Method and apparatus for beam failure recovery in MIMO systems

Abstract

A method and apparatus for beam failure recovery are described herein. The method may include receiving configuration information including parameters for beam failure recovery, determining whether to perform normal beam failure detection or partial beam failure detection based on the configuration information, and monitoring a plurality of beam failure detection reference signals (BFD-RS) based on the determination. The method may further include transmitting at least one message based on the monitored BFD-RS, receiving a response to the transmitted at least one message, and determining that the beam failure recovery is completed based on the received response. The at least one message may be at least one of a beam failure recovery request, a beam switch request, or a beam switch recommendation. The plurality of BFD-RS may include a greater number of BFD-RS when normal beam failure detection is performed than when partial beam failure detection is performed.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 329,229, filed April 8, 2022, the contents of each of which are incorporated herein by reference. [Background technology]

[0002] Multiple-input multiple-output (MIMO) methods may affect beam failure recovery (BFR) procedures. Deployment of MIMO systems (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) may be used to improve beam quality, mitigate beam failure, and increase the chances of beam failure recovery. However, such techniques may also increase system overhead and complexity / power as well as latency. As the number of transmission / reception points (TRPs) increases, the beam failure detection reference signal (BFD-RS) resources (i.e., q0) increase, and the new beam identification (NBI)-RS) resources (i.e., q1) also increase. A wireless transmit / receive unit (WTRU) may need to monitor a larger q0 set, i.e., more BFD-RS sets, as well as a large q1 set (NBI-RS set). Furthermore, larger signaling and RS overhead, as well as latency and performance, may be expected for the transmission and reception of monitoring, measurements, BFR requests, and corresponding network (NW) responses. Summary of the Invention

[0003] A method and apparatus for beam failure recovery are described herein. The method may include receiving configuration information including parameters for beam failure recovery, determining whether to perform normal beam failure detection or partial beam failure detection based on the configuration information, and monitoring a plurality of beam failure detection reference signals (BFD-RS) based on the determination. The method may further include transmitting at least one message based on the monitored BFD-RS, receiving a response to the transmitted at least one message, and determining that the beam failure recovery is completed based on the received response. The at least one message may be at least one of a beam failure recovery request, a beam switch request, or a beam switch recommendation. The plurality of BFD-RS may include a greater number of BFD-RS when normal beam failure detection is performed than when partial beam failure detection is performed. [Brief description of the drawings]

[0004] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which like reference numbers indicate similar elements and in which: [Figure 1A] 1 is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] 1 is a system diagram illustrating an example wireless transmit / receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A, according to one embodiment. [Figure 1C] 1 is a system diagram illustrating an example radio access network (RAN) and an example core network (CN) that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Figure 1D] 1B is a system diagram illustrating a further exemplary RAN and a further exemplary CN that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Diagram 2] FIG. 1 illustrates an exemplary method for an adaptive q0 mechanism. [Diagram 3] FIG. 1 illustrates a method for partial beam obstruction detection. [Figure 4] FIG. 13 is an example design for priority-based beam obstruction detection. [Diagram 5] FIG. 1 illustrates an example of a WTRU procedure for BFR with assistance information. [Figure 6] FIG. 1 illustrates an example method for a BFR-based random access procedure with implicit indication. [Figure 7] An example of a two-stage Beam Failure Recovery Request (BFRQ) management procedure is presented. [Figure 8] FIG. 1 illustrates an example of a two-stage BFRQ management procedure with a maximum number of retransmissions. [Figure 9] FIG. 1 illustrates an example method for adaptive BFRQ. [Figure 10] FIG. 1 illustrates an exemplary method in which a network (NW) may respond to a BFRQ. [Figure 11] A diagram showing an example method for WTRU control beam failure recovery. [Figure 12] A diagram showing an example procedure for WTRU control beam failure recovery. [Figure 13] 1 illustrates an example method of beam failure recovery procedure for MIMO (eg, massively distributed MIMO, cell-less MIMO, or user-centric MIMO). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] 1A is a diagram illustrating an example communications system 100 in which one or more disclosed embodiments may be implemented. Communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcasts, etc., to multiple wireless users. Communications system 100 may enable multiple wireless users to access such content through sharing of system resources, including wireless bandwidth. For example, the communications system 100 may use one or more channel access methods such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), zero-tail unique-word discrete Fourier transform Spread OFDM (ZT-UW-DFT-S-OFDM), unique word OFDM (UW-OFDM), resource block filtered OFDM, filter bank multicarrier (FBMC), and the like.

[0006] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network (CN) 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it will be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a station (STA), may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, landline or mobile subscriber units, subscription-based units, pagers, mobile phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, hotspots or Mi-Fi devices, Internet of Things (IoT) devices, watches or other wearables, head-mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in industrial and / or automated processing chain contexts), home electronic devices, devices operating in commercial and / or industrial wireless networks, etc. Any of the UEs 102a, 102b, 102c, and 102d may be interchangeably referred to as a WTRU.

[0007] The communication system 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node B, an eNodeB (eNB), a Next Generation Node B such as a Home Node B, a Home eNodeB, a gNodeB (base station), a New Radio (NR) Node B, a site controller, an access point (AP), a wireless router, etc. Although the base stations 114a, 114b are each illustrated as a single element, it will be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0008] The base station 114a may be part of the RAN 104, which may also include other base stations, such as a base station controller (BSC), a radio network controller (RNC), relay nodes, and / or network elements (not shown). The base station 114a and / or the base station 114b may be configured to transmit and / or receive wireless signals on one or more carrier frequencies, which may be referred to as cells (not shown). These frequencies may be licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide wireless service coverage for a particular geographic area, which may be relatively fixed or may change over time. A cell may be further divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In one embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and may utilize multiple transceivers for each sector of the cell, for example, using beamforming to transmit and / or receive signals in a desired spatial direction.

[0009] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0010] More specifically, as noted above, the communications system 100 may be a multiple access system, but may use one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base stations 114a and WTRUs 102a, 102b, 102c of the RAN 104 may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communications protocols such as High-Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High-Speed ​​Downlink Packet Access (HSDPA) and / or High-Speed ​​Uplink Packet Access (UL)).

[0011] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A) and / or LTE-Advanced Pro (LTE-A Pro).

[0012] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR radio access, which may establish the air interface 116 using NR.

[0013] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, e.g., using dual connectivity (DC) principles. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to and from multiple types of base stations (e.g., eNBs and gNBs).

[0014] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a wireless technology such as IEEE 802.11 (i.e., Wireless Fidelity, WiFi), IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access, WiMAX), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), or the like.

[0015] 1A may be, for example, a wireless router, a Home NodeB, a Home eNodeB, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity in a localized area, such as an office, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, etc. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology, such as IEEE 802.11, to establish a wireless local area network (WLAN). In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology, such as IEEE 802.15, to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may establish a picocell or a femtocell using a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.). As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not need to access the Internet 110 through the CN 106.

[0016] The RAN 104 may communicate with the CN 106, which may be any type of network configured to provide voice, data, application, and / or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have various quality of service (QoS) requirements, such as, for example, different throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A, it will be understood that the RAN 104 and / or the CN 106 may communicate directly or indirectly with other RANs that use the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may utilize NR radio technology, the CN 106 may also communicate with another RAN (not shown) employing GSM, UMTS, CDMA2000, WiMAX, E-UTRA, or WiFi radio technology.

[0017] The CN 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network providing plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), the user datagram protocol (UDP), and / or the internet protocol (IP) of the TCP / IP Internet protocol suite. The networks 112 may include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs that may use the same RAT as the RAN 104 or a different RAT.

[0018] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a, which may employ a cellular-based wireless technology, and a base station 114b, which may employ an IEEE 802 wireless technology.

[0019] 1B is a system diagram illustrating an example WTRU 102. As shown in FIG. 1B, the WTRU 102 may include, among other things, a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and / or other peripherals 138. It will be understood that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0020] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. Although FIG. 1B illustrates the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0021] The transmit / receive element 122 may be configured to transmit or receive signals to or from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In one embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0022] 1B as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0023] The transceiver 120 may be configured to modulate signals transmitted by the transmit / receive element 122 and demodulate signals received by the transmit / receive element 122. As mentioned above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as, for example, NR and IEEE 802.11.

[0024] The processor 118 of the WTRU 102 may be coupled to and may receive user-entered data from a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, etc. In other embodiments, the processor 118 may access information from and store data in memory that is not physically located on the WTRU 102, such as on a server or home computer (not shown).

[0025] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control the power to other components in the WTRU 102. The power source 134 may be any suitable device for providing power to the WTRU 102. For example, the power source 134 may include one or more dry batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0026] The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may obtain location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0027] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos and / or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a virtual reality and / or augmented reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors. The sensor may be one or more of a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor, a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, and the like.

[0028] The WTRU 102 may include a full-duplex radio where the transmission and reception of some or all of the signals (e.g., associated with a particular subframe of both the UL (e.g., for transmission) and DL (e.g., for reception)) may be simultaneous and / or together. The full-duplex radio may include an interference management unit to reduce and or substantially eliminate self-interference via either hardware (e.g., a choke) or signal processing via a processor (e.g., via a separate processor (not shown) or via processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio where the transmission and reception of some or all of the signals (e.g., associated with a particular subframe of either the UL (e.g., for transmission) or DL ​​(e.g., for reception)) may be simultaneous and / or together.

[0029] 1C is a system diagram illustrating the RAN 104 and the CN 106, according to one embodiment. As mentioned above, the RAN 104 may employ E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the CN 106.

[0030] The RAN 104 may include eNodeBs 160a, 160b, 160c, although it will be understood that the RAN 104 may include any number of eNodeBs while remaining consistent with an embodiment. The eNodeBs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In an embodiment, the eNodeBs 160a, 160b, 160c may implement MIMO technology. Thus, the eNodeB 160a may, for example, use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0031] Each of the eNodeBs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, etc. As shown in FIG 1C, the eNodeBs 160a, 160b, 160c may communicate with each other via an X2 interface.

[0032] 1C may include a mobility management entity (MME) 162, a serving gateway (SGW) 164, and a packet data network (PDN) gateway (PGW) 166. Although the foregoing elements are illustrated as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0033] The MME 162 may be connected to each of the eNodeBs 162a, 162b, 162c in the RAN 104 via an S1 interface and may function as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, activating / deactivating bearers, selecting a particular serving gateway during initial attachment of the WTRUs 102a, 102b, 102c, etc. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0034] The SGW 164 may be connected to each of the eNodeBs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during inter-eNodeB handover, triggering paging when DL data is available to the WTRUs 102a, 102b, 102c, and managing and storing the context of the WTRUs 102a, 102b, 102c.

