Certain aspects of the present disclosure provide techniques for configuring sidelink communications between user equipment's (UEs). Per one technique, during a discovery opportunity, a first UE and a second UE may identify a subset of beam pairs suitable for communication, and schedule a discontinuous transmission (DTX) occasion during the discovery opportunity. During the DTX occasion, the first UE and second UE may perform a beam refinement procedure to determine a beam pair (BP) over which to communicate, from the identified subset of beam pairs. The beam refinement procedure may include beam narrowing of at least one of the identified subset of beam pairs.

BACKGROUND

Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for beam configuration and selection for sidelink communications between two user equipments (UEs).

Description of Related Art

In some examples, a wireless multiple-access communication system may include a number of base stations (BSs), which are each capable of simultaneously supporting communication for multiple communication devices, otherwise known as user equipments (UEs). In an LTE or LTE-A network, a set of one or more BSs may define an eNodeB (eNB). In other examples (e.g., in a next generation, a new radio (NR), or 5G network), a wireless multiple access communication system may include a number of distributed units (DUs) (e.g., edge units (EUs), edge nodes (ENs), radio heads (RHs), smart radio heads (SRHs), transmission reception points (TRPs), etc.) in communication with a number of central units (CUs) (e.g., central nodes (CNs), access node controllers (ANCs), etc.), where a set of one or more DUs, in communication with a CU, may define an access node (e.g., which may be referred to as a BS, 5G NB, next generation NodeB (gNB or gNodeB), transmission reception point (TRP), etc.). A BS or a DU may communicate with a set of UEs on downlink (DL) channels (e.g., for transmissions from a BS or a DU to a UE) and uplink (UL) channels (e.g., for transmissions from a UE to a BS or a DU).

BRIEF SUMMARY

Certain aspects provide a method for wireless communications by a first UE. The method generally includes identifying, during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE, and performing, in conjunction with a discontinuous transmission (DTX) occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using a set of transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

Certain aspects provide a method for wireless communications by a first UE. The method generally includes identifying, during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE, and performing, in conjunction with a DTX occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using a set of receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

Certain aspects provide an apparatus for wireless communications. The apparatus generally includes means for identifying, during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE; and means for performing, in conjunction with a DTX occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

Certain aspects provide an apparatus for wireless communications. The apparatus generally includes means for identifying, during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE; and means for performing, in conjunction with a DTX occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves receiving reference signals using receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

Certain aspects provide an apparatus for wireless communications. The apparatus generally includes at least one processor and a memory configured to identify, during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE; and perform, in conjunction with a DTX occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

Certain aspects provide an apparatus for wireless communications. The apparatus generally includes at least one processor and a memory configured to identify, during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE; and perform, in conjunction with a DTX occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves receiving reference signals using receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

Certain aspects of the subject matter described in this disclosure can be implemented in a computer readable medium storing computer executable code thereon for wireless communications. The computer readable medium comprises code for identifying, by a first UE during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE; and code for performing, in conjunction with a DTX occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

Certain aspects of the subject matter described in this disclosure can be implemented in a computer readable medium storing computer executable code thereon for wireless communications. The computer readable medium comprises code for identifying, by a first UE during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE; and code for performing, in conjunction with a DTX occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves receiving reference signals using receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for configuring sidelink communications at frequency range 2 (FR2). During a discovery opportunity, a first user equipment (UE) and a second UE may identify a subset of beam pairs suitable for communication, and schedule a discontinuous transmission (DTX) occasion during the discovery opportunity. During the DTX occasion, the first UE and second UE may perform a beam refinement procedure to determine a beam pair (BP) over which to communicate, from the identified subset of beam pairs. The beam refinement procedure may include beam narrowing of at least one of the identified subset of beam pairs.

The techniques described herein may be used for various wireless communication technologies, such as long term evolution (LTE), 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 networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology such as new radio (NR) (e.g. 5G RA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS).

NR is an emerging wireless communications technology under development in conjunction with the 5G Technology Forum (5GTF). 3GPP LTE and LTE-Advanced (LTE-A) are releases of the UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP). cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, while aspects may be described herein using terminology commonly associated with 3G and/or 4G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems, such as 5G and later, including NR technologies.

NR supports beamforming and beam direction may be dynamically configured. Multiple input multiple output (MIMO) transmissions with precoding may also be supported. MIMO configurations in a downlink (DL) may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells.

Example Wireless Communications System

FIG.1illustrates an example wireless communication network100in which aspects of the present disclosure may be performed. For example, the wireless communication network100may include one or more base stations (BSs)110and/or one or more user equipments (UEs)120, such as UE120a(such as a transmitter UE) that includes a beam manager122athat may be configured to perform beam refinement for sidelink communications during discontinuous transmission (DTX) occasions, in accordance with operations900ofFIG.9. As shown inFIG.1, a UE120b(such as a receiver UE) includes a beam manager122bthat may be configured to perform beam refinement for sidelink communications during DTX occasions, in accordance with operations1000ofFIG.10.

The wireless communication network100may be a new radio (NR) system (e.g., a 5th generation (5G) NR network). As shown inFIG.1, the wireless communication network100may be in communication with a core network. The core network may in communication with one or more BSs110a-z(each also individually referred to herein as a BS110or collectively as BSs110) and/or UEs120a-y(each also individually referred to herein as a UE120or collectively as UEs120) in the wireless communication network100via one or more interfaces.

As illustrated inFIG.1, the wireless communication network100may include a number of BSs110and other network entities. A BS110may be a station that communicates with UEs120. Each BS110may provide communication coverage for a particular geographic area. In 3 GPP, the term “cell” can refer to a coverage area of a Node B (NB) and/or a NB subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term “cell” and next generation NodeB (gNB or gNodeB), NR BS, 5G NB, access point (AP), or transmission reception point (TRP) may be interchangeable. In some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile BS110. In some examples, the BSs110may be interconnected to one another and/or to one or more other BSs110or network nodes (not shown) in wireless communication network100through various types of backhaul interfaces, such as a direct physical connection, a wireless connection, a virtual network, or the like using any suitable transport network.

