Medium access control procedure for beam index indication

Abstract

Methods, systems, and devices for wireless communications are described. A user equipment (UE) may select a beam from a set of beams and transmit an indication of the selected beam in a medium access control (MAC) control element to establish a communication link with a base station. In some cases, the UE may select a beam and indicate the selection based on identifying a beam failure and / or determining to perform a random access procedure. When transmitting the indication of the selected beam, the UE may obtain uplink resources for transmission based on the availability of uplink resources. For example, if uplink resources are available, the UE may transmit the indication of the selected beam multiplexed with the uplink transmission. Alternatively, if uplink resources are unavailable, the UE may request uplink resources for transmitting the indication of the selected beam.

Description

[Technical Field]

[0001] cross reference This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 887,631, entitled "Media Access Control Procedures for Beam Index Indications," filed August 15, 2019, and PCT International Application No. PCT / CN2019 / 102367, entitled "Scheduling Request for Cell-Specific Resources," filed August 23, 2019, by He et al., and U.S. Patent Application No. 16 / 993,023, entitled "Media Access Control Procedures for Beam Index Indications," filed August 13, 2020, by He et al., each of which is assigned to the assignee of the present application. [Background technology]

[0002] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcasts, and so on. These systems may be capable of supporting communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include fourth-generation (4G) systems, such as Long Term Evolution (LTE), LTE-Advanced (LTE-A), or LTE-A Pro systems, and fifth-generation (5G) systems, sometimes referred to as New Radio (NR) systems. These systems may utilize technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-s-OFDM).

[0003] A wireless multiple-access communication system may include several base stations or network access nodes, each simultaneously supporting communication for multiple communication devices, sometimes known as user equipment (UE). In some cases, the UE and base station may communicate via beamforming techniques, where each wireless device uses a directional beam to transmit or receive signals from other wireless devices. For example, rather than transmitting signals in many directions (e.g., omnidirectionally), both the UE and base station may use a set of antennas to transmit or receive signals in a particular direction, resulting in a stronger signal being transmitted in that particular direction. However, the UE and base station may simultaneously form multiple beams to increase the likelihood of successful signal transmission and reception. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, techniques for directing a preferred beam (eg, a stronger beam) for subsequent communications are desired. [Means for solving the problem]

[0005] The described techniques relate to improved methods, systems, devices, and apparatuses that support a medium access control (MAC) procedure for beam index indication. Generally, the described techniques enable a user equipment (UE) to select a first beam (e.g., a preferred beam) from a set of beams and transmit an indication of the selected first beam in a MAC control element (CE) to a base station to establish a communication link with the base station. In some cases, the UE may select the first beam and indicate the selection based on the base station identifying a beam failure on at least one cell, determining to establish a communication link via a random access channel (RACH) procedure (e.g., a two-step RACH, a four-step RACH, etc.), or a combination thereof. When transmitting the indication of the selected beam, the UE may obtain uplink resources for transmission based on uplink resource availability (e.g., whether uplink resources are scheduled within N slots in the future) compared to a threshold. For example, if uplink resources are available, the UE may transmit the indication of the selected first beam multiplexed with the MAC CE. Alternatively, if uplink resources are unavailable, the UE may request uplink resources (e.g., via configured uplink resources, via a scheduling request, etc.) for transmitting an indication of the selected first beam.

[0006] A method for wireless communication in a UE is described that may include determining to establish a communication link between the UE and a serving cell of a base station, selecting, by the UE, a first beam from a set of candidate beams of the serving cell for establishing the communication link, and transmitting, in a MAC CE, an indication of the selected first beam to the base station over uplink resources based on a comparison of timing of uplink resource availability with a threshold.

[0007] An apparatus for wireless communication in a UE is described. The apparatus may include a processor, a memory coupled to the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to: determine to establish a communication link between the UE and a serving cell of a base station; select, by the UE, a first beam from a set of candidate beams of the serving cell to establish the communication link; and transmit, in a MAC CE, an indication of the selected first beam to the base station over uplink resources based on a comparison of timing of uplink resource availability and a threshold.

[0008] Another apparatus for wireless communication in a UE is described. The apparatus may include means for determining to establish a communication link between the UE and a serving cell of a base station, means for selecting, by the UE, a first beam from a set of candidate beams of the serving cell for establishing the communication link, and means for transmitting, in a MAC CE over uplink resources to the base station, an indication of the selected first beam based on a comparison of timing of uplink resource availability to a threshold.

[0009] A non-transitory computer-readable medium storing code for wireless communication in a UE is described. The code may include instructions executable by a processor to: determine to establish a communication link between the UE and a serving cell of a base station; select, by the UE, a first beam from a set of candidate beams of the serving cell to establish the communication link; and transmit, in a MAC CE, an indication of the selected first beam to the base station over uplink resources based on a comparison of timing of uplink resource availability and a threshold.

[0010] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for initiating a request for uplink resources for transmitting an indication of the selected first beam to a base station. Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for transmitting a request to a base station on uplink control resources indicating a beam of the failed serving cell, and receiving from the base station, in response to the transmitted request, an indication of uplink resources in a second serving cell for the UE to use to transmit the indication of the selected first beam.

[0011] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the request may include operations, features, means, or instructions for transmitting a request on dedicated uplink control resources configured to instruct the base station on a beam or set of beams configured for a first serving cell that may have failed, and receiving, in response to the transmitted request, downlink control information from a second serving cell of the base station indicating uplink resources of the second serving cell for the UE to use to transmit an indication of the selected first beam.

[0012] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for: transmitting a request on uplink control resources for transmission opportunities, the uplink control resources indicating to the base station that a beam of a serving cell may have failed and transmission opportunities on uplink control resources associated with the set of serving cells for indicating the serving cells whose beams may have failed; and receiving from the base station, in response to the transmitted request, an indication of uplink resources in a second serving cell, different from the serving cell, for the UE to use to transmit an indication of the selected first beam.

[0013] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the request includes a random access message of a random access procedure for establishing a communication link between the UE and a serving cell of the base station.

[0014] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, determining to establish a communication link may include operations, features, means, or instructions for communicating with a base station over the communication link, identifying a beam failure for the communication link between the UE and the serving cell, and determining to establish a communication link between the UE and the serving cell based on the identified beam failure.

[0015] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, transmitting an indication of the selected first beam in the MAC CE based on the comparison may include operations, features, means, or instructions for the UE to obtain uplink resources for transmitting the indication of the first beam; comparing a threshold number of slots to a number of slots between a current time and the uplink resources, where the threshold value includes the threshold number of slots; determining availability of the uplink resources based on the number of slots between the current time and the uplink resources being less than the threshold number of slots; and transmitting an indication of the selected first beam in the MAC CE based on the determined availability indicating that the number of slots between the current time and the uplink resources may be less than the threshold number of slots.

[0016] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, transmitting an indication of the selected first beam in the MAC CE based on the comparison may include operations, features, means, or instructions for the UE to obtain uplink resources for transmitting the indication of the first beam; comparing a threshold number of slots to a number of slots between a current time and the uplink resources, where the threshold comprises the threshold number of slots; determining availability of the uplink resources based on the number of slots between the current time and the uplink resources being less than the threshold number of slots; transmitting a request for the uplink resources to a base station based on the determined availability indicating that the number of slots between the current time and the uplink resources may be greater than the threshold number of slots; receiving an indication of the uplink resources in response to the transmitted request; and transmitting an indication of the selected first beam in the MAC CE on the indicated uplink resources.

[0017] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for receiving a configuration for beam failure recovery, wherein a request for uplink resources is transmitted based on the received configuration.

[0018] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, transmitting a request for uplink resources to a base station may include an act, feature, means, or instruction for transmitting a scheduling request sequence to the base station indicating the request.

[0019] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, the scheduling request sequence may be transmitted on an uplink resource corresponding to the highest priority logical channel configured for the UE.

[0020] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, transmitting an indication of the selected first beam may include an operation, feature, means, or instruction for transmitting a MAC CE in a RACH message of a RACH procedure to the base station.

[0021] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for determining, prior to availability of uplink resources by at least a threshold, that a second beam from a set of candidate beams may be available for transmitting an indication of the first beam, wherein the uplink resources include the first beam, and the indication of the selected first beam may be transmitted in a MAC CE on the second beam based on a determination that the second beam may be available.

[0022] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, an indication of the selected first beam may be transmitted on the second beam in a first message of a two-step RACH procedure.

[0023] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, an indication of the selected first beam may be transmitted on a second beam in a connection request message of a four-step RACH procedure.

[0024] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for implementing a logical channel prioritization procedure for a MAC protocol data unit (PDU) that includes a MAC CE, the logical channel prioritization procedure giving the MAC CE a higher priority than each other MAC CE in the MAC PDU, higher than the data in the MAC PDU, and lower than information in a Common Control Channel (CCCH) message in the MAC PDU.

[0025] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, means, or instructions for starting a timer and a counter based on determining to establish a communication link, incrementing the counter based on sending an indication of the selected first beam, and retransmitting the indication of the selected first beam in the MAC CE based on the timer expiring before a message can be received on the selected first beam and the counter falling below a counter threshold. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 illustrates an example system for wireless communication supporting a medium access control (MAC) procedure for beam index indication according to an aspect of the present disclosure. [Figure 2] FIG. 1 illustrates an example of a wireless communication system supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 3] FIG. 1 illustrates an example process flow supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 4] FIG. 1 illustrates an example process flow supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 5] FIG. 1 illustrates an example process flow supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 6] FIG. 10 is a block diagram of a device supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 7] FIG. 10 is a block diagram of a device supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 8] FIG. 10 is a block diagram of a communications manager supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. [Figure 9]FIG. 1 is a diagram of a system including a device supporting a MAC procedure for beam index indication, according to an aspect of the present disclosure. [Figure 10] 10 is a flowchart illustrating a method for supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. [Figure 11] 10 is a flowchart illustrating a method for supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. [Figure 12] 10 is a flowchart illustrating a method for supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] To overcome the high path loss associated with high carrier frequencies, base stations and user equipment (UE) may use beamforming techniques for uplink and downlink communications. In some cases, upon deciding to establish a communication link with a base station, the UE may identify a preferred beam (e.g., a first beam from a set of beams) to be used to establish the communication link and / or any subsequent communications. For example, the preferred beam may provide the strongest signal quality from the base station from a set of possible beams that the base station can use to transmit downlink signals to the UE. The UE may then transmit an indication of this preferred beam to the base station over a medium access control (MAC) control element (CE). Accordingly, the base station may then transmit subsequent downlink messages to the UE using the preferred beam.

[0028] In some cases, the UE may decide to establish a communication link based on identifying a previously occurring beam failure on at least one cell (e.g., a secondary cell (SCell)) in which the base station is located, where the preferred beam is used for a beam failure recovery procedure. Additionally or alternatively, the UE may decide to establish an initial connection with the base station or re-establish communication on another cell (e.g., a primary cell (PCell), a primary SCell (PSCell), a secondary PCell (SPCell), etc.) in which the base station is located, where the preferred beam may be used for a random access channel (RACH) procedure. When performing the RACH procedure, the UE may send an indication of the preferred beam to the base station in one of the messages for the RACH procedure (e.g., the first message in a two-step RACH procedure, the connection request / third message in a four-step RACH procedure, etc.).

[0029] Furthermore, the UE may transmit an indication of a preferred beam to the base station based on the availability of uplink resources compared to a threshold. For example, if uplink resources are scheduled and available within N slots (for example, or N transmission time intervals (TTIs) of different lengths), where N is a positive integer, after the UE decides to establish a communication link and identifies a preferred beam, the UE may multiplex the indication with a MAC protocol data unit (PDU) transmitted on the uplink resources. Alternatively, if uplink resources are unavailable, the UE may request additional uplink resources (e.g., via a scheduling request, based on configured uplink channel resources, etc.) to transmit an indication of a preferred beam.

[0030] Aspects of the present disclosure are described first in the context of a wireless communication system. Further, aspects of the present disclosure are described through additional wireless communication system and process flow examples. Aspects of the present disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts relating to MAC procedures for beam index indication.

[0031] 1 illustrates an example of a wireless communication system 100 supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The wireless communication system 100 includes a base station 105, a UE 115, and a core network 130. In some examples, the wireless communication system 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some cases, the wireless communication system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission-critical) communications, low-latency communications, or communications with low-cost and low-complexity devices.

[0032] The base stations 105 can communicate wirelessly with the UEs 115 via one or more base station antennas. The base stations 105 described herein may include or be referred to by those skilled in the art as base transceiver stations, radio base stations, access points, radio transceivers, Node Bs, eNode Bs (eNBs), next generation Node Bs or gigaNode Bs (any of which may be referred to as gNBs), Home Node Bs, Home eNode Bs, or some other suitable terminology. The wireless communication system 100 may include different types of base stations 105 (e.g., macro cell base stations or small cell base stations). The UEs 115 described herein may be capable of communicating with various types of base stations 105 and network equipment, including macro eNBs, small cell eNBs, gNBs, relay base stations, etc.