[0035] The SGW 164 may be connected to a PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0036] The CN 106 may facilitate communications with other networks. For example, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0037] Although the WTRU is illustrated in FIGS. 1A-1D as a wireless terminal, it is contemplated that in certain representative embodiments such a terminal may use a wired communications interface (e.g., temporarily or permanently) with the communications network.

[0038] In an exemplary embodiment, the other network 112 may be a WLAN.

[0039] A WLAN in infrastructure Basic Service Set (BSS) mode may have an Access Point (AP) of the BSS and one or more stations (STAs) associated with the AP. The AP may have access or interface to a Distribution System (DS) or another type of wired / wireless network that carries traffic within the BSS and / or outside the BSS. Traffic originating from outside the BSS to the STA may arrive through the AP and be delivered to the STA. Traffic originating from the STA to a destination outside the BSS may be sent to the AP to be delivered to the respective destination. Traffic between STAs within the BSS may be sent, for example, through the AP, where the source STA may send traffic to the AP, which may deliver the traffic to the destination STA. Traffic between STAs within the BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be sent between (e.g., directly between) the source STA and the destination STA using a direct link setup (DLS). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and STAs (e.g., all of the STAs) within or using the IBSS may communicate directly with each other. The IBSS mode of communication may be referred to herein as an "ad-hoc" communication mode.

[0040] When using an 802.11ac infrastructure mode of operation or a similar mode of operation, an AP may transmit a beacon on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., a 20 MHz wide bandwidth) or a dynamically configured width. The primary channel may be the operating channel of the BSS, but may be used by STAs to establish a connection with the AP. In certain representative embodiments, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) may be implemented, for example, in an 802.11 system. With CSMA / CA, STAs (e.g., all STAs), including the AP, may sense the primary channel. If the primary channel is sensed / detected and / or determined to be busy by a particular STA, the particular STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0041] A High Throughput (HT) STA may use a 40 MHz wide channel for communication, which may be formed, for example, through a combination of a primary 20 MHz channel and adjacent or non-adjacent 20 MHz channels.

[0042] A Very High Throughput (VHT) STA may support 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz wide channels. A 40 MHz and / or 80 MHz channel may be formed by combining multiple contiguous 20 MHz channels. A 160 MHz channel may be formed by combining eight contiguous 20 MHz channels or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. For the 80+80 configuration, after channel encoding, the data may pass through a segment parser that may split the data into two streams. Inverse Fast Fourier Transform (IFFT) processing and time domain processing may be performed separately on each stream. The streams may be mapped to two 80 MHz channels and the data may be transmitted by the transmitting STA. At the receiver of the receiving STA, the operations described above for the 80+80 configuration may be reversed and the combined data may be sent to the Medium Access Control (MAC).

[0043] Sub-1 GHz operation modes are supported by 802.11af and 802.11ah. The channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah compared to those used in 802.11n and 802.11ac. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support meter-type control / machine-type communications (MTC), such as MTC devices in macro coverage areas. MTC devices may have limited capabilities, including certain capabilities, for example, support for certain and / or limited bandwidths (e.g., only supporting these). The MTC device may include a battery that has a battery life above a threshold (eg, to maintain a very long battery life).

[0044] WLAN systems that may support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, include a channel that may be designated as a primary channel. The primary channel may have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be configured and / or limited by the STAs among all STAs operating in the BSS that support the smallest bandwidth operating mode. In an 802.11ah embodiment, the primary channel may be 1 MHz wide for STAs (e.g., MTC-type devices) that support (e.g., only) the 1 MHz mode, even if the AP and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or Network Allocation Vector (NAV) configuration may depend on the status of the primary channel. For example, if a STA (that only supports 1 MHz mode of operation) transmitting to an AP has a busy primary channel, all of the available frequency bands may be considered busy even if most of the available frequency bands are idle.

[0045] In the United States, the available frequency bands that can be used by 802.11ah are 902MHz to 928MHz. In South Korea, the available frequency bands are 917.5MHz to 923.5MHz. In Japan, the available frequency bands are 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz depending on the country code.

[0046] 1D is a system diagram illustrating the RAN 104 and the CN 106, according to one embodiment. As mentioned above, the RAN 104 may employ NR radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the CN 106.

[0047] The RAN 104 may include gNBs 180a, 180b, 180c, although it will be understood that the RAN 104 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In an embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 108b may utilize beamforming to transmit signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a may transmit and / or receive wireless signals to and from the WTRU 102a, for example, using multiple antennas. In one embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers to the WTRU 102a (not shown). A subset of these component carriers may be on an unlicensed spectrum, while the remaining component carriers may be on a licensed spectrum. In one embodiment, the gNBs 180a, 180b, 180c may implement Coordinated Multi-Point (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNBs 180a and 180b (and / or gNB 180c).

[0048] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with scalable numerology. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may vary for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of varying or scalable lengths (e.g., including varying numbers of OFDM symbols and / or varying lengths of absolute time durations).

[0049] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c without accessing another RAN (e.g., eNodeBs 160a, 160b, 160c, etc.). In a standalone configuration, the WTRUs 102a, 102b, 102c may utilize one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in unlicensed bands. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate with and connect to a gNB 180a, 180b, 180c while also communicating with and connecting to another RAN, such as an eNodeB 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement DC principles to communicate with one or more gNBs 180a, 180b, 180c and one or more eNodeBs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNodeBs 160a, 160b, 160c may act as mobility anchors for the WTRUs 102a, 102b, 102c, and the gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0050] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in UL and / or DL, support for network slicing, DC, interworking between NR and E-UTRA, routing of user plane data to User Plane Functions (UPFs) 184a, 184b, routing of control plane information to Access and Mobility Management Functions (AMFs) 182a, 182b, etc. As shown in FIG. 1D, the gNBs 180a, 180b, 180c may communicate with each other via an Xn interface.

[0051] 1D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one session management function (Session Management Function, SMF) 183a, 183b, and possibly a data network (Data Network, DN) 185a, 185b. Although the foregoing elements are illustrated as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0052] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via an N2 interface and may function as a control node. For example, the AMF 182a, 182b may be responsible for user authentication of the WTRUs 102a, 102b, 102c, support for network slicing (e.g., handling different protocol data unit (PDU) sessions having different requirements), selection of a particular SMF 183a, 183b, management of registration areas, termination of non-access stratum (NAS) signaling, mobility management, etc. The network slicing may be used by the AMF 182a, 182b to customize the CN support of the WTRUs 102a, 102b, 102c based on the type of service utilizing the WTRUs 102a, 102b, 102c. For example, different network slices may be established for different use cases, such as services relying on ultra-reliable low latency (URLLC) access, services relying on enhanced massive mobile broadband (eMBB) access, services for MTC access, etc. The AMF 182a, 182b may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies, such as WiFi.

[0053] The SMFs 183a, 183b may be connected to the AMFs 182a, 182b in the CN 106 via an N11 interface. The SMFs 183a, 183b may also be connected to the UPFs 184a, 184b in the CN 106 via an N4 interface. The SMFs 183a, 183b may select and control the UPFs 184a, 184b and configure the routing of traffic through the UPFs 184a, 184b. The SMFs 183a, 183b may perform other functions, such as managing and assigning UE IP addresses, managing PDU sessions, controlling policy enforcement and QoS, providing DL data notification, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0054] The UPFs 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPFs 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policy, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, etc.

[0055] The CN 106 may facilitate communication with other networks. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In one embodiment, the WTRUs 102a, 102b, 102c may be connected to the local DNs 185a, 185b through the UPFs 184a, 184b via an N3 interface to the UPFs 184a, 184b and an N6 interface between the UPFs 184a, 184b and the DNs 185a, 185b.

[0056] 1A-1D and the corresponding description thereof, one or more or all of the functions described herein with respect to one or more of the WTRUs 102a-102d, base stations 114a-114b, eNodeBs 160a-160c, MME 162, SGW 164, PGW 166, gNBs 180a-180c, AMFs 182a-182b, UPFs 184a-184b, SMFs 183a-183b, DNs 185a-185b, and / or any other devices described herein may be performed by one or more emulation devices (not shown). The emulation devices may be one or more devices configured to emulate one or more or all of the functions described herein. For example, the emulation devices may be used to test other devices and / or to simulate network and / or WTRU functions.

[0057] The emulation device may be designed to implement one or more tests of other devices in a lab environment and / or an operator network environment. For example, one or more emulation devices may perform one or more or all functions while fully or partially implemented and / or deployed as part of a wired and / or wireless communication network to test other devices in the communication network. One or more emulation devices may perform one or more or all functions while temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation device may be directly coupled to another device for the purpose of testing and / or performing tests using over-the-air wireless communication.

[0058] The one or more emulation devices may perform one or more functions, inclusive, while not being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices may be utilized in test scenarios in a test lab and / or in an undeployed (e.g., test) wired and / or wireless communication network to implement testing of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (which may include, for example, one or more antennas) may be used by the emulation devices to transmit and / or receive data.

[0059] Various methods of beam failure detection for MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO) systems have been proposed. An adaptive BFR-RS mechanism and solution has been proposed. A method of partial beam failure detection for MIMO is proposed. Partial beam failure detection can be used to reduce latency and delay and reduce system complexity of MIMO-based BFR. A method of priority-based beam failure detection used for MIMO systems has been proposed.

[0060] A new beam identification method for MIMO is proposed. For MIMO, a BFR assistance information with implicit indication and a RACH type method are proposed.

[0061] A method of beam failure recovery request for MIMO is proposed. To enable operational flexibility and performance for MIMO, a method of flexible beam failure recovery (BFR) management is proposed. BFRQ reliability enhancement and diversity transmission are proposed for MIMO.

[0062] A method of network response to BFRQ is proposed for MIMO. A method of WTRU controlled beam failure recovery is proposed for MIMO systems. A method for WTRU controlled BFR with beam failure recovery command is proposed. Event triggered and / or condition based BFR may be used. Based on certain criteria and conditions, a new set of NBI-RS resources may be triggered and the WTRU may switch from the original set of NBI-RS resources to measure the new set of NBI-RS resource sets. This may be used to prevent the WTRU from not finding the authorized NBI-RS resources and entering into a contention based random access procedure, which may have high latency and long delay.

[0063] In a fifth generation (5G) new radio (NR) system, a beam failure recovery procedure may include one or more stages. At least four examples of such stages of a beam failure recovery procedure can be described as follows: Stage 1: beam failure detection; Stage 2: new beam identification; Stage 3: beam failure recovery request; Stage 4: NW response.