A BS110may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs120with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs120with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs120having an association with the femto cell (e.g., UEs120in a Closed Subscriber Group (CSG), UEs120for users in the home, etc.). ABS110for a macro cell may be referred to as a macro BS. A BS110for a pico cell may be referred to as a pico BS. ABS110for a femto cell may be referred to as a femto BS or a home BS. In the example shown inFIG.1, the BSs110a,110band110cmay be macro BSs for the macro cells102a,102band102c, respectively. The BS110xmay be a pico BS for a pico cell102x. The BSs110yand110zmay be femto BSs for the femto cells102yand102z, respectively. ABS110may support one or multiple (e.g., three) cells.

The wireless communication network100may also include relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., a BS110or a UE120) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE120or a BS110). A relay station may also be a UE120that relays transmissions for other UEs. In the example shown inFIG.1, a relay station110rmay communicate with the BS110aand a UE120rin order to facilitate communication between the BS110aand the UE120r. A relay station may also be referred to as a relay BS, a relay, etc.

The wireless communication network100may be a heterogeneous network that includes BSs110of different types, e.g., macro BS, pico BS, femto BS, relays, etc. These different types of BSs110may have different transmit power levels, different coverage areas, and different impact on interference in the wireless communication network100. For example, macro BS may have a high transmit power level (e.g., 20 Watts) whereas pico BS, femto BS, and relays may have a lower transmit power level (e.g., 1 Watt).

The wireless communication network100may support synchronous or asynchronous operation. For synchronous operation, the BSs110may have similar frame timing, and transmissions from different BSs110may be approximately aligned in time. For asynchronous operation, the BSs110may have different frame timing, and transmissions from different BSs110may not be aligned in time. The techniques described herein may be used for both synchronous and asynchronous operation.

A network controller130may couple to a set of BSs110and provide coordination and control for these BSs110. The network controller130may communicate with the BSs110via a backhaul. The BSs110may also communicate with one another (e.g., directly or indirectly) via wireless or wireline backhaul.

While aspects of the examples described herein may be associated with LTE technologies, aspects of the present disclosure may be applicable with other wireless communications systems, such as NR. NR may utilize OFDM with a CP on the UL and the DL and include support for half-duplex operation using TDD. Beamforming may be supported and beam direction may be dynamically configured. Multiple input multiple output (MIMO) transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells.

InFIG.1, a solid line with double arrows indicates desired transmissions between a UE120and a serving BS110, which is a BS110designated to serve the UE120on the DL and/or UL. A finely dashed line with double arrows indicates interfering transmissions between a UE120and a BS110.

FIG.2illustrates example components of a BS110aand a UE120a(e.g., in the wireless communication network100ofFIG.1).

At the BS110a, a transmit processor220may receive data from a data source212and control information from a controller/processor240. The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical hybrid ARQ indicator channel (PHICH), physical downlink control channel (PDCCH), group common PDCCH (GC PDCCH), etc. The data may be for the physical downlink shared channel (PDSCH), etc. A medium access control (MAC)-control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. The MAC-CE may be carried in a shared channel such as a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

The transmit processor220may process (for example, encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor220may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell-specific reference signal (CRS). A transmit MIMO processor230may perform spatial processing (for example, precoding) on the data symbols, the control symbols, or the reference symbols, if applicable, and may provide output symbol streams to modulators (MODs) in transceivers232a-232t. Each modulator in transceivers232may process a respective output symbol stream (for example, for OFDM, etc.) to obtain an output sample stream. Each MOD in transceivers232may further process (for example, convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a DL signal. The DL signals from the MODs in transceivers232a-232tmay be transmitted via antennas234a-234t, respectively.

At the UE120a, antennas252a-252rmay receive DL signals from the BS110and may provide received signals to the demodulators (DEMODs) in transceivers254a-254r, respectively. Each DEMOD in the transceiver254may condition (for example, filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each DEMOD in the transceiver254may further process the input samples (for example, for OFDM, etc.) to obtain received symbols. A MIMO detector256may obtain received symbols from all the demodulators254a-254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor258may process (for example, demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE120to a data sink260, and provide decoded control information to a controller/processor280.

The memories242and282may store data and program codes for the BSa110and the UE120a, respectively. A scheduler244may schedule UEs for data transmission on the DL or UL.

Antennas252, processors266,258,264, and/or controller/processor280of the UE120aand/or antennas234, processors220,230,238, and/or controller/processor240of the BS110amay be used to perform various techniques and methods described herein. For example, as shown inFIG.2, the controller/processor280of the UE120ahas a beam manager281that may be configured to perform the operations illustrated inFIG.9, as well as other operations disclosed herein, in accordance with aspects of the present disclosure. Although shown at the controller/processor, other components of the UE120amay be used performing the operations described herein.

FIG.3is a diagram showing an example of a frame format300for NR. The transmission timeline for each of the DL and UL may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 ms) and may be partitioned into 10 subframes, each of 1 ms, with indices of 0 through 9. Each subframe may include a variable number of slots depending on the subcarrier spacing. Each slot may include a variable number of symbol periods (e.g., 7 or 14 symbols) depending on the subcarrier spacing. The symbol periods in each slot may be assigned indices. A mini-slot, which may be referred to as a sub-slot structure, refers to a transmit time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols).

In NR, a synchronization signal (SS) block is transmitted. The SS block includes a PSS, a SSS, and a two symbol PBCH. The SS block can be transmitted in a fixed slot location, such as the symbols0-3as shown inFIG.3. The PSS and SSS may be used by UEs for cell search and acquisition. The PSS may provide half-frame timing, the SS may provide the CP length and frame timing. The PSS and SSS may provide the cell identity. The PBCH carries some basic system information, such as DL system bandwidth, timing information within radio frame, SS burst set periodicity, system frame number, etc. The SS blocks may be organized into SS bursts to support beam sweeping. Further system information such as, remaining minimum system information (RMSI), system information blocks (SIBs), other system information (OSI) can be transmitted on a PDSCH in certain subframes. The SS block can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmW. The up to sixty-four transmissions of the SS block are referred to as the SS burst set. SS blocks in an SS burst set are transmitted in the same frequency region, while SS blocks in different SS bursts sets can be transmitted at different frequency locations.

