Media access control process with beam index indication

Abstract

Methods, systems, and apparatus for wireless communications are described. A user equipment (UE) may select a beam from a set of beams and send an indication of the selected beam in a media access control (MAC) control element to establish a communication link with a base station. In some cases, the user equipment may select the beam and indicate the selection based on identifying a beam failure and / or determining to perform a random access procedure. When sending the indication of the selected beam, the user equipment may obtain uplink resources for the transmission based on the availability of the uplink resources. For example, if the uplink resources are available, the user equipment may send the indication of the selected beam multiplexed with the uplink transmission. Alternatively, if the uplink resources are not available, the user equipment may request uplink resources for sending the indication of the selected beam.

Description

[0001] Cross-references

[0002] This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 887,631, filed on August 15, 2019, by He et al., entitled “Media Access Control Procedures for Beam Index Indications”; and PCT International Application No. PCT / CN2019 / 102367, filed on August 23, 2019, by He et al., entitled “Scheduling Request for Cell-Specific Resources”; and U.S. Patent Application No. 16 / 993,023, filed on August 13, 2020, by He et al., entitled “Media Access Control Procedures for Beam Index Indications”; each of which is assigned to the assignee of the present invention. Background Art

[0003] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcast, etc. These systems can support 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) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro (LTE-A) systems, and fifth generation (5G) systems, which may be referred to as new radio (NR) systems. These systems may employ techniques 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).

[0004] A wireless multiple access communication system may include multiple base stations or network access nodes, each of which supports communication of multiple communication devices simultaneously, which may also be referred to as user equipment (UE). In some cases, the user equipment and the base station may communicate via beamforming technology, wherein each wireless device uses a directional beam to send signals to or receive signals from other wireless devices. For example, both the user equipment and the base station may use a set of antennas to send or receive signals in a specific direction, rather than sending signals in many directions (e.g., omnidirectionally), so that the signal sent in the specific direction is stronger. However, the user equipment and the base station may form multiple beams at a time to increase the chances of successfully sending and receiving signals. Therefore, there is a need for a technology for indicating a preferred beam (e.g., a stronger beam) for subsequent communication. Summary of the Invention

[0005] The described technology relates to improved methods, systems, devices and apparatuses to support a media access control (MAC) process for beam index indication. In general, the described technology provides a user equipment (UE) with selecting a first beam (e.g., a preferred beam) from a set of beams and sending an indication of the selected first beam to a base station in a MAC control element (CE) to establish a communication link with the base station. In some cases, the user equipment may select the first beam and determine to establish the communication link via a random access channel (RACH) process (e.g., two-step RACH, four-step RACH, etc.) based on identifying a beam failure indication on at least one cell communicating with the base station, or a combination thereof. When sending the indication of the selected beam, the user equipment may obtain the uplink resource to be sent based on a comparison of the availability of the uplink resource with a threshold (e.g., whether the uplink resource is scheduled within the next N time slots). For example, if the uplink resource is available, the user equipment may send the indication of the selected first beam multiplexed with the MAC CE. Alternatively, if the uplink resources are not available, the user equipment may request uplink resources (e.g., via configured uplink resources, via a scheduling request, etc.) to send an indication of the selected first beam.

[0006] A method for wireless communication at a user equipment is described. The method may include: determining to establish a communication link between the user equipment and a serving cell of a base station; selecting, by the user equipment, a first beam from a set of candidate beams of the serving cell to establish the communication link; and sending, in a MAC CE, an indication of the selected first beam to the base station on the uplink resource based on a comparison of a timing of availability of the uplink resource with a threshold.

[0007] An apparatus for wireless communication at a user equipment (UE) is described. The apparatus may include a processor, a memory coupled to the processor, and instructions stored in the memory. The instructions are 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, to the base station in a MAC CE, an indication of the selected first beam on the uplink resource based on a comparison of a timing of availability of the uplink resource with a threshold.

[0008] Another apparatus for wireless communication at a user equipment (UE) is described. The apparatus may include components for 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 to establish the communication link; and transmitting, in a MAC CE, an indication of the selected first beam to the base station on the uplink resource based on a comparison of a timing of availability of the uplink resource with a threshold.

[0009] A non-transitory computer-readable medium storing code for wireless communication at a user equipment is described. The code may include instructions executable by a processor to determine to establish a communication link between the user equipment and a serving cell of a base station; select, by the user equipment, 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 on an uplink resource based on a comparison of a timing of availability of the uplink resource with a threshold.

[0010] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may also include operations, features, components, or instructions for initiating a request for uplink resources to transmit an indication of the selected first beam to the base station. Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, components, or instructions for transmitting the request on an uplink control resource, the request indicating the failed beam of the serving cell to the base station; and, in response to the transmitted request, receiving an indication of uplink resources in a second serving cell from the base station for use by the user equipment 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, components, or instructions for sending the request on a dedicated uplink control resource, the request being configured to indicate to the base station a beam or set of beams configured for the first service cell that may have failed; and in response to the sent request, receiving downlink information from a second service cell of the base station, the downlink information indicating uplink resources of the second service cell for use by the user equipment to send 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, components, or instructions for sending a request on an uplink control resource at a sending occasion, the uplink control resource indicating to the base station a beam of the service cell that may have failed, and the sending occasion of the uplink control resource associated with a set of service cells indicating a beam of the service cell that may have failed; and receiving, in response to the sent request, an indication of uplink resources in a second service cell different from the service cell, for use by the user equipment to send 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 to establish a communication link between the user equipment 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 the communication link may include operations, features, components, or instructions for communicating with the base station via the communication link, identifying a beam failure of the communication link between the user equipment and the serving cell, and determining to establish the communication link between the user equipment 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, sending an indication of the selected first beam in the MAC CE based on the comparison may include operations, features, components, or indications for obtaining the uplink resource for use by the user equipment to send the indication of the first beam; comparing a threshold number of time slots with a number of time slots between the current time and the uplink resource, wherein the threshold includes a threshold number of time slots; determining the availability of the uplink resource based on the number of time slots between the current time and the uplink resource being less than the threshold number of time slots; and sending the indication of the selected first beam in the MAC CE based on the determined availability indicating that the number of time slots between the current time and the uplink resource is less than the threshold number of time slots.

[0016] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, sending an indication of the selected first beam in the MAC CE based on the comparison may include operations, features, components, or indications for obtaining the uplink resource for use by the user equipment to send the indication of the first beam; comparing a threshold number of time slots with a number of time slots between the current time and the uplink resource, wherein the threshold includes a threshold number of time slots; determining the availability of the uplink resource based on the number of time slots between the current time and the uplink resource being less than the threshold number of time slots; sending a request for the uplink resource to the base station based on the determined availability indicating that the number of time slots between the current time and the uplink resource is greater than the threshold number of time slots; receiving an indication of the uplink resource in response to the sent request; and sending an indication of the selected first beam in the MAC CE on the indicated uplink resource.

[0017] Some examples of the methods, apparatuses, and non-transitory computer-readable media described herein may further include operations, features, components, or instructions for receiving a configuration for beam failure recovery and sending a request for the uplink resource based on the received configuration.

[0018] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, sending a request for the uplink resource to the base station may include operations, features, components, or instructions for sending a scheduling request sequence indicating the request to the base station.

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

[0020] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, sending the indication of the selected first beam may include operations, features, components, or instructions for sending the MAC CE to the base station in a RACH message of a RACH procedure.

[0021] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, components, or instructions for determining that a second beam among the multiple candidate beams is available to send an indication of the first beam at least a threshold earlier than availability of the uplink resource, wherein the uplink resource includes the first beam, and based on determining that the second beam is available, sending an indication of the selected first beam in a MAC on the second beam.

[0022] In some examples of the methods, apparatus, and non-transitory computer-readable media described herein, an indication of the selected first beam is sent 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, the indication of the selected first beam is sent on the 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, components, or instructions for performing a logical channel prioritization process for a MAC protocol data unit (PDU) including the MAC CE, wherein the logical channel prioritization process provides a priority to the MAC CE that is greater than each other MAC CE of the MAC PDU, greater than data of the MAC PDU, and less than information of a common control channel (CCCH) message of the MAC PDU.

[0025] Some examples of the methods, apparatus, and non-transitory computer-readable media described herein may further include operations, features, components, or instructions for starting a timer and a counter based on determining that the communication link is established; incrementing the counter based on sending an indication of the selected first beam; and resending the indication of the selected first beam in the MAC CE based on the timer expiring before receiving a message on the selected first beam and the counter being below a counter threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 An example of a wireless communication system supporting a medium access control (MAC) procedure for beam index indication according to aspects of the present disclosure is shown.

[0027] Figure 2 An example of a wireless communication system supporting a MAC procedure for beam index indication according to aspects of the present disclosure is shown.

[0028] Figure 3 、 Figure 4 and Figure 5 An example of a process flow of a MAC procedure supporting beam index indication according to aspects of the present disclosure is shown.

[0029] Figure 6 and Figure 7 A block diagram of a device supporting a MAC procedure for beam index indication according to aspects of the present disclosure is shown.

[0030] Figure 8 A block diagram of a communication manager supporting a MAC process for beam index indication according to aspects of the present disclosure is shown.

[0031] Figure 9 A diagram of a system including devices supporting a MAC procedure for beam index indication is shown in accordance with aspects of the present disclosure.

[0032] Figures 10 to 12 A flow chart illustrating a method of a MAC process supporting beam index indication according to aspects of the present disclosure is shown. DETAILED DESCRIPTION

[0033] 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, when determining to establish a communication link with a base station, the user equipment may identify a preferred beam (e.g., the first beam in a set of beams) for establishing 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, where the base station may use the set of possible beams to send a downlink signal to the user equipment. Subsequently, the user equipment may send an indication of the preferred beam to the base station on a media access control (MAC) control element (CE). Accordingly, the base station may then use the preferred beam to send subsequent downlink messages to the user equipment.

[0034] In some cases, the user equipment may determine to establish a communication link with the base station based on identifying a beam failure that previously occurred on at least one cell (e.g., a secondary cell (SCell)), wherein the preferred beam is used for a beam failure recovery process. Additionally or alternatively, the user equipment may determine to establish an initial connection with the base station or re-establish communication with the base station on another cell (e.g., a primary cell (PCell), a primary SCell (PSCell), a secondary PCell (SPCell), etc.), and the preferred beam may be used for a random access channel (RACH) process. When performing the RACH process, the user equipment may send an indication of the preferred beam to the base station in one of the messages of the RACH process (e.g., the first message in a two-step RACH process, the connection request / third message in a four-step RACH process, etc.).

[0035] In addition, the user equipment may send an indication of the preferred beam to the base station based on a comparison of the availability of uplink resources with a threshold. For example, if the uplink resource is scheduled and available within N time slots (e.g., or N transmission time intervals (TTIs) of different lengths), where N is a positive integer, then after the user equipment determines to establish the communication link and identifies the preferred beam, the user equipment may multiplex the indication with the MAC protocol data unit (PDU) sent on the uplink resource. Alternatively, if the uplink resource is not available, the user equipment may request additional uplink resources (e.g., based on the configured uplink channel resources, via a scheduling request, etc.) to send an indication of the preferred beam.

[0036] Various aspects of the present disclosure are initially described in the context of a wireless communication system. Furthermore, various aspects of the present disclosure are illustrated by additional wireless communication system and process flow examples. Various aspects of the present disclosure are further illustrated and described with reference to apparatus diagrams, system diagrams, and flow charts related to a MAC process for beam index indication.

[0037] Figure 1 An example of a wireless communication system 100 that supports a MAC procedure for beam index indication according to aspects of the present disclosure is shown. The wireless communication system 100 includes a base station 105, a user equipment 115, and a core network 130. In some examples, the wireless communication system 100 can be a long-term evolution network (LTE), an LTE-Advanced (LTE-A), an LTE-A Pro network, or a new radio (NR) network. In some cases, the wireless communication system 100 can support enhanced broadband communication, ultra-reliable (e.g., mission-critical) communication, low-latency communication, or communication with low-cost and low-complexity devices.