[0033] Each base station 105 may be associated with a particular geographic coverage area 110 in which communication with various UEs 115 is supported. Each base station 105 may provide communication coverage for its respective geographic coverage area 110 via a communication link 125, where the communication link 125 between the base station 105 and the UE 115 may use one or more carriers. The communication link 125 shown in the wireless communication system 100 may include an uplink transmission from the UE 115 to the base station 105 or a downlink transmission from the base station 105 to the UE 115. A downlink transmission may also be referred to as a forward link transmission, and an uplink transmission may also be referred to as a reverse link transmission.

[0034] A geographic coverage area 110 for a base station 105 may be divided into sectors that make up a portion of the geographic coverage area 110, and each sector may be associated with a cell. For example, each base station 105 may provide communication coverage for a macro cell, a small cell, a hotspot, or other type of cell, or various combinations thereof. In some examples, the base station 105 may be mobile and thus provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, and overlapping geographic coverage areas 110 associated with different technologies may be supported by the same base station 105 or by different base stations 105. The wireless communication system 100 may include a heterogeneous LTE / LTE-A / LTE-A Pro network or an NR network, for example, in which different types of base stations 105 provide coverage for various geographic coverage areas 110.

[0035] The term “cell” refers to a logical communication entity used for communication with a base station 105 (e.g., via a carrier) and may be associated with an identifier (e.g., physical cell identifier (PCID), virtual cell identifier (VCID)) to distinguish adjacent cells operating over the same or different carriers. In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., machine-type communication (MTC), narrowband Internet of Things (NB-IoT), enhanced mobile broadband (eMBB), or others) that may provide access for different types of devices. In some cases, the term “cell” may refer to a portion of a geographic coverage area 110 (e.g., a sector) over which the logical entity operates.

[0036] The UEs 115 may be dispersed throughout the wireless communication system 100, and each UE 115 may be fixed or mobile. The UEs 115 may also be referred to as mobile devices, wireless devices, remote devices, handheld devices, or subscriber devices, or some other suitable terminology, and a “device” may also be referred to as a unit, station, terminal, or client. The UEs 115 may be personal electronic devices such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, the UEs 115 may also refer to a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, an MTC device, or the like, which may be implemented in various items such as an appliance, a vehicle, a meter, etc.

[0037] Some UEs 115, such as MTC or IoT devices, may be low-cost or low-complexity devices and may enable automated communication between machines (e.g., via machine-to-machine (M2M) communication). M2M communication or MTC may refer to data communication technologies that allow devices to communicate with each other or with the base station 105 without human intervention. In some examples, M2M communication or MTC may include communication from devices that incorporate sensors or meters to measure or capture information and relay that information to a central server or application program that can utilize the information or present the information to a human who interacts with the program or application. Some UEs 115 may be designed to collect information or enable automated behavior of machines. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, medical monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business billing.

[0038] Some UEs 115 may be configured to utilize operating modes that reduce power consumption, such as half-duplex communication (e.g., a mode that supports one-way communication by transmitting or receiving, but not transmitting and receiving simultaneously). In some examples, half-duplex communication may be implemented at a reduced peak rate. Other power conservation techniques for the UE 115 include entering a power-saving “deep sleep” mode or operating over a limited bandwidth (e.g., pursuant to narrowband communication) when not engaged in active communication. In some cases, the UE 115 may be designed to support critical functions (e.g., mission-critical functions), and the wireless communication system 100 may be configured to provide ultra-reliable communication for these functions.

[0039] In some cases, the UE 115 may also be able to communicate directly with other UEs 115 (e.g., using a peer-to-peer (P2P) protocol or a device-to-device (D2D) protocol). One or more of a group of UEs 115 utilizing D2D communication may be within the geographic coverage area 110 of the base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of the base station 105 or may in some cases be unable to receive transmissions from the base station 105. In some cases, a group of UEs 115 communicating via D2D communication may use a one-to-many (1:M) system in which each UE 115 transmits to every other UE 115 in the group. In some cases, the base station 105 facilitates scheduling of resources for D2D communication. In other cases, D2D communication occurs between UEs 115 without the involvement of the base station 105.

[0040] The base stations 105 may communicate with the core network 130 and with each other. For example, the base stations 105 may interface with the core network 130 through backhaul links 132 (e.g., via an S1, N2, N3, or other interface). The base stations 105 may communicate with each other via backhaul links 134 (e.g., via an X2, Xn, or other interface), either directly (e.g., directly between the base stations 105) or indirectly (e.g., via the core network 130).

[0041] The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC), which may include at least one mobility management entity (MME), at least one serving gateway (S-GW), and at least one packet data network (PDN) gateway (P-GW). The MME may manage non-access stratum (e.g., control plane) functions such as mobility, authentication, and bearer management for UEs 115 served by base stations 105 associated with the EPC. User IP packets may be forwarded through the S-GW, which may itself be connected to a P-GW. The P-GW may provide IP address allocation and other functions. The P-GW may be connected to a network operator's IP services. The operator IP services may include access to the Internet, an intranet, an IP multimedia subsystem (IMS), or packet-switched (PS) streaming services.

[0042] At least some of the network devices, such as the base stations 105, may include subcomponents, such as access network entities, which may be examples of access node controllers (ANCs). Each access network entity may communicate with the UE 115 through some other access network transmission entity, which may be referred to as a radio head, a smart radio head, or a transmit / receive point (TRP). In some configurations, various functions of each access network entity or base station 105 may be distributed across various network devices (e.g., radio heads and access network controllers) or integrated into a single network device (e.g., the base station 105).

[0043] The wireless communication system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). The 300 MHz to 3 GHz region is commonly known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range in length from approximately 1 decimeter to 1 meter. UHF waves may be blocked or redirected by buildings and environmental features. However, the waves may penetrate structures sufficiently for a macrocell to provide service to UEs 115 located indoors. Transmission of UHF waves may be associated with smaller antennas and shorter distances (e.g., less than 100 km) compared to transmissions using smaller frequencies and longer waves in the high frequency (HF) or very high frequency (VHF) portions of the spectrum below 300 MHz.

[0044] The wireless communication system 100 may also operate in the very high frequency (SHF) region, which uses the frequency band from 3 GHz to 30 GHz, also known as the centimeter band. The SHF region includes bands such as the 5 GHz Industrial, Scientific, and Medical (ISM) band that may be used opportunistically by devices that may be able to tolerate interference from other users.

[0045] The wireless communication system 100 may also operate in the extremely high frequency (EHF) region of the spectrum (e.g., 30 GHz to 300 GHz), also known as the millimeter band. In some examples, the wireless communication system 100 may support millimeter wave (mmW) communications between the UE 115 and the base station 105, and the EHF antennas of each device may be smaller and more closely spaced than the UHF antennas. In some cases, this may facilitate the use of antenna arrays within the UE 115. However, propagation of EHF transmissions may be subject to greater atmospheric attenuation and shorter distances than SHF or UHF transmissions. The techniques disclosed herein may be utilized across transmissions using one or more different frequency ranges, and the designated use of bands across these frequency ranges may vary by country or regulatory body.

[0046] In some cases, the wireless communication system 100 may use both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communication system 100 may utilize licensed-assisted access (LAA), LTE-unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band, such as the 5 GHz ISM band. When operating in an unlicensed radio frequency spectrum band, wireless devices, such as the base station 105 and the UE 115, may utilize a listen-before-talk (LBT) procedure to ensure that the frequency channel is clear before transmitting data. In some cases, operation in an unlicensed band may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA). Operation in the unlicensed spectrum may include downlink transmissions, uplink transmissions, peer-to-peer transmissions, or a combination thereof. Duplexing in the unlicensed spectrum may be based on frequency division duplexing (FDD), time division duplexing (TDD), or a combination of both.

[0047] In some examples, the base station 105 or the UE 115 may be equipped with multiple antennas, which may be used to utilize techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. For example, the wireless communication system 100 may use a transmission scheme between a transmitting device (e.g., the base station 105) and a receiving device (e.g., the UE 115), where the transmitting device is equipped with multiple antennas and the receiving device is equipped with one or more antennas. MIMO communications may utilize multipath signal propagation to increase spectral efficiency by transmitting or receiving multiple signals via different spatial layers, which may be referred to as spatial multiplexing. Multiple signals may be transmitted by a transmitting device, for example, via different antennas or different combinations of antennas. Similarly, multiple signals may be received by a receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits related to the same data stream (e.g., the same codeword) or different data streams. Different spatial layers may be associated with different antenna ports used for channel measurements and reporting. MIMO techniques include single-user MIMO (SU-MIMO), in which multiple spatial layers are transmitted to the same receiving device, and multi-user MIMO (MU-MIMO), in which multiple spatial layers are transmitted to multiple devices.

[0048] Beamforming, sometimes referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting or receiving device (e.g., a base station 105 or a UE 115) to shape or steer an antenna beam (e.g., a transmit beam or a receive beam) along a spatial path between the transmitting and receiving devices. Beamforming may be achieved by combining signals communicated through antenna elements of an antenna array such that signals propagating at a particular orientation relative to the antenna array experience constructive interference and other signals experience destructive interference. Adjusting the signals communicated through the antenna elements may include the transmitting or receiving device applying some amplitude and phase offset to the signals carried through each of the antenna elements associated with the device. The adjustment associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., relative to the antenna array of the transmitting or receiving device, or to some other orientation).

[0049] In one example, the base station 105 may use multiple antennas or antenna arrays to perform beamforming operations for directional communication with the UE 115. For example, some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted multiple times by the base station 105 in different directions, which may include signals being transmitted according to different beamforming weight sets associated with the different directions of transmission. The transmissions in different beam directions may be used (e.g., by the base station 105 or a receiving device such as the UE 115) to identify beam directions for subsequent transmissions and / or receptions by the base station 105.

[0050] Some signals, such as data signals associated with a particular receiving device, may be transmitted by the base station 105 in a single beam direction (e.g., a direction associated with a receiving device such as the UE 115). In some examples, the beam direction associated with a transmission along the single beam direction may be determined based at least in part on signals transmitted in different beam directions. For example, the UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions, and the UE 115 may report to the base station 105 an indication of the signal it received with the best signal quality or an otherwise acceptable signal quality. Although these techniques are described with reference to signals transmitted by the base station 105 in one or more directions, the UE 115 may utilize similar techniques for transmitting a signal multiple times in different directions (e.g., to identify a beam direction for subsequent transmission or reception by the UE 115) or for transmitting a signal in a single direction (e.g., to transmit data to a receiving device).

[0051] A receiving device (e.g., a UE 115, which may be an example of a mmW receiving device) can attempt multiple receive beams when receiving various signals from the base station 105, such as a synchronization signal, a reference signal, a beam selection signal, or other control signals. For example, the receiving device may attempt multiple receive directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different receive beamforming weight sets applied to signals received at a set of antenna elements of an antenna array, or by processing received signals according to different receive beamforming weight sets applied to signals received at a set of antenna elements of an antenna array, any of which may be referred to as “listening” with different receive beams or receive directions. In some examples, the receiving device may use a single receive beam to receive along a single beam direction (e.g., when receiving a data signal). The single receive beam may be aligned with a beam direction determined at least in part based on listening with different receive beam directions (e.g., a beam direction determined to have the greatest signal strength, the greatest signal-to-noise ratio, or otherwise acceptable signal quality based at least in part on listening with multiple beam directions).

[0052] In some cases, antennas of a base station 105 or a UE 115 may be arranged in one or more antenna arrays that may support MIMO operation or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located in an antenna assembly such as an antenna tower. In some cases, antennas or antenna arrays associated with a base station 105 may be located in various geographic locations. A base station 105 may have an antenna array with several rows and columns of antenna ports that the base station 105 can use to support beamforming of communications with the UE 115. Similarly, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations.

[0053] In some cases, the wireless communication system 100 may be a packet-based network operating according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. The Radio Link Control (RLC) layer may perform packet segmentation and reassembly for communications on logical channels. The MAC layer may perform priority handling and multiplexing of logical channels onto transport channels. The MAC layer may also use hybrid automatic repeat request (HARQ) to perform retransmissions at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may establish, configure, and maintain an RRC connection between the UE 115 and the base station 105 or core network 130, which supports radio bearers for user plane data. In the physical layer, transport channels may be mapped to physical channels.

[0054] In some cases, the UE 115 and the base station 105 may support retransmission of data to increase the likelihood of successful reception of the data. HARQ feedback is one technique that increases the likelihood that data will be correctly received over the communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC)), forward error correction (FEC), and retransmission (e.g., automatic repeat request (ARQ)). HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., signal-to-noise conditions). In some cases, a wireless device may support same-slot HARQ feedback, in which the device may provide HARQ feedback in a particular slot for data received in a previous symbol in that slot. In other cases, the device may provide HARQ feedback in a subsequent slot or according to some other time interval.

