Device-to-device synchronization in wireless communications

Methods, systems, and devices for wireless communications are described in which synchronization of one or more direct communications links between a user equipment (UE) and one or more other UEs is provided by one or more sidelink synchronization signals. The sidelink synchronization signals may include a first sidelink synchronization signal that provides a relatively coarse synchronization (e.g., providing rough timing information about the start of the orthogonal frequency division multiplexing (OFDM) symbol, without providing any information identifying the source of the signal) that may be used to identify a search space for a second sidelink synchronization signal that provides relatively fine synchronization (e.g., identifying more precisely the OFDM symbol boundaries) and an identifier of the device that is transmitting the sidelink synchronization signals.

BACKGROUND

The following relates generally to wireless communications, and more specifically to device-to-device synchronization in wireless communications.

In some wireless communications systems, such as distributed wireless networks, wireless devices (e.g., UEs) may directly communicate with each other (e.g., via device-to-device (D2D) communications or sidelink communications). In order to establish direct communications between devices, various types of information (e.g., identification information, timing information, resource configurations, and the like) may need to be exchanged. Efficient communication of such information may be help enhance system performance and reliability.

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support device-to-device synchronization in wireless communications. In some aspects of the disclosure, a wireless device (e.g., a user equipment (UE), vehicle, headset, or other wireless node) may establish one or more direct communications links (e.g., sidelink or D2D links) with one or more other wireless devices. In some cases, a transmitting device (e.g., a transmitting UE or transmitting vehicle) may transmit one or more sidelink synchronization signals, and a receiving device may determine synchronization information for exchanging communications with the transmitting device based on the sidelink synchronization signals. In some cases, the sidelink synchronization signals may include a first sidelink synchronization signal that provides a relatively coarse synchronization (e.g., providing only rough timing information about the start of an orthogonal frequency division multiplexing (OFDM symbol), without providing any information identifying the source of the signal) that may be used to identify a search space for a second sidelink synchronization signal that provides relatively fine synchronization (e.g., identifying more precisely the OFDM symbol boundaries) and an identifier of the device that is transmitting the sidelink synchronization signals. Based on the sidelink synchronization signals, the receiving device may determine synchronization information for communications with the transmitting device, and may transmit a request to establish a sidelink connection with the transmitting device.

In some cases, the first sidelink synchronization signal may be a first sounding reference signal (SRS) that is transmitted by a first UE, and the second sidelink synchronization signal may be a second SRS transmitted by the first UE. In some cases, the first SRS may have a first reference signal sequence that is selected from relatively few reference signal sequences (e.g., from two or three available sequences) and that are relatively easily identified at a second UE that may search for such a first SRS. In some cases, the second SRS may have a second reference signal sequence that is selected from a relatively large number of reference signal sequences, where the particular reference signal sequence of the second SRS provides an identifier associated with the first UE (e.g., a physical cell ID or virtual cell ID assigned to the first UE for purposes of sidelink communications, which may also be referred to as a sidelink ID). The second SRS may allow for the second UE to further refine synchronization information for sidelink communications with the first UE. Additionally, in some cases, the sidelink synchronization signals may include a broadcast channel (e.g., a physical broadcast channel (PBCH)) or control channel (e.g., a physical downlink control channel (PDCCH)) transmission that may provide system information associated with the first UE for establishing sidelink communications.

In some cases, the first sidelink synchronization signal may be a primary synchronization signal (PSS) that is transmitted by the first UE, and the second sidelink synchronization signal may be a secondary synchronization signal (SSS) transmitted by the first UE. In some cases, the PSS transmitted by the first UE may be selected from a number of available PSS sequences that are provided for synchronizing with a base station based on synchronization signal block (SSB) transmissions of the base station. Further, the SSS transmitted by the first UE may be selected from a number of available SSS sequences that are provided for synchronizing with the base station based on SSB transmissions of the base station. In some cases, a subset of PSS and SSS sequences may be provided for sidelink communications and the first UE may transmit one of the subset of PSS and SSS sequences that may be used for synchronization of sidelink communications. In some cases, new PSS and SSS sequences distinct from those used for establishing connections between base stations and UEs may be defined for the purpose of generating and transmitting sidelink synchronization signals.

DETAILED DESCRIPTION

Some wireless communication systems may be used to facilitate direct communications with various devices, which may include direct device-to-device (D2D) communications using sidelink communication links. For example, direct communications between vehicles may use sidelink communications, and these systems may sometimes be referred to as vehicle-to-everything (V2X) or vehicle-to-vehicle (V2V) communication systems. In other cases, various user equipment (UE) or other wireless nodes may be in proximity with one or more other UEs or wireless nodes (e.g., for virtual reality (VR) gaming type applications) such that direct communications between the devices may help reduce an amount of data that is transmitted through one or more base stations, and may thereby enhance system efficiency.

In various aspects of the disclosure, sidelink synchronization techniques may allow for multiple wireless devices (e.g., multiple UEs) to establish synchronized sidelink communications links. In some cases, a UE may establish one or more direct communications links (e.g., sidelink or D2D links) with one or more other wireless devices. In some cases, a transmitting UE may transmit one or more sidelink synchronization signals, and a receiving UE may determine synchronization information for exchanging communications with the transmitting UE based on the sidelink synchronization signals. While various examples provided herein discuss sidelink communications with UEs, techniques discussed herein may be used for any wireless devices that may establish direct sidelink communications.