[0038] The base station 105 can communicate wirelessly with the user equipment 115 via one or more base station antennas. The base station 105 described herein may include or may be referred to by those skilled in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB), a next-generation NodeB or a gigabit NodeB (either of which may be referred to as a gNB), a home NodeB, a home eNodeB, 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 user equipment 115 described herein is capable of communicating with various types of base stations 105 and network infrastructure, including macro NBs, small cell eNBs, gNBs, relay base stations, etc.

[0039] Each base station 105 can be associated with a particular geographic coverage area 110 in which communications with various user devices 115 are supported. Each base station 105 can provide communication coverage for the corresponding geographic coverage area 110 via a communication link 125, and the communication link 125 between the base station 105 and the user device 115 can utilize one or more carriers. The communication link 125 shown in the wireless communication system 100 can include uplink transmissions from the user device 115 to the base station 105, or downlink transmissions from the base station 105 to the user device 115. Downlink transmissions can also be referred to as forward link transmissions, while uplink transmissions can also be referred to as reverse link transmissions.

[0040] The geographic coverage area 110 of the base station 105 can be divided into sectors that constitute a portion of the geographic coverage area 110, and each sector can be associated with a cell. For example, each base station 105 can provide communication coverage for a macro cell, a small cell, a hotspot, or other types of cells, or various combinations thereof. In some examples, the base station 105 can be mobile, thereby providing communication coverage for a mobile geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies can overlap, and overlapping geographic coverage areas 110 associated with different technologies can be supported by the same base station 105 or different base stations 105. The wireless communication system 100 may include, for example, a heterogeneous LTE / LTE-A / LTE-A Pro or NR network, in which different types of base stations 105 provide coverage for various geographic coverage areas 110.

[0041] The term "cell" refers to a logical communication entity used to communicate with base station 105 (e.g., via a carrier), and can be associated with an identifier (e.g., a physical cell identifier (PCID), a virtual cell identifier (VCID)) used to distinguish between adjacent cells operating via the same or different carriers. In some examples, a carrier can support multiple cells, and different cells can be configured according to different protocol types that can provide access to different types of devices (e.g., machine type communication (MTC), narrowband Internet of Things (NB-IoT), enhanced mobile broadband (eMBB), or other). In some cases, the term "cell" can refer to a portion of the geographic coverage area 110 (e.g., a sector) on which the logical entity operates.

[0042] The user devices 115 may be dispersed throughout the wireless communication system 100, and each user device 115 may be stationary or mobile. The user devices 115 may also be referred to as mobile devices, wireless devices, remote devices, handheld devices, or subscriber user devices, or some other suitable terminology, where "device" may also be referred to as a unit, station, terminal, or client. The user device 115 may be a personal electronic device, such as a cellular phone, a personal digital assistant (PDA), a tablet computer, a laptop computer, or a personal computer. In some examples, the user device 115 may also refer to a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or an MTC device, which may be implemented in various items such as appliances, vehicles, meters, and the like.

[0043] Some user devices 115, such as MTC or IoT devices, may be low-cost or low-complexity devices and may provide automated communication between machines (e.g., via machine-to-machine (M2M) communication). M2M communication or MTC may refer to data communication technology that allows devices to communicate with each other or with base station 105 without human intervention. In some examples, M2M communication or MTC may include communication from a device integrated with a sensor or meter to measure or capture information and relay that information to a central server or application, which may utilize or present the information to a person interacting with the program or application. Some user devices 115 may be designed to collect information or enable automated behavior of a machine. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, facility monitoring, healthcare monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based service charging.

[0044] Some user devices 115 can be configured to employ a reduced power consumption mode of operation, such as half-duplex communication (e.g., a mode that supports one-way communication via transmission or reception but does not support simultaneous transmission and reception). In some examples, half-duplex communication can be performed at a reduced peak rate. Other energy-saving techniques for user devices 115 include entering an energy-saving "deep sleep" mode when not engaged in active communications, or operating on a limited bandwidth (e.g., based on narrowband communication). In some cases, user devices 115 can be designed to support critical functions (e.g., mission-critical functions), and the wireless communication system 100 can be configured to provide ultra-reliable communication for these functions.

[0045] In some cases, user equipment 115 may also be able to communicate directly with other user equipment 115 (e.g., using a peer-to-peer (P2P) or device-to-device (D2D) protocol). One or more of a group of user equipment 115 utilizing D2D communication may be within the geographic coverage area 110 of base station 105. Other user equipment 115 in such a group may be outside the geographic coverage area 110 of base station 105 or unable to receive transmissions from base station 105. In some cases, multiple groups of user equipment 115 communicating via D2D communication may utilize a one-to-many (1:M) system, in which each user equipment 115 transmits to every other user equipment 115 in the group. In some cases, base station 105 facilitates resource scheduling for D2D communication. In other cases, D2D communication is performed between user equipment 115 without the involvement of base station 105.

[0046] The base stations 105 can communicate with the core network 130 and with each other. For example, the base stations 105 can interface with the core network 130 via a backhaul link 132 (e.g., via an S1, N2, N3, or other interface). The base stations 105 can communicate with each other directly (e.g., directly between the base stations 105) or indirectly (e.g., via the core network 130) via a backhaul link 134 (e.g., via an X2, Xn, or other interface).

[0047] The core network 130 may provide user authentication, access permission, 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, permission, and bearer management for user equipment 115 served by base stations 105 associated with the EPC. User IP packets may be sent through the S-GW, which itself may be connected to the P-GW. The P-GW may provide IP address allocation and other functions. The P-GW may be connected to the network operator's IP services. The P-GW operator's IP services may include access to the Internet, intranet, IP multimedia subsystem (IMS), or packet switched (PS) streaming services.

[0048] At least some network devices, such as 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 user equipment 115 through multiple other access network transmission entities, which may be referred to as radio heads, smart radio heads, or transmit / receive points (TRPs). 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 consolidated into a single network device (e.g., base station 105).

[0049] The wireless communication system 100 can operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz). Typically, the region from 300 MHz to 3 GHz is referred to as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately 1 decimeter to 1 meter long. UHF waves may be blocked or redirected by buildings and environmental features. However, the waves can penetrate structures enough to enable a macrocell to provide service to user devices 115 located indoors. Transmissions using UHF waves may be associated with smaller antennas and shorter distances (e.g., less than 100 kilometers) compared to transmissions using smaller frequencies and longer waves in the high frequency (HF) portion or very high frequency (VHF) portion of the spectrum below 300 MHz.

[0050] The wireless communication system 100 may also operate in the Super High Frequency (SHF) region using a frequency band from 3 GHz to 30 GHz (also known as the centimeter wave band). The SHF region includes frequency bands such as the 5 GHz Industrial, Scientific, and Medical (ISM) band, which may be used by devices that can tolerate interference from other users.

[0051] The wireless communication system 100 can also operate in the extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz), which is also referred to as the millimeter wave band. In some examples, the wireless communication system 100 can support millimeter wave (mmW) communications between user equipment 115 and base station 105, and the EHF antennas of the corresponding devices can be smaller and more closely spaced than UHF antennas. In some cases, this can facilitate the use of antenna arrays within the user equipment 115. However, the propagation of EHF transmissions may be more susceptible to greater atmospheric attenuation and shorter distances than SHF or UHF transmissions. The technology disclosed herein can be used in transmissions using one or more different frequency regions, and the designated use of frequency bands on these frequency regions may vary by country or regulatory agency.

[0052] In some cases, the wireless communication system 100 can utilize licensed and unlicensed radio frequency spectrum bands. For example, the wireless communication system 100 can employ license assisted access (LAA), unlicensed LTE (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 base stations 105 and user equipment 115 can employ a listen-before-talk (LBT) process to ensure that the frequency channel is clear before sending data. In some cases, operations in the unlicensed band can be based on carrier aggregation configuration and component carriers operating in a licensed band (e.g., LAA). Operations in the unlicensed spectrum can include downlink transmissions, uplink transmissions, peer-to-peer transmissions, or a combination of these. Duplexing in the unlicensed spectrum can be based on frequency division duplexing (FDD), time division duplexing (TDD), or a combination of both.

[0053] In some examples, the base station 105 or user device 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communication, or beamforming. For example, the wireless communication system 100 may employ a transmission scheme between a transmitting device (e.g., base station 105) and a receiving device (e.g., user device 115), wherein the transmitting device is equipped with multiple antennas and the receiving device is equipped with one or more antennas. MIMO communication may utilize multipath signal propagation to improve spectral efficiency by transmitting or receiving multiple signals via different spatial layers, which may be referred to as spatial multiplexing. For example, the multiple signals may be transmitted by the transmitting device via different antennas or different antenna combinations. Similarly, the receiving device may receive the multiple signals via different antennas or different antenna combinations. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams. Different spatial layers may be associated with different antenna ports for channel measurement and reporting. MIMO technology includes 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.

[0054] Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a 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 device and the receiving device. Beamforming may be achieved by combining signals transmitted via antenna elements of an antenna array so that signals propagating in a particular direction relative to the antenna array experience constructive interference, while other signals experience destructive interference. Adjustments to the signals transmitted via the antenna elements may include the transmitting device or the receiving device applying a particular amplitude and phase offset to the signals carried via each antenna element associated with the device. The adjustments associated with each antenna element may be defined by a set of beamforming weights associated with a particular direction (e.g., relative to the antenna array of the transmitting device or the receiving device, or relative to some other direction).

[0055] In one example, the base station 105 can use multiple antennas or antenna arrays to perform beamforming operations for directional communication with the user equipment 115. For example, some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) can be transmitted multiple times by the base station 105 in different directions, which can include transmitting signals according to different sets of beamforming weights associated with the different transmitted directions. The transmissions in different beam directions can be used to identify (e.g., by the base station 105 or a receiving device, such as the user equipment 115) a beam direction for subsequent transmission and / or reception by the base station 105.

[0056] 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 the receiving device, e.g., user device 115). In some examples, the beam direction associated with transmission along a single beam direction may be determined based at least in part on signals transmitted in different beam directions. For example, the user device 115 may receive one or more signals transmitted by the base station 105 in different directions, and the user device 115 may report to the base station 105 an indication of the highest signal quality or other acceptable signal quality signal received. Although these techniques are described with reference to signals transmitted by the base station 105 in one or more directions, the user device 115 may employ similar techniques to transmit signals multiple times in different directions (e.g., to identify a beam direction that the user device 115 subsequently transmits or receives), or to transmit signals in a single direction (e.g., to transmit data to a receiving device).

[0057] When receiving various signals, such as synchronization signals, reference signals, beam selection signals, or other control signals, from the base station 105, a receiving device (e.g., user equipment 115, which may be an example of a millimeter wave receiving device) may try multiple receive beams. For example, the receiving device may try 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 group 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 group of antenna elements of an antenna array. These may all be referred to as "listening" according to 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 data signals). The single receive beam may be aligned on a beam direction determined at least in part based on listening according to different receive beam directions (e.g., a beam direction determined to have the highest signal strength, the highest signal-to-noise ratio, or an acceptable signal quality based at least in part on listening according to multiple beam directions).

[0058] In some cases, the antennas of a base station 105 or a user device 115 may be located within one or more antenna arrays that may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some cases, the antennas or antenna arrays associated with a base station 105 may be located at different geographic locations. A base station 105 may have an antenna array with multiple rows and columns of antenna ports that the base station 105 may use to support beamforming for communications with a user device 115. Similarly, a user device 115 may have one or more antenna arrays that may support various MIMO or beamforming operations.

[0059] In some cases, the wireless communication system 100 can be a packet-based network operating according to a layered protocol stack. In the user plane, the communication at the bearer layer or the packet data convergence protocol (PDCP) layer can be IP-based. The radio link control (RLC) layer can perform packet segmentation and reassembly to communicate on the logical channel. The MAC layer can perform priority processing and multiplex the logical channels into transmission channels. The MAC layer can also use hybrid automatic repeat request (HARQ) to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the radio resource control (RRC) protocol layer can provide the establishment, configuration and maintenance of the RRC connection between the user equipment 115 and the base station 105 or the core network 130 supporting the radio bearer of the user plane data. At the physical layer, the transport channel can be mapped to the physical channel.

