Method and apparatus for beam failure recovery in MIMO systems

Abstract

Methods and apparatus for beam failure recovery are described herein. A method may include receiving configuration information including parameters for beam failure recovery; determining whether to perform regular beam fault detection or partial beam fault detection based on the configuration information; and monitoring a plurality of beam fault detection reference signals (BFD-RSs) based on the determination. A method may also 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 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 switching request, or a beam switching suggestion. The plurality of BFD-RSs may include a greater number of BFD-RSs when performing conventional beam fault detection than when performing partial beam fault detection.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 329,229, filed on April 8, 2022, the contents of which are incorporated herein by reference. Background Art

[0003] Multiple-input multiple-output (MIMO) methods may have an impact on the beam failure recovery (BFR) process. The deployment of MIMO systems (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) can be used to enhance beam quality, mitigate beam failures, and increase the chances of beam failure recovery. However, this technique can also increase system overhead and complexity / power as well as latency. As the number of transmit / receive points (TRPs) increases, the beam failure detection reference signal (BFD-RS) resources (i.e., q0) increase, and the new beam identifier (NBI-RS) resources (i.e., q1) also increase. The wireless transmit / receive unit (WTRU) may need to monitor a larger q0 set, i.e., more BFD-RS sets, and a large q1 set (NBI-RS set). In addition, greater signaling and RS overhead as well as latency and performance can be expected for monitoring, measurement, BFR request, and corresponding network (NW) response transmission and reception. Summary of the invention

[0004] Methods and apparatus for beam failure recovery are described herein. A method may include: receiving configuration information including parameters for beam failure recovery; determining whether to perform conventional beam failure detection or partial beam failure detection based on the configuration information; and monitoring multiple beam failure detection reference signals (BFD-RS) based on the determination. A method may also include: sending at least one message based on the monitored BFD-RS; receiving a response to the at least one message sent; and determining that the beam failure recovery is complete based on the received response. The at least one message may be at least one of a beam failure recovery request, a beam switching request, or a beam switching suggestion. The multiple BFD-RSs may include a greater number of BFD-RSs when performing conventional beam failure detection than when performing partial beam failure detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A more detailed understanding may be obtained from the following description given by way of example in conjunction with the accompanying drawings, in which like reference numerals indicate similar elements, and in which:

[0006] Figure 1A is a system diagram illustrating an example communication system in which one or more disclosed embodiments may be implemented;

[0007] Figure 1Bis an example of an embodiment in which Figure 1A A system diagram of an example wireless transmit / receive unit (WTRU) for use within the illustrated communication system;

[0008] Figure 1C is an example of an embodiment in which Figure 1A a system diagram of an example Radio Access Network (RAN) and an example Core Network (CN) used within the illustrated communication system;

[0009] Figure 1D is an example of an embodiment in which Figure 1A A system diagram of another example RAN and another example CN used within the illustrated communication system;

[0010] Figure 2 An example method for an adaptive q0 mechanism is illustrated;

[0011] Figure 3 A method for partial beam failure detection is illustrated;

[0012] Figure 4 is an illustration of an exemplary design of priority-based beam failure detection;

[0013] Figure 5 An example of a WTRU procedure for BFR with assistance information is illustrated;

[0014] Figure 6 An example method for a BFR-based random access procedure with implicit indication is illustrated;

[0015] Figure 7 An example of a two-stage beam failure recovery request (BFRQ) management process is illustrated;

[0016] Figure 8 An example of a two-stage BFRQ management process with a maximum number of retransmissions is illustrated;

[0017] Fig. 9 An example method for adaptive BFRQ is illustrated;

[0018] Fig.10 An example method by which a network (NW) may respond to a BFRQ is illustrated;

[0019] Fig.11 An example method for WTRU controlled beam failure recovery is illustrated;

[0020] Fig.12 An example procedure for WTRU controlled beam failure recovery is illustrated; and

[0021] Fig.13An example method of a beam failure recovery procedure for MIMO (eg, massively distributed MIMO, cell-free MIMO, or user-centric MIMO) is illustrated. DETAILED DESCRIPTION

[0022] Figure 1A 1 is a diagram illustrating an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple access system that provides content such as voice, data, video, messaging, broadcast, etc. to multiple wireless users. The communication system 100 may enable multiple wireless users to access such content through sharing of system resources (including wireless bandwidth). For example, the communication system 100 may employ 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 multi-carrier (FBMC), etc.

[0023] like Figure 1A As shown, the communication 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, but it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of the 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 send and / or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a subscription-based unit, a pager, a cellular phone, a personal digital assistant (PDA), a smart phone, a laptop, a netbook, a personal computer, a wireless sensor, a hotspot or Mi-Fi device, an Internet of Things (IoT) device, a watch or other wearable device, a head-mounted display (HMD), a vehicle, a drone, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in an industrial and / or automated process chain environment), a consumer electronic device, a device operating on a commercial and / or industrial wireless network, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be interchangeably referred to as a UE.

[0024] 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 evolved Node B (eNB), a Home Node B, a Home evolved Node B, a next generation Node B such as a gNode B (base station), a new radio (NR) Node B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0025] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), a relay node, etc. The base station 114a and / or the base station 114b may be configured to send and / or receive wireless signals on one or more carrier frequencies, which may be referred to as a cell (not shown). These frequencies may be in a licensed spectrum, an unlicensed spectrum, or a combination of licensed and unlicensed spectrums. A cell may provide coverage of wireless services to a specific geographic area, which may be relatively fixed or may change over time. The cell may be further divided into cell sectors. For example, a cell associated with the base station 114a may be divided into three sectors. Therefore, in one embodiment, the base station 114a may include three transceivers, i.e., one transceiver for each sector of the cell. In an 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, beamforming may be used to send and / or receive signals in a desired spatial direction.

[0026] 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).

[0027] More specifically, as noted above, the communication system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology, such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), that may use Wideband CDMA (WCDMA) to establish the air interface 116. WCDMA may include communication protocols, such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0028] In an 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) that may establish the air interface 116 using Long Term Evolution (LTE) and / or Advanced LTE (LTE-A) and / or Advanced LTE Pro (LTE-APro).

[0029] In an embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology (such as NR radio access) that may establish the air interface 116 using NR.

[0030] In an 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 together implement LTE radio access and NR radio access, for example using the dual connectivity (DC) principle. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions transmitted to / from multiple types of base stations (e.g., eNBs and gNBs).

[0031] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies 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), etc.

[0032] Figure 1A The base station 114b in the 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 local area, such as a business location, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, and the like. 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 an 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 utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a picocell or a femtocell. As Figure 1A As shown, the base station 114 b may have a direct connection to the Internet 110. Therefore, the base station 114 b may not need to access the Internet 110 via the CN 106.

[0033] The RAN 104 may be in communication with the CN 106, which may be any type of network configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. The data may have different quality of service (QoS) requirements, such as 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 described in detail in the accompanying drawings, the CN 106 may be configured to provide voice, data, applications, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. Figure 1AAlthough not shown in the figure, it will be appreciated that the RAN 104 and / or the CN 106 may be in direct or indirect communication with other RANs that employ 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 be in communication with another RAN (not shown) that employs GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

[0034] The CN 106 may also act 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 that provides 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) in the TCP / IP Internet protocol suite. The networks 112 may include wired communication networks 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, which may employ the same RAT as the RAN 104 or a different RAT.

[0035] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication 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 via different wireless links). Figure 1A The illustrated WTRU 102c may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0036] Figure 1B is a system diagram illustrating an example WTRU 102. Figure 1B As shown, 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 appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0037] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of 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 decoding, 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 Figure 1B The processor 118 and the transceiver 120 are depicted as separate components, but it is understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0038] The send / receive element 122 may be configured to send a signal to a base station (e.g., base station 114a) or receive a signal from the base station by an air interface 116. For example, in one embodiment, the send / receive element 122 may be an antenna configured to send and / or receive an RF signal. In an embodiment, the send / receive element 122 may be a transmitter / detector configured to send and / or receive, for example, IR, UV or visible light signals. In another embodiment, the send / receive element 122 may be configured to send and / or receive both RF signals and optical signals. It should be understood that the send / receive element 122 may be configured to send and / or receive any combination of wireless signals.

[0039] Although the transmit / receive element 122 Figure 1B 1 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.

[0040] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. For example, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as NR and IEEE 802.11.

[0041] The processor 118 of the WTRU 102 may be coupled to and may receive user input 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 a non-removable memory 130 and / or a removable memory 132. The non-removable memory 130 may include a random access memory (RAM), a 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, and the like. In other embodiments, the processor 118 may access information from and store data in a memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0042] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control power to other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0043] The processor 118 may also be coupled to the 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 the 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 received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by any suitable location-determination method while remaining consistent with an embodiment.

[0044] The processor 118 may also be coupled to other peripherals 138, which may include one or more software modules 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 video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, module, a frequency modulation (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, etc. The peripheral device 138 may include one or more sensors. The sensor may be one or more of the following: a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor; a geographic location sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, a humidity sensor, etc.

[0045] The WTRU 102 may include a full-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) and DL (e.g., for reception)) may be concurrent and / or simultaneous. The full-duplex radio may include an interference management unit for reducing and / or substantially eliminating self-interference via signal processing performed by hardware (e.g., a choke) or via a processor (e.g., a separate processor (not shown) or via the processor 118). In an embodiment, the WTRU 102 may include a half-duplex radio for which transmission and reception of some or all of the signals (e.g., associated with specific subframes for both UL (e.g., for transmission) or DL ​​(e.g., for reception)) may be concurrent and / or simultaneous.

[0046] Figure 1C 1 is a system diagram illustrating the RAN 104 and the CN 106 in accordance with an embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the CN 106.

[0047] The RAN 104 may include evolved Node-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of evolved Node-Bs while remaining consistent with an embodiment. The evolved Node-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the evolved Node-Bs 160a, 160b, 160c may implement MIMO technology. Thus, the evolved Node-B 160a, for example, may use multiple antennas to transmit wireless signals to and / or receive wireless signals from the WTRU 102a.

[0048] Each of the evolved Node Bs 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 UL and / or DL, etc. Figure 1C As shown, the eNode-Bs 160a, 160b, 160c may communicate with one another via an X2 interface.

