Communication device, base station, and communication method

Abstract

To provide user equipment and a communication method that are used in a mobile communication system capable of suppressing interruption of communication even when beam failures are detected for a plurality of TRPs when a cell is operated with a plurality of TRPs.SOLUTION: In a mobile communication system including UE, a base station, and a core network device, 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 message 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. When beam failures are detected for all of the N beam failure detection resource sets, the control unit 120 determines whether to start a random access procedure for the cell based on a state of recovery from the beam failures.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a user equipment and a communication method for use in a mobile communication system. [Background technology]

[0002] In recent years, the 3GPP (3rd Generation Partnership Project), a standardization project for mobile communication systems, has been considering the introduction of multiple transmission / reception point (TRP) transmission as an extension of MIMO (multi-input multi-output) (see Non-Patent Document 1). In such multiple TRP transmission, a single cell is formed from multiple distributed TRPs, and efficient transmission can be achieved by simultaneously using these multiple TRPs to perform wireless communication with a user device. Note that a TRP is also sometimes called a panel or an antenna panel.

[0003] It has been proposed that beam fault detection and recovery, which was previously performed on a cell-by-cell basis, be performed on a TRP-by-TRP basis when multiple TRPs are used in cell operation (see Non-Patent Documents 2 and 3). Specifically, a TRP-specific counter / timer is introduced to detect beam faults, and the user equipment counts beam fault events (beam fault instance indicators) notified from the physical layer to the medium access control (MAC) layer using a counter. If the count value reaches a specified number of times before the timer expires, beam fault is detected.

[0004] In addition, Non-Patent Document 2 describes a beam failure recovery method in which, when a special cell (SpCell) is operated using two TRPs and a user equipment detects beam failure for both TRPs, a random access procedure for the cell is initiated (triggered). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] 3GPP contribution RP-202803 “Summary for WI: Enhancement on MIMO for NR” [Non-patent document 2] 3GPP contribution R2-2105870 “Beam failure with mTRP” [Non-patent document 3] 3GPP contribution R2-2105341 “Discussion on RAN2 specification impacts of TRP-specific BFR” Summary of the Invention [Problem to be solved by the invention]

[0006] When operating a cell with multiple TRPs, even if the user equipment detects beam failure for all TRPs, it is possible to communicate with the cell if the beam failure has been recovered for any of the TRPs.

[0007] However, in the beam failure recovery method described in Non-Patent Document 2, the random access procedure is started without considering whether or not the beam failure has been recovered. Since data cannot be sent or received during the execution of the random access procedure, there is a problem that communication is interrupted.

[0008] Therefore, an object of the present invention is to provide a user equipment and a communication method that can suppress communication interruptions even when beam failures are detected for multiple TRPs when a cell is operated using multiple TRPs. [Means for solving the problem]

[0009] A user device according to a first aspect is a user 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), and includes a communication unit (110) that receives a message from the base station (200) for setting N beam failure detection resource sets (521#0, 521#1), and a control unit (120) that individually detects beam failure for each of the N beam failure detection resource sets (521#0, 521#1), and when the control unit (120) detects the beam failure for all of the N beam failure detection resource sets (521#0, 521#1), it decides whether to initiate a random access procedure for the cell (250) based on the status of recovery from the beam failure.

[0010] A communication method according to the second aspect is a communication method executed by a user 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), and includes the steps of receiving a message from the base station (200) that sets N beam failure detection resource sets (521#0, 521#1), individually detecting beam failure for each of the N beam failure detection resource sets (521#0, 521#1), and, when the beam failure is detected for all of the N beam failure detection resource sets (521#0, 521#1), deciding whether to initiate a random access procedure for the cell (250) based on the status of recovery from the beam failure. [Effects of the Invention]

[0011] According to one aspect of the present invention, it is possible to provide a user equipment and a communication method that can suppress communication interruptions even when beam failures are detected for multiple TRPs during cell operation using multiple TRPs. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a protocol stack in a mobile communication system according to an embodiment. [Figure 3] FIG. 10 is a diagram illustrating an example of operation when a beam failure is detected in a secondary cell (SCell) during cell operation using a single TRP. [Figure 4] FIG. 10 is a diagram illustrating an example of operation when a beam failure is detected in a special cell (SpCell) during cell operation using a single TRP. [Figure 5] FIG. 1 is a diagram illustrating an overview of multi-TRP transmission according to an embodiment. [Figure 6] FIG. 1 is a diagram illustrating a configuration of a UE according to an embodiment. [Figure 7] FIG. 2 is a diagram illustrating a configuration of a base station according to an embodiment. [Figure 8] FIG. 1 illustrates BFD operation per TRP according to one embodiment. [Figure 9] FIG. 2 is a diagram illustrating an example of the configuration of an RRC message according to an embodiment. [Figure 10] FIG. 1 illustrates BFD operation per TRP according to one embodiment. [Figure 11] FIG. 10 is a diagram illustrating a configuration example of a BWP setting (BWP-DownlinkDedecated) according to an embodiment. [Figure 12] A figure showing an example configuration of a BFD configuration list (BFD-ConfigurationList) according to one embodiment. [Figure 13] FIG. 1 illustrates operations within a UE according to an embodiment. [Figure 14] A diagram for explaining the operation when a reference signal resource for BFD is not provided in one embodiment. [Figure 15] A diagram for explaining the operation when a reference signal resource for BFD is not provided in one embodiment. [Figure 16] A diagram for explaining the operation when a reference signal resource for BFD is not provided in one embodiment. [Figure 17] FIG. 10 is a diagram illustrating coexistence with existing radio link monitoring according to an embodiment. [Figure 18] FIG. 2 is a diagram illustrating an example of the configuration of an RRC message according to an embodiment. [Figure 19] FIG. 10 is a diagram illustrating an example of the configuration of a radio link monitoring configuration (RadioLinkMonitoringConfig) according to an embodiment. [Figure 20] FIG. 10 is a diagram illustrating a comparative example of BFD / BFR operations in an SpCell according to an embodiment. [Figure 21] FIG. 10 is a diagram illustrating BFD-BFR operations in an SpCell according to an embodiment. [Figure 22] FIG. 10 is a diagram illustrating BFD-BFR operations in an SpCell according to an embodiment. [Figure 23] A diagram showing a specific example of the operation of a MAC entity in a UE according to one embodiment. [Figure 24] A diagram showing a specific example of the operation of a MAC entity in a UE according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0014] (Mobile communication system) First, a configuration of a mobile communication system 1 according to an embodiment will be described with reference to Fig. 1. The mobile communication system 1 is, for example, a system that complies with the 3GPP Technical Specification (TS). In the following, the mobile communication system 1 will be described using as an example a 5th Generation System (5GS) of the 3GPP standard, that is, a mobile communication system based on NR (New Radio).

[0015] The mobile communication system 1 includes a network 10 and user equipment (UE) 100 that communicates with the network 10. The network 10 includes a next generation radio access network (NG-RAN) 20 that is a 5G radio access network, and a 5G core network (5GC) 30 that is a 5G core network.

[0016] The UE 100 is a device used by a user. The UE 100 is a mobile device, such as a mobile phone terminal such as a smartphone, a tablet terminal, a laptop PC, a communication module, or a communication card. The UE 100 may be a vehicle (e.g., a car, a train, etc.) or a device provided therein. The UE 100 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided therein. The UE 100 may be a sensor or a device provided therein. Note that the UE 100 may be called by other names 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.

[0017] The NG-RAN 20 includes multiple 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 refer to wireless communication resources or to a communication target of the UE 100. Each base station 200 can perform wireless communication with the UE 100 located in its own cell. The base station 200 communicates with the UE 100 using a RAN protocol stack. The base station 200 provides NR user plane and control plane protocol termination for the UE 100 and is connected to the 5GC 30 via an NG interface. Such an NR base station 200 is sometimes referred to as a gNodeB (gNB).

[0018] The 5GC 30 includes a core network device 300. The core network device 300 includes, for example, an Access and Mobility Management Function (AMF) and / or a User Plane Function (UPF). The AMF performs mobility management for the UE 100. The UPF provides functions specialized for user plane processing. The AMF and the UPF are connected to the base station 200 via an NG interface.