[0060] In some cases, the user equipment 115 and the base station 105 can support the retransmission of data to increase the possibility of successfully receiving the data. HARQ feedback is a technology that increases the possibility of correctly receiving data through 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 can improve the throughput at the MAC layer under poor radio conditions (e.g., signal-to-noise ratio conditions). In some cases, a wireless device can support simultaneous slot HARQ feedback, wherein the device can provide HARQ feedback for data received in the previous symbol in a specific time slot in the time slot. In other cases, the device can provide HARQ feedback in a subsequent time slot or according to other time intervals.

[0061] The time interval in LTE or NR can be expressed as a multiple of a basic time unit, which can be, for example, T s = a sampling period of 1 / 30,720,000 seconds. The time intervals of the communication resources may be organized according to radio frames, wherein each radio frame has a duration of 10 milliseconds (ms), wherein the frame period may be expressed as Tf=307,200Ts. The radio frame may be identified by a system frame number (SFN) ranging from 0 to 1023. Each frame may include 10 subframes numbered from 0 to 9, and each subframe may have a duration of 1 ms. The subframe may be further divided into 2 time slots, wherein each time slot has a duration of 0.5 ms, and each time slot may contain 6 or 7 modulation symbol periods (e.g., depending on the length of the cyclic prefix pre-added to each symbol period). Excluding the cyclic prefix, each symbol period may contain 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 transmit time interval (TTI). In other cases, the minimum scheduling unit of the wireless communication system 100 may be shorter than a subframe, or may be dynamically selected (e.g., in a burst of shortened TTI (sTTI), or in a selected component carrier using sTTI).

[0062] In some wireless communication systems, a time slot can also be divided into multiple mini-slots containing one or more symbols. In some cases, a symbol of a mini-slot or a mini-slot can be the smallest scheduling unit. For example, the duration of each symbol can vary depending on the subcarrier spacing or the frequency band of operation. In addition, some wireless communication systems can implement time slot aggregation, in which multiple time slots or mini-slots are aggregated together and used for communication between user equipment 115 and base station 105.

[0063] The term "carrier" refers to a collection of radio frequency spectrum resources with a defined physical layer structure for supporting communications on the communication link 125. For example, a carrier of the communication link 125 may include a portion of a radio frequency spectrum band that operates according to the physical layer channels of 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 located according to a channel grid for discovery by user equipment 115. A carrier may be downlink or uplink (e.g., in FDD mode) or configured to carry both downlink and uplink communications (e.g., in TDD mode). In some examples, a signal waveform transmitted via 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).

[0064] The organization structure of the carrier may be different for different radio access technologies (e.g., LTE, LTE-A, LTE-A Pro, NR). For example, communications on a carrier may be organized according to TTIs or time slots, each of which may include user data and 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 to coordinate the operation of the carrier. In some examples (e.g., in a carrier aggregation configuration), a carrier may also have acquisition signaling or control signaling to coordinate the operation of other carriers.

[0065] Physical channels may be multiplexed on a carrier according to various techniques. Physical control channels and physical data channels may be multiplexed on a downlink carrier, for example using time division multiplexing (TDM), frequency division multiplexing (FDM), or a hybrid TDM-FDM technique. In some examples, control information sent in a physical control channel may be distributed in a concatenated manner between different control regions (e.g., between a common control region or common search space and one or more user equipment-specific control regions or user equipment-specific search spaces).

[0066] A carrier can be associated with a particular bandwidth of the radio frequency spectrum, and in some examples, the carrier bandwidth can be referred to as the "system bandwidth" of the carrier or the wireless communication system 100. For example, the carrier bandwidth can be one of a plurality of predetermined bandwidths of a carrier for a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 MHz). In some examples, each served user device 115 can be configured to operate on part or all of the carrier bandwidth. In other examples, some user devices 115 can be configured to operate using a narrowband protocol type associated with a predetermined portion or range (e.g., a set of subcarriers or RBs) within a carrier (e.g., an "in-band" deployment of a narrowband protocol type).

[0067] In a system using MCM technology, a resource element may consist of a symbol period (e.g., the duration of a modulation symbol) and a subcarrier, where the symbol period and the 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). Therefore, the more resource elements received by the user equipment 115 and the higher the order of the modulation scheme, the higher the data rate of the user equipment 115 may be. 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), and the use of multiple spatial layers may further increase the data rate of communication with the user equipment 115.

[0068] The devices of the wireless communication system 100 (e.g., base station 105 or user equipment 115) may have a hardware configuration that supports communication on a specific carrier bandwidth, or may be configured to support communication on one of a group of carrier bandwidths. In some examples, the wireless communication system 100 may include a base station 105 and / or user equipment 115 that supports simultaneous communication via carriers associated with more than one different carrier bandwidth.

[0069] The wireless communication system 100 may support communication with user equipment 115 on multiple cells or carriers, a feature that may be referred to as carrier aggregation or multi-carrier operation. Depending on the carrier aggregation configuration, the user equipment 115 may be configured with multiple downlink component carriers and one or more uplink component carriers. Carrier aggregation may be used with both FDD and TDD component carriers.

[0070] In some cases, the wireless communication system 100 can utilize an enhanced component carrier (eCC). An eCC has one or more characteristics, 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 can 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 can also be configured for unlicensed spectrum or shared spectrum (e.g., where more than one operator is allowed to use the spectrum). An eCC characterized by a wide carrier bandwidth can include one or more segments that can be used by user equipment 115 that cannot monitor the entire carrier bandwidth or is configured to use a limited carrier bandwidth (e.g., for energy conservation).

[0071] In some cases, an eCC may utilize a different symbol duration than other component carriers, which may include using a reduced symbol duration compared to the symbol duration of other component carriers. The shorter symbol duration may be associated with an increased spacing between adjacent subcarriers. A device utilizing an eCC, such as user equipment 115 or base station 105, 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 in a TTI) may be variable.

[0072] The wireless communication system 100 may be an NR system that may utilize any combination of licensed, shared, and unlicensed spectrum bands. The flexibility of eCC symbol duration and subcarrier spacing may allow the use of eCC on multiple spectrums. In some examples, NR shared spectrum may improve spectrum utilization and spectrum efficiency, particularly through dynamic vertical (e.g., across frequency domains) and horizontal (e.g., across time domains) sharing of resources.

[0073] A user device 115 attempting to access a wireless network may perform an initial cell search by detecting a primary synchronization signal (PSS) from the base station 105. The PSS may synchronize time slot timing and may indicate a physical layer identity value. The user device 115 may then receive a secondary synchronization signal (SSS). The SSS may synchronize radio frames and provide a cell identification value that may be combined with the physical layer identification value to identify the cell. The SSS may also enable detection of duplex mode and cyclic prefix length. Some systems, such as TDD systems, may transmit an SSS but not a PSS. The PSS and the SSS may be located in the center 62 and 72 subcarriers of a carrier, respectively. In some cases, the base station 105 may use multiple beams to transmit synchronization signals (e.g., PSS, SSS, etc.) in a beam scanning manner across the cell coverage area. In some cases, the PSS, SSS, and / or broadcast information (e.g., physical broadcast channel (PBCH)) may be transmitted in different synchronization signal (SS) blocks on respective directional beams, wherein one or more SS blocks may be included in an SS burst.

[0074] After receiving the PSS and SSS, the user equipment 115 may receive a master information block (MIB), which may be sent in the PBCH. The MIB may include system bandwidth information, SFN, and physical HARQ indicator channel (PHICH) configuration. After decoding the MIB, the user equipment 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 user equipment 115 to receive SIB2. SIB2 may include RRC configuration information related to RACH procedures, paging, PUCCH, PUSCH, power control, SRS, and cell barring.

[0075] After completing the initial cell synchronization, the user equipment 115 can decode the MIB, SIB1 and SIB2 before accessing the network. The MIB can be sent on the PBCH and can use the first 4 OFDMA symbols of the second time slot of the first subframe of each radio frame. The MIB can use the middle 6 RBs (72 subcarriers) in the frequency domain. The MIB carries some important information for the initial access of the user equipment, including the downlink channel bandwidth for the RB, PHICH configuration (duration and resource allocation) and SFN. The new MIB can be broadcast once every four radio frames (SFN mod 4 = 0) and replayed once every frame (10ms). Each repetition is scrambled with a different scrambling code.

[0076] After reading the MIB (new version or copy), the user equipment 115 can try different phases of the scrambling code until it obtains a successful CRC check. The phase of the scrambling code (0, 1, 2 or 3) enables the user equipment 115 to identify which of the four repetitions has been received. Therefore, the user equipment 115 can determine the current SFN by reading the SFN in the decoded transmission and adding the scrambling code phase. After receiving the MIB, the user equipment can receive one or more SIBs. Different SIBs can be defined depending on the type of system information transmitted. A new SIB1 can be sent in the fifth subframe of every eight frames (SFN mod 8=0) and rebroadcast every other frame (20ms). SIB1 includes access information, including cell identity information, and it can indicate whether the user equipment is allowed to camp on the cell. SIB1 also includes cell selection information (or cell selection parameters). In addition, SIB1 includes scheduling information for other SIBs. SIB2 can be dynamically scheduled based on the information in SIB1, and SIB2 includes access information and parameters related to shared channels. The period of SIB2 can be set to 8, 16, 32, 64, 128, 256 or 512 radio frames.

[0077] After the user equipment 115 decodes SIB2, it may send a RACH preamble (e.g., message 1 (Msg1) in a four-step RACH process) 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 user equipments 115 attempting to access the system simultaneously. The base station 105 may respond with a random access response (e.g., a second message (Msg2)) that provides an uplink resource grant, a timing advance, and a temporary cell radio network temporary identifier (C-RNTI). The user equipment 115 may then send an RRC connection request (e.g., a third message (Mg3)) along with a temporary mobile subscriber identity (TMSI) (if the user equipment 115 has previously connected to the same wireless network) or a random identifier. The RRC connection request may also indicate the reason why the user equipment 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)) addressed to the user equipment 115, which may provide a new C-RNTI. If the user equipment 115 receives the contention resolution message with the correct identifier, the user equipment 115 may proceed with the RRC setup. If the user equipment 115 does not receive the contention resolution message (e.g., if there is a collision with another user equipment 115), it may repeat the RACH procedure by sending a new RACH preamble. This exchange of messages for random access between the user equipment 115 and the base station 105 may be referred to as a four-step RACH procedure.

[0078] In other examples, a two-step RACH procedure can be performed for random access. For example, a wireless device operating in a licensed or unlicensed spectrum within the wireless communication system 100 can initiate a two-step RACH procedure to reduce the 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 can operate regardless of whether the wireless device (e.g., user equipment 115) has a valid timing advance (TA). For example, the user equipment 115 can use a valid TA to coordinate the timing of its transmissions to the base station 105 (e.g., to account for propagation delays) and can receive the valid TA as part of the two-step RACH procedure. In addition, the two-step RACH procedure can be applicable to any cell size and can work regardless of whether the RACH procedure is contention-based or contention-free, and can combine multiple RACH messages from a four-step RACH procedure. For example, the two-step RACH process may include a first message (e.g., message A (MsgA)) and a second message (e.g., message B (MsgB), wherein the first message combines Msg1 and Msg3 in the four-step RACH process, and the second message combines Msg2 and Msg4 in the four-step RACH process.

[0079] The two-step RACH procedure can be applicable to any cell size supported in the wireless communication system, can operate regardless of whether the user equipment 115 has a valid timing advance (TA), and can be applied to any RRC state of the user equipment 115 (e.g., idle state (RRC_IDLE), inactive state (RRC_INACTIVE), connected state (RRC_CONNECTED), etc.). In some cases, the two-step RACH procedure can reduce signaling overhead and latency, increase RACH capacity, save power of the user equipment 115, and provide synergy with other applications (e.g., positioning, mobility enhancement, etc.).

[0080] In some cases, for a base station 105 (e.g., a serving cell), a first set of periodic channel state information (CSI) reference signal (CSI-RS) resource configuration indices (q0) may be provided to a user equipment 115 via a first higher layer parameter (e.g., failureDetectionResources), and a second set of periodic CSI-RS resource configuration indices and / or SS / PBCH block indices (q1) may be provided to the user equipment 115 via a second higher layer parameter (e.g., candidateBeamRSList) for radio link quality measurement of the base station 105. Additionally or alternatively, if the first higher layer parameter is not provided to the user equipment 115, the user equipment 115 may determine that the set q0 includes an SS / PBCH block index and a periodic CSI-RS resource configuration index having the same value as a reference signal index in the reference signal set, the reference signal set being indicated by the transmit configuration indicator (TCI) state of the respective control resource set (CORESET) that the user equipment 115 uses to monitor a downlink channel (e.g., a physical downlink control channel (PDCCH)). The user equipment 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 a reference signal index having a quasi-co-location (QCL type)-Type D configuration for the corresponding TCI state. In addition, the user equipment 115 may expect a single-port reference signal in the set q0.

