Patent Description:
Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources.

These multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunications standard is a fifth generation (<NUM>) telecommunications standard referred to as "New Radio" (NR). NR is part of a continuous mobile broadband evolution promulgated by the Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with the Internet of Things (IoT)), and other requirements. Some aspects of <NUM> NR may be based on the fourth generation (<NUM>) telecommunications standard referred to as the Long Term Evolution (LTE) standard. There exists a need for further improvements in NR technology.

<NPL>" discloses using contention free PRACH resources for beam failure recovery request transmission. <NPL>" discloses a beam failure recovery request procedure via PRACH resource. <NPL>" suggests using a BFR MAC CE for reporting beam failure for an SCell. <NPL>" discloses enhancements of BFR. <NPL>" discloses beam failure detection for SCell. <NPL>" discloses contention-based beam failure recovery.

The following presents a simplified summary relating to one or more aspects disclosed herein. As such, the following summary should not be considered an extensive overview relating to all contemplated aspects, nor should the following summary be regarded to identify key or critical elements relating to all contemplated aspects or to delineate the scope associated with any particular aspect. Accordingly, the following summary has the sole purpose to present certain concepts relating to one or more aspects relating to the mechanisms disclosed herein in a simplified form to precede the detailed description presented below.

The present invention provides a method of beam failure recovery according to claim <NUM>, a method of beam failure recovery according to claim <NUM>, an apparatus for beam failure recovery according to claim <NUM>, and an apparatus for beam failure recovery according to claim <NUM>. Specific embodiments are subject of the dependent claims.

Objects and advantages associated with the aspects disclosed herein will be apparent to those skilled in the art based on the accompanying drawings and detailed description.

Additionally, well-known aspects of the disclosure may not be described in detail or may be omitted so as not to obscure more relevant details.

The disclosure set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The disclosure includes specific details for the purpose of providing a thorough understanding of various concepts.

It will be recognized that various actions described herein can be performed by specific circuits (e.g., Application Specific Integrated Circuits (ASICs)), by program instructions being executed by one or more processors, or by a combination of both. In addition, for each of the aspects described herein, the corresponding form of any such aspect may be implemented as, for example, "logic configured to" perform the described action.

As used herein, the terms "user equipment" (UE) and "base station" are not intended to be specific or otherwise limited to any particular Radio Access Technology (RAT), unless otherwise noted. In general, a UE may be any wireless communication device (e.g., a mobile phone, router, tablet computer, laptop computer, tracking device, wearable (e.g., smartwatch, glasses, augmented reality (AR) / virtual reality (VR) headset, etc.), vehicle (e.g., automobile, motorcycle, bicycle, etc.), Internet of Things (IoT) device, etc.) used by a user to communicate over a wireless communications network. A UE may be mobile or may (e.g., at certain times) be stationary, and may communicate with a Radio Access Network (RAN). As used herein, the term "UE" may be referred to interchangeably as an "access terminal" or "AT," a "client device," a "wireless device," a "subscriber device," a "subscriber terminal," a "subscriber station," a "user terminal" or UT, a "mobile terminal," a "mobile station," or variations thereof. Generally, UEs can communicate with a core network via a RAN, and through the core network the UEs can be connected with external networks such as the Internet and with other UEs. Of course, other mechanisms of connecting to the core network and/or the Internet are also possible for the UEs, such as over wired access networks, wireless local area network (WLAN) networks (e.g., based on Institute of Electrical and Electronics Engineers (IEEE) <NUM>, etc.) and so on.

A base station may operate according to one of several RATs in communication with UEs depending on the network in which it is deployed, and may be alternatively referred to as an access point (AP), a network node, a NodeB, an evolved NodeB (eNB), a New Radio (NR) Node B (also referred to as a gNB or gNodeB), etc. In addition, in some systems a base station may provide purely edge node signaling functions while in other systems it may provide additional control and/or network management functions. A communication link through which UEs can send signals to a base station is called an uplink (UL) channel (e.g., a reverse traffic channel, a reverse control channel, an access channel, etc.). A communication link through which the base station can send signals to UEs is called a downlink (DL) or forward link channel (e.g., a paging channel, a control channel, a broadcast channel, a forward traffic channel, etc.). As used herein the term traffic channel (TCH) can refer to either an UL / reverse or DL / forward traffic channel.

The term "base station" may refer to a single physical transmission point or to multiple physical transmission points that may or may not be co-located. For example, where the term "base station" refers to a single physical transmission point, the physical transmission point may be an antenna of the base station corresponding to a cell of the base station. Where the term "base station" refers to multiple co-located physical transmission points, the physical transmission points may be an array of antennas (e.g., as in a multiple-input multiple-output (MIMO) system or where the base station employs beamforming) of the base station. Where the term "base station" refers to multiple non-co-located physical transmission points, the physical transmission points may be a distributed antenna system (DAS) (a network of spatially separated antennas connected to a common source via a transport medium) or a remote radio head (RRH) (a remote base station connected to a serving base station). Alternatively, the non-co-located physical transmission points may be the serving base station receiving the measurement report from the UE and a neighbor base station whose reference radio frequency (RF) signals the UE is measuring.

According to various aspects, <FIG> illustrates an exemplary wireless communications system <NUM>. The wireless communications system <NUM> (which may also be referred to as a wireless wide area network (WWAN)) may include various base stations <NUM> and various UEs <NUM>. In an aspect, the base stations <NUM> may include eNBs where the wireless communications system <NUM> corresponds to an LTE network, or gNBs where the wireless communications system <NUM> corresponds to a <NUM> network, or a combination of both.

The base stations <NUM> may collectively form a RAN and interface with a core network <NUM> (e.g., an evolved packet core (EPC) or next generation core (NGC)) through backhaul links <NUM>, and through the core network <NUM> to one or more location servers <NUM>. In addition to other functions, the base stations <NUM> may perform functions that relate to one or more of transferring user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, RAN sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations <NUM> may communicate with each other directly or indirectly (e.g., through the EPC / NGC) over backhaul links <NUM>, which may be wired or wireless.

In an aspect, one or more cells may be supported by a base station <NUM> in each geographic coverage area <NUM>. A "cell" is a logical communication entity used for communication with a base station (e.g., over some frequency resource, referred to as a carrier frequency, component carrier, carrier, band, or the like), and may be associated with an identifier (e.g., a physical cell identifier (PCID), a virtual cell identifier (VCID)) for distinguishing cells operating via the same or a different carrier frequency. In some cases, different cells may be configured according to different protocol types (e.g., machine-type communication (MTC), narrowband IoT (NB-IoT), enhanced mobile broadband (eMBB), or others) that may provide access for different types of UEs. In some cases, the term "cell" may also refer to a geographic coverage area of a base station (e.g., a sector), insofar as a carrier frequency can be detected and used for communication within some portion of geographic coverage areas <NUM>.

In cellular networks, "macro cell" base stations provide connectivity and coverage to a large number of users over a certain geographical area. A macro network deployment is carefully planned, designed, and implemented to offer good coverage over the geographical region. Even such careful planning, however, cannot fully accommodate channel characteristics such as fading, multipath, shadowing, etc., especially in indoor environments. Thus, to improve indoor or other specific geographic coverage, such as for residential homes and office buildings, additional "small cell" base stations have begun to be deployed to supplement the coverage of conventional macro networks. Small cell base stations may also provide incremental capacity growth, richer user experience, and so on. Small cell base stations are generally lowpowered base stations that may include or be otherwise referred to as femto cells, pico cells, micro cells, etc..

While neighboring macro cell base station <NUM> geographic coverage areas <NUM> may partially overlap (e.g., in a handover region), some of the geographic coverage areas <NUM> may be substantially overlapped by a larger geographic coverage area <NUM>. For example, a small cell base station <NUM>' may have a geographic coverage area <NUM>' that substantially overlaps with the geographic coverage area <NUM> of one or more macro cell base stations <NUM>. A network that includes both small cell and macro cell base stations may be known as a heterogeneous network. A heterogeneous network may also include home eNBs (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG).

The communication links <NUM> between the base stations <NUM> and the UEs <NUM> may include UL (also referred to as reverse link) transmissions from a UE <NUM> to a base station <NUM> and/or DL (also referred to as forward link) transmissions from a base station <NUM> to a UE <NUM>. The communication links <NUM> may use MIMO antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links <NUM> may be through one or more carrier frequencies. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL).

When communicating in an unlicensed frequency spectrum, the WLAN STAs <NUM> and/or the WLAN AP <NUM> may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

When operating in an unlicensed frequency spectrum, the small cell base station <NUM>' may employ LTE or <NUM> technology and use the same <NUM> unlicensed frequency spectrum as used by the WLAN AP <NUM>. LTE in an unlicensed spectrum may be referred to as LTE-unlicensed (LTE-U), licensed assisted access (LAA), or MulteFire.