[0055] The time interval in LTE or NR is, for example, T s The time intervals of the communication resources may be organized according to radio frames, each having a duration of 10 milliseconds (ms), and the frame period is T f =307,200T sA radio frame may be identified by a system frame number (SFN) ranging from 0 to 1023. Each frame may include 10 subframes numbered 0 to 9, and each subframe may have a duration of 1 ms. A subframe may be further divided into two slots, each having a duration of 0.5 ms, and each slot may include 6 or 7 modulation symbol periods (e.g., depending on the length of a cyclic prefix prepended to each symbol period). Excluding the cyclic prefix, each symbol period may include 2048 sampling periods. In some cases, a subframe may be the smallest scheduling unit of the wireless communication system 100 and may be referred to as a transmission time interval (TTI). In other cases, the smallest scheduling unit of the wireless communication system 100 may be shorter than a subframe or may be dynamically selected (e.g., in bursts of shortened TTI (sTTI) or in selected component carriers using sTTI).

[0056] In some wireless communication systems, a slot may be further divided into multiple minislots, each containing one or more symbols. In some instances, a symbol or minislot of a minislot may be the smallest unit of scheduling. Each symbol may vary in time length depending, for example, on the subcarrier spacing or frequency band of operation. Furthermore, some wireless communication systems may implement slot aggregation, in which multiple slots or minislots are aggregated together and used for communication between the UE 115 and the base station 105.

[0057] The term “carrier” refers to a set of radio frequency spectrum resources having a defined physical layer structure for supporting communications over communication link 125. For example, a carrier of communication link 125 may include a portion of a radio frequency spectrum band operating according to physical layer channels for a given radio access technology. Each physical layer channel may carry user data, control information, or other signaling. A carrier may be associated with a predefined frequency channel (e.g., an Evolved Universal Mobile Telecommunications System Terrestrial Radio Access (E-UTRA) Absolute Radio Frequency Channel Number (EARFCN)) and may be arranged according to a channel raster for discovery by UE 115. A carrier may be downlink or uplink (e.g., in FDD mode) or may be configured to carry downlink and uplink communications (e.g., in TDD mode). In some examples, a signal waveform transmitted over a carrier may be composed of multiple subcarriers (e.g., using a multi-carrier modulation (MCM) technique such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM)).

[0058] The organizational structure of a carrier may vary for different radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR). For example, communications over a carrier may be organized according to TTIs or slots, each of which may include user data as well as control information or signaling to support decoding of the user data. A carrier may also include dedicated acquisition signaling (e.g., synchronization signals or system information, etc.) and control signaling that coordinates operation on the carrier. In some examples (e.g., in a carrier aggregation configuration), a carrier may also have acquisition signaling or control signaling that coordinates operation on other carriers.

[0059] Physical channels may be multiplexed on carriers according to various techniques. Physical control channels and physical data channels may be multiplexed on downlink carriers using, for example, time division multiplexing (TDM), frequency division multiplexing (FDM), or hybrid TDM-FDM techniques. In some examples, control information transmitted in physical control channels may be distributed among different control regions in a cascaded manner (e.g., between a common control region or common search space and one or more UE-specific control regions or UE-specific search spaces).

[0060] A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples, the carrier bandwidth may be referred to as the carrier or the “system bandwidth” of the wireless communication system 100. For example, the carrier bandwidth may be one of several predetermined bandwidths (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz) for a particular radio access technology carrier. In some examples, each served UE 115 may be configured to operate across some portion or all of the carrier bandwidth. In other examples, some UEs 115 may be configured for operation using narrowband protocol types associated with a predefined portion or range (e.g., a set of subcarriers or RBs) within the carrier (e.g., “in-band” deployment of narrowband protocol types).

[0061] In a system utilizing MCM techniques, a resource element may consist of one symbol period (e.g., the duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme). Thus, the more resource elements the UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. In a MIMO system, wireless communication resources may refer to a combination of radio frequency spectrum resources, time resources, and spatial resources (e.g., spatial layers), where the use of multiple spatial layers may further increase the data rate for communications with the UE 115.

[0062] A device (e.g., a base station 105 or a UE 115) of the wireless communication system 100 may have a hardware configuration that supports communication over a particular carrier bandwidth or may be configurable to support communication over one of a set of carrier bandwidths. In some examples, the wireless communication system 100 may include a base station 105 and / or a UE 115 that supports simultaneous communication over carriers associated with two or more different carrier bandwidths.

[0063] The wireless communication system 100 may support communication with the UE 115 over multiple cells or carriers, a capability sometimes referred to as carrier aggregation or multi-carrier operation. The UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both FDD and TDD component carriers.

[0064] In some cases, the wireless communication system 100 may use an enhanced component carrier (eCC). An eCC may be characterized by one or more features including a wider carrier or frequency channel bandwidth, a shorter symbol duration, a shorter TTI duration, or a modified control channel configuration. In some cases, an eCC may be associated with a carrier aggregation configuration or a dual connectivity configuration (e.g., when multiple serving cells have suboptimal or non-ideal backhaul links). An eCC may also be configured for use in unlicensed or shared spectrum (e.g., when two or more operators are authorized to use the spectrum). An eCC characterized by a wide carrier bandwidth may include one or more segments that can be used by UEs 115 that are not capable of monitoring the entire carrier bandwidth or are otherwise configured to use limited carrier bandwidth (e.g., to conserve power).

[0065] In some cases, the eCC may use a different symbol duration than the other component carriers, which may include using a reduced symbol duration compared to the symbol duration of the other component carriers. The shorter symbol duration may be associated with increased spacing between adjacent subcarriers. A device such as a UE 115 or base station 105 using an eCC may transmit a wideband signal (e.g., according to a frequency channel or carrier bandwidth of 20, 40, 60, 80 MHz, etc.) with a reduced symbol duration (e.g., 16.67 microseconds). A TTI in an eCC may consist of one or more symbol periods. In some cases, the TTI duration (i.e., the number of symbol periods within a TTI) may be variable.

[0066] The wireless communication system 100 may be, among other things, an NR system that may use any combination of licensed spectrum, shared spectrum, and unlicensed spectrum bands. Flexibility in eCC symbol duration and subcarrier spacing may enable the use of eCCs across multiple spectrums. In some examples, NR shared spectrum may increase spectrum utilization and spectral efficiency, particularly through dynamic vertical (e.g., across the frequency domain) and horizontal (e.g., across the time domain) sharing of resources.

[0067] A UE 115 attempting to access a wireless network may perform initial cell search by detecting a primary synchronization signal (PSS) from a base station 105. The PSS may enable slot timing synchronization and may indicate a physical layer identity value. The UE 115 may then receive a secondary synchronization signal (SSS). The SSS may enable radio frame synchronization and may provide a cell identity value, which may be combined with the physical layer identity value to identify a cell. The SSS may also enable detection of a duplex mode and a cyclic prefix length. Some systems, such as TDD systems, may transmit an SSS but not a PSS. Both the PSS and SSS may reside in the central 62 and 72 subcarriers of a carrier, respectively. In some cases, the base station 105 may transmit synchronization signals (e.g., PSS, SSS, etc.) using multiple beams in a beam-sweeping manner throughout the cell coverage area. In some cases, PSS, SSS, and / or broadcast information (e.g., physical broadcast channel (PBCH)) may be transmitted within different synchronization signal (SS) blocks on each directional beam, where one or more SS blocks may be included within an SS burst.

[0068] After receiving the PSS and SSS, the UE 115 may receive a Master Information Block (MIB), which may be transmitted on the PBCH. The MIB may include system bandwidth information, SFN, and Physical HARQ Indicator Channel (PHICH) configuration. After decoding the MIB, the UE 115 may receive one or more System Information Blocks (SIBs). For example, SIB1 may include cell access parameters and scheduling information for other SIBs. Decoding SIB1 may enable the UE 115 to receive SIB2. SIB2 may include RRC configuration information for RACH procedures, paging, PUCCH, PUSCH, power control, SRS, and cell barring.

[0069] After completing initial cell synchronization, the UE 115 may decode the MIB, SIB1, and SIB2 prior to accessing the network. The MIB may be transmitted on the PBCH and may use the first four OFDMA symbols of the second slot of the first subframe of each radio frame. In the frequency domain, the MIB may use the middle six RBs (72 subcarriers). The MIB carries several important pieces of information for UE initial access, including the downlink channel bandwidth for the RBs, the PHICH configuration (duration and resource allocation), and the SFN. A new MIB is broadcast every four radio frames (SFN mod 4=0) and may be rebroadcast every frame (10 ms). Each repetition is scrambled with a different scrambling code.

[0070] After reading the MIB (either the new version or a copy), the UE 115 may try different phases of the scrambling code until the CRC check is successful. The phase of the scrambling code (0, 1, 2, or 3) may allow the UE 115 to identify which of the four repetitions has been received. In this way, the UE 115 may determine the current SFN by reading the decoded SFN in the transmission and adding the scrambling code phase. After receiving the MIB, the UE may receive one or more SIBs. Different SIBs may be defined according to the type of system information being carried. A new SIB1 may be transmitted in the fifth subframe every eight frames (SFN mod 8=0) and may be rebroadcast every other frame (20 ms). SIB1 contains access information, including cell identification information, which may indicate whether the UE is allowed to camp on the cell. SIB1 also contains cell selection information (or cell selection parameters). In addition, SIB1 contains scheduling information for other SIBs. SIB2 may be dynamically scheduled according to the information in SIB1 and includes access information and parameters related to common and shared channels. The periodicity of SIB2 may be set to 8, 16, 32, 64, 128, 256, or 512 radio frames.

[0071] After decoding SIB2, the UE 115 may transmit a RACH preamble (e.g., message 1 (Msg1) in a four-step RACH procedure) to the base station 105. For example, the RACH preamble may be randomly selected from a set of 64 predetermined sequences. This random selection may enable the base station 105 to distinguish between multiple UEs 115 attempting to simultaneously access the system. The base station 105 may respond with a random access response (e.g., second message (Msg2)) providing an uplink resource grant, a timing advance, and a temporary cell radio network temporary identifier information (C-RNTI). The UE 115 may then transmit an RRC connection request (e.g., third message (Msg3)) along with a temporary mobile subscriber identity (TMSI) (if the UE 115 was previously connected to the same wireless network) or a random identifier. The RRC connection request may also indicate the reason the UE 115 is connecting to the network (e.g., emergency, signaling, data exchange, etc.). The base station 105 may respond to the connection request with a contention resolution message (e.g., a fourth message (Msg4)) directed to the UE 115, which may provide a new C-RNTI. If the UE 115 receives the contention resolution message with the correct identification information, the UE 115 may proceed with RRC setup. If the UE 115 does not receive the contention resolution message (e.g., in the case of a conflict with another UE 115), the UE 115 may repeat the RACH procedure by transmitting a new RACH preamble. Such a message exchange between the UE 115 and the base station 105 for random access may be referred to as a four-step RACH procedure.

[0072] In another example, a two-step RACH procedure may be implemented for random access. For example, a wireless device operating in a licensed or unlicensed spectrum in the wireless communication system 100 may initiate the two-step RACH procedure to reduce delay in establishing communication with the base station 105 (e.g., compared to a four-step RACH procedure). In some cases, the two-step RACH procedure may operate regardless of whether the wireless device (e.g., the UE 115) has a valid timing advance (TA). For example, the UE 115 may use a valid TA to coordinate the timing of its transmission with the base station 105 (e.g., to eliminate propagation delay) and may receive the valid TA as part of the two-step RACH procedure. Furthermore, the two-step RACH procedure may be applicable to any cell size, may work whether the RACH procedure is contention-based or contention-free, and may combine multiple RACH messages from the four-step RACH procedure. For example, a two-step RACH procedure may include a first message (e.g., Message A (MsgA)) that combines Msg1 and Msg3 of a four-step RACH procedure, and a second message (e.g., Message B (MsgB)) that combines Msg2 and Msg4 of the four-step RACH procedure.

[0073] The two-step RACH procedure may be applicable to any cell size supported in a wireless communication system, may be able to operate whether the UE 115 has a valid timing advance (TA), and may apply to any RRC state of the UE 115 (e.g., idle state (RRC_IDLE), inactive state (RRC_INACTIVE), connected state (RRC_CONNECTED), etc.). In some cases, the two-step RACH procedure may result in reduced signaling overhead and latency, enhanced RACH capacity, power savings for the UE 115, and synergies with other applications (e.g., positioning, mobility enhancements, etc.).