[0064] Stage 1, which refers to beam failure detection, can be described as follows: Beam failure detection may be a combined Layer 1 (L1) or Layer 2 (L2) procedure, with L1 (i.e., referring to a Layer 1 entity, or hardware (e.g., processor and transceiver) configured to detect, process, or transmit Layer 1 signals, or another logically equivalent layer) providing an indication of a beam failure instance (BFI) to the medium access control (MAC) layer. The network can configure a set of resources and reference signals for the WTRU to monitor the radio link quality. The configured BFD resource signal may be a channel state information reference signal (CSI- The beam failure indication may be a serving beam reference signal (RS) or a synchronization signal block (SSB). When the physical (PHY) layer detects that the signal-to-interference-and-noise ratio (SINR) of the serving beam reference signal falls below a threshold, i.e., 10% block error rate (BLER) of the virtual physical downlink control channel (PDCCH), it may trigger a beam failure instance or may cause the WTRU to recognize the beam failure instance and send a message to the MAC layer or another logical equivalent. The MAC layer may count the indications and declare the failure when a configured maximum number of beam failure indications (BFI) is reached.

[0065] A beam failure may be triggered, for example, based on the passage of a given duration or a given number of beam failure instances. The WTRU (e.g., at the MAC layer) may store timing information regarding the BFI. For example, the WTRU may measure a duration that starts when the WTRU receives the BFI. Alternatively or additionally, the WTRU may store the timing information in the form of a counter, which may, for example, be incremented by one for each further received BFI. For example, when a certain number of BFIs are observed such that the number exceeds a threshold (e.g., a configured or preconfigured maximum number of BFIs) within a given time window (e.g., a configured or preconfigured time window duration), the WTRU may determine (e.g., at the MAC layer) that a beam failure has occurred and may initiate a recovery procedure.

[0066] Stage 2, which refers to new beam identification, can be described as follows: After a beam failure is detected, the WTRU may need to search and find a new beam. The base station may configure a set of reference signals, e.g., CSI-RS resources, i.e., NBI-RS (or q1). The WTRU may measure the reference signals and find a suitable beam according to one or more criteria, which may be, for example, the beam with the strongest L1 reference signal received power (RSRP), the beam with L1-RSRP greater than a predefined or configured threshold, or the beam determined to be the "best" beam according to other criteria. If a suitable new beam is found that meets the above reference criteria, the WTRU may send a beam failure recovery request (BFRQ). If a suitable new beam is not found, the WTRU may initiate a contention-based 4-step random access for BFR purposes.

[0067] Stage 3 refers to the transmission of BFRQ and may be described as follows: Upon detecting beam failure, the WTRU may initiate a random access procedure for beam failure recovery purposes of the SpCell. For example, according to the RRC information element of BeamFailureRecoveryConfig, the random access procedure may be contention-based or contention-free. In the random access procedure, the WTRU may transmit a BFRQ to the base station / TRP.

[0068] Stage 4, which may refer to the transmission and / or reception of a NW response, may be described as follows: To receive a response to the BFRQ transmitted on the RACH, the WTRU may monitor a random access response (RAR) scrambled by the RA Radio Network Temporary Identifier (RNTI) (i.e., in the contention-based case) or the cell-specific RNTI (C-RNTI) (i.e., in the contention-free case) in a control resource set (CORESET) configured for BFR. Such a CORESET may be configured, for example, by an RRC information element of recoverySearchSpaceId for SpCell. The WTRU may retransmit the BFRQ until a maximum number of BFRQ retransmissions is reached or the BFR random access procedure is successfully completed. Once the RACH is successfully completed, the beam failure recovery procedure may be completed.

[0069] Various problems are described that prompt the solutions proposed herein.

[0070] Beam failure recovery procedures may be supported in the Release-15 and / or Release-16 technical specifications for use with a single TRP. Beam failure recovery procedures may be supported in the Release-17 technical specifications with up to two TRPs. TRP-specific beam failure recovery procedures may be supported in the Release-17 technical specifications.

[0071] MIMO may affect beam failure recovery procedures. Deployment of MIMO technology can be used to improve beam quality, mitigate beam failure, and increase the chances of beam failure recovery. However, this may also increase system overhead and complexity / power as well as latency. As the number of TRPs increases, the BFD-RS resource (i.e., q0) increases and the NBI-RS resource (i.e., q1) also increases. The WTRU may need to monitor more BFD-RS sets (i.e., larger q0 set) as well as more NBI-RS sets (i.e., larger q1 set). In addition, high signaling and RS overhead, as well as latency and performance, may be expected for monitoring, measurement, BFR requests, and corresponding NW response transmissions and / or receptions when MIMO is deployed.

[0072] q0 may be large for deployment of MIMO systems. The WTRU may be configured with up to three CORESETs in case of a single TRP. The WTRU may be required to monitor periodic CSI-RS resources quasi-colocated (QCLed) with the CORESET. The WTRU may be configured with up to five CORESETs in case of two TRPs. However, more TRPs may require monitoring more CORESETs and BFD-RS resources (e.g., CSI-RS resources) for MIMO systems. The beam failure recovery procedure may need to be extended to cover scenarios with a very large number of TRPs in case of MIMO deployment. One issue raised in these scenarios may be how to enhance BFR with low overhead and low complexity / power design. Another issue may be how to enable fast BFR and quickly manage beams with low latency and delay. Yet another issue may be how to enhance the reliability and performance of BFR. Yet another issue may be how to ensure that the WTRU continues and completes the BFR procedure even if the channel conditions deteriorate during the BFR procedure.

[0073] Various solutions to the above problem are described herein. In some solutions, a method of beam obstruction detection for MIMO may be provided.

[0074] The adaptive BFD-RS set, size, and periodicity are aspects of a possible solution. In the following paragraphs, a method of beam failure detection for MIMO is considered. As substantially described in the above paragraphs, the WTRU may monitor a BFD-RS set (also referred to herein as "q0" or "q0 set"). q0 may be large for deployment of MIMO systems. The more TRPs used, the more BFD-RS resources (e.g., CSI-RS resources) may need to be monitored.

[0075] If the size of q0 is limited to a small set, the system may not fully utilize the large TRP deployment. For example, frequent beam failures may occur and be detected. On the other hand, if a large q0 set is used, a large overhead may occur. In addition, high complexity and power may also be introduced.

[0076] An adaptation mechanism for q0 may be utilized to reduce complexity, overhead, and power, improve reliability, improve accuracy, and improve performance. An adaptive q0 set may be used. In addition, an adaptive q0 size may also be utilized. For example, in certain conditions where the beam quality may exceed a predefined or (pre)configured threshold, a small BFD-RS resource set of q0 may be used. If a beam failure is detected, the WTRU may need to perform one or more beam failure recovery procedures. In other conditions, for example, if the beam quality falls below a predefined or (pre)configured threshold, the WTRU may need to monitor and measure a much larger RS ​​resource set, e.g., the NBI-RS resource set, so a large BFD-RS resource set of q0 may be used to avoid entering into a beam failure recovery procedure at the cost of higher overhead and power. To balance performance and overhead, an adaptive q0 size may be utilized. Furthermore, different periodicities and sets may also be used.

[0077] If q0 does not have good quality, beam failure may be detected. Different q0 sets and / or different q0 sizes may be utilized. The WTRU may switch between different sized BFD-RS sets q0 to balance performance, overhead, and power. The configured switch or size switch may be triggered based on certain criteria and conditions, e.g., number and / or ratio of BFDs, number and / or ratio of NBIs, number and / or ratio of BFRQs, etc., which may be considered and used to make a decision to switch during q0 adaptation. The switch may also be triggered based on measurements such as L1-RSRP, L1-SINR, etc. Furthermore, the switch may also be triggered based on requirements, service type, QoS, etc. Furthermore, the switch may also be triggered based on the number of BFIs.

[0078] To reduce overhead and power, two or more different periodicities can be introduced, e.g., for different q0 sets. One periodicity may be used and associated with a large q0 set and another periodicity may be used and associated with a small q0 set. For example, a large periodicity may be used and associated with a large q0 set and a small periodicity may be used and associated with a small q0 set to reduce overhead, etc. By doing so, the WTRU can monitor the large q0 set less frequently for the longer periodicity and the small q0 set more frequently for the shorter periodicity.

[0079] To reduce the complexity, different measurement metrics can be used for different q0 sets. A virtual PDCCH BLER or L1-SINR can be used for the measurement metric. A virtual PDCCH BLER or L1-SINR measurement metric can be more accurate but also have high complexity. Meanwhile, an L1-RSRP measurement metric can be simple but less accurate. When different measurement metrics are used for different q0 sets, the complexity can be reduced and the power consumption can also be lower, and there can be some trade-off between performance, complexity, power, and overhead. For different q0 sets, one measurement metric may be used for q0 set 1 (i.e., the "first" q0 set) and associated with q0 set 1, and another measurement metric may be used for q0 set 2 (i.e., the "second" q0 set) and associated with q0 set 2. For different q0 sets or sizes, one measurement metric may be used and associated with q0 size 1, and another measurement metric may be used and associated with q0 size 2. For example, PDCCH BLER or L1-SINR may be used and associated with the small q0 set, L1-RSRP may be used and associated with the large q0 set, and so on.

[0080] Set-dependent and / or size-dependent measurement metrics may be utilized. If the WTRU monitors a larger q0 set, it may use L1-RSRP for quick screening. The quick screen may be a simple measurement using measured received power, such as an L1-RSRP measurement. This may reduce complexity and allow power savings. Once reduced to a smaller q0 set, the WTRU may switch to a virtual PDCCH BLER L1-SINR for improved reliability and achieve better accuracy. Predefined or (pre)configured hopping patterns and / or rules between q0 sets and / or sizes may also be used. The WTRU may hop between different q0 sets and different q0 sizes, for example, for large and small q0 sets, based on predefined or (pre)configured hopping patterns. Some monitoring rules may also be applied to different q0 sets and sizes. Also, the primary q0 set and secondary q0 set may be defined with different priorities. The method may also be applicable to the q1 set. In another example, the WTRU may be configured with a q0 set. The WTRU may measure beam quality of the q0 set of BFD-RSs using a first measurement metric (e.g., L1-RSRP). Based on the first measurement metric (e.g., L1-RSRP), the WTRU may select a subset (q0') of resources in the q0 set, e.g., one or more of the BFD-RSs with the highest measurement or those with measurements above a threshold. The WTRU may monitor beam quality using a second measurement metric (e.g., virtual PDCCH BLER) and may determine beam failure based on the q0' subset.