Transmit beams may be quasi-collocated, meaning that they appear to the receiver as having the same parameters, regardless of whether or not the transmitting antennas themselves are physically collocated. In NR, there are four types of quasicollocation (QCL) relations. If the source reference RF signal is QCL Type D, the receiver can use the source reference RF signal to estimate the spatial receive parameters of a second reference RF signal transmitted on the same channel.

In NR, the frequency spectrum in which wireless nodes (e.g., base stations <NUM>/<NUM>, UEs <NUM>/<NUM>) operate is divided into multiple frequency ranges, FR1 (from <NUM> to <NUM>), FR2 (from <NUM> to <NUM>), FR3 (above <NUM>), and FR4 (between FR1 and FR2). In a multi-carrier system, such as <NUM>, one of the carrier frequencies is referred to as the "primary carrier" or "anchor carrier" or "primary serving cell" or "PCell," and the remaining carrier frequencies are referred to as "secondary carriers" or "secondary serving cells" or "SCells.

For example, the base stations <NUM> / UEs <NUM> may use spectrum up to Y MHz (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) bandwidth per component carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The component carriers may or may not be adjacent to each other on the frequency spectrum. Allocation of carriers may be asymmetric with respect to the DL and UL (e.g., more or less carriers may be allocated for DL than for UL).

In carrier aggregation, the anchor carrier is the carrier operating on the primary frequency (e.g., FR1) utilized by a UE <NUM>/<NUM> and the cell in which the UE <NUM>/<NUM> either performs the initial radio resource control (RRC) connection establishment procedure or initiates the RRC connection re-establishment procedure. The primary carrier carries all common and UE-specific control channels. A secondary carrier is a carrier operating on a second frequency (e.g., FR2) that may be configured once the RRC connection is established between the UE <NUM> and the anchor carrier and that may be used to provide additional radio resources. The secondary carrier may contain only necessary signaling information and signals, for example, those that are UE-specific may not be present in the secondary carrier, since both primary uplink and downlink carriers are typically UE-specific. This means that different UEs <NUM>/<NUM> in a cell may have different downlink primary carriers. The same is true for the uplink primary carriers. The network is able to change the primary carrier of any UE <NUM>/<NUM> at any time. This is done, for example, to balance the load on different carriers. Because a "serving cell" (whether a PCell or an SCell) corresponds to a carrier frequency / component carrier over which some base station is communicating, the term "cell," "serving cell," "component carrier," "carrier frequency," and the like can be used interchangeably.

For example, still referring to <FIG>, the base stations <NUM> / UEs <NUM> may use spectrum up to Y MHz (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The component carriers may or may not be adjacent to each other on the frequency spectrum. Allocation of carriers may be asymmetric with respect to the DL and UL (e.g., more or less carriers may be allocated for DL than for UL). One of the component carriers utilized by a macro cell base station <NUM> may be an anchor carrier (or "PCell") and other component carriers utilized by the macro cell base stations <NUM> and/or the mmW base station <NUM>, for example, may be secondary carriers ("SCells").

In order to operate on multiple carrier frequencies, a base station <NUM> / UE <NUM> is equipped with multiple receivers and/or transmitters. For example, a UE <NUM> may have two receivers, Receiver <NUM> and Receiver <NUM>, where Receiver <NUM> is a multi-band receiver that can be tuned to band (i.e., carrier frequency) X or band Y, and Receiver <NUM> is a one-band receiver tuneable to band Z only. In this example, if the UE <NUM> is being served in band X, band X would be referred to as the PCell or the active carrier frequency, and Receiver <NUM> would need to tune from band X to band Y (an SCell) in order to measure band Y (and vice versa). In contrast, whether the UE <NUM> is being served in band X or band Y, because of the separate Receiver <NUM>, the UE <NUM> can measure band Z without interrupting the service on band X or band Y.

The wireless communications system <NUM> may further include one or more UEs, such as UE <NUM>, that connects indirectly to one or more communication networks via one or more device-to-device (D2D) peer-to-peer (P2P) links. In the example of <FIG>, UE <NUM> has a D2D P2P link <NUM> with one of the UEs <NUM> connected to one of the base stations <NUM> (e.g., through which UE <NUM> may indirectly obtain cellular connectivity) and a D2D P2P link <NUM> with WLAN STA <NUM> connected to the WLAN AP <NUM> (through which UE <NUM> may indirectly obtain WLAN-based Internet connectivity). In an aspect, the D2D communication link <NUM> may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). D2D communication may be through a variety of wireless D2D communications systems, such as for example, FlashLinQ, WiMedia, LTE Direct (LTE-D), WiFi Direct (WiFi-D), Bluetooth, ZigBee, Z-Wave, Wi-Fi based on the IEEE <NUM> standard, LTE, or NR.

The wireless communications system <NUM> may further include a UE <NUM> that may communicate with a macro cell base station <NUM> over a communication link <NUM> and/or the mmW base station <NUM> over a mmW communication link <NUM>. For example, the macro cell base station <NUM> may support a PCell and one or more SCells for the UE <NUM> and the mmW base station <NUM> may support one or more SCells for the UE <NUM>. In an aspect, the UE <NUM> may include a beam failure recovery (BFR) manager <NUM> that may enable the UE <NUM> to perform the UE operations described herein, such as, for example, the operations described with reference to <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>. Note that although only one UE in <FIG> is illustrated as having a BFR manager <NUM>, any of the UEs in <FIG> may be configured to perform the UE operations described herein.

According to various aspects, <FIG> illustrates an example wireless network structure <NUM>. For example, an NGC <NUM> (also referred to as a "5GC") can be viewed functionally as control plane functions <NUM> (e.g., UE registration, authentication, network access, gateway selection, etc.) and user plane functions <NUM>, (e.g., UE gateway function, access to data networks, IP routing, etc.) which operate cooperatively to form the core network. User plane interface (NG-U) <NUM> and control plane interface (NG-C) <NUM> connect the gNB <NUM> to the NGC <NUM> and specifically to the control plane functions <NUM> and user plane functions <NUM>. In an additional configuration, an eNB <NUM> may also be connected to the NGC <NUM> via NG-C <NUM> to the control plane functions <NUM> and NG-U <NUM> to user plane functions <NUM>. Further, eNB <NUM> may directly communicate with gNB <NUM> via a backhaul connection <NUM>. In some configurations, the New RAN <NUM> may only have one or more gNBs <NUM>, while other configurations include one or more of both eNBs <NUM> and gNBs <NUM>. Either gNB <NUM> or eNB <NUM> may communicate with UEs <NUM> (e.g., any of the UEs depicted in <FIG>). Another optional aspect may include location server <NUM> (which may correspond to location server <NUM>), which may be in communication with the NGC <NUM> to provide location assistance for UEs <NUM>. The location server <NUM> can be implemented as a plurality of separate servers (e.g., physically separate servers, different software modules on a single server, different software modules spread across multiple physical servers, etc.), or alternately may each correspond to a single server. The location server <NUM> can be configured to support one or more location services for UEs <NUM> that can connect to the location server <NUM> via the core network, NGC <NUM>, and/or via the Internet (not illustrated). Further, the location server <NUM> may be integrated into a component of the core network, or alternatively may be external to the core network.

According to various aspects, <FIG> illustrates another example wireless network structure <NUM>. For example, an NGC <NUM> (also referred to as a "5GC") can be viewed functionally as control plane functions, provided by an access and mobility management function (AMF) / user plane function (UPF) <NUM>, and user plane functions, provided by a session management function (SMF) <NUM>, which operate cooperatively to form the core network (i.e., NGC <NUM>). User plane interface <NUM> and control plane interface <NUM> connect the eNB <NUM> to the NGC <NUM> and specifically to SMF <NUM> and AMF/UPF <NUM>, respectively. In an additional configuration, a gNB <NUM> may also be connected to the NGC <NUM> via control plane interface <NUM> to AMF/UPF <NUM> and user plane interface <NUM> to SMF <NUM>. Further, eNB <NUM> may directly communicate with gNB <NUM> via the backhaul connection <NUM>, with or without gNB direct connectivity to the NGC <NUM>. In some configurations, the New RAN <NUM> may only have one or more gNBs <NUM>, while other configurations include one or more of both eNBs <NUM> and gNBs <NUM>. Either gNB <NUM> or eNB <NUM> may communicate with UEs <NUM> (e.g., any of the UEs depicted in <FIG>). The base stations of the New RAN <NUM> communicate with the AMF-side of the AMF/UPF <NUM> over the N2 interface and the UPF-side of the AMF/UPF <NUM> over the N3 interface.

