Patent ID: 12219507

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

This disclosure relates generally to wireless communications systems, also referred to as wireless communications networks. In various instances, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, 5thGeneration (5G) or new radio (NR) networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA), Institute of Electrical and Electronic Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA, and Global System for Mobile Communications (GSM) are part of universal mobile telecommunication system (UMTS). In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from an organization named “3rd Generation Partnership Project” (3GPP), and cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project which was aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. The present disclosure is concerned with the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

In particular, 5G networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of the new radio technology for 5G NR networks. The 5G NR will be capable of scaling to provide coverage (1) to a massive Internet of things (IoTs) with an ultra-high density (e.g., ˜1 M nodes/km2), ultra-low complexity (e.g., ˜10 s of bits/sec), ultra-low energy (e.g., ˜10+ years of battery life), and deep coverage with the capability to reach challenging locations; (2) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ˜99.9999% reliability), ultra-low latency (e.g., ˜1 ms), and users with wide ranges of mobility or lack thereof; and (3) with enhanced mobile broadband including extreme high capacity (e.g., ˜10 Tbps/km2), extreme data rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates), and deep awareness with advanced discovery and optimizations.

The 5G NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI); having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD)/frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO), robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in 5G NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than 3 GHz FDD/TDD implementations, subcarrier spacing may occur with 15 kHz, for example over 5, 10, 20 MHz, and the like bandwidth (BW). For other various outdoor and small cell coverage deployments of TDD greater than 3 GHz, subcarrier spacing may occur with 30 kHz over 80/100 MHz BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the 5 GHz band, the subcarrier spacing may occur with 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting with mmWave components at a TDD of 28 GHz, subcarrier spacing may occur with 120 kHz over a 500 MHz BW.

The scalable numerology of the 5G NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. For example, shorter TTI may be used for low latency and high reliability, while longer TTI may be used for higher spectral efficiency. The efficient multiplexing of long and short TTIs to allow transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with uplink/downlink scheduling information, data, and acknowledgement in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, adaptive uplink/downlink that may be flexibly configured on a per-cell basis to dynamically switch between uplink and downlink to meet the current traffic needs.

Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim.

The deployment of NR over an unlicensed spectrum is referred to as NR-unlicensed (NR-U). Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) are working on regulating 6 GHz as a new unlicensed band for wireless communications. The addition of 6 GHz bands allows for hundreds of megahertz (MHz) of bandwidth (BW) available for unlicensed band communications. Additionally, NR-U can also be deployed over 2.4 GHz unlicensed bands, which are currently shared by various radio access technologies (RATs), such as IEEE 802.11 wireless local area network (WLAN) or WiFi and/or license assisted access (LAA). Sidelink communications may benefit from utilizing the additional bandwidth available in an unlicensed spectrum. However, channel access in a certain unlicensed spectrum may be regulated by authorities. For instance, some unlicensed bands may impose restrictions on the power spectral density (PSD) and/or minimum occupied channel bandwidth (OCB) for transmissions in the unlicensed bands. For example, the unlicensed national information infrastructure (UNIT) radio band has a minimum OCB requirement of about 70 percent (%).

Some sidelink systems may operate over a 20 MHz bandwidth in an unlicensed band. ABS may configure a sidelink resource pool over the 20 MHz band for sidelink communications. A sidelink resource pool is typically partitioned into multiple frequency subchannels or frequency subbands (e.g., about 5 MHz each) and a sidelink UE may select a sidelink resource (e.g., a subchannel) from the sidelink resource pool for sidelink communication. To satisfy an OCB of about 70%, a sidelink resource pool may utilize a frequency-interlaced structure. For instance, a frequency-interlaced-based sidelink resource pools may include a plurality of frequency interlaces over the 20 MHz band, where each frequency interlace may include a plurality of resource blocks (RBs) distributed over the 20 MHz band. For example, the plurality of RBs of a frequency interlace may be spaced apart from each other by one or more other RBs in the 20 MHz unlicensed band. A sidelink UE may select a sidelink resource in the form of frequency interlaces from the sidelink resource pool for sidelink communication. In other words, sidelink transmissions may utilize a frequency-interlaced waveform to satisfy an OCB of the unlicensed band. However, S-SSBs may be transmitted in a set of contiguous RBs, for example, in about eleven contiguous RBs. As such, S-SSB transmissions alone may not meet the OCB requirement of the unlicensed band. Accordingly, it may be desirable for a sidelink sync UE to multiplex an S-SSB transmission with one or more channel state information reference signals (CSI-RSs) in a slot configured for S-SSB transmission so that the sidelink sync UE's transmission in the slot may comply with an OCB requirement.

The present application describes mechanisms for a sidelink UE to multiplex an S-SSB transmission with a CSI-RS transmission in a frequency band to satisfy an OCB of the frequency band. For instance, the sidelink UE may determine a multiplex configuration for multiplexing a CSI-RS transmission with an S-SSB transmission in a sidelink BWP. The sidelink UE may transmit the S-SSB transmission in the sidelink BWP during a sidelink slot. The sidelink UE may transmit one or more CSI-RSs in the sidelink BWP during the sidelink slot by multiplexing the CSI-RS and the S-SSB transmission based on the multiplex configuration.

In some aspects, the sidelink UE may transmit the S-SSB transmission at an offset from a lowest frequency of the sidelink BWP based on a synchronization raster (e.g., an NR-U sync raster). In some aspects, the sidelink UE may transmit the S-SSB transmission aligned to a lowest frequency of the sidelink BWP. For instance, a sync raster can be defined for sidelink such that the S-SSB transmission may be aligned to a lowest frequency of the sidelink BWP.

In some aspects, the multiplex configuration includes a configuration for multiplexing the S-SSB transmission with a frequency interlaced waveform sidelink transmission to meet the OCB requirement. For instance, the sidelink transmission may include a CSI-RS transmission multiplexed in frequency within a frequency interlace with RBs spaced apart in the sidelink BWP. In some instances, the sidelink UE may rate-match the CSI-RS transmission around RBs that are at least partially overlapping with the S-SSB transmission.

In some aspects, the multiplex configuration includes a configuration for multiplexing the S-SSB transmission with a subchannel-based sidelink transmission to meet the OCB requirement. For instance, the sidelink transmission may include a CSI-RS transmission multiplexed in time within a subchannel including contiguous RBs in the sidelink BWP. For instance, the S-SSB transmission may be transmitted at a low frequency portion of the sidelink BWP, and the CSI-RS may be transmitted in a subchannel located at a high frequency portion of the sidelink BWP to meet the OCB.

In some aspects, a BS may configure different sidelink resource pools for slots that are associated with S-SSB transmissions and for slots that are not associated with S-SSB transmissions. For instance, the BS may configure a first resource pool with a frequency-interlaced structure for slots that are not configured for S-SSB transmissions. The first resource pool may include a plurality of frequency interlaces (e.g., distributed RBs), where each frequency interlace may carry a PSCCH/PSSCH transmission. The BS may configure a second resource pool with a subchannel-based structure for slots that are configured for S-SSB transmission. The second resource pool may include a plurality of frequency subchannels (e.g., contiguous RBs), where each subchannel may carry a PSCCH/PSSCH transmission. To satisfy an OCB in a sidelink slot configured for an S-SSB transmission, the sidelink UE (e.g., a sidelink sync UE) may transmit an S-SSB transmission multiplexed with a CSI-RS transmission. For instance, the S-SSB transmission may be transmitted in frequency resources located at a lower frequency portion of a sidelink BWP and the CSI-RS transmission may be transmitted in frequency resources located at higher frequency portion of the sidelink BWP.

FIG.1illustrates a wireless communication network100according to some aspects of the present disclosure. The network100includes a number of base stations (BSs)105and other network entities. A BS105may be a station that communicates with UEs115and may also be referred to as an evolved node B (eNB), a next generation eNB (gNB), an access point, and the like. Each BS105may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS105and/or a BS subsystem serving the coverage area, depending on the context in which the term is used.

ABS105may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a pico cell, would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a femto cell, would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS or a home BS. In the example shown inFIG.1, the BSs105dand105emay be regular macro BSs, while the BSs105a-105cmay be macro BSs enabled with one of three dimension (3D), full dimension (FD), or massive MIMO. The BSs105a-105cmay take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS105fmay be a small cell BS which may be a home node or portable access point. ABS105may support one or multiple (e.g., two, three, four, and the like) cells.

The network100may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time.

The UEs115are dispersed throughout the wireless network100, and each UE115may be stationary or mobile. A UE115may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE115may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. In one aspect, a UE115may be a device that includes a Universal Integrated Circuit Card (UICC). In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs115that do not include UICCs may also be referred to as IoT devices or internet of everything (IoE) devices. The UEs115a-115dare examples of mobile smart phone-type devices accessing network100. A UE115may also be a machine specifically configured for connected communication, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. The UEs115e-115hare examples of various machines configured for communication that access the network100. The UEs115i-115kare examples of vehicles equipped with wireless communication devices configured for communication that access the network100. A UE115may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. InFIG.1, a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE115and a serving BS105, which is a BS designated to serve the UE115on the downlink (DL) and/or uplink (UL), desired transmission between BSs105, backhaul transmissions between BSs, or sidelink transmissions between UEs115.

In operation, the BSs105a-105cmay serve the UEs115aand115busing 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS105dmay perform backhaul communications with the BSs105a-105c, as well as small cell, the BS105f. The macro BS105dmay also transmits multicast services which are subscribed to and received by the UEs115cand115d. Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

The BSs105may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs105(e.g., which may be an example of an evolved NodeB (eNB) or an access node controller (ANC)) may interface with the core network130through backhaul links (e.g., S1, S2, etc.) and may perform radio configuration and scheduling for communication with the UEs115. In various examples, the BSs105may communicate, either directly or indirectly (e.g., through core network), with each other over backhaul links (e.g., X1, X2, etc.), which may be wired or wireless communication links.

The network100may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE115e, which may be a vehicle (e.g., a car, a truck, a bus, an autonomous vehicle, an aircraft, a boat, etc.). Redundant communication links with the UE115emay include links from the macro BSs105dand105e, as well as links from the small cell BS105f. Other machine type devices, such as the UE115f(e.g., a thermometer), the UE115g(e.g., smart meter), and UE115h(e.g., wearable device) may communicate through the network100either directly with BSs, such as the small cell BS105f, and the macro BS105e, or in multi-hop configurations by communicating with another user device which relays its information to the network, such as the UE115fcommunicating temperature measurement information to the smart meter, the UE115g, which is then reported to the network through the small cell BS105f. The network100may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as vehicle-to-vehicle (V2V), vehicle-to-everything (V2X), cellular-vehicle-to-everything (C-V2X) communications between a UE115i,115j, or115kand other UEs115, and/or vehicle-to-infrastructure (V21) communications between a UE115i,115j, or115kand a BS105.

In some implementations, the network100utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable.

In some instances, the BSs105can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB)) for downlink (DL) and uplink (UL) transmissions in the network100. DL refers to the transmission direction from a BS105to a UE115, whereas UL refers to the transmission direction from a UE115to a BS105. The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes, for example, about 10. Each subframe can be divided into slots, for example, about 2. Each slot may be further divided into mini-slots. In a FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a TDD mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions.

The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs105and the UEs115. For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS105may transmit cell specific reference signals (CRSs) and/or channel state information—reference signals (CSI-RSs) to enable a UE115to estimate a DL channel. Similarly, a UE115may transmit sounding reference signals (SRSs) to enable a BS105to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some instances, the BSs105and the UEs115may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for UL communication.

In some instances, the network100may be an NR network deployed over a licensed spectrum. The BSs105can transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)) in the network100to facilitate synchronization. The BSs105can broadcast system information associated with the network100(e.g., including a master information block (MIB), remaining minimum system information (RMSI), and other system information (OSI)) to facilitate initial network access. In some instances, the BSs105may broadcast the PSS, the SSS, and/or the MIB in the form of synchronization signal blocks (SSBs) over a physical broadcast channel (PBCH) and may broadcast the RMSI and/or the OSI over a physical downlink shared channel (PDSCH).

In some instances, a UE115attempting to access the network100may perform an initial cell search by detecting a PSS from a BS105. The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE115may then receive an SSS. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The SSS may also enable detection of a duplexing mode and a cyclic prefix length. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier.

After receiving the PSS and SSS, the UE115may receive a MIB. The MIB may include system information for initial network access and scheduling information for RMSI and/or OSI. After decoding the MIB, the UE115may receive RMSI and/or OSI. The RMSI and/or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical uplink control channel (PUCCH), physical uplink shared channel (PUSCH), power control, SRS, and cell barring.

After obtaining the MIB, the RMSI and/or the OSI, the UE115can perform a random access procedure to establish a connection with the BS105. For the random access procedure, the UE115may transmit a random access preamble and the BS105may respond with a random access response. Upon receiving the random access response, the UE115may transmit a connection request to the BS105and the BS105may respond with a connection response (e.g., contention resolution message).

After establishing a connection, the UE115and the BS105can enter a normal operation stage, where operational data may be exchanged. For example, the BS105may schedule the UE115for UL and/or DL communications. The BS105may transmit UL and/or DL scheduling grants to the UE115via a PDCCH. The BS105may transmit a DL communication signal to the UE115via a PDSCH according to a DL scheduling grant. The UE115may transmit a UL communication signal to the BS105via a PUSCH and/or PUCCH according to a UL scheduling grant.

In some aspects, the UE115cmay receive an indicator indicating a tracking reference signal (TRS) periodicity from the UE115a. The UE115cmay receive a TRS based on the TRS periodicity from the UE115a. The UE115cmay acquire time and/or frequency synchronization with the UE115abased on the TRS. The UE115cmay receive a physical sidelink shared channel (PSSCH) communication from the UE115abased on the time and/or frequency synchronization with the UE115a. Aspects of the present disclosure may increase time and/or frequency synchronization between the UE115cand the UE115a(e.g., sidelink UEs) thereby increasing the probability of successful decoding of communications by the UE115c.