Example Beam Management Procedures

In 5G new radio (NR), a beam management procedure for determining of beam pair links (BPLs) may be referred to as a P1 procedure.FIG.4illustrates an example P1 procedure402. A base station (BS)410(e.g., such as the BS110ain the wireless communication network100) may send a measurement request to a user equipment (UE)420(e.g., such as the UE120ain the wireless communication network100) and may subsequently transmit one or more signals (sometimes referred to as the “P1-signal”) to the UE420for measurement. In the P1 procedure402, the BS410transmits the signal with beam forming in a different spatial direction (corresponding to a transmit beam411,412, . . . ,417) in each symbol, such that several (e.g., most or all) relevant spatial locations of the cell of the BS410are reached. In this manner, the BS410transmits the signal using different transmit beams over time in different directions. In some examples, a synchronization signal block (SSB) is used as the P1-signal. In some examples, channel state information reference signal (CSI-RS), demodulation reference signal (DMRS), or another downlink (DL) signal can be used as the P1-signal.

In the P1 procedure402, to successfully receive at least a symbol of the P1-signal, the UE420finds (e.g., determines/selects) an appropriate receive beam (421,422, . . . ,426). Signals (e.g., SSBs) from multiple BSs can be measured simultaneously for a given signal index (e.g., SSB index) corresponding to a given time period. The UE420can apply a different receive beam during each occurrence (e.g., each symbol) of the P1-signal. Once the UE420succeeds in receiving a symbol of the P1-signal, the UE420and BS410have discovered a BPL (i.e., a UE receive (RX) beam used to receive the P1-signal in the symbol and a BS transmit (TX) beam used to transmit the P1-signal in the symbol). In some cases, the UE420does not search all of its possible UE RX beams until it finds best UE RX beam, since this causes additional delay. Instead, the UE420may select a RX beam once the RX beam is “good enough”, for example, having a quality (e.g., signal to noise ratio (SNR) or signal to interference and noise ratio (SINR)) that satisfies a threshold (e.g., predefined threshold). The UE420may not know which beam the BS410used to transmit the P1-signal in a symbol; however, the UE420may report to the BS410the time at which it observed the signal. For example, the UE420may report the symbol index in which the P1-signal was successfully received to the BS410. The BS410may receive this report and determine which BS TX beam the BS410used at the indicated time. In some examples, the UE420measures signal quality of the P1-signal, such as reference signal receive power (RSRP) or another signal quality parameter (e.g., SNR, channel flatness, etc.). The UE420may report the measured signal quality (e.g., RSRP) to the BS410together with the symbol index. In some cases, the UE420may report multiple symbol indices to the BS410, corresponding to multiple BS TX beams.

As a part of a beam management procedure, the BPL used between a UE420and a BS410may be refined/changed. For example, the BPL may be refined periodically to adapt to changing channel conditions, for example, due to movement of the UE420or other objects, fading due to Doppler spread, etc. The UE420can monitor the quality of a BPL (e.g., a BPL found/selected during the P1 procedure and/or a previously refined BPL) to refine the BPL when the quality drops (e.g., when the BPL quality drops below a threshold or when another BPL has a higher quality). In 5G NR, the beam management procedures for beam refinement of BPLs may be referred to as the P2 and P3 procedures to refine the BS-beam and UE-beam, respectively, of an individual BPL.

FIG.4further illustrates an example P2 procedure404and P3 procedure406. As shown inFIG.4, for the P2 procedure404, the BS410transmits symbols of a signal with different BS-beams (e.g., TX beams415,414,413) that are spatially close to the BS-beam of the current BPL. For example, the BS410transmits the signal in different symbols using neighboring TX beams (e.g., beam sweeps) around the TX beam of the current BPL. As shown inFIG.4, the TX beams used by the BS410for the P2 procedure404may be different from the TX beams used by the BS410for the P1 procedure402. For example, the TX beams used by the BS410for the P2 procedure404may be spaced closer together and/or may be more focused (e.g., narrower) than the TX beams used by the BS410for the P1 procedure. During the P2 procedure404, the UE420keeps its RX beam (e.g., RX beam424) constant. The UE420may measure the signal quality (e.g., RSRP) of the signal in the different symbols and indicate the symbol in which the highest signal quality was measured. Based on the indication, the BS410can determine the strongest (e.g., best, or associated with the highest signal quality) TX beam (i.e., the TX beam used in the indicated symbol). The BPL can be refined accordingly to use the indicated TX beam.

As shown inFIG.4, for the P3 procedure406, the BS420maintains a constant TX beam (e.g., the TX beam of the current BPL) and transmits symbols of a signal using the constant TX beam (e.g., TX beam414). During the P3 procedure406, the UE420scans the signal using different RX beams (e.g., RX beams423,424,425) in different symbols. For example, the UE420may perform a sweep using neighboring RX beams to the RX beam in the current BPL (i.e., the BPL being refined). The UE420may measure the signal quality (e.g., RSRP) of the signal for each RX beam and identify the strongest UE RX beam. The UE420may use the identified RX beam for the BPL. The UE420may report the signal quality to the BS410.

Example Sidelink Scenarios

FIGS.5A and5Bshow diagrammatic representations of example vehicle to everything (V2X) systems. For example, UEs such as vehicles shown in these V2X systems may communicate via sidelink channels and may perform sidelink channel state information (CSI) reporting.

The V2X systems, provided inFIGS.5A and5Bprovide two complementary transmission modes. A first transmission mode, shown by way of example inFIG.5A, involves direct communications (for example, also referred to as sidelink communications) between participants in proximity to one another in a local area. A second transmission mode, shown by way of example inFIG.5B, involves network communications through a network, which may be implemented over a Uu interface (for example, a wireless communication interface between a radio access network (RAN) and a UE).

Referring toFIG.5A, a V2X system500(for example, including vehicle to vehicle (V2V) communications) is illustrated with two vehicles502,504. The first transmission mode allows for direct communication between different participants in a given geographic location. As illustrated, a vehicle can have a wireless communication link506with an individual (V2P) (for example, via a UE) through a PC5 interface. Communications between the vehicles502and504may also occur through a PC5 interface508. In a like manner, communication may occur from a vehicle502to other highway components (for example, highway component510), such as a traffic signal or sign (V2I) through a PC5 interface512. With respect to each communication link illustrated inFIG.5A, two-way communication may take place between elements, therefore each element may be a transmitter and a receiver of information. The V2X system500may be a self-managed system implemented without assistance from a network entity. A self-managed system may enable improved spectral efficiency, reduced cost, and increased reliability as network service interruptions do not occur during handover operations for moving vehicles. The V2X system may be configured to operate in a licensed or unlicensed spectrum, thus any vehicle with an equipped system may access a common frequency and share information. Such harmonized/common spectrum operations allow for safe and reliable operation.