[0049] Figure 1C The illustrated CN 106 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 depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0050] The MME 162 may be connected to each of the evolved Node-Bs 162a, 162b, 162c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway during an initial attach 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.

[0051] The SGW 164 may be connected to each of the evolved Node-Bs 160a, 160b, 160c in the RAN 104 via an S1 interface. The SGW 164 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions, such as anchoring the user plane during inter-evolved Node-B handovers, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, and the like.

[0052] The SGW 164 may be connected to the 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.

[0053] 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 may be in communication with, an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts 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 networks and / or wireless networks owned and / or operated by other service providers.

[0054] Although the WTRU Figures 1A to 1D Although described as wireless terminals, it is contemplated that in certain representative embodiments, such terminals may (eg, temporarily or permanently) use a wired communications interface with a communications network.

[0055] In a representative embodiment, the other network 112 may be a WLAN.

[0056] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STA) associated with the AP. The AP may have access or an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic to and / or carries traffic away from the BSS. Traffic originating from outside the BSS and leading to the STA may be reached by the AP and may be delivered to the STA. Traffic originating from the STA and leading to a destination outside the BSS may be transmitted to the AP to be delivered to the corresponding destination. Traffic between STAs within the BSS may be transmitted by the AP, for example, wherein the source STA may transmit traffic to the AP, and the AP may deliver traffic to the destination STA. Traffic between STAs within the BSS may be considered and / or referred to as point-to-point traffic. Point-to-point traffic may be transmitted between the source STA and the destination STA (e.g., directly between them) using a direct link establishment (DLS). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunnel DLS (TDLS). A WLAN using an independent BSS (IBSS) mode may not have an AP, and STAs within or using the IBSS (eg, all STAs in the STA) may communicate directly with each other. The IBSS communication mode may sometimes be referred to herein as an "ad hoc" communication mode.

[0057] When using the 802.11ac infrastructure operating mode or a similar operating mode, the AP may send beacons 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 set width. The primary channel may be an operating channel of the BSS and may be used by the STA to establish a connection with the AP. In certain representative embodiments, carrier sense multiple access / collision avoidance (CSMA / CA) may be implemented, for example, in an 802.11 system. For CSMA / CA, a STA (e.g., each STA) (including the AP) may listen to the primary channel. In the case where the primary channel is listened / detected and / or determined to be busy by a specific STA, the specific STA may back off. One STA (e.g., only one station) may transmit at any given time in a given BSS.

[0058] High throughput (HT) STAs may communicate using a 40 MHz wide channel, for example, via a combination of a primary 20 MHz channel and adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel.

[0059] Very high throughput (VHT) STA can support 20MHz, 40MHz, 80MHz and / or 160MHz wide channels. 40MHz channels and / or 80MHz channels can be formed by combining continuous 20MHz channels. 160MHz channels can be formed by combining 8 continuous 20MHz channels, or by combining two non-continuous 80MHz channels (this can be called 80+80 configuration). For 80+80 configuration, after channel coding, the data can pass through a segment parser that can divide the data into two streams. Each stream can be processed by inverse fast Fourier transform (IFFT) and time domain processing separately. These streams can be mapped to two 80MHz channels, and data can be sent by the transmitter STA. At the receiver of the receiver STA, the above-mentioned operation for the 80+80 configuration can be reversed, and the combined data can be transmitted to the medium access control (MAC).

[0060] 802.11af and 802.11ah support operating modes below 1GHz. Channel operating bandwidths and carriers are reduced in 802.11af and 802.11ah relative to those used in 802.11n and 802.11ac. 802.11af supports 5MHz, 10MHz, and 20MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1MHz, 2MHz, 4MHz, 8MHz, and 16MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah may support meter type control / machine type communication (MTC), such as MTC devices in macro coverage areas. MTC devices may have certain capabilities, such as limited capabilities, including support for (e.g., only support for) certain bandwidths and / or limited bandwidths. MTC devices may include batteries with battery life above a threshold (e.g., to maintain very long battery life).

[0061] WLAN systems that can support multiple channels and channel bandwidths (such as 802.11n, 802.11ac, 802.11af, and 802.11ah) include channels that can be designated as primary channels. 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 set and / or limited by a STA (which supports the minimum bandwidth operating mode) from all STAs operating in the BSS. In the example of 802.11ah, for STAs (e.g., MTC-type devices) that support (e.g., only support) a 1MHz mode, the primary channel may be 1MHz wide, even if the AP and other STAs in the BSS support 2MHz, 4MHz, 8MHz, 16MHz, and / or other channel bandwidth operating modes. Carrier sensing and / or network allocation vector (NAV) settings may depend on the state of the primary channel. In the case where the primary channel is busy, for example, because a STA (which only supports a 1MHz operating mode) is transmitting to the AP, all available bands may be considered busy even if most of the available bands remain idle.

[0062] In the United States, the available frequency band for 802.11ah is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. The total bandwidth available for 802.11ah is 6MHz to 26MHz, depending on the country code.

[0063] Figure 1D1 is a system diagram illustrating the RAN 104 and the CN 106 in accordance with an embodiment. As noted 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 be in communication with the CN 106.

[0064] The RAN 104 may include gNBs 180a, 180b, 180c, though it will be appreciated 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 one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 180b may utilize beamforming to send signals to and / or receive signals from the gNBs 180a, 180b, 180c. Thus, the gNB 180a may, for example, use multiple antennas to send wireless signals to and / or receive wireless signals from the WTRU 102a. In an embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, gNB 180a may transmit multiple component carriers to WTRU 102a (not shown). A subset of these component carriers may be on unlicensed spectrum, while the remaining component carriers may be on licensed spectrum. In an embodiment, gNBs 180a, 180b, 180c may implement coordinated multi-point (CoMP) technology. For example, WTRU 102a may receive coordinated transmissions from gNB 180a and gNB 180b (and / or gNB 180c).

[0065] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using transmissions associated with parameter sets that may be scalable. For example, 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., containing varying numbers of OFDM symbols and / or varying absolute time lengths over time).

[0066] 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 while not accessing other RANs (e.g., such as the eNodeBs 160a, 160b, 160c). In a standalone configuration, the WTRUs 102a, 102b, 102c may use one or more of the gNBs 180a, 180b, 180c as mobility anchors. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in an unlicensed band. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate / connect with the gNB 180a, 180b, 180c while also communicating / connecting with another RAN, such as the eNode-B 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement the DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c substantially simultaneously. In a non-standalone configuration, the eNode-B 160a, 160b, 160c may act as a mobility anchor for the WTRUs 102a, 102b, 102c, and the gNB 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0067] Each of the gNBs 180a, 180b, 180c may be associated with a specific cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in UL and / or DL, support of network slicing, interworking between DC, NR, and E-UTRA, routing of user plane data towards a user plane function (UPF) 184a, 184b, routing of control plane information towards an access and mobility management function (AMF) 182a, 182b, etc. Figure 1D As shown, gNBs 180a, 180b, and 180c may communicate with each other via an Xn interface.

[0068] Figure 1DThe illustrated CN 106 may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one session management function (SMF) 183a, 183b, and possible data networks (DNs) 185a, 185b. Although the aforementioned elements are depicted as part of the CN 106, it should be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0069] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the N2 interface and may act as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRU 102a, 102b, 102c, support of network slicing (e.g., handling of different protocol data unit (PDU) sessions with different requirements), selecting a specific SMF 183a, 183b, management of registration areas, termination of non-access stratum (NAS) signaling, mobility management, etc. The AMF 182a, 182b may use network slicing to customize CN support for the WTRU 102a, 102b, 102c based on the type of services utilized by the WTRU 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.

[0070] The SMF 183a, 183b may be connected to the AMF 182a, 182b in the CN 106 via the N11 interface. The SMF 183a, 183b may also be connected to the UPF 184a, 184b in the CN 106 via the N4 interface. The SMF 183a, 183b may select and control the UPF 184a, 184b, and configure the traffic routing through the UPF 184a, 184b. The SMF 183a, 183b may perform other functions, such as managing and allocating UE IP addresses, managing PDU sessions, controlling policy implementation and QoS, providing DL data notification, etc. The PDU session type may be IP-based, non-IP-based, Ethernet-based, etc.

[0071] The UPF 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 via the 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 UPF 184, 184b may perform other functions, such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, etc.

[0072] The CN 106 may facilitate communications with other networks. For example, the CN 106 may include or may communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts 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 networks 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 DNs 185a, 185b via the UPFs 184a, 184b via the N3 interfaces to the UPFs 184a, 184b and the N6 interfaces between the UPFs 184a, 184b and the local DNs 185a, 185b.

[0073] Given that Figures 1A to 1D as well as Figures 1A to 1D Corresponding to the description of the present invention, one or more or all of the functions described herein with reference to one or more of the following items may be performed by one or more simulation devices (not shown): WTRU102a to 102d, base station 114a to 114b, evolved Node B 160a to 160c, MME 162, SGW 164, PGW 166, gNB180a to 180c, AMF 182a to 182b, UPF 184a to 184b, SMF 183a to 183b, DN 185a to 185b and / or any other device described herein. The simulation device may be one or more devices configured to mimic one or more or all of the functions described herein. For example, the simulation device may be used to test other devices and / or simulate network and / or WTRU functions.

[0074] The simulation device may be designed to implement one or more tests of other devices in a laboratory environment and / or in an operator network environment. For example, one or more simulation devices may perform one or more functions or all functions while being fully or partially implemented and / or deployed as part of a wired and / or wireless communication network in order to test other devices within the communication network. One or more simulation devices may perform one or more functions or all functions while being temporarily implemented / deployed as part of a wired and / or wireless communication network. The simulation device may be directly coupled to another device for the purpose of testing and / or performing tests using over-the-air wireless communications.

[0075] One or more simulation devices can perform one or more (including all) functions without being implemented / deployed as part of a wired and / or wireless communication network. For example, the simulation device can be used in a test scenario in a test laboratory and / or a non-deployed (e.g., testing) wired and / or wireless communication network to implement testing of one or more components. One or more simulation devices can be test equipment. Direct RF coupling and / or wireless communication via RF circuits (e.g., which may include one or more antennas) can be used by the simulation device to send and / or receive data.