FIG.2illustrates sidelink resources associated with a wireless communication network200according to some aspects of the present disclosure. The wireless communications network200may include a base station105aand UEs115a,115b, and115c, which may be examples of a BS105and a UE115as described with reference toFIG.1. Base station105aand UEs115aand115cmay communicate within geographic coverage area110aand via communication links205aand205b, respectively. UE115cmay communicate with UEs115aand115bvia sidelink communication links210aand210b, respectively. In some examples, UE115cmay transmit SCI to UEs115aand115bvia the sidelink control resources220. The SCI may include an indication of resources reserved for retransmissions by UE115c(e.g., the reserved resources225). In some examples, UEs115aand115bmay determine to reuse one or more of the reserved resources225.

In some aspects, a device in the wireless communication network200(e.g., a UE115, a BS105, or some other node) may convey SCI to another device (e.g., another UE115, a BS105, sidelink device or vehicle-to-everything (V2X) device, or other node). The SCI may be conveyed in one or more stages. The first stage SCI may be carried on the PSCCH while the second stage SCI may be carried on the corresponding PSSCH. For example, UE115cmay transmit a PSCCH/first stage SCI235(e.g., SCI-1) to each sidelink UE115in the network (e.g., UEs115aand115b) via the sidelink communication links210. The PSCCH/first stage SCI-1235may indicate resources that are reserved by UE115cfor retransmissions (e.g., the SCI-1 may indicate the reserved resources225for retransmissions). Each sidelink UE115may decode the first stage SCI-1 to determine where the reserved resources225are located (e.g., to refrain from using resources that are reserved for another sidelink transmission and/or to reduce resource collision within the wireless communications network200). Sidelink communication may include a mode 1 operation in which the UEs115are in a coverage area of BS105a. In mode 1, the UEs115may receive a configured grant from the BS105athat defines parameters for the UEs115to access the channel. Sidelink communication may also include a mode 2 operation in which the UEs115operate autonomously from the BS105aand perform sensing of the channel to gain access to the channel. In some aspects, during mode 2 sidelink operations, the sidelink UEs115may perform channel sensing to locate resources reserved by other sidelink transmissions. The first stage SCI-1 may reduce the need for sensing each channel. For example, the first stage SCI-1 may include an explicit indication such that the UEs115may refrain from blindly decoding each channel. The first stage SCI-1 may be transmitted via the sidelink control resources220. The sidelink control resources220may be configured resources (e.g., time resources or frequency resources) transmitted via a PSCCH235. In some examples, the PSCCH235may be configured to occupy a number of physical resource blocks (PRBs) within a selected frequency. The frequency may include a single subchannel250(e.g., 10, 12, 15, 20, 25, or some other number of RBs within the subchannel250). The time duration of the PSCCH235may be configured by the BS105a(e.g., the PSCCH235may span 1, 2, 3, or some other number of symbols255).

The first stage SCI-1 may include one or more fields to indicate a location of the reserved resources225. For example, the first stage SCI-1 may include, without limitation, one or more fields to convey a frequency domain resource allocation (FDRA), a time domain resource allocation (TDRA), a resource reservation period245(e.g., a period for repeating the SCI transmission and the corresponding reserved resources225), a modulation and coding scheme (MCS) for a second stage SCI-2240, a beta offset value for the second stage SCI-2240, a DMRS port (e.g., one bit indicating a number of data layers), a physical sidelink feedback channel (PSFCH) overhead indicator, a priority, one or more additional reserved bits, or a combination thereof. The beta offset may indicate the coding rate for transmitting the second stage SCI-2240. The beta offset may indicate an offset to the MCS index. The MCS may be indicated by an index ranging from 0 to 31. For example, if the MCS is set at index 16 indicating a modulation order of 4 and a coding rate of 378, the beta offset may indicate a value of 2 thereby setting the coding rate to 490 based on an MCS index of 18. In some examples, the FDRA may be a number of bits in the first stage SCI-1 that may indicate a number of slots238and a number of subchannels reserved for the reserved resources225(e.g., a receiving UE115may determine a location of the reserved resources225based on the FDRA by using the subchannel250including the PSCCH235and first stage SCI-1 as a reference). The TDRA may be a number of bits in the first stage SCI-1 (e.g., 5 bits, 9 bits, or some other number of bits) that may indicate a number of time resources reserved for the reserved resources225. In this regard, the first stage SCI-1 may indicate the reserved resources225to the one or more sidelink UEs115in the wireless communication network200.

In some aspects, the BS105may configure a sidelink UE115as a sidelink sync UE (e.g., the UE115c). When operating as a sidelink sync UE, the UE115may broadcast S-SSBs which may include synchronization signals (e.g., PSS and/or SSS) and sidelink system information, such as a sidelink BWP configuration, one or more sidelink transmit resource pools, and/or one or more sidelink receive resource pools, S-SSB transmission related parameters (e.g., sidelink slots238configured for S-SSB transmission and/or S-SSB transmission periodicity), and/or any other configuration information related to sidelink communications as will be discussed more fully below. Accordingly, other UEs (e.g., the UEs115dand115e) that are nearby the UE115c, but may be out of the coverage of the BS105may listen to and synchronize to the S-SSBs and communicate with each other based on the S-SSBs.

In some aspects, the UE115cmay receive an indicator indicating a tracking reference signal (TRS) periodicity from the UE115a. The UE115cmay receive a TRS based on the TRS periodicity from the UE115a. The UE115cmay acquire time and/or frequency synchronization with the UE115abased on the TRS. The UE115cmay receive a physical sidelink shared channel (PSSCH) communication from the UE115abased on the time and/or frequency synchronization with the UE115a. Aspects of the present disclosure may increase time and/or frequency synchronization between the UE115cand the UE115a(e.g., sidelink UEs) thereby increasing the probability of successful decoding of communications by the UE115c.

FIG.3illustrates tracking reference signal (TRS)322resources according to some aspects of the present disclosure. InFIG.3, the x-axis represents time in some arbitrary units and the y-axis represents frequency in some arbitrary units. In some aspects, a first sidelink UE (e.g., the UE115or the UE900) may receive an indicator indicating a tracking reference signal (TRS) periodicity310. The first sidelink UE may receive the indicator from a second sidelink UE. In some aspects, the first sidelink UE may periodically receive a TRS322from the second sidelink UE based on the TRS periodicity310. In this regard, the first sidelink UE may receive a TRS configuration including the indicator indicating the TRS periodicity310. The first sidelink UE may receive the TRS configuration from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH316, a PSCCH318, an RRC message, a MAC-CE message, or other suitable communication. Additionally or alternatively, the first sidelink UE may receive an indicator of the TRS periodicity310from a BS (e.g., the BS105or1000) via a PDCCH, a PDSCH, DCI, an RRC message, a MAC-CE message, or other suitable communication.

The TRS periodicity310may be based on a mobility associated with the first sidelink UE and/or the second sidelink UE. For example, the first sidelink UE and/or the second sidelink UE may be a stationary device (e.g., an IoT device such as a programmable logic controller (PLC) or roadside unit (RSU)) configured with a longer TRS periodicity310as compared to a mobile UE (e.g., a vehicle or a smartphone) configured with a shorter TRS periodicity310. A higher mobility device may be configured with a shorter TRS periodicity310in order to update the time/frequency synchronization to compensate for a Doppler frequency shift and/or other changes associated with the device changing positions. In some aspects, the second sidelink UE may transmit TRS(s)322at different TRS periodicities310based on the mobility of the first sidelink UE. In this regard, the first sidelink UE may transmit an indicator to the second UE indicating a mobility associated with the first sidelink UE. For example, the indicator may include a type (e.g., a class) of UE (e.g., a vehicle, a sensor, a PLC, a roadside unit) that indicates a mobility of the first sidelink UE. In some aspects, the first sidelink UE may transmit to the second sidelink UE an indication of the first sidelink UE's speed and/or direction. The first sidelink UE's speed and direction may be determined based on a GPS receiver, RF triangulation, or other suitable method. In some aspects, the second sidelink UE may transmit a new TRS periodicity310to the first sidelink UE when the mobility of the first sidelink UE changes (e.g., when the mobility change of the first sidelink UE satisfies a threshold).

The TRS periodicity310may indicate the times at which the first sidelink UE receives the TRS(s)322from the second sidelink UE. The first UE may receive an indicator indicating a TRS window314(e.g., a resource selection window). The TRS window314may be a time period in which the first sidelink UE receives the TRS(s)322. The TRS window314may be indicated in the communication that includes the indicator indicating the TRS periodicity310and/or the UE may receive the indicator indicating the TRS window314in a separate communication. For example, the first sidelink UE may receive the indicator indicating the TRS window314from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH316, a PSCCH318, an RRC message, a MAC-CE message, or other suitable communication. The TRS window314may indicate a starting time and/or an ending time in which the first sidelink UE may receive the TRS(s)322. In this regard, the starting time may correspond to a first slot312index and the ending time may correspond to a second slot312index (e.g., the last slot in the TRS window314). In some instances, the first sidelink UE may receive the TRS(s)322in any slot312between the first slot312index and the second slot312index defining the TRS window314, including the slots312associated with the first and second slot indexes. In this regard, the first sidelink UE may receive the symbol index indication in a time domain resource allocation (TDRA). The TDRA may be carried by SCI-1 via the PSCCH318. The second sidelink UE may randomly select a slot312within the TRS window314for transmitting the TRS(s)322.

In some aspects, the first sidelink UE may receive an indicator indicating which slot in the TRS window314the second sidelink UE will transmit the TRS(s)322. For example, the indicator may correspond to a TRS transmission window offset313from the beginning of the TRS window314and/or a slot index (e.g., slot index312(1),312(2), or312(3)). The slot312index may be indicated in the communication that includes the indicator indicating the TRS periodicity310and/or the indicator indicating the TRS window314, and/or the first sidelink UE may receive the indicator indicating the slot312index in a separate communication. For example, the first sidelink UE may receive the indicator indicating the slot312index from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH316, a PSCCH318, an RRC message, a MAC-CE message, or other suitable communication. Different TRS322transmitting UEs may select different offsets313from the beginning of the TRS window314in order to avoid resource collision among the sidelink UEs intending to transmit TRS(s)322. In some aspects, the second sidelink UE may select (e.g., randomly select) a different slot312in the TRS window314for each instance of periodic TRS322transmission. In this case, the second sidelink UE may transmit the indicator of the selected TRS slot312to the first sidelink UE before (e.g., x slots before) transmitting the TRS(s)322.

In some aspects the first sidelink UE may receive a communication including a TRS322from the second sidelink UE in slot312(1) that does not include a PSSCH316before (e.g., immediately before) receiving a communication from the second sidelink UE in slot312(2) that does include a PSSCH316. As shown inFIG.3, the first sidelink UE may receive the TRS322in slot312(1) without a PSSCH316before receiving a communication in slot312(2) with a PSSCH316in order to synchronize time and frequency (e.g., perform time/frequency compensation) with the second sidelink UE before decoding the PSSCH316. In this manner, the time and frequency may be better synchronized with the second sidelink UE increasing the probability of successful decoding of the PSSCH316as compared to receiving the TRS322in slot312(3) after the PSSCH316.

FIG.4illustrates tracking reference signal (TRS)322resources according to some aspects of the present disclosure. InFIG.4, the x-axis represents time in some arbitrary units and the y-axis represents frequency in some arbitrary units. In some aspects, a first sidelink UE (e.g., the UE115or the UE900) may receive a TRS322from the second sidelink UE based on the TRS periodicity, the TRS window, and/or the slot312index. In some aspects, the first sidelink UE may receive the TRS(s)322in time/frequency resources of a slot312indicated by the slot index. In this regard, the second sidelink UE may randomly select the time/frequency resources for transmitting the TRS(s)322. The first sidelink UE may receive the TRS(s)322in a symbol411of the slot312after one or more symbols411that include a physical sidelink control channel (PSCCH)318. The first sidelink UE may receive the TRS(s)322in a symbol411of the slot312after the PSCCH318to avoid puncturing the SCI-1 carried by the PSCCH318. The TRSs may be transmitted in symbols411that do not include a DMRS320to avoid collision with the DMRS320. The first sidelink UE may receive one or more TRSs322in the slot312. For example, the first sidelink UE may receive multiple TRSs322from multiple sidelink UEs including the second sidelink UE. In some instances, when the first sidelink UE receives multiple TRSs322in a slot312, the TRSs322may be separated by TRS resource separation410(e.g., n number of symbols in a comb-n pattern). The multiple TRSs322may be separated by one, two, three, four, or more symbols411in a comb-n pattern (e.g., where n equals one, two, three, four, or more). The first sidelink UE may receive the multiple TRSs322in symbols411after a PSCCH symbol318. In some aspects, the first sidelink UE may receive PSSCHs316in symbols411between the symbols411in which the first sidelink UE receives the TRSs322. For example, the first sidelink UE may receive the multiple TRSs322in symbols411(5) and411(9) and receive the PSSCHs316in symbols411(6)-411(8). In some aspects, the first sidelink UE may receive an indication from the second sidelink UE indicating the symbols411(e.g., the symbol indexes411(0) . . .411(13)) of the slot312in which the TRSs322will be received. In this regard, the first sidelink UE may receive the symbol index indication in a time domain resource allocation (TDRA). The TDRA may be carried by SCI-1 via the PSCCH318.

In some aspects, the first sidelink UE may receive multiple TRSs322in a slot312where each TRS322in the slot312is separated by m number of frequency subchannels in a comb-m pattern. The multiple TRSs322may be separated by one, two, three, four, or more subchannels in a comb-m pattern (e.g., where m equals one, two, three, four, or more). In some aspects, the first sidelink UE may receive an indication from the second sidelink UE indicating the subchannels413in which the TRSs322will be transmitted. In this regard, the first sidelink UE may receive the indication in a frequency domain resource allocation (FDRA). The FDRA may be carried by SCI-1 via a PSCCH318. In some aspects, the time/frequency resources and/or the comb pattern may be indicated to the first sidelink UE as a pattern index by the second sidelink UE via SCI. In some instances, the pattern index may indicate a preconfigured combination of time/frequency resources and the comb pattern. The first sidelink UE may receive the TRS(s)322from the second sidelink UE in corresponding time/frequency resources of periodic slots312. In other words, each of the periodic slots312that include the TRS(s)322from the second sidelink UE may include the TRS(s)322in the same symbol indexes411and/or the same frequency subchannels413.