[0081] Based on the set q0, the user equipment 115 may monitor the reference signal sets within the set q0 for beam failure detection as part of a beam failure recovery process to improve robustness of communications with the base station 105. For the beam failure recovery process, the user equipment 115 may detect the beam failure, identify a new candidate beam, send a beam failure recovery request to the base station 105, and monitor a response to the beam failure recovery response from the base station 105. Thus, as part of detecting the beam failure, the user equipment 115 may monitor a maximum set of reference signals belonging to the set q0. In some cases, the maximum number of reference signal sets may be two (2), although a greater number of reference signal sets may be used. As described above, the user equipment 115 may determine the set q0 based on the reference signals used to monitor the active core set (e.g., the reference signal set used by the user equipment 115 to monitor the TCI status indication of each core set of the PDCCH). In some cases, the user equipment 115 may perform a RACH procedure (e.g., contention-based random access (CBRA), four-step RACH, two-step RACH, etc.) as part of the beam failure recovery procedure to reestablish a connection with the base station 105.

[0082] In some wireless communications, the base station 105 (e.g., the network) may configure a MAC CE for the user equipment 115 to report a new preferred beam after a beam failure is triggered on an SCell cell. For example, this new MAC CE may include the index of the SCell cell where the beam failure is triggered and the index of the new preferred beam for the SCell cell. In some cases, this new MAC CE may be referred to as a beam index indication MAC CE. However, conventionally, the user equipment may not know which uplink resource to use to send the beam index indication, and / or may not fully utilize the beam index indication of a subset of the process.

[0083] The wireless communication system 100 can support an efficient technique for transmitting a beam index indication of a new preferred beam on an uplink resource based on the availability of the uplink resource and for transmitting the beam index indication for different communication establishment scenarios. For example, if the uplink resource is scheduled and available within N time slots after the user equipment 115 determines to establish the communication link and identifies the new preferred beam, the user equipment 115 can multiplex the beam index indication with the MAC PDU transmitted on the uplink resource. Alternatively, if the uplink resource is not available, the user equipment 115 can request additional uplink resources (e.g., based on configured uplink channel resources, via a scheduling request, etc.) to transmit the beam index indication. In addition, the user equipment 115 can transmit the beam index indication for the beam failure recovery process as described above and the RACH process for establishing communication with at least one cell of the base station 105. Therefore, the user equipment 115 may send the beam index indication in a message of 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).

[0084] Figure 2 An example of a wireless communication system 200 that supports a MAC process for beam index indication according to aspects of the present disclosure is shown. In some examples, the wireless communication system 200 can implement aspects of the wireless communication system 100. The wireless communication system 200 can include a base station 105-a and a user equipment 115-a, which can be examples of corresponding base stations 105 and user equipment 115, respectively, as described above with reference to FIG. Figure 1 As described herein, the base station 105-a and the user equipment 115-a may communicate with each other using beamforming techniques. For example, the base station 105-a may use one or more beams 205 to send downlink signals to the user equipment 115-a and / or receive uplink signals from the user equipment 115-a. In addition, the user equipment 115-a may use one or more beams 210 to send uplink signals to the base station 105-a and / or receive downlink signals from the base station 105-a. In some cases, the user equipment 115-a may communicate with the base station 105-a via one or more cells (e.g., PCell, SCell, PSCell, SPCell, etc.) on the base station 105-a.

[0085] In some cases, user equipment 115-a may identify a beam failure triggered on a cell (e.g., an SCell) of base station 105-a. User equipment 115-a may then measure the link quality of one or more candidate beams that are configured for the cell in which the beam failure is detected. For example, user equipment 115-a may measure the link quality of each of beams 205-a, 205-b, and 205-c transmitted by base station 105-a (e.g., by measuring a reference signal on each beam 205). In some cases, if the measurement is not readily available (e.g., if user equipment 115-a has not recently measured or has never measured the link quality), user equipment 115-a may perform the link quality measurement.

[0086] Thus, once the measurement is available, a beam indication 215 (e.g., a beam index indication) may be triggered. That is, the user equipment 115-a may select a beam 205 transmitted by the base station 105-a based on the link quality measurement, which beam 205 is preferred for subsequent downlink transmission (e.g., a beam failure recovery procedure). For example, the user equipment 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., the strongest received signal, the least amount of interference, etc.) compared to beam 205-a and beam 205-c. After the beam indication 215 (e.g., indicating beam 205-b) is triggered, a MAC CE (e.g., a beam index indication MAC CE) for carrying the beam indication 215 is generated to send the MAC CE carrying the beam indication 215 to the base station 105-a (e.g., the network) when uplink resources become available.

[0087] Thus, if there are upcoming uplink resources scheduled within N time slots in the future (e.g., or another length of TTI), the user equipment 115-a can multiplex the MAC CE carrying the beam indication 215 in the MAC PDU, and the beam indication 215 will be sent over the uplink resource. In some cases, it can be configured by the base station 105-a (e.g., via RRC signaling) or defined (e.g., pre-defined for the base station 105-a and the user equipment 115-a). In addition, the uplink resource can be a dynamic grant or a configured grant. Subsequently, the user equipment 115-a can send the beam indication 215 to the base station 105-a on the uplink resource (e.g., based on multiplexing the MAC CE carrying the beam indication 215 in the MAC PDU).

[0088] In addition or alternatively, if no uplink resources are readily available, or the uplink resources appear too late to signal the MAC CE carrying the beam indication 215 (e.g., low latency may be required to recover a failed beam and perform the beam recovery procedure), the user equipment 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 recovery procedure. Thus, when the beam indication 215 is triggered, the user equipment 115-a may use at least one valid opportunity of the dedicated uplink channel resources to direct (e.g., request) the base station 105-a to signal new uplink resources on the physical layer (e.g., to use new uplink resources to send the MAC CE carrying the beam indication 215). The signal (e.g., the signal of the new uplink resources) may be a known symbol sequence configured for the user equipment 115-a (e.g., or a TTI of different lengths).

[0089] Additionally or alternatively, instead of using the dedicated uplink channel, the user equipment 115-a may send a scheduling request sequence (e.g., initiate a scheduling request) via an uplink channel resource (e.g., a PUCCH resource) that is configured for scheduling requests to request uplink resources to send an indication of the selected first beam to the base station 105-a. In some cases, the scheduling request may be used by the user equipment 115-a to signal the arrival of new data, and the base station 105-a may then provide uplink resources for the new data. In addition, 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, in order to enable a failed beam to be quickly restored (e.g., a faster beam failure recovery process), the scheduling request for the MAC CE carrying the beam indication 215 may be sent via the uplink channel resource that is allocated to the data logical channel with the highest priority configured for the user equipment 115-a. In some cases, the user equipment 115-a may request the uplink resources for transmitting the beam indication 215 based on performing a RACH procedure. For example, after experiencing a beam failure on a cell (e.g., a serving cell, SCell, PCell, SPCell, PSCell, etc.), the user equipment 115-a may perform a RACH procedure to reconnect to the cell. As part of the RACH procedure, or once the RACH procedure is complete, the user equipment 115-a may request uplink resources from the cell, where the uplink resources may be used to transmit the beam indication 215.

[0090] When sending the scheduling request to request uplink resources for sending the beam indication 215 (e.g., the beam indication 215 of the selected first beam), the user equipment 115-a may send a one-bit indication to the base station 105-a (e.g., the network) to indicate that uplink resources are requested. In addition, the base station 105-a may configure multiple scheduling request configurations for the user equipment 115-a to send the scheduling request, so that the user equipment 115-a can send the scheduling request via uplink resources (e.g., PUCCH resources) in different scheduling request configurations. For example, the user equipment 115-a may use one of the different scheduling request configurations based on the priority of the data that triggered the scheduling request, wherein the mapping of the priorities of the different data to the different scheduling request configurations (e.g., an indication of which scheduling request configuration can be used for the priority of each data) is configured by the base station 105-a. However, the user equipment 115-a may not be able to indicate which serving cell (e.g., one or more SCells) the user equipment 115-a wants uplink resources from for sending the beam indication 215 (e.g., which serving cells have beams that can support the beam indication 215). For example, because the base station 105-a does not know whether the 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. Therefore, the user equipment 115-a may not receive permission to send the beam failure indication MAC CE (e.g., a MAC CE carrying the beam indication 215) for the uplink resources.

[0091] In some cases, to enable the user equipment 115-a to receive an indication (e.g., a grant) of the uplink resources to be used for transmitting the MAC CE carrying the beam indication 215, the base station 105-a (e.g., the network) may configure a dedicated PUCCH scheduling request configuration for beam failure recovery. Thus, when the user equipment 115-a requests uplink resources for transmitting the MAC CE carrying the beam indication 215 (e.g., the beam failure recovery MAC CE), the user equipment 115-a may transmit the scheduling request on one or more PUCCH resources (e.g., uplink resources) according to the dedicated PUCCH scheduling request configuration. For example, the dedicated PUCCH scheduling request configuration may include an indication of which PUCCH resource (e.g., a time and / or frequency resource in the PUCCH) to transmit the scheduling request.

[0092] Subsequently, when the base station 105-a receives the scheduling request (e.g., sent according to the dedicated PUCCH scheduling request configuration), the base station 105-a can recognize that the scheduling request is triggered by the beam failure recovery procedure. The base station 105-a can then send the downlink message (e.g., DCI) to grant the requested uplink resources for sending the MAC CE carrying the beam indication 215 on a downlink channel (e.g., PDCCH) in the special cell (SpCell) configured for the user equipment 115-a, where the requested uplink resources are also located in the SpCell. In some cases, the SpCell can include a PCell, a PSCell, or an additional cell configured for primary communication of the user equipment 115-a. By sending the indication of the uplink resources (e.g., the grant of the uplink resources) on the SpCell, the user equipment 115-a has a higher probability of being able to receive the indication of the uplink resources, based on the impossibility that all downlink (e.g., PDCCH) beams for the user equipment 115-a in the SpCell and the SCell fail at the same time. However, if the downlink beam in the SpCell fails, the user equipment 115-a can trigger a RACH-based recovery procedure to reestablish communication with the SpCell, and can send a request for the uplink resources to send the MAC CE carrying the beam indication 215 during a corresponding RACH procedure, and then send the MAC CE once the RACH procedure is completed.

[0093] Additionally or alternatively, a dedicated scheduling request configuration cannot be used for the beam failure recovery procedure. Instead, the user equipment 115-a can use a scheduling request configuration that is configured for a conventional scheduling request (e.g., triggered by new data as described above), but use that scheduling request configuration for the purposes 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 can be associated with a different serving cell or cells, where the mapping between serving cells and uplink control resources is one-to-one or many-to-one.

[0094] For example, for one-to-one mapping, the uplink control resources in the first transmission occasion (e.g., the first time slot, which may be time slot 0) may be associated with the first serving cell (e.g., serving cell 0), the uplink control resources in the second time slot (e.g., time slot 1) may be associated with the second serving cell (e.g., serving cell 1), and so on. In some cases, the uplink control resources in a time slot may be associated with multiple serving cells (e.g., the second time slot may be associated with the second serving cell, the third serving cell, and the fourth serving cell). Additionally or alternatively, for many-to-one mapping, the uplink control resources in the first time slot (e.g., time slot 0) may be associated with any serving cell other than the first serving cell, the uplink control resources in the second time slot may be associated with any serving cell other than the second serving cell, and so on. That is, for the many-to-one mapping, the user equipment 115-a can indicate a set of serving cells (for example, excluding the serving cell corresponding to the time slot number) on which the requested uplink resources for sending the MAC CE carrying the beam indication 215 can be allocated.