[0081] FIG. 2 illustrates an example method of adaptive q0 mechanism. The WTRU may be configured or pre-configured with conditions (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO) for determining the q0 set and / or size of the MIMO. For example, as shown at 210, the WTRU may receive configuration information in one or more messages or signals indicating such conditions for q0 determination. For example, the signals or messages may include RRC messages, Layer 2 messaging (e.g., control information such as one or more MAC control elements (CE), Layer 1 control information (e.g., downlink control information or DCI), or any logically equivalent message). As shown at 220, the WTRU may determine a q0 set for beam failure detection for MIMO. If it is a small q0 set, as shown at 230, the WTRU may monitor the q0 set with an associated short periodicity. If it is a large q0 set, as shown at 260, the WTRU may switch to monitoring the q0 set with an associated long periodicity to reduce power. The WTRU may determine to use L1-SINR as a measurement metric if q0 is a small q0 set with a short periodicity, as shown at 230. It should be understood that in other embodiments not shown, the WTRU may determine to use a different measurement metric for the small q0 set. On the other hand, as shown at 270, the WTRU may determine to use L1-RSRP as a measurement metric if q0 is a large q0 set configured with a long measurement periodicity to reduce complexity. It should be understood that in other embodiments not shown, the WTRU may determine to use a different measurement metric for the large q0 set. The WTRU may monitor the PDCCH beam using an associated measurement metric. As shown at 250, the WTRU may monitor the PDCCH beam using an L1-SINR measurement (or a different measurement metric determined for use with the small q0 set). The WTRU may perform such monitoring using a short measurement periodicity, for example, for a small q0 set.The WTRU may monitor the PDCCH beam using L1-RSRP measurements (or a different measurement metric determined for use with a large q0 set), as shown at 280. The WTRU may perform such monitoring using a long periodicity, e.g., for a large q0 set.

[0082] In the following paragraphs, a method for partial beam failure detection for MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO) systems is proposed. Partial beam failure detection is one possible solution to reduce latency and delay and reduce system complexity of MIMO-based BFR. In MIMO deployments, to avoid long delays caused by long procedures of beam failure recovery, the WTRU may declare partial beam failure based on certain criteria. For example, the WTRU may declare partial beam failure if a condition or set of conditions is met. One example is that partial beam failure is detected if the number of beams for which beam failure is detected is greater than a threshold, e.g., M. In this case, the WTRU may refrain from measuring the NBI-RS resource set. Instead, the WTRU may send a beam switch request (BSR), a beam switch recommendation, or a beam switch command (BSO) to the base station or one or more TRPs.

[0083] If all beams in the BFD-RS resource set are detected to have beam quality below a predefined or (pre)configured threshold, normal or full beam failure detection may be performed. In this case, the WTRU may proceed with measuring one or more RSs of the NBI-RS resource set. After measuring the NBI-RS RSs and finding a new beam, the WTRU may send a beam failure recovery request to the base station or one or more TRPs.

[0084] If the threshold M is configured to be equal to the number of BFD-RS resources in the set, the WTRU may recognize normal (complete) beam failure detection upon detecting beam failure for all beams of a BFD-RS resource set. If the threshold M is configured to be less than the number of BFD-RS resources in the set, the WTRU may recognize partial beam failure upon detection of beam failure for a number of beams of a BFD-RS resource set that exceeds the threshold M. Different values ​​of the threshold M may be configured for different BFD-RS resource sets. For example, M1, M2, M3, etc. may be configured for BFD-RS resource set 1, BFD-RS resource set 2, BFD-RS resource set 3, etc., respectively. Alternatively or additionally, a common value of M may be configured for all BFD-RS resource sets. For example, M may be configured for BFD-RS resource set 1, BFD-RS resource set 2, BFD-RS resource set 3, etc. Furthermore, a group-common threshold M may be configured for a group of BFD-RS resource sets. Other combinations may be possible. The threshold M (or multiple thresholds M1, M2, M3, etc.) may be configured together with or separately from the configuration of the BFD-RS or NBI-RS resource sets. For example, the WTRU may receive one or more including RRC messages, Layer 2 messaging (e.g., one or more MAC control elements (CEs), control information (e.g., downlink control information), or any logically equivalent message) indicating one or more thresholds.

[0085] BFD-RS resources corresponding to some TRPs may be configured to trigger partial beam failure detection, while BFD-RS resources corresponding to other TRPs may be configured to trigger normal (full) beam failure recovery. If BFD-RS resources corresponding to some TRPs are configured to trigger partial beam failure detection, the WTRU may not perform normal beam failure recovery upon detecting partial beam failure of BFD-RS resources associated with those TRPs. For BFD-RS corresponding TRPs with partial beam failure detection, the WTRU may send a beam switching request, recommendation, or command for those TRPs. The WTRU may not send a beam failure recovery request. Those TRPs configured to trigger partial beam failure detection may communicate with the WTRU to reconfigure the BFD-RS resource set. For TRPs for which normal beam failure recovery has been implemented, the WTRU may not send a beam switching command. Instead, the WTRU may send a beam failure recovery request for those TRPs with normal beam failure recovery.

[0086] Furthermore, if the BFD-RS resources corresponding to a set of TRPs are configured to trigger normal beam failure detection, beam failure detection may be performed for the TRPs, and it is still possible that beam failure recovery is performed for some TRPs of the set but not for others. That is, whether beam failure recovery is performed by the WTRU may be determined separately for different TRPs. For example, whether beam failure recovery is performed may be conditional on beam failure being detected or declared. If beam failure is not declared for one or more TRPs, beam failure recovery may not be performed by the WTRU for those TRPs. In other words, the WTRU may detect beam failure for TRP1 but not for TRP2. The WTRU may perform a beam failure recovery procedure for TRP1 but not for TRP2.

[0087] On the other hand, if the BFD-RS resources corresponding to a set of TRPs are configured to trigger partial beam failure detection, partial beam failure detection may be performed for the TRPs. The WTRU may send a beam switching request, beam switching recommendation, or beam switching command for all the TRPs.

[0088] The network (NW) may configure the WTRU with PDCCH resources, such as CORESET and search space set (SSS), for PDCCH monitoring at the WTRU. The NW may reconfigure the BFD-RS resource set. For example, the NW may send a PDCCH transmission (or another logically equivalent message) carrying a transmission configuration indication (TCI) to indicate the TCI status to the WTRU to monitor the PDCCH beam at the WTRU. The NW may reconfigure another better set of BFD-RS resources for beam failure detection and monitoring at the WTRU. The better set of BFD-RS resources may include BFD-RS resources where most or all of the BFD-RS resources in the set have better link quality (e.g., SINR or other metrics mentioned above, e.g., (pre)configured or indicated thresholds). If the better set of BFD-RS resources is reconfigured and indicated to the WTRU, the WTRU may not need to move to stage 2 for new beam identification and measure a large set of NBI-RS resource sets. Instead, the WTRU may monitor a PDCCH beam with a smaller but better set of BFD-RS resources, thereby avoiding or mitigating longer procedures for beam failure recovery.

[0089] This method may have the advantage of lower latency and reduced complexity. The latency may be reduced because the WTRU may not need to perform the entire beam failure recovery procedure. In addition, the WTRU may not need to measure a large set of NBI-RS resource sets, so the operational complexity may be lower for the WTRU. The threshold number of beams for which beam failure is detected before partial beam failure is declared, i.e., M, may be configured, pre-configured, or pre-defined by the NW or base station.

[0090] FIG. 3 illustrates a method for partial beam failure detection. As shown in FIG. 3, the base station / TRP 301 may transmit a BFD-RS that may be monitored, detected, and / or measured by the WTRU 302. The base station / TRP 301 may configure (or may have previously configured) the WTRU 302 with a set of RS resources, e.g., a set of CSI-RS resources for the BFD-RS. The WTRU 302 may monitor a beam for PDCCH transmissions (e.g., PDCCH DM-RS(s)) that are quasi-co-located with the CSI-RS (QCLed). If a beam failure is detected by the WTRU 302, the WTRU 302 may switch to monitoring another beam (e.g., the BFD-RS). The WTRU 302 may send a request, recommendation, or command to the base station / TRP 301 for beam switching. The base station / TRP 301 may send a message or signal indicating the TCI status to the WTRU 302 for beam switching. The base station / TRP 301 may reconfigure the BFD-RS resource set or configure a new BFD-RS resource set for the WTRU 302. For example, the base station / TRP 301 may activate or reactivate the TCI state, and the WTRU 302 may implicitly derive the BFD-RS resources from the active TCI state. By doing so, the WTRU 302 may have a better BFD-RS resource set and therefore a better beam for PDCCH monitoring. This may reduce the chance of beam failure.

[0091] In the following paragraphs, a method for priority-based beam failure detection for a MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) system is proposed. The WTRU may select a set of beams of Periodic CSI-RS (P-CSI-RS) resource configuration indexes to be used for beam failure detection.

[0092]

number

[0093] During monitoring

[0094]

number

[0095] The following priority criteria may be proposed:

[0096]

number

[0097]

number

[0098]

number

[0099] Consider the resources of the SCell as a second priority set, i.e., the resources of the SCell may have a lower priority than the PCell or PsCell, and the priority may depend on the ID of the SCell with respect to the IDs of the other SCells, which may have IDs ordered from low to high. For example, SCell#1 may have a higher priority than SCell#2, and so on. Within the resources of the same SCell, the priority of each of the resources may be based on the CSI-RS resource index from low to high. For example, the lowest CSI-RS resource index may be associated with the highest priority, and the highest CSI-RS resource index may have the lowest priority.

[0100]

number

[0101] FIG. 4 illustrates an example design for priority-based beam failure detection. For example, as shown in FIG. 4, with constrained CPU time, the WTRU may allow four CSI measurements (e.g., two L1-SINRs, two L1-RSRPs). In addition, the number of CSI-RS resources configured for the PCell / PsCell may be equal to two, the configured SCells may have indexes #1 and #2, and each SCell may be configured with two CSI-RS resource indexes. In this example design, the WTRU may perform only four CSI measurements. According to the proposed priority rule, the CSI-RS resources associated with the lowest two CSI-RS resource indexes for the PCell / PsCell may have higher priority than the CSI-RS of other SCells. Thus, as shown in FIG. 4, the CPU first performs measurements on the PCell (i.e., using P-CSI-RS resources #1 and #2). Further, as shown, the PCell P-CSI-RS resource with higher priority (i.e., resource #1) is measured first, followed by the PCell P-CSI-RS resource with lower priority (i.e., resource #2). Similarly, the WTRU may perform CSI measurements on the SCell resources based on their respective priority levels. As shown in Figure 4, SCell P-CSI-RS resource #1 has a higher priority than SCell P-CSI-RS resource #2.