The first sidelink UE may receive multiple TRSs322in symbols411following the PSCCH318where each TRS322in the slot411is separated by m number of frequency subchannels in a comb-m pattern. The multiple TRSs may be separated by one, two, three, four, or more subchannels in a comb-m pattern (e.g., where m equals one, two, three, four, or more). Each of the TRSs322may be transmitted in the same or different frequency subchannel(s)413. For example, a first TRS322may be transmitted in a first subchannel (e.g., subchannel index413(0)), a second TRS322may be transmitted in a second subchannel (e.g., subchannel index413(0+x)), a third TRS322may be transmitted in a third subchannel (e.g., subchannel index413(0+2x)), etc. Each of the subchannels413may be separated by x number of subchannels. In some aspects, the first sidelink UE may receive an indication in a FDRA from the second sidelink UE indicating the subchannels413in which the TRSs322will be transmitted. The FDRA may be carried by SCI (e.g., SCI-1 and/or SCI-2) via the PSCCH318.

In some aspects, the first sidelink UE may receive the TRS(s)322from the second sidelink UE in a slot312that includes a PSSCH316. The slot may include an indicator (e.g., a trigger) in the SCI-1 and/or the SCI-2 that indicates to the first sidelink UE that the slot includes the TRS(s)322and/or the PSSCH316. Before decoding the SCI-2, the first sidelink UE may not know that the slot includes a TRS322. The SCI-2 may have a common configuration among the sidelink UEs, including the first sidelink UE, such that the sidelink UEs may decode the SCI-2 from each sidelink UE that is transmitting a TRS322. The TRSs322may be transmitted in symbols411after the symbols411that include the SCI-2 (e.g., symbols411(4)-411(12)). The TRSs322may be transmitted in symbols411that do not include a DMRS320to avoid collision with the DMRS320. The first sidelink UE may decode the SCI-2 to determine if the PSSCH316is intended for the first sidelink UE by matching the UE destination ID in the SCI-2 with the ID associated with the first sidelink UE. The TRS(s)322may be carried by symbols411different from the symbols411carrying the PSSCH316enabling the transmit power associated with the TRS(s)322to remain constant.

In some aspects, the first sidelink UE may receive the TRS(s)322in time/frequency resources of a dedicated resource pool. The dedicated resource pool may reserve slots exclusively for periodic transmission of TRSs322. The transmission of PSSCHs316may be excluded from the resources of the dedicated resource pool. The resources of a dedicated resource pool may be determined and/or set by the second sidelink UE transmitting the TRS(s)322, another sidelink UE transmitting TRS(s)322(e.g., a master UE, a high-end sidelink UE such as a programmable logic controller or roadside unit), a BS (e.g., the BS105or1000), or other suitable device. The sidelink UEs intending to transmit PSSCHs316may receive an indication of the resources associated with the dedicated resource pool and avoid scheduling PSSCH316transmissions in those resources. The sidelink UEs intending to transmit PSSCHs316may receive the indication of the resources of the dedicated resource pool via SCI-1, SCI-2, or other suitable communication. The sidelink UEs intending to transmit TRS(s)322in the dedicated resource pool (e.g., reserved periodic slots) may select (e.g., randomly select) resources from the dedicated resource pool. For example, the second sidelink UE may select contiguous symbol indexes411(4)-411(7) and frequency comb index 0 in the reserved periodic slot312while another sidelink UE may select contiguous symbol indexes411(8)-411(11) and frequency comb index 1 in the reserved periodic slot312. Each of the sidelink UEs intending to transmit TRS(s)322may receive the indication of the dedicated resource pool and the resources selected by other TRS322transmitting UEs in order to avoid selecting resources previously selected by the other TRS322transmitting UEs.

In some aspects, one or more sidelink UEs may transmit PSSCHs316in the same slot312as the TRS(s)322transmitted by the second sidelink UE. In this case, the one or more sidelink UEs intending to transmit PSSCHs316may rate match around the resource elements scheduled to carry the TRS(s)322transmitted by the second sidelink UE and other sidelink UEs. The one or more UEs may schedule the transmission of the PSSCHs316in resource elements (REs) other than the REs used to carry the TRS(s)322to avoid interfering with the TRS(s)322. In some instances, the one or more sidelink UEs may determine the TRS rate match patterns by receiving SCI from the sidelink UEs that are scheduling the TRS(s)322. The SCI transmitted by the sidelink UEs that are scheduling the TRS(s)322may indicate the REs (e.g., a TRS resource pattern field) in the slot312that the one or more PSSCH316transmitting UEs need to avoid scheduling the PSSCHs316in. Additionally or alternatively, the sidelink UEs intending to transmit PSSCHs316may select slots312for PSSCH316transmission other than slots312that include TRS(s)322. In some instances, when a sidelink UE transmits a PSSCH316in the same symbol as a TRS such as symbols411(5) and411(9), the sidelink UE may boost the power transmission level of the PSSCH316to match the power level of the TRS322to maintain a constant power level in the REs of the symbols411(5) and411(9) that include the PSSCH and TRS.

In some aspects the first sidelink UE may receive a communication in a slot312including a TRS(s)322and a PSSCH316from the second sidelink UE. The first sidelink UE may utilize the TRS(s)322received in the slot312to synchronize time and frequency with the second sidelink UE before decoding the PSSCH316. In this manner, the time and frequency may be better synchronized with the second sidelink UE increasing the probability of successful decoding of the PSSCH316as compared to attempting to decode the PSSCH316before synchronizing the time and frequency with the second sidelink UE.

FIG.5illustrates tracking reference signal (TRS)322resources according to some aspects of the present disclosure. InFIG.5, the x-axis represents time in some arbitrary units and the y-axis represents frequency in some arbitrary units. In some aspects, the first sidelink UE may receive the TRS322(e.g., a standalone TRS322) from the second sidelink UE in a slot312that does not include a PSSCH. In this regard, the first sidelink UE may receive a communication from the second sidelink UE that includes an AGC symbol315, a PSCCH318, one or more TRSs322, and a guard symbol324. In some aspects, when multiple TRSs322are transmitted, the TRSs322may be transmitted in adjacent symbols411. The adjacent symbols411may be contiguous with no gaps between the symbols411. Any number of TRSs322may be transmitted within any symbol411. Any number of symbols411may include TRSs322. Additionally or alternatively, the first symbol, (e.g., symbol index411(0)) may carry the AGC symbol315, the next 2 or 3 symbols (e.g., symbol indexes411(1) and411(2) or symbol indexes411(1),411(2), and411(3)) may carry a PSCCH318, and the symbols411following the PSCCH318(e.g., symbol indexes411(4)-411(13)) may carry the TRSs322. The PSCCH318may carry SCI-1 and/or SCI-2. The first sidelink UE may decode the SCI-1 and/or the SCI-2. The SCI-1 and/or the SCI-2 may indicate (e.g., trigger) to the first sidelink UE that the symbols411after the PSCCH318may carry the TRSs322. The SCI-1 and/or the SCI-2 may indicate, without limitation, the periodicity, the TRS transmission window, the group ID, the time/frequency resources associated with the TRS(s) transmitted to the first sidelink UE, the time/frequency resources associated with the TRS resource pool, and/or the symbol index411(0)-411(13) associated with the TRS(s).

In some aspects, the first sidelink UE may receive an indicator (e.g. a trigger) indicating the second sidelink UE is transmitting a TRS322to the first sidelink UE. The first sidelink UE may receive the indicator from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2). The first sidelink UE may receive the TRSs322periodically based on the transmission periodicity of the TRS322. In some aspects, the second sidelink UE may transmit the indicator multiple times. In some aspects, the second sidelink UE may transmit the indicator multiple times within a time period (e.g., within a number of slots312). Transmitting the indicator multiple times may increase the probability that the first sidelink UE will receive the indicator. For example, if the first sidelink UE is a half-duplex sidelink UE, the first sidelink UE may be in transmit mode when the second sidelink UE transmits the indicator. By transmitting the indicator multiple times, the probability is increased that the half-duplex first sidelink UE will receive the indicator when the half-duplex first sidelink UE is in receive mode.

Additionally or alternatively, the first sidelink UE may receive the TRS(s)322(e.g., a standalone TRS) from the second sidelink UE in a slot312that does not include a PSSCH or a PSCCH318. The first sidelink UE may receive the TRS(s)322from the second sidelink UE in a slot312that includes an AGC symbol315, one or more TRS(s)322, and a guard symbol324. In some aspects, the TRS(s)322may be transmitted in adjacent symbols411that are contiguous with no gaps between the symbols411. Any number of TRS(s)322may be transmitted within any symbol411. Any number of symbols411may include TRS(s)322. The first sidelink UE may receive a communication in a previous slot312that carries an SCI-1 and/or SCI-2. The SCI-1 and/or the SCI-2 in the previous slot312may indicate to the first sidelink UE that a subsequent slot312may carry the TRS(s)322. The SCI-1 and/or the SCI-2 may indicate the symbol index411(0)-411(13) that includes the TRS322.

FIG.6illustrates a wireless communication network600according to some aspects of the present disclosure. The wireless communications network600may include sidelink UEs115a,115b,115c,115f,115i,115j, and115kwhich may be examples of a UE115as described with reference toFIG.1orFIG.2. The UE115amay communicate via sidelink communication to the UEs115b,115c,115f,115i,115j, and115k.

In some aspects, the UE115cmay receive a TRS from the UE115athat is intended for a plurality of sidelink UEs. The plurality of sidelink UEs may include the UE115c. In this regard, the UE115amay transmit the TRS in a groupcast communication. The groupcast communication may be intended for a group610of sidelink UEs to receive the TRS and synchronize time and/or frequency to the UE115a. The second sidelink UE may transmit the TRS(s) to the group610of sidelink UEs at a constant power level. The constant power level may be determined by the largest path loss associated the group610of sidelink UEs so that the sidelink UE having the largest path loss (e.g., the sidelink UE in the group furthest away from the UE115a) is able to receive the TRS(s). The UE115amay conserve resources by transmitting the TRS in a groupcast communication as compared to transmitting the TRSs in unicast communications to each member of the group610. The groupcast communication may include a group ID that identifies the group610of sidelink UEs to receive the TRS. In this regard, the UE115cmay receive (e.g., be assigned) a group ID associated with group610(1) via SCI-2 (e.g., a codepoint in the SCI-2) in the groupcast communication or a unicast communication from the UE115a. Additionally or alternatively, the UE115cmay receive (e.g., be assigned) a group ID associated with group610(1) from a BS (e.g., the BS105or1000) via RRC signaling. The UE115cmay determine that the groupcast ID associated with group610(1) includes the UE115c's ID. Based on the UE115cdetermining that the groupcast ID associated with group610(1) includes the UE115c's ID, the UE115cmay receive the TRS from the UE115a. The UE115cmay periodically receive the TRS based on whether the SCI-2 indicates a groupcast ID that includes the UE115c's ID. The UE115cmay update time/frequency tracking loop with the UE115abased on the TRS carried by the groupcast communication. The UE115cmay receive a TRS from multiple sidelink UEs and keep separate time/frequency tracking loops for each of the multiple sidelink UEs. For example, the UE115cmay receive a TRS from the UE115band/or the UE115fin addition to the UE115a.

In some aspects, the UE115cmay periodically receive the TRS from the UE115a. In this regard, the UE115cmay receive an indicator of the TRS periodicity from the UE115avia a PSSCH, a PSCCH, SCI, an RRC message, a MAC-CE message, or other suitable communication. Additionally or alternatively, the UE115cmay receive an indicator of the TRS periodicity from a BS (e.g., the BS105or1000) via a PDCCH, a PDSCH, DCI, an RRC message, a MAC-CE message, or other suitable communication. The TRS periodicity may be based on a mobility associated with the UE115cand/or the UE115a. For example, the UE115cand/or the UE115amay be a stationary device (e.g., an IoT device) configured with a longer TRS periodicity as compared to a mobile UE (e.g., a vehicle or a smartphone) configured with a shorter TRS periodicity. A higher mobility device may be configured with a shorter TRS period in order to update the time/frequency synchronization at a higher frequency to compensate for a Doppler frequency shift. In some aspects, the sidelink UEs may receive TRSs at different periodicities based on the sidelink UE's mobility. For example, the UE115a(e.g., the TRS TXer) may form groups610of sidelink UEs (e.g., the TRS RXers) based on the TRS RXers mobility. For example, the UE115a(e.g., the TRS TXer) may form group610(1) consisting of sidelink UEs115b(e.g., a smartphone),115c(e.g., a smartphone), and115f(e.g., an IoT device) having a low mobility. The UE115a(e.g., the TRS TXer) may form group610(2) consisting of sidelink UEs115i(e.g., a vehicle),115j(e.g., a vehicle), and115k(e.g., a vehicle) having a high mobility. The UE115amay form any number of groups610based on the TRS RXers mobility. The UE115amay assign a groupcast ID to each of the groups610(1) and610(2). Each of the groups610(1) and610(2) may have a different TRS periodicity. The UE115amay groupcast the TRSs based on the periodicity assigned to each group610(1) and610(2).

FIG.7is a signaling diagram of a communication method700according to some aspects of the present disclosure. Actions of the communication method700can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a communication device or other suitable means for performing the actions. For example, a wireless communication device, such as the UE115or UE900, may utilize one or more components, such as the processor902, the memory904, the periodic TRS module908, the transceiver910, the modem912, and the one or more antennas916, to execute the aspects of method700.

At action702, the UE115bmay transmit a TRS configuration to the UE115c. The UE115bmay transmit the TRS configuration to the UE115cvia SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. The TRS configuration may include, without limitation, an indicator indicating a TRS periodicity, time/frequency resources associated with the TRS(s), a groupcast ID, a TRS window, a TRS window offset, a comb pattern, a comb pattern index, and/or a TRS suspension duration indicator.

