in wireless communication using the downlink bandwidth portion.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a user device, a base station, and a communication method used in a mobile communication system.

Background Art

[0002] In recent years, in 3GPP (3rd Generation Partnership Project), which is a standardization project for mobile communication systems, the introduction of multi-transmission / reception point (TRP) transmission has been studied as an extension of MIMO (multi-input multi-output) (see Non-Patent Document 1). In such multi-TRP transmission, a plurality of TRPs provided dispersedly constitute one cell, and by performing wireless communication with a user device using these multiple TRPs simultaneously, efficient transmission can be realized. Note that a TRP may also be referred to as a panel or an antenna panel.

[0003] When operating a cell using multiple TRPs, it has been proposed to perform beam failure detection and recovery, which were conventionally performed on a cell-by-cell basis, on a TRP-by-TRP basis (see Non-Patent Documents 2 and 3). Specifically, a TRP-specific counter / timer for detecting a beam failure is introduced, and in a user device, a beam failure event (beam failure instance indicator) notified from the physical layer to the media access control (MAC) layer is counted by a counter, and when the count value exceeds a specified number of times before the timer expires, a beam failure is detected.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

[0005] In order to perform beam failure detection and recovery for each TRP during cell operation using multiple TRPs, it is considered necessary to separately set a beam failure detection resource set including a reference signal resource for detecting beam failure for each TRP in the user equipment. However, in the existing 3GPP technical specifications, there is no mechanism for setting a beam failure detection resource set for each TRP in the user equipment. Therefore, it is difficult to perform beam failure detection and recovery for each TRP.

[0006] Therefore, an object of the present invention is to provide a user equipment, a base station, and a communication method that enable beam failure detection and recovery to be performed for each TRP during cell operation using multiple TRPs. [Means for Solving the Problems]

[0007] The user equipment according to the first aspect is a user equipment (100) that performs wireless communication with a base station (200) that manages a cell (250) having N (N≥2) transmission / reception points (201#0, 201#1), and is a list for setting N beam obstruction detection resource sets (521#0, 521#1), and includes a radio resource control (RRC) message including a beam obstruction detection setting list (520) associated with a downlink bandwidth portion that is a part of the bandwidth of the cell (250). A communication unit (110) that receives from the base station (200), and in the wireless communication using the downlink bandwidth portion, based on the beam obstruction detection setting list (520), a control unit (120) that individually detects a beam obstruction for each of the N beam obstruction detection resource sets (521#0, 521#1).

[0008] The base station according to the second aspect is a base station (200) that manages a cell (250) having N (N≥2) transmission / reception points (201#0, 201#1) and performs wireless communication with a user equipment (100), and is a list for setting N beam obstruction detection resource sets (521#0, 521#1), and includes a communication unit (210) that transmits a radio resource control (RRC) message including a beam obstruction detection setting list (520) associated with a downlink bandwidth portion that is a part of the bandwidth of the cell (250) to the user equipment (100), and the beam obstruction detection setting list (520) is used for the user equipment (100) to individually detect a beam obstruction for each of the N beam obstruction detection resource sets (521#0, 521#1) in the wireless communication using the downlink bandwidth portion.

[0009] The communication method according to the third aspect is a communication method executed by a user equipment (100) that performs wireless communication with a base station (200) that manages a cell (250) having N (N ≥ 2) transmission / reception points (201#0, 201#1), including a list for setting N beam obstacle detection resource sets (521#0, 521#1), receiving from the base station (200) a radio resource control (RRC) message including a beam obstacle detection setting list (520) associated with a downlink bandwidth portion that is part of the bandwidth of the cell (250), and in the wireless communication using the downlink bandwidth portion, individually detecting a beam obstacle for each of the N beam obstacle detection resource sets (521#0, 521#1) based on the beam obstacle detection setting list (520).

Advantages of the Invention

[0010] According to one aspect of the present invention, it is possible to provide a user equipment, a base station, and a communication method that enable beam obstacle detection and recovery to be performed for each transmission / reception point (TRP) during cell operation by a plurality of TRPs.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Mode for Carrying Out the Invention

[0012] With reference to the drawings, a mobile communication system according to an embodiment will be described. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0013] (Mobile Communication System) First, with reference to FIG. 1, the configuration of a mobile communication system 1 according to an embodiment will be described. The mobile communication system 1 is a system compliant with, for example, the technical specifications (Technical Specification: TS) of 3GPP. Hereinafter, as the mobile communication system 1, a 5th Generation System (5GS) of the 3GPP standard, that is, a mobile communication system based on NR (New Radio) will be described as an example.

[0014] The mobile communication system 1 includes a network 10 and a user equipment (UE) 100 that communicates with the network 10. The network 10 includes an NG-RAN (Next Generation Radio Access Network) 20 which is a 5G radio access network, and a 5GC (5G Core Network) 30 which is a 5G core network.

[0015] UE100 is a device used by a user. UE100 is a movable device such as, for example, a mobile phone terminal such as a smartphone, a tablet terminal, a notebook PC, a communication module, or a communication card. UE100 may be a vehicle (e.g., a car, a train, etc.) or a device provided thereon. UE100 may be a transportation aircraft other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided thereon. UE100 may be a sensor or a device provided thereon. Note that UE100 may be called by another name such as a mobile station, a mobile terminal, a mobile device, a mobile unit, a subscriber station, a subscriber terminal, a subscriber device, a subscriber unit, a wireless station, a wireless terminal, a wireless device, a wireless unit, a remote station, a remote terminal, a remote device, or a remote unit.

[0016] NG-RAN20 includes a plurality of base stations 200. Each base station 200 manages at least one cell. A cell constitutes the smallest unit of a communication area. One cell belongs to one frequency (carrier frequency) and is composed of one component carrier. The term "cell" may represent a radio communication resource or may represent a communication target of UE100. Each base station 200 can perform wireless communication with UE100 present in its cell. The base station 200 communicates with UE100 using the protocol stack of the RAN. The base station 200 provides NR user plane and control plane protocol termination towards UE100 and is connected to 5GC30 via the NG interface. Such an NR base station 200 may be referred to as a gNodeB (gNB).

[0017] 5GC30 includes a core network device 300. The core network device 300 includes, for example, an AMF (Access and Mobility Management Function) and / or a UPF (User Plane Function). The AMF performs mobility management of UE100. The UPF provides a function specialized for user plane processing. The AMF and the UPF are connected to the base station 200 via the NG interface.

[0018] Next, with reference to FIG. 2, a configuration example of a protocol stack in the mobile communication system 1 according to the embodiment will be described.

[0019] The protocol for the radio section between the UE 100 and the base station 200 has a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an RRC (Radio Resource Control) layer.

[0020] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Between the PHY layer of the UE 100 and the PHY layer of the base station 200, data and control information are transmitted via a physical channel.

[0021] The physical channel is composed of a plurality of OFDM symbols in the time domain and a plurality of subcarriers in the frequency domain. One subframe is composed of a plurality of OFDM symbols in the time domain. A resource block is a resource allocation unit and is composed of a plurality of OFDM symbols and a plurality of subcarriers. A frame can be composed of 10 ms and can include 10 subframes composed of 1 ms. A subframe can include a number of slots corresponding to the subcarrier spacing.

[0022] Among the physical channels, the physical downlink control channel (PDCCH) plays a central role, for example, for purposes such as downlink scheduling assignment, uplink scheduling grant, and transmission power control.

[0023] In NR, the UE 100 can use a bandwidth narrower than the system bandwidth (i.e., the cell bandwidth). The base station 200 sets a bandwidth part (BWP) consisting of consecutive PRBs for the UE 100. The UE 100 transmits and receives data and control signals in the active BWP. Up to, for example, four BWPs can be set for the UE 100. Each BWP may have a different subcarrier spacing or may have overlapping frequencies. When multiple BWPs are set for the UE 100, the base station 200 can specify which BWP to activate by means of downlink control. Thereby, the base station 200 can dynamically adjust the UE bandwidth according to the amount of UE 100's data traffic, etc., and can reduce UE power consumption.

[0024] The base station 200 can set up to three control resource sets (CORESETs) for each of up to four BWPs on the serving cell, for example. A CORESET is a radio resource for control information that the UE 100 should receive. Up to 12 CORESETs can be set for the UE 100 on the serving cell. Each CORESET has an index from 0 to 11. For example, a CORESET is composed of six resource blocks (PRBs) and one, two, or three consecutive OFDM symbols in the time domain.