[0019] Next, with reference to FIG. 2, an example of the configuration of a protocol stack in the mobile communication system 1 according to the embodiment will be described.

[0020] The protocol for the wireless section between UE 100 and base station 200 includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a radio resource control (RRC) layer.

[0021] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the base station 200 via a physical channel.

[0022] A physical channel consists of multiple OFDM symbols in the time domain and multiple subcarriers in the frequency domain. One subframe consists of multiple OFDM symbols in the time domain. A resource block is a resource allocation unit and consists of multiple OFDM symbols and multiple subcarriers. A frame can be configured for 10 ms and can include 10 subframes, each of which is 1 ms long. A subframe can include the number of slots corresponding to the subcarrier spacing.

[0023] Among the physical channels, the Physical Downlink Control Channel (PDCCH) plays a central role for purposes such as downlink scheduling assignment, uplink scheduling grant, and transmit power control.

[0024] In NR, the UE 100 can use a bandwidth narrower than the system bandwidth (i.e., the cell bandwidth). The base station 200 configures the UE 100 with a bandwidth portion (BWP) consisting of consecutive PRBs. The UE 100 transmits and receives data and control signals in the active BWP. For example, up to four BWPs can be configured for the UE 100. Each BWP may have a different subcarrier spacing or may overlap in frequency. When multiple BWPs are configured for the UE 100, the base station 200 can specify which BWP to activate by controlling the downlink. This allows the base station 200 to dynamically adjust the UE bandwidth according to the amount of data traffic of the UE 100, etc., and can reduce UE power consumption.

[0025] For example, the base station 200 can configure up to three control resource sets (CORESETs) for each of up to four BWPs on the serving cell. A CORESET is a radio resource for control information to be received by the UE 100. Up to 12 CORESETs can be configured for the UE 100 on the serving cell. Each CORESET has an index of 0 to 11. For example, a CORESET consists of six resource blocks (PRBs) and one, two, or three consecutive OFDM symbols in the time domain.

[0026] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of base station 200 via a transport channel. The MAC layer of base station 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to UE 100.

[0027] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the base station 200 via logical channels.

[0028] The PDCP layer performs header compression / decompression and encryption / decryption.

[0029] An SDAP (Service Data Adaptation Protocol) layer may be provided above the PDCP layer, which maps IP flows, which are units for QoS control by the core network, to radio bearers, which are units for QoS control by the AS (Access Stratum).

[0030] The RRC layer controls logical channels, transport channels, and physical channels in response to the establishment, re-establishment, and release of radio bearers. RRC signaling for various settings is transmitted between the RRC layer of the UE 100 and the RRC layer of the base station 200. layer and the RRC of the base station 200 layer When there is an RRC connection between the UE 100 and the RRC layer and the RRC of the base station 200 layer When there is no RRC connection between the UE 100 and the RRC layer and the RRC of the base station 200 layer The UE 100 is in an RRC inactive state when the RRC connection between the UE 100 and the

[0031] The NAS layer located above the RRC layer performs session management and mobility management for 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 and the like in addition to a radio interface protocol.

[0032] (Beam Failure Detection and Recovery Overview) Next, an outline of beam failure detection and restoration will be described with reference to FIGS.

[0033] Compared to LTE (Long Term Evolution), a fourth-generation radio access technology, NR is capable of wideband transmission using high-frequency bands such as millimeter waves or terahertz waves. NR achieves high beam gain by utilizing highly directional beamforming using multiple antennas between the base station 200 and the UE 100 to compensate for radio wave attenuation in such high-frequency bands. NR employs beam control technology to establish and maintain beam pairs between the base station 200 and the UE 100. Beam failure detection and recovery technology is one such beam control technology.

[0034] Regarding beam failure detection (BFD), the base station 200 configures the UE 100 with a downlink reference signal resource for detecting a beam failure. Such a reference signal resource is either an SSB (SS / PBCH Block) or a 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. Alternatively, 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 a Master Information Block (MIB). The CSI-RS is a reference signal transmitted so that the UE 100 can measure the state of the wireless channel.

[0035] If the SSB is within the downlink BWP band, the UE 100 can detect beam failure using the SSB. If the SSB is not within the downlink BWP band, the UE 100 can detect beam failure using the CSI-RS set by the base station 200.

[0036] In the UE 100, the MAC layer counts beam failure events (beam failure instance indicators) notified from the physical layer using a counter, and detects (declares) beam failure if the count value reaches or exceeds a specified number of times before the timer expires.

[0037] FIG. 3 shows an example of operation when a beam failure is detected in a secondary cell (SCell) during cell operation using a single TRP.

[0038] 3 shows an example in which base station 200 manages SCell 250B configured by one TRP 201. Base station 200 (TRP 201) forms a total of three beams, beam #0 to beam #2. UE 100 detects beam failure in SCell 250B during communication using beam #0.

[0039] In this case, UE 100 triggers beam failure recovery (BFR) by starting transmission of a beam failure recovery MAC control element (BFR MAC CE). Here, UE 100 selects a beam suitable for the SCell (e.g., beam #1) and indicates the selected beam information along with information about the beam failure by the BFR MAC CE. When UE 100 receives a PDCCH indicating an uplink grant for a new transmission of the HARQ process used to transmit the BFR MAC CE, recovery from beam failure of SCell 250B is completed.

[0040] 4 shows an example of operation when a beam failure is detected in a special cell (SpCell) during cell operation using a single TRP. The SpCell may also be referred to as a primary cell (PCell).

[0041] 4 shows an example in which base station 200 manages SpCell 250A configured by one TRP 201. Base station 200 (TRP 201) forms a total of three beams, beam #0 to beam #2. UE 100 detects beam failure in SpCell 250A during communication using beam #0.

[0042] In this case, UE 100 triggers BFR by initiating a random access procedure to SpCell 250A. Here, UE 100 selects an appropriate beam (e.g., beam #1) to perform BFR. When the random access procedure is completed, BFR is completed.

[0043] (Overview of multiple TRP transmission) Next, an overview of multiple TRP (multi-TRP) transmission according to the embodiment will be described with reference to FIG.

[0044] In multiple TRP transmission, the base station 200 configures one cell 250 with multiple TRPs 201 that are distributed. In FIG. 5, two TRPs (TRP201#0 and TRP201#0) are illustrated as multiple TRPs 201. However, the base station 200 may configure one cell 250 with three or more TRPs 201. The following mainly describes the case where one cell 250 is configured with two TRPs 201.

[0045] In multiple TRP transmission, different data can be transmitted from multiple TRPs 201 for spatial multiplexing to increase the data rate, or the same data can be transmitted from multiple TRPs 201 for diversity to improve the reliability and robustness of the transmission.

[0046] There are two types of multiple-TRP transmission: a single PDCCH scheme and a multiple-PDCCH scheme. In a single-PDCCH-based scheme, one TRP 201 transmits a PDCCH (downlink control information (DCI)) and schedules a set of PDSCH layers for each TRP 201. In contrast, in a multiple-PDCCH scheme, each TRP 201 schedules its own PDSCH individually. In the following, we will mainly consider the multiple-PDCCH scheme.

[0047] In a scheme using multiple PDCCHs, it is possible to use a different CORESET for each TRP 201. Specifically, there is a one-to-one correspondence between the TRP 201 and a CORESET pool index. When the base station 200 configures a CORESET in the UE 100, the base station 200 notifies the UE 100 of the CORESET pool index to which the CORESET belongs. Therefore, the CORESET pool index can be considered to be an index that identifies the TRP 201.

[0048] In the embodiment, when a cell is operated using such multiple TRPs 201, it is assumed that BFD / BFR, which was conventionally performed on a cell 250 basis, is performed on a TRP 201 basis. Specifically, a counter / timer specific to the TRP 201 is introduced to detect beam failure, and in the UE 100, a counter counts beam failure instance indicators notified from the physical layer to the MAC layer, and if the count value reaches or exceeds a specified number of times before the timer expires, beam failure is detected.