FIG.5Bshows a V2X system550for communication between a vehicle552and a vehicle554through a network entity556. These network communications may occur through discrete nodes, such as a BS (for example, an eNB or gNB), that sends and receives information to and from (for example, relays information between) vehicles552,554. The network communications through vehicle to network (V2N) links558and510may be used, for example, for long range communications between the vehicles552,554, such as for communicating the presence of a car accident a distance ahead along a road or highway. Other types of communications may be sent by the BS to the vehicles552,554, such as traffic flow conditions, road hazard warnings, environmental/weather reports, and service station availability, among other examples. Such data can be obtained from cloud-based sharing services.

In some circumstances, two or more subordinate entities (for example, UEs) may communicate with each other using sidelink signals. As described above, V2V and V2X communications are examples of communications that may be transmitted via a sidelink. Other applications of sidelink communications may include public safety or service announcement communications, communications for proximity services, communications for UE-to-network relaying, device-to-device (D2D) communications, peer-to-peer (P2P) communications, IoE communications, IoT communications, mission-critical mesh communications, among other suitable applications. Generally, a sidelink may refer to a direct link between one subordinate entity (for example, a UE1) and another subordinate entity (for example, a UE2). As such, a sidelink may be used to transmit and receive a communication (also referred to herein as a “sidelink signal”) without relaying the communication through a scheduling entity (for example, a BS), even though a scheduling entity may be utilized for scheduling or control purposes. In some examples, a sidelink signal may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum).

Various sidelink channels may be used for sidelink communications, including a physical sidelink discovery channel (PSDCH), a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH may carry discovery expressions that enable proximal devices to discover each other. The PSCCH may carry control signaling such as sidelink resource configurations and other parameters used for data transmissions. The PSSCH may carry the data transmissions.

For the operation regarding the PSSCH, a UE performs either transmission or reception in a slot on a carrier. New radio (NR) sidelink supports for a UE a case where all the symbols in a slot are available for sidelink, as well as another case where only a subset of consecutive symbols in a slot is available for sidelink.

The PSFCH may carry feedback such as CSI related to a sidelink channel quality. A sequence-based PSFCH format with one symbol (not including AGC training period) may be supported. The following formats may be possible: a PSFCH format based on PUCCH format 2 and a PSFCH format spanning all available symbols for sidelink in a slot.

FIG.6provides an overview of sidelink communications (broadcast and groupcast device-to-device or D2D) between UEs. As noted above, with reference toFIGS.5A and5B, sidelink generally refers to the link between two UEs or user-relays that can be used in different scenarios and for different applications.

For example, for applications with in-coverage operation, both UEs are in a BS coverage, but directly communicate. This can be assumed for enabling some gaming applications. For applications with partial-coverage operation, one UE is in-coverage, and acts as a relay to extend the coverage for other UEs. For application with out-of-coverage operation, UEs are outside the BS coverage, but still need to communicate. This type of operation is important for mission critical applications, such as V2X and public safety.

As illustrated inFIG.6, resource allocation for sidelink communications can be done in different ways. In a first mode, such as a Mode1, the BS “schedules” the sidelink resources to be used by the UE for the sidelink transmission.

For a second mode, such as a Mode2, the UE determines the sidelink resources (the BS does not schedule the sidelink transmission resources within sidelink resources configured by the BS). In this case, the UE autonomously selects the sidelink resources for transmission. A UE can assist in sidelink resource selection for other UEs. A UE may configured with an NR configured grant for sidelink transmission and the UE may schedule sidelink transmissions for other UEs.

Example Sidelink DTX Configuration with Beam Refinement

User equipments (UEs) may communicate on different operating frequency ranges such as frequency range 1 (FR1) that includes sub-6 GHz frequency bands and FR2 that includes frequency bands from 24.25 GHz to 52.6 GHz. There are various challenges presented when the UEs are operating in the FR2.

Sidelink communication (e.g. vehicle to everything (V2X)) over FR2 bands typically requires periodic beam discovery and beam alignment.FIG.7illustrates an example of periodic beam discovery opportunity (shown at t0, t1, t2. . . tn) with a periodicity Tdiscper. Each occasion has a fixed duration, shown as Tsynch, during which the UEs perform a beam sweep to determine possible beam pair links (BPLs). During these durations, the UEs may transmit synchronization signals and perform random access channel (RACH) procedures to establish, re-establish, or update connections. The UEs typically maintain a schedule to “listen” (receive) or “talk” (transmit) based on some algorithm.

The discovery periodicity Tdiscpermay be relatively large for sidelink communications (e.g., several hundred ms). The FR2 communication links may not be stable over this time. In some cases, a UE may be in a discontinuous reception (DRX) mode (when a UE only receives periodically) or a discontinuous transmission (DTX) mode (when a UE only transmits periodically) to conserve power. In DRX/DTX modes, the UEs may only monitor communication links intermittently, which may cause beam errors and misalignment, leading to low link robustness.

The FR2 communication links can be intermittent, especially with highly mobile UEs, as these links are easily blocked by common materials such as foliage, concrete, metals, and the like. Further, the FR2 communication links often require beam-formed access with narrow/pencil beams, which may go out of alignment relatively easily due to small relative motion between mobile UEs. Further, based on practical hardware constraints, the UEs can form at least one, and typically just a few beams at a time.

Moreover, communication devices operating over FR2 have higher power consumption than those operating over FR1. Hence, DTX and DRX modes may be used in an effort to limit power consumption by FR2 communication devices.

Since beam discovery periods can be far apart in time, as noted above, peer UEs may need to do a lengthy (e.g., exhaustive) beam search during beam discovery opportunities in order to select one or a few dominant beams to communicate over.