[0025] The MAC layer performs priority control of data, retransmission processing by hybrid ARQ (HARQ), and random access procedures, etc. Data and control information are transmitted between the MAC layer of the UE 100 and the MAC layer of the base station 200 via a transport channel. The MAC layer of the base station 200 includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) of the uplink and downlink and the resources allocated to the UE 100.

[0026] The RLC layer transmits data to the RLC layer on the receiving side by utilizing the functions of the MAC layer and the PHY layer. Between the RLC layer of the UE100 and the RLC layer of the base station 200, data and control information are transmitted via logical channels.

[0027] The PDCP layer performs header compression / expansion and encryption / decryption.

[0028] An SDAP (Service Data Adaptation Protocol) layer may be provided as the upper layer of the PDCP layer. The SDAP (Service Data Adaptation Protocol) layer performs mapping between the IP flow, which is the unit for the core network to perform QoS control, and the radio bearer, which is the unit for the AS (Access Stratum) to perform QoS control.

[0029] The RRC layer controls logical channels, transport channels, and physical channels in response to the establishment, re - establishment, and release of radio bearers. Between the RRC layer of the UE100 and the RRC layer of the base station 200, RRC signaling for various settings is transmitted. When there is an RRC connection between the RRC of the UE100 layer and the RRC of the base station 200 layer the UE100 is in the RRC connected state. When there is no RRC connection between the RRC of the UE100 layer and the RRC of the base station 200 layer the UE100 is in the RRC idle state. When the RRC connection between the RRC of the UE100 layer and the RRC of the base station 200 layer is suspended, the UE100 is in the RRC inactive state.

[0030] The NAS layer located above the RRC layer manages the session management and mobility management of the UE 100. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the core network device 300 (AMF). Note that the UE 100 has an application layer etc. in addition to the protocol of the radio interface.

[0031] (Overview of Beam Failure Detection and Recovery) Next, with reference to FIGS. 3 and 4, an overview of beam failure detection and recovery will be described.

[0032] Compared with LTE (Long Term Evolution), which is a fourth-generation radio access technology, NR enables broadband transmission in high-frequency bands such as the millimeter wave band or the terahertz wave band. In NR, in order to compensate for the radio wave attenuation in the radio waves of such high-frequency bands, highly directional beamforming using a large number of antennas is utilized between the base station 200 and the UE 100 to obtain a high beam gain. In NR, a beam control technology for establishing and maintaining a beam pair between the base station 200 and the UE 100 has been introduced. The beam failure detection and recovery technology is one of such beam control technologies.

[0033] Regarding beam failure detection (BFD), the base station 200 sets the downlink reference signal resources for the UE 100 to detect beam failure. Such reference signal resources are either SSB (SS / PBCH Block) or CSI-RS (Channel State Information Reference Signal). The SSB includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a PBCH (Physical Broadcast Channel), and a demodulation reference signal (DMRS). For example, the SSB may be composed of four consecutive OFDM symbols in the time domain. Also, the SSB may be composed of 240 consecutive subcarriers (i.e., 20 resource blocks) in the frequency domain. The PBCH is a physical channel that carries the master information block (MIB). The CSI-RS is a reference signal transmitted for the UE 100 to measure the state of the radio channel.

[0034] Note that if the SSB is within the bandwidth of the downlink BWP, the UE 100 can detect beam failure using the SSB. If the SSB is not within the bandwidth of the downlink BWP, the UE 100 can detect beam failure using the CSI-RS set by the base station 200.

[0035] In the UE 100, the MAC layer counts the beam failure events (beam failure instance indicators) notified by the physical layer using a counter, and when the count value exceeds a specified number before the timer expires, it detects (declares) beam failure.

[0036] Fig. 3 shows an example of the operation when beam failure is detected in a secondary cell (SCell) during cell operation by a single TRP.

[0037] In Fig. 3, an example is shown in which the base station 200 manages an SCell 250B composed of one TRP 201. The base station 200 (TRP 201) forms a total of three beams, namely beam #0 to beam #2. The UE 100 detects beam failure during communication using beam #0 in the SCell 250B.

[0038] In this case, the UE 100 triggers beam failure recovery (BFR) by starting to transmit a beam failure recovery MAC control element (BFR MAC CE). Here, the UE 100 selects a beam suitable for the SCell (for example, beam #1) and indicates the selected beam information together with the information on the beam failure by the BFR MAC CE. When the UE 100 receives a PDCCH indicating a new transmission of the uplink grant for the HARQ process used for the transmission of the BFR MAC CE, the recovery from the beam failure of the SCell 250B is completed.

[0039] FIG. 4 shows an operation example when a beam failure is detected in a special cell (SpCell) during cell operation by a single TRP. The SpCell may be referred to as a primary cell (PCell).

[0040] In FIG. 4, an example of the base station 200 managing the SpCell 250A constituted by one TRP 201 is shown. The base station 200 (TRP 201) forms a total of three beams from beam #0 to beam #2. The UE 100 detects a beam failure during communication using beam #0 in the SpCell 250A.

[0041] In this case, the UE 100 triggers BFR by starting a random access procedure for the SpCell 250A. Here, the UE 100 selects a beam (for example, beam #1) appropriate for executing BFR. When the random access procedure is completed, BFR is completed.

[0042] (Overview of multi-TRP transmission) Next, with reference to FIG. 5, the overview of multi-TRP (multiple TRP) transmission according to the embodiment will be described.

[0043] In multi-TRP transmission, the base station 200 forms one cell 250 with a plurality of TRPs 201 that are dispersedly provided. In FIG. 5, two TRPs (TRP201#0 and TRP201#0) are illustrated as the plurality of TRPs 201. However, the base station 200 may form one cell 250 with three or more TRPs 201. In the following, the case where the number of TRPs 201 forming one cell 250 is two will be mainly described.

[0044] In multi-TRP transmission, it is possible to perform spatial multiplexing by transmitting different data from a plurality of TRPs 201 to increase the data rate. Alternatively, it is also possible to perform diversity by transmitting the same data from a plurality of TRPs 201 to improve the reliability and robustness of transmission.

[0045] There are a scheme using a single PDCCH and a scheme using a plurality of PDCCHs in multi-TRP transmission. In the single PDCCH-based scheme, one TRP 201 transmits a PDCCH (downlink control information (DCI)) and schedules a set of PDSCH layers of each TRP 201. In contrast, in the scheme using a plurality of PDCCHs, each TRP 201 individually schedules its own PDSCH. In the following, the scheme using a plurality of PDCCHs is mainly assumed.

[0046] In the scheme using a plurality of PDCCHs, it is possible to make the CORESET different for each TRP 201. Specifically, the TRP 201 and the CORESET pool index are associated in a one-to-one manner. When the base station 200 sets the CORESET for the UE 100, it notifies the UE 100 of the CORESET pool index to which the CORESET belongs. Therefore, the CORESET pool index can be regarded as an index for identifying the TRP 201.

[0047] In an embodiment, when operating cells using such a plurality of TRP201s, it is assumed that BFD·BFR, which was conventionally performed in units of cell 250, is performed in units of TRP201. Specifically, a counter timer unique to TRP201 for detecting beam obstacles is introduced, and in UE100, a beam obstacle instance indicator notified from the physical layer to the MAC layer is counted by the counter. When the count value exceeds a specified number of times before the timer expires, a beam obstacle is detected.

[0048] In order to perform BFD·BFR in units of such TRP201, it is considered necessary to separately set a beam failure detection resource set (hereinafter referred to as "BFD resource set") including a reference signal resource for detecting beam failures for each TRP201 in UE100. However, in the existing 3GPP technical specifications, there is no mechanism for setting a BFD resource set for each TRP201 in UE100. In one embodiment, it is possible to perform BFD·BFR in units of TRP201.

[0049] Also, if it is essential to separately set the reference signal resource for BFD for each TRP201 in UE100, there is a concern that the signaling amount for BFD·BFR will increase. In one embodiment, a mechanism is realized that enables BFD·BFR even for a BFD resource set / TRP201 for which the reference signal resource for BFD is not provided.

[0050] Also, existing radio link monitoring (i.e., detection of radio link failure (RLF) and detection of beam failure) is performed in units of cell 250, not in units of TRP201. In one embodiment, it is possible to appropriately coexist such existing technology with BFD in units of TRP201.