At action704, the UE115amay transmit a TRS configuration to the UE115c. The UE115bmay transmit the TRS configuration to the UE115cvia SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. The TRS configuration may include, without limitation, an indicator indicating a TRS periodicity, time/frequency resources associated with the TRS(s), a groupcast ID, a TRS window, a TRS window offset, a comb pattern, a comb pattern index, and/or a TRS suspension duration indicator.

At action706, the UE115bmay transmit a first TRS(s) to the UE115c. The UE115bmay transmit the first TRS(s) to the UE115cas described above with reference toFIGS.3-6.

At action708, the UE115amay transmit a second TRS(s) to the UE115c. The UE115amay transmit the second TRS(s) to the UE115cas described above with reference toFIGS.3-6.

At action710, the UE115cmay synchronize time and/or frequency with the UE115bbased on the first TRS(s) received at action706. The TRS may assist the UE115cto synchronize time and/or frequency tracking with the UE115band each of the sidelink UEs that the UE115creceives TRSs from. The TRS may be a specific configuration of the CSI-RS. In some aspects, the TRS may be configured as a non-zero power (NZP) CSI-RS resource set. The TRS may allow the UE115cto track frequency and time variations with a high resolution (e.g., enable fine tuning of time/frequency tracking). Improved time/frequency synchronization may benefit the performance of data transfer between the UE115cand the UE115b.

At action712, the UE115cmay synchronize time and/or frequency with the UE115abased on the second TRS(s) received at action708. The TRS may assist the UE115cto synchronize time and/or frequency tracking with the UE115a.

At action714, the UE115bmay transmit a PSSCH to the UE115c. In this regard, the UE115bmay transmit a communication in a slot including a TRS (e.g., an additional TRS) and a PSSCH to the UE115c.

At action716, the UE115cmay decode the PSSCH. The UE115cmay utilize the TRSs received at action706to synchronize time and/or frequency with the UE115bbefore decoding the PSSCH. In this manner, the time and/or frequency may be better synchronized between the UE115band the UE115cincreasing the probability of successful decoding of the PSSCH by the UE115cas compared to decoding the PSSCH before synchronizing the time and/or frequency.

At action718, the UE115bmay transmit a third TRS(s) to the UE115c. In some aspects, the UE115bmay periodically transmit TRS(s) to the UE115cbased on the TRS periodicity (e.g., the TRS periodicity310b) transmitted in the TRS configuration to the UE115cat action702. In this manner, the UE115cmay receive TRSs from the UE115bon a regular basis, which can increase the accuracy of the time/frequency synchronization with the UE115b. Each of the sidelink UEs transmitting the TRS(s) to the UE115cmay transmit the TRS(s) in the same slot or a different slot from the UE115b. The UE115amay synchronize time and frequency with each of the sidelink UEs that the UE115creceives TRSs from. In some aspects, the UE115cmay synchronize time and frequency with a subset of the sidelink UEs that the UE115creceives TRSs from. The UE115cmay update time/frequency tracking loops for each of the sidelink UEs and/or a subset of the sidelink UEs that it receives TRSs from.

At action720, the UE115amay transmit a fourth TRS(s) to the UE115c. In some aspects, the UE115amay periodically transmit TRS(s) to the UE115cbased on the TRS periodicity (e.g., the TRS periodicity310a) transmitted in the TRS configuration to the UE115cat action704. The TRS periodicity310amay be different from or the same as the TRS periodicity310b. In this manner, the UE115cmay receive TRSs from the UE115aon a regular basis, which can increase the accuracy of the time/frequency synchronization with the UE115a.

At action722, the UE115amay transmit a PSSCH to the UE115c. In this regard, the UE115bmay transmit a communication in a slot including a TRS (e.g., an additional TRS) and a PSSCH to the UE115c.

At action724, the UE115cmay decode the PSSCH. The UE115cmay utilize the TRSs received at action706and/or at action720to synchronize time and/or frequency with the UE115abefore decoding the PSSCH. In this manner, the time and/or frequency may be better synchronized between the UE115aand the UE115cincreasing the probability of successful decoding of the PSSCH by the UE115cas compared to decoding the PSSCH before synchronizing the time and/or frequency.

FIG.8is a signaling diagram of a communication method800according to some aspects of the present disclosure. Actions of the communication method800can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a communication device or other suitable means for performing the actions. For example, a wireless communication device, such as the UE115or UE900, may utilize one or more components, such as the processor902, the memory904, the periodic TRS module908, the transceiver910, the modem912, and the one or more antennas916, to execute the aspects of communication method800.

At action802, the UE115amay transmit a UE group ID to the UE115b. In this regard, the UE115amay transmit the UE group ID to the UE115bvia SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication.

At action804, the UE115amay transmit a UE group ID to the UE115c. In this regard, the UE115amay transmit the UE group ID to the UE115cvia SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication.

At action806, the UE115amay transmit a TRS to the UE115band the UE115c. In this regard, the UE115amay transmit a groupcast communication including a TRS. The UE115amay transmit a TRS that is intended for a group of sidelink UEs. The group of sidelink UEs may include the UE115band the UE115c. The groupcast communication may be intended for the UE115band the UE115cto receive the TRS and synchronize time and/or frequency to the UE115a. The UE115amay conserve resources by transmitting the TRS in a groupcast communication as compared to transmitting the TRSs in separate unicast communications to the UE115band the UE115c. The groupcast communication may include a group ID transmitted at actions802and804that identifies the UE115band/or the UE115cto receive the TRS.

At action810, the UE115bmay synchronize time and/or frequency to the UE115abased on the TRS received at action806. The UE115bmay determine that the groupcast ID includes the UE115b's ID. Based on the UE115bdetermining that the groupcast ID includes the UE115b's ID, the UE115bmay synchronize time and/or frequency to the UE115abased on the TRS. The UE115bmay periodically receive the TRS based on whether the SCI-2 indicates a groupcast ID that includes the UE115b's ID.

At action812, the UE115cmay synchronize time and/or frequency to the UE115abased on the TRS received at action806. The UE115cmay determine that the groupcast ID includes the UE115c's ID. Based on the UE115cdetermining that the groupcast ID includes the UE115c's ID, the UE115cmay synchronize time and/or frequency to the UE115abased on the TRS. The UE115cmay periodically receive the TRS based on whether the SCI-2 indicates a groupcast ID that includes the UE115c's ID.

At action814, the UE115amay transmit a PSSCH to the UE115c. In this regard, the UE115amay transmit a communication in a slot including a TRS (e.g., an additional TRS) and a PSSCH to the UE115c.

At action816, the UE115cmay decode the PSSCH. The UE115cmay utilize the TRSs received at action806to synchronize time and/or frequency with the UE115abefore decoding the PSSCH. In this manner, the time and/or frequency may be better synchronized between the UE115aand the UE115cincreasing the probability of successful decoding of the PSSCH by the UE115cas compared to decoding the PSSCH before synchronizing the time and/or frequency.

At action818, the UE115amay transmit a PSSCH to the UE115b. In this regard, the UE115amay transmit a communication in a slot including a TRS (e.g., an additional TRS) and a PSSCH to the UE115b.

At action820, the UE115bmay decode the PSSCH. The UE115bmay utilize the TRSs received at action806to synchronize time and/or frequency with the UE115abefore decoding the PSSCH. In this manner, the time and/or frequency may be better synchronized between the UE115aand the UE115bincreasing the probability of successful decoding of the PSSCH by the UE115cas compared to decoding the PSSCH before synchronizing the time and/or frequency.

At action822, the UE115amay determine that its transmit buffer is empty. The UE115amay suspend (e.g., temporarily discontinue) the periodic transmission of the TRS(s) to the UE115band/or the UE115c. The UE115amay suspend the periodic transmission of the TRS(s) to the UE115band/or the UE115cbased on a transmit buffer status associated with the UE115a. For example, if the UE115a(e.g., the TRS transmitter) has no data to transmit to the UE115band/or the UE115cand/or is not expecting to transmit data to the UE115band/or the UE115cduring the next few TRS periods, the UE115amay suspend transmission of the TRS(s) until the UE115ahas data to transmit to the UE115band/or the UE115c. Suspending transmission of the periodic TRS(s) may conserve time/frequency resources in the wireless network and conserve processing/power resources in the UE115a, the UE115b, and/or the UE115c.

At action824, the UE115amay transmit a TRS suspension indicator to the UE115bindicating that the periodic TRS transmission will be suspended.

At action826, the UE115amay transmit a TRS suspension indicator to the UE115cindicating that the periodic TRS transmission will be suspended.

In some aspects, the UE115amay transmit the TRS suspension indicator via SCI (e.g., SCI-1 and/or SCI-2). The TRS suspension indicator may include a duration of time of the TRS transmission suspension. The duration of time may be indicated by a number of TRS transmission periods, a number of slots, a number of frames, a set time (e.g., a number of milliseconds), or other suitable time duration. The time duration of TRS transmission suspension may be a preset (e.g., preconfigured) time duration and/or indicated in the TRS suspension indicator. In some aspects, when the time duration of TRS transmission suspension is preset, the UE115amay resume TRS transmission without further indication to the UE115aand/or UE115c. In some aspects, the UE115amay transmit an additional TRS suspension indicator before the time duration expires to extend the period of time of TRS transmission suspension. When the UE115ahas data to transmit after suspending the TRS transmission, the UE115amay transmit an indicator indicating that the periodic TRS transmission will be resumed. In this regard, the UE115amay transmit the TRS resumption indicator via SCI (e.g., SCI-1 and/or SCI-2). The UE115amay transmit the resumed periodic TRS(s) in a TRS window of a slot indicated by SCI.

FIG.9is a block diagram of an exemplary UE900according to some aspects of the present disclosure. The UE900may be the UE115in the network100or200as discussed above. As shown, the UE900may include a processor902, a memory904, a periodic TRS module908, transceiver910including a modem subsystem912and a radio frequency (RF) unit914, and one or more antennas916. These elements may be coupled with each other and in direct or indirect communication with each other, for example via one or more buses.

The processor902may include a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor902may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The memory904may include a cache memory (e.g., a cache memory of the processor902), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some instances, the memory904includes a non-transitory computer-readable medium. The memory904may store instructions906. The instructions906may include instructions that, when executed by the processor902, cause the processor902to perform the operations described herein with reference to the UEs115in connection with aspects of the present disclosure, for example, aspects ofFIGS.2-8and11-12. Instructions906may also be referred to as code. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements.

The periodic TRS module908may be implemented via hardware, software, or combinations thereof. For example, the periodic TRS module908may be implemented as a processor, circuit, and/or instructions906stored in the memory904and executed by the processor902.

In some aspects, the periodic TRS module908may be configured to receive an indicator indicating a tracking reference signal (TRS) periodicity from a second sidelink UE. The periodic TRS module908may be configured to receive a TRS based on the TRS periodicity. The periodic TRS module908may be configured to acquire time and frequency synchronization with the second sidelink UE based on the TRS and receive a PSSCH communication based on the time and frequency synchronization with the second sidelink UE.

As shown, the transceiver910may include the modem subsystem912and the RF unit914. The transceiver910can be configured to communicate bi-directionally with other devices, such as the BSs105and/or the UEs115. The modem subsystem912may be configured to modulate and/or encode the data from the memory904and the periodic TRS module908according to a modulation and coding scheme (MCS), e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit914may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data from the modem subsystem912(on outbound transmissions) or of transmissions originating from another source such as a UE115or a BS105. The RF unit914may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver910, the modem subsystem912and the RF unit914may be separate devices that are coupled together to enable the UE900to communicate with other devices.

The RF unit914may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas916for transmission to one or more other devices. The antennas916may further receive data messages transmitted from other devices. The antennas916may provide the received data messages for processing and/or demodulation at the transceiver910. The antennas916may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit914may configure the antennas916.

In some instances, the UE900can include multiple transceivers910implementing different RATs (e.g., NR and LTE). In some instances, the UE900can include a single transceiver910implementing multiple RATs (e.g., NR and LTE). In some instances, the transceiver910can include various components, where different combinations of components can implement RATs.

In some aspects, the processor902may be coupled to the memory904, the periodic TRS module908, and/or the transceiver910. The processor902and may execute operating system (OS) code stored in the memory904in order to control and/or coordinate operations of the periodic TRS module908and/or the transceiver910. In some aspects, the processor902may be implemented as part of the periodic TRS module908.

FIG.10is a block diagram of an exemplary BS1000according to some aspects of the present disclosure. The BS1000may be a BS105as discussed above. As shown, the BS1000may include a processor1002, a memory1004, an periodic TRS module1008, a transceiver1010including a modem subsystem1012and a RF unit1014, and one or more antennas1016. These elements may be coupled with each other and in direct or indirect communication with each other, for example via one or more buses.

The processor1002may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor1002may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The memory1004may include a cache memory (e.g., a cache memory of the processor1002), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some instances, the memory1004may include a non-transitory computer-readable medium. The memory1004may store instructions1006. The instructions1006may include instructions that, when executed by the processor902, cause the processor902to perform operations described herein, for example, aspects ofFIGS.2-8and11-12. Instructions1006may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement(s).

The periodic TRS module1008may be implemented via hardware, software, or combinations thereof. For example, the periodic TRS module1008may be implemented as a processor, circuit, and/or instructions1006stored in the memory1004and executed by the processor1002.

The periodic TRS module1008may be used for various aspects of the present disclosure, for example, aspects ofFIGS.2-8and11-12. In some aspects, the periodic TRS module1008may be configured to transmit an indicator indicating a tracking reference signal (TRS) periodicity to a second sidelink UE. The periodic TRS module1008may be configured to transmit a TRS to the second sidelink UE based on the TRS periodicity. The periodic TRS module1008may be configured to transmit, to the second sidelink UE synchronized in time and frequency with the first sidelink UE, a physical sidelink shared channel (PSSCH) communication.