In some cases, the sidelink synchronization signals may include a first sidelink synchronization signal that provides a relatively coarse synchronization (e.g., roughly at an orthogonal frequency division multiplexing (OFDM) symbol frame level without identifying the source transmitting the synchronization signals) that may be used to identify a search space for a second sidelink synchronization signal that provides relatively fine synchronization (e.g., at an OFDM symbol level) and an identifier of the transmitting UE. Based on the sidelink synchronization signals, the receiving UE may determine synchronization information for communications with the transmitting UE, and may transmit a request to establish a sidelink connection with the transmitting UE.

In some cases, the first sidelink synchronization signal may be a first sounding reference signal (SRS) that is transmitted by a first UE, and the second sidelink synchronization signal may be a second SRS transmitted by the first UE. In some cases, the first SRS may have a first reference signal sequence that is selected from relatively few reference signal sequences (e.g., from two or three available sequences) and that are relatively easily identified at a second UE that may search for such a first SRS. In some cases, the second SRS may have a second reference signal sequence that is selected from a relatively large number of reference signal sequences, where the particular reference signal sequence of the second SRS provides an identifier associated with the first UE (e.g., a physical cell ID, virtual cell ID, or sidelink ID assigned to the first UE for purposes of sidelink communications). The second SRS may allow for the second UE to further refine synchronization information for sidelink communications with the first UE. Such SRS techniques may be beneficial because existing UEs are already able to transmit SRS to base stations, and thus designing sidelink synchronization signals based on SRS will add relatively little additional UE transmitter complexity for sidelink support. Further UEs may also be equipped to receive SRS for the purpose of monitoring neighbor-cell uplink loading, or to monitor cross-link interference in dynamic time division duplexing (TDD) scenarios where the uplink and downlink slots or OFDM symbols are not aligned across neighboring cells. Thus, SRS-based sidelink synchronization signals may also add relatively little additional UE receiver complexity for sidelink support.

In other cases, the sidelink synchronization signals may also be based on other downlink reference signals, such as a channel state information reference signal (CSI-RS), which may take advantage of certain properties such as wider comb-spacings which are available with CSI-RS as compared with SRS. In this case, UEs can re-use existing CSI-RS components and techniques, and may use new functionality to transmit CSI-RS. Additionally or alternatively, in some cases, the sidelink synchronization signals may include a broadcast channel (e.g., a physical broadcast channel (PBCH)) or control channel (e.g., a physical downlink control channel (PDCCH) or physical uplink control channel (PUCCH)) transmission that may provide system information associated with the first UE for establishing sidelink communications. For UE-to-base station communications, existing UEs are equipped to receive PBCH, but do not transmit PBCH. Thus, in order to reuse existing UE architecture, the content normally carried on PBCH could instead be carried on other channels such as PDCCH, PUCCH, physical downlink shared channel (PDSCH), or physical uplink shared channel (PUSCH), to limit additional UE complexity for sidelink support.

Further, it is noted that in some cases, some of the component functions of synchronization signals realized by primary synchronization signals (PSS), secondary synchronization signals (SSS) and PBCH in access-link communications (e.g., UE-to-base station communications, or the Uu interface in NR) may be omitted in case of sidelink communications, by virtue of being provided by alternative mechanisms. For example, the sidelink-related PBCH payload information could be relayed directly from the base stations to the UEs participating in sidelink communications, thus avoiding the need for a sidelink PBCH. The sidelink PSS could be omitted by having the UEs acquire sidelink SSS directly, using the timing they have already acquired from their serving base-stations as a starting point for the sidelink SSS search. Further, which synchronization channels are transmitted and which are omitted may be altered dynamically, based on base station configuration, or for example, based on whether the UEs communicating on the sidelink are being served by the same or by different base stations.

In other cases, the first sidelink synchronization signal may be a PSS that is transmitted by the first UE, and the second sidelink synchronization signal may be an SSS transmitted by the first UE. In some cases, the PSS transmitted by the first UE may be selected from a number of available PSS sequences that are provided for synchronizing with a base station based on synchronization signal block (SSB) transmissions of the base station. Further, the SSS transmitted by the first UE may be selected from a number of available SSS sequences that are provided for synchronizing with the base station based on SSB transmissions of the base station. In some cases, a subset of PSS and SSS sequences may be provided for sidelink communications and the first UE may transmit one of the subset of PSS and SSS sequences that may be used for synchronization of sidelink communications. In some cases, new PSS and SSS sequences that are distinct from those used for access link connections between base stations and UEs may be defined for the purpose of generating and transmitting sidelink synchronization signals.

Such techniques may provide for relatively efficient determination of synchronization between sidelink devices, and may thus enhance reliability and efficiency of a sidelink communications system. Further, techniques discussed herein may use some signals or signal formats that are used for communications between base stations and UEs for sidelink communications, thus enhancing efficiency at the UEs by allowing processing and communications using techniques that are also used for communications with base stations.