[0051] Also, even if the UE 100 detects beam failures for all the TRPs 201, if any of the TRPs 201 has recovered from the beam failure, communication (data transmission and reception) can be performed. If a random access procedure for recovery from the beam failure is started without considering whether or not recovery from the beam failure has occurred, data transmission and reception cannot be performed during the execution of the random access procedure, resulting in communication interruption. In one embodiment, such communication interruption can be suppressed.

[0052] (Configuration of User Equipment) Next, with reference to FIG. 6, the configuration of the UE 100 according to one embodiment will be described. The UE 100 includes a communication unit 110 and a control unit 120.

[0053] The communication unit 110 performs wireless communication with the base station 200 by transmitting and receiving wireless signals to and from the base station 200. The communication unit 110 has at least one transmission unit 111 and at least one reception unit 112. The transmission unit 111 and the reception unit 112 may be configured to include a plurality of antennas and RF circuits. The antenna converts a signal into a radio wave and radiates the radio wave into space. Also, the antenna receives a radio wave in space and converts the radio wave into a signal. The RF circuit performs analog processing of signals transmitted and received via the antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, and the like.

[0054] The control unit 120 performs various controls in the UE 100. The control unit 120 controls the communication with the base station 200 via the communication unit 110. The operations of the UE 100 described above and below may be operations under the control of the control unit 120. The control unit 120 may include at least one processor capable of executing a program and a memory for storing the program. The processor may execute the program to perform the operations of the control unit 120. The control unit 120 may also include a digital signal processor that performs digital processing of signals transmitted and received via the antenna and the RF circuit. The digital processing includes the processing of the RAN protocol stack. Note that the memory stores the program executed by the processor, the parameters related to the program, and the data related to the program. The memory may include at least one of ROM (Read Only Memory), EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), RAM (Random Access Memory), and flash memory. All or part of the memory may be included in the processor.

[0055] In the UE 100 according to an embodiment, the communication unit 110 performs wireless communication with a base station 200 that manages a cell 250 having N (N ≥ 2) TRPs 201. The communication unit 110 receives an RRC message including a list for setting N BFD resource sets, which is a beam failure detection setting list (hereinafter referred to as "BFD setting list") associated with a downlink BWP that is a part of the bandwidth of the cell 250, from the base station 200. In the wireless communication using the downlink BWP, the control unit 120 individually detects beam failure for each of the N BFD resource sets based on the BFD setting list. As a result, when operating the cell 250 using a plurality of TRPs 201, it becomes possible to set the BFD resource set for each TRP 201 in the UE 100 at the RRC layer, so that BFD·BFR can be performed for each TRP 201. As a result, even if a failure occurs in one TRP 201, communication can be continued with the other TRP 201, so that the fault tolerance of communication can be improved.

[0056] Also, in the UE 100 according to an embodiment, when there is a BFD resource set that does not provide a reference signal resource for detecting beam failure, the control unit 120 uses a predetermined reference signal resource instead of the reference signal resource to detect beam failure for the BFD resource set. For example, the control unit 120 identifies an active transmission configuration indication (TCI) state for PDCCH based on the CORESET pool index associated with the BFD resource set, and uses the reference signal resource indicated by the active TCI state as a predetermined reference signal resource to detect beam failure for the BFD resource set. As a result, when operating the cell 250 using a plurality of TRPs 201, it becomes possible to perform BFD·BFR for a TRP that does not have a reference signal resource provided. As a result, it becomes possible to reduce the signaling amount.

[0057] Also, in the UE100 according to one embodiment, the communication unit 110 receives an RRC message from the base station 200, which includes a radio link monitoring setting for setting radio link monitoring in units of cells 250 and a BFD setting list for setting N BFD resource sets. The control unit 120 detects RLF in units of cells 250 based on the radio link monitoring setting, and individually detects beam failures for each of the N BFD resource sets 521#0 and 521#1 based on the BFD setting list 520. Thereby, when operating the cell 250 using a plurality of TRPs 201, it becomes possible to appropriately coexist radio link monitoring in units of cells 250 and BFD in units of TRPs 201. As a result, two-stage failure detection and recovery by RLF detection / recovery in units of cells 250 and BFD / BFR in units of TRPs 201 can be realized, and thus the communication fault tolerance can be enhanced.

[0058] Also, in the UE100 according to one embodiment, when the control unit 120 detects beam failures for all of the N BFD resource sets, it determines whether to start a random access procedure for the cell 250 (specifically, the SpCell) based on the recovery status from the beam failures. For example, the control unit 120 that detects a beam failure for one BFD resource set starts a random access procedure for the cell 250 only when it detects beam failures for other BFD resource sets and no BFD resource set has recovered from the beam failure. Thereby, by reflecting the BFR status in the start condition of the random access procedure, communication can be continued as long as possible.

[0059] (Configuration of Base Station) Next, with reference to FIG. 7, the configuration of the base station 200 according to one embodiment will be described. The base station 200 includes N TRPs 201 (TRP201#0 and TRP201#1 in the example of FIG. 7), a communication unit 210, a network interface 220, and a control unit 230.

[0060] Each TRP201 includes a plurality of antennas and is configured to be beamforming capable. The TRP201 may be referred to as a panel or an antenna panel. The antenna converts a signal into a radio wave and radiates the radio wave into space. Also, the antenna receives a radio wave in space and converts the radio wave into a signal. Each TRP201 is distributed and arranged to form one cell 250. When the base station 200 manages a plurality of cells, the base station 200 may have N TRP201s for each cell.

[0061] The communication unit 210 receives, for example, a radio signal from the UE100 and transmits a radio signal to the UE100. The communication unit 210 has at least one transmission unit 211 and at least one reception unit 212. The transmission unit 211 and the reception unit 212 may be configured to include an RF circuit. The RF circuit performs analog processing of signals transmitted and received via the antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, and the like.

[0062] The network interface 220 transmits and receives signals to and from the network. The network interface 220 receives, for example, a signal from an adjacent base station connected via an Xn interface, which is a base station-to-base station interface, and transmits a signal to the adjacent base station. Also, the network interface 220 receives, for example, a signal from a core network device 300 connected via an NG interface and transmits a signal to the core network device 300.

[0063] The control unit 230 performs various controls in the base station 200. For example, the control unit 230 controls communication with the UE 100 via the communication unit 210. Also, for example, the control unit 230 controls communication with nodes (e.g., neighboring base stations, core network devices 300) via the network interface 220. The operations of the base station 200 described above and below may be operations under the control of the control unit 230. The control unit 230 may include at least one processor capable of executing a program and a memory for storing the program. The processor may execute the program to perform the operations of the control unit 230. The control unit 230 may also include a digital signal processor that performs digital processing of signals transmitted and received via an antenna and an RF circuit. The digital processing includes processing of the RAN protocol stack. Note that the memory stores the program executed by the processor, parameters related to the program, and data related to the program. All or part of the memory may be included in the processor.

[0064] The base station 200 according to one embodiment manages the cell 250 having N TRPs 201 and performs wireless communication with the UE 100. The communication unit 210 transmits to the UE 100 an RRC message that is a list for setting N BFD resource sets and includes a BFD setting list associated with a downlink BWP that is a part of the bandwidth of the cell 250. The BFD setting list is used for the UE 100 to individually detect beam failures for each of the N BFD resource sets in wireless communication using the downlink BWP. As a result, when operating the cell 250 using a plurality of TRPs 201, it becomes possible to set the BFD resource set for each TRP 201 in the RRC layer for the UE 100, so that the UE 100 can perform BFD·BFR for each TRP 201. As a result, even if a failure occurs in one TRP 201, the UE 100 can continue communication using the other TRP 201, thus enhancing the communication fault tolerance.

[0065] In addition, in the base station 200 according to an embodiment, the control unit 230 generates an RRC message including a radio link monitoring setting for setting radio link monitoring in units of cells 250 and a BFD setting list for setting N BFD resource sets. The communication unit 210 transmits the RRC message to the UE 100. The radio link monitoring setting includes information indicating a reference signal resource and information indicating the use of the reference signal resource. When the control unit 120 sets the BFD setting list in the UE 100, as the use of the reference signal resource in the radio link monitoring setting, detection of RLF is set without setting detection of beam failure. As a result, when operating the cell 250 using a plurality of TRPs 201, it becomes possible to appropriately coexist radio link monitoring in units of cells 250 and BFD in units of TRPs 201. As a result, since the UE 100 can realize two-stage failure detection and recovery by RLF detection and recovery in units of cells 250 and BFD and BFR in units of TRPs 201, it becomes possible to improve the fault tolerance of communication.