[0095] 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. Together with the scheduling request, the MAC layer may indicate which SCell(s) need to be avoided in order to receive an indication of the requested uplink resources (e.g., an uplink grant for the uplink resources) and subsequently send the MAC CE carrying the beam indication 215. In some cases, downlink beams (e.g., PDCCH beams) on multiple SCells may have the same QCL relationship (e.g., the signals from the QCL SCells experience similar channel conditions and pass through similar channels, so that the user equipment 115-a may assume that the signals come from the same location), and based on the QCL relationship, the user equipment 115-a may assume that when a beam failure occurs, these SCells may also fail together. When the physical layer receives the scheduling request, the physical layer may send the scheduling request via any valid uplink control resource except the uplink control resource associated with the SCell to be avoided (e.g., as indicated by the mapping scheme described above).

[0096] In some cases, both the SpCell (e.g., pCell, PSCell, etc.) and the SCell may fail (e.g., experience a beam failure), which may affect how the user equipment 115-a performs the beam failure recovery process and sends the beam indication 215 (e.g., for when the SCell fails as described above). For example, if the SpCell beam failure has been triggered and a corresponding RACH-based recovery (e.g., reestablishing communication with the SpCell) has been initiated when the beam failure recovery of the SCell is triggered, the user equipment 115-a may wait for the SpCell beam failure recovery (e.g., via RACH-based recovery) to complete before sending the MAC CE carrying the beam indication 215 for the SCell beam failure recovery. Therefore, the user equipment 115-a may send the MAC CE carrying the beam indication 215 based on the uplink grant provided in the second RACH message (e.g., msg2) of the RACH for the SpCell beam failure recovery.

[0097] Additionally or alternatively, if a beam failure occurs on the SCell before a beam failure occurs on the SpCell, the user equipment 115-a may take different actions. For example, if the user equipment 115-a has already triggered the scheduling request for beam failure recovery of the SCell (e.g., requesting uplink resources to send the MAC CE carrying the beam indication 215) when beam failure recovery of the SpCell is triggered, the user equipment 115-a may first perform RACH-based beam failure recovery for the SpCell, and then may send the MAC CE carrying the beam indication 215 for beam failure recovery of the SCell in the uplink grant provided in the second message (e.g., msg2) of the RACH for beam failure recovery of the SpCell. Additionally or alternatively, if the MAC CE carrying the beam indication 215 for the SCell beam failure recovery has been sent when the SpCell beam failure recovery is triggered, but the base station 105-a has not yet reconfigured the downlink beam for the SpCell, the user equipment 115-a may first perform the SpCell beam failure recovery (e.g., RACH-based recovery) before completing the beam failure recovery of the SCell.

[0098] In some cases, the user equipment 115-a and / or the base station 105-a configure a timer and a counter for the SCell beam failure recovery, and reestablishes the connection with the SCell via the indicated beam (e.g., the selected first beam) by sending the MAC CE carrying the beam indication 215. Therefore, if the base station 105-a does not reconfigure the downlink beam for the failed SCell before the configured timer expires, the user equipment 115-a may send the MAC CE carrying the beam indication 215 again (e.g., as described above, on the uplink resources requested by the user equipment 115-a and / or the uplink resources indicated by the base station 105-a). With each sending / re-sending of the MAC CE carrying the beam indication 215, the user equipment 115-a may increase the counter by one (1) and may continue to attempt to send the MAC CE until the limit of the counter (e.g., a counter threshold) is reached. If the limit of the counter is reached, a radio link failure may be triggered. In some cases, the radio link failure may cause the user equipment 115 - a to perform a RACH to identify a new SCell for establishing a secondary communication link.

[0099] When performing a beam failure recovery procedure using the MAC CE carrying the beam indication 215, as described above, the user equipment 115-a may multiplex the MAC CE carrying the beam indication 215 into a MAC PDU (e.g., when uplink resources are available). Furthermore, when the MAC CE carrying the beam indication 215 is multiplexed into a MAC PDU along with other data, the MAC CE carrying the beam indication 215 may be given a high priority during a logical channel prioritization (LCP) procedure (e.g., to ensure prompt recovery of a failed beam). The priority of the MAC CE carrying the beam indication 215 may be lower than that of a common control channel (CCCH) message, but higher than the remaining MAC CEs and data of any attached logical channels.

[0100] In some implementations, the MAC CE carrying the beam indication 215 can be used for additional purposes. For example, the user equipment 115-a can indicate a preferred beam 205 (e.g., beam 205-b) during a RACH procedure. In some cases, the user equipment 115-a can determine to perform a RACH procedure to establish an initial connection with the base station 105-a, or to reestablish communication with a cell (e.g., PCell, PSCell, SPCell) of the base station 105-a. Each physical RACH (PRACH) opportunity can be associated with a reference signal (e.g., a candidate beam for the user equipment 115-a). By selecting a PRACH opportunity to send a PRACH preamble, the user equipment 115-a can indicate (e.g., implicitly) to the base station 105-a which beam is preferred for the base station 105-a to use to perform the remaining RACH procedure or send subsequent downlink signals. However, the base station 105-a can be configured with up to 128 beams. Thus, when many candidate beams 205 are configured, the user equipment 115-a may have to wait a long time to reach the PRACH opportunity of the 128 beams associated with the preferred beam (for example, if the preferred beam is last in time or is late in time when the base station 105-a cycles through the beams of PRACH opportunities).

[0101] To reduce the amount of time the user equipment 115-a waits, the user equipment 115-a may select a suitable beam to send the PRACH preamble, where the suitable beam is available sooner than the preferred beam but may have lower signal quality than the preferred beam. The user equipment 115-a may then indicate the preferred beam in the MAC CE carrying the beam indication 215 after sending the PRACH preamble. In some cases, the MAC CE carrying the beam indication 215 may be included in the payload of MsgA in a two-step RACH procedure (e.g., a physical uplink shared channel (PUSCH) payload) or in Msg3 in a four-step RACH procedure.

[0102] Additionally or alternatively, to reduce access latency, user equipment 115-a may initiate a RACH procedure before measuring the link quality of all reference signals. Thus, once user equipment 115-a finds a beam with suitable link quality for performing a RACH procedure, user equipment 115-a may begin the RACH procedure. However, during the RACH procedure, user equipment 115-a may continue to measure the link quality of the remaining beams. In some cases, if a better candidate beam is found during this continuous measurement process, user equipment 115-a may indicate the most recently preferred beam in the MAC CE carrying beam indication 215. Similar to the above-described technique, the MAC CE carrying 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, and so on. When using the appropriate beam and / or continuing the link quality measurement, the multiplexing rules described above may be applied so that the MAC CE carrying beam indication 215 has a greater probability of being included in MsgA or Msg3.

[0103] Figure 3 An example of a process flow 300 for a MAC process supporting beam index indication according to aspects of the present disclosure is shown. In some examples, the process flow 300 can implement aspects of the wireless communication system 100 and / or 200. The process flow 300 can include a base station 105-b and a user equipment 115-b, which can be examples of corresponding base stations 105 and user equipment 115, respectively, as described above with reference to FIG. Figures 1 to 2 As described herein, the base station 105 - b and the user equipment 115 - b may communicate with each other using beamforming techniques.

[0104] In the following description of process flow 300, the operations between user equipment 115-b and base station 105-b may be presented in an order different from that shown, or the operations performed by base station 105-b and user equipment 115-b may be performed in a different order or at a different time. Certain operations may also be excluded from process flow 300, or other operations may be added to process flow 300. It should be understood that although base station 105-b and user equipment 115-b are shown as performing various operations of process flow 300, any wireless device may perform the operations shown.

[0105] At 305, the user equipment 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 user equipment 115-b and one or more beams of the base station 105-b associated with a serving cell.

[0106] At 310, user equipment 115-b may identify a beam failure for the communication link between user equipment 115-b and a serving cell (e.g., SCell) of base station 105-b. For example, a parameter associated with the beam of the communication link (e.g., RSRP, RSRQ, SINR, etc. for the connection beam measured by user equipment 115-b) may be below a threshold.

[0107] At 315 , the user equipment 115 - b may determine to establish the communication link (eg, a new communication link, reestablish an old communication link, etc.) between the user equipment 115 - b and the serving cell based on the identified beam failure.

[0108] At 320, the user equipment 115-b may select a first beam (e.g., a preferred beam) from the set of candidate beams for the serving cell to establish the communication link. In some cases, the user equipment 115-b may then initiate a request for uplink resources (e.g., a scheduling request) to send an indication of the selected first beam to the base station. In some cases, the request may include a RACH message of a RACH procedure to establish the communication link between the user equipment 115-b and the serving cell of the base station 105-b.

[0109] At 325, user equipment 115-b may obtain uplink resources for use by user equipment 115-b to transmit the indication of the first beam. In some cases, user equipment 115-b may compare a threshold number of time slots to a number of time slots between the current time and the uplink resource and determine availability of the uplink resource based on the number of time slots between the current time and the uplink resource being less than the threshold number of time slots.

[0110] Additionally or alternatively, the user equipment 115-b may send a request (e.g., a scheduling request) based on the determined availability, indicating that the number of time slots between the current time and the uplink resource is greater than a threshold number of time slots. Thus, the user equipment 115-b may receive an indication of the uplink resource in response to the sent request, and may send an indication of the selected first beam in the MAC CE on the indicated uplink resource. In some cases, the user equipment 115-b may receive a configuration for beam failure recovery and send a request for the uplink resource based on the received configuration, wherein the received configuration for beam failure recovery includes a sequence of symbols specific to the user equipment. Additionally or alternatively, the user equipment 115-b may send a scheduling request sequence indicating the request to the base station 105-b, wherein the scheduling request sequence is sent on the uplink resource corresponding to the highest priority logical channel configured for the user equipment. In some cases, the user equipment 115-b may perform a RACH procedure to request the uplink resource for sending the indication of the selected first beam.

[0111] When the user equipment 115-b initiates a request for uplink resources for sending an indication of the selected first beam, as described above at 320, the user equipment 115-b may perform subsequent actions based on initiating the request. For example, at 325-a, the user equipment 115-b may first identify an uplink control resource for sending the request. In some cases, the uplink control resource may include an uplink control resource of a transmission occasion (e.g., TTI, time slot, subframe, etc.) in which the user equipment 115-b may send the request. In addition, the user equipment 115-b may determine and select the uplink control resource for sending the request to indicate which serving cell and / or uplink resource the user equipment 115-b wants to send the indication of the selected first beam. For example, the index of the transmission opportunity within the set of transmission opportunities for sending the request may indicate a serving cell in which a beam failure has occurred. In addition, the index may indicate that the base station 105-b does not send permission for uplink resources on the serving cell / beam. This relationship between transmission opportunities and serving cells can be considered a one-to-one mapping. Additionally or alternatively, the index of the transmission opportunity within the set of transmission opportunities used to transmit the request can indicate the set of serving cells on which the beam has not failed and / or on which the requested uplink resources should be allocated. This relationship between transmission opportunities and multiple serving cells can be considered a many-to-one mapping.

[0112] At 325-b, the user equipment 115-b may send the request on an uplink control resource, the request indicating the failed beam of the serving cell to the base station 105-b. In some cases, the request may include a configuration of an uplink control resource associated with a beam failure recovery procedure, and the user equipment 115-b may send the request on a dedicated uplink control resource, the dedicated uplink control resource being configured to indicate to the base station 105-b the failed beam or beam set configured for the first serving cell. Additionally or alternatively, as described above, the user equipment 115-b may send the request on an uplink control resource of a transmission occasion, wherein the uplink control resource indicates to the base station 105-b the failed beam of the serving cell, and the transmission occasion of the uplink control resource associated with the serving cell set may indicate the serving cell on which the beam has failed (e.g., based on the one-to-one mapping, the many-to-one mapping, etc.).

[0113] At 325-c, the user equipment 115-b may receive, from the base station 105-b, in response to the sent request, an indication of uplink resources in a second serving cell for the user equipment 115-b to use to send the indication of the selected first beam. In some cases, in response to the sent request, the user equipment 115-b may receive, from the second serving cell of the base station 105-b, a DCI indicating uplink resources of the second serving cell for the user equipment 115-b to use to send the indication of the selected first beam. For example, the second serving cell may include a PCell, a PSCell, or a SpCell (e.g., a special serving cell) of the user equipment 115-b. Additionally or alternatively, the user equipment 115-b may receive, from the base station, in response to the sent request, an indication of uplink resources in the second serving cell that is different from the serving cell having the beam failure for the user equipment 115-b to use to send the indication of the selected first beam.