[0049] To perform BFD / BFR on a TRP 201 basis, it is considered necessary to configure a beam fault detection resource set (hereinafter referred to as a "BFD resource set") including reference signal resources for detecting beam faults in the UE 100 individually for each TRP 201. However, existing 3GPP technical specifications do not provide a mechanism for configuring a BFD resource set for each TRP 201 in the UE 100. In one embodiment, BFD / BFR can be performed on a TRP 201 basis.

[0050] Furthermore, if it is required to configure the reference signal resource for BFD in the UE 100 individually for each TRP 201, there is a concern that the amount of signaling for BFD-BFR may increase. In one embodiment, a mechanism is realized that enables BFD-BFR even for a BFD resource set / TRP 201 for which a reference signal resource for BFD is not provided.

[0051] Furthermore, existing radio link monitoring (i.e., detection of radio link failure (RLF) and detection of beam failure) is performed on a cell 250 basis, not on a TRP 201 basis. In one embodiment, it is possible to appropriately coexist such existing technology with BFD on a TRP 201 basis.

[0052] Furthermore, even if the UE 100 detects beam failures for all TRPs 201, communication (data transmission / reception) is possible if any of the TRPs 201 has recovered from the beam failure. If a random access procedure for recovery from the beam failure is started without considering whether or not the beam failure has been recovered, data transmission / reception is not possible during the execution of the random access procedure, resulting in a communication interruption. In one embodiment, such communication interruptions can be suppressed.

[0053] (Configuration of user device) Next, a configuration of the UE 100 according to an embodiment will be described with reference to Fig. 6. The UE 100 includes a communication unit 110 and a control unit 120.

[0054] The communication unit 110 performs wireless communication with the base station 200 by transmitting and receiving radio 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 multiple antennas and RF circuits. The antenna converts a signal into radio waves and radiates the radio waves into space. The antenna also receives radio waves in space and converts the radio waves into a signal. The RF circuit performs analog processing of the signal transmitted and received via the antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, etc.

[0055] The control unit 120 performs various controls in the UE 100. The control unit 120 controls communication with the base station 200 via the communication unit 110. The operations of the UE 100 described above and below may be controlled by the control unit 120. The control unit 120 may include at least one processor capable of executing a program and a memory that stores the program. The processor may execute the program to perform the operations of the control unit 120. The control unit 120 may 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 processing of a RAN protocol stack. The memory stores programs executed by the processor, parameters related to the programs, and data related to the programs. The memory may include at least one of a read-only memory (ROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a random access memory (RAM), and a flash memory. All or a part of the memory may be included in the processor.

[0056] In an embodiment of the UE 100, the communication unit 110 performs wireless communication with the base station 200 that manages the cell 250 having N (N≧2) TRPs 201. The communication unit 110 receives an RRC message from the base station 200, which includes a beam failure detection configuration list (hereinafter referred to as a "BFD configuration list") that configures N BFD resource sets and is associated with a downlink BWP that is a portion of the bandwidth of the cell 250. The control unit 120 individually detects beam failure for each of the N BFD resource sets based on the BFD configuration list during wireless communication using the downlink BWP. This makes it possible to configure a BFD resource set for each TRP 201 in the UE 100 in the RRC layer when the cell 250 is operated using multiple TRPs 201, thereby enabling BFD / BFR to be performed on a TRP 201-by-TRP 201 basis. As a result, even if a failure occurs in one TRP 201, communication can be continued using the other TRP 201, thereby improving communication fault tolerance.

[0057] Furthermore, in the UE 100 according to one embodiment, when there is a BFD resource set that does not provide a reference signal resource for detecting a beam failure, the control unit 120 detects a beam failure for the BFD resource set by using a predetermined reference signal resource instead of the reference signal resource. For example, the control unit 120 identifies an active Transmission Configuration Indicator (TCI) state for the PDCCH based on a CORESET pool index associated with the BFD resource set, and detects a beam failure for the BFD resource set by using the reference signal resource indicated by the active TCI state as the predetermined reference signal resource. This makes it possible to perform BFD / BFR even for TRPs that do not provide reference signal resources when a cell 250 using multiple TRPs 201 is operated. As a result, it is possible to reduce the amount of signaling.

[0058] Furthermore, in the UE 100 according to one embodiment, the communication unit 110 receives from the base station 200 an RRC message including a radio link monitoring configuration for configuring radio link monitoring for each cell 250 and a BFD configuration list for configuring N BFD resource sets. The control unit 120 detects RLF for each cell 250 based on the radio link monitoring configuration, and individually detects beam failure for each of the N BFD resource sets 521#0 and 521#1 based on the BFD configuration list 520. This enables appropriate coexistence of radio link monitoring for each cell 250 and BFD for each TRP 201 when the cell 250 is operated using multiple TRPs 201. As a result, two-stage fault detection and recovery can be realized: RLF detection and recovery for each cell 250, and BFD and BFR for each TRP 201, thereby improving the fault tolerance of communications.

[0059] Furthermore, in the UE 100 according to one embodiment, when the control unit 120 detects beam failures for all N BFD resource sets, the control unit 120 determines whether to start a random access procedure for the cell 250 (specifically, the SpCell) based on the status of recovery from the beam failure. For example, the control unit 120, which has detected beam failure for one BFD resource set, starts the random access procedure for the cell 250 only when it detects beam failures for other BFD resource sets and none of the BFD resource sets have recovered from the beam failure. In this way, the BFR status is reflected in the conditions for starting the random access procedure, thereby making it possible to continue communication as long as possible.

[0060] (Base station configuration) Next, a configuration of a base station 200 according to an embodiment will be described with reference to Fig. 7. The base station 200 includes N TRPs 201 (TRP 201#0 and TRP 201#1 in the example of Fig. 7), a communication unit 210, a network interface 220, and a control unit 230.

[0061] Each TRP 201 includes multiple antennas and is configured to be capable of beamforming. The TRP 201 may also be referred to as a panel or antenna panel. The antenna converts signals into radio waves and radiates the radio waves into space. The antenna also receives radio waves in space and converts the radio waves into signals. The TRPs 201 are distributed and form one cell 250. When the base station 200 manages multiple cells, the base station 200 may have N TRPs 201 for each cell.

[0062] The communication unit 210 receives a radio signal from the UE 100 and transmits the radio signal to the UE 100, for example. 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 a signal transmitted and received via an antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, etc.

[0063] The network interface 220 transmits and receives signals to and from the network. For example, the network interface 220 receives signals from adjacent base stations connected via an Xn interface, which is an interface between base stations, and transmits signals to the adjacent base stations. The network interface 220 also receives signals from the core network device 300 connected via an NG interface, and transmits signals to the core network device 300.

[0064] The control unit 230 performs various controls in the base station 200. The control unit 230 controls, for example, communication with the UE 100 via the communication unit 210. The control unit 230 also controls, for example, communication with a node (e.g., a neighboring base station, the core network device 300) via the network interface 220. The operations of the base station 200 described above and below may be operations controlled by the control unit 230. The control unit 230 may include at least one processor capable of executing a program and a memory that stores the program. The processor may execute the program to perform the operations of the control unit 230. The control unit 230 may 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 processing of a protocol stack of the RAN. The memory stores the program executed by the processor, parameters related to the program, and data related to the program. All or a part of the memory may be included in the processor.

[0065] A base station 200 according to one embodiment manages a cell 250 having N TRPs 201 and performs wireless communication with a UE 100. The communication unit 210 transmits to the UE 100 an RRC message including a BFD configuration list, which is a list for configuring N BFD resource sets and is associated with a downlink BWP, which is a portion of the bandwidth of the cell 250. The BFD configuration list is used by the UE 100 to individually detect beam failures for each of the N BFD resource sets in wireless communication using the downlink BWP. This allows the UE 100 to configure a BFD resource set for each TRP 201 in the RRC layer when the cell 250 is operated using multiple TRPs 201, thereby enabling the UE 100 to perform BFD / BFR on a TRP 201-by-TRP 201 basis. As a result, even if a failure occurs in one TRP 201, the UE 100 can continue communication using the other TRP 201, thereby improving communication fault tolerance.