[0076] Various methods for beam failure detection for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) systems are proposed. Adaptive BFR-RS mechanisms and solutions are proposed. Partial beam failure detection methods are proposed for MIMO. For MIMO-based BFR, partial beam failure detection can be used to reduce latency and delay as well as reduce system complexity. Priority-based beam failure detection methods are proposed for MIMO systems.

[0077] A new beam identification method for MIMO is proposed. BFR auxiliary information and a method with implicit indication of RACH type are proposed for MIMO.

[0078] A beam failure recovery request method for MIMO is proposed. A flexible beam failure recovery (BFR) management method is proposed to achieve operational flexibility and performance of MIMO. BFRQ reliability enhancement and diversity transmission are proposed for MIMO.

[0079] A method of network response BFRQ is proposed for MIMO. A method of WTRU controlled beam failure recovery is proposed for MIMO systems. A method of WTRU controlled BFR with beam failure recovery command is proposed. Event triggers and / or conditional BFR can be used. Based on certain criteria and conditions, a new set of NBI-RS resources can be triggered and the WTRU can switch from the original set of NBI-RS resources to measure the new set of NBI-RS resources. This can be used to prevent the WTRU from not finding any qualified NBI-RS resources and entering a contention-based random access process, which may have large latency and long delays.

[0080] In a fifth generation (5G) new radio (NR) system, a beam failure recovery process may include one or more phases. At least four examples of such phases of a beam failure recovery process may be described as follows: Phase 1: beam failure detection; Phase 2: new beam identification; Phase 3: beam failure recovery request; Phase 4: NW response.

[0081] Stage 1 involving beam failure detection can be described as follows. Beam failure detection may be a combined layer 1 (L1) or layer 2 (L2) process in which an L1 (i.e., referring to a layer 1 entity or hardware (e.g., a processor and a transceiver) or another logically equivalent layer configured to detect, process, or send a layer 1 signal provides an indication of a beam failure instance (BFI) to the medium access control (MAC) layer. The network may 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-RS) or a synchronization signal block (SSB). When the physical (PHY) layer detects that the signal to interference and noise ratio (SINR) of the reference signal of the serving beam is below a threshold (i.e., an assumed 10% block error rate (BLER) of the physical downlink control channel (PDCCH), it may trigger a beam failure instance or may cause the WTRU to identify a beam failure instance and transmit a message to the MAC layer or another logically equivalent layer. The MAC layer may count the indications and declare a failure when the configured maximum number of beam failure indications (BFIs) has been reached.

[0082] A beam failure may be triggered based on, for example, 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 related to the BFI. For example, the WTRU may measure the duration starting from 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. When a certain number of BFIs are observed, for example, such that the number exceeds a threshold (e.g., a configured or preconfigured maximum number of BFAs) 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 start a recovery procedure.

[0083] Phase 2 involving new beam identification can be described as follows. After detecting a beam failure, the WTRU may need to search for and find a new beam. The base station may configure a set of reference signals, such as CSI-RS resources, i.e., NBI-RS (or q1). The WTRU may measure the reference signals and find a suitable beam based on one or more criteria, which may be, for example, a beam with the strongest L1 reference signal received power (RSRP), a beam with an L1-RSRP greater than a predefined or configured threshold, or a beam determined to be the "best" beam based on other criteria. If a suitable new beam is found that meets the above criteria, the WTRU may transmit a beam failure recovery request (BFRQ). If no suitable new beam is found, the WTRU may initiate a contention-based 4-step random access for the purpose of BFR.

[0084] Phase 3 involving the transmission of the BFRQ may be described as follows. Upon detecting a beam failure, the WTRU may initiate a random access procedure for the SpCell for beam failure recovery purposes. For example, depending on the RRC information element of BeamFailureRecoveryConfig, the random access procedure may be contention-based or contention-free. During the random access procedure, the WTRU may send a BFRQ to the base station / TRP.

[0085] Phase 4, which may involve transmission and / or reception of NW responses, may be described as follows. In order to receive a response to the BFRQ sent in the RACH, the WTRU may monitor the random access response (RAR) scrambled by the RA radio network temporary identifier (RNTI) (i.e., in a contention-based case) or the cell-specific RNTI (C-RNTI) (i.e., in a contention-free case) in the control resource set (CORESET) configured for BFR. Such a CORESET may be configured, for example, by the RRC information element of the recoverySearchSpaceId for the SpCell. The WTRU may retransmit the BFRQ until the maximum number of BFRQ retransmissions is reached or the BFR random access procedure is successfully completed. Upon successful completion of the RACH, the beam failure recovery procedure may be completed.

[0086] The various problems that motivate the solutions proposed in this paper are described.

[0087] The beam failure recovery procedure may be supported in Release 15 and / or 16 technical specifications for a single TRP. The beam failure recovery procedure may be supported for up to two TRPs in Release 17 technical specifications. The TRP-specific beam failure recovery procedure may be supported in Release 17 technical specifications.

[0088] MIMO may have an impact on the beam failure recovery process. The deployment of MIMO technology can be used to enhance beam quality, mitigate beam failures 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 resources (i.e., q0) increase and the NBI-RS resources (i.e., q1) also increase. The WTRU may need to monitor more BFD-RS sets (i.e., larger q0 sets) as well as more NBI-RS sets (i.e., large q1 sets). In addition, when MIMO is deployed, high signaling and RS overhead as well as latency and performance can be expected for monitoring, measurement, BFR request and corresponding NW response transmission and / or reception.

[0089] Due to the deployment of MIMO systems, q0 may be large. In the case of a single TRP, the WTRU may be configured with up to three CORESETs. The WTRU may need to monitor periodic CSI-RS resources that are quasi-co-located (QCL-ed) with the CORESET. In the case of 2 TRPs, the WTRU may be configured with up to 5 CORESETs. However, the more TRPs, the higher the number of CORESETs and BFD-RS resources (e.g., CSI-RS resources) that the MIMO system may need to monitor. In the case of MIMO deployment, the beam failure recovery process may need to be extended to cover scenarios with a very large number of TRPs. One problem that arises in these scenarios may be how to enhance BFR with low overhead and low complexity / power design. Another problem may be how to achieve fast BFR and manage beams quickly with low latency and delay. Yet another problem may be how to enhance the reliability and performance of BFR. Yet another problem may be how to ensure that the WTRU can continue and complete the BFR process even if channel conditions deteriorate during the BFR process.

[0090] Various solutions to the above problems are described herein. In some solutions, methods for beam failure detection for MIMO may be provided.

[0091] Adaptive BFD-RS sets, sizes, and periodicity are aspects of potential solutions. In the following paragraphs, a method for beam failure detection for MIMO is considered. As basically described in the above paragraphs, the WTRU may monitor a BFD-RS set (also referred to herein as "q0" or "q0 set"). Due to the deployment of MIMO systems, q0 may be large. The more TRPs used, the higher the number of BFD-RS resources (e.g., CSI-RS resources) that may need to be monitored.

[0092] If the size of q0 is limited to a small set, the system may not be able to fully exploit large-scale TRP deployment. For example, frequent beam failures may occur and may be detected. On the other hand, if a large q0 set is used, large overhead may occur. In addition, high complexity and power may also be introduced.

[0093] The adaptive mechanism of q0 can be used to reduce complexity, overhead and power as well as enhance reliability, improve accuracy and higher performance. Adaptive q0 sets can be used. In addition, adaptive q0 sizes can also be used. Under certain conditions, for example, the beam quality may be higher than a predefined or (pre) configured threshold, and a small BFD-RS resource set for q0 may be used. If a beam failure is detected, the WTRU may need to perform one or more beam failure recovery procedures. Under other conditions, for example, when the beam quality is lower than a predefined or (pre) configured threshold, a large BFD-RS resource set for q0 can be used to avoid entering the beam failure recovery process at the cost of higher overhead and power, because the WTRU may need to monitor and measure a much larger set of RS resources, such as an NBI-RS resource set. In order to balance performance and overhead, adaptive q0 size can be used. In addition, different periods and sets can also be used.

[0094] If q0 is not of good quality, a beam failure may be detected. Different q0 sets and / or different q0 sizes may be utilized. The WTRU may switch between BFD-RS sets q0 of different sizes to balance performance, overhead, and power. Set switching or size switching may be triggered based on certain criteria and conditions, for example, the number and / or ratio of BFDs, the number and / or ratio of NBIs, the number and / or ratio of BFRQs, etc. may be considered and used to make a decision to switch during q0 adaptation. In addition, switching may also be triggered based on measurements such as L1-RSRP, L1-SINR, etc. In addition, switching may also be triggered based on requirements, service type, QoS, etc. In addition, switching may also be triggered based on the number of BFIs.

[0095] In order to reduce overhead and power, for example, for different q0 sets, two or more different periods may be introduced. One period may be used for and associated with a large q0 set, and another period may be used for and associated with a small q0 set. For example, a large period may be used for and associated with a large q0 set, and a small period may be used for and associated with a small q0 set to reduce overhead, etc. By doing so, the WTRU may monitor the large q0 set less frequently due to a longer period, and monitor the small q0 set more frequently due to a shorter period.

[0096] To reduce complexity, different measurement metrics may be used for different q0 sets. Assumed PDCCH BLER or L1-SINR may be used for measurement metrics. Assumed PDCCH BLER or L1-SINR measurement metrics may be more accurate, but may also have high complexity. On the other hand, the L1-RSRP measurement metric may be simple, but may have lower accuracy. If different measurement metrics are used for different q0 sets, complexity can be reduced, power consumption can also be reduced, and there may be some tradeoff between performance, complexity, power, and overhead. For different q0 sets, one measurement metric may be used for and associated with q0 set 1 (i.e., the "first" q0 set), and another measurement metric may be used for and associated with q0 set 2 (i.e., the "second" q0 set). For different q0 sets or sizes, one measurement metric may be used for and associated with q0 size 1, and another measurement metric may be used for and associated with q0 size 2. For example, PDCCH BLER or L1-SINR may be used for and associated with a small q0 set, while L1-RSRP may be used for and associated with a large q0 set, and so on.