[0114] At 330, based on a comparison of the timing of the availability of the uplink resource to a threshold (e.g., a threshold number of time slots), the user equipment 115-b may send an indication of the selected first beam in a MAC CE to the base station 105-b on the uplink resource. In some cases, the user equipment 115-b may receive a configuration indicating the threshold from the base station 105-b (e.g., via RRC signaling). In addition, the user equipment 115-b may perform a logical channel prioritization procedure for the MAC PDU including the MAC CE, wherein the logical channel prioritization procedure provides a priority for the MAC CE that is greater than each other MAC CE of the MAC PDU, greater than the data of the MAC PDU, and less than information of the CCCH message of the MAC PDU. In some cases, the user equipment 115-b may send an indication of the selected first beam in the MAC CE based on the determined availability indicating that the number of time slots between the current time and the uplink resource is less than the threshold number of time slots.

[0115] In some cases, user equipment 115-b may identify a beam failure of a second communication link between user equipment 115-b and a second service cell, the second service cell comprising a PCell, a PSCell, or a SpCell. Accordingly, user equipment 115-b may initiate a RACH procedure to reestablish the second communication link with the second service cell, wherein an indication of the selected first beam is sent after the RACH procedure for reestablishing the second communication link with the second service cell is completed. In some cases, the beam failure of the second communication link may be identified before the second beam failure of the communication link. Alternatively, the beam failure of the second communication link may be identified after the second beam failure of the communication link. However, in both cases, as described above, user equipment 115-b may send an indication of the selected first beam after the RACH procedure for reestablishing the second communication link with the second service cell is completed.

[0116] In addition, in some cases, the user equipment 115-b may start a timer and a counter based on determining that the communication link is established. Subsequently, the user equipment 115-b may increment the counter based on transmitting the indication of the selected first beam, and may retransmit the indication of the selected first beam in the MAC CE based on the timer expiring before receiving a message (e.g., from the base station 105-b) on the selected first beam and the counter being below a counter threshold. Furthermore, when the counter threshold is reached or exceeded, the user equipment 115-b may trigger a radio link failure based on the counter satisfying the counter threshold.

[0117] Figure 4An example of a process flow 400 for a MAC process supporting beam index indication according to aspects of the present disclosure is shown. In some examples, the process flow 400 can implement aspects of the wireless communication system 100 and / or 200. The process flow 400 can include a base station 105-c and a user equipment 115-c, which can be examples of corresponding base stations 105 and user equipment 115, respectively, as described above with reference to FIG. Figures 1 to 3 As described herein, the base station 105-c and the user equipment 115-c may use beamforming techniques to communicate with each other. The process flow 400 may include similar steps for selecting a beam and sending an indication of the selected beam as described above with reference to Figure 3 However, the user equipment 115-c may select the beam and indicate the selected beam for a RACH procedure (e.g., a four-step RACH procedure) instead of a beam failure recovery procedure.

[0118] In the following description of process flow 400, operations between user equipment 115-c and base station 105-c may be presented in a different order than shown, or operations performed by base station 105-c and user equipment 115-c may be performed in a different order or at a different time. Certain operations may also be excluded from process flow 400, or other operations may be added to process flow 400. It should be understood that although base station 105-c and user equipment 115-c are shown as performing various operations of process flow 400, any wireless device may perform the operations shown.

[0119] At 405, the user equipment 115-c may determine to establish a communication link between the user equipment 115-c and a serving cell of the base station 105-c. For example, the user equipment 115-c may have entered 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 user equipment 115-c may experience a beam failure of the serving cell, and the user equipment 115-c may perform the four-step RACH procedure to re-establish a communication link with the serving cell, rather than performing beam failure recovery. In some cases, the user equipment 115-c may perform the four-step RACH procedure, rather than the beam failure recovery procedure, based on whether the serving cell is a PCell, a PSCell, or an SPCell, where the beam failure of the PCell, PSCell, or SPCell results in the need to establish a new communication link.

[0120] At 410, the user equipment 115-c may transmit a RACH preamble (eg, a first message) for the four-step RACH procedure. Subsequently, at 415, the user equipment 115-c may receive a random access response (eg, a second message) for the four-step RACH procedure.

[0121] At 420, the user equipment 115-c may select a first beam (e.g., a preferred beam) from the set of candidate beams for the serving cell. In some cases, the user equipment 115-c may select the first beam based on information received in the random access response. Additionally or alternatively, the user equipment 115-c may receive the random access response from multiple beams transmitted by the base station 105-c (e.g., via a beam scanning operation to improve reliability of successful reception of the random access response at the user equipment 115-c, etc.) and may measure signal quality of the multiple beams to select the first beam.

[0122] At 425, the user equipment 115-c may determine a beam to send an indication of the selected first beam to the base station 105-c. In some cases, the user equipment 115-c may determine that a second beam in the set of candidate beams is available for sending an indication of the selected first beam at least the threshold earlier than availability of uplink resources, wherein the uplink resources include the first beam. Additionally or alternatively, the user equipment 115-c may measure a signal quality parameter (e.g., RSRP, RSRQ, SINR, or other quality parameter of the beam) of the candidate beam set of the serving cell, including the first beam and the second beam, and may determine that the second beam is superior to the first beam based on the measured signal quality parameters of the first beam and the second beam.

[0123] At 430, the user equipment 115-c may send an indication of the selected first beam (e.g., the preferred beam) in a MAC CE in a random access message of the four-step RACH procedure to the base station 105-c. For example, the indication of the selected first beam may be sent on the second beam in a connection request message (e.g., message 3) of the four-step RACH procedure.

[0124] At 435, the user equipment 115-c may receive a contention resolution message (e.g., message 4) for the four-step RACH procedure from the base station 105-c, and the base station 105-c may complete the four-step RACH procedure. In some cases, the base station 105-c may send the contention resolution message on the selected first beam indicated by the user equipment 115-c in the connection request message.

[0125] Figure 5 An example of a process flow 500 for a MAC process supporting beam index indication according to aspects of the present disclosure is shown. In some examples, the process flow 500 can implement aspects of the wireless communication system 100 and / or 200. The process flow 500 can include a base station 105-d and a user equipment 115-d, which can be examples of corresponding base stations 105 and user equipment 115, respectively, as described above with reference to FIG. Figures 1 to 4As described herein, the base station 105-d and the user equipment 115-d may use beamforming techniques to communicate with each other. The process flow 500 may include similar steps for selecting a beam and sending an indication of the selected beam, as described above with reference to Figure 3 and Figure 4 However, unlike process flow 300 but similar to process flow 400, user equipment 115-d may select the beam and indicate the selected beam for a RACH procedure (e.g., a two-step RACH procedure) rather than a beam failure recovery procedure.

[0126] In the following description of process flow 500, the operations between user equipment 115-d and base station 105-d may be presented in a different order than shown, or the operations performed by base station 105-d and user equipment 115-d may be performed in a different order or at a different time. Certain operations may also be excluded from process flow 500, or other operations may be added to process flow 500. It should be understood that although base station 105-d and user equipment 115-d are shown as performing various operations of process flow 500, any wireless device may perform the operations shown.

[0127] At 505, similar to process flow 400, user equipment 115-d may determine to establish a communication link between user equipment 115-d and a serving cell of base station 105-d. However, user equipment 115-d may be configured and capable of performing a two-step RACH procedure, rather than a four-step RACH procedure.

[0128] Thus, at 510, the user equipment 115-d may select a first beam from a set of candidate beams for the serving cell. In some cases, the user equipment 115-d may make this selection based on a previous signal quality measurement of the candidate beam or an ongoing signal quality measurement of the candidate beam. The signal quality measurement may include one or more of RSRP, RSRQ, SINR, or other signal quality measurements of the candidate beam.

[0129] At 515, the user device 115-d may be similar to the one referenced above. Figure 4 The described techniques (e.g., based on a signal quality parameter measurement, etc., the second beam is available before the indicated uplink resource is available) determine the beam on which to transmit the indication of the selected first beam. For example, the user device 115-d may determine to use the second beam to transmit the indication of the selected first beam.

[0130] At 520, the user equipment 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, rather than sending an indication of the selected first beam in the connection request message of the four-step RACH procedure.

[0131] At 525, user equipment 115-d may receive a second message (e.g., MsgB) of the two-step RACH procedure from base station 105-d. In some cases, base station 105-d may transmit the second message of the two-step RACH procedure using the selected first beam indicated by user equipment 115-d in the first message of the two-step RACH procedure.

[0132] Figure 6 A block diagram 600 illustrates a device 605 that supports a MAC process for beam index indication according to aspects of the present disclosure. The device 605 may be an example of aspects of the user equipment 115 as described herein. The device 605 may include a receiver 610, a communication manager 615, and a transmitter 620. The device 605 may also include one or more processors, a memory coupled to the one or more processors, and instructions stored in the memory that are executable by the one or more processors to enable the one or more processors to perform the processes for beam index indication discussed herein. Each of these components may be in communication with one another (e.g., via one or more buses).

[0133] The receiver 610 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to the medium access control process indicated by the beam index, etc.). The information may be passed to other components of the device 605. The receiver 610 may be a reference Figure 9 Examples of various aspects of the transceiver 920 are described. The receiver 610 can utilize a single antenna or a group of antennas.

[0134] The communication manager 615 may determine to establish a communication link between the user equipment and the serving cell of the base station. In some cases, the communication manager 615 may select a first beam from a set of candidate beams of the serving cell for the user equipment to establish the communication link. In addition, the communication manager 615 may send an indication of the selected first beam to the base station in a MAC control element on the uplink resource based on a comparison of the timing of the availability of the uplink resource to a threshold. The communication manager 615 may be an example of various aspects of the communication manager 910 described herein.

[0135] The communication manager 615 can be implemented as an integrated circuit or chipset of the device 605, and the receiver 610 and the transmitter 620 can be implemented as analog components (e.g., amplifiers, filters, antennas) coupled to the device 605 to implement wireless transmission and reception. The actions performed by the communication manager 615 described herein can be performed to achieve one or more potential advantages. At least one implementation can enable the communication manager 615 to establish a communication link with a base station using a preferred beam. Based on implementing this establishment, one or more processors of the device 605 (e.g., a processor controlling the communication manager 615 or in conjunction with the communication manager 615) can promote increased spectral efficiency, higher data rates, and in some examples, can promote efficiency enhancements for high reliability and low latency operation, among other benefits.

[0136] The communication manager 615 or its subcomponents 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 the communication manager 615 or its subcomponents 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.

[0137] The communication manager 615 or its subcomponents can be physically located in different locations, including being distributed so that part of the functionality is implemented by one or more physical components in different physical locations. In some examples, according to various aspects of the present disclosure, the communication manager 615 or its subcomponents can be separate and distinct components. In some examples, according to various aspects of the present disclosure, the communication manager 615 or its subcomponents can be combined with one or more other hardware components, including but not limited to input / output (I / O) components, transceivers, network servers, another computing device, one or more other components described in the present disclosure, or a combination thereof.

[0138] The transmitter 620 can transmit signals generated by other components of the device 605. In some examples, the transmitter 620 can be collocated with the receiver 610 in the transceiver module. For example, the transmitter 620 can be a reference Figure 9 Examples of various aspects of the transceiver 920 are described. The transmitter 620 can utilize a single antenna or a group of antennas.

[0139] Figure 7A block diagram 700 is shown of a device 705 that supports a MAC process for beam index indication according to aspects of the present disclosure. The device 705 can be an example of aspects of the device 605 or the user equipment 115 as described herein. The device 705 can include a receiver 710, a communication manager 715, and a transmitter 735. The device 705 can also include a processor. Each of these components can communicate with each other (e.g., via one or more buses).

[0140] The receiver 710 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to MAC processes indicated by beam indexes, etc.). The information may be passed to other components of the device 705. The receiver 710 may be a reference Figure 9 Examples of various aspects of the transceiver 920 are described. The receiver 710 can utilize a single antenna or a group of antennas.