[0102] A method for new beam identification for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) is proposed herein. Furthermore, a method for providing BFR assistance information for enhanced MIMO is proposed. The WTRU may be configured to determine parameters, may be pre-configured with such parameters, or may receive configuration information (e.g., via MAC CE, RRC, other higher layer signaling, or logical equivalents thereof) providing parameters to be used in identifying one or more new beams, and if a candidate beam set is configured for determining and / or reporting NBI, the WTRU may determine a candidate beam set for NBI.

[0103]

number

[0104] The assistance information includes the CSI-RS RSRP for each TRP in the candidate set (i.e.,

[0105]

number

[0106] The WTRU may use the PRACH / RACH opportunity (RO), PUCCH, or MAC CE (PUSCH), or another logical equivalent, to transmit assistance information when initiating BFR. The WTRU may be configured with a dedicated periodic PRACH opportunity, a dedicated periodic PUCCH or a dedicated periodic PUCCH-BFR-SR resource, a periodic PRACH opportunity plus a periodic PUCCH or a periodic PRACH opportunity plus a dedicated periodic PUCCH-BFR-SR resource, a periodic PUCCH plus a periodic PUCCH-BFR-SR resource, a periodic PRACH opportunity plus a periodic PUCCH and a dedicated periodic PUCCH-BFR-SR resource, or another logical equivalent. The configured BFRQ resource may benefit the WTRU when reporting / initiating BFR with assistance information for the network to determine which TCI state or group of TCI states is suitable for the WTRU. The selection of whether to use PRACH, PUCCH, or MAC CE (PUSCH) may be based on certain criteria, such as reporting configuration and / or payload size (content of assistance information). For example, the payload size may be based on individual reports, average per TRP report, or average per TRP group report. The selection of PRACH, PUCCH, or MAC CE may not only depend on the payload size but also on the transmission opportunity. For example, if a BFRQ is triggered and the WTRU is configured to report BFR assistance information along with the BFRQ, the next upcoming transmission opportunity of the BFRQ may utilize PRACH (e.g., mainly for PCell / PsCell) or PUCCH (e.g., for SCell) resources. If the PRACH and PUCCH transmissions cannot carry a large enough load, the WTRU may drop part of the BFR assistance information of the entire BFR assistance information and select a RACH opportunity (RO) or a PUCCH transmission opportunity of the BFRQ. Otherwise, the WTRU may still use the SR method for the BFR assistance information over the MAC CE. The selection procedure is illustrated in FIG. 5 and described in further detail below.

[0107] FIG. 5 shows an example of a procedure performed by a WTRU for beam failure recovery with or without transmitting assistance information. As shown in FIG. 5, the WTRU initiates a beam failure recovery procedure at 510. At 520, the WTRU evaluates whether it is configured to transmit assistance information when initiating BFR. If not, the WTRU transmits a BFRQ without BFR assistance information at 521. If the WTRU is configured to transmit assistance information when initiating BFR, the WTRU evaluates whether the next transmission opportunity uses a PRACH resource or a PUCCH resource at 530. If not, the WTRU transmits a BFRQ using a scheduling request (SR) at 531 and transmits the assistance information separately using a PUSCH at 532. On the other hand, if the next transmission opportunity uses a PRACH resource or a PUCCH resource, the WTRU further evaluates whether the payload size of the BFR assistance information exceeds a given size x at 540. If yes, the WTRU transmits a BFRQ using a SR at 531 and transmits the assistance information via a PUSCH at 532. If the assistance information does not exceed a given size x, the WTRU transmits a BFRQ using a PRACH or PUCCH transmission opportunity including the assistance information as shown at 550. Once the BFRQ is transmitted, the WTRU waits for a BFRQ response from the network as shown at 560. The response may include, for example, an updated (or activated) TCI state or an indication of the TCI state. If no response is received at 570, the WTRU again evaluates the next transmission opportunity. If a response is received, at 580, the WTRU monitors a new beam or set of beams according to the updated TCI state before terminating the BFR procedure as shown at 590.The assistance information may include, but is not limited to, an index of the identified NBI-RS, an index of the failed NBI-RS, an index of the failed BFD-RS or set, a cell index of the failed cell, individual L1-RSRP of the NBI-RS, an average L1-RSRP (e.g., an average per CSI-RS set, per CSI-RS set group, per TRP, per TRP group, etc.), a differential L1-RSRP relative to the average, a differential L1-RSRP relative to a threshold, etc.

[0108] In addition, the network may activate and deactivate the PUCCH when the PUCCH resources for the BFRQ are not used to reduce overhead. The network may decide to activate or deactivate based on some criteria, such as the number of BFRQs in a certain period (whether the BFRQ occurs frequently or not).

[0109] For a large payload carrying the assistance information, if the one-shot PUCCH transmission is not enough to carry the payload, the WTRU may use a second or third PUCCH transmission with the same or different format (e.g., long PUCCH format) to transmit the assistance information. For example, the first PUCCH transmission may be used for BFRQ request and indication of higher priority information such as CRI, SSBRI, NBI-RS index, and then the second PUCCH transmission may carry the BFRQ assistance information, e.g., CSI-RS RSRP per TRP, etc. The number of reports and report size may be configured and may depend on the capabilities of the WTRU. In addition, if the payload size, i.e., the BFR assistance information, is larger than a threshold, the WTRU may request a BFR scheduling request (BFR-SR). When the network receives the BFR-SR, the network may schedule a UL grant for the WTRU to transmit a PUSCH transmission (e.g., MAC CE or another logical equivalent) to carry the BFR assistance information.

[0110] For MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO) systems, a method is proposed to perform different RACH procedure types based on an implicit indication. In stage 2 of the BFR procedure, the WTRU can check the q1 candidate beam set, which may be a much larger set than the q0 set, and determine whether BFR is performed for the MIMO system. A large q1 set can improve the performance of new beam identification, but at the same time, it may also incur large overhead and long latency. If the NBI is not successful, the WTRU can initiate a contention-based random access. This may incur long delays and high overhead as the entire random access procedure is performed.

[0111] If the NBI is not successful, the WTRU may select a RACH procedure type based on certain criteria and / or conditions. For example, the WTRU may perform a two-step RACH procedure if high speed, low latency, and low delay are required. The WTRU may perform a four-step RACH procedure if higher reliability (but longer delay), etc. are required. Furthermore, the WTRU may perform a two-step or four-step RACH procedure based on the service type, beam conditions, traffic requirements, or other criteria.

[0112] A method may be needed to distinguish between initial random access and random access triggered by beam failure. An implicit indication may be used. Partitions of PRACH and / or RACH resources and / or DMRS ports and / or PUSCH resources may be used for the implicit indication. For example, one partition may be dedicated to initial random access and another partition may be dedicated to BFR.

[0113] If a two-step RACH procedure is performed, a partition of PRACH resources / RACH opportunities (RO) and / or DMRS ports and / or PUSCH resources and / or PUSCH opportunities may be used for MsgA.

[0114] FIG. 6 illustrates an example method for a BFR-based random access procedure with implicit indication. As shown in FIG. 6 at 610, a WTRU may not be able to identify a new beam and issue an NBI. In such a case, at 620, the WTRU may select between two types of RACH procedures, namely, a two-step or a four-step random access procedure. The RACH type selection may be based on a service type, a condition, a criterion, or other parameters. In some examples, if low latency is required, the WTRU may initiate a two-step RACH procedure. In some examples, such as when higher reliability is required, the WTRU may initiate a four-step RACH procedure, shown at 630. In some examples, if a smaller number of messaging is required to reduce the total number of BFR-related messaging, the WTRU may select the two-step RACH procedure, as shown in FIG. 6 at 650, since the two-step RACH procedure uses a total of two messages compared to the four messages used in the four-step RACH procedure. This option may reduce the cumulative number of BFR-related messages exchanged in a massive MIMO system.

[0115] To distinguish between initial random access and beam failure triggered random access, an implicit indication can be used for lower overhead. In the case of implicit indication, in the case of 4-step RACH, the PRACH and / or RACH opportunity (RO) and / or PRACH resources in Msg1 may be partitioned to indicate initial random access and BFR triggered random access. In the case of implicit indication, in the case of 2-step RACH procedure, the PRACH and / or RO and / or PRACH resources and / or DMRS ports and / or PUSCH resources in MsgA may be partitioned to indicate initial random access and BFR triggered random access. Based on the partition, in the case of 4-step RACH, the WTRU may use the BFR partition on the PRACH / RO resources in Msg1 for random access, as shown at 640 in the example of FIG. 6. Based on the partition, in the case of 2-step RACH, the WTRU may use the BFR partition on the PRACH / RO resources and / or PUSCH resources in MsgA for random access, as further shown at 660 in the example of FIG. 6. Resource partitioning may be performed across a combination of time, frequency, and code domains.

[0116] A method for beam failure recovery request for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) is proposed. To enable operational flexibility and performance for MIMO, a method for flexible beam failure recovery (BFR) management is proposed. A method of two-stage BFR request (BFRQ) for flexible BFR management may be considered. To reduce overhead and enable flexible BFR management, two-stage BFRQ may be used. In such a method, small information with a small payload size may be transmitted in a first stage BFRQ, followed by large information with a large payload size as needed. Large information with a large payload size may be transmitted in a second stage BFRQ.

[0117] The WTRU may transmit a first stage BFRQ and may expect to receive a NW response. The WTRU may transmit a second stage BFRQ with more information if necessary, and the first NW response may indicate whether more information is needed.

[0118] By doing so, flexible BFR management can be achieved and signaling overhead can be managed. Furthermore, a trade-off between overhead and reliability can be achieved. The first NW response can indicate whether a second stage BFRQ is needed. It is also possible to use a second stage BFR report (BFRR) instead of a second stage BFRQ. The first NW response can indicate whether more information is needed and what format can be used for the more information. If second stage information is needed, the WTRU can choose between BFRQ and BFRR.

[0119] After transmitting the second stage BFRQ or BFRR, the WTRU may expect to receive a subsequent NW response, which is a second NW response.

[0120] Due to different information sizes, different containers may be used for the first stage information (e.g., BFRQ) and the second stage information (e.g., BFRQ, BFRR). For example, the first stage information or BFRQ may use PRACH transmission, and the second stage information, BFRQ or BFRR, may use PUCCH transmission. The PUCCH transmission may be transmitted, for example, without an uplink grant. The second stage information, BFRQ or BFRR, may also use MAC CE or a logical equivalent. In some examples, BFRQ may use PUCCH transmission or a logical equivalent, and BFRR may use MAC CE or a logical equivalent.

[0121] In some examples, the first stage information may use PUCCH transmission, or a logical equivalent that may be configured, and the second stage information may use MAC CE, or a logical equivalent, if an uplink grant is present.