As illustrated inFIG.8A, for a given DTX pattern, because the UEs only intermittently monitor links in DTX mode, communication links may be lost or become unusable. In FR2, this may happen due to a slight change in relative speed, a change in relative orientation (as shown inFIG.8B), or a selected beam pair (BP) becoming blocked. In such cases, during the DTX on period, transmitting using same BP will lead to failure and the UE will need to wait until the next beam discovery period to re-discover beams and update the (BP) link. As a result, performance may suffer.

Aspects of the present disclosure, however, provide techniques that may be considered enhancements for DTX UEs operating using highly directional transmissions, such as V2X UEs in FR2.

According to certain aspects, certain DTX occasions may start with a short beam-refinement phase where a transmitter (Tx) UE sends sync/pilots over a subset of transmit beams identified during a previous beam discovery period. This may take much less time than an exhaustive search where all possible beams are used. A receiver (Rx) UE listens on a subset of beams based on the Tx beams (which may be indicated by the Tx UE). This phase may help quickly determine current dominant beam(s) and, in some cases, a beam refinement phase can be used to select narrower beams (increase beamforming gain) to increase link quality, and thus a communication rate. The depicted mechanism may lead to an increase in link robustness while still providing the power savings of the DTX-DRX procedure.

FIG.9illustrates example operations900for wireless communications. For example, the operations900may be performed by a first UE (such as a Tx UE) (e.g., the UE120aofFIG.1in the wireless communication network100) to perform beam refinement during a DTX on period used for sidelink communication with another UE such as a second UE (e.g., the UE120bofFIG.1in the wireless communication network100). The operations900may be implemented as software components that are executed and run on one or more processors (e.g., the controller/processor280ofFIG.2). Further, the transmission and reception of signals by the first UE in the operations900may be enabled, for example, by one or more antennas (e.g., the antennas252ofFIG.2). In certain aspects, the transmission and/or reception of signals by the first UE may be implemented via a bus interface of one or more processors (e.g., the controller/processor280) obtaining and/or outputting signals.

The operations900begin, at910, by identifying, during a discovery opportunity, a plurality of transmit beams for sidelink communications with the second UE.

At920, the first UE performs, in conjunction with a DTX occasion of the first UE, a beam refinement procedure with the second UE. The beam refinement procedure involves sending reference signals using a set of transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

For example, the transmit beams used for the beam refinement procedure may be a subset of the transmit beams identified during the discovery opportunity or may be one or more narrower beams than the transmit beams identified during the discovery opportunity. In some cases, the (narrow/refined) transmit beams used for the beam refinement procedure may not be identified during the discovery procedure. For example, the first UE may send pilots on these beams, based on the spatial configuration. In some cases, a wider transmit beam (that may not have been used for discovery) may be split into several narrower transmit beams.

FIG.10illustrates example operations1000that may be considered complementary to operations900ofFIG.9. For example, the operations1000may be performed by a first UE (such as a Rx UE) (e.g., the UE120aofFIG.1in the wireless communication network100) to perform beam refinement during a DTX on period of a second UE (such as a Tx UE) (e.g., the UE120bofFIG.1in the wireless communication network100) performing operations900ofFIG.9. The operations1000may be implemented as software components that are executed and run on one or more processors (e.g., the controller/processor280ofFIG.2). Further, the transmission and reception of signals by the first UE in the operations1000may be enabled, for example, by one or more antennas (e.g., the antennas252ofFIG.2). In certain aspects, the transmission and/or reception of signals by the first UE may be implemented via a bus interface of one or more processors (e.g., the controller/processor280) obtaining and/or outputting signals.

The operations1000begin, at1010, by identifying, during a discovery opportunity at a first UE, a plurality of receive beams for sidelink communications with the second UE.

At1020, the first UE performs, in conjunction with a DTX occasion of the second UE, the beam refinement procedure with the first UE. The beam refinement procedure involves receiving reference signals using a set of receive beams that are a subset of or differ from receive beams identified during the discovery opportunity.

For example, the receive beams used for the beam refinement procedure may be a subset of the receive beams identified during the discovery opportunity or may be narrower receive beams. As with the transmit beams, in some cases, the (narrow/refined) receive beams used for the beam refinement procedure may not be identified during the discovery procedure. For example, the first UE may split a wider receive beam (that may not have been used for discovery) into several narrower receive beams

Operations ofFIGS.9and10may be understood with reference toFIG.11, which illustrates how a Tx UE1115and a Rx UE1120may perform a beam refinement procedure during DTX on periods. As illustrated, a full scan may be performed during a beam discovery period at tn.

Between beam discovery opportunities (tnand tn+1), each DTX occasion may start with a beam refinement procedure (at1130). Performing the beam refinement procedure at the start of the DTX occasion may allow the results to be applied for subsequent data transmission (at1125) during a remaining part of the DTX occasion. The beam refinement procedure could be performed at other times of a DTX occasion, for example, at or near the end (and the results applied in a subsequent DTX occasion).

As illustrated, the beam refinement procedure may involve a quick scan where the Tx UE1115sends synchronization signals/pilots over a subset of transmit beams while the Rx UE1120listens on a subset of receive beams. This is in contrast to an exhaustive search where all beams are used.

As illustrated in the second DTX occasion, the beam refinement procedure may be used to align narrower beams in a beam-set. In some cases, the beam refinement procedure may be used to align the narrower beams only after one or more dominant beams have been confirmed during consecutive beam refinement periods.

In some cases, DTX alignment (alignment of DTX on periods) can be performed based on spatial direction of links. In some cases, UEs may align their DTX cycles to accommodate transmission and reception time division multiplexing (TDM). For example, the Tx UE1115and the Rx UE1120may TDM their DTX cycles so that the Tx UE1115and the Rx UE1120are scheduled to transmit in different times. This may help increase communication link robustness and take care of movement/mis-alignment caused during OFF periods.

Although only DTX occasion1125is discussed above, and only two shown inFIG.11, there may be any number of these periods between two successive discovery opportunities1110. Additionally, although both quick scan and beam narrowing are discussed together, one or more refinement procedure may include a quick scan, beam narrowing, or both, within a given refinement procedure.