[0097] A set-dependent and / or size-dependent measurement metric can be utilized. When the WTRU monitors a larger q0 set, L1-RSRP can be used for fast screening. Fast screening can be a simple measurement using measured received power, such as L1-RSRP measurement, etc. This can reduce complexity and achieve power savings. When it is reduced to a smaller q0 set, the WTRU can switch to the assumed PDCCH BLER L1-SINR for reliability enhancement and better accuracy. Predefined or (pre) configured hopping patterns and / or rules between q0 sets and / or sizes can also be used. The WTRU can jump between different q0 sets and different q0 sizes based on a predefined or (pre) configured hopping pattern, for example, for a large q0 set and a small q0 set. Some monitoring rules can also be applied to different q0 sets and sizes. In addition, the main q0 set and the secondary q0 set can also be defined with different priorities. This method is also applicable to the q1 set. In another example, the WTRU may be configured with a q0 set. The WTRU may measure the beam quality of the BFD-RS of the q0 set 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 of resources (q0') of the q0 set, such as one or more of the BFD-RS with the highest measurement or the BFD-RS with a measurement above a threshold. The WTRU may monitor the beam quality using a second measurement metric (e.g., assumed PDCCH BLER) and may determine beam failure based on the q0' subset.

[0098] Figure 2An example method for an adaptive q0 mechanism is illustrated. The WTRU may be configured or pre-configured with conditions to determine the q0 set and / or size for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO). For example, as shown at 210, the WTRU may receive configuration information indicating these conditions for q0 determination in one or more messages or signals. For example, the signal or message may include an RRC message, a layer 2 message (e.g., one or more MAC control elements (CEs), control information such as layer 1 control information (e.g., downlink control information or DCI), or any logically equivalent message). As shown at 220, the WTRU may determine the 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 period. If it is a large q0 set, as shown at 260, the WTRU may switch to monitoring the q0 set with an associated long period to reduce power. If q0 is a small q0 set with a short period, the WTRU may determine to use L1-SINR as the measurement metric, as shown at 230. It should be understood that in other embodiments not shown, the WTRU may determine to use another measurement metric for the small q0 set. On the other hand, as shown at 270, if q0 is a large q0 set configured with a long measurement period to reduce complexity, the WTRU may determine to use L1-RSRP as the measurement metric. It should be understood that in other embodiments not shown, the WTRU may determine to use another measurement metric for the large q0 set. The WTRU may use the associated measurement metric to monitor the PDCCH beam. As shown at 250, the WTRU may use L1-SINR measurement (or a different measurement metric determined for use with a small q0 set) to monitor the PDCCH beam. For example, in the case of a small q0 set, the WTRU may use a short measurement period to perform such monitoring. As shown at 280, the WTRU may use L1-RSRP measurement (or a different measurement metric determined for use with a large q0 set) to monitor the PDCCH beam. For example, in the case of a large q0 set, the WTRU may use a long period to perform this monitoring.

[0099] In the following paragraphs, a method for partial beam failure detection is proposed for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) systems. For MIMO-based BFR, partial beam failure detection is a possible solution to reduce latency and delay and reduce system complexity. In MIMO deployments, in order to avoid long delays due to the long process of beam failure recovery, the WTRU may declare a partial beam failure based on specific criteria. For example, if a condition or a set of conditions is met, the WTRU may declare a partial beam failure. An example is that if the number of beams in which beam failures are detected is greater than a threshold (e.g., M), a partial beam failure is detected. In this case, the WTRU may prohibit measuring the NBI-RS resource set. Instead, the WTRU may transmit a beam switching request (BSR), a beam switching suggestion, or a beam switching order (BSO) to the base station or one or more TRPs.

[0100] If all beams in the BFD-RS resource set are detected to have a beam quality below a predefined or (pre)configured threshold, a regular or full beam failure detection may be performed. In this case, the WTRU may continue to measure one or more RSs in the NBI-RS resource set. After measuring the RSs of the NBI-RS and finding a new beam, the WTRU may then transmit a beam failure recovery request to the base station or one or more TRPs.

[0101] If the threshold M is set equal to the number of BFD-RS resources in the set, the WTRU may identify a conventional (complete) beam failure detection when a beam failure of all beams of a BFD-RS resource set is detected. If the threshold M is set less than the number of BFD-RS resources in the set, the WTRU may identify a partial beam failure when a beam failure of the number of beams in a BFD-RS resource set exceeding the threshold M is detected. 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 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. In addition, a group common threshold M may be configured for a group of BFD-RS resource sets. Other combinations are also 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 set. For example, the WTRU may receive one or more of an RRC message, a Layer 2 message (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.

[0102] The BFD-RS resources corresponding to some TRPs may be configured to trigger partial beam failure detection, while the BFD-RS resources corresponding to other TRPs may be configured to trigger normal (full) beam failure recovery. If the BFD-RS resources corresponding to some TRPs are configured to trigger partial beam failure detection, the WTRU may not perform normal beam failure recovery when a partial beam failure of the BFD-RS resources associated with those TRPs is detected. For those BFD-RS corresponding to TRPs with partial beam failure detection, the WTRU may transmit a beam switching request, suggestion, or command for those TRPs. The WTRU may not transmit 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 those TRPs for which normal beam failure recovery is implemented, the WTRU may not transmit a beam switching command. Conversely, the WTRU may transmit a beam failure recovery request for those TRPs with normal beam failure recovery.

[0103] In addition, if the BFD-RS resources corresponding to a group of TRPs are configured to trigger regular beam failure detection, it is still possible that beam failure detection may be performed for the TRPs and beam failure recovery may be performed for some TRPs in the group but not for other TRPs. 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 depend on whether a beam failure has been detected or declared. If a beam failure is not declared for one or more TRPs, the WTRU may not perform beam failure recovery for those TRPs. In other words, the WTRU may detect a beam failure for TRP1, but not for TRP2. The WTRU may perform a beam failure recovery procedure for TRP1, but not for TRP2.

[0104] 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 can be performed for these TRPs. The WTRU may send a beam switching request, a beam switching suggestion, or a beam switching command for all TRPs.

[0105] The network (NW) may configure PDCCH resources for the WTRU, such as a CORESET and a search space set (SSS) for PDCCH monitoring at the WTRU. The NW may reconfigure the set of BFD-RS resources. For example, the NW may send a PDCCH transmission (or another logically equivalent message) carrying a transmission configuration indication (TCI) to indicate the TCI state to the WTRU for monitoring 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. A 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 above, for example, a (pre)configured or indicated threshold). If a better set of BFD-RS resources is reconfigured and indicated to the WTRU, the WTRU may not need to move to Phase 2 for new beam identification and measure a large set of NBI-RS resources. Instead, the WTRU may monitor the PDCCH beam in a smaller but better set of BFD-RS resources. By doing so, lengthy procedures for beam failure recovery may be avoided or mitigated.

[0106] This approach may have the advantages of lower latency and reduced complexity. Latency may be reduced because the WTRU may not need to perform the entire beam failure recovery process. In addition, the complexity of operation at the WTRU may be lower because the WTRU may not need to measure a large set of NBI-RS resources. A threshold, M, for the number of beams whose beam failure is detected before a partial beam failure may be declared, which may be configured, preconfigured, or predefined by the NW or base station.

[0107] Figure 3 The method of partial beam failure detection is illustrated. Figure 3 As shown, 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 the WTRU 302 (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 the beam (e.g., PDCCH DM-RS) for PDCCH transmissions that are quasi-co-located (QCL-ed) with the CSI-RS. If a beam failure is detected by the WTRU 302, the WTRU 302 may switch to monitoring another beam (e.g., in the BFD-RS). The WTRU 302 may send a request, suggestion, or command for beam switching to the base station / TRP 301. 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 activated TCI state. By doing so, the WTRU 302 may have a better set of BFD-RS resources, and therefore a better beam for PDCCH monitoring. This may reduce the chance of beam failure.

[0108] In the following paragraphs, a method for priority-based beam failure detection is proposed for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) systems. The WTRU may need to monitor a set of beams. Wherein periodic CSI-RS (P-CSI-RS) resource configuration index -= 1…M is used for beam failure detection. If M is large and the CSI processing unit of the WTRU is limited in the frequency or timing at which it can perform measurements, the WTRU may need to perform a priority-based beam failure detection process to monitor the P-CSI resources or a portion of the P-CSI resources. For example, the WTRU may be configured with a large set of P-CSI-RS resource indices, and those resources may be sorted with respect to priority or sorted by partition, where different partitions have different associated priorities. The WTRU may start with, for example, a high priority partition or the highest priority partition of the P-CSI-RS / BFD-RS resources to perform beam failure detection. The priority may depend on requirements, service type, quality of service (QoS), etc. For example, for high priority services (such as URLLC), the WTRU may monitor the entire set (all partitions), which may have a large overhead. For low priority services, the WTRU may not monitor all resources in the set, but may only monitor certain partitions.

[0109] When monitoring When P-CSI-RS / BFD-RS are monitored, the P-CSI-RS / BFD-RS may have an associated priority, and the number of P-CSI-RS / BFD-RS monitored may depend on the capabilities of the WTRU, i.e., the capabilities or capacity of the CPU. If the monitored set exceeds its capabilities, the WTRU may discard the low priority set from monitoring.

[0110] The following priority criteria may be proposed. For a cell configured for a PCell or a PsCell One or more P-CSI-RS resources may have a higher value than any configured for the SCell. A P-CSI-RS resource may have a corresponding index associated with a priority value that is higher than the priority value associated with the P-CSI-RS resource configured for the SCell. The CSI-RS resource indexes may be sorted from low to high based on their associated priority values. For example, the lowest resource index of the CSI-RS may have the highest priority, while the highest resource index of the CSI-RS may have the lowest priority. For example, resources for URLLC services may be allocated with the lowest CSI-RS resource index compared to resources for other channels.

[0111] The resources used for SCell are considered as a second priority set, i.e., the resources used for SCell can have a lower priority than PCell or PsCell, and the priority can depend on the ID of the SCell relative to the IDs of other SCells, which can have IDs ordered from low to high. For example, SCell#1 can have a higher priority than SCell#2, and so on. Within the resources used for the same SCell, the priority of each resource can be based on the CSI-RS resource index from low to high. For example, the lowest resource index of the CSI-RS can be associated with the highest priority, while the highest resource index of the CSI-RS can have the lowest priority.