[0122] FIG. 7 illustrates an example of a two-stage BFRQ management procedure. The WTRU may detect a beam failure, as shown at 710 in FIG. 7. If a beam failure is detected, the WTRU may attempt to identify a new beam, as shown at 720. Once a new beam is identified, the WTRU may transmit a BFR request (first BFR request), as shown at 730. The WTRU may expect to receive a NW response (first NW response), as shown at 740. The WTRU may evaluate whether a second BFR request is needed, as shown at 750. The base station / TRP may instruct the WTRU to transmit the second BFR request. If the WTRU receives an indication in the NW response that a second BFR request is needed, the WTRU may transmit a second BFRQ, as shown at 770, and wait for a subsequent NW response, as shown at 780. If the WTRU receives the second NW response within a predefined or (pre)configured window, the BFR procedure is successfully completed, as shown at 760. If the second BFR request is not indicated in the first NW response, the WTRU may not continue to transmit the second BFRQ and receive subsequent NW responses. In this case, the BFR procedure is also declared successfully completed, as shown at 760. The second BFR request may be indicated in a downlink control information (DCI) carried in a physical downlink control channel (PDCCH) transmission of the first NW response. A new control field in the DCI may include an indicator of the second BFR request to enable a two-stage BFRQ procedure.

[0123] FIG. 8 illustrates an example of a two-stage BFRQ management procedure with a maximum number of retransmissions. As shown in FIG. 8, at 810, the WTRU may detect a beam failure. If a beam failure is detected, the WTRU may attempt to identify a new beam, as shown in 820. Once a new beam is identified, the WTRU may transmit a BFR request (first BFR request), as shown in 830. At 840, the WTRU may expect to receive a network response (first network response). If a second BFR request is required, the base station / TRP may instruct the WTRU via the network response to transmit the second BFR request. If a second BFR request is not required and is not indicated by the network response, the WTRU and / or the base station / TRP may consider the BFR procedure successful, as shown in 852. If the WTRU receives an indication in the network response that a second BFR request is required, the WTRU may transmit a second BFRQ and wait for a second network response (as shown at 853) or a subsequent network response (as shown at 853), as shown at 851. If the WTRU determines that it has received a second network response, as shown at 860, the BFR procedure may be considered to have completed successfully (versus that shown at 852). Otherwise, if the second BFRQ retransmission does not reach a maximum number of re-transmission (re-Tx) attempts, as shown at 870, the WTRU may retransmit the second BFRQ and wait for a subsequent NW response, as shown at 872. If the second BFRQ retransmission reaches a maximum, the WTRU may declare the BFR procedure to have failed, as shown at 871.

[0124] If the first network response does not indicate that the WTRU should send a second BFR request, the WTRU may not need to continue sending the second BFRQ and receiving subsequent NW responses, after which the BFR procedure may be declared successfully completed.

[0125] The maximum number of retransmissions of the first BFRQ and the second BFRQ may be configured differently to trade off performance, or to improve reliability, reduce latency, or reduce overhead, etc. Additionally, the maximum number of common retransmissions of the first BFRQ and the second BFRQ may also be configured.

[0126] Methods for BFRQ reliability improvement and diversity transmission are proposed for MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO). During BFR stage 3, the WTRU may transmit a BFRQ to the base station / TRP according to one or more of the following procedures.

[0127] The BFRQ may be transmitted on a new beam corresponding to a single NBI or on multiple beams corresponding to multiple NBIs. For example, the BFRQ may be performed explicitly by uplink physical signaling (e.g., PRACH transmission).

[0128] Multiple NBIs may be associated with one TRP (e.g., NBI-RS Set 1) or multiple TRPs (e.g., NBI-RS Sets 1, 2, ..., M). For high reliability and low latency, the WTRU may be triggered to transmit a BFRQ on multiple beams corresponding to multiple NBIs. The WTRU may transmit a single BFRQ in multiple beams corresponding to multiple NBIs or multiple BFRQs in multiple beams corresponding to multiple NBIs. This may increase overhead. For low complexity and low overhead, the WTRU may be triggered to transmit a single BFRQ on a single beam corresponding to a single NBI (or one TRP). This may result in low complexity and low overhead at the expense of low reliability.

[0129] The BFRQ may be repeated to reduce PRACH or HARQ retransmissions. To improve beam failure recovery procedures, an adaptive multi-stage BFRQ or an incremental number of beams corresponding to multiple NBIs for (re)transmissions may be utilized. The WTRU may (re)transmit the BFRQ on either a single beam or multiple beams. For example, the WTRU may initially transmit the BFRQ on a single beam and retransmit the BFRQ on multiple beams. The WTRU may retransmit the BFRQ on an increased number of beams. For example, for the first BFRQ retransmission, the WTRU may use two beams, for the second BFRQ retransmission, the WTRU may use three beams, and so on. By doing so, the WTRU may increase the chances of successfully (re)transmitting the BFRQ while maintaining the overall overhead at a particular level. The adaptation process may use a BFRQ failure counter, where each time instance of the BFRQ retransmission is increased in capacity (e.g., a larger number of beams).

[0130] Selection of the number of BFRQs and / or the number of beams can be based on the relative difference of the received signal quality, such as BLER, versus a threshold signal quality. A larger (or smaller) gap between the received signal quality and the threshold signal quality may require a higher (lower) number of NBIs.

[0131] FIG. 9 illustrates an example method for adaptive transmission of BFRQ. As shown in FIG. 9, at 910, a WTRU capable of detecting a beam failure event monitors a BFRQ transmission against one or several quality thresholds. If the beam quality or radio link quality of the monitored BFRQ transmission falls below a set threshold, a beam failure event is detected and a counter tracking the number of beam failure events (BFEs) may be set to "0". To generate a BFRQ retransmission, the WTRU may take into account a trade-off between reliability and overhead by evaluating the difference between the link quality and one or several quality thresholds. The WTRU may then transmit the BFRQ via a random access procedure based on a desired selection of a trade-off between reliability and overhead, e.g., via a number of NBIs, a number of BFRQs, etc. For example, at 920, if the relative difference in link quality is greater than a given amount, the WTRU may recognize a BFE for high reliability (e.g., multiple BFRQs in multiple NBIs), as shown at 921. At 920, if the relative difference in link quality exceeds a given amount x, the WTRU may recognize the BFE for low overhead (e.g., a single BFRQ in a single NBI), as shown at 922. The network may then provide a response regarding the BFR procedure received by the WTRU, as shown at 930. If the BFR procedure fails and the BFE counter falls below a configured maximum (e.g., based on timing constraints), the WTRU may be requested to generate one or more additional BFRQs with broader capabilities (e.g., additional NBIs). The indication from the network may be explicit (e.g., common or dedicated downlink signaling) or implicit (downlink resource selection). The process may continue until the BFR is indicated as successful, and parameters such as the difference between the measured threshold and the quality threshold may be updated via dedicated downlink signaling (e.g., uplink grant) or implicitly via downlink resource selection. The threshold update may be based on the performance of the BFRQ retransmission process for a better tradeoff between reliability and complexity for future beam failure events.If this is not the case, the BFR procedure may be unsuccessful in re-establishing the connection and a link recovery procedure may be required.

[0132] Methods in which the network can respond to the BFRQ are described for MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO). After receiving the BFRQ, the network can decide to confirm or reject the BFRQ based on metrics such as service availability, resource availability, etc. In some methods, the network can send a confirmation of the new NBI in the DCI as a new DCI field NBI_confirmation. If the NBI_confirmation field is set to 1, the WTRU can use the new NBI. For example, if the NBI_confirmation field is 0, the WTRU can receive a new TCI state / panel selection that overrides the WTRU's recommendation for the new beam.

[0133] FIG. 10 illustrates an example of how the network may respond to a BFRQ. As shown at 1010, the network receives the BFRQ transmitted by the WTRU. The network decides at 1020 whether to acknowledge or reject the BFRQ based on one or more metrics described in the paragraph above. If the network acknowledges the BFRQ at 1030, the network sends a message to the WTRU including a parameter or field acknowledging the BFRQ. As shown at 1033, the parameter or field may be a 1-bit (or 2-bit) field having a value of 0 or 1. Upon transmission / reception of the message acknowledging the BFRQ, the network and the WTRU may start using one or more new beams as shown at 1034. If the network rejects the BFRQ at 1030, the parameter or field value is set to 0, as shown at 1031, indicating that the network has rejected the BFRQ.

[0134] In some method sets, after receiving the BFRQ, the network may directly override the WTRU's recommendation by sending a TCI Status / Panel Selection message to the WTRU, as shown at 1032 in Figure 10. The WTRU may then use the new beam indicated by the network.

[0135] In some sets of methods, in the DCI or another logically equivalent message, the WTRU may receive a new field indicating the TCI state to confirm or override the WTRU's recommendation for the beam. This is a new field with a longer bit width, such as 4 bits, to indicate the TCI state. As an example, 1111 may indicate confirmation, and other combinations may indicate 15 other potential TCI states.

[0136] A method of WTRU controlled beam failure recovery is proposed for MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO). A WTRU controlled BFR with beam failure recovery command is proposed. Event-triggered and / or condition-based BFR may be used. Based on certain criteria and conditions, a new set of NBI-RS resources may be triggered and the WTRU may switch from the original set of NBI-RS resources to measure the new set of NBI-RS resource sets. This may be used to prevent the WTRU from not finding the authorized NBI-RS resources and entering into a contention-based random access procedure, which may have large latency and long delays.

[0137] In some cases, q1 may be bad, the original NBI-RS resource may not be of good quality, or the NBI or new beam may not be found. In such cases, a contention-based 4-step random access may be triggered.

[0138] In addition, even if the new beam identification passes, there may be a high probability that the BFRQ will not reach the TRP when the beam condition is poor. In such a case, the BFR procedure cannot be continued and the beam failure recovery may not be completed.

[0139] Based on the pre-configuration, the WTRU can control the BFR. The WTRU can autonomously switch to a new NBI-RS resource set. The WTRU can find an NBI from the new NBI-RS resource set.

[0140] A primary and secondary set of q1 or NBI-RS resource sets may be defined. The WTRU may monitor and measure the primary NBI-RS resource set. The secondary NBI-RS resource set may be triggered if the channel and / or beam quality and / or conditions deteriorate, become unreliable, or fall below a certain threshold. The WTRU may first monitor and measure the primary NBI-RS resource set and switch to the secondary NBI-RS resource set if the channel and / or beam quality and / or conditions deteriorate. The WTRU may autonomously perform NBI-RS resource set switching based on criteria and / or conditions.

[0141] Additionally, associated measurement metrics may be configured or pre-configured. One measurement metric may be associated with a primary set and another measurement metric may be associated with a secondary set. For example, L1-SINR may be used and associated with a primary NBI-RS resource set, and L1-RSRP may be used and associated with a secondary NBI-RS resource set. In some examples, L1-RSRP may be used and associated with both the primary and secondary NBI-RS resource sets.