Aspects of the disclosure are initially described in the context of a wireless communications system. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to device-to-device synchronization in wireless communications.

Wireless communications system100may support direct communication between UEs115over a sidelink communications link140(e.g., using a peer-to-peer (P2P), D2D protocol, or V2X protocol). Sidelink communication may be used for D2D media-sharing, V2V communication, V2X communication (or cellular V2X (cV2X) communication), emergency rescue applications, etc. One or more of a group of UEs115utilizing D2D communications may be within the geographic coverage area110of a base station105. Other UEs115in such a group may be outside the geographic coverage area110of a base station105, or be otherwise unable to receive transmissions from a base station105. In some cases, groups of UEs115communicating via D2D communications may utilize a one-to-many (1:M) system in which each UE115transmits to every other UE115in the group. In some cases, a base station105facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between UEs115without the involvement of a base station105.

In some cases, wireless communications system100may be a packet-based network that operate according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. In cases where D2D or V2X communications are used via sidelink communications link140, a D2D or V2X layer may provide related protocols, and in some cases, may use ProSe direct communications protocols (e.g., PC5 signaling). A Radio Link Control (RLC) layer may, in some cases, perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use hybrid automatic repeat request (HARQ) to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE115and a base station105or core network130supporting radio bearers for user plane data. At the Physical (PHY) layer, transport channels may be mapped to physical channels.

In some cases, two or more UEs115may establish direct connections (e.g., via sidelink communications link140) in which timing synchronization is established based on one or more sidelink synchronization signals that may be transmitted by a transmitting UE115.

In some cases, the sidelink synchronization signals may include a first sidelink synchronization signal that provides a relatively coarse synchronization (e.g., a rough identification of OFDM symbol boundaries without identifying the device transmitting the signal) that may be used to identify a search space for a second sidelink synchronization signal that provides relatively fine synchronization (e.g., identifying more precisely the OFDM symbol boundaries) and an identifier of the transmitting UE. Based on the sidelink synchronization signals, the receiving UE may determine synchronization information for communications with the transmitting UE, and may transmit a request to establish a sidelink connection with the transmitting UE.

FIG.2illustrates an example of a wireless communications system200that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. In some examples, wireless communications system200may implement aspects of wireless communications system100. Wireless communications system200may include a base station105-a, a first UE115-a, and a second UE115-b, which may be examples of corresponding devices in wireless communications system100. It is noted that communications between two UEs115are illustrated in wireless communications system200for the sake of brevity, and the techniques described below may be applicable to multiple UEs115within a system.

In some cases, UEs115may establish an access link215with the base station105-a(e.g., a Uu interface as defined in LTE or NR), and may establish a sidelink communications link205with each other. The sidelink communications link205may be a direct connection that does not go through the base station105-a. In some examples, UEs115may execute one or more sets of codes or sequences, to control the functional elements of the device, and perform some or all of the functions described herein. In some cases, a communications manager at each UE115may manage sidelink communications and synchronization parameters used in the sidelink communications link205. While various examples described herein illustrate D2D communications using NR between UEs115, it will be understood that techniques provided herein may be used in other communications systems that may use different radio access technologies and communications protocols.

In some examples, a base station105-amay communicate with first UE115-aand the second UE115-bvia bidirectional access links215in a geographic coverage area. Base station105-amay, for example, grant resources for sidelink communication via sidelink communications link205to one or more UEs115(e.g., UE115-aand UE115-b). The first UE115-aand second UE115-bmay perform sidelink communications on granted sidelink resources. In some cases, the base station105-amay transmit configuration information220via the access links215to the first UE115-aand the second UE115-b.

In some cases, the first UE115-amay transmit one or more sidelink synchronization signals210to the second UE115-b(and in some cases, one or more other UEs) that may be used for timing synchronization that is used for establishing the sidelink communications link205. In some cases, the sidelink synchronization signals210may include a first sidelink synchronization signal that provides a relatively coarse synchronization that may be used to identify a search space for a second sidelink synchronization signal that provides relatively fine synchronization and an identifier of the first UE115-a. Based on the sidelink synchronization signals, the second UE115-bmay determine synchronization information for communications with the first UE115-a, and may transmit a request to establish a sidelink connection with the first UE115-a.

In some cases, the first sidelink synchronization signal may be a first SRS that is transmitted by the first UE115-a, and the second sidelink synchronization signal may be a second SRS transmitted by the first UE115-a. In some cases, the first SRS may have a first reference signal sequence that is selected from relatively few reference signal sequences (e.g., from two or three available sequences) and that are relatively easily identified at the second UE115-bthat may search for such a first SRS. In some cases, the second SRS may have a second reference signal sequence that is selected from a relatively large number of reference signal sequences, where the particular reference signal sequence of the second SRS provides an identifier associated with the first UE115-a(e.g., a physical cell ID or virtual cell ID assigned to the first UE115-afor purposes of sidelink communications). The second SRS may allow for the second UE115-bto further refine synchronization information for sidelink communications with the first UE115-a. Additionally, in some cases, the sidelink synchronization signals210may include a broadcast channel (e.g., a PBCH) transmission that may provide system information associated with the first UE115-afor establishing the sidelink communications link205.