[0112] and The associated measurement metric may be based on the L1-SINR of the primary set (eg, PCell / PsCell) and the L1-RSRP of the secondary set. It should be appreciated that other measurement metrics discussed herein may be used in other examples.

[0113] Figure 4 is a diagram of an exemplary design for priority-based beam failure detection. Figure 4 As shown, within the constrained CPU time, the WTRU may be allowed four CSI measurements (e.g., two L1-SINRs, two L1-RSRPs). In addition, the number of configured CSI-RS resources for the PCell / PsCell may be equal to 2, the configured SCells may have indexes #1 and #2, and each SCell may be configured with two CSI-RS resource indexes, respectively. In this exemplary design, the WTRU is only able to perform 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 a higher priority than the CSI-RS of other SCells. Therefore, as Figure 4 As shown, the CPU first performs measurements for the PCell (i.e., using P-CSI-RS resources #1 and #2). As further shown, the PCell P-CSI-RS resources with a higher priority (i.e., resource #1) are measured first, while the PCell P-CSI-RS resources with a lower priority (i.e., resource #2) are measured later. Similarly, the WTRU may perform CSI measurements on SCell resources based on their respective priorities. Figure 4 As shown, SCell P-CSI-RS resource #1 has a higher priority than SCell P-CSI-RS resource #2.

[0114] Methods for identification of new beams for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) are presented herein. In addition, methods for providing BFR assistance information for enhanced MIMO are presented. The WTRU may be configured to determine parameters pre-configured with these parameters, or receive configuration information (e.g., via MAC CE, RRC, other higher layer signaling, or a logical equivalent thereof) that provides parameters to be used in identification of one or more new beams, and if a candidate beam set is configured for determining and / or reporting an NBI, the WTRU may check a candidate beam set for the NBI If a new beam is identified based on determined, configured or preconfigured parameters, the WTRU may send, for example, a BFRQ including information indicating the NBI, or the NBI with additional information that may assist the network in making an evaluation. Reporting of the NBI only or the NBI with auxiliary information may depend on the configuration or preconfiguration information received. The WTRU may be preconfigured or configured with content provided in the auxiliary information, for example, via a MAC CE, RRC signaling, other higher layer signaling, or another logical equivalent. The WTRU may report a beam that is determined to be suitable according to one or more criteria described herein (e.g., a single best or qualified beam (e.g., CRI, SSBRI, or NBI-RS index)) or multiple suitable or qualified beams with auxiliary information (e.g., CRI, SSBRI, NBI-RS index), etc. For example, a qualified beam may have an L1-RSRP above a (pre)configured threshold.

[0115] The auxiliary information may include not only the CSI-RS RSRP of each TRP in the candidate set (i.e., The WTRU may report differential RSRP measurements instead of separate CSI-RS RSRP measurements to reduce signaling overhead. This is because the reference signal measurement value must pass the threshold Q in,LR (rsrp-ThresholdSSB or rsrp-ThresholdSSBBFR) in order to "discover" or find the NBI. Therefore, the following RSRP reporting method can be proposed to reduce signaling overhead; for example, for each NBI RSRP, either report its RSRP and Q in,LR (Note: NBI RSRP≥Q in,LR), either reporting its RSRP and the Q of the first NBI in,LR and reports the difference in RSRP of the first NBI relative to the RSRP of the remaining NBIs.

[0116] The WTRU may use PRACH / RACH opportunities (RO), PUCCH or MAC CE (PUSCH) or another logical equivalent to transmit assistance information when initiating BFR. The WTRU may be configured with dedicated periodic PRACH opportunities, dedicated periodic PUCCH or dedicated periodic PUCCH-BFR-SR resources, periodic PRACH opportunities plus periodic PUCCH or periodic PRACH opportunities plus dedicated periodic PUCCH-BFR-SR resources, periodic PUCCH plus periodic PUCCH-BFR-SR resources, periodic PUCCH plus periodic PUCCH-BFR-SR resources, periodic PRACH opportunities plus periodic PUCCH and dedicated periodic PUCCH-BFR-SR resources, or another logical equivalent. More configured BFRQ resources may benefit the WTRU when reporting / initiating BFR with assistance information for the network to determine which TCI state or set of TCI states is applicable to the WTRU. The choice 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 the assistance information), etc. For example, the payload size may be based on a single report, an average of reports per TRP, or an average of reports per TRP group. The selection of PRACH, PUCCH, or MAC CE may depend not only on the payload size, but also on the transmission opportunity. For example, when BFRQ is triggered and the WTRU is configured to report BFR assistance information along with BFRQ, the next upcoming transmission opportunity of BFRQ may utilize PRACH (e.g., primarily for PCell / PsCell) or PUCCH (e.g., for SCell) resources. If the PRACH and PUCCH transmissions are not able to carry a large enough load, the WTRU may discard part of the BFR assistance information in the entire BFR assistance information and select a RACH opportunity (RO) or PUCCH transmission opportunity for BFRQ. Otherwise, the WTRU may still use the SR method for BFR assistance information via MAC CE. The selection process is as follows: Figure 5 , and will be described in further detail below.

[0117] Figure 5 An example of a procedure performed by a WTRU for beam failure recovery with and without the transmission of assistance information is illustrated. Figure 5As shown, at 510, the WTRU starts the beam failure recovery process. At 520, the WTRU evaluates whether it is configured to transmit auxiliary information when initiating BFR. If not, at 521, the WTRU transmits a BFRQ without including the BFR auxiliary information. If the WTRU is configured to transmit auxiliary information when initiating BFR, at 530, the WTRU evaluates whether the next transmission opportunity uses PRACH or PUCCH resources. If not, at 531, the WTRU uses a scheduling request (SR) to transmit the BFRQ, and at 532, the auxiliary information is transmitted separately using the PUSCH. On the other hand, if the next transmission opportunity uses PRACH or PUCCH resources, at 540, the WTRU further evaluates whether the payload size of the BFR auxiliary information exceeds a given size x. If yes, at 531, the WTRU uses an SR to transmit the BFRQ, and at 532, the auxiliary information is transmitted via the PUSCH. If the assistance information does not exceed a given size x, the WTRU transmits a BFRQ including the assistance information using a PRACH or PUCCH transmit opportunity, as shown at 550. Once the BFRQ has been transmitted, the WTRU waits for a BFRQ response from the network, as shown at 560. The response may include, for example, an indication of an updated (or activated) TCI state or multiple TCI states. At 570, if no response is received, the WTRU again evaluates the next transmit opportunity. If a response has been received, at 580, the WTRU monitors the new beam or set of beams according to the updated TCI state before terminating the BFR process as shown at 590. The auxiliary information may include, but is not limited to, the index of the identified NBI-RS, the index of the failed NBI-RS, the index of the failed BFD-RS or set, the cell index of the failed cell, a single L1-RSRP for the NBI-RS, an average L1-RSRP (e.g., the average value for each CSI-RS set, each CSI-RS set group, each TRP, each TRP group, etc.), a differential L1-RSRP relative to the average, a differential L1-RSRP relative to a threshold, etc.).

[0118] In addition, when the PUCCH resources used for BFRQ are not used to reduce overhead, the network can activate and deactivate PUCCH. The network can decide to activate or deactivate based on some criteria, such as the number of BFRQs in a period of time (whether BFRQ occurs frequently).

[0119] For large payloads carrying auxiliary information, if a single PUCCH transmission is not sufficient to carry the payload, the WTRU may send the auxiliary information using a second or third PUCCH transmission with the same or different format (e.g., long PUCCH format) for transmission. For example, a first PUCCH transmission may be used for an indication of a BFRQ request and higher priority information such as CRI, SSBRI, NBI-RS index, and then a second PUCCH transmission may carry BFRQ auxiliary information such as CSI-RS RSRP for each TRP, etc. The number of reports and the report size may be configurable and may depend on the capabilities of the WTRU. In addition, if the payload size (i.e., BFR auxiliary information) is greater than a threshold, the WTRU may request a BFR scheduling request (BFR-SR). Once the network receives the BFR-SR, the network may schedule an UL grant for the WTRU to transmit a PUSCH transmission (e.g., MAC CE or another logical equivalent) for carrying the BFR auxiliary information.

[0120] A method for performing different RACH procedure types based on implicit indication is proposed for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) systems. In phase 2 of the BFR procedure, the WTRU may check the q1 candidate beam set (which may be a much larger set than the q0 set) to determine whether BFR for the MIMO system is being performed. A large q1 set may enhance the performance of new beam identification, but may also incur large overhead and long latency. If the NBI is unsuccessful, the WTRU may initiate a contention-based random access. This may result in long delays and high overhead since the entire random access procedure is performed.

[0121] If the NBI is unsuccessful, the WTRU may select the RACH procedure type based on certain criteria and / or conditions. For example, if fast, low latency, and low delay are required, the WTRU may perform a 2-step RACH procedure. If higher reliability (although longer delay) is required, etc., the WTRU may perform a 4-step RACH procedure. In addition, the WTRU may perform a 2-step or 4-step RACH procedure based on the service type, beam conditions, service requirements, or other criteria.

[0122] A method may be needed to distinguish between an initial random access or a random access triggered by a beam failure. An implicit indication may be used. Partitioning PRACH and / or RACH resources and / or DMRS ports and / or PUSCH resources may be used for implicit indication. For example, one partition may be dedicated to initial random access and another partition may be dedicated to BFR.

[0123] In case of performing a 2-step RACH procedure, partitioning of PRACH resources / RACH opportunities (RO) and / or DMRS ports and / or PUSCH resources and / or PUSCH opportunities may be used for MsgA.

[0124] Figure 6 An example method of a BFR-based random access procedure with implicit indication is illustrated. Figure 6 As shown at 610, the WTRU may not be able to identify the new beam and may not be able to send out an NBI. In this case, at 620, the WTRU may select between two types of RACH procedures, namely a 2-step or 4-step random access procedure. The RACH type selection may be based on the service type, condition, criterion, or other parameters. In some examples, if low latency is required, the WTRU may initiate a 2-step RACH procedure. In some examples, such as if higher reliability is required, the WTRU may initiate a 4-step RACH procedure, as shown at 630. In some examples, to reduce the total number of BFR related message transmissions, if a lower number of message transmissions is required, the WTRU may select a 2-step RACH procedure, such as Figure 6 As shown at 650 in FIG. 6 , because the 2-step RACH process uses a total of two messages compared to the four messages used in the 4-step RACH process, this option can in turn reduce the cumulative number of BFR-related messages exchanged in a massive MIMO system.