FIG.12depicts an example1200scenario for deploying beam refinement according to disclosed embodiments. The example1200assumes a first UE1205has undergone a discovery opportunity with a second UE1215and has identified a set of BPLs, including a first BPL1220(direct line of sight), a second BPL1225(communication through a third UE1235), and a third BPL1230(communication through a fourth UE1240. For successful communication, UEs1205and1215choose BPL1220for communications at to.

At t1, corresponding to a DTX occasion, the first UE1205is obscured from the second UE1215by an obstacle1210(a 10 m width of foliage). Due to the speed of the first UE1205, it will take 300 ms to traverse the obstacle1210, potentially blocking communications for 6 50 ms DTX occasions, until the next discovery opportunity, potentially preventing communications during this traversal time. According to disclosed embodiments, rather wait for the next discovery opportunity, a beam refinement procedure may be performed at a start of the DTX occasion, on a subset of the identified BPLs. As a result of this beam refinement procedure, the third BPL1230may be identified as suitable for communications (since the first BPL1220and the second BPL1225are obstructed by the foliage). Thus, for a remainder of the DTX occasion, the third BPL1230may be used, thus enabling at least some communications.

FIG.13illustrates an example beam refinement procedure call-flow diagram1300according to embodiments of the present disclosure.

During an initial connection set-up/update, for example, similar to a discovery opportunity discussed above, a Tx UE (such as UE1) may identify a set of transmit beams for communicating with an Rx UE (such as UE2). As illustrated, UE1may indicate its DTX schedule to UE2. UE1may also indicate (e.g., in a beam refinement request) a subset of beams to use for beam refinement (e.g., by Tx beam ID). For example, UE1may identify that 3 beams are to be used and may identify their quasi co-location (QCL) relationship. The DTX schedule may indicate a fixed time duration at the beginning of a DTX period for refinement. UE2may also provide its DTX schedule, send a response to the beam refinement request from UE1, and send its own request for beam refinement (to which UE1may respond).

In some cases, UE2may indicate whether UE2is capable of performing the beam sense/refinement during a DTX occasion. If UE2is capable, UE2may indicate (in the beam refinement response) the number of Rx beams UE2sweeps for each of the Tx beams. In some cases, UE2may reject the beam refinement request, for example, due to one of hardware capability, conflict with higher priority Tx or Rx, or to avoid an increase in wake time.

In some cases, after the set-up phase is completed, the peer UEs exchange an RRC connection update message indicating the beam pairs to be used in the current DTX occasion.

In some cases, if UE2determines that one (or possibly a few, in embodiments where multi-beam is possible), beam is dominant (e.g., based on reference signal received power for one or more successive DTX occasions), UE2may take various actions. For example, UE2may continue with a current beam refinement procedure indicated in the DTX information. In some cases, UE2may request UE1to refine (narrow) beams in the next DTX occasion to increase link quality. In another case, UE2may indicate to UE1that one or more identified beam pairs are stable and request turning off of the beam refinement procedure for a number of DTX occasions (e.g., to increase the OFF period, especially when already transmitting at a high modulation and coding scheme). In another case, UE2may indicate to UE1to reduce the refinement procedure to occur less often (e.g., perform the refinement procedure one time for every three DTX occasions).

On the other hand, UE2may also take one or more actions if UE2identifies that some beam pairs have deteriorated considerably (and some are still useable). In one case, UE2may use the best possible BP in the set. In another case, UE2may request (e.g., via RRC messaging) that UE1to transmit the reference signal in other possible directions (similar to the “full scan” mentioned above). In such a case, UE1may reject the request (e.g., due to lack of resources, time constraints, priority Tx/Rx transmissions) or may accept the request and send the Tx beam configurations. In the latter case, UE2may send UE1an indication of the Rx beams it will use to scan for the Tx reference signal. In some case, UE1may continue to transmit data over deteriorated beam pairs if new beam pairs are not found, and if/once a new BP is found with better quality, UE1and UE2may exchange RRC connection updates.

In some cases, resources allocated for beam refinement (sensing during the discovery opportunity or during the refinement procedure) are not fixed. In one embodiment, UE1may need to reserve resource to transmit refinement pilots/sequences. In some cases, UE may indicate via sidelink control information (SCI) that these resources are being reserved for beam sensing/refinement. In some cases, UE2may allocate the same resources for different Tx UEs for sensing and refinement. In some cases, such resources may be allocated by a third node (e.g., gNB, RSU, sync UE, etc.) and not the UEs themselves. In some cases, the signaling indicating such resource allocation may be made on FR1, while the beam refinement is performed on FR2.

In some cases, if sufficient resources are not available for carrying out a beam refinement procedure, UE1may send an indication that refinement resources are not available. In such cases, transmission may be done on a previously agreed upon beam pair(s).

In some cases, each transmission time interval (e.g., frame/subframe) may have some fixed refinement resources (e.g., semi-static/static case). For example, the first 4 sub-frames of every 10thframe may have frequency resources (e.g., a band or within a band) reserved for beam refinement. In some cases, the availability of such resources may be indicated by a gNB, by a sync UE, or may be pre-configured.

FIG.14illustrates a communications device1400that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated inFIG.9. The communications device1400includes a processing system1402coupled to a transceiver1408(e.g., a transmitter and/or a receiver). The transceiver1408is configured to transmit and receive signals for the communications device1400via an antenna1410, such as the various signals as described herein. The processing system1402is configured to perform processing functions for the communications device1400, including processing signals received and/or to be transmitted by the communications device1400.

The processing system1402includes a processor1404coupled to a computer-readable medium/memory1412via a bus1406. In certain aspects, the computer-readable medium/memory1412is configured to store instructions (e.g., a computer-executable code) that when executed by the processor1404, cause the processor1404to perform the operations illustrated inFIG.9, or other operations for performing the various techniques discussed herein. In certain aspects, computer-readable medium/memory1412stores code1414for identifying and code1416for performing. The code1414for identifying may include code for identifying, during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE. The code1416for performing may include code for performing, in conjunction with a DTX occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

The processor1404may include circuitry configured to implement the code stored in the computer-readable medium/memory1412, such as for performing the operations illustrated inFIG.9, as well as other operations for performing the various techniques discussed herein. For example, the processor1404includes circuitry1418for identifying and circuitry1420for performing. The circuitry1418for identifying may include circuitry for identifying, during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE. The circuitry1420for performing may include circuitry for performing, in conjunction with a DTX occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

FIG.15illustrates a communications device1500that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated inFIG.10. The communications device1500includes a processing system1502coupled to a transceiver1508(e.g., a transmitter and/or a receiver). The transceiver1508is configured to transmit and receive signals for the communications device1500via an antenna1510, such as the various signals as described herein. The processing system1502is configured to perform processing functions for the communications device1500, including processing signals received and/or to be transmitted by the communications device1500.