Additionally or alternatively, the periodic TRS module1008can be implemented in any combination of hardware and software, and may, in some implementations, involve, for example, processor1002, memory1004, instructions1006, transceiver1010, and/or modem1012.

As shown, the transceiver1010may include the modem subsystem1012and the RF unit1014. The transceiver1010can be configured to communicate bi-directionally with other devices, such as the UEs115and/or600. The modem subsystem1012may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit1014may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data from the modem subsystem1012(on outbound transmissions) or of transmissions originating from another source such as a UE115or UE900. The RF unit1014may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver1010, the modem subsystem1012and/or the RF unit1014may be separate devices that are coupled together at the BS1000to enable the BS1000to communicate with other devices.

The RF unit1014may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas1016for transmission to one or more other devices. This may include, for example, a configuration indicating a plurality of sub-slots within a slot according to aspects of the present disclosure. The antennas1016may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver1010. The antennas1016may include multiple antennas of similar or different designs in order to sustain multiple transmission links.

In some instances, the B S1000can include multiple transceivers1010implementing different RATs (e.g., NR and LTE). In some instances, the B S1000can include a single transceiver1010implementing multiple RATs (e.g., NR and LTE). In some instances, the transceiver1010can include various components, where different combinations of components can implement RATs.

In some aspects, the processor1002may be coupled to the memory1004, the periodic TRS module1008, and/or the transceiver1010. The processor1002may execute OS code stored in the memory1004to control and/or coordinate operations of the periodic TRS module1008, and/or the transceiver1010. In some aspects, the processor1002may be implemented as part of the periodic TRS module1008. In some aspects, the processor1002is configured to transmit via the transceiver1010, to a UE, an indicator indicating a configuration of sub-slots within a slot.

FIG.11is a flow diagram of a communication method1100according to some aspects of the present disclosure. Aspects of the method1100can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the aspects. For example, a wireless communication device, such as the UE115or UE900, may utilize one or more components, such as the processor902, the memory904, the periodic TRS module908, the transceiver910, the modem912, and the one or more antennas916, to execute aspects of method1100. The method1100may employ similar mechanisms as in the networks100and200and the aspects and actions described with respect toFIGS.2-8. As illustrated, the method1100includes a number of enumerated aspects, but the method1100may include additional aspects before, after, and in between the enumerated aspects. In some aspects, one or more of the enumerated aspects may be omitted or performed in a different order.

At action1110, the method1100includes a first sidelink UE (e.g., the UE115or the UE900) receiving an indicator indicating a tracking reference signal (TRS) periodicity. The first sidelink UE may receive the indicator from a second sidelink UE. In some aspects, the first sidelink UE may periodically receive a TRS from the second sidelink UE based on the TRS periodicity. In this regard, the first sidelink UE may receive a TRS configuration including the indicator indicating the TRS periodicity. The first sidelink UE may receive the TRS configuration from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. Additionally or alternatively, the first sidelink UE may receive an indicator of the TRS periodicity from a BS (e.g., the BS105or1000) via a PDCCH, a PDSCH, DCI, an RRC message, a MAC-CE message, or other suitable communication.

The TRS periodicity may be based on a mobility associated with the first sidelink UE and/or the second sidelink UE. For example, the first sidelink UE and/or the second sidelink UE may be a stationary device (e.g., an IoT device such as a programmable logic controller (PLC) or roadside unit (RSU)) configured with a longer TRS period as compared to a mobile UE (e.g., a vehicle or a smartphone) configured with a shorter TRS period. A higher mobility device may be configured with a shorter TRS period in order to update the time/frequency synchronization at a higher frequency to compensate for a Doppler frequency shift and/or other changes associated with the device changing positions. In some aspects, the second sidelink UE may transmit TRS(s) at different periodicities based on the mobility of the first sidelink UE. In this regard, the first sidelink UE may transmit an indicator to the second UE indicating a mobility associated with the first sidelink UE. For example, the indicator may include a type (e.g., a class) of UE (e.g., a vehicle, a sensor, a PLC, a roadside unit) that indicates a mobility of the first sidelink UE. In some aspects, the first sidelink UE may transmit to the second sidelink UE an indication of the first sidelink UE's speed and/or direction. The first sidelink UE's speed and direction may be determined based on a GPS receiver, RF triangulation, or other suitable method. In some aspects, the second sidelink UE may transmit a new TRS periodicity to the first sidelink UE when the mobility of the first sidelink UE changes (e.g., mobility change of the first sidelink UE satisfies a threshold).

The TRS periodicity may indicate the times at which the first sidelink UE receives the TRS(s) from the second sidelink UE. The first UE may receive an indicator indicating a TRS window (e.g., a resource selection window). The TRS window may be a time period in which the first sidelink UE receives the TRS(s). The TRS window may be indicated in the communication, at action1110, that includes the indicator indicating the TRS periodicity and/or the UE may receive the indicator indicating the TRS window in a separate communication. For example, the first sidelink UE may receive the indicator indicating the TRS window from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. The TRS window may indicate a starting time and/or an ending time in which the first sidelink UE may receive the TRS(s). In this regard, the starting time may correspond to a first slot index and the ending time may correspond to a second slot index (e.g., the last slot in the TRS window). In some instances, the first sidelink UE may receive the TRS(s) in any slot between the first slot index and the second slot index defining the TRS window, including the slots associated with the first and second slot indexes. In this regard, the first sidelink UE may receive the symbol index indication in a time domain resource allocation (TDRA). The TDRA may be carried by SCI-1 via the PSCCH. The second sidelink UE may randomly select a slot within the TRS window for transmitting the TRS(s).

In some aspects, the first sidelink UE may receive an indicator indicating which slot in the TRS window the second sidelink UE will transmit the TRS(s). For example, the indicator may correspond to an offset from the beginning of the TRS window and/or a slot index. The slot index may be indicated in the communication at action1110that includes the indicator indicating the TRS periodicity and/or the indicator indicating the TRS window, and/or the first sidelink UE may receive the indicator indicating the slot index in a separate communication. For example, the first sidelink UE may receive the indicator indicating the slot index from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. Different TRS transmitting UEs may select different offsets from the beginning of the TRS window in order to avoid resource collision among the sidelink UEs intending to transmit TRS(s). In some aspects, the second sidelink UE may select (e.g., randomly select) a different slot in the TRS window for each instance of periodic TRS transmission. In this case, the second sidelink UE may transmit the indicator of the selected TRS slot to the first sidelink UE before (e.g., x slots before) transmitting the TRS(s).

At action1120, the method1100includes the first sidelink UE (e.g., the UE115or the UE900) receiving a TRS from the second sidelink UE based on the TRS periodicity, the TRS window, and/or the slot index. In some aspects, the first sidelink UE may receive the TRS(s) in time/frequency resources of a slot indicated by the slot index. In this regard, the second sidelink UE may randomly select the time/frequency resources for transmitting the TRS(s). The first sidelink UE may receive the TRS(s) in a symbol of the slot after one or more symbols that include a physical sidelink control channel (PSCCH). The first sidelink UE may receive the TRS(s) in a symbol of the slot after the PSCCH to avoid puncturing the SCI-1 carried by the PSCCH. The first sidelink UE may receive one or more TRSs in the slot. For example, the first sidelink UE may receive multiple TRSs from multiple sidelink UEs including the second sidelink UE. In some instances, when the first sidelink UE receives multiple TRSs in a slot the TRSs may be separated by n number of symbols in a comb-n pattern. The multiple TRSs may be separated by one, two, three, four, or more symbols in a comb-n pattern (e.g., where n equals one, two, three, four, or more). The first sidelink UE may receive the multiple TRSs in symbols after a PSCCH symbol. In some aspects, the first sidelink UE may receive PSSCHs in symbols between the symbols in which the first sidelink UE receives the TRSs. For example, the first sidelink UE may receive the multiple TRSs in symbols 5 and 9 and receive the PSSCHs in symbols 6-8. In some aspects, the first sidelink UE may receive an indication from the second sidelink UE indicating the symbols (e.g., the symbol indexes) of the slot in which the TRSs will be received. In this regard, the first sidelink UE may receive the symbol index indication in a time domain resource allocation (TDRA). The TDRA may be carried by SCI-1 via the PSCCH.

In some aspects, the first sidelink UE may receive multiple TRSs in a slot where each TRS in the slot is separated by m number of frequency subchannels in a comb-m pattern. The multiple TRSs may be separated by one, two, three, four, or more subchannels in a comb-m pattern (e.g., where m equals one, two, three, four, or more). In some aspects, the first sidelink UE may receive an indication from the second sidelink UE indicating the subchannels in which the TRSs will be transmitted. In this regard, the first sidelink UE may receive the indication in a frequency domain resource allocation (FDRA). The FDRA may be carried by SCI-1 via a PSCCH. In some aspects, the time/frequency resources and/or the comb pattern may be indicated to the first sidelink UE as a pattern index by the second sidelink UE via SCI. In some instances, the pattern index may indicate a preconfigured combination of time/frequency resources and the comb pattern. The first sidelink UE may receive the TRS(s) from the second sidelink UE in corresponding time/frequency resources of periodic slots. In other words, each of the periodic slots that include the TRS(s) from the second sidelink UE may include the TRS(s) in the same symbol indexes and/or the same frequency subchannels.

The first sidelink UE may receive multiple TRSs in symbols following the PSCCH where each TRS in the slot is separated by m number of frequency subchannels in a comb-m pattern. The multiple TRSs may be separated by one, two, three, four, or more subchannels in a comb-m pattern (e.g., where m equals one, two, three, four, or more). Each of the TRSs may be transmitted in the same or different frequency subchannel(s). For example, a first TRS may be transmitted in a first subchannel (e.g., subchannel index 0), a second TRS may be transmitted in a second subchannel (e.g., subchannel index 0+x), a third TRS may be transmitted in a third subchannel (e.g., subchannel index 0+2x), etc. Each of the subchannels may be separated by x number of subchannels. The first sidelink UE may receive the TRS configuration from the second sidelink UE indicating the time/frequency resources associated with the TRSs. In some aspects, the first sidelink UE may receive an indication in a TDRA from the second sidelink UE indicating the symbols in which the TRSs will be transmitted. The TDRA may be carried by SCI (e.g., SCI-1 and/or SCI-2) via the PSCCH. In some aspects, the first sidelink UE may receive an indication in a FDRA from the second sidelink UE indicating the subchannels in which the TRSs will be transmitted. The FDRA may be carried by SCI (e.g., SCI-1 and/or SCI-2) via the PSCCH.

In some aspects, the first sidelink UE may receive the TRS(s) from the second sidelink UE in a slot that includes a PSSCH. The slot may include an indicator (e.g., a trigger) in the SCI-1 and/or the SCI-2 that indicates to the first sidelink UE that the slot includes the TRS(s) and/or the PSSCH. Before decoding the SCI-2, the first sidelink UE may not know that the slot includes a TRS. The SCI-2 may have a common configuration among the sidelink UEs, including the first sidelink UE, such that the sidelink UEs may decode the SCI-2 from each sidelink UE that is transmitting a TRS. The TRSs may be transmitted in symbols after the symbols that include the SCI-2. The TRSs may be transmitted in symbols that do not include a DMRS to avoid collision with the DMRS. The first sidelink UE may decode the SCI-2 to determine if the PSSCH is intended for the first sidelink UE by matching the UE destination ID in the SCI-2 with the ID associated with the first sidelink UE. The TRS(s) may be carried by symbols different from the symbols carrying the PSSCH enabling the transmit power associated with the TRS(s) to remain constant.

In some aspects, the first sidelink UE may receive the TRS(s) in time/frequency resources of a dedicated resource pool. The dedicated resource pool may reserve slots exclusively for periodic transmission of TRSs. The transmission of PSSCHs may be excluded from the resources of the dedicated resource pool. The resources of a dedicated resource pool may be determined and/or set by the second sidelink UE transmitting the TRS(s), another sidelink UE transmitting TRS(s) (e.g., a high-end sidelink UE such as a programmable logic controller or roadside unit), a BS (e.g., the BS105or1000), or other suitable device. The sidelink UEs intending to transmit PSSCHs may receive an indication of the resources associated with the dedicated resource pool and avoid scheduling PSSCH transmissions in those resources. The sidelink UEs intending to transmit PSSCHs may receive the indication of the resources of the dedicated resource pool via SCI-1, SCI-2, or other suitable communication. The sidelink UEs intending to transmit TRS(s) in the dedicated resource pool (e.g., reserved periodic slots) may select (e.g., randomly select) resources from the dedicated resource pool. For example, the second sidelink UE may select contiguous symbol indexes 4-7 and frequency comb index 0 in the reserved periodic slot while another sidelink UE may select contiguous symbol indexes 8-11 and frequency comb index 1 in the reserved periodic slot. Each of the sidelink UEs intending to transmit TRS(s) may receive the indication of the dedicated resource pool and the resources selected by other TRS transmitting UEs in order to avoid selecting resources previously selected by the other TRS transmitting UEs.

In some aspects, one or more sidelink UEs may transmit PSSCHs in the same slot as the TRS(s) transmitted by the second sidelink UE. In this case, the one or more sidelink UEs intending to transmit PSSCHs may rate match around the resource elements scheduled to carry the TRS(s) transmitted by the second sidelink UE and other sidelink UEs. The one or more UEs may schedule the transmission of the PSSCHs in resource elements other than the REs used to carry the TRS(s) to avoid interfering with the TRS(s). In some instances, the one or more sidelink UEs may determine the TRS rate match patterns by receiving SCI from the sidelink UEs that are scheduling the TRS(s). The SCI transmitted by the sidelink UEs that are scheduling the TRS(s) may indicate the REs (e.g., a TRS resource pattern field) in the slot that the one or more PSSCH transmitting UEs need to avoid scheduling the PSSCHs in. Additionally or alternatively, the sidelink UEs intending to transmit PSSCHs may select slots for PSSCH transmission other than slots that include TRS(s). In some instances, when a sidelink UE transmits a PSSCH in the same symbol as a TRS, the sidelink UE may boost the power transmission level of the PSSCH to match the power level of the TRS to maintain a constant power level in the REs of the symbol that include the PSSCH and TRS.