[0066] (Beam failure detection operation in units of TRP) Next, with reference to FIGS. 8 to 10, the BFD operation in units of the TRP 201 according to an embodiment will be described.

[0067] As shown in FIG. 8, in step S101, the base station 200 (communication unit 210) that manages the cell 250 having N TRPs 201 transmits an RRC message including a list for setting N BFD resource sets, the BFD setting list associated with the downlink BWP which is a part of the bandwidth of the cell 250, to the UE 100. The UE 100 (communication unit 110) receives the RRC message. The RRC message is an RRC message specific to the UE, and may be, for example, an RRC Reconfiguration message.

[0068] In this way, by associating the downlink BWP with the BFD configuration list, the BFD configuration list can be individually set for each downlink BWP. Therefore, an optimal BFD configuration list can be set according to the requirements for the downlink BWP.

[0069] In step S102, the UE 100 (control unit 120) individually detects beam failures for each of the N BFD resource sets based on the BFD configuration list set by the base station 200 in the wireless communication using the downlink BWP (beam monitoring). When the UE 100 (control unit 120) detects a beam failure for any of the BFD resource sets, it starts (triggers) a BFR procedure to recover from the detected beam failure.

[0070] As shown in FIG. 9, an RRC message according to an embodiment includes a BWP configuration (BWP- DownlinkDedicated ) 500 that sets a downlink BWP (specifically, a UE-specific downlink BWP) for the UE 100. The BWP configuration (BWP- DownlinkDedicated ) 500 is an information element that sets UE-specific parameters of the downlink BWP. The BWP configuration (BWP- DownlinkDedicated ) 500 can include a radio link monitoring configuration (RadioLinkMonitoringConfig) 510 that sets radio link monitoring in units of cells 250 and a BFD configuration list (BFD-ConfigurationList) 520 that sets N BFD resource sets. By including the BFD configuration list (BFD-ConfigurationList) 520 in the BWP configuration (BWP- DownlinkDedicated ) 500, the BFD configuration list (BFD-ConfigurationList) 520 can be set for each downlink BWP set for the UE 100. The UE 100 (control unit 120) is configured with the BWP configuration (BWP- DownlinkDedicated)When the downlink BWP set to 500 is used for wireless communication, that is, when the downlink BWP is the active BWP, beam monitoring is performed using the BFD configuration list (BFD-ConfigurationList) 520 associated with the downlink BWP.

[0071] Here, the BFD configuration list (BFD-ConfigurationList) 520 is an information element different from the radio link monitoring configuration (RadioLinkMonitoringConfig) 510. Specifically, the radio link monitoring configuration (RadioLinkMonitoringConfig) 510 is an information element defined in the existing technical specifications, and the BFD configuration list (BFD-ConfigurationList) 520 is a new information element not defined in the existing technical specifications. In this way, by introducing a new information element for BFD in the TRP201 unit, BFD in the TRP201 unit becomes possible and coexistence with the existing radio link monitoring becomes possible.

[0072] The BFD Configuration List 520 includes N BFD Resource Sets 521. For example, when N = 2, the BFD Configuration List 520 includes two BFD Resource Sets 521#0 and 521#1. Each BFD Resource Set 521 includes reference signal resources on the downlink. The reference signal resources are either SSB or CSI-RS. Here, the reference signal resources in the BFD Resource Set 521 are configured as reference signal resources for beam failure detection. In other words, the reference signal resources in the BFD Resource Set 521 are not configured as reference signal resources for RLF detection. Although details will be described later, in one embodiment, RLF detection is performed in units of cell 250 using the RadioLinkMonitoringConfig 510, and beam failure detection is performed in units of TRP201 using the BFD Configuration List 520.

[0073] In one embodiment, the N BFD Resource Sets 521 are associated with N TRP201s in a one-to-one manner. For example, the BFD Resource Set 521#0 is associated with the TRP201#0, and the BFD Resource Set 521#1 is associated with the TRP201#1. This enables BFD in units of TRP201.

[0074] Also, in one embodiment, each BFD Resource Set 521 includes one or more reference signal resources, and each of the one or more reference signal resources may be associated with a beam in a one-to-one manner. For example, as shown in FIG. 10, assume that TRP201#0 forms three beams #0 to #2, and TRP201#1 forms three beams #0 to #2. In such a case, the base station 200 (control unit 230) sets, by means of an RRC message, a BFD Resource Set 521#0 associated with TRP201#0 and a BFD Resource Set 521#1 associated with TRP201#1 for the UE100. Then, the base station 200 (control unit 230) sets, in the BFD Resource Set 521#0, three reference signal resources associated with the three beams #0 to #2 in a one-to-one manner. Also, the base station 200 (control unit 230) sets, in the BFD Resource Set 521#1, three reference signal resources associated with the three beams #0 to #2 in a one-to-one manner. Thereby, the UE100 (control unit 120) can detect beam failures for each TRP and for each beam.

[0075] Next, with reference to FIGS. 11 and 12, a specific example of an RRC message according to one embodiment will be described. FIGS. 11 and 12 show description examples in the technical specification (TS38.331) of the 3GPP RRC layer.

[0076] As shown in FIG. 11, the BWP Setup for setting a UE-specific downlink BWP for the UE100 DownlinkDedicated)500 can include a RadioLinkMonitoringConfig 510 for setting radio link monitoring in units of cell 250, and a BFD-ConfigurationList-r17 520 for setting N BFD resource sets. Here, "-r17" means an information element introduced in Release 17 of the 3GPP standard, but it may also be introduced after Release 18. In the following, the notation "-r17" will be omitted as appropriate.

[0077] Note that the BFD-ConfigurationList 520 set in the UE 100 can be released (Release) by a release instruction from the base station 200. For example, when the base station 200 changes from cell operation by a plurality of TRPs to cell operation by a single TRP, the base station 200 sends a release instruction to the UE 100 to release the BFD-ConfigurationList 520 set in the UE 100. The UE 100 releases the set BFD-ConfigurationList 520 in response to receiving the release instruction.

[0078] As shown in FIG. 12, the BFD-ConfigurationList 520 includes up to maxNrOfBFD-ResourceSets BFD Resource Sets 521.

[0079] Each BFD resource set (BFD Resource Set) 521 can include a BFD resource set identifier (bfd-ResourceSetId) that identifies the BFD resource set, an addition / modification list (bfd-ResourcesToAddModList) for adding / modifying one or more reference signal resources, a release list (bfd-ResourcesToReleaseList) for releasing one or more reference signal resources, a maximum count value of beam failure instance indicators from the physical layer (beamFailureInstanceMaxCountPerRS), and a timer value for detecting beam failure (beamFailureDetectionTimerPerRS).

[0080] The BFD resource set identifier (bfd-ResourceSetId) is an identifier that identifies the BFD resource set. The BFD resource set identifier (bfd-ResourceSetId) can be regarded as an identifier that identifies the corresponding TRP 201. The BFD resource set identifier (bfd-ResourceSetId) may be associated with the CORESET pool index (coresetPoolIndex) on a one-to-one basis. For example, "0" of the BFD resource set identifier (bfd-ResourceSetId) is associated with "0" of the CORESET pool index (coresetPoolIndex), and "1" of the BFD resource set identifier (bfd-ResourceSetId) is associated with "1" of the CORESET pool index (coresetPoolIndex).

[0081] The addition / modification list (bfd-ResourcesToAddModList) is a list of one or more reference signal resources (BeamFailureDetectionRS) to be added / modified. Specifically, the addition / modification list (bfd-ResourcesToAddModList) is a list of reference signals for detecting beam failure, and the limitations on reference signals that can be set by the network (base station 200) are specified in the technical specifications (for example, Table 5-1 of TS38.213). The network (base station 200) sets a maximum predetermined number of reference signal resources for each resource set. Although details will be described later, for each BFD resource set (BFD Resource Set) 521, if no reference signal is provided for BFD purposes, UE100 performs beam monitoring based on the active TCI state for the PDCCH associated with the corresponding CORESET pool index (coresetPoolIndex).

[0082] The reference signal resource (BeamFailureDetectionRS) to be set includes a reference signal resource identifier (beamFailureDetectionRS-Id) that identifies the reference signal resource, and a reference signal resource (detectionResource) that is the reference signal to be used by UE100 for BFD. The reference signal resource (detectionResource) is set with an SSB index (ssb-Index) or a CSI-RS index (csi-RS-Index).