The functions of the AMF include registration management, connection management, reachability management, mobility management, lawful interception, transport for session management (SM) messages between the UE <NUM> and the SMF <NUM>, transparent proxy services for routing SM messages, access authentication and access authorization, transport for short message service (SMS) messages between the UE <NUM> and the short message service function (SMSF) (not shown), and security anchor functionality (SEAF). The AMF also interacts with the authentication server function (AUSF) (not shown) and the UE <NUM>, and receives the intermediate key that was established as a result of the UE <NUM> authentication process. In the case of authentication based on a UMTS (universal mobile telecommunications system) subscriber identity module (USIM), the AMF retrieves the security material from the AUSF. The functions of the AMF also include security context management (SCM). The SCM receives a key from the SEAF that it uses to derive access-network specific keys. The functionality of the AMF also includes location services management for regulatory services, transport for location services messages between the UE <NUM> and the location management function (LMF) <NUM> (which may correspond to location server <NUM>), as well as between the New RAN <NUM> and the LMF <NUM>, evolved packet system (EPS) bearer identifier allocation for interworking with the EPS, and UE <NUM> mobility event notification. In addition, the AMF also supports functionalities for non-Third Generation Partnership Project (3GPP) access networks.

Functions of the UPF include acting as an anchor point for intra-/inter-RAT mobility (when applicable), acting as an external protocol data unit (PDU) session point of interconnect to the data network (not shown), providing packet routing and forwarding, packet inspection, user plane policy rule enforcement (e.g., gating, redirection, traffic steering), lawful interception (user plane collection), traffic usage reporting, quality of service (QoS) handling for the user plane (e.g., UL/DL rate enforcement, reflective QoS marking in the DL), UL traffic verification (service data flow (SDF) to QoS flow mapping), transport level packet marking in the UL and DL, DL packet buffering and DL data notification triggering, and sending and forwarding of one or more "end markers" to the source RAN node.

The functions of the SMF <NUM> include session management, UE Internet protocol (IP) address allocation and management, selection and control of user plane functions, configuration of traffic steering at the UPF to route traffic to the proper destination, control of part of policy enforcement and QoS, and downlink data notification. The interface over which the SMF <NUM> communicates with the AMF-side of the AMF/UPF <NUM> is referred to as the N11 interface.

Another optional aspect may include a LMF <NUM>, which may be in communication with the NGC <NUM> to provide location assistance for UEs <NUM>. The LMF <NUM> can be implemented as a plurality of separate servers (e.g., physically separate servers, different software modules on a single server, different software modules spread across multiple physical servers, etc.), or alternately may each correspond to a single server. The LMF <NUM> can be configured to support one or more location services for UEs <NUM> that can connect to the LMF <NUM> via the core network, NGC <NUM>, and/or via the Internet (not illustrated).

In an aspect, the UE <NUM> illustrated in <FIG> and <FIG> may be configured to perform the UE operations described herein. For example, the UE <NUM> may be configured to detect a beam failure of a first downlink beam received at the UE <NUM> from a base station (e.g., gNB <NUM>), send, to the base station, a RACH request identifying one or more candidate downlink beams received at the UE <NUM> from the base station, and receive, from the base station, a response to the RACH request. The response may identify a second downlink beam from the one or more candidate downlink beams to replace the first downlink beam, and may also indicate a type of beam recovery associated with the second downlink beam for which the base station has reserved downlink beam resources.

In an aspect, the gNB <NUM> illustrated in <FIG> and <FIG> may be configured to perform the base station operations described herein. For example, the gNB <NUM> may be configured to receive, from a UE (e.g., UE <NUM>), a RACH request identifying one or more candidate downlink beams received at the UE from the gNB <NUM>, and send, to the UE, a response to the RACH request. The response may identify a second downlink beam from the one or more candidate downlink beams to replace a first downlink beam, and may also indicate a type of beam recovery associated with the second downlink beam for which downlink beam resources have been reserved.

According to various aspects, <FIG> illustrates an exemplary base station <NUM> (e.g., an eNB, a gNB, a small cell AP, a WLAN AP, etc.) in communication with an exemplary UE <NUM> in a wireless network, according to aspects of the disclosure. The base station <NUM> may correspond to any of the base stations described herein, such as base stations <NUM>, <NUM>, and <NUM> in <FIG> or gNB <NUM> or eNB <NUM> in <FIG> and <FIG>. The UE <NUM> may correspond to any of of the UEs described herein, such as UEs <NUM>, <NUM>, <NUM>, <NUM> in <FIG> or UE <NUM> in <FIG> and <FIG>. In the DL, IP packets from the core network (NGC <NUM> / EPC <NUM>) may be provided to a controller/processor <NUM>. The controller/processor <NUM> implements functionality for a radio resource control (RRC) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor <NUM> provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-RAT mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through automatic repeat request (ARQ), concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, scheduling information reporting, error correction, priority handling, and logical channel prioritization.

The transmit (TX) processor <NUM> and the receive (RX) processor <NUM> implement Layer <NUM> functionality associated with various signal processing functions. Each stream may then be mapped to an orthogonal frequency division multiplexing (OFDM) subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. Each spatial stream may then be provided to one or more different antennas <NUM> via a separate transmitter 318a. Each transmitter 318a may modulate an RF carrier with a respective spatial stream for transmission.

At the UE <NUM>, each receiver 354a receives a signal through its respective antenna <NUM>. Each receiver 354a recovers information modulated onto an RF carrier and provides the information to the RX processor <NUM>. The TX processor <NUM> and the RX processor <NUM> implement Layer <NUM> functionality associated with various signal processing functions. The RX processor <NUM> then converts the OFDM symbol stream from the time-domain to the frequency domain using a fast Fourier transform (FFT). The soft decisions are then decoded and de-interleaved to recover the data and control signals that were originally transmitted by the base station <NUM> on the physical channel. The data and control signals are then provided to the controller/processor <NUM>, which implements Layer <NUM> and Layer <NUM> functionality.

In the UL, the controller/processor <NUM> provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the core network. The controller/processor <NUM> is also responsible for error detection.

Similar to the functionality described in connection with the DL transmission by the base station <NUM>, the controller/processor <NUM> provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through hybrid automatic repeat request (HARQ), priority handling, and logical channel prioritization.

Channel estimates derived by the channel estimator <NUM> from a reference signal or feedback transmitted by the base station <NUM> may be used by the TX processor <NUM> to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor <NUM> may be provided to different antenna <NUM> via separate transmitters 354b. Each transmitter 354b may modulate an RF carrier with a respective spatial stream for transmission. In an aspect, the transmitters 354b and the receivers 354a may be one or more transceivers, one or more discrete transmitters, one or more discrete receivers, or any combination thereof.

Each receiver 318b receives a signal through its respective antenna <NUM>. Each receiver 318b recovers information modulated onto an RF carrier and provides the information to a RX processor <NUM>. In an aspect, the transmitters 318a and the receivers 318b may be one or more transceivers, one or more discrete transmitters, one or more discrete receivers, or any combination thereof.

IP packets from the controller/processor <NUM> may be provided to the core network. The controller/processor <NUM> is also responsible for error detection.

In an aspect, the UE <NUM> illustrated in <FIG> may be configured to perform the UE operations described herein. For example, the receiver(s) 354a may be configured to detect a beam failure of a first downlink beam received at the UE <NUM> from a base station (e.g., base station <NUM>), the transmitter(s) 354b may be configured to send, to the base station, a RACH request identifying one or more candidate downlink beams received at the UE <NUM> from the base station, and the receiver(s) 354a may be configured to receive, from the base station, a response to the RACH request. The response may identify a second downlink beam from the one or more candidate downlink beams to replace the first downlink beam, and may also indicate a type of beam recovery associated with the second downlink beam for which the base station has reserved downlink beam resources.

In an aspect, the base station <NUM> illustrated in <FIG> and <FIG> may be configured to perform the base station operations described herein. For example, the receiver(s) 318b may be configured to receive, from a UE (e.g., UE <NUM>), a RACH request identifying one or more candidate downlink beams received at the UE from the base station <NUM>, and the transmitter(s) 318a may be configured to send, to the UE, a response to the RACH request. The response may identify a second downlink beam from the one or more candidate downlink beams to replace a first downlink beam, and may also indicate a type of beam recovery associated with the second downlink beam for which downlink beam resources have been reserved.