[0141] The communication manager 715 can be an example of aspects of the communication manager 615 described herein. The communication manager 715 can include a link establishment component 720, a beam selector 725, and a selected beam indicator 730. The communication manager 715 can be an example of aspects of the communication manager 910 described herein.

[0142] The link establishing component 720 may determine to establish a communication link between the user equipment and the serving cell of the base station.

[0143] The beam selector 725 may select the first beam in the candidate beam set of the serving cell to establish the communication link by the user equipment.

[0144] The selected beam indicator 730 may send an indication of the selected first beam to the base station in a MAC CE on the uplink resource based on a comparison of the timing of the availability of the uplink resource with a threshold.

[0145] The transmitter 735 can transmit signals generated by other components of the device 705. In some examples, the transmitter 735 can be collocated with the receiver 710 in the transceiver module. For example, the transmitter 735 can be a reference Figure 9 Examples of various aspects of the transceiver 920 are described. The transmitter 735 can utilize a single antenna or a group of antennas.

[0146] In some cases, the link establishment component 720, beam selector 725, and selected beam indicator 730 can each be, or at least be, part of a processor (e.g., a transceiver processor, a radio processor, a transmitter processor, or a receiver processor). The processor can be coupled to a memory and execute instructions stored in the memory that enable the processor to perform or facilitate the features of the link establishment component 720, beam selector 725, and selected beam indicator 730 discussed herein. The transceiver processor can be collocated and / or in communication with the transceiver of the device (e.g., to direct its operation). The radio processor can be collocated and / or in communication with the radio (e.g., an NR radio, an LTE radio, a Wi-Fi radio) of the device (e.g., to direct its operation). The transmitter processor can be collocated and / or in communication with the transmitter of the device (e.g., to direct its operation). The receiver processor can be collocated and / or in communication with the receiver of the device (e.g., to direct its operation).

[0147] Figure 8 A block diagram 800 illustrates a communication manager 805 supporting a MAC process for beam index indication in accordance with aspects of the present disclosure. The communication manager 805 may be an example of aspects of the communication manager 615, the communication manager 715, or the communication manager 910 described herein. The communication 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 be in direct or indirect communication with one another (e.g., via one or more buses).

[0148] The link establishing component 810 may determine to establish a communication link between the user equipment and a serving cell of a base station.

[0149] The beam selector 815 may select a first beam from a set of candidate beams of the serving cell for the user equipment to establish the 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 user equipment may transmit the request on an uplink control resource, indicating the failed beam of the serving cell to the base station, and, in response to the transmitted request, receive an indication of uplink resources in a second serving cell from the base station for the user equipment to use to transmit the indication of the selected first beam.

[0150] The selected beam indicator 820 can send an indication of the selected first beam to the base station in a MAC CE on the uplink resource based on a comparison of the timing of the availability of the uplink resource with a threshold. In some examples, the selected beam indicator 820 can receive a configuration indicating the threshold from the base station.

[0151] The beam failure identifier 825 can communicate with the base station via the communication link and can identify a beam failure in the communication link between the user equipment and the serving cell. Therefore, the beam failure identifier 825 can determine to establish a communication link between the user equipment and the serving cell based on the identified beam failure.

[0152] The uplink resource availability component 830 can obtain the uplink resource for the user equipment to send the indication of the first beam, compare the time slot threshold number with the number of time slots between the current time and the uplink resource, wherein the threshold includes the time slot threshold number, and determine the availability of the uplink resource based on the number of time slots between the current time and the uplink resource being less than the time slot threshold number. In some examples, the uplink resource availability component 830 can send the indication of the selected first beam in the MAC CE based on the determined availability, wherein the determined availability indicates that the number of time slots between the current time and the uplink resource is less than the time slot threshold number. Optionally, the uplink resource availability component 830 can send a request for uplink resources to the base station based on the determined availability, wherein the availability indicates that the number of time slots between the current time and the uplink resource is greater than the time slot threshold number. Thus, the uplink resource availability component 830 may receive an indication of the uplink resources in response to the sent request and may send an indication of the selected first beam in the MAC CE on the indicated uplink resources.

[0153] The uplink resource request component 835 may receive a configuration for beam failure recovery, and the request for uplink resources may be sent based on the received configuration. In some cases, the received configuration for beam failure recovery may include a sequence of symbols specific to the user equipment. Additionally or alternatively, the uplink resource request component 835 may send a scheduling request sequence indicating the request to the base station. In some cases, the scheduling request sequence may be sent on an uplink resource corresponding to the highest priority logical channel configured for the user equipment.

[0154] In some cases, the uplink resource request component 835 may send the request on an uplink control resource that indicates to the base station the failed beam in the serving cell, and may receive, in response to the sent request, an indication of uplink resources in a second serving cell from the base station for the user equipment to use to transmit 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 send the request on a dedicated uplink control resource that is configured to indicate to the base station the beam or beam set configured for the failed first serving cell, and may subsequently receive, in response to the sent request, DCI from the second serving cell of the base station that indicates uplink resources of the second serving cell for the user equipment to use to transmit the indication of the selected first beam. In some cases, the second serving cell may include a PCell, PSCell, or SpCell of the user equipment.

[0155] Additionally or alternatively, the uplink resource request component 835 may transmit the request on an uplink control resource of a transmission occasion, which indicates to the base station that the beam of the serving cell has failed, and a transmission opportunity of uplink control resources associated with a serving cell set to indicate the serving cell whose beam has failed. In some cases, the index of a transmission opportunity within the transmission opportunity set may indicate the serving cell whose beam has failed. Alternatively, the index of a transmission opportunity within the transmission opportunity set may indicate a serving cell set whose beam has not failed, a serving cell set to which the requested uplink resource should be allocated, or a combination thereof.

[0156] The RACH selected beam indicator 840 can send the MAC control element in a RACH (e.g., random access) message of a RACH procedure to the base station. In some examples, the RACH selected beam indicator 840 can determine that a second beam in the candidate beam set is available to send an indication of the first beam at least a threshold earlier than the availability of the uplink resource, wherein the uplink resource includes the first beam, and based on determining that the second beam is available, send an indication of the selected first beam in a MAC CE on the second beam. Additionally or alternatively, the RACH selected beam indicator 840 can measure signal quality parameters of the candidate beam set (including the first beam and the second beam) of the serving cell, determine that the second beam is superior to the first beam based on the measured signal quality parameters of the first beam and the second beam, and send an indication of the second beam in a signal of the RACH procedure based on determining that the second beam is preferred. In some cases, the indication of the selected first beam may be sent on the second beam in the first message of the two-step RACH procedure (e.g., Msg A). Additionally or alternatively, the indication of the selected first beam may be sent on the second beam in the connection request message of the four-step RACH procedure (e.g., Message 3).

[0157] In some cases, the RACH selected beam indicator 840 can identify a beam failure in a second communication link between the user equipment and a second serving cell, where the second serving cell may include a PCell, a PSCell, or an SpCell. Subsequently, the RACH selected beam indicator 840 can initiate a RACH procedure to reestablish a second communication link with the second serving cell, wherein an indication of the selected first beam is sent after the RACH procedure for reestablishing the second communication link with the second serving cell is completed. In some cases, the beam failure in the second communication link can be identified before the second beam failure in the communication link occurs. Alternatively, the beam failure in the second communication link can be identified after the second beam failure in the communication link occurs.

[0158] The prioritization component 845 can perform a logical channel prioritization process for the MAC PDU including the MAC CE, wherein the logical channel prioritization process provides the MAC CE with a priority greater than each other MAC CE of the MAC PDU, greater than the data of the MAC PDU, and less than the information of the CCCH message of the MAC PDU.

[0159] The beam indication transmission counter 850 may start a timer and a counter based on determining that the communication link is established, and may increment the counter based on transmitting the indication of the selected first beam. Additionally, the beam indication transmission counter 850 may retransmit the indication of the selected first beam in the MAC CE based on the timer expiring and the counter falling below a counter threshold before receiving a message on the selected first beam. In some cases, the beam indication transmission counter 850 may trigger a radio link failure based on the counter meeting the counter threshold.

[0160] In some cases, the link establishment component 810, beam selector 815, selected beam indicator 820, beam failure identifier 825, uplink resource availability component 830, uplink resource request component 835, RACH selected beam indicator 840, prioritization component 845, and beam indication transmission counter 850 can each be, or at least be, part of a processor (e.g., a transceiver processor, a radio processor, a transmitter processor, or a receiver processor). The processor can be coupled to a memory and execute instructions stored in the memory that enable the processor to perform or facilitate the features of the link establishment component 810, beam selector 815, selected beam indicator 820, beam failure identifier 825, uplink resource availability component 830, uplink resource request component 835, RACH selected beam indicator 840, prioritization component 845, and beam indication transmission counter 850 discussed herein.

[0161] Figure 9 A schematic diagram of a system 900 including a device 905 that supports a MAC process for beam index indication according to aspects of the present disclosure is shown. The device 905 may be an example of or include components of the device 605, device 705, or user equipment 115 described herein. The device 905 may include components for two-way voice and data communication, including components for sending and receiving communications, including a communication manager 910, an I / O controller 915, a transceiver 920, an antenna 925, a memory 930, and a processor 940. These components may communicate electronically via one or more buses (e.g., bus 945).

[0162] The communication manager 910 may determine to establish a communication link between the user equipment and the serving cell of the base station. In some cases, the communication manager 910 may select a first beam in a set of candidate beams of the serving cell to establish the communication link by the user equipment. In addition, the communication manager 910 may send an indication of the selected first beam to the base station in a MAC CE on the uplink resources based on a comparison of the timing of the availability of uplink resources with a threshold. At least one implementation may enable the communication manager 910 to establish a communication link with the base station using a preferred beam. Based on the implementation establishment, one or more processors of the device 905 (e.g., a processor controlling the communication manager 910 or in combination with the communication manager 910) may promote improved spectral efficiency, higher data rates, and in some examples, may promote efficiency enhancements for high reliability and low latency operations, in addition to other benefits.

[0163] The I / O controller 915 can manage the input and output signals of the device 905. The I / O controller 915 can also manage peripheral devices that are not integrated into the device 905. In some cases, the I / O controller 915 can represent a physical connection or port to an external peripheral device. In some cases, the I / O controller 915 can utilize an operating system, such as or other known operating systems. In other cases, the I / O controller 915 may represent or interact with a modem, keyboard, mouse, touch screen, 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 via the I / O controller 915 or via hardware components controlled by the I / O controller 915.

[0164] As described above, the transceiver 920 can communicate bidirectionally via one or more antennas, wired or wireless links. For example, the transceiver 920 can represent a wireless transceiver and can communicate bidirectionally with another wireless transceiver. The transceiver 920 can also include a modem to modulate the packet and provide the modulated packet to the antenna for transmission, as well as demodulate the packet received from the antenna.

[0165] In some cases, the wireless device may include a single antenna 925. However, in some cases, the device may have more than one antenna 925, which may be capable of sending or receiving multiple wireless transmissions simultaneously.

[0166] 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, including instructions that, when executed, cause the processor to perform the various functions described herein. In some cases, the memory 930 may include a basic I / O system (BIOS), etc., which may control basic hardware or software operations, such as interaction with peripheral components or devices.

[0167] 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 integrated into the processor 940. The processor 940 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 930) to cause the device 905 to perform various functions (e.g., functions or tasks of a MAC process supporting beam index indication).

[0168] The code 935 may include instructions for implementing various aspects of the present disclosure, including instructions for supporting wireless communications. The code 935 may be stored in a non-transitory computer-readable medium, such as system memory or other types of memory. In some cases, the code 935 may not be directly executable by the processor 940, but may enable a computer (e.g., when compiled and executed) to perform the functions described herein.

[0169] Figure 10 A flow chart illustrating a method 1000 for a MAC process supporting beam index indication according to aspects of the present disclosure is shown. As described herein, the operations of the method 1000 may be implemented by the user equipment 115 or a component thereof. For example, the operations of the method 1000 may be implemented by reference to Figures 6 to 9 In some examples, the user device may execute a set of instructions to control the functional elements of the user device to perform the functions described below. Additionally or alternatively, the user device may use dedicated hardware to perform various aspects of the functions described below.