[0083] The release list (bfd-ResourcesToReleaseList) is a list of reference signal resource identifiers (beamFailureDetectionRS-Id) of the reference signal resources to be released.

[0084] The maximum count value (beamFailureInstanceMaxCountPerRS) indicates the number of beam failure events for which the UE 100 triggers the BFR procedure (i.e., the number of beam failure instance indicators from the physical layer). For example, the value "n1" corresponds to one beam failure instance indicator, and the value "n2" corresponds to two beam failure instances. The timer value (beamFailureDetectionTimerPerRS) is a timer for BFD.

[0085] As described above, when the MAC layer of the UE 100 (control unit 120) is notified of beam failure events (beam failure instance indicators) from the physical layer a specified number of times within a specified time, it detects beam failure. Each BFD resource set (BFD Resource Set) 521 includes information for setting the specified time and the specified number of times independently of other BFD resource sets. The maximum count value (beamFailureInstanceMaxCountPerRS) indicating the specified number of times and the timer (beamFailureDetectionTimerPerRS) indicating the specified time are set for each BFD resource set (BFD Resource Set) 521, that is, for each TRP 201. This enables the conditions for detecting beam failure to be optimized for each TRP 201.

[0086] As shown in FIG. 13, in the UE 100, the physical (PHY) layer evaluates the radio link quality for each configured BFD resource set. The radio link quality may be the block error rate (BLER) of the PDCCH. For example, when the radio link quality of all reference signal resources in the BFD resource set is worse than a threshold, the physical layer periodically outputs a beam failure instance indicator to the MAC layer together with the BFD resource set identifier (bfd-ResourceSetId) of the BFD resource set. This period is set to the larger of, for example, the period of the minimum reference signal in the BFD resource set and 2 ms. Note that the BFD resource set identifier (bfd-ResourceSetId) may be used as the beam failure instance indicator.

[0087] Each BFD resource set (BFD Resource Set) 521 may include information for setting a threshold value to be compared with the wireless link quality measured at the physical layer independently of other BFD resource sets. When the wireless link quality in any BFD resource set (BFD Resource Set) 521 is worse than the threshold value associated with the BFD resource set (BFD Resource Set) 521, the physical layer notifies the MAC layer of a beam failure event (beam failure instance indicator) indicating the BFD resource set (BFD Resource Set) 521. Thereby, since the threshold value to be compared with the wireless link quality can be set individually for each BFD resource set (BFD Resource Set) 521, that is, for each TRP201, the condition for detecting a beam failure event can be optimized for each TRP201.

[0088] The MAC layer manages a timer and a counter for each configured BFD resource set and performs BFD·BFR for each BFD resource set. In FIG. 13, an example is shown in which there are two BFD resource sets and the MAC layer manages timer #0 and counter #0 for BFD resource set #0 and timer #1 and counter #1 for BFD resource set #1.

[0089] When the MAC layer receives a beam failure instance indicator together with a BFD resource set identifier (bfd-ResourceSetId) from the physical layer, it starts the timer corresponding to the BFD resource set identifier (bfd-ResourceSetId) and increments (i.e., adds 1) the counter corresponding to the BFD resource set identifier (bfd-ResourceSetId). When the count value of the counter becomes equal to or greater than a specified number of times before the timer expires, the MAC layer detects a beam failure for the BFD resource set corresponding to the counter. Details of such operations will be described later.

[0090] (Operation When a Reference Signal Resource for Beam Failure Detection is Not Provided) Next, with reference to FIGS. 14 to 16, the operation when a reference signal resource for BFD according to an embodiment is not provided will be described.

[0091] When it is necessary to individually set a reference signal resource for BFD (BeamFailureDetectionRS) for each TRP201 to the UE100, there is a concern that the signaling amount for BFD will increase. In one embodiment, a mechanism is realized that enables BFD·BFR also for a BFD resource set (BFD Resource Set) or a TRP201 for which a reference signal resource for BFD (BeamFailureDetectionRS) is not provided.

[0092] Here, beamforming in NR will be described. To perform the multi-beam operation of PDCCH, NR supports the TCI state setting, which is a higher-layer setting for beamforming, for each CORESET. When UE100 monitors the PDCCH search space associated with a CORESET, UE100 receives the PDCCH in the CORESET based on the TCI state setting configured for the CORESET. The beam information for PDCCH reception is implicitly recognized by UE100 through the quasi-co-location (QCL) relationship between the downlink reference signal (especially CSI-RS associated with a beam) and the demodulation reference signal (DMRS) of PDCCH. The DMRS of PDCCH is in a quasi-co-location relationship with the downlink reference signal by QCL-TypeA and / or QCL-TypeD. QCL-TypeA corresponds to channel statistical properties observed on the UE100 side, such as Doppler shift, Doppler spread, average delay, and delay spread. QCL-TypeD corresponds to the reception beam information on the UE100 side. In the case of QCL-TypeD, it may be assumed that the spatial parameters are the same for the downlink reference signal and the DMRS of PDCCH. When the DMRS of PDCCH is in a quasi-co-location relationship with the QCL-TypeD downlink reference signal, UE100 can receive the PDCCH using the same spatial reception parameters as those used for receiving the downlink reference signal in beamforming.

[0093] As shown in FIG. 14, the base station 200 can explicitly set the QCL relationship to the UE 100 by RRC signaling. The UE 100 has a plurality of TCI states set for the CORESET in order to receive the PDCCH. Each TCI state includes parameters regarding the downlink reference signal resource and the QCL relationship between the downlink reference signal regarding QCL-TypeA and QCL-TypeD and the DMRS ports of the PDCCH. The UE 100 uses only one beam to receive one PDCCH. Therefore, when a plurality of TCI states are set for the CORESET, the base station 200 activates one of the TCI states used for the CORESET using an activation command by MAC CE.

[0094] In one embodiment, the UE 100 that performs wireless communication with the base station 200 that manages the cell 250 having N TRPs 201 includes a communication unit 110 that receives from the base station 200 a BFD configuration list 520 that sets N BFD resource sets 521, and a control unit 120 that individually detects beam failures for each of the N BFD resource sets 521 based on the BFD configuration list 520. When there is a BFD resource set 521 that does not provide a reference signal resource (BeamFailureDetectionRS) for BFD, the control unit 120 uses a predetermined reference signal resource instead of the reference signal resource (BeamFailureDetectionRS) to detect beam failures for the BFD resource set 521.

[0095] As shown in FIG. 15, when there is a BFD resource set 521 (hereinafter referred to as BFD resource set 521#0) that does not provide a reference signal resource (BeamFailureDetectionRS), the UE 100 (control unit 120) determines an active TCI state for the PDCCH based on the CORESET pool index #0 associated with the BFD resource set 521#0, and uses the reference signal resource indicated by the active TCI state as a predetermined reference signal resource to detect beam failure for the BFD resource set 521#0. For example, the UE 100 (control unit 120) determines a downlink reference signal (e.g., CSI-RS) indicated by an active TCI state among the TCI states (i.e., TCI states for the PDCCH) set for the CORESET belonging to the CORESET pool index #0 as a reference signal resource for BFD. Thereby, even when the BFD resource set 521 does not provide a reference signal resource (BeamFailureDetectionRS), it becomes possible to perform BFD using the downlink reference signal indicated by the active TCI state for the PDCCH.

[0096] FIG. 16 shows a specific example of such an operation. Note that FIG. 16 shows an example described in the technical specification (TS38.213) of the physical layer of 3GPP.

[0097] As shown in FIG. 16, when the UE 100 is set in the bfd-ConfigurationList 520 for the BWP of the serving cell, a set q0 of periodic CSI-RS resource setting indexes is provided to each BFD resource set 521 identified by the bfd-ResourceSetId by the add / change list (bfd-ResourcesToAddModList).

[0098] If the UE 100 does not have the set q0 provided by the bfd-ResourcesToAddModList for the BFD Resource Set 521, the UE 100 determines to include in the set q0 a periodic CSI-RS resource setting index having the same value as the reference signal index of the downlink reference signal set indicated by the TCI state of each CORESET belonging to the CORESET pool index associated with the bfd-ResourceSetId used for monitoring the PDCCH. When there are two reference signal indexes in the TCI state, include in the set q0 the reference signal index for which the qcl-Type of the corresponding TCI state is set to "typeD".