<FIG> is a diagram <NUM> illustrating an example of a DL frame structure, according to aspects of the disclosure. <FIG> is a diagram <NUM> illustrating an example of channels within the DL frame structure, according to aspects of the disclosure. <FIG> is a diagram <NUM> illustrating an example of an UL frame structure, according to aspects of the disclosure. <FIG> is a diagram <NUM> illustrating an example of channels within the UL frame structure, according to aspects of the disclosure. Other wireless communications technologies may have a different frame structures and/or different channels. In the time domain, a frame (<NUM>) may be divided into <NUM> equally sized subframes (<NUM> each). Each subframe may include two consecutive time slots (<NUM> each).

A resource grid may be used to represent the two time slots, each time slot including one or more time concurrent resource blocks (RBs) (also referred to as physical RBs (PRBs)) in the frequency domain. The resource grid is further divided into multiple resource elements (REs). An RE may correspond to one symbol length in the time domain and one subcarrier in the frequency domain. For a normal cyclic prefix, an RB may contain <NUM> consecutive subcarriers in the frequency domain and <NUM> consecutive symbols (for DL, OFDM symbols; for UL, SC-FDMA symbols) in the time domain, for a total of <NUM> REs. For an extended cyclic prefix, an RB may contain <NUM> consecutive subcarriers in the frequency domain and <NUM> consecutive symbols in the time domain, for a total of <NUM> REs.

As illustrated in <FIG>, some of the REs carry DL reference (pilot) signals (DL-RS) for channel estimation at the UE. The DL-RS may include cell-specific reference signals (CRS) (also sometimes called "common reference signals"), UE-specific reference signals (UE-RS), and channel state information reference signals (CSI-RS). <FIG> illustrates CRS for antenna ports <NUM>, <NUM>, <NUM>, and <NUM> (indicated as R<NUM>, R<NUM>, R<NUM>, and R<NUM>, respectively), UE-RS for antenna port <NUM> (indicated as R<NUM>), and CSI-RS for antenna port <NUM> (indicated as R).

<FIG> illustrates an example of various channels within a DL subframe of a frame. The physical control format indicator channel (PCFICH) is within symbol <NUM> of slot <NUM>, and carries a control format indicator (CFI) that indicates whether the physical downlink control channel (PDCCH) occupies <NUM>, <NUM>, or <NUM> symbols (<FIG> illustrates a PDCCH that occupies <NUM> symbols). The PDCCH carries DL control information (DCI) within one or more control channel elements (CCEs), each CCE including nine RE groups (REGs), each REG including four consecutive REs in an OFDM symbol. A UE may be configured with a UE-specific enhanced PDCCH (ePDCCH) that also carries DCI. The ePDCCH may have <NUM>, <NUM>, or <NUM> RB pairs (<FIG> shows two RB pairs, each subset including one RB pair). The physical HARQ indicator channel (PHICH) is also within symbol <NUM> of slot <NUM> and carries the HARQ indicator (HI) that indicates HARQ acknowledgement (ACK) / negative ACK (NACK) feedback based on the physical uplink shared channel (PUSCH). The primary synchronization channel (PSCH) may be within symbol <NUM> of slot <NUM> within subframes <NUM> and <NUM> of a frame. The PSCH carries a primary synchronization signal (PSS) that is used by a UE to determine subframe/symbol timing and a physical layer identity. The secondary synchronization channel (SSCH) may be within symbol <NUM> of slot <NUM> within subframes <NUM> and <NUM> of a frame. The SSCH carries a secondary synchronization signal (SSS) that is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the PCI, the UE can determine the locations of the aforementioned DL-RS. The physical broadcast channel (PBCH), which carries a master information block (MIB), may be logically grouped with the PSCH and SSCH to form a synchronization signal (SS) block. The MIB provides a number of RBs in the DL system bandwidth, a PHICH configuration, and a system frame number (SFN).

As illustrated in <FIG>, some of the REs carry demodulation reference signals (DMRS) for channel estimation at the base station. The UE may additionally transmit sounding reference signals (SRS) in the last symbol of a subframe.

<FIG> illustrates an example of various channels within an UL subframe of a frame, according to aspects of the disclosure. A physical random access channel (PRACH) may be within one or more subframes within a frame based on the PRACH configuration. The PRACH may include six consecutive RB pairs within a subframe. The PRACH allows the UE to perform initial system access and achieve UL synchronization. A physical uplink control channel (PUCCH) may be located on edges of the UL system bandwidth.

As noted above, some wireless communications networks, such as NR, may employ beamforming at mmW or near mmW frequencies to increase the network capacity. The use of mmW frequencies may be in addition to microwave frequencies (e.g., in the "sub-<NUM>" GHz, or FR1, band) that may also be supported for use in communication, such as when carrier aggregation is used. <FIG> is a diagram <NUM> illustrating a base station <NUM> in communication with a UE <NUM>, according to aspects of the disclosure. In an aspect, the base station <NUM> and the UE <NUM> may correspond to any of the base stations and UEs described herein that are capable of beamforming, such as the base station <NUM> and UE <NUM>, respectively, in <FIG>.

Referring to <FIG>, the base station <NUM> may transmit a beamformed signal to the UE <NUM> on one or more beams 502a, 502b, 502c, 502d, 502e, 502f, <NUM>, <NUM>, each having a beam identifier that can be used by the UE <NUM> to identify the respective beam. Where the base station is beamforming towards the UE <NUM> with a single array of antennas, the base station <NUM> may perform a "beam sweep" by transmitting first beam 502a, then beam 502b, and so on until lastly transmitting beam <NUM>. Alternatively, the base station <NUM> may transmit beams 502a-<NUM> in some pattern, such as beam 502a, then beam <NUM>, then beam 502b, then beam <NUM>, and so on. Where the base station <NUM> is beamforming towards the UE <NUM> using multiple arrays of antennas, each antenna array may perform a beam sweep of a subset of the beams 502a-<NUM>. Alternatively, each of beams 502a-<NUM> may correspond to a single antenna or antenna array.

The UE <NUM> may receive the beamformed signal from the base station <NUM> on one or more receive beams 504a, 504b, 504c, 504d. Note that for simplicity, the beams illustrated in <FIG> represent either transmit beams or receive beams, depending on which of the base station <NUM> and the UE <NUM> is transmitting and which is receiving. Thus, the UE <NUM> may also transmit a beamformed signal to the base station <NUM> on one or more of the beams 504a-504d, and the base station <NUM> may receive the beamformed signal from the UE <NUM> on one or more of the beams 502a-<NUM>. Because communication at high mmW frequencies utilizes directionality (e.g., communication via directional beams 502a-h and 504a-d) to compensate for higher propagation loss, the base station <NUM> and the UE <NUM> may need to align their transmit (and receive) beams during both initial network access and subsequent data transmissions to ensure maximum gain. The base station <NUM> and the UE <NUM> may determine the best beams for communicating with each other, and the subsequent communications between the base station <NUM> and the UE <NUM> may be via the selected beams.

Thus, the base station <NUM> and the UE <NUM> may perform beam training to align the transmit and receive beams of the base station <NUM> and the UE <NUM>. For example, depending on environmental conditions and other factors, the base station <NUM> and the UE <NUM> may determine that the best transmit and receive beams are 502d and 504b, respectively, or beams 502e and 504c, respectively. The direction of the best transmit beam for the base station <NUM> may or may not be the same as the direction of the best receive beam, and likewise, the direction of the best receive beam for the UE <NUM> may or may not be the same as the direction of the best transmit beam.

However, due to UE mobility/movement, beam reconfiguration at the base station <NUM>, and/or other factors, a DL beam (e.g., comprising a DL control link), which may have been the preferred active beam, may fail to be detected at the UE <NUM>, or the signal quality may fall below a threshold, causing the UE <NUM> to consider it as a beam/link failure. A beam recovery procedure may be employed to recover from such a beam failure. A beam failure may refer to, for example, failure to detect a strong (e.g., with signal power greater than a threshold) active beam, which may, in some aspects, correspond to a control channel communicating control information from the network. In certain aspects, in order to facilitate beam failure detection, a UE (e.g., UE <NUM>) may be preconfigured with beam identifiers (IDs) of a first set of beams (referred to as "set_q0") to be monitored, a monitoring period, an RSRP threshold, etc. The recovery may be triggered when an RSRP associated with the one or more monitored beams (as detected by the UE <NUM>) falls below a threshold. The recovery process may include the UE <NUM> identifying a new beam, for example, from a second set of possible beams (corresponding to beam IDs that may be included in a second set, referred to as "set_q1"), and performing a RACH procedure using preconfigured time and frequency resources corresponding to the new preferred beam. The beam IDs corresponding to the beams in the second set of beams (set_q1) may be preconfigured at the UE <NUM> for use for beam failure recovery purposes. For example, the UE <NUM> may monitor DL beams (based on the beam IDs and resources identified in the second set), perform measurements, and determine (e.g., based on the measurements) which beam out of all received and measured beams may be the best for reception at the UE <NUM> from the UE's <NUM> perspective.