The processing system1502includes a processor1504coupled to a computer-readable medium/memory1512via a bus1506. In certain aspects, the computer-readable medium/memory1512is configured to store instructions (e.g., a computer-executable code) that when executed by the processor1504, cause the processor1504to perform the operations illustrated inFIG.10, or other operations for performing the various techniques discussed herein. In certain aspects, computer-readable medium/memory1512stores code1514for identifying and code1516for performing. The code1514for identifying may include code for identifying, during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE. The code1516for performing may include code for performing, in conjunction with a DTX occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves receiving reference signals using receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

The processor1504may include circuitry configured to implement the code stored in the computer-readable medium/memory1512, such as for performing the operations illustrated inFIG.10, as well as other operations for performing the various techniques discussed herein. For example, the processor1504includes circuitry1518for identifying and circuitry1520for performing. The circuitry1518for identifying may include circuitry for identifying, during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE. The circuitry1520for performing may include circuitry for performing, in conjunction with a DTX occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves receiving reference signals using receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

EXAMPLE ASPECTS

Implementation examples are described in the following numbered aspects.

In a first aspect, a method for wireless communications by a first user equipment (UE), comprising: identifying, during a discovery opportunity, a plurality of transmit beams for sidelink communications with a second UE; and performing, in conjunction with a discontinuous transmission (DTX) occasion of the first UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves sending reference signals using transmit beams that are a subset of or differ from the transmit beams identified during the discovery opportunity.

In a second aspect, alone or in combination with the first aspect, the beam refinement procedure is performed at a start of the DTX occasion.

In a third aspect, alone or in combination with one or more of the first and second aspects, aligning DTX occasions based on results of the beam refinement procedure or to accommodate the beam refinement procedure.

In a fourth aspect, alone or in combination with one or more of the first through third aspects, signaling the second UE an indication of the subset of transmit beams for the beam refinement procedure.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, receiving, from the second UE, an indication the second UE is capable of performing the beam refinement procedure.

In a sixth aspect, alone or in combination with one or more of the first through fifth aspects, the indication includes a number of receive beams the second UE is to sweep for each of the transmit beams used in the beam refinement procedure.

In a seventh aspect, alone or in combination with one or more of the first through sixth aspects, sending a request to the second UE to perform the beam refinement procedure; and performing the beam refinement procedure only if the second UE accepts the request.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, after performing the beam refinement procedure, exchanging information with the second UE regarding one or more beam pair to be used in a current or subsequent DTX occasion.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, taking one or more actions if feedback from the second UE indicates one or more of the subset of transmit beams are dominant.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the one or more actions comprise using narrow beams during a beam refinement procedure for a subsequent DTX occasion.

In an eleventh aspect, alone or in combination with one or more of the first through tenth aspects, the feedback comprises a request from the second UE to refine the transmit beams used in the beam refinement procedure in a subsequent DTX occasion; and the one or more actions comprise refining the transmit beams per the request.

In a twelfth aspect, alone or in combination with one or more of the first through eleventh aspects, the feedback comprises a request from the second UE to at least temporarily stop performing the beam refinement procedure in one or more subsequent DTX occasions; and the one or more actions comprise at least temporarily stopping performing the beam refinement procedure per the request.

In a thirteenth aspect, alone or in combination with one or more of the first through twelfth aspects, the feedback comprises a request from the second UE to perform the beam refinement procedure less frequently; and the one or more actions comprise performing the beam refinement procedure less frequently per the request.

In a fourteenth aspect, alone or in combination with one or more of the first through thirteenth aspects, taking one or more actions if feedback from the second UE indicates one or more of the subset of transmit beams has deteriorated.

In a fifteenth aspect, alone or in combination with one or more of the first through fourteenth aspects, the feedback indicates at least one of the subset of transmit beams is still usable; and the one or more actions comprise using a beam pair involving the usable beam for one or successive DTX occasions.

In a sixteenth aspect, alone or in combination with one or more of the first through fifteenth aspects, the feedback comprises a request for the first UE to send reference signals in different directions using transmit beams other than the subset of transmit beams; and the one or more actions comprise sending the reference signals per the request.

In a seventeenth aspect, alone or in combination with one or more of the first through sixteenth aspects, sending the second UE information regarding the other transmit beams used to send the reference signals.

In an eighteenth aspect, alone or in combination with one or more of the first through seventeenth aspects, receiving feedback indicating one or more of the other beams was suitable; and exchanging information with the second UE regarding one or more beam pairs with one of the suitable beams to be used in a current or subsequent DTX occasion.

In a nineteenth aspect, alone or in combination with one or more of the first through eighteenth aspects, indicating, to the second UE, resources allocated for the beam refinement procedure.

In a twentieth aspect, alone or in combination with one or more of the first through nineteenth aspects, receiving, from another entity, an indication of resources allocated for the beam refinement procedure.

In a twenty-first aspect, alone or in combination with one or more of the first through twentieth aspects, beam refinement is performed in a first frequency range; and resources allocated for the beam refinement procedure are signaled via a second frequency range.

In a twenty-second aspect, alone or in combination with one or more of the first through twenty-first aspects, signaling the second UE an indication that sufficient resources are not available for the beam refinement procedure; and transmitting, during a DTX occasion, using a previously agreed beam pair.

In a twenty-third aspect, alone or in combination with one or more of the first through twenty-second aspects, fixed resources are allocated for the beam refinement procedure for a set of transmission time intervals (TTIs).

In a twenty-fourth aspect, alone or in combination with one or more of the first through twenty-third aspects, sending a request to one or more other UEs to adjust their DTX occasions to accommodate beam refinement procedures.

In a twenty-fifth aspect, alone or in combination with one or more of the first through twenty-fourth aspects, the request is sent via an offset alignment message that contains at least one of a time offset or updated common measurement period.