[0142] A base station (e.g., a base station) can configure a secondary NBI-RS resource set in addition to the primary NBI-RS set. When the channel conditions deteriorate (e.g., L1-RSRP < T1, L1-SINR < T2), the WTRU can switch to the secondary set. Other conditions or criteria such as the number of PDCCH transmissions sent without an ACK response, missing PDCCH transmissions, the number of NACKs, or the NACK / ACK ratio > a threshold can also be considered.

[0143] A WTRU control BFR with a beam failure recovery command can be used. The WTRU can send the beam failure recovery command to the NW and the control BFR procedure. The WTRU can notify the base station / TRP of its decision. The WTRU can request the base station / TRP to switch to a new NBI-RS resource set and a new beam for measurement and monitoring.

[0144] The WTRU can use a new beam (e.g., within a secondary NBI-RS resource set determined by the WTRU or a new NBI-RS resource set, rather than within the primary NBI-RS resource set determined by the base station) to send further communication with the base station and / or TRP, e.g., a BFRQ, to the base station / TRP. After the BFR procedure has completed successfully, both the base station / TRP and the WTRU can switch to the new beam selected by the WTRU.

[0145] The primary and secondary NBI-RS resource sets may not be uniform and may have different sizes for the resource sets. The primary NBI-RS resource set may always have a high priority. The secondary NBI-RS resource set may have a lower priority. Additionally, the secondary NBI-RS may have multiple resource sets, each with a different associated priority. The WTRU may be enabled or configured with this capability. The WTRU may transmit a Beam Failure Recovery Order (BFRO) over a selected beam selected from the secondary NBI-RS resource set when the channel and / or beam conditions deteriorate or fall below a certain threshold. Otherwise, the WTRU may initiate a four-step random access procedure with a long delay.

[0146] FIG. 11 illustrates an example method of WTRU controlled beam failure recovery. The base station / TRP 1101 may transmit a BFD-RS that may be detected or received by the WTRU 1102. The WTRU 1102 may monitor the PDCCH beam accordingly. For example, the WTRU 1102 may monitor the PDCCH DMRS (i.e., the PDCCH beam) QCL'd with the CSI-RS. If the quality of the PDCCH beam is not good, e.g., the measurement is below a certain threshold, beam failure is detected. The WTRU 1102 may then start monitoring the NBI-RS to search for a new beam with a certified link (e.g., the measurement is above a certain threshold). If no such beam is found, e.g., the L1-RSRP is below a certain threshold T, the WTRU may switch to a new NBI-RS. For example, the WTRU 1102 may autonomously switch to a new NBI-RS, or a secondary NBI-RS resource set, to search for a new certified beam. If a new beam is identified, the WTRU 1102 may send a BFR command (BFRO) to the base station / TRP 1101. The base station / TRP 1101 may acknowledge the received BFRO. The WTRU 1102 may control the BFR procedure during a situation where channel / beam conditions deteriorate. Because the WTRU 1102 may determine that it has another opportunity to find a new beam in a new set of NBI-RS resources, the WTRU 1102 may avoid the opportunity to initiate a contention-based random access procedure with a long delay.

[0147] 12 shows an example procedure for a WTRU controlled beam failure recovery procedure. As shown at 1210, a WTRU may be configured to utilize autonomous WTRU controlled beam failure recovery for a MIMO (e.g., massively distributed MIMO, cell-less MIMO, or user-centric MIMO) system. The autonomous WTRU controlled beam failure recovery functionality may be enabled by the WTRU based on, e.g., a configuration message, a condition.

[0148] The WTRU may monitor the BFD-RS for the MIMO system, as shown at 1220. The WTRU may first measure the primary NBI-RS resource, as shown at 1230. The WTRU may transmit the BFRQ, as shown at 1240, using the NBI selected from the primary NBI-RS resource set. The WTRU may evaluate the beam / channel quality of the primary NBI-RS resource set, as shown at 1250. If the beam / channel quality deteriorates (e.g., measurements of L1-RSRP, L1-SINR, etc., fall below a (pre)configured threshold), the WTRU may autonomously switch to the secondary NBI-RS resource set, as shown at 1254. The WTRU may continue the beam failure recovery procedure and measure the secondary NBI-RS resource, as shown at 1255. The WTRU may transmit the BFRQ, as shown at 1256, using the NBI selected from the secondary NBI-RS resource set. The WTRU may receive the DCI over the PDCCH for a response from the base station / TRP, as shown at 1260. At 1270, the WTRU may complete a beam failure recovery procedure using the secondary NBI-RS for MIMO.

[0149] At 1250, if the beam / channel quality has not deteriorated (e.g., measurements such as L1-RSRP, L1-SINR, etc. do not fall below a (pre)configured threshold), the WTRU may remain on the primary NBI-RS resource set, as shown at 1251. The WTRU may continue the beam failure recovery procedure and measure the primary NBI-RS resources, as shown at 1252. The WTRU may transmit a BFRQ with an NBI selected from the primary NBI-RS resource set, at 1253. The WTRU may receive a DCI over the PDCCH for response from the base station / TRP, as seen at 1260. At 1270, the WTRU may complete the beam failure recovery procedure using the primary NBI-RS for MIMO.

[0150] FIG. 13 illustrates an example of a method of beam failure recovery procedure for MIMO. It should be noted that the flow diagram provided in FIG. 13 may include a combination of different methods described in more detail separately in the above paragraphs. Therefore, further understanding of FIG. 13 may be obtained from other parts of the detailed description. From the example of FIG. 13, it should be clear to a person skilled in the art that various different solutions for beam failure recovery proposed herein may be implemented alone or in any combination. It should be clear to a person skilled in the art that other embodiments not directly shown in FIG. 13 are possible (e.g., embodiments that do not include each step shown in FIG. 13, or embodiments that include other steps not shown in FIG. 13).

[0151] As shown in Figure 13, the WTRU may be configured to perform a MIMO-based beam failure recovery procedure. At 1310, the WTRU may be configured with various different parameters for beam failure recovery, including, for example, a beam failure detection type, an adaptive BFD-RS set, and a priority value associated with RS resources. In some embodiments, the WTRU may be configured with a BFR assistance information reporting type, as described in more detail in the paragraph above. The WTRU may be further configured with flexible BFR management capabilities, as described in more detail in the paragraph above.

[0152] As shown at 1320, the WTRU may perform partial beam failure detection if configured. Otherwise, as shown at 1321, the WTRU may perform normal (or full) beam failure detection if configured (to reduce MIMO complexity), as further described in the following paragraphs. For the partial beam failure detection case, at 1326, the WTRU may monitor the BFD-RS based on a priority associated with the BFD-RS resource. As shown at 1327, the WTRU may monitor the BFD-RS using different metrics (e.g., L1-SINR, L1-RSRP) associated with different monitoring periodicities to further reduce the complexity resulting from MIMO. The WTRU may, for example, send a beam failure recovery request (BFRQ) or a beam switch request (BSR) based on the configured beam failure detection type. The WTRU may send a BFD-RS index along with the BFRQ, BSR, or beam switch recommendation.

[0153] At 1328, the WTRU may send a BFRQ with the BFD-RS index, or the WTRU may send a beam switch request (BSR) or a beam switch recommendation with the BFD-RS index. After the WTRU sends the BFRQ, BSR, or beam switch recommendation, at 1329, the WTRU may receive BFD-RS reconfiguration information using the beam indicated in the transmission configuration indication (TCI) state and monitor the reconfigured BFD-RS resource set to reduce BFR complexity for MIMO.

[0154] If full beam failure detection is performed at 1321, the WTRU may monitor all BFD-RS in the set and may monitor the BFD-RS resources using a single metric (e.g., L1-SINR). The WTRU may be configured to transmit a BFRQ including one or more NBI-RS indices if an NBI is found, as shown at 1323 and 1324.

[0155] If a complete beam failure detection is performed and no NBI is found, as shown at 1323, the WTRU may select a RACH type (e.g., a two-step or four-step RACH procedure) at 1325, for example according to one or more methods described in the paragraphs above. The WTRU may perform random access based on the selected random access type and a configuration or a selected indication type (e.g., an implicit indication as shown in FIG. 13, or an explicit indication) to indicate whether a RACH procedure is performed for initial access for beam failure triggered random access. In case of an implicit indication, for example, the WTRU may perform a RACH procedure using resources related to beam failure recovery. If the WTRU performs random access, as shown at 1351, the WTRU does not transmit a BFRQ and the BFR procedure is considered to be completed.

[0156] As shown at 1330, the WTRU may determine whether to transmit a BFRQ with assistance information, for example, if the BFR assistance information type is configured to improve performance of a MIMO-based BFR procedure.

[0157] The WTRU may transmit a first BFRQ with a small payload (e.g., without assistance information as shown at 1331 or with assistance information as shown at 1332). The WTRU may receive DCI using a PDCCH transmission sent by the network in response to the BFRQ to reduce overhead associated with MIMO.

[0158] The WTRU may receive and decode the PDCCH transmission and obtain the DCI, as shown at 1340. If the DCI in the response indicates a subsequent request type, i.e., a second BFR request (BFRQ) type or a BFR report (BFRR) type, at 1340, the WTRU may transmit a second request signal having the indicated type (BFRQ or BFRR) with a larger payload, as shown at 1352, and the WTRU may receive the second DCI using a second PDCCH transmission from the network, as shown at 1353, to improve performance and flexibility for MIMO. If the initial DCI does not indicate a subsequent request type or indicates that a second BFRQ is required, as shown at 1351, the BFR procedure may be considered complete.

[0159] The WTRU may retransmit the request signal / channel with the indicated type (BFRQ or BFRR) using an adaptive NBI and an incremental NBI for each retransmission if no DCI is received from the network in response. The WTRU may receive the DCI in the retransmitted PDCCH transmission.

[0160] The WTRU may complete the beam failure recovery procedure within a maximum number of retransmissions of the first and / or second BFRQ for MIMO and may declare the beam failure recovery procedure successful for MIMO, otherwise the WTRU may declare the beam failure recovery procedure for MIMO failed.

[0161] Further examples according to one or more of the above mentioned solutions are provided herein.