If beam correspondence is assumed (i.e., the direction of the best receive beam used by the UE <NUM> is also considered the best direction for the transmit beam used by the UE <NUM>), then the UE <NUM> may assume the same beam configuration for both reception and transmission. That is, based on monitoring DL reference signals from the base station <NUM>, the UE <NUM> can determine its preferred UL transmit beam weights, which will be the same as for the DL receive beam used for receiving the DL reference signals.

Where beam correspondence is not assumed (e.g., deemed not suitable in the given scenario or for other reasons), the UE <NUM> may not derive the UL transmit beam from the DL receive beam. Instead, separate signaling is needed to select the UL transmit and DL receive beam weights and for the UL-to-DL beam pairing. The UE <NUM> may perform a RACH procedure (e.g., using the preconfigured time and frequency resources indicated in the second set of beams, set_q1) to identify the UL transmit beam. Performing the RACH procedure using the preconfigured time and frequency resources may comprise, for example, transmitting a RACH preamble on one or more UL transmit beams (corresponding to the beam IDs in the second set of beams, set_q1) on allocated RACH resources corresponding to the one or more beams. Based on the RACH procedure, the UE <NUM> may be able to determine and confirm with the base station <NUM> which UL direction may be the best beam direction for an UL channel (e.g., PUCCH). In this manner, both UL transmit and DL receive beams may be reestablished and beam recovery may be completed.

In certain aspects, carrier aggregation may be utilized where the communication between the base station <NUM> and the UE <NUM> is supported by multiple carrier components (e.g., a PCell and one or more SCells). For example, the PCell may correspond to a microwave frequency band and/or other relatively lower frequency band (e.g., an FR1 band or sub-<NUM> band) compared to the mmW frequency band, while the one or more SCells may correspond to mmW frequency bands (e.g., an FR2 band). In an aspect, when PCell and SCell operation is supported in the communications system and there is no correspondence between UL receive and DL transmit beams, assistance from the PCell may be leveraged to enhance an SCell recovery procedure. In other words, if the beam/link failure occurs in the SCell, assistance from the PCell may be leveraged to facilitate the SCell beam recovery procedure. Such an approach may reduce the delays and latencies associated with the beam recovery procedure and allow for faster recovery of a failed link in the SCell.

In the examples illustrated below, for simplicity, the PCell and SCell are shown to be associated with a single base station (e.g., the hardware/circuitry for implementing the PCell and SCell may be collocated at the same base station). However, in some other configurations, the PCell and SCell may be associated with different base stations that may be synchronized.

<FIG> is a diagram <NUM> of an exemplary RACH-based SpCell beam failure recovery procedure, according to aspects of the disclosure. In the example of <FIG>, a PCell or a primary (i.e., in active use) SCell (together referred to as an "SpCell") is supported by a base station <NUM> (illustrated as a "gNB," and which may correspond to any of the base stations described herein, such as base station <NUM>). A UE <NUM> (which may correspond to any of the UEs described herein, such as UE <NUM>) monitors the received signal strength (e.g., RSRP) of periodic reference signals transmitted by the base station <NUM> on a first set ("set _q0") of DL transmit beams <NUM> of the SpCell. The first set of DL transmit beams <NUM> may correspond to one or more of beams 502a-h in <FIG> in the mmW frequency range. The first set of DL transmit beams <NUM> is referred to as the "failure detection resource set" because the base station <NUM> sends the beam IDs of the beams in the first set of DL transmit beams <NUM> to the UE <NUM> to enable the UE <NUM> to monitor these beams to determine whether or not the DL control link (i.e., a control channel communicating control information from the network) between the base station <NUM> and the UE <NUM> is active. In the example of <FIG>, the first set of DL transmit beams <NUM> includes two beams. However, there may be only one beam or more than two beams in the first set of DL transmit beams <NUM>.

At <NUM>, the UE <NUM> fails to detect a periodic reference signal transmitted on at least one of the beams in the first set of DL transmit beams <NUM>, and/or detects that a quality metric (e.g., RSRP) associated with the reference signal has fallen below a signal quality threshold (represented in <FIG> as "Qout"). The Qout threshold may be configured by the base station <NUM>. More specifically, the Layer <NUM> ("L1" in <FIG>) functionality of the UE <NUM> (e.g., implemented in the RX processor <NUM>) detects that the measured quality metric of the periodic reference signal is below the Qout threshold, and sends an out-of-sync (OOS) indication to the controller / processor <NUM> (which implements the Layer <NUM> and Layer <NUM> functionality of the UE <NUM>). In response to receiving the OOS indication, the controller / processor <NUM> of the UE <NUM> starts a beam failure detection (BFD) timer and initializes a beam failure indicator (BFI) counter to "<NUM>.

At <NUM>, the UE <NUM> again fails to detect the periodic reference signal transmitted on the at least one of the beams in the first set of DL transmit beams <NUM>, and/or again detects that the quality metric associated with the reference signal has fallen below the Qout threshold. Again, more specifically, the Layer <NUM> functionality of the UE <NUM> detects that the measured quality metric of the periodic reference signal is below the Qout threshold, and sends another OOS indication to the controller / processor <NUM>. The controller / processor <NUM> increments the BFI count to "<NUM>. " Because the BFI count has reached the maximum count ("MaxCnt") threshold while the BFD timer is running, the UE <NUM> determines that there has been a beam failure of the at least one beam (e.g., a DL control beam) in the first set of DL transmit beams <NUM>. Because there is a failure of a DL control beam (corresponding to the DL control channel communicating control information from the network), the UE <NUM> assumes that there is also a failure of the corresponding UL control beam (corresponding to the UL control channel for communicating control information to the network). As such, the UE <NUM> needs to identify a new DL control beam and re-establish an UL control beam.

Thus, at <NUM>, in response to the beam failure detection at <NUM>, the UE <NUM> initiates a beam failure recovery procedure. More specifically, the controller / processor <NUM> of the UE <NUM> requests that the Layer <NUM> functionality of the UE <NUM> (implemented by the RX processor <NUM>) identify at least one beam in a second set ("set_q1") of DL transmit beams <NUM> that carries a periodic reference signal with a received signal strength greater than a signal quality threshold (represented as "Qin"). The second set of DL transmit beams <NUM> may correspond to one or more of beams 502a-h in <FIG> in the mmW frequency range. The second set of DL transmit beams <NUM> is referred to as the "candidate beam reference signal list. " The UE <NUM> may receive both the beam IDs of the beams in the second set of DL transmit beams <NUM> and the Qin threshold from the base station <NUM>. In the example of <FIG>, the second set of DL transmit beams <NUM> includes four beams, one of which (shaded) carries periodic reference signals having a received signal strength greater than the Qin threshold. However, as will be appreciated, there may be more or fewer than four beams in the second set of DL transmit beams <NUM>, and there may be more than one beam that meets the Qin threshold. The RX processor <NUM> reports the identified candidate beam to the controller / processor <NUM>. The identified candidate beam can then be used as the new DL control beam, although not necessarily immediately.

At <NUM>, to re-establish an UL control beam, the UE <NUM> performs a RACH procedure on the one or more candidate DL transmit beams identified at <NUM> (one in the example of <FIG>). More specifically, the controller / processor <NUM> instructs the RX processor <NUM> to send a RACH preamble (which may be pre-stored or provided to the UE <NUM> by the base station <NUM>) to the base station <NUM>. The RX processor <NUM> sends the RACH preamble (also referred to as a Message <NUM> ("Msg1")) on one or more UL transmit beams corresponding to the one or more candidate DL transmit beams identified at <NUM> on preconfigured RACH resources for the one or more candidate UL transmit beams. The preconfigured RACH resources may correspond to the SpCell (e.g., in the mmW band). Although not illustrated in <FIG>, at <NUM>, the UE <NUM> also starts a beam failure recovery (BFR) timer that defines a contention-free random access (CFRA) window.

The one or more candidate DL transmit beams identified at <NUM> can include beams that are different than the DL transmit beam associated with the beam failure. As used herein, a "beam" is defined by beam weights associated with an antenna array of the UE <NUM>. Hence, in some aspects, whether used for UL transmission by the UE <NUM> or DL reception by the UE <NUM>, the weights applied to each antenna in the array to construct the transmitted or received beam define the beam. As such, the one or more candidate UL transmit beams on which the RACH preamble is sent may have different weights than the DL transmit beam associated with the beam failure, even if such candidate UL transmit beam is in generally a similar direction as the DL transmit beam indicated to be failing.