In other cases, the first sidelink synchronization signal may be a PSS that is transmitted by the first UE115-a, and the second sidelink synchronization signal may be an SSS transmitted by the first UE115-a. In some cases, the PSS transmitted by the first UE115-amay be selected from a number of available PSS sequences that are provided for synchronizing with the base station105-abased on SSB transmissions of the base station105-a. Further, the SSS transmitted by the first UE115-amay be selected from a number of available SSS sequences that are provided for synchronizing with the base station105-abased on SSB transmissions of the base station105-a. In some cases, a subset of PSS and SSS sequences may be provided in the configuration information220for sidelink communications and the first UE115-amay transmit one of the subset of PSS and SSS sequences that may be used for synchronization of sidelink communications link205. For example, the base station105-amay configure a PSS sequence, and a set of SSS sequences in a specific range or a selected set physical cell IDs or virtual cell IDs, for use as the sidelink synchronization signals210. Accordingly, one or more synchronization signals may be used for sidelink synchronization signals210, such as one or a combination of a PSS, an SSS, a PBCH (e.g., that is transmitted using DFT-s-OFDM or CP-OFDM), a CSI-RS, a control channel signal (e.g., a PDCCH signal), or a shared channel signal (e.g., a PDSCH or PUSCH signal, which may also be transmitted using DFT-s-OFDM or CP-OFDM).

In some cases, the UEs115and, the base station105, or both may use beamformed wireless communications, in which one or more beams may be identified for use in the sidelink communications link205. In some cases, beam index information may be provided by the base station105-ain the configuration information220that identifies one or more beams (e.g., a range of beams within 64 available beams in frequency range two (FR2) above 6 GHz, or one or more beams within four or eight available beams in frequency range one (FR1) below 6 GHz). In some cases, a bit mask-based signaling may be used to signal beam or quasi-co-location (QCL) related information for the sidelink synchronization signals210, such that the second UE115-bmonitors for the sidelink synchronization signals210on the identified beams. In some cases, a synchronization raster may be provided that indicates frequency ranges for locations where the sidelink synchronization signals210are transmitted. In some cases, such a synchronization raster may be adjusted over time (e.g., based on UE115movement, a number of UEs115present that may participate sidelink operations at a given region/location, or scheduling considerations of the base station105-a).

In some cases, the second UE115-bmay identify the sidelink synchronization signals210and may transmit a connection request to the first UE115-ato establish the sidelink communications link205. In some cases, the connection request may be transmitted using one or more identified resources that are configured for connection request transmissions to the first UE115-a. In some cases, one or more random access channel (RACH) resources may be allocated for sidelink connection requests. In some cases, some RACH resources may be associated with one or more beams, and such a resource and its QCL association may have associated sidelink synchronization signals210. This association may itself be conveyed in the sidelink PBCH, or in sidelink system information block (SIB) transmissions (analogous to SIB1carrying remaining minimum system information (RMSI) for the Uu interface in NR), or may be conveyed directly by the serving base station. Additionally or alternatively, the base station105-amay configure a specific time window for device discovery and measurement for a specific device or groups of devices, such as UEs115. In such cases, the UEs115may perform synchronization during the specific time windows, which may have associated beams and sidelink synchronization signals. In some cases, the first UE115-amay indicate to the base station105-aor the second UE115-b, or both that the sidelink synchronization signals210are to be changed. For example, the first UE115-amay signal a change of sidelink synchronization signals210in terms of QCL related parameters of the first UE115-a(e.g., beam direction or transmit timing). In some cases, the first UE115-amay indicate its mobility state (e.g., fixed, moving, rotating, or combinations thereof) to the base station105-aor the second UE115-b(e.g., directly or through the base station105-a), and the mobility state may be used to determine one or more of the sidelink synchronization signals210. For example, the base station105-amay configure some SSS sequences for high mobility cases, and some other SSS sequences for low mobility cases, or some RACH resources may be identified based on mobility.

Such synchronization techniques may allow for sidelink communications on the sidelink communications link205to be synchronized, such that the second UE115-bmay determine when some transmissions are to be received from the first UE115-a. Further, the second UE115-bmay use the synchronization information to transmit communications to the first UE115-athat are aligned with time boundaries at the first UE115-a.

FIG.3illustrates an example of a wireless communications system300that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. In some examples, wireless communications system300may implement aspects of wireless communications system100or200. In this example, a first UE115-cmay communicate directly with a second UE115-dand a third UE115-evia sidelink communication links305.

In this example, the first UE115-cmay transmit sidelink synchronization signals310that are received at each of the second UE115-dand the third UE115-e, and that may be used to synchronize communications between the UEs115. In some cases, the first UE115-cmay receive configuration information from a base station (e.g., a base station105ofFIGS.1or2) that configures one or more reference signal sequences (e.g., one or more SRS sequences) or one or more synchronization signal sequences (e.g., one or more PSS/SSS sequences) for use as the sidelink synchronization signals310. In this example, the first UE115-cmay transmit one or more indications to the second UE115-dor the third UE115-e, or both that may indicate information associated with configuration or updated configuration for sidelink synchronization signals310.