[0066] Furthermore, in the base station 200 according to one embodiment, the control unit 230 generates an RRC message including a radio link monitoring configuration for configuring radio link monitoring on a cell-by-cell basis and a BFD configuration list for configuring N BFD resource sets. The communication unit 210 transmits the RRC message to the UE 100. The radio link monitoring configuration includes information indicating reference signal resources and information indicating the use of the reference signal resources. When configuring the BFD configuration list for the UE 100, the control unit 120 configures RLF detection without configuring beam fault detection as the use of the reference signal resources in the radio link monitoring configuration. This enables appropriate coexistence of radio link monitoring on a cell-by-cell basis and BFD on a TRP 201-by-TRP 201 basis when operating a cell 250 using multiple TRPs 201. As a result, the UE 100 can achieve two-stage fault detection and recovery using RLF detection and recovery on a cell-by-cell basis and BFD and BFR on a TRP 201-by-TRP 201 basis, thereby improving the fault tolerance of communications.

[0067] (Beam obstruction detection operation per TRP) Next, with reference to Figures 8 to 10, a BFD operation in units of TRP 201 according to one embodiment will be described.

[0068] As shown in Fig. 8, in step S101, the base station 200 (communication unit 210) managing the cell 250 having N TRPs 201 transmits to the UE 100 an RRC message including a BFD configuration list that is a list for configuring N BFD resource sets and that is associated with a downlink BWP that is a part of the bandwidth of the cell 250. The UE 100 (communication unit 110) receives the RRC message. Note that the RRC message is a UE-specific RRC message, and may be, for example, an RRC Reconfiguration message.

[0069] By associating a downlink BWP with a BFD configuration list in this way, a BFD configuration list can be configured individually for each downlink BWP, making it possible to configure an optimal BFD configuration list according to the requirements of the downlink BWP.

[0070] In step S102, in the wireless communication using the downlink BWP, the UE 100 (control unit 120) individually detects a beam failure for each of the N BFD resource sets (beam monitoring) based on the BFD configuration list configured by the base station 200. When the UE 100 (control unit 120) detects a beam failure for any of the BFD resource sets, the UE 100 (control unit 120) starts (triggers) a BFR procedure for recovering from the detected beam failure.

[0071] As shown in FIG. 9 , the RRC message according to one embodiment includes a BWP configuration (BWP-) that configures a downlink BWP (specifically, a UE-specific downlink BWP) in the UE 100. DownlinkDedicated ) 500 included. BWP setting (BWP- DownlinkDedicated ) 500 is an information element for configuring UE-specific parameters of the downlink BWP. DownlinkDedicated The BWP configuration (BWP-) 500 can include a radio link monitoring configuration (RadioLinkMonitoringConfig) 510 for configuring radio link monitoring in units of cells 250, and a BFD configuration list (BFD-ConfigurationList) 520 for configuring N BFD resource sets. DownlinkDedicated By including the BFD configuration list (BFD-ConfigurationList) 520 in the BFD configuration list (BFD-ConfigurationList) 500, it becomes possible to set the BFD configuration list (BFD-ConfigurationList) 520 for each downlink BWP to be set in the UE 100. DownlinkDedicatedWhen the downlink BWP configured in BFD-ConfigurationList 500 is used for wireless communication, i.e., when the downlink BWP is an active BWP, beam monitoring is performed using the BFD configuration list (BFD-ConfigurationList) 520 associated with the downlink BWP.

[0072] 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 existing technical specifications, and the BFD configuration list (BFD-ConfigurationList) 520 is a new information element not defined in existing technical specifications. In this way, by introducing a new information element for BFD on a TRP201 basis, BFD on a TRP201 basis becomes possible, and coexistence with existing radio link monitoring becomes possible.

[0073] The BFD configuration list (BFD-ConfigurationList) 520 includes N BFD resource sets (BFD Resource Sets) 521. For example, if N=2, the BFD configuration list (BFD-ConfigurationList) 520 includes two BFD resource sets (BFD Resource Sets) 521#0 and 521#1. Each BFD resource set (BFD Resource Set) 521 includes a reference signal resource in the downlink. The reference signal resource is either SSB or CSI-RS. Here, the reference signal resource in the BFD resource set (BFD Resource Set) 521 is configured as a reference signal resource intended for detecting a beam failure. In other words, the reference signal resource in the BFD resource set (BFD Resource Set) 521 is not configured as a reference signal resource intended for detecting RLF. Details will be described later, but in one embodiment, RLF detection is performed on a cell 250 basis using a radio link monitoring configuration (RadioLinkMonitoringConfig) 510, and beam failure detection is performed on a TRP 201 basis using a BFD configuration list (BFD-ConfigurationList) 520.

[0074] In one embodiment, N BFD resource sets 521 are associated one-to-one with N TRPs 201. For example, BFD resource set 521#0 is associated with TRP 201#0, and BFD resource set 521#1 is associated with TRP 201#1. This enables BFD on a TRP 201 basis.

[0075] Furthermore, in one embodiment, each BFD resource set (BFD Resource Set) 521 may include one or more reference signal resources, and each of the one or more reference signal resources may be associated one-to-one with a beam. For example, as shown in FIG. 10, it is assumed 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) configures, by an RRC message, a BFD resource set (BFD Resource Set) 521#0 associated with TRP201#0 and a BFD resource set (BFD Resource Set) 521#1 associated with TRP201#1 in the UE 100. Then, the base station 200 (control unit 230) configures three reference signal resources in the BFD resource set (BFD Resource Set) 521#0, which are associated one-to-one with the three beams #0 to #2. Furthermore, the base station 200 (control unit 230) configures three reference signal resources in one-to-one correspondence with the three beams #0 to #2 in the BFD resource set 521#1, which enables the UE 100 (control unit 120) to detect beam failure for each TRP 201 and for each beam.

[0076] Next, a specific example of an RRC message according to an embodiment will be described with reference to Fig. 11 and Fig. 12. Fig. 11 and Fig. 12 show an example of description in the technical specification (TS38.331) of the RRC layer of 3GPP.

[0077] As shown in FIG. 11, a BWP setting (BWP- DownlinkDedicated) 500 can include a radio link monitoring configuration (RadioLinkMonitoringConfig) 510 that configures radio link monitoring in units of cells 250, and a BFD configuration list (BFD-ConfigurationList-r17) 520 that configures N BFD resource sets. Here, "-r17" means that this is an information element introduced in Release 17 of the 3GPP standard, but may be introduced in Release 18 or later. In the following, the notation "-r17" will be omitted as appropriate.

[0078] The BFD configuration list (BFD-ConfigurationList) 520 configured in the UE 100 can be released by a release instruction from the base station 200. For example, when changing from cell operation using multiple TRPs to cell operation using a single TRP, the base station 200 transmits to the UE 100 a release instruction to release the BFD configuration list (BFD-ConfigurationList) 520 configured in the UE 100. In response to receiving the release instruction, the UE 100 releases the configured BFD configuration list (BFD-ConfigurationList) 520.

[0079] As shown in FIG. 12, the BFD configuration list (BFD-ConfigurationList) 520 includes up to maxNrOfBFD-ResourceSets BFD resource sets (BFD Resource Sets) 521.

[0080] Each BFD resource set (BFD Resource Set) 521 may include a BFD resource set identifier (bfd-ResourceSetId) that identifies the BFD resource set, an add / modify list (bfd-ResourcesToAddModList) that adds / modifies one or more reference signal resources, a release list (bfd-ResourcesToReleaseList) that releases 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).

[0081] The BFD resource set identifier (bfd-ResourceSetId) is an identifier that identifies a BFD resource set. The BFD resource set identifier (bfd-ResourceSetId) can be considered to be an identifier that identifies the corresponding TRP 201. The BFD resource set identifier (bfd-ResourceSetId) may be in one-to-one correspondence with the CORESET pool index (coresetPoolIndex). For example, "0" in the BFD resource set identifier (bfd-ResourceSetId) corresponds to "0" in the CORESET pool index (coresetPoolIndex), and "1" in the BFD resource set identifier (bfd-ResourceSetId) corresponds to "1" in the CORESET pool index (coresetPoolIndex).