At <NUM>, the base station <NUM> transmits a response (referred to as a "Msg1 response") to the UE <NUM> with a cell-radio network temporary identifier (C-RNTI) via a PDCCH associated with the SpCell. For example, the response may comprise cyclic redundancy check (CRC) bits scrambled by the C-RNTI. After the RX processor <NUM> of the UE <NUM> processes the received response with the C-RNTI via the SpCell PDCCH from the base station <NUM> and determines that the received PDCCH is addressed to the C-RNTI, the controller / processor <NUM> determines that the beam failure recovery procedure has completed and stops the BFR timer started at <NUM>. In an aspect, the C-RNTI may be mapped to a beam direction determined by the base station <NUM> to be the best direction for an UL channel (e.g., PUCCH) for the UE <NUM>. Accordingly, upon receipt of the response with C-RNTI from the base station <NUM>, the UE <NUM> may be able to determine the optimal UL transmit beam that is best suited for the UL channel.

The operations at <NUM> are part of a first scenario in which the UE <NUM> successfully recovers from the beam failure detected at <NUM>. However, such a recovery may not always occur, or at least not before the BFR timer started at <NUM> times out. If the BFR timer expires before the beam failure recovery procedure completes successfully, then at <NUM>, the UE <NUM> determines that a radio link failure (RLF) has occurred.

In the example of <FIG>, the SCell beam recovery procedure is completed without assistance from the PCell. An issue with the beam failure recovery procedure described with reference to <FIG> is that the base station <NUM> and UE <NUM> may need to repeat operations <NUM> to <NUM> an unknown number of times to determine the UL transmit beam that is best suited for the UL channel. Additionally, dedicated RACH resources may be needed on the SCell and additional overhead (e.g., due to RACH messages and signaling) may also be associated. While the dedicated RACH resources may be used by the UE <NUM> in the event of beam failure recovery, at other times the dedicated resources are held up for no reason and are not usable for other purposes, which is an undesirable effect. As such, a more efficient beam failure recovery procedure would be beneficial.

As noted above, when PCell and SCell operation is supported in a communications system and there is no correspondence between UL and DL beams, assistance from the PCell can be leveraged to enhance an SCell recovery procedure. For example, beam failure detection can be performed based on a virtual control resource set (CORESET) in the SCell, and the CORESET beam (of Type D spatial QCL) could be the PDSCH beam (of Type D spatial QCL). More specifically, in some scenarios, the actual control signaling for scheduling the PDSCH can occur through the PCell. Thus, in order to detect a control signal failure in the SCell, reference signals in the SCell are used with the above-noted QCL assumptions to serve as virtual CORESETs.

<FIG> is a diagram <NUM> of an exemplary SCell beam recovery procedure with PCell assistance and without assuming any beam correspondence, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by a base station <NUM> (illustrated as a "gNB") and a UE <NUM>, which may correspond to any of the base stations and UEs described herein.

In the example beam recovery procedure of <FIG>, the beam recovery CORESET (for beam recovery in the SCell) may not be activated unless needed, and thus, the beam recovery resources are not blocked from being used by the base station <NUM> for other purposes. Thus, the example beam recovery procedure of <FIG> may facilitate on-demand activation of RACH resources for the SCell via the PCell.

At <NUM>, the UE <NUM> detects an SCell DL transmit beam failure, as described above with reference to <NUM> and <NUM> of <FIG>. Upon the detection of the SCell DL transmit beam failure, the UE <NUM> may trigger a beam recovery procedure.

At <NUM>, the UE <NUM> sends a special scheduling request (SR) via the PCell (which may operate on a sub-<NUM> frequency band) to the base station <NUM>. The scheduling request may be a specifically configured SR for SCell beam failure recovery procedures, and may provide an indication to the base station <NUM> via the PCell that the SCell DL transmit beam failure has occurred.

At <NUM>, in response to receiving the special SR, the base station <NUM>, via the PCell, requests a beam index report from the UE <NUM>. Specifically, the base station <NUM> may transmit a specialized PDCCH order, for example, a specially configured message transmitted via the PCell, that includes a request for a Layer <NUM> RSRP report for SCell DL transmit beams and/or a request for reporting a beam ID corresponding to a preferred DL transmit beam as determined by the UE <NUM>.

At <NUM>, in response to the request for the beam index report for SCell DL transmit beams, and based on the information regarding the beam IDs and corresponding resources, the UE <NUM> measures DL reference signals (e.g., synchronization signal blocks (SSBs) and/or other reference signals) communicated via DL transmit beams to identify the best/preferred DL transmit beam direction, as discussed above with respect to <NUM> of <FIG>. The UE <NUM> may generate a Layer <NUM> RSRP report for the DL transmit beams based on the measurements. Also, based on the measurements, the UE <NUM> may identify a preferred DL transmit beam (or set of beams) for a directional DL channel (e.g., PDCCH). The UE <NUM> may send the Layer <NUM> RSRP report and/or the beam ID of the preferred DL transmit beam to the base station <NUM> via a PUCCH in the PCell.

At <NUM>, based on the received report via the PUCCH in the PCell, the base station <NUM> triggers on-demand RACH for SCell recovery. For example, the base station <NUM> may reserve a set of RACH resources associated with the SCell for performing RACH. The set of resources associated with the SCell beam recovery may include resources (e.g., in the frequency band corresponding to the SCell) for transmitting RACH preambles via candidate UL transmit beams.

At <NUM>, the UE <NUM> performs a RACH procedure on one or more UL transmit beams corresponding to the one or more candidate DL transmit beams identified at <NUM>. More specifically, the UE <NUM> sends a RACH preamble (which may be pre-stored or provided to the UE <NUM> by the base station <NUM>) to the base station <NUM>, as described above with reference to <NUM> of <FIG>. The UE <NUM> sends the RACH preamble (i.e., "Msg1") on the one or more candidate UL transmit beams on the RACH resources configured at <NUM>. The configured RACH resources may correspond to the SCell (e.g., in the mmW band).

At <NUM>, the base station <NUM> transmits a response (referred to as a "Msg1 response" or a "Msg2") to the UE <NUM> as discussed above with reference to <NUM> of <FIG>. After the UE <NUM> processes the received response, the UE <NUM> may be able to determine the optimal UL transmit beam that is best suited for the uplink channel.

At <NUM>, the UE <NUM> reconfigures the transmission configuration indicator (TCI) state for the PUCCH. The reconfiguration of the TCI state confirms that the UL transmit beam identified at <NUM> is to be used for the PUCCH.

Although the foregoing has described beam failure recovery procedures in which the UE establishes a new UL control beam, as will be appreciated, the techniques described herein are equally applicable to selecting a new UL transmit beam and/or DL receive beam in response to failure of the PCell or SCell. For example, when selecting a new DL receive beam for the PCell or the SCell, in <FIG>, the Msg1 transmitted at <NUM> could identify candidate receive beams for the PCell or SCell, and the response at <NUM> could identify one of those beams to use for the PCell or SCell, rather than identifying an UL control beam. In that case, it is useful for the UE <NUM> to be able to determine what type of beam recovery the Msg1 response received at <NUM> is associated with, for example, PCell beam recovery (for the uplink transmit beam and/or the downlink receive beam), SCell beam recovery (for the uplink transmit beam and/or the downlink receive beam), or UL transmit/control beam recovery. More generally, it is useful for the UE to be able to determine the type of beam a message in a beam recovery procedure is associated with, for example, whether the beam is associated with a PCell or an SCell. Additionally or alternatively, it is useful for the UE to be able to determine whether the beam is an uplink beam or a downlink beam. In situations where the beam is associated with an SCell, information about the type of beam associated with the beam recovery procedure can include whether it is a downlink-only beam or a downlink and uplink beam. Furthermore, information relating to whether the SCell is selfscheduled (has its own control resources) or cross-scheduled (does not have its own control resources) may also be included in information relating to the type of beam. To address this issue, the present disclosure proposes three solutions. The first solution is to configure a separate BFR CORESET for each of the different types of beam recoveries, i.e., PCell beam recovery, SCell beam recovery, and/or UL transmit/control beam recovery. The second solution is to configure the same BFR CORESET for each of the different types of beam recovery, but to scramble the PDCCH with different RNTIs for the different types of beam recovery. The third solution is to configure the same BFR CORESET for each of the different types of beam recovery, and to use the same DCI but with additional bits to convey which type of recovery response it is.

<FIG> is a diagram 800A illustrating an example of the first solution, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by a base station <NUM> (illustrated as a "gNB") in communication with a UE <NUM>, which may correspond to any of base stations and UEs described herein. In the first solution, the base station <NUM> reserves unique beam recovery resources (e.g., CORESET) for each use case (e.g., PCell recovery, SCell recovery, or UL beam recovery). That is, the base station <NUM> reserves a different CORESET for each type of beam recovery (e.g., PCell recovery, SCell recovery, UL beam recovery).