[0170] At 1005, the user equipment may determine to establish a communication link between the user equipment and a serving cell of a base station. The operations of 1005 may be performed according to the methods described herein. In some examples, aspects of the operations of 1005 may be described with reference to Figures 6 to 9 The link establishment component described is executed.

[0171] At 1010, the user equipment may select a first beam from a set of candidate beams of the serving cell to establish the communication link by the user equipment. The operations of 1010 may be performed according to the methods described herein. In some examples, aspects of operation 1010 may be described with reference to Figures 6 to 9 The beam selector described is implemented.

[0172] At 1015, based on the comparison of the timing of the availability of uplink resources with the threshold, the user equipment may send an indication of the selected first beam to the base station in a MAC CE on the uplink resources. The operation of 1015 may be performed according to the method described herein. In some examples, such as reference Figures 6 to 9 As described, aspects of the operation of 1015 may be performed by the selected beam director.

[0173] Figure 11 A flow chart illustrating a method 1100 for a MAC process supporting beam index indication according to aspects of the present disclosure is shown. As described herein, the operations of the method 1100 may be implemented by the user equipment 115 or a component thereof. For example, the operations of the method 1100 may be implemented by reference to Figures 6 to 9 In some examples, the user device may execute a set of instructions to control the functional elements of the user device to perform the functions described below. Additionally or alternatively, the user device may use dedicated hardware to perform various aspects of the functions described below.

[0174] At 1105, the user equipment may communicate with the base station via the communication link. The operations of 1105 may be performed according to the methods described herein. In some examples, such as reference Figures 6 to 9 As described, aspects of the operation of 1105 may be performed by a beam failure identifier.

[0175] At 1110, the user equipment may identify a beam failure of a communication link between the user equipment and the serving cell. The operations of 1110 may be performed according to the methods described herein. In some examples, such as reference Figures 6 to 9 As described, aspects of the operation of 1110 may be performed by a beam failure identifier.

[0176] At 1115, the user equipment may determine to establish a communication link between the user equipment and the serving cell of the base station. The operations of 1115 may be performed according to the methods described herein. In some examples, aspects of the operations of 1115 may be described with reference to Figures 6 to 9 The link establishment component described is executed.

[0177] At 1120, the user equipment may determine to establish a communication link between the user equipment and the serving cell based on the identified beam failure. The operations of 1120 may be performed according to the methods described herein. In some examples, aspects of the operations of 1120 may be described with reference to Figures 6 to 9 The beam failure identifier described is implemented.

[0178] At 1125, the user equipment may select a first beam from the set of candidate beams of the serving cell to establish the communication link by the user equipment. The operations of 1125 may be performed according to the methods described herein. In some examples, aspects of the operations of 1125 may be described with reference to Figures 6 to 9 The beam selector described is implemented.

[0179] At 1130, based on a comparison of the timing of the availability of uplink resources with a threshold, the user equipment may send an indication of the selected first beam to the base station in a MAC CE on the uplink resources. The operations of 1130 may be performed according to the methods described herein. In some examples, aspects of the operations of 1130 may be described with reference to Figures 6 to 9 The selected beam designator described is executed.

[0180] Figure 12 A flow chart illustrating a method 1200 for a MAC process supporting beam index indication according to aspects of the present disclosure is shown. As described herein, the operations of the method 1200 may be implemented by the user equipment 115 or a component thereof. For example, the operations of the method 1200 may be implemented by reference to Figures 6 to 9 In some examples, the user device may execute a set of instructions to control the functional elements of the user device to perform the functions described below. Additionally or alternatively, the user device may use dedicated hardware to perform various aspects of the functions described below.

[0181] At 1205, the user equipment may determine to establish a communication link between the user equipment and a serving cell of a base station. The operations of 1205 may be performed according to the methods described herein. In some examples, aspects of the operations of 1205 may be described with reference to Figures 6 to 9 The link establishment component described is executed.

[0182] At 1210, the user equipment may select a first beam from a set of candidate beams of the serving cell to establish the communication link by the user equipment. The operations of 1210 may be performed according to the methods described herein. In some examples, aspects of the operations of 1210 may be described with reference to Figures 6 to 9 The beam selector described is implemented.

[0183] At 1215, based on a comparison of the timing of the availability of uplink resources with a threshold, the user equipment may send an indication of the selected first beam to the base station in a MAC CE on the uplink resources. The operations of 1215 may be performed according to the methods described herein. In some examples, aspects of the operations of 1215 may be described with reference to Figures 6 to 9 The selected beam designator described is executed.

[0184] At 1220, the user equipment may send the MAC CE to the base station in a RACH message of a RACH procedure. The operations of 1220 may be performed according to the methods described herein. In some examples, aspects of operation 1220 may be described with reference to Figures 6 to 9 The described RACH is performed by the selected beam pointer.

[0185] It should be noted that the methods described herein describe possible implementations, and that the operations and steps may be rearranged or otherwise modified, and that other implementations are possible. Furthermore, aspects from two or more methods may be combined.

[0186] The techniques described herein can be used in various wireless communication systems, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and other systems. CDMA systems can implement radio technologies such as CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers the IS-2000, IS-95, and IS-856 standards. IS-2000 versions are 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 can implement radio technologies such as Global System for Mobile Communications (GSM).

[0187] OFDMA systems can implement radio technologies such as Ultra Mobile Broadband (UMB), Evolved UTRA (UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, and others. UTRA and E-UTRA are part of the Universal Mobile Telecommunications System. LTE, LTE-A, and LTE-A Pro are versions 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 called the 3rd Generation Partnership Project (3GPP). CDMA2000 and UMB are described in documents from an organization called the 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. Although aspects of LTE, LTE-A, LTE-A Pro, or NR systems may be described for example purposes, and the terminology of LTE, LTE-A, LTE-A Pro, or NR may be used in much of the description, the techniques described herein may be applicable beyond LTE, LTE-A, LTE-A Pro, or NR applications.

[0188] A macro cell typically covers a relatively large geographic area (e.g., a radius of several kilometers) and can allow unrestricted access to user devices that subscribe to services with the network provider. Compared to a macro cell, a small cell can be associated with a low-power base station and can operate in the same or different (e.g., licensed, unlicensed, etc.) frequency band as the macro cell. According to various examples, a small cell may include a pico cell, a femto cell, and a micro cell. For example, a pico cell can cover a small geographic area and can allow unrestricted access to user devices that subscribe to services with the network provider. A femto cell can also cover a small geographic area (e.g., a home) and can provide restricted access to user devices associated with the femto cell (e.g., user devices in a closed subscriber group (CSG), user devices of users in a home, etc.). The eNB for a macro cell may be referred to as a macro eNB. The eNB for a small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB, or a home eNB. The eNB can support one or more (e.g., two, three, four, etc.) cells and may also support communications using one or more component carriers.

[0189] The wireless communication systems described herein can support synchronous or asynchronous operation. For synchronous operation, the base stations can have similar frame timing, and transmissions from different base stations can be roughly aligned in time. For asynchronous operation, the base stations can have different frame timing, and transmissions from different base stations may not be aligned in time. The techniques described herein can be used for either synchronous or asynchronous operation.

[0190] The information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0191] The various illustrative blocks and modules described in conjunction with the present disclosure may be implemented or executed with 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, a plurality of microprocessors, a combination of one or more microprocessors and a DSP core, or any other such configuration).

[0192] 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. Features implementing functions may also be physically located in different locations, including being distributed so that portions of the functions are implemented in different physical locations.

[0193] Computer-readable media include non-transitory computer storage media and communication media, which include any media that are convenient for sending a computer program from one place to another. Non-transitory storage media can be any available media that a general or special-purpose computer can access. As an example and not limitation, non-transitory computer-readable media can include RAM, ROM, electrically erasable programmable ROM (EEPROM), flash memory, compact disc (CD) ROM or other optical disc storage devices, magnetic disk storage devices or other magnetic storage devices, or can be used to carry or store desired program code components and any other non-transitory media that can be accessed by a general or special-purpose computer or a general or special-purpose processor in the form of an instruction or data structure. In addition, any connection is properly referred to as a computer-readable medium. For example, if the software is sent from a website, server or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave), the coaxial cable, fiber optic cable, twisted pair, DSL or wireless technology (such as infrared, radio and microwave) are all included in the definition of medium. Disk and disc, as used herein, includes CD, laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

[0194] As used herein, including in the claims, "or" used in a list of items (e.g., a list of items preceded by a phrase such as "at least one" or "one or more") means an inclusive list, for example, a list having at least 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). In addition, as used herein, the phrase "based on" should not be interpreted as referring to a closed set of conditions. For example, an exemplary step described as "based on condition A" can be based on condition A and condition B without departing from the scope of this disclosure. In other words, as used herein, the phrase "based on" should be interpreted in the same manner as the phrase "based at least in part on."

[0195] In the drawings, similar components or features may have the same reference number. In addition, various components of the same type may be distinguished by following the reference number with a dash and a second reference number to distinguish between similar components. If only the first reference number is used in the specification, the description applies to any similar component having the same first reference number, regardless of the second or subsequent reference numbers.

[0196] The description set forth herein, in conjunction with the accompanying drawings, describes example configurations and does not represent all examples that may be implemented or within the scope of the claims. The term "exemplary" as used herein means "serving as an example, instance, or illustration," rather than "preferred" or "superior to other examples." To provide an understanding of the described techniques, the detailed description includes specific details. However, these techniques can be implemented without these specific details. In some cases, well-known structures and devices are shown in block diagram form to avoid obscuring the concepts of the examples.

[0197] The description provided here enables those skilled in the art to make or use the present disclosure. Various modifications to the present disclosure will be 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 present disclosure. Therefore, the present disclosure is not limited to the examples and designs described herein, but rather conforms to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for wireless communication at a user equipment (UE), comprising: receiving, from a base station, a PUCCH configuration indicating one or more PUCCH resources for beam failure recovery in the SCell; identifying a beam failure in the SCell; sending, using at least one of the one or more PUCCH resources, a request for the base station to signal new uplink resources for transmitting a beam indication; receiving, from the base station, a grant of the new uplink resources for transmitting the beam indication; selecting, for the base station, a beam for beam failure recovery in the SCell based on identifying the beam failure; and The beam indication indicating the selected beam is sent to the base station in a medium access control (MAC) control element (CE) using the new uplink resource.

2. The method according to claim 1, wherein Communication between the UE and the base station is performed via the PCell.

3. The method according to any one of claims 1 to 2, wherein Sending the beam indication includes: The MAC CE carrying the beam indication is multiplexed into the MAC PDU.

4. The method according to claim 3, wherein: When the MAC CE is multiplexed into the MAC PDU together with other data, the MAC CE is given a higher priority in the LCP procedure.

5. The method according to any one of claims 1 to 2, wherein The beam indication is a beam index indication.

6. An apparatus for wireless communication at 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 the SCell; means for identifying a beam failure in the SCell; means for sending, using at least one of the one or more PUCCH resources, a request by the base station to signal new uplink resources for transmitting a beam indication; means for receiving, from the base station, a grant of the new uplink resources for transmitting the beam indication; a means for selecting, for the base station, a beam for beam failure recovery in the SCell based on identifying the beam failure; and means for sending said beam indication in a Medium Access Control (MAC) Control Element (CE) to said base station indicating said selected beam using said new uplink resources.

7. The device according to claim 6, wherein Communication between the UE and the base station is performed via the PCell.

8. The device according to any one of claims 6 to 7, wherein: The means for sending the beam indication comprises: A component used to multiplex the MAC CE carrying the beam indication into a MAC PDU.

9. The device according to claim 8, wherein When the MAC CE is multiplexed into the MAC PDU together with other data, the MAC CE is given a higher priority in the LCP procedure.

10. The device according to any one of claims 6 to 7, wherein: The beam indication is a beam index indication.

11. An apparatus for wireless communication at a user equipment (UE), comprising: processor, a memory coupled to the processor; and The instructions stored in the memory are executable by the processor, causing the apparatus to perform the method according to any one of claims 1 to 5.

12. A non-transitory computer-readable medium storing a code for wireless communication at a user equipment (UE), the code comprising instructions executable by a processor to perform the method according to any one of claims 1 to 5.

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