[0082] The add / modify list (bfd-ResourcesToAddModList) is a list of one or more reference signal resources (BeamFailureDetectionRS) to be added or modified. Specifically, the add / modify list (bfd-ResourcesToAddModList) is a list of reference signals for detecting beam failure, and the restrictions on reference signals that the network (base station 200) can configure are specified in technical specifications (e.g., Table 5-1 of TS38.213). The network (base station 200) configures a maximum predetermined number of reference signal resources for each resource set. As will be described in detail later, for each BFD resource set (BFD Resource Set) 521, if no reference signal is provided for BFD purposes, the UE 100 performs beam monitoring based on the active TCI state for the PDCCH associated with the corresponding CORESET pool index (coresetPoolIndex).

[0083] The configured reference signal resource (BeamFailureDetectionRS) includes a reference signal resource identifier (beamFailureDetectionRS-Id) that identifies the reference signal resource, and a reference signal resource (detectionResource) that is a reference signal to be used for BFD by the UE 100. An SSB index (ssb-Index) or a CSI-RS index (csi-RS-Index) is configured in the reference signal resource (detectionResource).

[0084] The release list (bfd-ResourcesToReleaseList) is a list of reference signal resource identifiers (beamFailureDetectionRS-Id) of reference signal resources to be released.

[0085] The maximum count value (beamFailureInstanceMaxCountPerRS) indicates the number of beam failure events (i.e., the number of beam failure instance indicators from the physical layer) that the UE 100 will trigger the BFR procedure. 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.

[0086] As described above, the MAC layer of the UE 100 (control unit 120) detects a beam failure when a beam failure event (beam failure instance indicator) is notified from the physical layer a specified number of times within a specified time. Each BFD Resource Set 521 includes information for setting the specified time and the specified number of times independently from other BFD Resource Sets. A maximum count value (beamFailureInstanceMaxCountPerRS) indicating the specified number of times and a timer (beamFailureDetectionTimerPerRS) indicating the specified time are set for each BFD Resource Set 521, i.e., for each TRP 201. This makes it possible to optimize the conditions for detecting beam failure for each TRP 201.

[0087] 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 a block error rate (BLER) of the PDCCH. For example, if the radio link quality of all reference signal resources in a 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, for example, the smallest reference signal period in the BFD resource set or 2 ms, whichever is larger. Note that the BFD resource set identifier (bfd-ResourceSetId) may be used as the beam failure instance indicator.

[0088] Each BFD Resource Set 521 may include information for setting a threshold value to be compared with the radio link quality measured at the physical layer, independently of other BFD Resource Sets. When the radio link quality in any BFD Resource Set 521 is worse than the threshold value associated with the 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 521. This allows the threshold value to be compared with the radio link quality to be individually set for each BFD Resource Set 521, i.e., for each TRP 201, making it possible to optimize the conditions for detecting a beam failure event for each TRP 201.

[0089] The MAC layer manages the timers and counters for each configured BFD resource set and performs BFD-BFR for each BFD resource set. Figure 13 shows an example 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.

[0090] When the MAC layer receives a beam failure instance indicator together with the BFD resource set identifier (bfd-ResourceSetId) from the physical layer, it starts a timer corresponding to the BFD resource set identifier (bfd-ResourceSetId) and increments (i.e., adds 1) a counter corresponding to the BFD resource set identifier (bfd-ResourceSetId). If the count value of the counter reaches or exceeds 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 this operation will be described later.

[0091] (Operation when reference signal resources for beam failure detection are not provided) Next, with reference to Figures 14 to 16, an operation in a case where a reference signal resource for BFD according to one embodiment is not provided will be described.

[0092] There is a concern that the amount of signaling for BFD may increase if it is required to configure the reference signal resource for BFD (BeamFailureDetectionRS) in the UE 100 individually for each TRP 201. In one embodiment, a mechanism is realized that enables BFD-BFR even for a BFD resource set (BFD Resource Set) or a TRP 201 for which the reference signal resource for BFD (BeamFailureDetectionRS) is not provided.

[0093] Here, beamforming in NR will be described. To perform multi-beam operation of PDCCH, NR supports TCI state configuration, which is a higher layer configuration for beamforming, for each CORESET. When UE 100 monitors a PDCCH search space associated with CORESET, UE 100 receives PDCCH in CORESET based on the TCI state configuration configured for CORESET. Beam information for PDCCH reception is implicitly recognized by UE 100 by a quasi-co-location (QCL) relationship between a downlink reference signal (particularly, a CSI-RS associated with a beam) and a demodulation reference signal (DMRS) of PDCCH. The DMRS of PDCCH has a quasi-co-location relationship with the downlink reference signal by QCL-Type A and / or QCL-Type D. QCL-Type A corresponds to channel statistical properties observed on the UE 100 side, such as Doppler shift, Doppler spread, average delay, and delay spread. QCL-Type D corresponds to received beam information on the UE 100 side. In the case of QCL-TypeD, it may be assumed that the spatial parameters of the downlink reference signal and the DMRS of the PDCCH are the same. When the DMRS of the PDCCH is in a quasi-co-located relationship with the downlink reference signal of QCL-TypeD, the UE 100 can receive the PDCCH using the same spatial reception parameters that it uses to receive the downlink reference signal by beamforming.

[0094] As shown in FIG. 14, base station 200 can explicitly configure a QCL relationship for UE 100 by RRC signaling. Multiple TCI states are configured for UE 100 for CORESET to receive the PDCCH. Each TCI state includes parameters related to downlink reference signal resources and a QCL relationship between the downlink reference signal and the DMRS port of the PDCCH for QCL-Type A and QCL-Type D. UE 100 uses only one beam to receive one PDCCH. Therefore, when multiple TCI states are configured for CORESET, base station 200 activates one of the TCI states used for CORESET using an activation command by the MAC CE.

[0095] In one embodiment, a UE 100 that performs wireless communication with a base station 200 that manages a cell 250 having N TRPs 201 includes a communication unit 110 that receives a BFD configuration list (BFD-ConfigurationList) 520 that configures N BFD resource sets (BFD Resource Sets) 521 from the base station 200, and a control unit 120 that individually detects a beam failure for each of the N BFD resource sets (BFD Resource Sets) 521 based on the BFD configuration list 520. When there is a BFD resource set (BFD Resource Set) 521 that does not provide a reference signal resource (BeamFailureDetectionRS) for BFD, the control unit 120 detects a beam failure for the BFD resource set (BFD Resource Set) 521 by using a predetermined reference signal resource instead of the reference signal resource (BeamFailureDetectionRS).

[0096] As shown in Fig. 15, when there is a BFD resource set (BFD Resource Set) 521 (here, BFD resource set 521#0) that does not provide a reference signal resource (BeamFailureDetectionRS), the UE 100 (control unit 120) identifies an active TCI state for PDCCH based on a CORESET pool index #0 associated with the BFD resource set (BFD Resource Set) 521#0, and detects a beam failure for the BFD resource set (BFD Resource Set) 521#0 by using the reference signal resource indicated by the active TCI state as a predetermined reference signal resource. 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 set for a CORESET belonging to CORESET pool index #0 (i.e., TCI states for PDCCH), as the reference signal resource for BFD (BeamFailureDetectionRS). This makes it possible to perform BFD using the downlink reference signal indicated by the active TCI state for the PDCCH even if the BFD resource set (BFD Resource Set) 521 does not provide a reference signal resource (BeamFailureDetectionRS).

[0097] A specific example of such an operation is shown in Fig. 16. Note that Fig. 16 shows an example of description in the 3GPP physical layer technical specification (TS38.213).

[0098] As shown in Figure 16, when the UE 100 is configured with a BFD configuration list (bfd-ConfigurationList) 520 for the BWP of the serving cell, the add-modify list (bfd-ResourcesToAddModList) provides a set of periodic CSI-RS resource configuration indexes q0 for each BFD resource set (BFD Resource Set) 521 identified by a BFD resource set identifier (bfd-ResourceSetId).