FIGS.4A through4Cillustrate examples of synchronization signal resources400that support device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. In some examples, synchronization signal resources400may implement aspects of wireless communications system100,200, or300.

In the example ofFIG.4A, synchronization signal resources400-amay include a number of OFDM symbols405, in which some of the OFDM symbols405are configured for synchronization signal transmissions. In this example, a first sidelink synchronization signal410and a second sidelink synchronization signal415may be configured in a signal structure to be transmitted in adjacent OFDM symbols405within the synchronization signal resources400-a. In some cases, a synchronization signal configuration may be provided that indicates the resources that are configured for the first sidelink synchronization signal410and the second sidelink synchronization signal415.

In some cases, a predetermined set of available synchronization signal resources may be available, and the synchronization signal configuration may indicate which resources of the set of available synchronization signal resources are to be used for sidelink synchronization signals. For example, the synchronization signal configuration may provide an index value that may be mapped to particular synchronization signal resources that are to be used for the first sidelink synchronization signal410and the second sidelink synchronization signal415. Further, in some cases, such an index value may also be mapped to particular reference signal sequences (e.g., SRS sequences) or synchronization signal sequences (e.g., PSS/SSS sequences) that are to be used for the first sidelink synchronization signal410and the second sidelink synchronization signal415. Additionally or alternatively, the synchronization signal configuration may provide (e.g., based on a mapping to an index value) beam index information or raster scan information that are to be used for the first sidelink synchronization signal410and the second sidelink synchronization signal415.

In some cases, as illustrated inFIG.4B, synchronization signal resources400-bmay include a number of OFDM symbols405, in which some OFDM symbols405are also configured for PBCH420transmissions. In this example, first sidelink synchronization signal410and a second sidelink synchronization signal415may be configured in a signal structure to be transmitted in adjacent OFDM symbols405as withFIG.4A, and the PBCH420transmissions may be in an OFDM symbol405that is adjacent to the second sidelink synchronization signal415. In some cases, a synchronization signal configuration may be provided that indicates the signal structure of the synchronization signal resources400-bthat are configured for the first sidelink synchronization signal410, the second sidelink synchronization signal415, and the PBCH420transmission. In some cases, the signal structure may indicate the number of symbols for each of the sidelink synchronization signals (e.g., a number of PSS symbols, a number of SSS symbols and a number of PBCH symbols).

In some cases, the synchronization signal configuration may indicate that no symbols are configured for sidelink synchronization signals, such as illustrated in synchronization signal resources400-cofFIG.4C, in which no OFDM symbols405are configured for sidelink synchronization signals. Such a configuration may be provided, for example, due to a known timing relationship with other transmissions within the network, and a serving base station may provide such a configuration to allow for scheduling of other transmissions. In some cases, the base station may subsequently provide an updated configuration such as illustrated inFIGS.4A or4B. Further, in some cases, one or more of the sidelink synchronization signals may not be configured for transmission, such as, in the example ofFIG.4A, where PBCH may not be transmitted due to a timing relationship and/or beam index information being known at each UE that is to participate in the sidelink communications.

FIG.5illustrates an example of a process flow500that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. In some examples, process flow500may implement aspects of wireless communications system100,200, or300. Process flow500may be implemented by a first UE115-fand a second UE115-g, or any other examples of UEs115as described herein. Alternative examples of the following may be implemented, where some steps are performed in a different order than described or are not performed at all. In some cases, steps may include additional features not mentioned below, or further steps may be added.

At505, the first UE115-fmay determine a sidelink synchronization signal configuration. In some cases, the first UE115-fmay determine the sidelink synchronization signal configuration based on a configuration provided by a serving base station. At510, the second UE115-gmay determine the sidelink synchronization signal configuration. In some cases, the second UE115-galso may determine the sidelink synchronization signal configuration based on a configuration provided by a serving base station. In other cases, the second UE115-gmay determine the sidelink synchronization signal configuration based on information provided by the first UE115-f(e.g., based on updated information provided in a prior established sidelink connection with the first UE115-f). In some cases, the sidelink synchronization signal configuration may also include beam information related to one or more particular beams that may be used for transmission of the sidelink synchronization signals (e.g., based on a configured beam index, raster scan associated with the sidelink synchronization signals, specific time window for device discovery and measurement, or the like).

At515, the first UE115-fmay configure sidelink synchronization signals for transmission. In some cases, the sidelink synchronization signals may include one or more of a first sidelink synchronization signal that provides coarse synchronization for the second UE115-gor a second sidelink synchronization signal that provides an identifier of the first UE115-f(e.g., a physical or virtual cell ID, or sidelink ID, that is indicated by a sequence of the second sidelink synchronization signal). The first UE115-fmay, at520, transmit the sidelink synchronization signals.