[0099] (Coexistence with existing radio link monitoring) Next, with reference to FIGS. 17 to 19, coexistence with existing radio link monitoring will be described. Note that FIG. 19 shows an example described in the technical specification (TS38.331) of the 3GPP RRC layer.

[0100] As described above, existing radio link monitoring (i.e., detection of RLF and detection of beam failure) is performed in units of cell 250, not in units of TRP201.

[0101] In one embodiment, for the detection of beam failure, it is performed in units of TRP201, not in units of cell 250. Regarding the detection of RLF in units of cell 250 in existing radio link monitoring, since it can coexist with BFD in units of TRP201, the detection of RLF in units of cell 250 can be set in the UE 100. On the other hand, since the detection of beam failure in units of cell 250 in existing radio link monitoring conflicts with the detection of beam failure in units of TRP201, the detection of beam failure in units of cell 250 cannot be set in the UE 100.

[0102] As shown in FIG. 17, in step S301, the base station 200 (control unit 230) that manages the cell 250 having N TRPs 201 generates an RRC message including a radio link monitoring configuration (RadioLinkMonitoringConfig) for setting radio link monitoring in units of the cell 250 and a BFD configuration list (BFD-ConfigurationList) for setting N BFD resource sets (BFD Resource Set). The base station 200 (communication unit 210) transmits the generated RRC message to the UE 100. The UE 100 (communication unit 110) receives the RRC message.

[0103] In step S302, the UE 100 (control unit 120) performs radio link monitoring for detecting RLF in units of the cell 250 based on the radio link monitoring configuration (RadioLinkMonitoringConfig). Also, the UE 100 (control unit 120) performs beam monitoring for individually detecting beam failure for each of the N BFD resource sets based on the BFD configuration list (BFD-ConfigurationList). That is, the UE 100 (control unit 120) performs beam monitoring in units of the TRP 201.

[0104] When the UE 100 (control unit 120) detects a beam failure for any of the BFD resource sets by beam monitoring based on the BFD configuration list (BFD-ConfigurationList), it performs processing for recovering from the detected beam failure, for example, transmission processing of BFR MAC CE. Also, when the UE 100 (control unit 120) detects RLF for the cell 250 by radio link monitoring based on the radio link monitoring configuration (RadioLinkMonitoringConfig), it performs processing for recovering from the detected RLF, for example, RRC re-establishment processing. By such two-stage failure detection and recovery, it becomes possible to enhance the fault tolerance of communication.

[0105] As shown in FIGS. 18 and 19, in the RRC message, in the BWP setting (BWP- DownlinkDedicated ), the RadioLinkMonitoringConfig 510 included in 500 contains, as setting information, a reference signal resource for radio link monitoring (RS for RLM) 511 and the purpose 512 of the reference signal resource (RS for RLM) 511. When the base station 200 (control unit 230) sets the BFD-ConfigurationList 520 for the UE 100, as the purpose 512, it sets the detection of rlf without setting the detection of beam failure.

[0106] Specifically, in terms of the technical specification, as the purpose 512 of the reference signal resource (RS for RLM) 511, there are three options: "beam failure", "rlf", and "both". However, when setting the BFD-ConfigurationList 520 for the UE 100, a limitation is defined such that only rlf can be set as the purpose 512 of the reference signal resource (RS for RLM) 511. Therefore, when the BFD-ConfigurationList 520 is set, the UE 100 (control unit 120) does not detect beam failure based on the RadioLinkMonitoringConfig 510, but instead detects rlf in units of cell 250. This makes it possible to appropriately coexist the existing radio link monitoring and the detection of beam failure in units of TRP201.

[0107] Even when the BFD-ConfigurationList 520 is set, due to unexpected errors, it is also conceivable that the base station 200 sets beam failure or both as the purpose 512 of the reference signal resource (RS for RLM) 511. Therefore, when the BFD-ConfigurationList 520 is set and beam failure or both are set as the purpose 512 of the reference signal resource (RS for RLM) 511, the UE 100 (control unit 120) may read the purpose 512 of the reference signal resource (RS for RLM) 511 as RLF (rlf).

[0108] (Beam Failure Detection and Recovery Operation in SpCell) Next, with reference to FIGS. 20 to 22, the BFD and BFR operations in the SpCell according to an embodiment will be described. Here, it is assumed that the UE 100 performs wireless communication with a cell 250 (specifically, SpCell) having two TRPs 201#0 and #1. However, one cell 250 may be configured by three or more TRPs 201. Also, it is assumed that the BFD resource set 521 for each TRP 201 has already been set in the UE 100.

[0109] Prior to the description of the BFD and BFR operations in the SpCell according to an embodiment, a comparative example will be described with reference to FIG. 20.

[0110] In step S401, the UE 100 (control unit 120) detects beam failure for the BFD resource set 521#0 associated with the TRP 201#0 and starts (triggers) a BFR that involves transmitting a BFR MAC CE.

[0111] In step S402, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#1 associated with the TRP 201#1. In response to detecting a beam failure for both BFD resource sets 521#0 and #1 (i.e., both TRP 201#0 and #1), the UE 100 (control unit 120) determines to start a random access procedure for the cell 250 (SpCell).

[0112] In step S403, for the BFD resource set 521#0 associated with the TRP 201#0, the BFR is successfully completed in the UE 100 (control unit 120), and the UE 100 is in a state where data transmission and reception with the TRP 201#0 are possible.

[0113] In step S404, the UE 100 (control unit 120) starts a random access procedure for the cell 250 (SpCell). During the execution of the random access procedure, the UE 100 (control unit 120) is unable to transmit and receive data with the cell 250 (SpCell).

[0114] In step S405, even though the UE 100 is in a state where data transmission and reception with the TRP 201#0 are possible, due to the random access procedure, the UE 100 becomes unable to communicate (transmit and receive data) with the cell 250 (SpCell).

[0115] Thus, even when the UE 100 detects a beam failure for the TRP 201#0 and #1, if the UE 100 has recovered from the beam failure for the TRP 201#0, communication with the cell 250 (SpCell) is possible. However, if the random access procedure is started (step S404) without considering the situation of whether recovery from the beam failure has occurred, data transmission and reception are not possible during the execution of the random access procedure, resulting in communication interruption.

[0116] Therefore, when the UE 100 (control unit 120) according to one embodiment detects beam failures for all of the N BFD resource sets 521 associated with the N TRPs 201, it determines whether to start a random access procedure for the cell 250 (SpCell) based on the recovery status from the beam failures. For example, the UE 100 (control unit 120) starts a random access procedure for the cell 250 (SpCell) only when it detects a beam failure for one of the N BFD resource sets 521, detects beam failures for the other BFD resource sets 521, and has not recovered from the beam failures for any of the BFD resource sets 521. This makes it possible to suppress the communication with the cell 250 (SpCell) from becoming unavailable due to the random access procedure.

[0117] Referring to FIG. 21, an example operation 1 of BFD·BFR in the SpCell according to one embodiment will be described.

[0118] In step S431, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#0 associated with the TRP 201#0 and starts a BFR involving the transmission of a BFR MAC CE.

[0119] In step S432, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#1 associated with the TRP 201#1.

[0120] In step S433, the BFR for the BFD resource set 521#0 associated with the TRP 201#0 is successfully completed in the UE 100 (control unit 120), and the data transmission / reception with the TRP 201#0 becomes possible.

[0121] In step S434, the UE 100 (control unit 120) determines not to start a random access procedure for cell 250 (SpCell) in response to the successful completion of the BFR for the BFD resource set 521#0 associated with the TRP 201#0.

[0122] In step S435, the UE 100 (control unit 120) communicates (transmits and receives data) with the cell 250 (SpCell) in a state where communication with the cell 250 (SpCell) is possible. Note that the UE 100 (control unit 120) may start a BFR involving the transmission of a BFR MAC CE for the BFD resource set 521#1 associated with the TRP 201#1.

[0123] As described above, in one embodiment, the UE 100 (control unit 120) that has detected a beam failure for the BFD resource set 521#1 determines not to start a random access procedure for the cell 250 (SpCell) when it has detected a beam failure for the BFD resource set 521#0 and has recovered from the beam failure for the BFD resource set 521#0. This makes it possible to suppress the communication with the cell 250 (SpCell) from becoming unavailable due to the random access procedure. Further, the UE 100 (control unit 120) may start a BFR procedure (i.e., the transmission process of the BFR MAC CE) for recovering from the beam failure for the BFD resource set 521#1 while determining not to start a random access procedure for the cell 250 (SpCell). This makes it possible to attempt to recover communication with the TRP 201#1.