[0074] In some cases, the UE 115 may be provided with a first set (q) of periodic channel state information (CSI) reference signal (CSI-RS) resource configuration indices for the base station 105 (e.g., the serving cell) by a first upper layer parameter (e.g., failureDetectionResources) and a second set (q) of periodic CSI-RS resource configuration indices and / or SS / PBCH block indices by a second upper layer parameter (e.g., candidateBeamRSList) for radio link quality measurements on the base station 105. Additionally or alternatively, if the UE 115 is not provided with the first upper layer parameter, the UE 115 may determine set q to include SS / PBCH block indices and periodic CSI-RS resource configuration indices that have the same values ​​as reference signal indices in a reference signal set indicated by a transmission configuration indicator (TCI) state for a respective control resource set (CORESET) that the UE 115 uses to monitor a downlink channel (e.g., a physical downlink control channel (PDCCH)). The UE 115 may expect the set q0 to include up to two reference signal indices, and if there are two RS indices, the set q0 includes reference signal indices with a quasi-co-location (QCL) Type D configuration for the corresponding TCI state. Additionally, the UE 115 may expect a single-port reference signal in the set q0.

[0075] Based on set q0, UE 115 can monitor a set of reference signals in set q0 for beam failure detection as part of a beam failure recovery procedure to improve the robustness of communications with base station 105. For the beam failure recovery procedure, UE 115 can detect beam failure, identify new candidate beams, send a beam failure recovery request to base station 105, and monitor for a response to the beam failure recovery response from base station 105. Thus, as part of detecting beam failure, UE 115 can monitor up to a maximum set of reference signals belonging to set q0. In some cases, the maximum number of sets of reference signals may be two (2), although a larger number of sets of reference signals may be used. As described above, UE 115 can determine set q0 from the reference signals used to monitor the active CORESET (e.g., the reference signal set indicated by the TCI state for each CORESET that UE 115 uses to monitor the PDCCH). In some cases, the UE 115 may perform a RACH procedure (e.g., contention-based random access (CBRA), 4-step RACH, 2-step RACH, etc.) as part of a beam failure recovery procedure to re-establish a connection with the base station 105.

[0076] In some wireless communications, the base station 105 (e.g., a network) may configure a MAC CE for the UE 115 to report a new preferred beam after a beam failure is triggered on an SCell. For example, this new MAC CE may include the index of the SCell for which beam failure was triggered and the index of the new preferred beam for the SCell. In some cases, this new MAC CE may be referred to as a beam index indication MAC CE. However, conventionally, the UE may not know which uplink resources to use to send the beam index indication and / or may not fully utilize the beam index indication for a subset of procedures.

[0077] The wireless communication system 100 may support efficient techniques for transmitting a beam index indication of a new preferred beam on uplink resources based on the availability of uplink resources and for transmitting the beam index indication for different communication establishment scenarios. For example, after the UE 115 decides to establish a communication link and identifies a new preferred beam, if uplink resources are scheduled and available within N slots, the UE 115 may multiplex the beam index indication transmitted on the uplink resources with a MAC PDU. Alternatively, if uplink resources are unavailable, the UE 115 may request additional uplink resources (e.g., via a scheduling request, based on configured uplink channel resources, etc.) for transmitting the beam index indication. Furthermore, the UE 115 may transmit a beam index indication for the beam failure recovery procedure described above as well as for a RACH procedure for establishing communication with at least one cell of the base station 105. Thus, the UE 115 may transmit the beam index indication in a message of the RACH procedure (e.g., a first message in a two-step RACH procedure, a connection request / third message in a four-step RACH procedure).

[0078] FIG. 2 illustrates an example of a wireless communication system 200 supporting a MAC procedure for beam index indication according to aspects of the present disclosure. In some examples, the wireless communication system 200 may implement aspects of the wireless communication system 100. The wireless communication system 200 may include a base station 105-a and a UE 115-a, which may be examples of the corresponding base station 105 and UE 115, respectively, as described above with reference to FIG. 1. As described herein, the base station 105-a and the UE 115-a may use beamforming techniques to communicate with each other. For example, the base station 105-a may use one or more beams 205 to transmit downlink signals to and / or receive uplink signals from the UE 115-a. Furthermore, the UE 115-a may use one or more beams 210 to transmit uplink signals to and / or receive downlink signals from the base station 105-a. In some cases, the UE 115-a may communicate with the base station 105-a via one or more cells of the base station 105-a (e.g., a PCell, a SCell, a PSCell, an SPCell, etc.).

[0079] In some cases, the UE 115-a may identify a beam failure triggered on a cell (e.g., an SCell) of the base station 105-a. The UE 115-a may then measure the link quality of one or more candidate beams configured for the cell in which the beam failure was detected. For example, the UE 115-a may measure the link quality of each of the beams 205-a, 205-b, and 205-c transmitted by the base station 105-a (e.g., by measuring a reference signal on each beam 205). In some cases, the UE 115-a may perform link quality measurements when measurements are not readily available (e.g., the UE 115-a has not measured link quality recently or has never measured link quality).

[0080] Thus, the beam indication 215 (e.g., beam index indication) may be triggered when measurements become available. That is, the UE 115-a may select a preferred beam 205 transmitted by the base station 105-a for a subsequent downlink transmission (e.g., beam failure recovery procedure) based on the link quality measurements. For example, the UE 115-a may select beam 205-b (e.g., a preferred beam) for the base station 105-a to perform a beam failure recovery procedure based on beam 205-b having the best signal quality (e.g., strongest received signal, least amount of interference, etc.) compared to beams 205-a and 205-c. After the beam indication 215 (e.g., indicating beam 205-b) is triggered, a MAC CE (e.g., beam index indication MAC CE) for carrying the beam indication 215 may be generated when uplink resources become available to send a MAC CE carrying the beam indication 215 to the base station 105-a (e.g., a network).

[0081] Thus, if there is no upcoming uplink resource scheduled within N slots (for example, or another length TTI) in the future, the UE 115-a may multiplex the MAC CE carrying the beam instruction 215 in a MAC PDU to be transmitted over this uplink resource. In some cases, N may be configured by the base station 105-a (e.g., by RRC signaling) or defined (e.g., predefined for the base station 105-a and the UE 115-a). Furthermore, the uplink resource may be either a dynamic grant or a configured grant. Subsequently, the UE 115-a may then transmit the beam instruction 215 to the base station 105-a on the uplink resource (e.g., based on multiplexing the MAC CE carrying the beam instruction 215 in the MAC PDU).

[0082] Additionally or alternatively, if there are no readily available uplink resources or if the uplink resources occur too late to signal a MAC CE carrying the beam instruction 215 (e.g., low latency may be needed to recover the failed beam and perform a beam failure recovery procedure), the UE 115-a may request uplink resources via an uplink channel (e.g., a physical uplink control channel (PUCCH)). For example, the base station 105-a may configure uplink channel resources dedicated to the beam failure recovery procedure. Thus, when the beam instruction 215 is triggered, the UE 115-a can use at least one available opportunity of this dedicated uplink channel resource to instruct (e.g., request) the base station 105-a to signal new uplink resources on the physical layer (e.g., to use the new uplink resources to transmit a MAC CE carrying the beam instruction 215). This signal (eg, of a new uplink resource) may be a known symbol sequence (as an example, or a TTI of a different length) configured for the UE 115-a.

[0083] Additionally or alternatively, rather than using a dedicated uplink channel, the UE 115-a may send a scheduling request sequence (e.g., initiate a scheduling request) via uplink channel resources (e.g., PUCCH resources) configured for scheduling requests to request uplink resources for transmitting an indication of the selected first beam to the base station 105-a. In some cases, the scheduling request may be used by the UE 115-a to signal new data arrival, and the base station 105-a may then grant uplink resources for the new data. Furthermore, the base station 105-a may configure different sets of uplink channel resources for different data logical channels based on the configured priorities of the data logical channels. Thus, to enable rapid recovery of a failed beam (e.g., faster beam failure recovery procedure), the scheduling request for the MAC CE carrying the beam indication 215 may be sent via uplink channel resources assigned to the data logical channel with the highest priority configured for the UE 115-a. In some cases, the UE 115-a may request uplink resources for transmitting the beam indication 215 based on having performed a RACH procedure. For example, after experiencing a beam failure on a cell (e.g., a serving cell, an SCell, a PCell, an SPCell, a PSCell, etc.), the UE 115-a may perform a RACH procedure to reconnect to the cell. As part of the RACH procedure or once the RACH procedure is completed, the UE 115-a may request uplink resources from the cell, where the uplink resources may be used to transmit the beam indication 215.

[0084] When transmitting a scheduling request to request uplink resources for transmitting beam indication 215 (e.g., of the selected first beam), UE 115-a may transmit a one-bit indication to base station 105-a (e.g., a network) to indicate that uplink resources are requested. Furthermore, base station 105-a may configure multiple scheduling request configurations for UE 115-a to transmit the scheduling request, thereby allowing UE 115-a to transmit the scheduling request via uplink resources (e.g., PUCCH resources) in different scheduling request configurations. For example, UE 115-a may use one of the different scheduling request configurations based on data of a certain priority that triggered the scheduling request, where a mapping of data of different priorities to different scheduling request configurations (e.g., an indication of which scheduling request configuration can be used for data of each priority) is configured by base station 105-a. However, the UE 115-a may not be able to indicate for which serving cell (e.g., one or more SCells) the UE 115-a seeks uplink resources for transmitting the beam indication 215 (e.g., which serving cell has a beam that can support the beam indication 215). For example, because the base station 105-a does not know that this scheduling request is for a beam failure recovery procedure (e.g., if dedicated PUCCH resources are not allocated for this purpose) or on which serving cell the beam failure occurred, the base station 105-a may send a downlink message (e.g., downlink control information (DCI)) to grant the requested uplink resources on the failed downlink (e.g., PDCCH) beam. Thus, the UE 115-a may not be able to receive a grant indicating uplink resources for sending the beam failure indication MAC CE (e.g., the MAC CE carrying the beam indication 215).

[0085] In some cases, the base station 105-a (e.g., a network) may configure a dedicated PUCCH scheduling request configuration for beam failure recovery to enable the UE 115-a to receive an indication (e.g., a grant) of an uplink resource to be used for transmitting a MAC CE carrying the beam indication 215. Thus, when the UE 115-a requests an uplink resource for transmitting a MAC CE (e.g., a beam failure recovery MAC CE) carrying the beam indication 215, the UE 115-a may transmit the scheduling request via one or more PUCCH resources (e.g., uplink resources) in accordance with this dedicated PUCCH scheduling request configuration. For example, the dedicated PUCCH scheduling request configuration may include an indication of which PUCCH resource (e.g., time and / or frequency resource in the PUCCH) the scheduling request should be transmitted on.

[0086] Subsequently, when the base station 105-a receives this scheduling request (e.g., transmitted in accordance with a dedicated PUCCH scheduling request configuration), the base station 105-a can identify that the scheduling request is triggered by a beam failure recovery procedure. The base station 105-a can then send a downlink message (e.g., DCI) to grant the requested uplink resources for transmitting a MAC CE carrying the beam indication 215 via a downlink channel (e.g., PDCCH) in a special cell (SpCell) configured for the UE 115-a, where the requested uplink resources are also located in the SpCell. In some cases, the SpCell may include a PCell, a PSCell, or an additional cell configured for primary communication for the UE 115-a. By sending an indication of uplink resources (e.g., a grant for uplink resources) on the SpCell, UE 115-a is more likely to receive the indication of uplink resources based on the unlikelihood that downlink (e.g., PDCCH) beams in both the SpCell and the SCell fail at the same time for UE 115-a. However, if the downlink beam in the SpCell fails, UE 115-a may trigger a RACH-based recovery procedure to re-establish communication with the SpCell, send a MAC CE to carry the beam indication 215 during the corresponding RACH procedure, and then send a request for uplink resources for sending the MAC CE once the RACH procedure is completed.

[0087] Additionally or alternatively, the dedicated scheduling request configuration may not be used for the beam failure recovery procedure. Instead, the UE 115-a uses a scheduling request configuration configured for a conventional scheduling request (e.g., triggered by new data as described above), but the scheduling request configuration may be used for the purpose of the beam failure recovery procedure. For example, each uplink control resource (e.g., a PUCCH resource used to transmit the scheduling request) in the scheduling request configuration may be associated with one or more different serving cells, where the mapping between the serving cell and the uplink control resource is either one-to-one or many-to-one.

[0088] For example, in the case of one-to-one mapping, the uplink control resource in the first transmission opportunity (e.g., the first slot, which may be slot 0) may be associated with the first serving cell (e.g., serving cell 0), the uplink control resource in the second slot (e.g., slot 1) may be associated with the second serving cell (e.g., serving cell 1), and so on. In some cases, the uplink control resource in a slot may be associated with multiple serving cells (e.g., the second slot may be associated with the second serving cell, the third serving cell, and the fourth serving cell). Additionally or alternatively, in the case of many-to-one mapping, the uplink control resource in the first slot (e.g., slot 0) may be associated with any serving cell except the first serving cell, and the uplink control resource in the second slot may be associated with any serving cell except the second serving cell, and so on. That is, in the case of many-to-one mapping, the UE 115-a can indicate a set of serving cells (e.g., excluding the serving cell corresponding to the slot number) on which the requested uplink resources can be allocated for transmitting a MAC CE carrying the beam indication 215.