[0125] To distinguish between the initial random access and the random access triggered by beam failure, implicit indication can be used with lower overhead. For implicit indication, in the case of 4-step RACH, the PRACH and / or RACH opportunity (RO) and / or PRACH resources in Msg1 can be partitioned to indicate the initial random access and the random access triggered by BFR. For implicit indication, in the case of 2-step RACH process, the PRACH and / or RO and / or PRACH resources and / or DMRS ports and / or PUSCH resources in MsgA can be partitioned to indicate the initial random access and the random access triggered by BFR. Based on this partition, in the case of 4-step RACH, and as Figure 6 As shown at 640 in the example of FIG. 1 , the WTRU may use the BFR partition on the PRACH / RO resources in Msg1 for random access. Figure 6 As further shown at 660 in the example of FIG. 5 , based on the partitioning, in the case of 2-step RACH, the WTRU may use the BFR partitioning on the PRACH / RO and / or PUSCH resources in MsgA for random access. Resource partitioning may be performed on a combination of the time domain, the frequency domain, and the code domain.

[0126] A method for beam failure recovery request for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO) is proposed. A method for flexible beam failure recovery (BFR) management is proposed to achieve operational flexibility and performance of MIMO. A two-stage BFR request (BFRQ) method for flexible BFR management can be considered. Two-stage BFRQ can be used to reduce overhead and achieve flexible BFR management. In this method, a small piece of information with a small payload size can be transmitted in a stage 1 BFRQ, followed by a large piece of information with a larger payload size if necessary. A large piece of information with a large payload size can be transmitted in a stage 2 BFRQ.

[0127] The WTRU may transmit a first phase BFRQ and may expect to receive a NW response. If necessary, the WTRU may transmit a second phase BFRQ with more information, and whether further information is needed may be indicated in the first NW response.

[0128] By doing so, flexible BFR management can be achieved and signaling overhead can be managed. In addition, a trade-off between overhead and reliability can be achieved. The first NW response may indicate whether a second stage BFRQ is required. A second stage BFR report (BFRR) may also be used instead of a second stage BFRQ. The first NW response may indicate whether more information is required and in which format the more information may be used. In the case where second stage information is required, the WTRU may choose between BFRQ and BFRR.

[0129] After transmitting the second stage BFRQ or BFRR, the WTRU may expect to receive a subsequent NW response as a second NW response.

[0130] Due to different information sizes, different containers may be used for stage 1 information (e.g., BFRQ) and stage 2 information (e.g., BFRQ, BFRR). For example, stage 1 information or BFRQ may be sent using PRACH, and stage 2 information, BFRQ, or BFRR may be sent using PUCCH. For example, PUCCH transmission may be transmitted without an uplink grant. Stage 2 information, BFRQ, or BFRR may also use MAC CE or a logical equivalent. In some examples, BFRQ may be sent using PUCCH or a logical equivalent, and BFRR may use MAC CE or a logical equivalent.

[0131] In some examples, if there is an uplink grant, stage 1 information may be sent using a PUCCH or a logical equivalent that may be configured, and stage 2 information may use a MAC CE or a logical equivalent.

[0132] Figure 7 An example of a two-stage BFRQ management process is shown. Figure 7 As shown at 710, the WTRU may detect a beam failure. If a beam failure is detected, the WTRU may attempt to identify a new beam, as shown at 720. Once the new beam is identified, the WTRU may send a BFR request (first BFR request) as shown at 730. At 740, the WTRU may expect to receive a NW response (first NW response). The WTRU may evaluate whether a second BFR request is needed, as shown at 750. The base station / TRP may instruct the WTRU to send a 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 process is successfully completed, as shown at 760. If a second BFR request is not indicated in the first NW response, the WTRU may not proceed to send a second BFRQ and receive a subsequent NW response. In this case, the BFR process is also declared successfully completed, as shown at 760. The second BFR request may be indicated in the downlink control information (DCI) carried in the 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 the two-stage BFRQ process.

[0133] Figure 8 An example of a two-stage BFRQ management process with a maximum number of retransmissions is illustrated. Figure 8As shown 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 at 820. Once the new beam is identified, the WTRU may send a BFR request (first BFR request), as shown at 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 indicate to the WTRU via the network response to send the second BFR request. If a second BFR request is not required and the network response does not indicate a second BFR request, the WTRU and / or the base station / TRP considers the BFR procedure successful, as shown at 852. If the WTRU receives an indication in the network response that a second BFR request is required, as shown at 851, 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). If, at 860, the WTRU determines that it has received the second network response, the BFR procedure may be considered to have completed successfully (as opposed to what was shown at 852). Otherwise, if the second BFRQ retransmission does not reach the maximum number of retransmission (re-Tx) attempts 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 the maximum number, the WTRU may declare the BFR process failed, as shown at 871.

[0134] If the first network response does not indicate that the WTRU should transmit a second BFR request, then the WTRU may not need to continue sending a second BFRQ and receiving subsequent NW responses. The BFR procedure may then be declared completed successfully.

[0135] The maximum number of retransmissions of the first BFRQ and the second BFRQ may be configured differently for performance tradeoffs, or for enhanced reliability, reduced latency, or lower overhead, etc. In addition, a common maximum number of retransmissions of the first BFRQ and the second BFRQ may also be configured.

[0136] Methods for BFRQ reliability enhancement and diversity transmission are proposed for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO). During BFR Phase 3, the WTRU may transmit a BFRQ to the base station / TRP according to one or more of the following procedures.

[0137] BFRQ may be transmitted in a new beam corresponding to a single NBI or in multiple beams corresponding to multiple NBIs. For example, BFRQ may be explicitly performed through uplink physical signaling (eg, PRACH transmission).

[0138] Multiple NBIs may be associated with one TRP (e.g., NBI-RS set 1) or across 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 in multiple beams corresponding to multiple NBIs. The WTRU may send a single BFRQ in multiple beams corresponding to multiple NBIs or multiple BFRQs in multiple beams corresponding to multiple NBIs. This in turn may result in increased overhead. For low complexity and low overhead, the WTRU may be triggered to transmit a single BFRQ in a single beam corresponding to a single NBI (or one TRP). This in turn may result in low complexity and low overhead at the expense of low reliability.

[0139] The BFRQ may be repeated to reduce PRACH retransmissions or HARQ retransmissions. The beam failure recovery process may be enhanced with adaptive multi-stage BFRQ or an increasing number of beams corresponding to multiple NBIs for (re)transmission. The WTRU may (re)transmit the BFRQ with a single beam or with multiple beams. For example, the WTRU may initially send the BFRQ with a single beam and retransmit the BFRQ with multiple beams. The WTRU may retransmit the BFRQ with an increasing number of beams. For example, for the first BFRQ retransmission, the WTRU may use two beams, and 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 still keeping the total overhead at a certain level. The adaptive process may use a BFRQ failure counter, where each time instance of the BFRQ retransmission has an increased capacity (e.g., a higher number of beams).

[0140] The selection of the number of BFRQs and / or the number of beams may be based on the relative difference between the received signal quality and a threshold signal quality (such as BLER). A larger (or smaller) gap between the received signal quality and the threshold signal quality may require a higher (lower) number of NBIs.

[0141] Fig. 9 An example method for adaptive transmission of BFRQ is illustrated. Fig. 9As shown, at 910, a WTRU capable of detecting beam failure events monitors BFRQ transmissions against one or more quality thresholds. In the event that the beam quality or radio link quality for the monitored BFRQ transmissions drops below a set threshold, a beam failure event may be detected and a counter tracking the number of beam failure events (BFEs) may be set to "0". In order to generate BFRQ retransmissions, the WTRU may consider the tradeoff between reliability and overhead by evaluating the difference between the link quality and one or more quality thresholds. The WTRU may then transmit the BFRQ through a random access procedure based on the desired choice of tradeoff between reliability and overhead (e.g., by the number of NBIs, the number of BFRQs, etc.). For example, if at 920, the relative difference in link quality is greater than a given amount, the WTRU may identify a BFE for high reliability (e.g., multiple BFRQs in multiple NBIs), as shown at 921. If at 920, the relative difference in link quality exceeds a given amount x, the WTRU may identify a 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, which is received by the WTRU, as shown at 930. If the BFR procedure is unsuccessful and the BFE counter is below a set maximum value (e.g., based on timing constraints), the WTRU may be requested to generate one or more additional BFRQs (e.g., additional NBIs) with broader capabilities. The indication from the network may be explicit (e.g., public or dedicated downlink signaling) or implicit (selection of downlink resources). The process may continue until the BFR is indicated as successful, where parameters such as the difference between the measured threshold and the quality threshold may be updated through dedicated downlink signaling (e.g., uplink grant) or implicitly via the selection of downlink resources. The update of the threshold may be based on the performance of the BFRQ retransmission process for a better tradeoff between reliability and complexity for future beam failure events. Otherwise, the BFR process may fail to reestablish the connection and a link recovery process may be required.

[0142] Methods by which the network may respond to a BFRQ are described for MIMO (e.g., massively distributed MIMO, cell-free MIMO, or user-centric MIMO). After receiving the BFRQ, the network may decide to acknowledge or reject the BFRQ based on metrics such as service availability, resource availability. In some methods, the network may transmit 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 may use the new NBI. For example, if the NBI_confirmation field is 0, the WTRU may receive a new TCI state / panel selection that overrides the WTRU's suggestion for a new beam.

[0143] Fig.10 An example method in which the network may respond to a BFRQ is illustrated. As shown at 1010, the network receives a BFRQ sent by the WTRU. At 1020, the network decides whether to confirm or reject the BFRQ based on one or more metrics described in the above paragraphs. If the network confirms the BFRQ at 1030, the network transmits a message to the WTRU, which includes a parameter or field confirming the BFRQ. As shown at 1033, the parameter or field may be a one-bit (or two-bit) field with a value of 0 or 1. Upon sending / receiving the message confirming the BFRQ, the network and the WTRU may begin using one or more new beams, as shown at 1034. If, at 1030, the network rejects the BFRQ, the parameter or field value is set to 0, indicating that the network rejects the BFRQ, as shown at 1031.