At525, the second UE115-gmay identify the sidelink synchronization signals and perform timing synchronization. In some cases, the second UE115-gmay identify a search space for a first sidelink synchronization signal (e.g., an SRS or PSS having a predetermined sequence) and attempt to decode the first sidelink synchronization signal based on multiple hypotheses for a location and a particular sequence of the first sidelink synchronization signal. The first sidelink synchronization signal may provide a coarse timing (e.g., frame level synchronization) for communications of the first UE115-fBased on a successful decoding of the first sidelink synchronization signal, the second UE115-gmay identify a search space and one or more sequences that may be used to transmit the second sidelink synchronization signal, and the second UE115-dmay attempt to decode the second sidelink synchronization signal using multiple hypotheses associated with the determined search space and sequences. Upon detecting the second sidelink synchronization signal, the second UE115-gmay determine fine timing (e.g., symbol level synchronization) for communications of the first UE115-fFurther, based on a sequence used for the second sidelink synchronization signal, the second UE115-gmay identify a cell ID of the first UE115-fthat is to be used for sidelink communications with the first UE115-f

At530, the first UE115-fand the second UE115-gmay establish a sidelink connection. In some cases, the second UE115-gmay determine resources (e.g., random access resources associated with one or more of the first or second sidelink synchronization signals, or resources indicated in system information (e.g., in PBCH) provided by the first UE115-f) for transmission of a connection request to the first UE115-fThe second UE115-gmay transmit the connection request using the determined resources, which may be received at the first UE115-f, and the first UE115-fand the second UE115-gmay exchange messages (e.g., RACH procedure messages and connection establishment messages) to establish the sidelink connection.

FIG.6illustrates an example of a process flow600that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. In some examples, process flow600may implement aspects of wireless communications system100,200, or300. Process flow600may be implemented by a base station105-b, a first UE115-hand a second UE115-i, or any other examples of base stations105and UEs115as described herein. Alternative examples of the following may be implemented, where some steps are performed in a different order than described or are not performed at all. In some cases, steps may include additional features not mentioned below, or further steps may be added.

At605, the base station105-bmay determine a sidelink synchronization signal configuration. In some cases, the base station105-bmay determine the sidelink synchronization signal based on channel conditions at the first UE115-h(e.g., a frequency range to be used for the sidelink communications, mobility of the first UE115-h, scheduling information for other devices served by the base station105-b). In some cases, the base station105-bmay identify a sidelink synchronization signal sequence (e.g., a PSS sequence or a first SRS sequence) that is to be used for a first sidelink synchronization signal, and a set of sidelink synchronization signal sequences to be used for a second sidelink synchronization signal (e.g., an SSS or a second SRS sequence). In some cases, the base station105-bmay identify one or more beams that are to be used for sidelink communications, and the sidelink synchronization signals may be determined based on the one or more identified beams (e.g., a PSS/SSS or SRSs that are associated with the one or more identified beams).

At610, the base station105-bmay transmit configuration information to the first UE115-h. Likewise, at615, the base station may transmit configuration information to the second UE115-i. In some cases, the base station105-bmay transmit the configuration to each of the UEs115in control signaling on an access link that is established between the base station105-band each UE115.

At615, the first UE115-hmay transmit the sidelink synchronization signals, which may be received at the second UE115-i. In some cases, the sidelink synchronization signals may include one or more of a first sidelink synchronization signal that provides coarse synchronization for the second UE115-ior a second sidelink synchronization signal that provides an identifier of the first UE115-h(e.g., a physical or virtual cell ID, or sidelink ID, that is indicated by a sequence of the second sidelink synchronization signal).

At620, the second UE115-imay identify the sidelink synchronization signals and determine timing synchronization. In some cases, the second UE115-imay identify a search space for a first sidelink synchronization signal (e.g., an SRS or PSS having a predetermined sequence) and attempt to decode the first sidelink synchronization signal according based on multiple hypotheses for a location and particular sequence of the first sidelink synchronization signal. The first sidelink synchronization signal may provide a coarse timing for communications of the first UE115-h. Based on a successful decoding of the first sidelink synchronization signal, the second UE115-imay identify a search space and one or more sequences that may be used to transmit the second sidelink synchronization signal, and the second UE115-dmay attempt to decode the second sidelink synchronization signal using multiple hypotheses associated with the determined search space and sequences. Upon detecting the second sidelink synchronization signal, the second UE115-imay determine fine timing for communications of the first UE115-h. Further, based on a sequence used for the second sidelink synchronization signal, the second UE115-imay identify a cell ID of the first UE115-hthat is to be used for sidelink communications with the first UE115-h.

At625, the first UE115-hand the second UE115-imay perform a sidelink connection establishment. In some cases, the second UE115-imay determine resources (e.g., random access resources associated with one or more of the first or second sidelink synchronization signals, or resources indicated in system information (e.g., in PBCH) provided by the first UE115-h) for transmission of a connection request to the first UE115-h. The second UE115-imay transmit the connection request using the determined resources, which may be received at the first UE115-h, and the first UE115-hand the second UE115-imay exchange messages (e.g., RACH procedure messages and connection establishment messages) to establish the sidelink connection. At630, the first UE115-hand the second UE115-imay communicate via the established sidelink connection.

The receiver710may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to device-to-device synchronization in wireless communications, etc.). Information may be passed on to other components of the device705. The receiver710may be an example of aspects of the transceiver1020described with reference toFIG.10. The receiver710may utilize a single antenna or a set of antennas.