[0124] With reference to FIG. 22, a BFD·BFR operation example 2 in the SpCell according to one embodiment will be described.

[0125] In step S451, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#0 associated with the TRP 201#0 and starts a BFR involving the transmission of a BFR MAC CE.

[0126] In step S452, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#1 associated with the TRP 201#1, and starts a BFR involving the transmission of a BFR MAC CE.

[0127] In step S453, the UE 100 (control unit 120) determines that the BFR for the BFD resource set 521#0 associated with the TRP 201#0 is incomplete (unsuccessful).

[0128] In step S454, the UE 100 (control unit 120) determines that the BFR for the BFD resource set 521#1 associated with the TRP 201#1 is incomplete (unsuccessful).

[0129] In step S455, in response to detecting a beam failure for all of the N BFD resource sets 521 and that none of the BFD resource sets 521 have recovered from the beam failure, the UE 100 (control unit 120) starts a random access procedure for the cell 250 (SpCell).

[0130] (Specific Example of MAC Entity Operation in User Equipment) Next, with reference to FIGS. 23 and 24, a specific example of the operation of the MAC entity (i.e., an entity of the MAC layer) in the UE 100 according to an embodiment will be described. The operation of the MAC entity may be part of the operation of the control unit 120 of the UE 100. FIGS. 23 and 24 show operation examples in the case described in the 3GPP MAC layer technical specification (TS38.321).

[0131] As shown in FIG. 23, when one or more BFD resource sets are configured for each serving cell for which BFD is configured (step S501), the MAC entity performs the operations of steps S502 to S521.

[0132] When the MAC entity receives a beam failure instance indicator from a lower layer (i.e., the physical layer) for a BFD resource set 521 identified by a BFD resource set identifier (bfd-ResourceSetId) (step S502), it performs the operations of steps S503 to S510.

[0133] In step S503, the MAC entity starts or restarts a timer (beamFailureDetectionTimerPerRS) set for the BFD resource set 521 identified by the BFD resource set identifier (bfd-ResourceSetId).

[0134] In step S504, the MAC entity increments, i.e., adds "1", a count value (BFI_COUNTER_BFD_RS) set for the BFD resource set 521 identified by the BFD resource set identifier (bfd-ResourceSetId). Note that the initial value of the count value (BFI_COUNTER_BFD_RS) is "0".

[0135] When the count value (BFI_COUNTER_BFD_RS) becomes greater than or equal to a maximum count value (beamFailureInstanceMaxCountPerRS) set for the BFD resource set 521 identified by the BFD resource set identifier (bfd-ResourceSetId), the MAC entity performs the operations of steps S506 to S510.

[0136] Here, when the serving cell is the SpCell (step S506), and a beam failure is detected in another BFD Resource Set 521 and has not been recovered yet by the beam recovery procedure (step S507), in step S508, the MAC entity starts a random access procedure on the SpCell for beam recovery.

[0137] On the other hand, when the serving cell is not the SpCell, or when another BFD Resource Set 521 has been recovered by the beam recovery procedure (step S509), the MAC entity triggers a BFR for the BFD Resource Set 521 in step S510.

[0138] When the corresponding timer (beamFailureDetectionTimerPerRS) expires for each BFD Resource Set 521 (step S511), the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero in step S513.

[0139] Also, when any of the timer (beamFailureDetectionTimerPerRS), maximum count value (beamFailureInstanceMaxCountPerRS), and reference signal resource for BFD (reference signal resource used for beam failure detection) associated with the BFD Resource Set 521 is reset by the upper layer (i.e., the RRC layer) (step S512), the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero in step S513.

[0140] The MAC entity executes the operations of steps S515 to S517 when the serving cell is the SpCell and the random access procedure for the BFR of the SpCell is successfully completed (step S514).

[0141] In step S515, the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero.

[0142] In step S516, the MAC entity stops the timer (beamFailureDetectionTimerPerRS) if the timer (beamFailureDetectionTimerPerRS) is set.

[0143] In step S517, the MAC entity determines that the BFR has been successfully completed.

[0144] On the other hand, when the serving cell is the SCell and the MAC entity receives a PDCCH addressed to the C-RNTI indicating an uplink grant for a new transmission for the HARQ process used for transmitting the BFR MAC MAC including the BFR information of the BFD resource set 521 (step S518), or when the SCell is deactivated (step S519), the MAC entity executes the operations of steps S520 and S521. Note that the BFR MAC MAC includes a normal BFR MAC CE and a Truncated BFR MAC CE.

[0145] In step S520, the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero.

[0146] In step S521, the MAC entity determines that the BFR has been successfully completed, and cancels all the BFRs triggered for the BFD resource set 521.

[0147] As shown in FIG. 24, if the MAC entity determines that at least one BFR has been triggered and not cancelled for the SCell or the BFD resource set 521 for which the candidate beam evaluation is being performed according to the requirements specified in TS38.133 in the BFR procedure, the operations in steps S532 to S537 are executed.

[0148] If the uplink shared channel (UL-SCH) resource is available for new transmission and the UL-SCH resource can accommodate the BFR MAC CE and its sub-header as a result of logical channel prioritization (LCP) (step S532), in step S533, the MAC entity instructs the multiplexing and assembly procedure to generate the BFR MAC CE.

[0149] On the other hand, if the UL-SCH resource is available for new transmission and the UL-SCH resource can accommodate the Truncated BFR MAC CE and its sub-header as a result of LCP (step S534), in step S535, the MAC entity instructs the multiplexing and assembly procedure to generate the Truncated BFR MAC CE.

[0150] On the other hand, if neither of the conditions in steps S532 and S534 is satisfied (step S536), in step S537, the MAC entity triggers a scheduling request (SR) for the BFR of the SCell for each SCell or BFD resource set 521 for which the candidate beam evaluation is being performed according to the requirements specified in TS38.133 and the BFR has been triggered and not cancelled.

[0151] When a MAC entity transmits a MAC PDU that includes a BFR MAC CE or a Truncated BFR MAC CE containing beam failure information for a SCell or a BFD Resource Set 521, it cancels all BFRS triggered for the SCell or the BFD Resource Set 521 (step S538).

[0152] In this way, a user equipment 100 that performs wireless communication with a base station 200 that manages a cell 250 having N transmit / receive points 201 includes a communication unit 110 that receives from the base station 200 a message for setting N BFD Resource Sets 521, and a control unit 120 that individually detects beam failure for each of the N BFD Resource Sets 521. The control unit 120 triggers a BFR for one BFD Resource Set in which beam failure is detected. The communication unit 110 transmits an SR requesting a resource for transmitting a BFR MAC MAC including information on the detected beam failure or the BFR MAC CE. When a MAC protocol data unit PDU including the BFR MAC MAC is transmitted, the control unit 120 cancels all BFRS triggered for the one BFD Resource Set. This makes it possible to appropriately perform BFR in units of TRP201.

[0153] In UE100, the control unit 120 detects a beam failure in response to the physical layer in UE100 notifying a beam failure event a specified number of times within a specified time for each of the N BFD resource sets (BFD Resource Set) 521. As described above, each of the N BFD resource sets (BFD Resource Set) 521 includes information for independently setting a timer (beamFailureDetectionTimerPerRS) indicating the specified time and a maximum count value (beamFailureInstanceMaxCountPerRS) indicating the specified number of times, independent of other BFD resource sets.

[0154] In UE100, when the control unit 120 is notified of a beam failure event from the physical layer for the one BFD resource set (BFD Resource Set) 521, the control unit 120 starts or restarts the timer (beamFailureDetectionTimerPerRS) associated with the one BFD resource set (BFD Resource Set) 521 and increments the count value (BFI_COUNTER_BFD_RS) associated with the one BFD resource set (BFD Resource Set) 521. This enables appropriate BFD to be performed in units of TRP201.

[0155] In UE100, when the timer (beamFailureDetectionTimerPerRS) associated with the one BFD resource set (BFD Resource Set) 521 expires, the control unit 120 resets the count value (BFI_COUNTER_BFD_RS) associated with the one BFD resource set (BFD Resource Set) 521. This enables appropriate BFD to be performed in units of TRP201.