[0099] If the set q0 is not provided by the addition and modification list (bfd-ResourcesToAddModList) for the BFD resource set (BFD Resource Set) 521, the UE 100 determines to include in set q0 a periodic CSI-RS resource configuration 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 resource set identifier (bfd-ResourceSetId) used for monitoring the PDCCH. If the TCI state has two reference signal indices, the reference signal index whose qcl-Type of the corresponding TCI state is set to "typeD" is included in set q0.

[0100] (Coexistence with existing wireless link monitoring) Next, coexistence with existing radio link monitoring will be described with reference to Figures 17 to 19. Note that Figure 19 shows an example of description in the 3GPP RRC layer technical specification (TS38.331).

[0101] As described above, existing radio link monitoring (i.e., RLF detection and beam obstruction detection) is performed on a cell 250 basis, not on a TRP 201 basis.

[0102] In one embodiment, beam failure detection is performed on a TRP 201 basis, rather than on a cell 250 basis. RLF detection on a cell 250 basis in existing radio link monitoring can coexist with BFD on a TRP 201 basis, and therefore RLF detection on a cell 250 basis can be configured in UE 100. On the other hand, beam failure detection on a cell 250 basis in existing radio link monitoring conflicts with beam failure detection on a TRP 201 basis, and therefore beam failure detection on a cell 250 basis cannot be configured in UE 100.

[0103] 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) that sets radio link monitoring for each cell 250, and a BFD configuration list (BFD-ConfigurationList) that sets N BFD resource sets (BFD Resource Sets). 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.

[0104] In step S302, UE 100 (control unit 120) performs radio link monitoring to detect RLF on a cell 250 basis based on a radio link monitoring configuration (RadioLinkMonitoringConfig). Also, UE 100 (control unit 120) performs beam monitoring to individually detect beam failure for each of N BFD resource sets based on a BFD configuration list (BFD-ConfigurationList). That is, UE 100 (control unit 120) performs beam monitoring on a TRP 201 basis.

[0105] When UE100 (control unit 120) detects a beam failure for any BFD resource set through beam monitoring based on the BFD configuration list (BFD-ConfigurationList), it performs processing to recover from the detected beam failure, for example, BFR MAC CE transmission processing. Also, when UE100 (control unit 120) detects an RLF for cell 250 through radio link monitoring based on the radio link monitoring configuration (RadioLinkMonitoringConfig), it performs processing to recover from the detected RLF, for example, RRC re-establishment processing. Such two-stage failure detection and recovery can improve the fault tolerance of communications.

[0106] As shown in Figures 18 and 19, in the RRC message, BWP setup (BWP- DownlinkDedicated Radio link monitoring configuration (RadioLinkMonitoringConfig) 510 included in BFD-ConfigurationList 500 includes, as configuration information, reference signal resources for radio link monitoring (RS for RLM) 511 and a purpose 512 of the reference signal resources (RS for RLM) 511. When configuring BFD configuration list (BFD-ConfigurationList) 520 in UE 100, base station 200 (control unit 230) does not configure beam failure detection but configures RLF (rlf) detection as purpose 512.

[0107] Specifically, in the technical specifications, there are three options for the purpose 512 of the reference signal resource (RS for RLM) 511: "beam failure," "RLF (rlf)," and "both." However, when the BFD configuration list (BFD-ConfigurationList) 520 is configured in the UE 100, a restriction is specified that only RLF (rlf) can be configured as the purpose 512 of the reference signal resource (RS for RLM) 511. Therefore, when the BFD configuration list (BFD-ConfigurationList) 520 is configured, the UE 100 (control unit 120) detects RLF on a cell 250 basis, without detecting beam failure based on the radio link monitoring configuration (RadioLinkMonitoringConfig) 510. This enables the existing radio link monitoring and the detection of beam failure on a TRP 201 basis to coexist appropriately.

[0108] Note that even when the BFD configuration list (BFD-ConfigurationList) 520 is configured, it is possible that, due to an unexpected error, the base station 200 may set beam failure or both as the purpose 512 of the reference signal resource (RS for RLM) 511. Therefore, when the BFD configuration list (BFD-ConfigurationList) 520 is configured 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 interpret the purpose 512 of the reference signal resource (RS for RLM) 511 as RLF (rlf).

[0109] (Beam fault detection and recovery operations in SpCell) Next, BFD-BFR operation in an SpCell according to one embodiment will be described with reference to Fig. 20 to Fig. 22. Here, it is assumed that the UE 100 performs radio communication with a cell 250 (specifically, an SpCell) having two TRPs 201 #0 and #1. However, one cell 250 may be configured with three or more TRPs 201. It is also assumed that a BFD resource set 521 for each TRP 201 has already been configured in the UE 100.

[0110] Before describing the BFD / BFR operation in the SpCell according to one embodiment, a comparative example will be described with reference to FIG.

[0111] In step S401, 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 (triggers) BFR involving the transmission of a BFR MAC CE.

[0112] 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 the beam failure for both the BFD resource sets 521#0 and #1 (i.e., both the TRPs 201#0 and #1), the UE 100 (control unit 120) determines to start a random access procedure for the cell 250 (SpCell).

[0113] In step S403, the UE 100 (control unit 120) successfully completes BFR for the BFD resource set 521#0 associated with the TRP201#0, and is ready to transmit and receive data to and from the TRP201#0.

[0114] In step S404, the UE 100 (control unit 120) starts a random access procedure for the cell 250 (SpCell). The UE 100 (control unit 120) cannot transmit or receive data to or from the cell 250 (SpCell) while the random access procedure is being executed.

[0115] In step S405, although the UE 100 (control unit 120) is in a state where data transmission and reception with the TRP 201#0 is possible, the UE 100 is unable to communicate (transmit and receive data) with the cell 250 (SpCell) due to the random access procedure.

[0116] In this way, even if the UE 100 detects beam failures for the TRP 201#0 and #1, if the beam failure for the TRP 201#0 has been recovered, communication with the cell 250 (SpCell) is possible. However, if the random access procedure is started (step S404) without considering whether the beam failure has been recovered, data cannot be transmitted or received during the execution of the random access procedure, resulting in an interruption of communication.

[0117] 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, the UE 100 (control unit 120) determines whether to initiate a random access procedure for the cell 250 (SpCell) based on the status of recovery from the beam failure. For example, when the UE 100 (control unit 120) detects beam failure for one BFD resource set 521 among the N BFD resource sets 521, the UE 100 (control unit 120) initiates the random access procedure for the cell 250 (SpCell) only when the UE 100 detects beam failure for the other BFD resource sets 521 and none of the BFD resource sets 521 has recovered from the beam failure. This makes it possible to prevent communication with the cell 250 (SpCell) from becoming impossible due to the random access procedure.

[0118] A first example of the BFD / BFR operation in the SpCell according to one embodiment will be described with reference to FIG.

[0119] In step S431, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#0 associated with the TRP201#0, and starts BFR involving the transmission of a BFR MAC CE.

[0120] 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.

[0121] In step S433, the UE 100 (control unit 120) successfully completes BFR for the BFD resource set 521#0 associated with the TRP201#0, and is now in a state where data transmission and reception with the TRP201#0 is possible.

[0122] In step S434, UE100 (control unit 120) decides not to initiate a random access procedure for cell 250 (SpCell) in response to successful completion of BFR for BFD resource set 521#0 associated with TRP201#0.

[0123] In step S435, the UE 100 (control unit 120) is in a state where it can communicate (transmit and receive data) with the cell 250 (SpCell), and performs communication with the cell 250 (SpCell). Note that the UE 100 (control unit 120) may start BFR involving transmission of a BFR MAC CE for the BFD resource set 521#1 associated with the TRP201#1.

[0124] 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 initiate a random access procedure for the cell 250 (SpCell) when it detects 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 prevent communication with the cell 250 (SpCell) from becoming impossible due to the random access procedure. Furthermore, the UE 100 (control unit 120) may determine not to initiate a random access procedure for the cell 250 (SpCell) and may also initiate a BFR procedure (i.e., a BFR MAC CE transmission process) for recovering from the beam failure for the BFD resource set 521#1. This makes it possible to attempt to restore communication with the TRP 201#1.