[0089] Thus, when beam failure recovery is triggered on an SCell (e.g., a secondary serving cell), the MAC layer may trigger a scheduling request and send the scheduling request to the physical layer. Along with this scheduling request, the MAC layer may indicate which SCell to avoid in order to receive an indication of the requested uplink resources (e.g., an uplink grant for the uplink resources) and subsequently transmit a MAC CE carrying beam instructions 215. In some cases, downlink beams (e.g., PDCCH beams) on multiple SCells may have the same QCL relationship (e.g., signals from the QCL SCells experience similar channel conditions and traverse similar channels such that UE 115-a may assume the signals come from the same location), and based on the QCL relationship, UE 115-a may assume that the SCells may fail together when a beam failure occurs. When the physical layer receives the scheduling request, the physical layer may send the scheduling request over any valid uplink control resource except for the uplink control resource associated with the SCell to be avoided (e.g., as indicated by the mapping scheme described above).

[0090] In some cases, both the SpCell (e.g., a PCell, a PSCell, etc.) and the SCell may fail (e.g., experience beam failure), which may affect how UE 115-a performs beam failure recovery procedures and transmits beam indication 215 (e.g., for when an SCell fails, as described above). For example, if an SpCell beam failure has already been triggered and a corresponding RACH-based recovery (e.g., to re-establish communication with the SpCell) has been initiated when beam failure recovery for the SCell is triggered, UE 115-a may wait for the SpCell beam failure recovery (e.g., via RACH-based recovery) to complete before sending a MAC CE carrying beam indication 215 for the SCell beam failure recovery. Thus, UE 115-a may transmit a MAC CE carrying beam indication 215 based on an uplink grant provided in the second RACH message (e.g., msg2) of the RACH for SpCell beam failure recovery.

[0091] Additionally or alternatively, if a beam failure on an SCell occurs before a beam failure on an SpCell, UE 115-a may take different actions. For example, if UE 115-a has already triggered a scheduling request for SCell beam failure recovery (e.g., to request uplink resources for transmitting a MAC CE carrying beam instruction 215) when SpCell beam failure recovery is triggered, UE 115-a may first perform RACH-based beam failure recovery for the SpCell, and then send a MAC CE carrying beam instruction 215 for SCell beam failure recovery in an uplink grant provided in a second message (e.g., msg2) of the RACH for SpCell beam failure recovery. Additionally or alternatively, if a MAC CE carrying beam instructions 215 for SCell beam failure recovery has already been sent when SpCell beam failure recovery is triggered but the base station 105-a has not reconfigured the downlink beam for the SCell, the UE 115-a may first perform SpCell beam failure recovery (e.g., RACH-based recovery) before completing beam failure recovery for the SCell.

[0092] In some cases, the UE 115-a and / or the base station 105-a may configure a timer and counter for SCell beam failure recovery by transmitting a MAC CE carrying a beam indication 215 to re-establish a connection with the SCell via an indicated beam (e.g., a selected first beam). Thus, if the base station 105-a has not reconfigured the downlink beam for the failed SCell before the configured timer expires, the UE 115-a may send the MAC CE carrying the beam indication 215 again (e.g., on uplink resources requested by the UE 115-a and / or indicated by the base station 105-a, as described above). With each transmission / retransmission of the MAC CE carrying the beam indication 215, the UE 115-a may increment a counter by one and may continue attempting to send the MAC CE until a counter limit (e.g., a counter threshold) is reached. If the counter limit is reached, the UE 115-a may trigger a radio link failure. In some cases, as a result of a radio link failure, the UE 115-a may perform a RACH to identify a new SCell for establishing a secondary communication link.

[0093] When using a MAC CE carrying beam indication 215 for beam failure recovery procedures, the UE 115-a may multiplex the MAC CE carrying beam indication 215 into a MAC PDU as described above (e.g., when uplink resources are available). Furthermore, the MAC CE carrying beam indication 215 can be given high priority during a logical channel prioritization (LCP) procedure when the MAC CE carrying beam indication 215 is multiplexed into a MAC PDU with other data (e.g., to ensure rapid recovery of a failed beam). The priority for the MAC CE carrying beam indication 215 may be lower than common control channel (CCCH) messages, but higher than the rest of the MAC CE and data of any additional logical channels.

[0094] In some implementations, the MAC CE carrying the beam indication 215 may be used for additional purposes. For example, the UE 115-a may indicate a preferred beam 205 (e.g., beam 205-b) during the RACH procedure. In some cases, the UE 115-a may decide to perform the RACH procedure to establish an initial connection with the base station 105-a or to re-establish communication with the base station 105-a's cell (e.g., PCell, PSCell, SPCell). Each physical RACH (PRACH) opportunity may be associated with a reference signal (e.g., a candidate beam for the UE 115-a). By selecting which PRACH opportunity to send the PRACH preamble, the UE 115-a can (e.g., implicitly) indicate to the base station 105-a which beam is preferred for the base station 105-a to use to perform the remainder of the RACH procedure or to transmit subsequent downlink signals. However, the base station 105-a can configure up to 128 beams. Therefore, if many candidate beams 205 are configured, the UE 115-a may wait a long time to reach the PRACH opportunities of the 128 beams associated with the preferred beam (e.g., if the preferred beam is last in time or possibly later in time as the base station 105-a cycles through such beams for PRACH opportunities).

[0095] To reduce the amount of time UE 115-a waits, UE 115-a may select an appropriate beam for sending the PRACH preamble, where the appropriate beam may be available sooner than the preferred beam but may have lower signal quality than the preferred beam. UE 115-a may then indicate the preferred beam following transmission of the PRACH preamble in a MAC CE carrying beam indication 215. In some cases, this MAC CE carrying beam indication 215 may be included in either the payload of MsgA in a two-step RACH (e.g., a physical uplink shared channel (PUSCH) payload) or msg3 in a four-step RACH procedure.

[0096] Additionally or alternatively, to reduce access latency, the UE 115-a may initiate the RACH procedure before measuring the link quality of all reference signals. Thus, once the UE 115-a finds a beam with adequate link quality for performing the RACH procedure, the UE 115-a can begin the RACH procedure. However, the UE 115-a may continue to measure the link quality of the remaining beams during the RACH procedure. In some cases, if a better candidate beam is found during this continuous measurement process, the UE 115-a may indicate the latest preferred beam in the MAC CE carrying the beam indication 215. Similar to the techniques described above, the MAC CE carrying the beam indication 215 may be included in Msg3 in a four-step RACH procedure, in the payload of a retransmitted MsgA in a two-step RACH procedure, or the like. When both using an appropriate beam and / or continuing link quality measurements, the multiplexing rules described above may be applied to increase the likelihood that the MAC CE carrying the beam indication 215-a will be included in msgA or msg3.

[0097] 3 illustrates an example process flow 300 supporting a MAC procedure for beam index indication according to an aspect of the disclosure. In some examples, the process flow 300 may implement aspects of the wireless communication systems 100 and / or 200. The process flow 300 may include a base station 105-b and a UE 115-b, which may be examples of corresponding base stations 105 and UEs 115, respectively, as described above with reference to FIGS. 1-2. As described herein, the base station 105-b and the UE 115-b may use beamforming techniques to communicate with each other.

[0098] In the following description of process flow 300, operations between the UE 115-b and the base station 105-b may be transmitted in a different order than shown, or operations performed by the base station 105-b and the UE 115-b may be performed in a different order or at different times. Some operations may also be omitted from process flow 300, or other operations may be added to process flow 300. While the base station 105-b and the UE 115-b are shown performing some of the operations of process flow 300, it should be understood that any wireless device may perform the operations shown.

[0099] At 305, the UE 115-b may communicate with the base station 105-b via a communication link. The communication link may include one or more beams of the UE 115-b and one or more beams of the base station 105-b associated with a serving cell.

[0100] At 310, the UE 115-b may identify a beam failure for a communication link between the UE 115-b and a serving cell (e.g., an SCell) of the base station 105-b. For example, a parameter associated with a beam of the communication link (e.g., an RSRP, RSRQ, SINR, etc. for the connected beam, as measured by the UE 115-b) may fall below a threshold.

[0101] At 315, the UE 115-b may determine to establish a communication link between the UE 115-b and the serving cell (e.g., a new communication link, re-establish an old communication link, etc.) based on the identified beam failure.

[0102] At 320, the UE 115-b may select a first beam (e.g., a preferred beam) from a set of candidate beams of the serving cell to establish a communication link. In some cases, the UE 115-b may subsequently initiate a request for uplink resources (e.g., a scheduling request) to send an indication of the selected first beam to the base station. Further, in some cases, the request may include a RACH message of a RACH procedure to establish a communication link between the UE 115-b and the serving cell of the base station 105-b.

[0103] At 325, UE 115-b may obtain uplink resources for UE 115-b to transmit the indication of the first beam. In some cases, UE 115-b may compare a threshold number of slots with the number of slots between the current time and the uplink resources and determine the availability of the uplink resources based on the number of slots between the current time and the uplink resources being less than the threshold number of slots.

[0104] Additionally or alternatively, the UE 115-b may transmit a request (e.g., a scheduling request) based on the determined availability indicating that the number of slots between the current time and the uplink resources is greater than a threshold number of slots. Accordingly, the UE 115-b may receive an indication of uplink resources in response to the transmitted request and may transmit an indication of the selected first beam in the MAC CE on the indicated uplink resources. In some cases, the UE 115-b may receive a configuration for beam failure recovery, where the request for uplink resources is transmitted based on the received configuration, and the received configuration for beam failure recovery includes a symbol sequence dedicated to the UE. Additionally or alternatively, the UE 115-b may transmit a scheduling request sequence indicating the request to the base station 105-b, where the scheduling request sequence is transmitted on uplink resources corresponding to the highest priority logical channel configured for the UE. In some cases, the UE 115-b may perform a RACH procedure to request uplink resources for transmitting the indication of the selected first beam.

[0105] When the UE 115-b initiates a request for uplink resources that can be used to transmit an indication of the selected first beam, as described above at 320, the UE 115-b may perform subsequent actions based on initiating the request. For example, at 325-a, the UE 115-b may first identify uplink control resources for transmitting the request. In some cases, the uplink control resources may include uplink control resources of transmission opportunities (e.g., TTIs, slots, subframes, etc.) in which the UE 115-b can transmit the request. Furthermore, the UE 115-b may determine and select uplink control resources for transmitting the request to indicate which serving cell and / or uplink resources the UE 115-b desires for transmitting the indication of the selected first beam. For example, the index of the transmission opportunity within the set of transmission opportunities used to transmit the request may indicate a serving cell whose beam failed. Furthermore, the index may indicate to the base station 105-b not to transmit a grant for the uplink resources on that serving cell / beam. This relationship between transmission opportunities and serving cells may be considered a one-to-one mapping. Additionally or alternatively, the index of a transmission opportunity within the set of transmission opportunities used to transmit the request may indicate a set of serving cells with no beam failures and / or to which the requested uplink resources should be allocated. This relationship between transmission opportunities and multiple serving cells may be considered a many-to-one mapping.

[0106] At 325-b, the UE 115-b may transmit a request on an uplink control resource that indicates to the base station 105-b the beam of the serving cell that failed. In some cases, the request may include a configuration of an uplink control resource associated with a beam failure recovery procedure, and the UE 115-b may transmit the request on a dedicated uplink control resource configured to indicate to the base station 105-b the beam or set of beams configured for the first serving cell that failed. Additionally or alternatively, the UE 115-b may transmit the request on an uplink control resource of a transmission opportunity, as described above, where the uplink control resource indicates to the base station 105-b that the beam of the serving cell has failed, and the transmission opportunity on the uplink control resource associated with the set of serving cells can indicate the serving cell whose beam failed (e.g., based on a one-to-one mapping, a many-to-one mapping, etc.).

[0107] At 325-c, the UE 115-b may receive from the base station 105-b, in response to the transmitted request, an indication of uplink resources in the second serving cell for the UE 115-b to use to transmit an indication of the selected first beam. In some cases, the UE 115-b may receive, in response to the transmitted request, DCI from the second serving cell of the base station 105-b indicating uplink resources of the second serving cell for the UE 115-b to use to transmit an indication of the selected first beam. For example, the second serving cell may include a PCell, a PSCell, or an SpCell (e.g., a special serving cell) of the UE 115-b. Additionally or alternatively, in response to the transmitted request, UE 115-b may receive from the base station an indication of uplink resources in a second serving cell different from the serving cell in which the beam failure occurred, for UE 115-b to use to transmit an indication of the selected first beam.