At <NUM>, the UE <NUM> sends a special beam failure recovery request (BFRQ) Msg1 to the base station <NUM>, similar to the RACH preamble sent at <NUM> of <FIG>. The BFRQ Msg1 may be transmitted on one or more candidate UL transmit beams, such as the one or more candidate UL transmit beams corresponding to the one or more candidate DL transmit beams identified at <NUM>/<NUM> of <FIG> or <NUM> of <FIG>. However, in the example of <FIG>, the one or more candidate UL transmit beams are for the PCell rather than an SCell, and are intended to identify a new PCell rather than a new UL transmit/control beam. In addition, rather than simply being transmitted on the candidate beam(s), the BFRQ Msg1 may also specify the type of recovery, here, PCell recovery.

At <NUM>, the base station <NUM> sends a response to the Msg1 in the CORESET reserved for a PCell beam failure recovery, similar to <NUM> of <FIG> and/or <NUM> of <FIG>, except that the recovery is for the PCell DL transmit beam. That is, according to one alternative of the present invention, the type of beam recovery is indicated by an identification of the reserved CORESET. In an aspect, the response indicates the candidate beam determined by the base station <NUM> to be the best DL transmit beam for the PCell, and for which the base station <NUM> has reserved resources. Accordingly, upon receipt of the response from the base station <NUM>, the UE <NUM> uses the identified candidate DL transmit beam as the new beam for the PCell.

At <NUM>, the UE <NUM> reconfigures the TCI state for the PDCCH (because the recovery is for the PCell, not the UL control beam), similar to <NUM> of <FIG>. The reconfiguration of the TCI state confirms that the identified DL transmit beam is to be used for the PDCCH for the PCell.

<FIG> is a diagram 800B illustrating a second example of the first solution, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by the base station <NUM> in communication with the UE <NUM>. At <NUM>, the UE <NUM> sends a special BFRQ Msg1 to the base station <NUM>, similar to the RACH preamble sent at <NUM> of <FIG>. The BFRQ Msg1 may be transmitted on one or more candidate UL transmit beams, such as the one or more candidate UL transmit beams corresponding to the one or more candidate DL transmit beams identified at <NUM>/<NUM> of <FIG> or <NUM> of <FIG>. However, in the example of <FIG>, the one or more candidate UL transmit beams are for the SCell, and are intended to identify a new SCell rather than a new UL transmit beam. In addition, rather than simply being transmitted on the candidate beam(s), the BFRQ Msg1 may also specify the type of recovery, here, SCell recovery.

At <NUM>, the base station <NUM> sends a response to the Msg1 in the CORESET for a SCell beam failure recovery, similar to <NUM> of <FIG> and/or <NUM> of <FIG>, except that the recovery is for the SCell DL transmit beam. In an aspect, the response indicates the candidate beam determined by the base station <NUM> to be the best DL transmit beam for the SCell, and for which the base station <NUM> has reserved resources. Accordingly, upon receipt of the response from the base station <NUM>, the UE <NUM> uses the identified candidate DL transmit beam as the new beam for the SCell.

At <NUM>, the UE <NUM> reconfigures the TCI state for the PDCCH (because the recovery is for the SCell, not the UL control beam), similar to <NUM> of <FIG>. The reconfiguration of the TCI state confirms that the identified DL transmit beam is to be used for the PDCCH for the SCell.

<FIG> is a diagram 900A illustrating an example of the second solution, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by a base station <NUM> (illustrated as a "gNB") in communication with a UE <NUM>, which may correspond to any of base stations and UEs described herein. In the second solution, according to one alternative of the present invention, the base station <NUM> configures the same beam failure recovery CORESET, but scrambles the PDCCH with different RNTIs for the different types of recovery (e.g., PCell, SCell, or UL control beam). In that way, the same beam recovery resources (e.g., RACH resources) can be used, but with different scrambling sequences for each use case (e.g., PCell recovery, SCell recovery, or UL beam recovery).

At <NUM>, the UE <NUM> sends a special BFRQ Msg1 to the base station <NUM>, similar to the BFRQ Msg1 sent at <NUM> of <FIG> and <NUM> of <FIG>. The BFRQ Msg1 may be transmitted on one or more candidate UL transmit beams, such as the one or more candidate UL transmit beams corresponding to the one or more candidate beams identified at <NUM>/<NUM> of <FIG> or <NUM> of <FIG>. However, in the example of <FIG>, the one or more candidate beams are for the PCell rather than an SCell, and are intended to identify a new PCell rather than a new UL transmit beam for the SCell. In addition, rather than simply being transmitted on the candidate beam(s), the BFRQ Msg1 may also specify the type of recovery, here, PCell recovery.

At <NUM>, the base station <NUM> sends a response to the Msg1 in the CORESET for a PCell beam failure recovery, similar to <NUM> of <FIG> and/or <NUM> of <FIG>, except that the recovery is for the PCell DL transmit beam. In an aspect, the response may comprise the PDCCH scrambled by an RNTI corresponding to the type of recovery (e.g., PCell recovery, SCell recovery, or UL beam recovery). The UE <NUM> may be informed of the particular RNTI in order to decode the response. Because the RNTI is different for each type of recovery, any type of beam failure recovery procedure can reuse the same resources (e.g., RACH resources). In an aspect, the response indicates the candidate beam determined by the base station <NUM> to be the best DL transmit beam for the PCell, and for which the base station <NUM> has reserved resources. Accordingly, upon receipt of the response from the base station <NUM>, the UE <NUM> uses the identified candidate DL transmit beam as the new beam for the PCell.

<FIG> is a diagram 900B illustrating a second example of the second solution, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by the base station <NUM> in communication with the UE <NUM>. At <NUM>, the UE <NUM> sends a special BFRQ Msg1 to the base station <NUM>, similar to the BFRQ Msg1 sent at <NUM> of <FIG>. The BFRQ Msg1 may be transmitted on one or more candidate UL transmit beams, such as the one or more candidate UL transmit beams corresponding to the one or more candidate beams identified at <NUM>/<NUM> of <FIG> or <NUM> of <FIG>. However, in the example of <FIG>, the one or more candidate beams are for the SCell, and are intended to identify a new DL transmit beam for the SCell rather than a new UL transmit beam for the SCell. In addition, rather than simply being transmitted on the candidate beam(s), the BFRQ Msg1 may also specify the type of recovery, here, SCell recovery.

At <NUM>, the base station <NUM> sends a response to the Msg1 in the CORESET for a SCell beam failure recovery, similar to <NUM> of <FIG> and/or <NUM> of <FIG>, except that the recovery is for the SCell DL transmit beam. In an aspect, the response may comprise the PDCCH scrambled by a different RNTI (from the RNTI in the example of <FIG> for PCell recovery). In an aspect, the response indicates the candidate beam determined by the base station <NUM> to be the best DL transmit beam for the SCell, and for which the base station <NUM> has reserved resources. Accordingly, upon receipt of the response from the base station <NUM>, the UE <NUM> uses the identified candidate DL transmit beam as the new beam for the SCell.

<FIG> is a diagram 1000A illustrating an example of the third solution, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by a base station <NUM> (illustrated as a "gNB") in communication with a UE <NUM>, which may correspond to any of base stations and UEs described herein. In the third solution, according to one alternative of the present invention, the base station <NUM> configures the same beam failure recovery CORESET for each type of recovery and uses the same DCI, but adds additional bits to the DCI to convey the type of recovery. For example, the base station <NUM> can reuse the carrier indicator field (CIF) used for carrier scheduling, or some other similar mechanism.

At <NUM>, the UE <NUM> sends a special BFRQ Msg1 to the base station <NUM>, similar to the BFRQ Msg1 sent at <NUM> of <FIG> and <NUM> of <FIG>. The BFRQ Msg1 may be transmitted on one or more candidate UL transmit beams, such as the one or more candidate UL transmit beams corresponding to the one or more candidate beams identified at <NUM>/<NUM> of <FIG> or <NUM> of <FIG>. However, in the example of <FIG>, the one or more candidate beams are for the PCell rather than an SCell, and are intended to identify a new DL transmit beam for the Cell rather than a new UL transmit beam for the SCell. In addition, rather than simply being transmitted on the candidate beam(s), the BFRQ Msg1 may also specify the type of recovery, here, PCell recovery.