[0144] In some method collections, such as Fig.10 As shown at 1032. After receiving the BFRQ, the network may directly override the WTRU's suggestion by transmitting a TCI status / panel selection message to the WTRU. The WTRU may then use the new beam indicated by the network.

[0145] In some set 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 suggestion for the beam. This will be a new field with a longer bit width (such as 4 bits) to indicate the TCI state. As an example, 1111 may represent confirmation, and other combinations may represent the other 15 potential TCI states.

[0146] A method for 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 commands is proposed. Event triggers and / or conditional 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 resources. This may be used to prevent the WTRU from not being able to find any qualified NBI-RS resources and entering a contention based random access procedure which may have large latency and long delays.

[0147] In some cases, q1 may be very poor, the original NBI-RS resource may not be of good quality, or the NBI or new beam may not be found. In this case, a contention-based 4-step random access may be triggered.

[0148] Furthermore, even if it passes the new beam identification, however, when the beam condition is poor, the BFRQ is likely to fail to reach the TRP. In this case, the BFR process may not be able to continue and beam failure recovery may not be completed.

[0149] Based on pre-configuration, the WTRU may control the BFR. The WTRU may autonomously switch to a new set of NBI-RS resources. The WTRU may find the NBI from the new set of NBI-RS resources.

[0150] A primary set and a secondary set of NBI-RS resource sets may be defined for q1 or NBI-RS resource sets. The WTRU may monitor and measure the primary NBI-RS resource set. The secondary NBI-RS resource set may be triggered when the channel and / or beam quality and / or conditions deteriorate, become unreliable, or drop 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 switching of NBI-RS resource sets based on criteria and / or conditions.

[0151] In addition, the associated measurement metrics may be configured or preconfigured. One measurement metric may be associated with the primary set and another measurement metric may be associated with the secondary set. For example, L1-SINR may be available for and associated with the primary NBI-RS resource set and L1-RSRP may be available for and associated with the secondary NBI-RS resource set. In some examples, L1-RSRP may be available for and associated with both the primary NBI-RS resource set and the secondary NBI-RS resource set.

[0152] In addition to the primary NBI-RS set, a base station (e.g., the base station) may also configure a secondary NBI-RS resource set. If the channel conditions deteriorate (e.g., L1-RSRP < T1, L1-SINR < T2), the WTRU may switch to the secondary set. Other conditions or criteria may also be considered, such as the number of PDCCH transmissions sent without an ACK response, lost PDCCH transmissions, the number of NACKs, or the NACK / ACK ratio > threshold, etc.

[0153] A WTRU-controlled BFR with a beam failure recovery command may be used. The WTRU may send a beam failure recovery command to the NW and control the BFR process. The WTRU may notify its decision to the base station / TRP. The WTRU may request the base station / TRP to switch to a new NBI-RS resource set and a new beam for measurement and monitoring.

[0154] The WTRU may use a new beam (e.g., not in the primary NBI-RS resource set determined by the base station, but in the secondary NBI-RS resource set or a new NBI-RS resource set determined by the WTRU) to further communicate with the base station and / or the TRP, e.g., send a BFRQ to the base station / TRP. After the BFR process is successfully completed, both the base station / TRP and the WTRU may switch to the new beam selected by the WTRU.

[0155] The primary NBI-RS resource set and the secondary NBI-RS resource set 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. In addition, the secondary NBI-RS may have multiple resource sets, each with a different associated priority. The WTRU may be enabled or configured with this feature. When the channel and / or beam conditions deteriorate or fall below a certain threshold, the WTRU may send a beam failure recovery command (BFRO) via a selected beam from the secondary NBI-RS resource set. Otherwise, the WTRU may initiate a 4-step random access procedure with a long delay.

[0156] Fig.11An example method for WTRU controlled beam failure recovery is illustrated. The base station / TRP 1101 may send a BFD-RS, which 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) that is QCLed with the CSI-RS. If the quality of the PDCCH beam is not good, such as a measurement value below a certain threshold, a beam failure is detected. The WTRU 1102 may then begin monitoring the NBI-RS to search for a new beam with a qualified link (e.g., a measurement value above a certain threshold). If no such beam is found, such as if 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 set of secondary NBI-RS resources to search for a new qualified 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. During situations where channel / beam conditions deteriorate, the WTRU 1102 may control the BFR procedure. Since the WTRU 1102 may determine that there is another chance 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.

[0157] Fig.12 An example procedure for a WTRU controlled beam failure recovery procedure is illustrated. 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-free MIMO, or user-centric MIMO) system. The feature of autonomous WTRU controlled beam failure recovery may be enabled for use by the WTRU based on, for example, a configuration message, a condition.

[0158] As shown at 1220, the WTRU may monitor the BFD-RS for the MIMO system. The WTRU may first measure the primary NBI-RS resources, as shown at 1230. At 1240, the WTRU may send a BFRQ using an NBI selected from the primary NBI-RS resource set. At 1250, the WTRU evaluates the beam / channel quality for the primary NBI-RS resource set. If the beam / channel quality deteriorates (e.g., measurements such as L1-RSRP, L1-SINR are below a (pre)configured threshold), the WTRU may autonomously switch to a secondary NBI-RS resource set, as shown at 1254. As shown at 1255, the WTRU may continue the beam failure recovery procedure and measure the secondary NBI-RS resources. At 1256, the WTRU may send a BFRQ using an NBI selected from the secondary NBI-RS set. The WTRU may receive a DCI for a response from the base station / TRP via the PDCCH, as shown at 1260. At 1270, the WTRU may use the secondary NBI-RS for MIMO to complete the beam failure recovery procedure.

[0159] If at 1250, the beam / channel quality has not deteriorated (e.g., measurements such as L1-RSRP, L1-SINR are not below a (pre-)configured threshold), the WTRU may stay in 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. At 1253, the WTRU may send a BFRQ using the NBI selected from the primary NBI-RS resource set. The WTRU may receive a DCI for the response from the base station / TRP via the PDCCH, as shown at 1260. At 1270, the WTRU may complete the beam failure recovery procedure using the primary NBI-RS for MIMO.

[0160] Fig.13 An example method for a beam failure recovery process for MIMO is illustrated. It should be noted that Fig.13 The flowchart provided in the figure may involve a combination of different methods described separately and further described in the above paragraphs. Therefore, the detailed description can be obtained from other parts of the detailed description. Fig.13 Further understanding of Fig.13 It should be clear to those skilled in the art that the various different solutions for beam failure recovery proposed herein can be implemented individually or in any combination. It is obvious to those skilled in the art that Fig.13 Other embodiments not directly depicted in Fig.13 The implementation plan for each step described in, or including Fig.13Implementations of other steps not described in the present invention) are possible.

[0161] like Fig.13 As shown, the WTRU may be configured to perform a MIMO-based beam failure recovery procedure. At 1310, the WTRU may be configured with various parameters for beam failure recovery, including, for example, beam failure detection type, adaptive BFD-RS set, and priority values ​​associated with RS resources. In some embodiments, the WTRU may be configured with a BFR assistance information reporting type, which is described in more detail in the above paragraphs. The WTRU may also be configured with a flexible BFR management feature, which is also described in more detail in the above paragraphs.

[0162] As shown at 1320, if configured, the WTRU may perform partial beam failure detection. Otherwise, as shown at 1321, if configured, the WTRU may perform regular (or full) beam failure detection (to reduce the complexity of MIMO), which will be further described in the following paragraphs. Regarding the case of partial beam failure detection, at 1326, the WTRU may monitor the BFD-RS based on the priority order associated with the BFD-RS resources. As shown at 1327, the WTRU may monitor the BFD-RS using different metrics (e.g., L1-SINR, L1-RSRP) associated with different monitoring periods to further reduce the complexity caused by MIMO. The WTRU may send a beam failure recovery request (BFRQ) or a beam switching request (BSR) based on, for example, the configured beam failure detection type. The WTRU may send a BFD-RS with a BFRQ, a BSR, or a beam switching suggestion.

[0163] At 1328, the WTRU may send a BFRQ with a BFD-RS index, or the WTRU may send a beam switch request (BSR) or a beam switch suggestion with a BFD-RS index. After the WTRU has sent the BFRQ, BSR, or beam switch suggestion, at 1329, the WTRU may receive BFD-RS reconfiguration information using the beam indicated in the transmit configuration indication (TCI) state and monitor the reconfigured BFD-RS resource set to reduce BFR complexity in MIMO.

[0164] If full beam failure detection is performed at 1321, the WTRU may monitor all BFD-RS of the set and may use a single metric (e.g., L1-SINR) to monitor the BFD-RS resources. As shown at 1323 and 1324, if an NBI is found, the WTRU may be configured to send a BFRQ including one or more NBI-RS indices.

[0165] If full beam failure detection is performed and no NBI is found as indicated at 1323, then at 1325 the WTRU may select a RACH type (e.g., a 2-step or 4-step RACH procedure), for example, according to one or more of the methods described in the above paragraphs. The WTRU may perform random access based on the selected random access type and a configured or selected indication type for indicating whether to perform a RACH procedure for an initial access of a random access triggered by a beam failure (e.g., such as Fig.13 In the case of a random access, the WTRU does not send a BFRQ and the BFR procedure is considered complete, as shown at 1351.

[0166] The WTRU may determine whether to send a BFRQ with assistance information as shown at 1330. For example, if the BFR assistance information type is configured to enhance the performance of the MIMO-based BFR process.

[0167] The WTRU may send 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 transmitted by the network in response to the BFRQ to reduce overhead associated with MIMO.

[0168] The WTRU may receive and decode the PDCCH transmission and obtain the DCI as shown at 1340. If, at 1340, the DCI in the response indicates a subsequent request type, i.e., a second BFR request (BFRQ) type or a BFR report (BFRR) type is required, the WTRU may send a second request signal with a large payload indicating the type (BFRQ or BFRR), as shown at 1352, and the WTRU may receive a second DCI using a second PDCCH transmission from the network, as shown at 1353, to enhance the performance and flexibility of MIMO. If the first DCI does not indicate a subsequent request type or that a second BFRQ is required, as shown at 1351, the BFR process may be considered complete.