[0125] A second example of the BFD / BFR operation in the SpCell according to one embodiment will be described with reference to FIG.

[0126] In step S451, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#0 associated with the TRP201#0, and starts BFR involving the transmission of a BFR MAC CE.

[0127] In step S452, the UE 100 (control unit 120) detects a beam failure for the BFD resource set 521#1 associated with the TRP201#1, and starts BFR involving the transmission of a BFR MAC CE.

[0128] In step S453, the UE 100 (control unit 120) determines that BFR is incomplete (unsuccessful) for the BFD resource set 521#0 associated with the TRP201#0.

[0129] In step S454, the UE 100 (control unit 120) determines that BFR is incomplete (unsuccessful) for the BFD resource set 521#1 associated with the TRP201#1.

[0130] In step S455, UE 100 (control unit 120) detects beam failure for all N BFD resource sets 521 and initiates a random access procedure for cell 250 (SpCell) in response to the fact that none of the BFD resource sets 521 have recovered from beam failure.

[0131] (Example of operation of MAC entity in user equipment) Next, 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 with reference to Fig. 23 and Fig. 24. The operation of the MAC entity may be part of the operation of the control unit 120 of the UE 100. Note that Fig. 23 and Fig. 24 show an example of the operation as described in the 3GPP MAC layer technical specification (TS38.321).

[0132] As shown in FIG. 23, when one or more BFD resource sets 521 are configured for each serving cell in which BFD is configured (step S501), the MAC entity performs the operations of steps S502 to S521.

[0133] When the MAC entity receives a beam failure instance indicator from a lower layer (i.e., physical layer) for a BFD resource set (BFD Resource Set) 521 identified by a BFD resource set identifier (bfd-ResourceSetId) (step S502), it performs the operations of steps S503 to S510.

[0134] In step S503, the MAC entity starts or restarts a timer (beamFailureDetectionTimerPerRS) configured for the BFD resource set (BFD Resource Set) 521 identified by the BFD resource set identifier (bfd-ResourceSetId).

[0135] In step S504, the MAC entity increments the count value (BFI_COUNTER_BFD_RS) set for the BFD resource set (BFD Resource Set) 521 identified by the BFD resource set identifier (bfd-ResourceSetId), that is, adds "1." Note that the initial value of the count value (BFI_COUNTER_BFD_RS) is "0."

[0136] The MAC entity performs steps S506 to S510 when the count value (BFI_COUNTER_BFD_RS) becomes equal to or greater than the maximum count value (beamFailureInstanceMaxCountPerRS) set for the BFD resource set (BFD Resource Set) 521 identified by the BFD resource set identifier (bfd-ResourceSetId).

[0137] Here, if the serving cell is an SpCell (step S506) and a beam failure is detected in another BFD Resource Set 521 and has not yet been restored by the beam restoration procedure (step S507), the MAC entity initiates a random access procedure on the SpCell for beam restoration in step S508.

[0138] On the other hand, if the serving cell is not an SpCell or if another BFD Resource Set 521 has been restored by the beam restoration procedure (step S509), the MAC entity triggers BFR for the BFD Resource Set 521 in step S510.

[0139] When the corresponding timer (beamFailureDetectionTimerPerRS) for each BFD Resource Set 521 expires (step S511), the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero in step S513.

[0140] The MAC entity also stores a BFD resource set (BFD Resource Set) 521 and associated timers (beamFailureDetectionTimerPerRS), maximum count values ​​(beamFailureInstanceMaxCountPerRS), and reference signal resources (reference signal resource When any of the BFI_COUNTER_BFD_RS and the BFI_COUNTER_BFD_RS used for beam failure detection is reconfigured by a higher layer (i.e., RRC layer) (step S512), the count value (BFI_COUNTER_BFD_RS) is set (reset) to zero in step S513.

[0141] If the serving cell is an SpCell and the random access procedure for BFR of the SpCell is successfully completed (step S514), the MAC entity performs the operations of steps S515 to S517.

[0142] In step S515, the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero.

[0143] In step S516, the MAC entity stops the timer (beamFailureDetectionTimerPerRS) if the timer (beamFailureDetectionTimerPerRS) is set.

[0144] In step S517, the MAC entity determines that the BFR has been successfully completed.

[0145] On the other hand, when the serving cell is an SCell and the MAC entity receives a PDCCH addressed to a C-RNTI indicating an uplink grant for a new transmission for the HARQ process used for transmitting the BFR MAC including the BFR information of the BFD Resource Set 521 (step S518), or when the SCell is deactivated (step S519), the MAC entity performs the operations of steps S520 and S521. CE and Truncated BFR MAC CE.

[0146] In step S520, the MAC entity sets (resets) the count value (BFI_COUNTER_BFD_RS) to zero.

[0147] In step S521, the MAC entity determines that the BFR has been completed successfully and cancels all BFRs triggered for the BFD Resource Set 521.

[0148] As shown in FIG. 24, if the MAC entity determines in the BFR procedure that at least one BFR has been triggered and not canceled for an SCell or BFD Resource Set 521 for which candidate beams are being evaluated in accordance with the requirements specified in TS38.133, it performs the operations of steps S532 to S537.

[0149] If uplink shared channel (UL-SCH) resources are available for a new transmission and the UL-SCH resources can accommodate the BFR MAC CE and its subheader 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.

[0150] On the other hand, if UL-SCH resources are available for new transmission and can accommodate the Truncated BFR MAC CE and its subheader as a result of the LCP (step S534), then in step S535 the MAC entity instructs the multiplexing and assembly procedure to generate the Truncated BFR MAC CE.

[0151] On the other hand, if neither the conditions of steps S532 nor S534 are met (step S536), in step S537, the MAC entity triggers a scheduling request (SR) for BFR of the SCell for each SCell or BFD Resource Set 521 for which candidate beams have been evaluated in accordance with the requirements specified in TS38.133 and BFR has been triggered and not canceled.

[0152] When a MAC PDU is transmitted and the PDU includes a BFR MAC CE or a Truncated BFR MAC CE that includes beam failure information for the SCell or the BFD Resource Set 521, the MAC entity cancels all BFRs that have been triggered for the SCell or the BFD Resource Set 521 (step S538).

[0153] As described above, the user equipment 100 that performs radio communication with the base station 200 that manages the cell 250 having N transmission / reception points 201 includes a communication unit 110 that receives a message for configuring N BFD resource sets 521 from the base station 200, and a control unit 120 that individually detects a beam failure for each of the N BFD resource sets 521. The control unit 120 triggers BFR for one BFD resource set in which a beam failure has been detected. The communication unit 110 transmits a BFR MAC (Bit Rate Control Unit) including information about the detected beam failure, or an SR requesting resources for transmitting the BFR MAC CE. When a MAC protocol data unit (PDU) including a BFR MAC is transmitted, the control unit 120 cancels all BFRs triggered for the one BFD resource set. This enables BFR to be performed appropriately for each TRP 201.

[0154] In the UE 100, the control unit 120 detects a beam failure in response to a beam failure event being notified a specified number of times within a specified time period from the physical layer in the UE 100 for each of the N BFD resource sets 521. As described above, each of the N BFD resource sets 521 includes information for setting a timer (beamFailureDetectionTimerPerRS) indicating the specified time period and a maximum count value (beamFailureInstanceMaxCountPerRS) indicating the specified number of times, independently of other BFD resource sets.

[0155] In the UE 100, when a beam failure event is notified from the physical layer for the one BFD resource set (BFD Resource Set) 521, the control unit 120 starts or restarts a timer (beamFailureDetectionTimerPerRS) associated with the one BFD resource set (BFD Resource Set) 521, and increments a count value (BFI_COUNTER_BFD_RS) associated with the one BFD resource set (BFD Resource Set) 521. This makes it possible to appropriately perform BFD on a TRP 201 basis.

[0156] In the UE 100, when a timer (beamFailureDetectionTimerPerRS) associated with the one BFD resource set (BFD Resource Set) 521 expires, the control unit 120 resets a count value (BFI_COUNTER_BFD_RS) associated with the one BFD resource set (BFD Resource Set) 521. This makes it possible to appropriately perform BFD on a TRP 201 basis.