[0108] At 330, the UE 115-b may transmit an indication of the selected first beam in a MAC CE on uplink resources to the base station 105-b based on a comparison of the timing of uplink resource availability with a threshold (e.g., a threshold number of slots). In some cases, the UE 115-b may receive a configuration from the base station 105-b (e.g., via RRC signaling) indicating the threshold. Further, the UE 115-b may perform a logical channel prioritization procedure for the MAC PDU that includes the MAC CE, where the logical channel prioritization procedure gives the MAC CE a higher priority than each other MAC CE in the MAC PDU, higher than data in the MAC PDU, and lower than information in a CCCH message in the MAC PDU. In some cases, the UE 115-b may transmit an indication of the selected first beam in the MAC CE based on the determined availability indicating that the number of slots between the current time and the uplink resources is less than the threshold number of slots.

[0109] In some cases, UE 115-b may identify a beam failure for a second communication link between UE 115-b and a second serving cell, where the second serving cell includes a PCell, a PSCell, or an SpCell. Accordingly, UE 115-b may initiate a RACH procedure for re-establishing the second communication link with the second serving cell, where an indication of the selected first beam is transmitted after the RACH procedure for re-establishing the second communication link with the second serving cell is completed. In some cases, a beam failure for the second communication link may be identified before the second beam failure for the communication link. Alternatively, a beam failure for the second communication link may be identified after the second beam failure for the communication link. However, in both cases, as described above, UE 115-b may transmit an indication of the selected first beam after the RACH procedure for re-establishing the second communication link with the second serving cell is completed.

[0110] Further, in some cases, the UE 115-b may start a timer and a counter based on determining to establish a communication link. Subsequently, the UE 115-b may increment the counter based on transmitting an indication of the selected first beam and may retransmit the indication of the selected first beam in a MAC CE based on the timer expiring before a message is received (e.g., from the base station 105-b) on the selected first beam and the counter falling below a counter threshold. Further, when the counter threshold is met or exceeded, the UE 115-b may trigger a radio link failure based on the counter satisfying the counter threshold.

[0111] FIG. 4 illustrates an example process flow 400 supporting a MAC procedure for beam index indication according to aspects of the present disclosure. In some examples, the process flow 400 may implement aspects of the wireless communication systems 100 and / or 200. The process flow 400 may include a base station 105-c and a UE 115-c, which may be examples of corresponding base stations 105 and UEs 115, respectively, as described above with reference to FIGS. 1-3. As described herein, the base station 105-c and the UE 115-c may use beamforming techniques to communicate with each other. The process flow 400 may include similar steps as described above with reference to FIG. 3 for selecting a beam and transmitting an indication of the selected beam. However, the UE 115-c may select a beam and indicate the selected beam for a RACH procedure (e.g., a four-step RACH procedure) rather than a beam failure recovery procedure.

[0112] In the following description of process flow 400, operations between the UE 115-c and the base station 105-c may be transmitted in a different order than shown, or operations performed by the base station 105-c and the UE 115-c may be performed in a different order or at different times. Some operations may be omitted from process flow 400, or other operations may be added to process flow 400. While the base station 105-c and the UE 115-c are shown performing some of the operations of process flow 400, it should be understood that any wireless device may perform the operations shown.

[0113] At 405, the UE 115-c may determine to establish a communication link between the UE 115-c and a serving cell of the base station 105-c. For example, the UE 115-c may be within the geographic coverage area of ​​the base station 105-c and determine to establish an initial communication link with the base station 105-c via a four-step RACH procedure. Additionally or alternatively, the UE 115-c may experience a beam failure with the serving cell, and rather than performing beam failure recovery, the UE 115-c may perform a four-step RACH procedure to re-establish a communication link with the serving cell. In some cases, the UE 115-c may perform a four-step RACH procedure rather than a beam failure recovery procedure based on the serving cell being a PCell, a PSCell, or an SPCell, where a new communication link is established as a result of the beam failure with the PCell, PSCell, or SPCell.

[0114] The UE 115-c may transmit a RACH preamble (e.g., a first message) of the four-step RACH procedure at 410. Subsequently, the UE 115-c may receive a random access response (e.g., a second message) of the four-step RACH procedure at 415.

[0115] At 420, the UE 115-c may select a first beam (e.g., a preferred beam) from a set of candidate beams for the serving cell. In some cases, the UE 115-c may select the first beam based on information received in the random access response. Additionally or alternatively, the UE 115-c may receive the random access response from multiple beams transmitted by the base station 105-c (e.g., through a beam sweeping operation to increase the reliability of successful reception of the random access response at the UE 115-c) and may measure the signal quality of the multiple beams to select the first beam.

[0116] At 425, the UE 115-c may determine a beam for transmitting an indication of the selected first beam to the base station 105-c. In some cases, the UE 115-c may determine that a second beam of the set of candidate beams is available for transmitting an indication of the selected first beam prior to at least a threshold amount of uplink resource availability, where the uplink resources include the first beam. Additionally or alternatively, the UE 115-c may measure signal quality parameters (e.g., RSRP, RSRQ, SINR, or other quality parameters for the beams) of the set of candidate beams of the serving cell, including the first beam and the second beam, and may determine that the second beam is more preferable than the first beam based on the measured signal quality parameters for the first beam and the second beam.

[0117] At 430, the UE 115-c may transmit an indication of the selected first beam (e.g., a preferred beam) to the base station 105-c in a MAC CE in a random access message of the four-step RACH procedure. For example, the indication of the selected first beam may be transmitted on the second beam in a connection request message (e.g., message 3) of the four-step RACH procedure.

[0118] At 435, the UE 115-c may receive a contention resolution message (e.g., message 4) for the four-step RACH procedure from the base station 105-c, which may complete the four-step RACH procedure. In some cases, the base station 105-c may transmit the contention resolution message on the selected first beam that the UE 115-c indicated in the connection request message.

[0119] FIG. 5 illustrates an example process flow 500 supporting a MAC procedure for beam index indication according to aspects of the present disclosure. In some examples, the process flow 500 may implement aspects of the wireless communication systems 100 and / or 200. The process flow 500 may include a base station 105-d and a UE 115-d, which may be examples of corresponding base stations 105 and UEs 115, respectively, as described above with reference to FIGS. 1-4. As described herein, the base station 105-d and the UE 115-d may use beamforming techniques to communicate with each other. The process flow 500 may include steps similar to those described above with reference to FIGS. 3 and 4 for selecting a beam and transmitting an indication of the selected beam. However, unlike process flow 300, but similar to process flow 400, the UE 115-d may select a beam and indicate the selected beam for a RACH procedure (e.g., a two-step RACH procedure) rather than a beam failure recovery procedure.

[0120] In the following description of process flow 500, operations between the UE 115-d and the base station 105-d may be transmitted in a different order than shown, or operations performed by the base station 105-d and the UE 115-d may be performed in a different order or at different times. Some operations may be omitted from process flow 500, or other operations may be added to process flow 500. While the base station 105-d and the UE 115-d are shown as performing some of the operations of process flow 500, it should be understood that any wireless device may perform the illustrated operations.

[0121] At 505, similar to process flow 400, the UE 115-d may determine to establish a communication link between the UE 115-d and the serving cell of the base station 105-d, except that rather than performing a four-step RACH procedure, the UE 115-d may be configured and capable of performing a two-step RACH procedure.

[0122] Thus, at 510, UE 115-d may select a first beam from a set of candidate beams of the serving cell. In some cases, UE 115-d may base this selection on previous signal quality measurements of the candidate beam or on ongoing signal quality measurements of the candidate beam. The signal quality measurements may include one or more of RSRP, RSRQ, SINR, or other signal quality measurements for the candidate beam.

[0123] At 515, UE 115-d may determine a beam for transmitting an indication of the selected first beam, similar to the techniques described above with reference to FIG. 4 (e.g., based on the second beam being available before the indicated uplink resources are available, signal quality parameter measurements, etc.). For example, UE 115-d may determine to use the second beam to transmit an indication of the selected first beam.

[0124] At 520, rather than sending an indication of the selected first beam in the connection request message of the four-step RACH procedure, UE 115-d may send an indication of the selected first beam on the second beam in the first message (e.g., MsgA) of the two-step RACH procedure.

[0125] At 525, the UE 115-d may receive a second message (e.g., MsgB) of the two-step RACH procedure from the base station 105-d. In some cases, the base station 105-d may transmit the second message of the two-step RACH procedure using the selected first beam indicated by the UE 115-d in the first message of the two-step RACH procedure.

[0126] 6 shows a block diagram 600 of a device 605 supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The device 605 may be an example of an aspect of a UE 115 as described herein. The device 605 may include a receiver 610, a communications manager 615, and a transmitter 620. The device 605 may also include one or more processors, memory coupled to the one or more processors, and instructions stored in the memory executable by the one or more processors to enable the one or more processors to perform the procedures for beam index indication discussed herein. Each of these components may communicate with one another (e.g., via one or more buses).

[0127] The receiver 610 may receive information such as packets, user data, or control information associated with various information channels (e.g., information regarding MAC procedures for control channels, data channels, and beam index indication, etc.). The information may be passed to other components of the device 605. The receiver 610 may be an example of an aspect of the transceiver 920 described with reference to FIG. 9. The receiver 610 may use a single antenna or a set of antennas.

[0128] The communications manager 615 may determine to establish a communications link between the UE and a serving cell of the base station. In some cases, the communications manager 615 may select, by the UE, a first beam from a set of candidate beams of the serving cell to establish the communications link. Further, the communications manager 615 may transmit an indication of the selected first beam to the base station in a MAC control element over the uplink resources based on a comparison of the timing and a threshold of uplink resource availability. The communications manager 615 may be an example of an aspect of the communications manager 910 described herein.

[0129] The communications manager 615 may be implemented as an integrated circuit or chipset for the device 605, and the receiver 610 and transmitter 620 may be implemented as analog components (e.g., amplifiers, filters, antennas) coupled with the device 605 to enable wireless transmission and reception. Actions performed by the communications manager 615 as described herein may be implemented to realize one or more potential advantages. At least one implementation may enable the communications manager 615 to establish a communications link with a base station using a preferred beam. Based on the establishing implementation, one or more processors of the device 605 (e.g., a processor controlling or integrated with the communications manager 615) can facilitate improvements to spectral efficiency, higher data rates, and in some examples, enhanced efficiency for reliable and low-latency operation, among other benefits.

[0130] Communications manager 615, or a subcomponent thereof, may be implemented in hardware, in code executed by a processor (e.g., software or firmware), or any combination thereof. If implemented in code executed by a processor, the functions of communications manager 615, or a subcomponent thereof, may be performed by a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in this disclosure.

[0131] The communications manager 615 or its subcomponents may be physically located in various locations, including being distributed such that portions of its functionality are implemented by one or more physical components at different physical locations. In some examples, the communications manager 615 or its subcomponents may be separate and distinct components according to various aspects of the present disclosure. In some examples, the communications manager 615 or its subcomponents may be combined with one or more other hardware components, including, but not limited to, an input / output (I / O) component, a transceiver, a network server, another computing device, one or more other components described in this disclosure, or combinations thereof according to various aspects of the present disclosure.

[0132] The transmitter 620 may transmit signals generated by other components of the device 605. In some examples, the transmitter 620 may be co-located with the receiver 610 in a transceiver module. For example, the transmitter 620 may be an example of an aspect of the transceiver 920 described with reference to FIG. 9. The transmitter 620 may use a single antenna or a set of antennas.

[0133] 7 shows a block diagram 700 of a device 705 supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The device 705 may be an example of an aspect of the device 605 or the UE 115 described herein. The device 705 may include a receiver 710, a communications manager 715, and a transmitter 735. The device 705 may also include a processor. Each of these components may communicate with one another (e.g., via one or more buses).

[0134] The receiver 710 may receive information such as packets, user data, or control information associated with various information channels (e.g., information regarding MAC procedures for control channels, data channels, and beam index indication, etc.). The information may be passed to other components of the device 705. The receiver 710 may be an example of an aspect of the transceiver 920 described with reference to FIG. 9. The receiver 710 may use a single antenna or a set of antennas.

[0135] Communications manager 715 may be an example of an aspect of communications manager 615 described herein. Communications manager 715 may also include link establishment component 720, beam selector 725, and selected beam indicator 730. Communications manager 715 may be an example of an aspect of communications manager 910 described herein.

[0136] The link establishment component 720 may determine to establish a communication link between the UE and a serving cell of the base station.

[0137] The beam selector 725 may select, by the UE, a first beam from a set of candidate beams of the serving cell to establish a communication link.

[0138] The selected beam indicator 730 may transmit an indication of the selected first beam in a MAC CE to the base station on the uplink resources based on a comparison of the timing of the availability of the uplink resources with a threshold.

[0139] The transmitter 735 may transmit signals generated by other components of the device 705. In some examples, the transmitter 735 may be co-located with the receiver 710 in a transceiver module. For example, the transmitter 735 may be an example of an aspect of the transceiver 920 described with reference to FIG. 9. The transmitter 735 may use a single antenna or a set of antennas.