[0169] If no DCI is received from the network in response, the WTRU may retransmit the request signal / channel with the indicated type (BFRQ or BFRR) using adaptive NBI and incrementing NBI for each retransmission. The WTRU may receive DCI in the retransmitted PDCCH transmission.

[0170] The WTRU may complete the beam failure recovery procedure within the maximum number of retransmissions of the first BFRQ and / or the second BFRQ for MIMO and may declare the beam failure recovery procedure for MIMO successful. Otherwise, the WTRU may declare the beam failure recovery procedure for MIMO failed.

[0171] Further examples based on one or more of the above solutions are provided herein.

[0172] 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 also be configured with a flexible BFR management feature. The WTRU may perform one or more of the following steps. For example, if configured, the WTRU may perform partial beam failure detection, otherwise if configured, perform conventional beam failure detection (to reduce the complexity of MIMO). The WTRU may monitor the BFD-RS based on the priority order associated with the BFD-RS resources and using different metrics associated with different monitoring periods (e.g., L1-SINR, L1-RSRP) (to further reduce the complexity caused by 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 based on the beam failure detection type. If the partial beam failure detection type is configured, the WTRU may send a BFRQ with a BFD-RS index. If the partial beam failure detection type is configured, the WTRU may send a BSR or beam switching suggestion with a BFD-RS index (to reduce latency for MIMO). If the normal beam failure detection type is configured, the WTRU may send a BFRQ with an NBI-RS index. The WTRU may receive BFD-RS reconfiguration information using the beam indicated in the transmit configuration indication (TCI) state and monitor the reconfigured BFD-RS resource set if the partial beam failure detection type is configured (to reduce BFR complexity in MIMO). If the BFR assistance information type is configured, the WTRU may send a BFRQ with assistance information (to enhance the performance of BFR over MIMO). If no NBI is found, the WTRU may select a random access type 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).

[0173] The WTRU may send a first BFRQ with a small payload and receive a DCI or another logically equivalent message in a PDCCH transmission as a NW response (to reduce overhead associated with MIMO). If the DCI of the NW response indicates a subsequent request type, i.e., a BFR request (BFRQ) type or a BFR report (BFRR) type is required, the WTRU may receive and decode the PDCCH transmission and obtain the DCI. The WTRU may then send a second request signal / channel of the indication type (BFRQ or BFRR) with a large payload. The WTRU may receive a second DCI in a second PDCCH of the NW response (to enhance the performance and flexibility of MIMO). If no DCI is received in the PDCCH of the NW response, the WTRU may retransmit the request signal / channel with the indication type (BFRQ or BFRR) using 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 the maximum number of retransmissions of the first BFRQ and / or the second BFRQ for MIMO and declare the beam failure recovery procedure for MIMO successful. Otherwise, the WTRU may declare the beam failure recovery procedure for MIMO failed.

[0174] In some examples, the WTRU may autonomously perform and control a beam failure recovery procedure for MIMO. The WTRU may be configured and enabled to have a feature 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 RS for MIMO. The WTRU may measure the primary NBI-RS resources. The WTRU may send a BFRQ with an NBI selected from the primary NBI-RS resource set. If the beam / channel quality deteriorates (e.g., measurements such as L1-RSRP, L1-SINR are below a (pre)configured threshold), the WTRU may autonomously switch to a secondary NBI-RS resource set. The WTRU may continue the beam failure recovery procedure and measure the secondary NBI-RS resources. The WTRU may send a BFRQ with an NBI selected from the secondary NBI-RS resource set. The WTRU may receive a DCI in the PDCCH for a response from the base station / TRP. The WTRU may complete the beam failure recovery procedure for MIMO.

[0175] Although the features and elements are described above in specific combinations, it will be understood by those skilled in the art that each feature or element may be used alone or in any combination with other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (sent via a wired connection or a wireless connection) 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 built-in 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 the software may be used to implement a radio frequency transceiver for a WTRU, UE, terminal, base station, RNC, or any host computer. Although the features and elements are described for massively distributed MIMO, they may also be applied to cell-free MIMO or user-centric MIMO.

Claims

1. A method for beam failure recovery in a system utilizing a multiple-input multiple-output (MIMO) antenna scheme, the method include: Receive configuration information including beam failure recovery parameters, where the beam failure recovery parameters include: information indicating a number of resources of a first beam failure detection (BFD) reference signal (RS) resource set to be monitored; and priority information associated with each resource in the resources of the first set of BFD-RS resources; Monitoring the indicated number of resources of the first set of BFD-RS resources based on the priority information associated with each of the resources, wherein monitoring the indicated number of resources of the first set of BFD-RS resources comprises: measuring a first signal quality metric of a first subset of resources of the first set of BFD-RS resources using a first measurement period; and measuring a second signal quality metric of a second subset of resources of the first set of BFD-RS resources using a second measurement period; Sending a message for obtaining a second set of BFD-RS resources, the message comprising an index associated with one of the resources of the first set of BFD-RS resources; receiving reconfiguration 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-resource set; sending at least a first beam failure recovery request message (BFRQ) for performing beam failure recovery using one of the resources of the new BFD-RS resource set; and A response to the at least first BFRQ is received, the response indicating that a beam failure recovery procedure is complete.

2. The method according to claim 1, in, The response to the at least first BFRQ includes downlink control information (DCI), which includes information confirming the first BFRQ for performing beam failure recovery using one of the resources of the second BFD-RS resource set.

3. The method according to claim 1, in, The response to the at least first BFRQ includes downlink control information (DCI), which includes information covering the first BFRQ for performing beam failure recovery using one of the resources of the second BFD-RS resource set, wherein the DCI also indicates that different resources are used for beam failure recovery.

4. The method of claim 1, wherein the response to the at least first BFRQ comprises downlink control information (DCI), the downlink control information (DCI) comprising information indicating that a second BFRQ is to be sent, in, The method also includes sending the second BFRQ and receiving a DCI in response to the second BFRQ, and wherein the DCI in response to the second BFRQ includes one of confirming or covering information of the second BFRQ.

5. The method according to claim 1, in, The beam failure recovery parameters include information indicating whether auxiliary information is included when sending BFRQ; wherein the auxiliary information includes one or more of the following: a new beam identifier (NBI), a signal quality measurement associated with the new beam identifier, or a difference between a signal quality measurement associated with the new beam identifier and a threshold.

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

7. The method according to claim 5, in, The auxiliary information is sent using resources associated with a physical random access channel (PRACH) opportunity, a random access channel (RACH) opportunity, or a physical uplink control channel (PUCCH), a medium access control element (MAC CE).

8. The method according to claim 1, in, The message for obtaining the second set of BFD-RS resources is one of a BFRQ, a beam switching request (BSR), a beam switching suggestion, or a beam switching command.

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

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

11. A wireless transmit / receive unit (WTRU) configured to perform beam failure recovery in a system utilizing a multiple-input multiple-output (MIMO) scheme, the WTRU include: processor; and Transceiver; The processor and the transceiver are configured to receive configuration information including beam failure recovery parameters, the beam failure recovery parameters including: information indicating a number of resources of a first beam failure detection (BFD) reference signal (RS) resource set to be monitored; and priority information associated with each resource in the resources of the first set of BFD-RS resources; The processor and the transceiver are configured to monitor the indicated number of resources of the first set of BFD-RS resources based on the priority information associated with each of the resources, wherein monitoring the indicated number of resources of the first set of BFD-RS resources comprises: The processor and the transceiver are configured to measure a first signal quality metric of a first subset of resources of the first set of BFD-RS resources using a first measurement period; and The processor and the transceiver are configured to measure a second signal quality metric of a second subset of resources of the first set of BFD-RS resources using a second measurement period; The processor and the transceiver are configured to send a message for obtaining a second set of BFD-RS resources, the message comprising an index associated with one of the resources of the first set of BFD-RS resources; The processor and the transceiver are configured to receive reconfiguration 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-resource set; The processor and the transceiver are configured to send at least a first beam failure recovery request message (BFRQ) for performing beam failure recovery using one of the resources of the new BFD-RS resource set; and The processor and the transceiver are configured to receive a response to the at least first BFRQ, the response indicating that a beam failure recovery procedure is complete.

12. The WTRU of claim 11, in, The response to the at least first BFRQ includes downlink control information (DCI), which includes information confirming the first BFRQ for performing beam failure recovery using one of the resources of the second BFD-RS resource set.

13. The WTRU of claim 11, in, The response to the at least first BFRQ includes downlink control information (DCI), which includes information covering the first BFRQ for performing beam failure recovery using one of the resources of the second BFD-RS resource set, wherein the DCI also indicates that different resources are used for beam failure recovery.

14. The WTRU of claim 11, in, The response to the at least first BFRQ includes downlink control information (DCI), the downlink control information (DCI) including information indicating sending a second BFRQ, wherein the processor and the transceiver are also configured to send the second BFRQ and receive the DCI in response to the second BFRQ, and wherein the DCI in response to the second BFRQ includes one of confirming or covering the information of the second BFRQ.

15. The WTRU of claim 11, in, The beam failure recovery parameters include information indicating whether auxiliary information is included when sending BFRQ; wherein the auxiliary information includes one or more of the following: a new beam identifier (NBI), a signal quality measurement associated with the new beam identifier, or a difference between a signal quality measurement associated with the new beam identifier and a threshold.

16. The WTRU of claim 15, in, The NBI identifies one of a beam associated with a highest signal quality measurement or a beam having a signal quality metric exceeding the threshold.

17. The WTRU of claim 15, in, The auxiliary information is sent using resources associated with a physical random access channel (PRACH) opportunity, a random access channel (RACH) opportunity, or a physical uplink control channel (PUCCH), a medium access control element (MAC CE).

18. The WTRU of claim 11, in, The message for obtaining the second set of BFD-RS resources is one of a BFRQ, a beam switching request (BSR), a beam switching suggestion, or a beam switching command.

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

20. The WTRU of claim 11, in, The first signal quality metric is a layer 1 (L1) signal to interference plus noise ratio (SINR), and wherein the second signal quality metric is L1 reference signal received power (RSRP).

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