[0156] In UE100, when any of the timer (beamFailureDetectionTimerPerRS), maximum count value (beamFailureInstanceMaxCountPerRS), and reference signal resource for BFD (reference signal resource used for beam failure detection) associated with the one BFD resource set (BFD Resource Set) 521 is reset by the base station 200, the count value (BFI_COUNTER_BFD_RS) associated with the one BFD resource set (BFD Resource Set) 521 is reset. This enables appropriate BFD for each TRP201 unit.

[0157] In UE100, after transmitting the BFR MAC, the communication unit 110 receives a PDCCH indicating an uplink grant for the HARQ process used for transmitting the BFR MAC for the one BFD resource set (BFD Resource Set) 521 when the cell 250 is an SCell. In response to receiving the PDCCH, the control unit 120 resets the count value (BFI_COUNTER_BFD_RS) associated with the one BFD resource set (BFD Resource Set) 521, considers the BFR to be successful, and cancels all BFRs triggered for the one BFD resource set (BFD Resource Set) 521. This enables appropriate BFD for each TRP201 unit.

[0158] (Other Embodiments) The operation sequences (and operation flows) in the above embodiments do not necessarily have to be executed in chronological order along the order described in the flowcharts or sequence diagrams. For example, the steps in the operations may be executed in an order different from the order described as the flowchart or sequence diagram, or may be executed in parallel. Also, some of the steps in the operations may be deleted, and additional steps may be added to the process. Further, the operation sequences (and operation flows) in the above embodiments may be implemented separately and independently, or may be implemented by combining two or more operation sequences (and operation flows). For example, some steps of one operation flow may be added to another operation flow, or some steps of one operation flow may be replaced with some steps of another operation flow.

[0159] In the above embodiment, the base station 200 may include a plurality of units. The plurality of units may include a first unit that hosts the higher layer included in the protocol stack and a second unit that hosts the lower layer included in the protocol stack. The higher layer may include the RRC layer, the SDAP layer, and the PDCP layer, and the lower layer may include the RLC layer, the MAC layer, and the PHY layer. The first unit may be a CU (central unit), and the second unit may be a DU (Distributed Unit). The plurality of units may include a third unit that performs processing below the PHY layer. The second unit may perform processing above the PHY layer. The third unit may be an RU (Radio Unit). The base station 200 may be one of the plurality of units and may be connected to other units among the plurality of units. Also, the base station 200 may be an IAB (Integrated Access and Backhaul) donor or an IAB node.

[0160] In the above embodiments, the mobile communication system 1 has been described by taking a mobile communication system based on NR as an example. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a system compliant with any TS of LTE or other generation systems (e.g., the sixth generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA user plane and control plane protocol terminations towards the UE 100 in LTE. The mobile communication system 1 may be a system compliant with a TS of a standard other than the 3GPP standard.

[0161] A program may be provided that causes a computer to execute each process performed by the UE 100 or the base station 200. The program may be recorded on a computer-readable medium. By using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Also, circuits for executing each process performed by the UE 100 or the base station 200 may be integrated, and at least a part of the UE 100 or the base station 200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0162] In the above embodiments, "transmit" may mean performing processing of at least one layer in the protocol stack used for transmission, or may mean physically transmitting a signal wirelessly or via wire. Alternatively, "transmit" may mean a combination of performing the processing of the at least one layer and physically transmitting a signal wirelessly or via wire. Similarly, "receive" may mean performing processing of at least one layer in the protocol stack used for reception, or may mean physically receiving a signal wirelessly or via wire. Alternatively, "receive" may mean a combination of performing the processing of the at least one layer and physically receiving a signal wirelessly or via wire. Similarly, "obtain / acquire" may mean obtaining information from stored information, may mean obtaining information from information received from other nodes, or may mean obtaining the information by generating the information. Similarly, "include" and "comprise" do not mean including only the listed items, and may include only the listed items or may include additional items in addition to the listed items. Similarly, in the present disclosure, "or" does not mean an exclusive disjunction but means a disjunction.

[0163] As described above, the embodiments have been described in detail with reference to the drawings, but the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the gist.

Description of Reference Numerals

[0164] 1: Mobile communication system 10: Network 100: UE (User Equipment) 110: Communication unit 111: Transmission unit 112: Reception unit 120: Control unit 200: Base station 201: TRP (Transmission / Reception Point) 210: Communication Unit 211: Transmission Unit 212: Reception Unit 220: Network Interface 230: Control Unit 250: Cell 300: Core Network Device 520: BFD Setting List 521: BFD Resource Set

Claims

1. A communication device (100) that performs wireless communication with a base station (200) that manages a cell (250) having N (N≥2) transmission / reception points (201#0, 201#1), a communication unit (110) that receives from the base station (200) a radio resource control (RRC) message including BWP-DownlinkDedicated that includes settings of three or more reference signal resources including a reference signal resource for wireless link monitoring and reference signal resources for each of N beam obstruction detections; performs wireless link monitoring for the reference signal resource for the wireless link monitoring based on the setting of the wireless link monitoring, and a control unit (120) that individually detects beam obstruction for the reference signal resources for each of the N beam obstruction detections based on the setting for each of the N beam obstruction detections, wherein the BWP-DownlinkDedicated is used to set communication device-specific parameters for the downlink bandwidth part of the cell Communication device (100).

2. The BWP-DownlinkDedicated includes the setting of the wireless link monitoring and the setting for each of the N beam obstruction detections The communication device according to claim 1.

3. When the reference signal resources for each of the N beam obstruction detections are set, the use of the reference signal resource for the wireless link monitoring is set only for wireless link failure The communication device according to claim 1 or 2.

4. The setting for each of the N beam obstruction detections includes an addition / change list for adding and / or changing one or more reference signal resources, a release list for releasing one or more reference signal resources, a maximum count value of a beam obstruction instance indicator from the physical layer, and a timer value for detecting the beam obstruction The communication device (100) according to any one of claims 1 to 3.

5. A base station (200) that manages a cell (250) having N (N≥2) transmission / reception points (201#0, 201#1) and performs wireless communication with a communication device (100), A communication unit (210) that transmits to the communication device (100) a radio resource control (RRC) message including a BWP-DownlinkDedicated including settings of three or more reference signal resources including a reference signal resource for wireless link monitoring and reference signal resources for each of N beam obstruction detections. The reference signal resource for the wireless link monitoring is used to perform wireless link monitoring based on the settings of the wireless link monitoring. The reference signal resource for each of the N beam obstruction detections is used to individually detect beam obstructions based on the settings for each of the N beam obstruction detections. Base station (200).

6. The BWP-DownlinkDedicated includes the settings of the wireless link monitoring and the settings for each of the N beam obstruction detections. The base station according to claim 5.

7. When setting the reference signal resource for each of the N beam obstruction detections, set the use of the reference signal resource for the wireless link monitoring only for wireless link failures. The base station according to claim 5 or 6.

8. The settings for each of the N beam obstruction detections include an addition / change list for adding and / or changing one or more reference signal resources, a release list for releasing one or more reference signal resources, a maximum count value of a beam obstruction instance indicator from the physical layer, and a timer value for detecting the beam obstruction. The base station (200) according to any one of claims 5 to 7.

9. A communication method executed by a communication device (100) that performs wireless communication with a base station (200) that manages a cell (250) having N (N≥2) transmission / reception points (201#0, 201#1), Receiving from the base station (200) a radio resource control (RRC) message including a BWP-DownlinkDedicated including settings of three or more reference signal resources including a reference signal resource for wireless link monitoring and reference signal resources for each of N beam obstruction detections. Based on the setting of wireless link monitoring, perform wireless link monitoring for the reference signal resource for the wireless link monitoring, and based on the setting for each of the N beam obstruction detections, individually detect beam obstruction for the reference signal resource for each of the N beam obstruction detections. The BWP-DownlinkDedicated is used to set communication device-specific parameters for the downlink bandwidth portion of the cell. Communication method. **Claim 10** The BWP-DownlinkDedicated includes the setting of the wireless link monitoring and the setting for each of the N beam obstruction detections. The communication method according to claim 9. **Claim 11** When the reference signal resource for each of the N beam obstruction detections is set, the use of the reference signal resource for the wireless link monitoring is set only for wireless link failure. The communication method according to claim 9 or 10. **Claim 12** The setting for each of the N beam obstruction detections includes an addition / change list for adding and / or changing one or more reference signal resources, a release list for releasing one or more reference signal resources, a maximum count value of beam obstruction instance indicators from the physical layer, and a timer value for detecting the beam obstruction. The communication method according to any one of claims 9 to 11.

Images