[0140] In some cases, the link establishment component 720, the beam selector 725, and the selected beam indicator 730 may each be, or at least a part of, a processor (e.g., a transceiver processor, or a radio processor, or a transmitter processor, or a receiver processor). The processor may be coupled to a memory and may execute instructions stored in the memory that enable the processor to implement or facilitate features of the link establishment component 720, the beam selector 725, and the selected beam indicator described herein. The transceiver processor may be co-located with and / or communicate with (e.g., direct the operation of) a transceiver of a device. The radio processor may be co-located with and / or communicate with (e.g., direct the operation of) a radio of a device (e.g., an NR radio, an LTE radio, a Wi-Fi radio). The transmitter processor may be co-located with and / or communicate with (e.g., direct the operation of) a transmitter of a device. The receiver processor may be co-located with and / or in communication with (e.g., direct the operation of) the receiver of the device.

[0141] 8 shows a block diagram 800 of a communications manager 805 supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The communications manager 805 may be an example of an aspect of communications manager 615, communications manager 715, or communications manager 910 described herein. The communications manager 805 may include a link establishment component 810, a beam selector 815, a selected beam indicator 820, a beam failure identifier 825, an uplink resource availability component 830, an uplink resource request component 835, a RACH selected beam indicator 840, a prioritization component 845, and a beam indication transmission counter 850. Each of these modules may communicate directly or indirectly with each other (e.g., via one or more buses).

[0142] The link establishment component 810 may determine to establish a communication link between the UE and a serving cell of the base station.

[0143] The beam selector 815 may select, by the UE, a first beam from a set of candidate beams of the serving cell to establish a communication link. In some cases, the beam selector 815 may initiate a request for uplink resources for transmitting an indication of the selected first beam to the base station. In some examples, the UE may transmit a request on uplink control resources instructing the base station on a beam of the failed serving cell, and in response to the transmitted request, the UE may receive from the base station an indication of uplink resources in a second serving cell for use in transmitting the indication of the selected first beam.

[0144] The selected beam indicator 820 may transmit an indication of the selected first beam in a MAC CE to the base station over the uplink resources based on a comparison of the timing of uplink resource availability with a threshold. In some examples, the selected beam indicator 820 may receive a configuration from the base station indicating the threshold.

[0145] The beam failure identifier 825 may communicate with the base station over the communication link and may identify a beam failure for the communication link between the UE and the serving cell. Accordingly, the beam failure identifier 825 may determine to establish a communication link between the UE and the serving cell based on the identified beam failure.

[0146] The uplink resource availability component 830 may obtain uplink resources for the UE to transmit an indication of the first beam, compare a threshold number of slots to a number of slots between a current time and the uplink resources, where the threshold includes the threshold number of slots, and determine the availability of the uplink resources based on the number of slots between the current time and the uplink resources being less than the threshold number of slots. In some examples, the uplink resource availability component 830 may transmit an indication of the selected first beam in a MAC CE based on the determined availability indicating that the number of slots between the current time and the uplink resources is less than the threshold number of slots. Alternatively, the uplink resource availability component 830 may transmit a request for uplink resources to the base station based on the determined availability indicating that the number of slots between the current time and the uplink resources is greater than the threshold number of slots. Thus, the uplink resource availability component 830 may receive an indication of uplink resources in response to the transmitted request and may transmit an indication of the selected first beam in a MAC CE on the indicated uplink resources.

[0147] The uplink resource request component 835 may receive a configuration for beam failure recovery, and a request for uplink resources is transmitted based on the received configuration. In some cases, the received configuration for beam failure recovery may include a symbol sequence dedicated to the UE. Additionally or alternatively, the uplink resource request component 835 may transmit a scheduling request sequence to the base station indicating the request. In some cases, the scheduling request sequence may be transmitted on uplink resources corresponding to the highest priority logical channel configured for the UE.

[0148] In some cases, the uplink resource request component 835 may transmit a request on uplink control resources instructing the base station on the beam of the failed serving cell, and in response to the transmitted request, the UE may receive from the base station an indication of uplink resources in the second serving cell for use in transmitting the indication of the selected first beam. Additionally or alternatively, the request may include a configuration of uplink control resources associated with a beam failure recovery procedure, and the uplink resource request component 835 may transmit a request on dedicated uplink control resources configured to instruct the base station on the beam or set of beams configured for the failed first serving cell, and subsequently, in response to the transmitted request, the UE may receive from the second serving cell of the base station a DCI instructing the uplink resources of the second serving cell for use in transmitting the indication of the selected first beam. In some cases, the second serving cell may include the UE's PCell, PSCell, or SpCell.

[0149] Additionally or alternatively, the uplink resource request component 835 can transmit a request on uplink control resources for a transmission opportunity, the uplink control resources being associated with a set of serving cells such that the uplink control resources indicate to the base station that a beam of the serving cell has failed, and the transmission opportunity on the uplink control resource indicates the serving cell for which the beam has failed. In some cases, the index of the transmission opportunity within the set of transmission opportunities may indicate the serving cell for which the beam has failed. Alternatively, the index of the transmission opportunity within the set of transmission opportunities may indicate a set of serving cells for which the beam has not failed, a set of serving cells to which the requested uplink resources should be allocated, or a combination thereof.

[0150] The RACH selection beam indicator 840 may transmit a MAC control element in a RACH (e.g., random access) message of a RACH procedure to the base station. In some examples, the RACH selection beam indicator 840 may determine that a second beam of a set of candidate beams is available for transmitting an indication of a first beam prior to the availability of uplink resources by at least a threshold, where the uplink resources include the first beam, and the indication of the selected first beam is transmitted in a MAC CE on the second beam based on the determination that the second beam is available. Additionally or alternatively, the RACH selection beam indicator 840 may measure signal quality parameters of a set of candidate beams of the serving cell including the first beam and the second beam, determine that the second beam is preferable to the first beam based on the measured signal quality parameters for the first beam and the second beam, and transmit an indication of the second beam in a signal of the RACH procedure based on the determination that the second beam is preferable. In some cases, an indication of the selected first beam may be transmitted on the second beam in the first message (e.g., MsgA) of the two-step RACH procedure. Additionally or alternatively, an indication of the selected first beam may be transmitted on the second beam in the connection request message (e.g., message 3) of the four-step RACH procedure.

[0151] In some cases, the RACH selection beam indicator 840 can identify a beam failure for a second communication link between the UE and a second serving cell, where the second serving cell may include a PCell, a PSCell, or an SpCell. Subsequently, the RACH selection beam indicator 840 can initiate a RACH procedure for re-establishing the second communication link with the second serving cell, where an indication of the selected first beam is transmitted after the RACH procedure for re-establishing the second communication link with the second serving cell is completed. In some cases, the beam failure for the second communication link may be identified before the second beam failure for the communication link. Alternatively, the beam failure for the second communication link may be identified after the second beam failure for the communication link.

[0152] The prioritization component 845 may implement a logical channel prioritization procedure for the MAC PDU containing the MAC CE, where the logical channel prioritization procedure gives the MAC CE a higher priority than each other MAC CE in the MAC PDU, higher than the data in the MAC PDU, and lower than the information in the CCCH messages in the MAC PDU.

[0153] The beam indication transmission counter 850 may start a timer and a counter based on determining to establish a communication link and may increment the counter based on transmitting an indication of the selected first beam. Furthermore, the beam indication transmission counter 850 may retransmit the indication of the selected first beam in the MAC CE based on the timer expiring before a message is received on the selected first beam and the counter falling below a counter threshold. In some cases, the beam indication transmission counter 850 may trigger a radio link failure based on the counter satisfying a counter threshold.

[0154] In some cases, the link establishment component 810, the beam selector 815, the selected beam indicator 820, the beam failure discriminator 825, the uplink resource availability component 830, the uplink resource request component 835, the RACH selected beam indicator 840, the prioritization component 845, and the beam direction transmission counter 850 may each be, or at least a part of, a processor (e.g., a transceiver processor, or a radio processor, or a transmitter processor, or a receiver processor). The processor may be coupled to a memory and execute instructions stored in the memory that enable the processor to implement or facilitate features of the link establishment component 810, the beam selector 815, the selected beam indicator 820, the beam failure discriminator 825, the uplink resource availability component 830, the uplink resource request component 835, the RACH selected beam indicator 840, the prioritization component 845, and the beam direction transmission counter 850 discussed herein.

[0155] 9 shows a diagram of a system 900 including a device 905 supporting a MAC procedure for beam index indication according to an aspect of the disclosure. The device 905 may be or include examples of components of device 605, device 705, or UE 115 as described herein. The device 905 may include components for two-way voice and data communication, including components for transmitting and receiving communications, including a communications manager 910, an I / O controller 915, a transceiver 920, an antenna 925, a memory 930, and a processor 940. These components may be in electronic communication via one or more buses (e.g., bus 945).

[0156] The communications manager 910 may determine to establish a communications link between the UE and a serving cell of the base station. In some cases, the communications manager 910 may select, by the UE, a first beam from a set of candidate beams of the serving cell to establish the communications link. Furthermore, the communications manager 910 may transmit an indication of the selected first beam to the base station in a MAC CE over uplink resources based on a comparison of the timing of uplink resource availability with a threshold. At least one implementation may enable the communications manager 910 to establish a communications link with the base station using the preferred beam. Based on the establishing implementation, one or more processors of the device 905 (e.g., a processor controlling or integrated with the communications manager 910) can facilitate improvements to spectral efficiency, higher data rates, and, in some examples, enhanced efficiency for reliable and low-latency operation, among other benefits.

[0157] The I / O controller 915 may manage input and output signals for the device 905. The I / O controller 915 may also manage peripheral devices not integrated within the device 905. In some cases, the I / O controller 915 may represent a physical connection or port to an external peripheral. In some cases, the I / O controller 915 may use an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS / 2®, UNIX®, LINUX®, or another known operating system. In other cases, the I / O controller 915 may represent or interact with a modem, keyboard, mouse, touchscreen, or similar device. In some cases, the I / O controller 915 may be implemented as part of a processor. In some cases, a user may interact with the device 905 through the I / O controller 915 or through hardware components controlled by the I / O controller 915.

[0158] The transceiver 920 may communicate bidirectionally via one or more antennas, wired or wireless links, as described above. For example, the transceiver 920 may represent a wireless transceiver and may communicate bidirectionally with another wireless transceiver. The transceiver 920 may also include a modem for modulating packets for transmission and providing the modulated packets to an antenna, and for demodulating packets received from the antenna.

[0159] In some cases, a wireless device may include a single antenna 925. However, in some cases, the device may have two or more antennas 925 that may be capable of simultaneously transmitting or receiving multiple wireless transmissions.

[0160] The memory 930 may include random access memory (RAM) and read-only memory (ROM). The memory 930 may store computer-readable computer-executable code 935, which includes instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 930 may include a basic input / output system (BIOS), which may control basic hardware or software operations, such as interaction with peripheral components or devices, among other things.

[0161] The processor 940 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a central processing unit (CPU), a microcontroller, an ASIC, an FPGA, a programmable logic device, discrete gate or transistor logic components, discrete hardware components, or any combination thereof). In some cases, the processor 940 may be configured to operate a memory array using a memory controller. In other cases, the memory controller may be incorporated into the processor 940. The processor 940 may be configured to execute computer-readable instructions stored in a memory (e.g., memory 930) to cause the device 905 to perform various functions (e.g., functions or tasks supporting a MAC procedure for beam index indication).

[0162] The code 935 may include instructions for implementing aspects of the present disclosure, including instructions for supporting wireless communication. The code 935 may be stored in a non-transitory computer-readable medium, such as system memory or other type of memory. In some cases, the code 935 may not be directly executable by the processor 940, but may (e.g., when compiled and executed) cause a computer to perform functions described herein.

[0163] FIG. 10 shows a flowchart illustrating a method 1000 for supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The operations of method 1000 may be implemented by the UE 115 or components thereof, as described herein. For example, the operations of method 1000 may be performed by a communications manager described with reference to FIGS. 6-9. In some examples, the UE may execute a set of instructions to control functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform aspects of the functions described below.

[0164] At 1005, the UE may determine to establish a communication link between the UE and a serving cell of the base station. The operations of 1005 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1005 may be performed by a link establishment component such as those described with reference to FIGS. 6-9.

[0165] At 1010, the UE may select a first beam from a set of candidate beams of the serving cell for establishing a communication link by the UE. The operations of 1010 may be performed according to methods described herein. In some examples, aspects of the operations of 1010 may be performed by a beam selector such as those described with reference to FIGS. 6-9.

[0166] At 1015, the UE may transmit an indication of the selected first beam in the MAC CE to the base station over the uplink resources based on a comparison of the timing of uplink resource availability with a threshold. The operation of 1015 may be implemented according to methods described herein. In some examples, aspects of the operation of 1015 may be implemented by a selected beam indicator as described with reference to FIGS. 6-9.