At <NUM>, the base station <NUM> sends a response to the Msg1 in the CORESET for a PCell beam failure recovery, similar to <NUM> of <FIG> and/or <NUM> of <FIG>, except that the recovery is for the PCell DL transmit beam. In an aspect, the response may comprise the PDCCH scrambled by an RNTI. In an aspect, the RNTI is the same for each type of recovery (e.g., PCell recovery, SCell recovery, or UL beam recovery) so that any beam failure recovery procedure can reuse the same resources (e.g., RACH resources). In addition, the DCI in the response may be the same for each type of recovery. To differentiate the recovery type, the base station <NUM> adds additional bits to the response that are different depending on the type of recovery. The UE <NUM> may be informed of the mapping of these additional bits to the different types of recovery in order to decode the response. In an aspect, the response indicates the candidate beam determined by the base station <NUM> to be the best DL transmit beam for the PCell, and for which the base station <NUM> has reserved resources. Accordingly, upon receipt of the response from the base station <NUM>, the UE <NUM> uses the identified candidate DL transmit beam as the new beam for the PCell.

<FIG> is a diagram 1000B illustrating an example of the third solution, according to aspects of the disclosure. The procedure illustrated in <FIG> may be performed by the base station <NUM> in communication with the UE <NUM>. At <NUM>, the UE <NUM> sends a special BFRQ Msg1 to the base station <NUM>, similar to the BFRQ Msg1 sent at <NUM> of <FIG>. The BFRQ Msg1 may be transmitted on one or more candidate UL transmit beams, such as the one or more candidate UL transmit beams corresponding to the one or more candidate beams identified at <NUM>/<NUM> of <FIG> or <NUM> of <FIG>. However, in the example of <FIG>, the one or more candidate beams are for the SCell, and are intended to identify a new DL transmit for the SCell rather than a new UL transmit beam for the SCell. In addition, rather than simply being transmitted on the candidate beam(s), the BFRQ Msg1 may also specify the type of recovery, here, SCell recovery.

At <NUM>, the base station <NUM> sends a response to the Msg1 in the CORESET for an SCell beam failure recovery, similar to <NUM> of <FIG> and/or <NUM> of <FIG>, except that the recovery is for the SCell transmit beam. In an aspect, the response may comprise the PDCCH scrambled by the same RNTI as in <FIG>, with the same DCI bits, but with additional bits to differentiate SCell recovery from PCell recovery. In an aspect, the response indicates the candidate beam determined by the base station <NUM> to be the best DL transmit beam for the PCell, and for which the base station <NUM> has reserved resources. Accordingly, upon receipt of the response from the base station <NUM>, the UE <NUM> uses the identified candidate DL transmit beam as the new beam for the SCell.

<FIG> illustrates an exemplary method <NUM> of beam failure recovery in a wireless communications system, such as wireless communications system <NUM>, according to aspects of the disclosure. The method <NUM> may be performed by a UE, such as any of the UEs described herein.

At <NUM>, the UE (e.g., RX processor <NUM> via receiver(s) <NUM>) detects a beam failure of a first downlink (transmit) beam received at the UE from a base station (e.g., any of the base stations described herein), as at <NUM> and <NUM> of <FIG> and <NUM> of <FIG>. The first downlink beam may be associated with a PCell or an SCell supported by the base station.

At <NUM>, the UE (e.g., TX processor <NUM> via transmitter(s) <NUM>) sends, to the base station, a RACH request identifying one or more candidate downlink beams received at the UE from the base station, as at <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and <NUM> of <FIG>. The RACH request may be sent using an uplink beam different than the uplink beam associated with the beam failure. As such, in one example, the beam failure indication can be sent using the same weights for receiving a candidate beam (from the one or more candidate beams) having different weights than the downlink beam indicated to be failing, even if such candidate beam is in generally a similar direction as the downlink beam indicated to be failing. Additionally or alternatively, the beam failure indication may be sent using a different carrier frequency and/or different resources than the downlink beam associated with the beam failure. The one or more candidate downlink beams included in the RACH request may, in some implementations, have been previously indicated by the base station and stored in, for example, BeamFailureRecoveryConfig parameter(s) in the RRC layer. Such beam failure recovery parameters can be received from the base station in a unicast message using the PDCCH or PDSCH or broadcast in the PDSCH. In various examples, contention-free RACH information can be carried in the broadcast PDSCH.

At <NUM>, in response to sending the RACH request, the UE (e.g., RX processor <NUM> via receiver(s) <NUM>) receives, from the base station, a response to the RACH request, the response identifying a second downlink beam from the one or more candidate downlink beams to replace the first downlink beam and indicating a type of beam recovery associated with the second downlink beam for which the base station has reserved downlink beam resources, as at <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and <NUM> of <FIG>.

<FIG> illustrates an exemplary method <NUM> of beam failure recovery in a wireless communications system, such as wireless communications system <NUM>, according to aspects of the disclosure. The method <NUM> may be performed by a base station, such as any of the base stations <NUM> described herein.

At <NUM>, the base station (e.g., RX processor <NUM> via receiver(s) <NUM>) optionally receives a message from a UE (e.g., any of the UEs described herein) indicating that a beam failure has occurred at the UE, as at <NUM> of <FIG>. The beam failure may be a failure of a DL transmit beam associated with a PCell supported by the base station or an SCell supported by the base station. Operation <NUM> is optional because the UE need not send a message indicating that a beam failure has occurred, but rather, can simply send a RACH request, as at <NUM>. As noted above with reference to <NUM>, like the RACH request, the message indicating that a beam failure has occurred can be sent using a beam different than the beam associated with the beam failure.

At <NUM>, the base station (e.g., RX processor <NUM> via receiver(s) <NUM>) receives, from the UE, a RACH request identifying one or more candidate downlink beams received at the UE from the base station, as at <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and <NUM> of <FIG>.

At <NUM>, in response to receiving the RACH request, the base station (e.g., TX processor <NUM> via transmitter(s) <NUM>) sends, to the UE, a response to the RACH request, the response identifying a second downlink beam from the one or more candidate downlink beams to replace the first downlink beam and indicating a type of beam recovery associated with the second downlink beam for which downlink beam resources have been reserved, as at <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, <NUM> of <FIG>, and <NUM> of <FIG>.

It should be understood that any reference to an element herein using a designation such as "first," "second," and so forth does not generally limit the quantity or order of those elements. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements. In addition, terminology of the form "at least one of A, B, or C" or "one or more of A, B, or C" or "at least one of the group consisting of A, B, and C" used in the description or the claims means "A or B or C or any combination of these elements. " For example, this terminology may include A, or B, or C, or A and B, or A and C, or A and B and C, or 2A, or 2B, or 2C, and so on.

In view of the descriptions and explanations above, those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both.

Accordingly, it will be appreciated, for example, that an apparatus or any component of an apparatus may be configured to (or made operable to or adapted to) provide functionality as taught herein. This may be achieved, for example: by manufacturing (e.g., fabricating) the apparatus or component so that it will provide the functionality; by programming the apparatus or component so that it will provide the functionality; or through the use of some other suitable implementation technique. As one example, an integrated circuit may be fabricated to provide the requisite functionality. As another example, an integrated circuit may be fabricated to support the requisite functionality and then configured (e.g., via programming) to provide the requisite functionality. As yet another example, a processor circuit may execute code to provide the requisite functionality.

Moreover, the methods, sequences, and/or algorithms described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in random access memory (RAM), flash memory, read-only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In the alternative, the storage medium may be integral to the processor (e.g., cache memory).

Claim 1:
A method of beam failure recovery in a wireless communications system, comprising:
detecting (<NUM>; <NUM>), by a user equipment, UE (<NUM>, <NUM>, <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>), a beam failure of a first downlink beam received at the UE from a base station (<NUM>, <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>; <NUM>);
sending (<NUM>; <NUM>, <NUM>; <NUM>, <NUM>; <NUM>, <NUM>; <NUM>), by the UE to the base station, a random access channel, RACH, request identifying one or more candidate downlink beams received at the UE from the base station; and
receiving (<NUM>; <NUM>, <NUM>; <NUM>, <NUM>; <NUM>, <NUM>; <NUM>), at the UE from the base station, a response to the RACH request, the response identifying a second downlink beam from the one or more candidate downlink beams to replace the first downlink beam and indicating a type of beam recovery associated with the second downlink beam for which the base station has reserved downlink beam resources;
wherein the type of beam recovery is indicated by an identification of a different control resource set, CORESET, for each of a primary cell, PCell, recovery and a secondary cell, SCell, recovery; or
wherein the type of beam recovery is indicated by an identification of the same CORESET scrambled with a different radio network temporary identifier, RNTI, for each of the PCell recovery and the SCell recovery; or
wherein the type of beam recovery is indicated by the same CORESET, the same downlink control information, DCI, and different additional bits to distinguish the PCell recovery and the SCell recovery.