The communications manager715, when the device705is acting as a first UE, may identify a set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE, the set of sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, transmit the set of sidelink synchronization signals based on the identifying, receive, from the second UE, a sidelink connection request based on the transmitted set of sidelink synchronization signals, and establish the sidelink communications link with the second UE responsive to the sidelink connection request.

The communications manager715may also, when the device705is acting as a second UE, identify a set of resources to monitor for sidelink synchronization signals for synchronizing a sidelink communications link between a first UE and the second UE, the sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, receive the first sidelink synchronization signal from the first UE on the set of resources, determine, based on the first sidelink synchronization signal, a coarse timing for the second sidelink synchronization signal, receive, based on the coarse timing, the second sidelink synchronization signal, determine, based on the second sidelink synchronization signal, a fine timing for synchronizing communications with the first UE and the identifier of the first UE, and transmit, to the first UE, a sidelink connection request based on the fine timing and the identifier of the first UE. The communications manager715may be an example of aspects of the communications manager1010described herein. The actions performed by the communications manager715as described herein may be implemented to realize one or more potential advantages. One implementation may allow a UE115to save power and increase battery life by efficiently determining synchronization of sidelink communications. Additionally or alternatively, the UE115may further reduce complexity by implementing signals or signal formats that are used for communications between base stations and UEs. Another implementation may provide improved quality and reliability of service at the UE115, as latency and the number of separate resources allocated to the UE115may be reduced.

The transmitter720may transmit signals generated by other components of the device705. In some examples, the transmitter720may be collocated with a receiver710in a transceiver module. For example, the transmitter720may be an example of aspects of the transceiver1020described with reference toFIG.10. The transmitter720may utilize a single antenna or a set of antennas.

FIG.8shows a block diagram800of a device805that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The device805may be an example of aspects of a device705, or a UE115as described herein. The device805may include a receiver810, a communications manager815, and a transmitter840. The device805may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

The receiver810may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to device-to-device synchronization in wireless communications, etc.). Information may be passed on to other components of the device805. The receiver810may be an example of aspects of the transceiver1020described with reference toFIG.10. The receiver810may utilize a single antenna or a set of antennas.

The communications manager815may be an example of aspects of the communications manager715as described herein. The communications manager815may include a sidelink synchronization manager820, a sidelink transmission manager825, a sidelink random access manager830, and a sidelink connection establishment manager835. The communications manager815may be an example of aspects of the communications manager1010described herein.

The sidelink synchronization manager820, when the communications manager815is at a first UE that transmits sidelink synchronization signals, may identify a set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE, the set of sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE. The sidelink transmission manager825may transmit the set of sidelink synchronization signals based on the identifying. The sidelink random access manager830may receive, from the second UE, a sidelink connection request based on the transmitted set of sidelink synchronization signals. The sidelink connection establishment manager835may establish the sidelink communications link with the second UE responsive to the sidelink connection request.

The sidelink synchronization manager820, when the communications manager815is at a second UE that monitors for sidelink synchronization signals, may identify a set of resources to monitor for sidelink synchronization signals for synchronizing a sidelink communications link between a first UE and the second UE, the sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, receive the first sidelink synchronization signal from the first UE on the set of resources, determine, based on the first sidelink synchronization signal, a coarse timing for the second sidelink synchronization signal, receive, based on the coarse timing, the second sidelink synchronization signal, and determine, based on the second sidelink synchronization signal, a fine timing for synchronizing communications with the first UE and the identifier of the first UE. The sidelink random access manager830may transmit, to the first UE, a sidelink connection request based on the fine timing and the identifier of the first UE. Based on monitoring for sidelink synchronization signals, a processor of a UE115(e.g., controlling the receiver810, the transmitter840, or the transceiver1020as described with reference toFIG.10) may efficiently determine timing for synchronization signals. Further, the processor of UE115may transmit a sidelink connection request. The processor of the UE115may turn on one or more processing units for establishing sidelink communications, increase a processing clock, or a similar mechanism within the UE115. As such, when the sidelink communications are established, the processor may be ready to respond more efficiently through the reduction of a ramp up in processing power.

The transmitter840may transmit signals generated by other components of the device805. In some examples, the transmitter840may be collocated with a receiver810in a transceiver module. For example, the transmitter840may be an example of aspects of the transceiver1020described with reference toFIG.10. The transmitter840may utilize a single antenna or a set of antennas.

FIG.9shows a block diagram900of a communications manager905that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The communications manager905may be an example of aspects of a communications manager715, a communications manager815, or a communications manager1010described herein. The communications manager905may include a sidelink synchronization manager910, a sidelink transmission manager915, a sidelink random access manager920, a sidelink connection establishment manager925, and a sidelink configuration manager930. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

The sidelink synchronization manager910, when the communications manager905is at a first UE that transmits sidelink synchronization signals, may identify a set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE, the set of sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE.