In some aspects, the first sidelink UE may periodically receive TRS(s) from sidelink UEs, including the second sidelink UE, based on the periodicity. In this manner, the first sidelink UE may receive TRSs from multiple sidelink UEs on a regular basis, which can increase the accuracy of the time/frequency synchronization with the TRS transmitting sidelink UEs. Each of the sidelink UEs transmitting the TRS(s) to the first sidelink UE may transmit the TRS(s) in the same slot or a different slot from the second sidelink UE. The first sidelink UE may synchronize time and frequency with each of the sidelink UEs that the first sidelink UE receives TRSs from. In some aspects, the first sidelink UE may synchronize time and frequency with a subset of the sidelink UEs that the first sidelink UE receives TRSs from. The first sidelink UE may update time/frequency tracking loops for each of the sidelink UEs and/or a subset of the sidelink UEs that it receives TRSs from.

The first sidelink UE may receive a PSSCH in a slot different from the slot(s) that the first sidelink UE receives the TRS(s) in. The slot that the first sidelink UE receives the PSSCH in may not include a TRS(s). The first sidelink UE may receive the PSSCH based on updating time/frequency tracking loops with the second sidelink UE (or other sidelink UE) based on TRS(s) received in a slot previous to the slot that includes the PSSCH.

In some aspects, the first sidelink UE may receive a TRS that is intended for a plurality (e.g., a group) of sidelink UEs. The group of sidelink UEs may include the first sidelink UE. For example, the second sidelink UE may transmit the TRS in a groupcast communication. The groupcast communication may be intended for a group of sidelink UEs to receive the TRS and synchronize time and frequency to the second sidelink UE. The second sidelink UE may transmit the TRS(s) to the group at a constant power level. The constant power level may be determined by the largest path loss associated the group of sidelink UEs so that the sidelink UE having the largest path loss (e.g., the sidelink UE in the group furthest away from the second sidelink UE) is able to receive the TRS(s). The second sidelink UE may conserve resources by transmitting the TRS in a groupcast communication as compared to transmitting the TRSs in unicast communications to each member of the group. The groupcast communication may include a group ID that identifies the group of sidelink UEs to receive the TRS. In this regard, the first sidelink UE may receive (e.g., be assigned) a group ID via SCI-1 and/or SCI-2 (e.g., a codepoint in the SCI-1 and/or SCI-2) in the groupcast communication or a unicast communication from the second sidelink UE. If the SCI-1 includes the groupcast ID and the TRS configuration, the slot may include a PSCCH to carry the SCI-1 and exclude the PSSCH. If the SCI-2 includes the groupcast ID and the TRS configuration, the slot may include a PSSCH to carry the SCI-2 and exclude the PSCCH Additionally or alternatively, the first sidelink UE may receive (e.g., be assigned) a group ID from a BS (e.g., the BS105or1000) via RRC signaling. The first sidelink UE may determine that the groupcast ID includes the first sidelink UE's ID. Based on the first sidelink UE determining that the groupcast ID includes the first sidelink UE's ID, the first sidelink UE may receive the TRS(s). The first sidelink UE may periodically receive the TRS(s) based on whether the SCI-1 and/or SCI-2 indicates a groupcast ID that includes the first sidelink UE's ID. The first sidelink UE may update time/frequency tracking loop with the second sidelink UE based on the TRS(s) carried by the groupcast communication.

In some aspects, the first sidelink UE may receive the TRS (e.g., a standalone TRS) from the second sidelink UE in a slot that does not include a PSSCH. In this regard, the first sidelink UE may receive a communication from the second sidelink UE that includes an AGC symbol, a PSCCH, one or more TRSs, and a guard symbol. In some aspects, when multiple TRSs are transmitted, the TRSs may be transmitted in adjacent symbols. The adjacent symbols may be contiguous with no gaps between the symbols. Any number of TRSs may be transmitted within any symbol. Any number of symbols may include TRSs. Additionally or alternatively, the first symbol, (e.g., symbol index 0) may carry the AGC, the next 2 or 3 symbols (e.g., symbol indexes 1 and 2 or symbol indexes 1, 2, and 3) may carry a PSCCH, and the symbols following the PSCCH (e.g., symbol indexes 4-13) may carry the TRSs. The PSCCH may carry SCI-1 and/or SCI-2. The first sidelink UE may decode the SCI-1 and/or the SCI-2. The SCI-1 and/or the SCI-2 may indicate (e.g., trigger) to the first sidelink UE that the symbols after the PSCCH may carry the TRSs. The SCI-1 and/or the SCI-2 may indicate, without limitation, the periodicity, the TRS transmission window, the group ID, the time/frequency resources associated with the TRS(s) transmitted to the first sidelink UE, the time/frequency resources associated with the TRS resource pool, and/or the slot index associated with the TRS(s).

In some aspects, the first sidelink UE may receive an indicator (e.g. a trigger) indicating the second sidelink UE is transmitting a TRS to the first sidelink UE. The first sidelink UE may receive the indicator from the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2). The first sidelink UE may receive the TRSs periodically based on the indicator indicating the transmission periodicity of the TRS. In some aspects, the second sidelink UE may transmit the indicator multiple times. In some aspects, the second sidelink UE may transmit the indicator multiple times within a time period (e.g., within a number of slots). Transmitting the indicator multiple times may increase the probability that the first sidelink UE will receive the indicator. For example, if the first sidelink UE is a half-duplex sidelink UE, the first sidelink UE may be in transmit mode when the second sidelink UE transmits the indicator. By transmitting the indicator multiple times, the probability is increased that the half-duplex first sidelink UE will receive the indicator when the half-duplex first sidelink UE is in receive mode.

In some aspects the first sidelink UE may receive a communication including a TRS from the second sidelink UE in a slot that does not include a PSSCH before (e.g., immediately before) receiving a communication from the second sidelink UE that does include a PSSCH. The first sidelink UE may receive the TRS in a slot without a PSSCH before receiving a communication in a slot with a PSSCH in order to synchronize time and frequency (e.g., perform time/frequency compensation) with the second sidelink UE before decoding the PSSCH. In this manner, the time and frequency may be better synchronized with the second sidelink UE increasing the probability of successful decoding of the PSSCH as compared to receiving the TRS in a slot after the PSSCH.

In some aspects the first sidelink UE may receive a communication in a slot including a TRS(s) and a PSSCH from the second sidelink UE. The first sidelink UE may utilize the TRS(s) received in the slot to synchronize time and frequency with the second sidelink UE before decoding the PSSCH. In this manner, the time and frequency may be better synchronized with the second sidelink UE increasing the probability of successful decoding of the PSSCH as compared to attempting to decode the PSSCH before synchronizing the time and frequency with the second sidelink UE.

Additionally or alternatively, the first sidelink UE may receive the TRS(s) (e.g., a standalone TRS) from the second sidelink UE in a slot that does not include a PSSCH or a PSCCH. The first sidelink UE may receive the TRS(s) from the second sidelink UE in a slot that includes an AGC symbol, one or more TRS(s), and a guard symbol. In some aspects, the TRS(s) may be transmitted in adjacent symbols that are contiguous with no gaps between the symbols. Any number of TRS(s) may be transmitted within any symbol. Any number of symbols may include TRS(s). The first sidelink UE may receive a communication in a previous slot that carries an SCI-1 and/or SCI-2. The SCI-1 and/or the SCI-2 in the previous slot may indicate to the first sidelink UE that a subsequent slot may carry the TRS(s). The SCI-1 and/or the SCI-2 may indicate an index associated with the slot that includes the TRS.

In some aspects, the second sidelink UE may suspend (e.g., temporarily discontinue) the periodic transmission of the TRS(s) to the first UE. The second sidelink UE may suspend the periodic transmission of the TRS(s) to the first UE based on a transmit buffer status associated with the second UE. For example, if the second sidelink UE (e.g., the TRS transmitter) has no data to transmit to the first sidelink UE or other sidelink UEs and/or is not expecting to transmit data to the first sidelink UE or other sidelink UEs during the next few TRS periods, the second sidelink UE may suspend transmission of the TRS(s) until the second sidelink UE has data to transmit to the first sidelink UE or another sidelink UE. Suspending transmission of the periodic TRS(s) may conserve time/frequency resources in the wireless network and conserve processing/power resources in the first sidelink UE and/or the second sidelink UE. The first sidelink UE may receive an indicator from the second sidelink UE indicating that the periodic TRS transmission will be suspended. In this regard, the first sidelink UE may receive the TRS suspension indicator from the second sidelink UE in SCI (e.g., SCI-1 and/or SCI-2). The TRS suspension indicator may include a duration of time of the TRS transmission suspension. The duration of time may be indicated by a number of TRS transmission periods, a number of slots, a number of frames, a set time (e.g., a number of milliseconds), or other suitable time duration. The time duration of TRS transmission suspension may be a preset (e.g., preconfigured) time duration and/or indicated in the TRS suspension indicator. In some aspects, when the time duration of TRS transmission suspension is preset, the second sidelink UE may resume TRS transmission without further indication to the first sidelink UE. In some aspects, the second sidelink UE may transmit an additional TRS suspension indicator before the time duration expires to extend the period of time of TRS transmission suspension. When the second sidelink UE has data to transmit after suspending the TRS transmission, first sidelink UE may receive an indicator from the second sidelink UE indicating that the periodic TRS transmission will be resumed. In this regard, the first sidelink UE may receive the TRS resumption indicator from the second sidelink UE in SCI (e.g., SCI-1 and/or SCI-2). The first sidelink UE may receive the resumed periodic TRS(s) in a TRS window of a slot indicated by SCI. The first sidelink UE may acquire time and frequency synchronization with the second sidelink UE based on the TRS(S) and receive the data via a PSSCH in a subsequent slot. Additionally or alternatively, the first sidelink UE may receive the resumed periodic TRS(s) in a TRS window of a slot indicated by SCI, acquire frequency synchronization with the second sidelink UE based on the TRS(s), and receive the data via a PSSCH in the same slot as the TRS(s).

At action1130, the method1100includes the first sidelink UE (e.g., the UE115or the UE900) acquiring time and frequency synchronization with the second sidelink UE based on the TRS(s) received at action1120. The TRS(s) may assist the first sidelink UE to synchronize time and frequency tracking with the second sidelink UE and each of the sidelink UEs that the first sidelink UE receives TRSs from. The TRS(s) may be a specific configuration of the CSI-RS. In some aspects, the TRS(s) may be configured as a non-zero power (NZP) CSI-RS resource set. The TRS(s) may allow the first sidelink UE to track frequency and time variations with a high resolution (e.g., enable fine tuning of time/frequency tracking). The first sidelink UE may use a combination of periodic TRS(s) across multiple slots (e.g., a number of previous slots that include the TRS(s)) to acquire time and frequency synchronization with the second sidelink UE. Improved time/frequency synchronization may benefit the performance of data transfer between the first sidelink UE and the sidelink UE.

At action1140, the method1100includes the first sidelink UE (e.g., the UE115or the UE900) receiving a PSSCH communication. The first sidelink UE may receive the PSSCH communication based on the acquired time and frequency synchronization with the second sidelink UE at action1130. The first sidelink UE may receive the PSSCH in the same slot as the TRS(s) and/or in a slot following the slot(s) that includes the periodic TRS(s). In some instances, the first sidelink UE may receive the PSSCH in a slot immediately following a slot that includes a periodic TRS. In some instances, the first sidelink UE may receive the PSSCH in a slot following a slot that includes a periodic TRS that is separated from the slot including the periodic TRS by one or more slots. The first sidelink UE may utilize the TRSs received in the same slot as the PSSCH and/or in prior slots that include the TRS(s) to synchronize time and frequency with the second sidelink UE before decoding the PSSCH. In this manner, the time and frequency may be better synchronized with the second sidelink UE increasing the probability of successful decoding of the PSSCH as compared to the first sidelink UE attempting to decode the PSSCH before synchronizing time and frequency with the second sidelink UE.

FIG.12is a flow diagram of a communication method1200according to some aspects of the present disclosure. Aspects of the method1200can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the aspects. For example, a wireless communication device, such as the UE115or UE900, may utilize one or more components, such as the processor902, the memory904, the periodic TRS module908, the transceiver910, the modem912, and the one or more antennas916, to execute aspects of method1200. The method1200may employ similar mechanisms as in the networks100and200and the aspects and actions described with respect toFIGS.2-8. As illustrated, the method1200includes a number of enumerated aspects, but the method1200may include additional aspects before, after, and in between the enumerated aspects. In some aspects, one or more of the enumerated aspects may be omitted or performed in a different order.

At action1210, the method1200includes a first sidelink UE (e.g., the UE115or the UE900) transmitting an indicator indicating a tracking reference signal (TRS) periodicity. The first sidelink UE may transmit the indicator to a second sidelink UE. In some aspects, the first sidelink UE may periodically transmit a TRS to the second sidelink UE based on the TRS periodicity. In this regard, the first sidelink UE may transmit a TRS configuration including the indicator indicating the TRS periodicity. The first sidelink UE may transmit the TRS configuration to the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. Additionally or alternatively, the second sidelink UE may receive an indicator of the TRS periodicity from a BS (e.g., the BS105or1000) via a PDCCH, a PDSCH, DCI, an RRC message, a MAC-CE message, or other suitable communication.