[0167] FIG. 11 shows a flowchart illustrating a method 1100 for supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The operations of method 1100 may be implemented by the UE 115 or components thereof, as described herein. For example, the operations of method 1100 may be performed by a communications manager described with reference to FIGS. 6-9. In some examples, the UE may execute a set of instructions to control functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform aspects of the functions described below.

[0168] At 1105, the UE may communicate with the base station via the communication link. The operations of 1105 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1105 may be performed by a beam failure identifier such as those described with reference to FIGS. 6-9.

[0169] At 1110, the UE may identify a beam failure for the communication link between the UE and the serving cell. The operations of 1110 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1110 may be performed by a beam failure identifier such as those described with reference to FIGS. 6-9.

[0170] At 1115, the UE may determine to establish a communication link between the UE and the serving cell of the base station. The operations of 1115 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1115 may be performed by a link establishment component such as those described with reference to FIGS. 6-9.

[0171] At 1120, the UE may determine to establish a communication link between the UE and the serving cell based on the identified beam failure. The operations of 1120 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1120 may be performed by a beam failure identifier such as those described with reference to FIGS. 6-9.

[0172] At 1125, the UE may select a first beam from the set of candidate beams of the serving cell for establishing a communication link by the UE. The operations of 1125 may be performed according to methods described herein. In some examples, aspects of the operations of 1125 may be performed by a beam selector such as those described with reference to FIGS. 6-9.

[0173] At 1130, the UE may transmit an indication of the selected first beam in the MAC CE to the base station over the uplink resources based on a comparison of the timing of uplink resource availability with a threshold. The operation of 1130 may be performed according to methods described herein. In some examples, aspects of the operation of 1130 may be performed by a selected beam indicator such as those described with reference to FIGS. 6-9.

[0174] FIG. 12 shows a flowchart illustrating a method 1200 for supporting a MAC procedure for beam index indication according to an aspect of the present disclosure. The operations of method 1200 may be implemented by the UE 115 or components thereof, as described herein. For example, the operations of method 1200 may be performed by a communications manager described with reference to FIGS. 6-9. In some examples, the UE may execute a set of instructions to control functional elements of the UE to perform the functions described below. Additionally or alternatively, the UE may use dedicated hardware to perform aspects of the functions described below.

[0175] At 1205, the UE may determine to establish a communication link between the UE and a serving cell of the base station. The operations of 1205 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1205 may be performed by a link establishment component such as those described with reference to FIGS. 6-9.

[0176] At 1210, the UE may select a first beam from a set of candidate beams of the serving cell for establishing a communication link by the UE. The operations of 1210 may be performed in accordance with methods described herein. In some examples, aspects of the operations of 1210 may be performed by a beam selector such as those described with reference to FIGS. 6-9.

[0177] At 1215, the UE may transmit an indication of the selected first beam in the MAC CE to the base station over the uplink resources based on a comparison of the timing of uplink resource availability with a threshold. The operation of 1215 may be implemented according to methods described herein. In some examples, aspects of the operation of 1215 may be implemented by a selected beam indicator as described with reference to FIGS. 6-9.

[0178] At 1220, the UE may transmit the MAC CE in a RACH message of the RACH procedure to the base station. The operation of 1220 may be performed according to methods described herein. In some examples, aspects of the operation of 1220 may be performed by a RACH selection beam indicator as described with reference to FIGS. 6-9.

[0179] It should be noted that the methods described herein represent possible implementations, that operations and steps may be rearranged or possibly modified, and that other implementations are possible. Furthermore, aspects from two or more of these methods may be combined.

[0180] The techniques described herein may be used in various wireless communication systems such as Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single-Carrier Frequency Division Multiple Access (SC-FDMA) systems, and other systems. CDMA systems may implement radio technologies such as CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 releases are sometimes commonly referred to as CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 1xEV-DO, High Rate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. TDMA systems may implement radio technologies such as Global System for Mobile Communications (GSM).

[0181] An OFDMA system may implement radio technologies such as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are parts of the Universal Mobile Telecommunications System (UMTS). LTE, LTE-A, and LTE-A Pro are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, LTE-A Pro, NR, and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). CDMA2000 and UMB are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). The techniques described herein may be used for the systems and radio technologies mentioned herein as well as other systems and radio technologies. Aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described as examples, and the terminology LTE, LTE-A, LTE-A Pro, or NR may be used throughout much of the description, although the techniques described herein are applicable to other than LTE, LTE-A, LTE-A Pro, or NR applications.

[0182] A macro cell generally covers a relatively large geographic area (e.g., a few kilometers in radius) and may allow unrestricted access by UEs with a service subscription with the network provider. A small cell may be associated with a lower-power base station compared to a macro cell, and the small cell may operate in the same or a different frequency band (e.g., licensed, unlicensed, etc.) as the macro cell. Small cells may include pico cells, femto cells, and micro cells, according to various examples. A pico cell, for example, may cover a small geographic area and allow unrestricted access by UEs with a service subscription with the network provider. A femto cell may also cover a small geographic area (e.g., a home) and may provide restricted access by UEs with an association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG), UEs for users in the home, etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a small cell may be referred to as a small cell eNB, pico eNB, femto eNB, or home eNB. An eNB may support one or more (eg, two, three, four, etc.) cells and may also support communication using one or more component carriers.

[0183] The wireless communication systems described herein may support synchronous or asynchronous operation. For synchronous operation, base stations may have similar frame timing, and transmissions from different base stations may be approximately aligned in time. For asynchronous operation, base stations may have different frame timing, and transmissions from different base stations may not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operation.

[0184] The information and signals described herein may be represented using any of a wide variety of technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0185] The various example blocks and modules described in connection with the disclosure herein may be implemented or performed using a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but alternatively, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0186] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted via a computer-readable medium as one or more instructions or code. Other examples and implementations are within the scope of this disclosure and the appended claims. For example, due to the nature of software, the functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or any combination thereof. The features implementing the functions may also be physically located in various locations, including being distributed such that portions of the functions are implemented in different physical locations.

[0187] Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. Non-transitory storage media may be any available medium that can be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include RAM, ROM, Electrically Erasable Programmable Read Only Memory (EEPROM), Flash memory, Compact Disc (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer or processor. Also, any connection is properly termed a computer-readable medium. For example, if software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included within the definition of medium. As used herein, disk and disc include CDs, laser discs, optical discs, digital versatile discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically and discs reproduce data optically using lasers. Combinations of the above are also included within the scope of computer-readable media.

[0188] As used herein, including in the claims, the use of "or" in a list of items (e.g., a list of items ending with a phrase such as "at least one of" or "one or more of") indicates an inclusive list, such as, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). Also, the phrase "based on" as used herein should not be construed as a reference to a closed set of conditions. For example, an example step described as "based on condition A" may be based on both condition A and condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase "based on" is intended to be construed the same as the phrase "based at least in part on."

[0189] In the accompanying drawings, similar components or features may have the same reference label. Furthermore, various components of the same type may be distinguished by following the reference label with a dash and a second label that distinguishes between the similar components. If only a first reference label is used herein, the description is applicable to any of the similar components having the same first reference label, regardless of a second reference label, or other subsequent reference label.

[0190] The description set forth herein with reference to the accompanying drawings describes exemplary configurations and does not represent every example that may be implemented or that falls within the scope of the claims. As used herein, the term "exemplary" means "serving as an example, instance, or illustration" and does not mean "preferred" or "advantageous over other examples." The detailed description includes specific details for the purpose of providing an understanding of the described techniques. However, these techniques may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

[0191] The description herein is provided to enable any person skilled in the art to make or use the disclosure. Various modifications of the disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. [Explanation of symbols]

[0192] 100 Wireless Communication System 105 Base station 110 Geographic Coverage Areas 115 UE 125 communication links 130 Core Network 132 backhaul links 134 backhaul links 200 Wireless Communication Systems 605 devices 610 Receiver 615 Communications Manager 620 Transmitter 705 devices 710 Receiver 715 Communications Manager 720 Link Establishment Components 725 Beam Selector 730 Selective Beam Indicator 735 transmitter 805 Communications Manager 810 Link Establishment Components 815 Beam Selector 820 Selective Beam Indicator 825 Beam Failure Identifier 830 Uplink Resource Availability Component 835 Uplink Resource Request Component 840 RACH Selected Beam Indicator 845 Prioritization Components 850 Beam Indication Transmit Counter 900 System 905 devices 910 Communications Manager 915 I / O Controller 920 Transceiver 925 Antenna 930 memory 935 computer-readable computer-executable code 940 processor 945 Bus

Claims

1. 1. A method for wireless communication in a user equipment (UE), comprising: receiving, from a base station, a PUCCH configuration indicating one or more PUCCH resources for beam failure recovery in an SCell; Identifying a beam failure in the SCell and determining to establish a communication link between the UE and a serving cell of a base station; sending a request to the base station to signal a new uplink resource for transmitting a beam instruction, using at least one of the one or more PUCCH resources; receiving, in response to the transmitted request, from the base station, a grant of the new uplink resources in a second serving cell for transmitting the beam indication; selecting a beam for the base station for the beam failure recovery in the SCell from a plurality of candidate beams of the serving cell based on identifying the beam failure; and and transmitting the beam indication indicating the selected beam to the base station in a medium access control (MAC) control element (CE) using the new uplink resources based at least in part on the availability of the new uplink resources.

2. The method of claim 1 , wherein communication between the UE and the base station is performed over a PCell.

3. the step of transmitting beam instructions comprises:

3. The method of claim 1, comprising multiplexing the MAC CE carrying the beam indication into a MAC PDU.

4. The method of claim 3, wherein the MAC CE is given higher priority during an LCP procedure when the MAC CE is multiplexed with other data in the MAC PDU.

5. The method of any one of claims 1 to 4, wherein the beam indication is a beam index indication.

6. 1. An apparatus for wireless communication in a user equipment (UE), comprising: means for receiving, from a base station, a PUCCH configuration indicating one or more PUCCH resources for beam failure recovery in a SCell; means for identifying a beam failure in the SCell and determining to establish a communication link between the UE and a serving cell of a base station; means for transmitting a request to the base station to signal new uplink resources for transmitting a beam instruction, using at least one of the one or more PUCCH resources; means for receiving from the base station, in response to the transmitted request, a grant of the new uplink resources in a second serving cell for transmitting the beam indication; means for selecting a beam for the base station for the beam failure recovery in the SCell to establish a communication link from a plurality of candidate beams of the serving cell based on identifying the beam failure; and means for transmitting the beam indication indicating the selected beam to the base station in a medium access control (MAC) control element (CE) using the new uplink resources based at least in part on the availability of the new uplink resources.

7. The apparatus of claim 6 , wherein communication between the UE and the base station is performed over a PCell.

8. The means for transmitting the beam instruction comprises:

8. The apparatus of claim 6, comprising: means for multiplexing the MAC CE carrying the beam indication into a MAC PDU.

9. 10. The apparatus of claim 8, wherein the MAC CE is given higher priority during an LCP procedure when the MAC CE is multiplexed with other data in the MAC PDU.

10. The apparatus of any one of claims 6 to 9, wherein the beam indication is a beam index indication.

11. 1. A method for wireless communication in a base station, comprising: transmitting, to a user equipment (UE), a PUCCH configuration indicating one or more PUCCH resources for beam failure recovery in an SCell; receiving, on at least one of the one or more PUCCH resources, a request from the UE for signaling a new uplink resource for transmitting a beam indication to establish a communication link between the UE and a serving cell of the base station from a beam failure recovery identified in the SCell; transmitting, in response to the transmitted request, to the UE, a grant of the new uplink resources in a second serving cell for transmitting the beam indication; receiving the beam indication from the UE on new uplink resources in a medium access control (MAC) control element (CE) indicating a selected beam for the beam failure recovery based at least in part on the availability of the new uplink resources, wherein the selected beam is a beam selected for establishing the communication link from a plurality of candidate beams of the serving cell based on an identified beam failure.

12. The method of claim 11 , wherein the beam designation is a beam index designation.

13. 1. An apparatus for wireless communication at a base station, comprising: means for transmitting, to a user equipment (UE), a PUCCH configuration indicating one or more PUCCH resources for beam failure recovery in an SCell; means for receiving, on at least one of the one or more PUCCH resources, a request from the UE for signaling a new uplink resource for transmitting a beam indication to establish a communication link between the UE and a serving cell of the base station from a beam failure recovery identified in the SCell; and means for transmitting, in response to the transmitted request, to the UE, a grant of the new uplink resources in a second serving cell for transmitting the beam indication; and means in a medium access control (MAC) control element (CE) for receiving from the UE on the new uplink resources the beam indication indicating a selected beam for the beam failure recovery based at least in part on the availability of the new uplink resources, wherein the selected beam is a beam selected to establish the communication link from a plurality of candidate beams of the serving cell based on an identified beam failure.

14. The apparatus of claim 13 , wherein the beam indication is a beam index indication.

15. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 5.

16. A computer program comprising instructions that, when executed by a computer, cause the computer to carry out the method according to claim 11 or 12.

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