[0157] In the UE 100, the control unit 120 sets a timer (beamFailureDetectionTimerPerRS), a maximum count value (beamFailureInstanceMaxCountPerRS), and a reference signal resource for BFD associated with the one BFD resource set (BFD Resource Set) 521. signal resource When any of the BFD resource sets (used for beam failure detection) is reconfigured by the base station 200, the count value (BFI_COUNTER_BFD_RS) associated with the BFD resource set 521 is reset. This makes it possible to perform BFD appropriately for each TRP 201.

[0158] In the UE 100, after transmitting the BFR MAC, the communication unit 110 receives a PDCCH in which the cell 250 is an SCell and indicates an uplink grant for the HARQ process used to transmit the BFR MAC for the one BFD Resource Set 521. In response to receiving the PDCCH, the control unit 120 resets a count value (BFI_COUNTER_BFD_RS) associated with the one BFD Resource Set 521, considers the BFR to be successful, and cancels all BFRs triggered for the one BFD Resource Set 521. This makes it possible to appropriately perform BFD for each TRP 201.

[0159] (Other embodiments) The operational sequences (and operational flows) in the above-described embodiments do not necessarily have to be executed in chronological order according to the order depicted in the flow diagrams or sequence diagrams. For example, the steps in the operations may be executed in an order different from that depicted in the flow diagrams or sequence diagrams, or may be executed in parallel. Some of the steps in the operations may be deleted, or additional steps may be added to the processing. The operational sequences (and operational flows) in the above-described embodiments may be executed independently, or two or more operational sequences (and operational flows) may be executed in combination. For example, some steps in one operational flow may be added to another operational flow, or some steps in one operational flow may be replaced with some steps in another operational flow.

[0160] In the above-described embodiment, the base station 200 may include multiple units. The multiple units may include a first unit hosting a higher layer included in a protocol stack and a second unit hosting a lower layer included in the protocol stack. The higher layer may include an RRC layer, an SDAP layer, and a PDCP layer, and the lower layer may include an RLC layer, a MAC layer, and a PHY layer. The first unit may be a central unit (CU), and the second unit may be a distributed unit (DU). The multiple units may include a third unit performing processing below the PHY layer. The second unit may perform processing above the PHY layer. The third unit may be a radio unit (RU). The base station 200 may be one of the multiple units or may be connected to other units of the multiple units. Furthermore, the base station 200 may be an integrated access and backhaul (IAB) donor or an IAB node.

[0161] In the above-described embodiment, an NR-based mobile communication system has been described as an example of the mobile communication system 1. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a system compliant with a TS of either LTE or another generation system (e.g., 6th generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA user plane and control plane protocol termination for 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.

[0162] 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. Using the computer-readable medium, the program can be installed 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. Furthermore, circuits that execute 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 (chip set, SoC).

[0163] In the above embodiments, "transmit" may mean performing processing at least one layer in a protocol stack used for transmission, or may mean physically transmitting a signal wirelessly or via a wired connection. Alternatively, "transmit" may mean a combination of performing processing at least one layer and physically transmitting a signal wirelessly or via a wired connection. Similarly, "receive" may mean performing processing at least one layer in a protocol stack used for reception, or may mean physically receiving a signal wirelessly or via a wired connection. Alternatively, "receive" may mean a combination of performing processing at least one layer and physically receiving a signal wirelessly or via a wired connection. Similarly, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. Similarly, "include" and "comprise" do not mean including only the enumerated items, but may mean including only the enumerated items or including additional items in addition to the enumerated items. Similarly, in this disclosure, "or" does not mean an exclusive or, but rather a logical or.

[0164] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention. [Explanation of symbols]

[0165] 1: Mobile communication system 10: Network 100: UE (user equipment) 110: Communications Department 111: Transmitter 112: Receiving unit 120: Control unit 200:Base station 201: TRP (Transmitting / Receiving Point) 210: Communications Department 211: Transmission unit 212: Receiving unit 220: Network Interface 230: Control unit 250: Cell 300: Core network equipment 520: BFD configuration list 521: BFD resource set

Claims

1. A communication device (100) that performs wireless communication with a base station (200) that manages a cell having N (N≧2) transmission / reception points, a communication unit (110) for receiving a radio resource control (RRC) message from the base station (200) including information for setting N beam failure detection resource sets; a control unit (120) that individually detects beam failures for each of the N beam failure detection resource sets; The control unit (120) initiates a random access procedure when beam failure recovery (BFR) is triggered for all of the N beam failure detection resource sets and the BFR has not been successfully completed for any of the beam failure detection resource sets; The RRC message includes BWP-DownlinkDedicated, which is an information element for setting parameters specific to the communication device of a downlink bandwidth portion; The BWP-DownlinkDedicated includes information for configuring a reference signal resource for radio link monitoring on a cell-by-cell basis and information for configuring the N beam failure detection resource sets. A communication device (100).

2. The control unit (120) initiates a random access procedure for the special cell (SpCell) when the BFR is triggered for all of the N beam failure detection resource sets of the special cell (SpCell) and the BFR has not been successfully completed for any of the beam failure detection resource sets. The communication device (100) of claim 1.

3. When the control unit (120) detects the beam failure for one beam failure detection resource set among the N beam failure detection resource sets, the control unit (120) detects the beam failure for other beam failure detection resource sets, and initiates the random access procedure only if the BFR has not been successfully completed for any of the beam failure detection resource sets. A communication device (100) according to claim 1 or 2.

4. When the control unit (120) detects the beam failure for one beam failure detection resource set, the control unit (120) starts the random access procedure only if the cell is the SpCell, the beam failure for the other beam failure detection resource set is detected, and the BFR for any beam failure detection resource set has not been successfully completed. The communication device (100) of claim 2.

5. When the control unit (120) detects the beam failure for the one beam failure detection resource set, the control unit (120) detects the beam failure for the other beam failure detection resource set, and when the BFR for the other beam failure detection resource set is successfully completed, determines not to start the random access procedure. The communication device (100) of claim 3.

6. A base station (200) that manages a cell having N (N≧2) transmission / reception points, a transmitter (211) for transmitting a radio resource control (RRC) message including information for setting N beam failure detection resource sets to a communication device (100); and a control unit (230) that controls the communication device (100) to individually detect beam failure for each of the N beam failure detection resource sets based on information that sets the N beam failure detection resource sets; If beam failure restoration (BFR) is triggered for all of the N beam failure detection resource sets and the BFR has not been successfully completed for any of the beam failure detection resource sets, a random access procedure is performed; The RRC message includes BWP-DownlinkDedicated, which is an information element for setting parameters specific to the communication device of a downlink bandwidth portion; The BWP-DownlinkDedicated includes information for setting reference signal resources for radio link monitoring on a cell-by-cell basis and information for setting the N beam fault detection resource sets. Base station (200).

7. If the BFR is triggered for all of the N beam failure detection resource sets of a special cell (SpCell) and the BFR is not successfully completed for any of the beam failure detection resource sets, a random access procedure for the SpCell is performed. The base station (200) of claim 6.

8. 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), comprising: receiving a radio resource control (RRC) message from the base station (200) including information for configuring N beam failure detection resource sets; Detecting beam failures individually for each of the N beam failure detection resource sets; If beam failure recovery (BFR) is triggered for all of the N beam failure detection resource sets (521#0, 521#1) and the BFR has not been successfully completed for any of the beam failure detection resource sets, initiate a random access procedure; The RRC message includes BWP-DownlinkDedicated, which is an information element for setting parameters specific to the communication device of a downlink bandwidth portion; The BWP-DownlinkDedicated includes information for configuring a reference signal resource for radio link monitoring on a cell-by-cell basis and information for configuring the N beam failure detection resource sets. Communication method.

9. If the BFR is triggered for all of the N beam failure detection resource sets of a special cell (SpCell) and the BFR has not been successfully completed for any of the beam failure detection resource sets, start a random access procedure for the SpCell. The communication method according to claim 8.

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