[0162] In some examples, the WTRU performs a MIMO-based beam failure recovery procedure. The WTRU may be configured with a beam failure detection type, an adaptive BFD-RS set, and a priority associated with the RS resource. The WTRU may be configured with a BFR assistance information reporting type. The WTRU may further be configured with a flexible BFR management function. The WTRU may perform one or more of the following steps. For example, the WTRU may perform partial beam failure detection if configured, and perform normal beam failure detection if configured otherwise (to reduce MIMO complexity). The WTRU may monitor the BFD-RS based on the priority associated with the BFD-RS resource and using different metrics (e.g., L1-SINR, L1-RSRP) associated with different monitoring periodicities (to further reduce the complexity resulting from MIMO). The WTRU may send a beam failure recovery request (BFRQ) or a beam switching request (BSR) based on the beam failure detection type. The WTRU may send a BFD-RS index or an NBI-RS index depending on the beam failure detection type. If a partial beam failure detection type is configured, the WTRU may transmit a BFRQ with the BFD-RS index. If a partial beam failure detection type is configured (to reduce MIMO latency), the WTRU may transmit a BSR or beam switch recommendation with the BFD-RS index. If a normal beam failure detection type is configured, the WTRU may transmit a BFRQ with the NBI-RS index. The WTRU may receive BFD-RS reconfiguration information using the beam indicated in the transmission configuration indication (TCI) state and monitor the reconfigured BFD-RS resource set if a partial beam failure detection type is configured (to reduce BFR complexity for MIMO). If a BFR assistance information type is configured (to improve performance of MIMO-based BFR), the WTRU may transmit a BFRQ with the assistance information.The WTRU may select a random access type if the NBI is not found and perform random access based on the selected random access type (2-step or 4-step) and the configured indication type (explicit or implicit indication).

[0163] The WTRU may transmit a first BFRQ with a small payload and receive a DCI or another logically equivalent message in a PDCCH transmission that is a NW response (to reduce overhead associated with MIMO). If the DCI in the NW response indicates that a subsequent request type is required, i.e., a BFR request (BFRQ) type or a BFR report (BFRR) type, the WTRU may receive and decode the PDCCH transmission and obtain the DCI. The WTRU may then transmit a second request signal / channel with an indicated type (BFRQ or BFRR) with a large payload. The WTRU may receive the second DCI in a second PDCCH in the NW response (to increase performance and flexibility for MIMO). If the DCI in the PDCCH in the NW response is not received, the WTRU may retransmit the request signal / channel with the indicated type (BFRQ or BFRR) with an adaptive NBI and an incremental NBI for each retransmission. The WTRU may receive the DCI in the retransmitted PDCCH. The WTRU may complete the beam failure recovery procedure within a maximum number of retransmissions of the first and / or second BFRQ for MIMO and declare the beam failure recovery procedure successful for MIMO, otherwise the WTRU may declare the beam failure recovery procedure for MIMO failed.

[0164] In some examples, the WTRU may autonomously perform and control the beam failure recovery procedure for MIMO. The WTRU may be configured and enabled with the functionality of autonomous WTRU controlled beam failure recovery for MIMO. The WTRU may perform one or more of the following steps: The WTRU may monitor the BFD-RS for MIMO. The WTRU may measure the primary NBI-RS resources. The WTRU may transmit a BFRQ with an NBI selected from the primary NBI-RS resource set. If the beam / channel quality deteriorates (e.g., measurements of L1-RSRP, L1-SINR, etc., fall below a (pre)configured threshold), the WTRU may autonomously switch to the secondary NBI-RS resource set. The WTRU may continue the beam failure recovery procedure and measure the secondary NBI-RS resources. The WTRU may transmit a BFRQ with an NBI selected from the secondary NBI-RS resource set. The WTRU may receive DCI on the PDCCH for a response from the base station / TRP. The WTRU may complete the beam failure recovery procedure for MIMO.

[0165] Although the features and elements are described above in certain combinations, one skilled in the art will understand that each feature or element may be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs). A processor associated with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer. Although features and elements for massively distributed MIMO are described, they may also be applicable to cell-less MIMO or user-centric MIMO.

Claims

1. A method for recovering beam interference in a system utilizing a multi-input multi-output (MIMO) antenna system, Receiving configuration information including beam fault recovery parameters, wherein the beam fault recovery parameters are Information indicating the number of resources in the first beam fault detection (BFD) reference signal (RS) resource set to be monitored, Priority information associated with each of the resources in the first BFD-RS resource set, This includes, Monitoring the number of the indicated resources in the first BFD-RS resource set based on the priority information associated with each of the resources, wherein monitoring the number of the indicated resources in the first BFD-RS resource set is Using a first measurement periodicity, a first signal quality metric is measured for a first subset of resources in the first BFD-RS resource set, Using a second measurement periodicity, a second signal quality metric is measured for a second subset of resources in the first BFD-RS resource set, This includes, Sending a message to obtain a second BFD-RS resource set, wherein the message includes an index associated with one of the resources of the first BFD-RS resource set. Receiving reconstruction information indicating the second BFD-RS resource set, wherein the second BFD-RS resource set includes resources selected based on one of the resources of the first BFD-RS resource set. To perform beam fault recovery using one of the resources of the second BFD-RS resource set, at least a first beam fault recovery request message (BFRQ) is sent, Receiving at least a response to the first BFRQ indicating that the beam fault recovery procedure has been completed, Methods that include...

2. The method according to claim 1, wherein at least the response to the first BFRQ includes downlink control information (DCI) that includes information confirming the first BFRQ to perform beam fault recovery using one of the resources of the second BFD-RS resource set.

3. The method according to claim 1, wherein at least the response to the first BFRQ includes downlink control information (DCI) that overrides the first BFRQ to perform beam fault recovery using one of the resources of the second BFD-RS resource set, the DCI further indicates different resources to be used for beam fault recovery.

4. The method according to claim 1, wherein at least the response to the first BFRQ includes downlink control information (DCI) that includes information indicating that a second BFRQ is to be transmitted, the method further comprises transmitting the second BFRQ and receiving DCI in response to the second BFRQ, the DCI in response to the second BFRQ including one of the information that confirms or overrides the second BFRQ.

5. The method according to claim 1, wherein the beam fault recovery parameter includes information indicating whether support information should be included when transmitting a BFRQ, and the support information includes one or more of a new beam identifier (NBI), a signal quality measurement associated with the new beam identifier, and the difference between the signal quality measurement associated with the new beam identifier and a threshold.

6. The method according to claim 5, wherein the NBI identifies one of the beams associated with the highest signal quality measurement or the beam having a signal quality metric that exceeds the threshold.

7. The method according to claim 5, wherein the support information is transmitted using resources associated with a physical random access channel (PRACH) opportunity, a random access channel (RACH) opportunity, or a physical uplink control channel (PUCCH), or a media access control element (MAC CE).

8. The method according to claim 1, wherein the message for obtaining the second BFD-RS resource set is one of BFRQ, Beam Switching Request (BSR), Beam Switching Recommendation, or Beam Switching Command.

9. The method according to claim 1, wherein the message transmitted to obtain the second BFD-RS resource set includes an indication of a transmission configuration indication (TCI) state, and the reconfiguration information is received using parameters based on the indicated TCI state.

10. The method according to claim 1, wherein the first signal quality metric is the Layer 1 (L1) signal-to-interference noise ratio (SINR), and the second signal quality metric is the L1 reference signal received power (RSRP).

11. A wireless transceiver unit (WTRU) configured to perform beam fault recovery in a system utilizing a multi-input multi-output (MIMO) scheme, Processor and Equipped with a transceiver, The processor and the transceiver are configured to receive configuration information including beam fault recovery parameters, and the beam fault recovery parameters are Information indicating the number of resources in the first beam fault detection (BFD) reference signal (RS) resource set to be monitored, Includes priority information associated with each of the resources in the first BFD-RS resource set, The processor and the transceiver are configured to monitor the number of the indicated resources in the first BFD-RS resource set based on the priority information associated with each of the resources, and monitoring the number of the indicated resources in the first BFD-RS resource set is The processor and the transceiver are configured to measure a first signal quality metric for a first subset of resources in the first BFD-RS resource set using a first measurement periodicity, The processor and the transceiver are configured to measure a second signal quality metric for a second subset of resources in the first BFD-RS resource set using a second measurement periodicity. Includes, The processor and the transceiver are configured to send a message for obtaining a second BFD-RS resource set, the message including an index associated with one of the resources of the first BFD-RS resource set. The processor and the transceiver are configured to receive reconfiguration information indicating the second BFD-RS resource set, the second BFD-RS resource set includes resources selected based on one of the resources of the first BFD-RS resource set. The processor and the transceiver are configured to send at least a first beam fault recovery request message (BFRQ) to perform beam fault recovery using one of the resources of the second BFD-RS resource set. The processor and the transceiver are configured to receive at least a response to the first BFRQ indicating that the beam fault recovery procedure has been completed. WTRU.

12. The WTRU according to claim 11, wherein at least the response to the first BFRQ includes downlink control information (DCI) that confirms the first BFRQ to perform beam fault recovery using one of the resources of the second BFD-RS resource set.

13. The WTRU according to claim 11, wherein at least the response to the first BFRQ includes downlink control information (DCI) that overrides the first BFRQ to perform beam fault recovery using one of the resources of the second BFD-RS resource set, the DCI further indicates different resources to be used for beam fault recovery.

14. The WTRU according to claim 11, wherein the response to at least a first BFRQ includes downlink control information (DCI) which includes information indicating that a second BFRQ is to be transmitted, and the processor and the transceiver are further configured to transmit the second BFRQ and receive DCI in response to the second BFRQ, and the DCI in response to the second BFRQ includes one of the information which confirms or overrides the second BFRQ.

15. The WTRU according to claim 11, wherein the beam fault recovery parameter includes information indicating whether support information should be included when transmitting a BFRQ, the support information including one or more of a new beam identifier (NBI), a signal quality measurement associated with the new beam identifier, and the difference between the signal quality measurement associated with the new beam identifier and a threshold.

16. The WTRU according to claim 15, wherein the NBI identifies one of the beams associated with the highest signal quality measurement or the beam having a signal quality metric that exceeds the threshold.

17. The WTRU according to claim 15, wherein the support information is transmitted using resources associated with a physical random access channel (PRACH) opportunity, a random access channel (RACH) opportunity, or a physical uplink control channel (PUCCH), or a media access control element (MAC CE).

18. The WTRU according to claim 11, wherein the message for obtaining the second BFD-RS resource set is one of BFRQ, Beam Switching Request (BSR), Beam Switching Recommendation, or Beam Switching Command.

19. The WTRU according to claim 11, wherein the message transmitted to obtain the second BFD-RS resource set includes an indication of a TCI (transmission configuration indication) state, and the reconfiguration information is received using parameters based on the indicated TCI state.

20. The WTRU according to claim 11, wherein the first signal quality metric is the Layer 1 (L1) signal-to-interference noise ratio (SINR), and the second signal quality metric is the L1 reference signal received power (RSRP).

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