The TRS periodicity may be based on a mobility associated with the first sidelink UE and/or the second sidelink UE. For example, the first sidelink UE and/or the second sidelink UE may be a stationary device (e.g., an IoT device such as a programmable logic controller (PLC) or roadside unit (RSU)) configured with a longer TRS period as compared to a mobile UE (e.g., a vehicle or a smartphone) configured with a shorter TRS period. A higher mobility device may be configured with a shorter TRS period in order to update the time/frequency synchronization at a higher frequency to compensate for a Doppler frequency shift and/or other changes associated with the device changing positions. In some aspects, the first sidelink UE may transmit TRS(s) at different periodicities based on the mobility of the second sidelink UE. In this regard, the second sidelink UE may transmit an indicator to the first sidelink UE indicating a mobility associated with the second sidelink UE. For example, the indicator may include a type (e.g., a class) of UE (e.g., a vehicle, a sensor, a PLC, a roadside unit) that indicates a mobility of the second sidelink UE. In some aspects, the second sidelink UE may transmit to the first sidelink UE an indication of the second sidelink UE's speed and/or direction. The second sidelink UE's speed and direction may be determined based on a GPS receiver, RF triangulation, or other suitable method. In some aspects, the first sidelink UE may transmit a new TRS periodicity to the second sidelink UE when the mobility of the second sidelink UE changes (e.g., mobility change of the second sidelink UE satisfies a threshold).

The TRS periodicity may indicate the times at which the first sidelink UE transmits the TRS(s) to the second sidelink UE. The first UE may transmit an indicator indicating a TRS window (e.g., a resource selection window). The TRS window may be a time period in which the first sidelink UE transmits the TRS(s). The TRS window may be indicated in the communication, at action1210, that includes the indicator indicating the TRS periodicity and/or the first sidelink UE may transmit the indicator indicating the TRS window in a separate communication. For example, the first sidelink UE may transmit the indicator indicating the TRS window to the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. The TRS window may indicate a starting time and/or an ending time in which the first sidelink UE may transmit the TRS(s). In this regard, the starting time may correspond to a first slot index and the ending time may correspond to a second slot index (e.g., the last slot in the TRS window). In some instances, the first sidelink UE may transmit the TRS(s) in any slot between the first slot index and the second slot index defining the TRS window, including the slots associated with the first and second slot indexes. In this regard, the first sidelink UE may transmit the symbol index indication in a time domain resource allocation (TDRA). The TDRA may be carried by SCI-1 via the PSCCH. The first sidelink UE may randomly select a slot within the TRS window for transmitting the TRS(s).

In some aspects, the first sidelink UE may transmit an indicator indicating which slot in the TRS window the first sidelink UE will transmit the TRS(s). For example, the indicator may correspond to an offset from the beginning of the TRS window and/or a slot index. The slot index may be indicated in the communication at action1210that includes the indicator indicating the TRS periodicity and/or the indicator indicating the TRS window, and/or the first sidelink UE may transmit the indicator indicating the slot index in a separate communication. For example, the first sidelink UE may transmit the indicator indicating the slot index to the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2), a PSSCH, a PSCCH, an RRC message, a MAC-CE message, or other suitable communication. Different TRS transmitting UEs may select different offsets from the beginning of the TRS window in order to avoid resource collision among the sidelink UEs intending to transmit TRS(s). In some aspects, the first sidelink UE may select (e.g., randomly select) a different slot in the TRS window for each instance of periodic TRS transmission. In this case, the first sidelink UE may transmit the indicator of the selected TRS slot to the second sidelink UE before (e.g., x slots before) transmitting the TRS(s).

At action1220, the method1200includes the first sidelink UE (e.g., the UE115or the UE900) transmitting a TRS to the second sidelink UE based on the TRS periodicity, the TRS window, and/or the slot index. In some aspects, the first sidelink UE may transmit the TRS(s) in time/frequency resources of a slot indicated by the slot index. In this regard, the first sidelink UE may randomly select the time/frequency resources for transmitting the TRS(s). The first sidelink UE may transmit the TRS(s) in a symbol of the slot after one or more symbols that include a physical sidelink control channel (PSCCH). The first sidelink UE may transmit the TRS(s) in a symbol of the slot after the PSCCH to avoid puncturing the SCI-1 carried by the PSCCH. The first sidelink UE may transmit one or more TRSs in the slot. For example, the first sidelink UE may transmit multiple TRSs to multiple sidelink UEs including the second sidelink UE. In some instances, when the first sidelink UE transmits multiple TRSs in a slot the TRSs may be separated by n number of symbols in a comb-n pattern. The multiple TRSs may be separated by one, two, three, four, or more symbols in a comb-n pattern (e.g., where n equals one, two, three, four, or more). The first sidelink UE may transmit the multiple TRSs in symbols after a PSCCH symbol. In some aspects, the first sidelink UE may transmit PSSCHs in symbols between the symbols in which the first sidelink UE transmits the TRSs. For example, the first sidelink UE may transmit the multiple TRSs in symbols 5 and 9 and transmit the PSSCHs in symbols 6-8. In some aspects, the first sidelink UE may transmit an indication to the second sidelink UE indicating the symbols (e.g., the symbol indexes) of the slot in which the TRSs will be transmitted. In this regard, the first sidelink UE may transmit the symbol index indication in a time domain resource allocation (TDRA). The TDRA may be carried by SCI-1 via the PSCCH.

In some aspects, the first sidelink UE may transmit multiple TRSs in a slot where each TRS in the slot is separated by m number of frequency subchannels in a comb-m pattern. The multiple TRSs may be separated by one, two, three, four, or more subchannels in a comb-m pattern (e.g., where m equals one, two, three, four, or more). In some aspects, the first sidelink UE may transmit an indication to the second sidelink UE indicating the subchannels in which the TRSs will be transmitted. In this regard, the first sidelink UE may transmit the indication in a frequency domain resource allocation (FDRA). The FDRA may be carried by SCI-1 via a PSCCH. In some aspects, the time/frequency resources and/or the comb pattern may be indicated to the second sidelink UE as a pattern index by the first sidelink UE via SCI. In some instances, the pattern index may indicate a preconfigured combination of time/frequency resources and the comb pattern. The first sidelink UE may transmit the TRS(s) to the second sidelink UE in corresponding time/frequency resources of periodic slots. In other words, each of the periodic slots that include the TRS(s) from the first sidelink UE may include the TRS(s) in the same symbol indexes and/or the same frequency subchannels.

The first sidelink UE may transmit multiple TRSs in symbols following the PSCCH where each TRS in the slot is separated by m number of frequency subchannels in a comb-m pattern. The multiple TRSs may be separated by one, two, three, four, or more subchannels in a comb-m pattern (e.g., where m equals one, two, three, four, or more). Each of the TRSs may be transmitted in the same or different frequency subchannel(s). For example, a first TRS may be transmitted in a first subchannel (e.g., subchannel index 0), a second TRS may be transmitted in a second subchannel (e.g., subchannel index 0+x), a third TRS may be transmitted in a third subchannel (e.g., subchannel index 0+2x), etc. Each of the subchannels may be separated by x number of subchannels. The first sidelink UE may transmit the TRS configuration to the second sidelink UE indicating the time/frequency resources associated with the TRSs. In some aspects, the first sidelink UE may transmit an indication in a TDRA to the second sidelink UE indicating the symbols in which the TRSs will be transmitted. The TDRA may be carried by SCI (e.g., SCI-1 and/or SCI-2) via the PSCCH. In some aspects, the first sidelink UE may transmit an indication in a FDRA to the second sidelink UE indicating the subchannels in which the TRSs will be transmitted. The FDRA may be carried by SCI (e.g., SCI-1 and/or SCI-2) via the PSCCH.

In some aspects, the first sidelink UE may transmit the TRS(s) to the second sidelink UE in a slot that includes a PSSCH. The slot may include an indicator (e.g., a trigger) in the SCI-1 and/or the SCI-2 that indicates to the second sidelink UE that the slot includes the TRS(s) and/or the PSSCH. Before decoding the SCI-2, the second sidelink UE may not know that the slot includes a TRS. The SCI-2 may have a common configuration among the sidelink UEs, including the second sidelink UE, such that the sidelink UEs may decode the SCI-2 from each sidelink UE that is transmitting a TRS. The TRSs may be transmitted in symbols after the symbols that include the SCI-2. The TRSs may be transmitted in symbols that do not include a DMRS to avoid collision with the DMRS. The second sidelink UE may decode the SCI-2 to determine if the PSSCH is intended for the second sidelink UE by matching the UE destination ID in the SCI-2 with the ID associated with the second sidelink UE. The TRS(s) may be carried by symbols different from the symbols carrying the PSSCH enabling the transmit power associated with the TRS(s) to remain constant.

In some aspects, the first sidelink UE may transmit the TRS(s) in time/frequency resources of a dedicated resource pool. The dedicated resource pool may reserve slots exclusively for periodic transmission of TRSs. The transmission of PSSCHs may be excluded from the resources of the dedicated resource pool. The resources of a dedicated resource pool may be determined and/or set by the first sidelink UE transmitting the TRS(s), another sidelink UE transmitting TRS(s) (e.g., a high-end sidelink UE such as a programmable logic controller or roadside unit), a BS (e.g., the BS105or1000), or other suitable device. The sidelink UEs intending to transmit PSSCHs may receive an indication of the resources associated with the dedicated resource pool and avoid scheduling PSSCH transmissions in those resources. The sidelink UEs intending to transmit PSSCHs may receive the indication of the resources of the dedicated resource pool via SCI-1, SCI-2, or other suitable communication. The sidelink UEs intending to transmit TRS(s) in the dedicated resource pool (e.g., reserved periodic slots) may select (e.g., randomly select) resources from the dedicated resource pool. For example, the first sidelink UE may select contiguous symbol indexes 4-7 and frequency comb index 0 in the reserved periodic slot while another sidelink UE may select contiguous symbol indexes 8-11 and frequency comb index 1 in the reserved periodic slot. Each of the sidelink UEs intending to transmit TRS(s) may receive the indication of the dedicated resource pool and the resources selected by other TRS transmitting UEs in order to avoid selecting resources previously selected by the other TRS transmitting UEs.

In some aspects, one or more sidelink UEs may transmit PSSCHs in the same slot as the TRS(s) transmitted by the first sidelink UE. In this case, the one or more sidelink UEs intending to transmit PSSCHs may rate match around the resource elements scheduled to carry the TRS(s) transmitted by the first sidelink UE and other sidelink UEs. The one or more UEs may schedule the transmission of the PSSCHs in resource elements other than the REs used to carry the TRS(s) to avoid interfering with the TRS(s). In some instances, the one or more sidelink UEs may determine the TRS rate match patterns by receiving SCI from the sidelink UEs that are scheduling the TRS(s). The SCI transmitted by the sidelink UEs that are scheduling the TRS(s) may indicate the REs (e.g., a TRS resource pattern field) in the slot that the one or more PSSCH transmitting UEs need to avoid scheduling the PSSCHs in. Additionally or alternatively, the sidelink UEs intending to transmit PSSCHs may select slots for PSSCH transmission other than slots that include TRS(s). In some instances, when a sidelink UE transmits a PSSCH in the same symbol as a TRS, the sidelink UE may boost the power transmission level of the PSSCH to match the power level of the TRS to maintain a constant power level in the REs of the symbol that include the PSSCH and TRS.

In some aspects, the first sidelink UE may periodically transmit TRS(s) to sidelink UEs, including the second sidelink UE, based on the periodicity. In this manner, the first sidelink UE may transmit TRSs to multiple sidelink UEs on a regular basis, which can increase the accuracy of the time/frequency synchronization with the TRS receiving sidelink UEs. Each of the sidelink UEs transmitting the TRS(s) to the second sidelink UE may transmit the TRS(s) in the same slot or a different slot from the first sidelink UE. The first sidelink UE may synchronize time and frequency with each of the sidelink UEs that the first sidelink UE transmits TRSs to. In some aspects, the first sidelink UE may synchronize time and frequency with a subset of the sidelink UEs that the first sidelink UE transmits TRSs to. The first sidelink UE may update time/frequency tracking loops for each of the sidelink UEs and/or a subset of the sidelink UEs that it transmits TRSs to.

The first sidelink UE may transmit a PSSCH in a slot different from the slot(s) that the first sidelink UE transmits the TRS(s) in. The slot that the first sidelink UE transmits the PSSCH in may not include a TRS(s). The first sidelink UE may transmit the PSSCH based on updating time/frequency tracking loops with the second sidelink UE (or other sidelink UE) based on TRS(s) transmitted in a slot previous to the slot that includes the PSSCH.

In some aspects, the first sidelink UE may transmit a TRS that is intended for a plurality (e.g., a group) of sidelink UEs. The group of sidelink UEs may include the second sidelink UE. For example, the first sidelink UE may transmit the TRS in a groupcast communication. The groupcast communication may be intended for a group of sidelink UEs to receive the TRS and synchronize time and frequency to the first sidelink UE. The first sidelink UE may transmit the TRS(s) to the group at a constant power level. The constant power level may be determined by the largest path loss associated the group of sidelink UEs so that the sidelink UE having the largest path loss (e.g., the sidelink UE in the group furthest away from the first sidelink UE) is able to receive the TRS(s). The first sidelink UE may conserve resources by transmitting the TRS in a groupcast communication as compared to transmitting the TRSs in unicast communications to each member of the group. The groupcast communication may include a group ID that identifies the group of sidelink UEs to receive the TRS. In this regard, the first sidelink UE may transmit (e.g., assign) a group ID via SCI-1 and/or SCI-2 (e.g., a codepoint in the SCI-1 and/or SCI-2) in the groupcast communication or a unicast communication to the second sidelink UE. If the SCI-1 includes the groupcast ID and the TRS configuration, the slot may include a PSCCH to carry the SCI-1 and exclude the PSSCH. If the SCI-2 includes the groupcast ID and the TRS configuration, the slot may include a PSSCH to carry the SCI-2 and exclude the PSCCH. Additionally or alternatively, the second sidelink UE may receive (e.g., be assigned) a group ID from a BS (e.g., the BS105or1000) via RRC signaling. The second sidelink UE may determine that the groupcast ID includes the second sidelink UE's ID. Based on the second sidelink UE determining that the groupcast ID includes the second sidelink UE's ID, the second sidelink UE may receive the TRS(s). The second sidelink UE may periodically receive the TRS(s) based on whether the SCI-1 and/or SCI-2 indicates a groupcast ID that includes the second sidelink UE's ID. The second sidelink UE may update time/frequency tracking loop with the first sidelink UE based on the TRS(s) carried by the groupcast communication.