In a twenty-sixth aspect, alone or in combination with one or more of the first through twenty-fifth aspects, limiting the number of beam refinement procedures performed by at least one of: refraining from indicating a beam refinement period of the first UE to one or more other UEs; or sending at least one other UE a message to disable beam refinement periods for DTX occasions.

In a twenty-seventh aspect, a method for wireless communications by a first user equipment (UE), comprising: identifying, during a discovery opportunity, a plurality of receive beams for sidelink communications with a second UE; and performing, in conjunction with a discontinuous transmission (DTX) occasion of the second UE, a beam refinement procedure with the second UE, wherein the beam refinement procedure involves receiving reference signals using receive beams that are a subset of or differ from the receive beams identified during the discovery opportunity.

In a twenty-eighth aspect, alone or in combination with the twenty-seventh aspect, the beam refinement procedure is performed at a start of the DTX occasion.

In a twenty-ninth aspect, alone or in combination with one or more of the twenty-seventh and twenty-eighth aspects, receiving, from the second UE, an indication of the subset of transmit beams for the beam refinement procedure.

In a thirtieth aspect, alone or in combination with one or more of the twenty-seventh through twenty-ninth aspects, sending, to the second UE, an indication the first UE is capable of performing the beam refinement procedure.

In a thirty-first aspect, alone or in combination with one or more of the twenty-seventh through thirtieth aspects, the indication includes a number of receive beams the first UE is to sweep for each of the transmit beams used in the beam refinement procedure.

In a thirty-second aspect, alone or in combination with one or more of the twenty-seventh through thirty-first aspects, receiving a request from the second UE to perform the beam refinement procedure; and performing the beam refinement procedure only after sending a response to accept the request.

In a thirty-third aspect, alone or in combination with one or more of the twenty-seventh through thirty-second aspects, after performing the beam refinement procedure, exchanging information with the second UE regarding one or more beam pair to be used in a current or subsequent DTX occasion.

In a thirty-fourth aspect, alone or in combination with one or more of the twenty-seventh through thirty-third aspects, providing feedback to the second UE that indicates one or more of the subset of transmit beams are dominant.

In a thirty-fifth aspect, alone or in combination with one or more of the twenty-seventh through thirty-fourth aspects, using narrow beams during a beam refinement procedure for a subsequent DTX occasion.

In a thirty-sixth aspect, alone or in combination with one or more of the twenty-seventh through thirty-fifth aspects, the feedback comprises a request to refine the transmit beams used in the beam refinement procedure in a subsequent DTX occasion.

In a thirty-seventh aspect, alone or in combination with one or more of the twenty-seventh through thirty-sixth aspects, the feedback comprises a request to at least temporarily stop performing the beam refinement procedure in one or more subsequent DTX occasions.

In a thirty-eighth aspect, alone or in combination with one or more of the twenty-seventh through thirty-seventh aspects, the feedback comprises a request to perform the beam refinement procedure less frequently.

In a thirty-ninth aspect, alone or in combination with one or more of the twenty-seventh through thirty-ninth aspects, providing the second UE feedback that indicates one or more of the subset of transmit beams has deteriorated.

In a fortieth aspect, alone or in combination with one or more of the twenty-seventh through thirty-ninth aspects, the feedback indicates at least one of the subset of transmit beams is still usable; and the beam refinement procedure is performed using a beam pair involving the usable beam for one or successive DTX occasions.

In a forty-first aspect, alone or in combination with one or more of the twenty-seventh through fortieth aspects, the feedback comprises a request for the first UE to send reference signals in different directions than a subset of transmit beams previously used for a beam refinement procedure.

In a forty-second aspect, alone or in combination with one or more of the twenty-seventh through forty-first aspects, receiving, from the second UE, information regarding the other transmit beams used to send the reference signals.

In a forty-third aspect, alone or in combination with one or more of the twenty-seventh through forty-second aspects, sending feedback, to the second UE, indicating one or more of the other beams was suitable; and exchanging information with the second UE regarding one or more beam pairs with one of the suitable beams to be used in a current or subsequent DTX occasion.

In a forty-fourth aspect, alone or in combination with one or more of the twenty-seventh through forty-third aspects, receiving, from the second UE, an indication of resources allocated for the beam refinement procedure.

In a forty-fifth aspect, alone or in combination with one or more of the twenty-seventh through forty-fourth aspects, receiving, from another entity, an indication of resources allocated for the beam refinement procedure.

In a forty-sixth aspect, alone or in combination with one or more of the twenty-seventh through forty-fifth aspects, the beam refinement is performed in a first frequency range; and resources allocated for the beam refinement procedure are signaled via a second frequency range.

In a forty-seventh aspect, alone or in combination with one or more of the twenty-seventh through forty-sixth aspects, receiving, from the second UE, signaling of an indication that sufficient resources are not available for the beam refinement procedure; and receiving, during a DTX occasion, using a previously agreed beam pair.

In a forty-eighth aspect, alone or in combination with one or more of the twenty-seventh through forty-seventh aspects, fixed resources are allocated for the beam refinement procedure for a set of transmission time intervals (TTIs).

In a forty-ninth aspect, alone or in combination with one or more of the twenty-seventh through forty-eighth aspects, sending a request to one or more other UEs to adjust their DTX occasions to accommodate beam refinement procedures.

In a fiftieth aspect, alone or in combination with one or more of the twenty-seventh through forty-ninth aspects, the request is sent via an offset alignment message that contains at least one of a time offset or updated common measurement period.

In a fifty-first aspect, alone or in combination with one or more of the twenty-seventh through fiftieth aspects, limiting the number of beam refinement procedures performed by at least one of: refraining from indicating a beam refinement period of the first UE to one or more other UEs; or sending at least one other UE a message to disable beam refinement periods for DTX occasions.

An apparatus for wireless communication, comprising at least one processor; and a memory coupled to the at least one processor, the memory comprising code executable by the at least one processor to cause the apparatus to perform the method of any of the first through fifty-first aspects.

An apparatus comprising means for performing the method of any of the first through fifty-first aspects.

A computer readable medium storing computer executable code thereon for wireless communications that, when executed by at least one processor, cause an apparatus to perform the method of any of the first through fifty-first aspects.

ADDITIONAL CONSIDERATIONS