In some aspects, the first sidelink UE may transmit the TRS (e.g., a standalone TRS) to the second sidelink UE in a slot that does not include a PSSCH. In this regard, the first sidelink UE may transmit a communication to the second sidelink UE that includes an AGC symbol, a PSCCH, one or more TRSs, and a guard symbol. In some aspects, when multiple TRSs are transmitted, the TRSs may be transmitted in adjacent symbols. The adjacent symbols may be contiguous with no gaps between the symbols. Any number of TRSs may be transmitted within any symbol. Any number of symbols may include TRSs. Additionally or alternatively, the first symbol, (e.g., symbol index 0) may carry the AGC, the next 2 or 3 symbols (e.g., symbol indexes 1 and 2 or symbol indexes 1, 2, and 3) may carry a PSCCH, and the symbols following the PSCCH (e.g., symbol indexes 4-13) may carry the TRSs. The PSCCH may carry SCI-1 and/or SCI-2. The second sidelink UE may decode the SCI-1 and/or the SCI-2. The SCI-1 and/or the SCI-2 may indicate (e.g., trigger) to the second sidelink UE that the symbols after the PSCCH may carry the TRSs. The SCI-1 and/or the SCI-2 may indicate, without limitation, the periodicity, the TRS transmission window, the group ID, the time/frequency resources associated with the TRS(s) transmitted to the second sidelink UE, the time/frequency resources associated with the TRS resource pool, and/or the slot index associated with the TRS(s).

In some aspects, the first sidelink UE may transmit an indicator (e.g. a trigger) indicating the first sidelink UE is transmitting a TRS to the second sidelink UE. The first sidelink UE may transmit the indicator to the second sidelink UE via SCI (e.g., SCI-1 and/or SCI-2). The first sidelink UE may transmit the TRSs periodically based on the indicator indicating the transmission periodicity of the TRS. In some aspects, the first sidelink UE may transmit the indicator multiple times. In some aspects, the first sidelink UE may transmit the indicator multiple times within a time period (e.g., within a number of slots). Transmitting the indicator multiple times may increase the probability that the second sidelink UE will receive the indicator. For example, if the second sidelink UE is a half-duplex sidelink UE, the second sidelink UE may be in transmit mode when the first sidelink UE transmits the indicator. By transmitting the indicator multiple times, the probability is increased that the half-duplex second sidelink UE will receive the indicator when the half-duplex second sidelink UE is in receive mode.

In some aspects the first sidelink UE may transmit a communication including a TRS to the second sidelink UE in a slot that does not include a PSSCH before (e.g., immediately before) transmitting a communication to the second sidelink UE that does include a PSSCH. The first sidelink UE may transmit the TRS in a slot without a PSSCH before transmitting a communication in a slot with a PSSCH in order to synchronize time and frequency (e.g., perform time/frequency compensation) with the first sidelink UE. In this manner, the time and frequency may be better synchronized between the first and the second sidelink UEs increasing the probability of successful decoding of the PSSCH by the second sidelink UE as compared to transmitting the TRS in a slot after the PSSCH.

In some aspects the first sidelink UE may transmit a communication in a slot including a TRS(s) and a PSSCH to the second sidelink UE. The second sidelink UE may utilize the TRS(s) received in the slot to synchronize time and frequency with the first sidelink UE before decoding the PSSCH. In this manner, the time and frequency may be better synchronized with the first sidelink UE increasing the probability of successful decoding of the PSSCH as compared to attempting to decode the PSSCH before synchronizing the time and frequency with the first sidelink UE.

Additionally or alternatively, the first sidelink UE may transmit the TRS(s) (e.g., a standalone TRS) to the second sidelink UE in a slot that does not include a PSSCH or a PSCCH. The first sidelink UE may transmit the TRS(s) to the second sidelink UE in a slot that includes an AGC symbol, one or more TRS(s), and a guard symbol. In some aspects, the TRS(s) may be transmitted in adjacent symbols that are contiguous with no gaps between the symbols. Any number of TRS(s) may be transmitted within any symbol. Any number of symbols may include TRS(s). The first sidelink UE may transmit a communication in a previous slot that carries an SCI-1 and/or SCI-2. The SCI-1 and/or the SCI-2 in the previous slot may indicate to the second sidelink UE that a subsequent slot may carry the TRS(s). The SCI-1 and/or the SCI-2 may indicate an index associated with the slot that includes the TRS.

In some aspects, the first sidelink UE may suspend (e.g., temporarily discontinue) the periodic transmission of the TRS(s) to the second sidelink UE. The first sidelink UE may suspend the periodic transmission of the TRS(s) to the second sidelink UE based on a transmit buffer status associated with the first sidelink UE. For example, if the first sidelink UE (e.g., the TRS transmitter) has no data to transmit to the second sidelink UE or other sidelink UEs and/or is not expecting to transmit data to the second sidelink UE or other sidelink UEs during the next few TRS periods, the first sidelink UE may suspend transmission of the TRS(s) until the first sidelink UE has data to transmit to the second sidelink UE or another sidelink UE. Suspending transmission of the periodic TRS(s) may conserve time/frequency resources in the wireless network and conserve processing/power resources in the first sidelink UE and/or the second sidelink UE. The first sidelink UE may transmit an indicator to the second sidelink UE indicating that the periodic TRS transmission will be suspended. In this regard, the first sidelink UE may transmit the TRS suspension indicator to the second sidelink UE in SCI (e.g., SCI-1 and/or SCI-2). The TRS suspension indicator may include a duration of time of the TRS transmission suspension. The duration of time may be indicated by a number of TRS transmission periods, a number of slots, a number of frames, a set time (e.g., a number of milliseconds), or other suitable time duration. The time duration of TRS transmission suspension may be a preset (e.g., preconfigured) time duration and/or indicated in the TRS suspension indicator. In some aspects, when the time duration of TRS transmission suspension is preset, the first sidelink UE may resume TRS transmission without further indication to the second sidelink UE. In some aspects, the first sidelink UE may transmit an additional TRS suspension indicator before the time duration expires to extend the period of time of TRS transmission suspension. When the first sidelink UE has data to transmit after suspending the TRS transmission, the first sidelink UE may transmit an indicator to the second sidelink UE indicating that the periodic TRS transmission will be resumed. In this regard, the first sidelink UE may transmit the TRS resumption indicator to the second sidelink UE in SCI (e.g., SCI-1 and/or SCI-2). The first sidelink UE may transmit the resumed periodic TRS(s) in a TRS window of a slot indicated by SCI. The second sidelink UE may acquire time and frequency synchronization with the first sidelink UE based on the TRS(S) and receive the data via a PSSCH in a subsequent slot. Additionally or alternatively, the first sidelink UE may transmit the resumed periodic TRS(s) in a TRS window of a slot indicated by SCI, acquire frequency synchronization with the second sidelink UE based on the TRS(s), and transmit the data via a PSSCH in the same slot as the TRS(s).

At action1230, the method1200includes the first sidelink UE (e.g., the UE115or the UE900) transmitting, to the second sidelink UE synchronized in time and frequency with the first sidelink UE, a PSSCH communication based on the TRS(s) transmitted at action1220. The TRS(s) may assist the second sidelink UE to synchronize time and frequency tracking with the first sidelink UE and each of the sidelink UEs that the first sidelink UE transmits TRSs to. The TRS(s) may be a specific configuration of the CSI-RS. In some aspects, the TRS(s) may be configured as a non-zero power (NZP) CSI-RS resource set. The TRS(s) may allow the second sidelink UE to track frequency and time variations with a high resolution (e.g., enable fine tuning of time/frequency tracking). The second sidelink UE may use a combination of periodic TRS(s) across multiple slots (e.g., a number of previous slots that include the TRS(s)) to acquire time and frequency synchronization with the first sidelink UE. Improved time/frequency synchronization may benefit the performance of data transfer between the first sidelink UE and the sidelink UE.

In some aspects, the first sidelink UE may transmit the PSSCH in the same slot as the TRS(s) and/or in a slot following the slot(s) that includes the periodic TRS(s). In some instances, the first sidelink UE may transmit the PSSCH in a slot immediately following a slot that includes a periodic TRS. In some instances, the first sidelink UE may transmit the PSSCH in a slot following a slot that includes a periodic TRS that is separated from the slot including the periodic TRS by one or more slots. The second sidelink UE may utilize the TRSs received in the same slot as the PSSCH and/or in prior slots that include the TRS(s) to synchronize time and frequency with the first sidelink UE before decoding the PSSCH. In this manner, the time and frequency may be better synchronized with the first sidelink UE increasing the probability of successful decoding of the PSSCH as compared to the second sidelink UE attempting to decode the PSSCH before synchronizing time and frequency with the first sidelink UE.

Further aspects of the present disclosure include the following:

Aspect 1 includes a method of wireless communication performed by a first sidelink user equipment (UE), the method comprising receiving, from a second sidelink UE, an indicator indicating a tracking reference signal (TRS) periodicity; receiving, from the second sidelink UE, a TRS based on the TRS periodicity; acquiring time and frequency synchronization with the second sidelink UE based on the TRS; and receiving a physical sidelink shared channel (PSSCH) communication based on the time and frequency synchronization with the second sidelink UE.

Aspect 2 includes the method of aspect 1, further comprising receiving, from the second sidelink UE, an indicator indicating an index associated with a first slot in a TRS window, wherein the receiving the TRS comprises receiving the TRS in the first slot in the TRS window; receiving, from a third sidelink UE, an indicator indicating a second index associated with a second slot in the TRS window; and receiving a second TRS in the second slot in the TRS window.

Aspect 3 includes the method of any of aspects 1-2, wherein the receiving the TRS comprises at least one of receiving the TRS in a symbol of a slot after an automatic gain control (AGC) symbol; or receiving the TRS in a symbol of a slot after a physical sidelink control channel (PSCCH) symbol.

Aspect 4 includes the method of any of aspects 1-3, further comprising receiving a second TRS in resource elements of a first slot, and wherein the receiving the TRS comprises receiving the TRS in resource elements of a second slot, wherein the resource elements of the second slot correspond to the resource elements of the first slot; the acquiring time and frequency synchronization with the second sidelink UE is further based on the second TRS; and the receiving the PSSCH comprises receiving the PSSCH in a third slot.

Aspect 5 includes the method of any of aspects 1-4, further comprising receiving, from the second sidelink UE, an indicator indicating at least one of time resources associated with the TRS; or frequency resources associated with the TRS.

Aspect 6 includes the method of any of aspects 1-5, further comprising receiving, from the second sidelink UE, an indicator indicating a group ID associated with a plurality of sidelink UEs, wherein the TRS is associated with the plurality of sidelink UEs; and the plurality of sidelink UEs includes the first sidelink UE.

Aspect 7 includes the method of any of aspects 1-6, wherein the receiving the PSSCH communication comprises receiving the PSSCH communication in a same slot as the TRS, wherein the PSSCH communication is rate matched around the TRS.

Aspect 8 includes the method of any of aspects 1-7, further comprising receiving, from the second sidelink UE, a second TRS in a first slot, wherein the receiving the TRS comprises receiving the TRS in the first slot; and the receiving the PSSCH communication comprises receiving the PSSCH communication in a second slot, the second slot being different than the first slot.

Aspect 9 includes the method of any of aspects 1-8, further comprising receiving, from the second sidelink UE, an indicator indicating a suspension of TRS transmission by the second sidelink UE.

Aspect 10 includes the method of any of aspects 1-9, wherein the TRS periodicity is based on a mobility associated with the first sidelink UE.

Aspect 11 includes a method of wireless communication performed by a first sidelink user equipment (UE), the method comprising transmitting, to a second sidelink UE, an indicator indicating a tracking reference signal (TRS) periodicity; transmitting, to the second sidelink UE, a TRS based on the TRS periodicity; and transmitting, to the second sidelink UE synchronized in time and frequency with the first sidelink UE, a physical sidelink shared channel (PSSCH) communication.

Aspect 12 includes the method of aspect 11, wherein the transmitting the TRS comprises at least one of transmitting the TRS in a symbol of a slot after an automatic gain control (AGC) symbol; or transmitting the TRS in a symbol of a slot after a physical sidelink control channel (PSCCH) symbol.

Aspect 13 includes the method of any of aspects 11-12, further comprising transmitting a second TRS in resource elements of a first slot, and wherein the transmitting the TRS comprises transmitting the TRS in resource elements of a second slot, wherein the resource elements of the second slot correspond to the resource elements of the first slot; and the transmitting the PSSCH comprises transmitting the PSSCH in a third slot.

Aspect 14 includes the method of any of aspects 11-13, further comprising transmitting, to the second sidelink UE, an indicator indicating at least one of time resources associated with the TRS; or frequency resources associated with the TRS.

Aspect 15 includes the method of any of aspects 11-14, further comprising transmitting, to the second sidelink UE, an indicator indicating a suspension of TRS transmission based on a buffer status associated with the first sidelink UE.

Aspect 16 includes a non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions comprising one or more instructions that, when executed by one or more processors of a first sidelink user equipment (UE), cause the one or more processors to perform any one of aspects 1-10.

Aspect 16 includes a non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions comprising one or more instructions that, when executed by one or more processors of a first sidelink user equipment (UE), cause the one or more processors to perform any one of aspects 11-15.

Aspect 17 includes a first sidelink user equipment (UE) comprising one or more means to perform any one or more of aspects 1-10.

Aspect 19 includes a first sidelink user equipment (UE) comprising one or more means to perform any one or more of aspects 11-15.

Aspect 20 includes a first sidelink user equipment (UE) comprising a memory, a transceiver and at least one processor coupled to the memory and the transceiver, wherein the first sidelink UE is configured to perform any one or more of aspects 1-10.

Aspect 21 includes a first sidelink user equipment (UE) comprising a memory, a transceiver and at least one processor coupled to the memory and the transceiver, wherein the first sidelink UE is configured to perform any one or more of aspects 11-15.

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

The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed 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 in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

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 over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list of [at least one of A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular instances illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.