In some examples, when the communications manager905is at a second UE that receives sidelink synchronization signals, the sidelink synchronization manager910may identify a set of resources to monitor for sidelink synchronization signals for synchronizing a sidelink communications link between a first UE and the second UE, the sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE. In some examples, the sidelink synchronization manager910may receive the first sidelink synchronization signal from the first UE on the set of resources. In some examples, the sidelink synchronization manager910may determine, based on the first sidelink synchronization signal, a coarse timing for the second sidelink synchronization signal. In some examples, the sidelink synchronization manager910may receive, based on the coarse timing, the second sidelink synchronization signal. In some examples, the sidelink synchronization manager910may determine, based on the second sidelink synchronization signal, a fine timing for synchronizing communications with the first UE and the identifier of the first UE.

In some examples, the sidelink synchronization manager910may receive beam index information from a serving base station that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and where the set of sidelink synchronization signals are associated with predefined synchronization signals of the subset of transmission beams. In some examples, the sidelink synchronization manager910may determine that an updated set of sidelink synchronization signals are to be transmitted based on one or more updated QCL parameters of the first UE. In some examples, the sidelink synchronization manager910may transmit an indication of the updated set of sidelink synchronization signals to at least one of the second UE or a base station.

In some examples, the sidelink synchronization manager910may determine, at the first UE, a mobility state of the first UE, where the set of synchronization signals is based on the mobility state. In some examples, the sidelink synchronization manager910may transmit an indication of the mobility state to one or more of the second UE or a base station.

In some examples, when the communications manager905is at a second UE that receives sidelink synchronization signals, the sidelink synchronization manager910may receive, from the first UE or a base station, an indication that an updated set of sidelink synchronization signals are to be transmitted based on one or more updated QCL parameters of the first UE. In some examples, the sidelink synchronization manager910may receive, from the first UE or a base station, an indication of a mobility state of the first UE. In some examples, the sidelink synchronization manager910may determine the set of resources to monitor for sidelink synchronization signals based on the mobility state. In some examples, the sidelink synchronization manager910may update the set of resources based on the updated set of sidelink synchronization signals.

In some cases, the set of sidelink synchronization signals further include a physical broadcast channel transmission that provides system information for the sidelink communications link, such as one or more of random access resources to be used by the second UE for transmission of the sidelink connection request, or beam information for the sidelink communications link.

In some cases, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization. In some cases, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal.

In some cases, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization. In some cases, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal.

The sidelink transmission manager915, when the communications manager905is at a first UE that transmits sidelink synchronization signals, may transmit the set of sidelink synchronization signals based on the identifying. The sidelink random access manager920may receive, from the second UE, a sidelink connection request based on the transmitted set of sidelink synchronization signals.

In some examples, the sidelink random access manager920, when the communications manager905is at a second UE that receives sidelink synchronization signals, may transmit, to the first UE, a sidelink connection request based on the fine timing and the identifier of the first UE.

The sidelink connection establishment manager925may establish the sidelink communications link responsive to the sidelink connection request.

The sidelink configuration manager930may receive, from a serving base station, configuration information that indicates the set of sidelink synchronization signals. In some examples, the sidelink configuration manager930may physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals are provided in a signal structure configured by a serving base station, and where the first sidelink synchronization signal and the second sidelink synchronization signal are determined based on the indicated physical resources. In some examples, the sidelink configuration manager930may receive updated beam index information. In some examples, the sidelink configuration manager930may update the set of sidelink synchronization signals based on the updated beam index information. In some examples, the sidelink configuration manager930may receive, from a serving base station, an indication of a time window for device discovery and measurement, and where the set of sidelink synchronization signals is determined based on the time window.

In some examples, the sidelink configuration manager930may identify physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals that are provided in a signal structure configured by a serving base station, and where the set of resources is determined based on the indicated physical resources. In some examples, the sidelink configuration manager930may receive beam index information from a serving base station that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and where the sidelink synchronization signals are associated with predefined synchronization signals of the subset of transmission beams. In some examples, the sidelink configuration manager930may receive updated beam index information. In some examples, the sidelink configuration manager930may update the set of sidelink synchronization signals based on the updated beam index information. In some examples, the sidelink configuration manager930may receive, from a serving base station, an indication of a time window for device discovery and measurement, and where the set of resources is determined based on the time window.

In some cases, the first reference signal sequence is selected from a first subset of available reference signal sequences that provide the coarse synchronization, and the second reference signal sequence is selected from a second subset of available reference signal sequences, and where the first reference signal sequence is associated with a range of cell identifications configured for sidelink communications, and the second reference signal sequence is associated with a specific cell identification within the range of cell identifications. In some cases, the primary synchronization signal is associated with a range of cell identifications configured for sidelink communications, and the secondary synchronization signal is associated with a specific cell identification within the range of cell identifications. In some cases, the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information.

In some cases, the beam index information is provided in a bit mask that indicates the subset of transmission beams or in a synchronization raster that indicates the subset of transmission beams. In some cases, the beam index information is provided in an indication of random access resources that are available for the sidelink connection request that each have an associated beam. In some cases, the sidelink synchronization signals further include a physical broadcast channel transmission that provides system information for the sidelink communications link, such as one or more of random access resources to be used by the second UE for transmission of the sidelink connection request, or beam information for the sidelink communications link. In some cases, the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information.

FIG.10shows a diagram of a system1000including a device1005that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The device1005may be an example of or include the components of device705, device805, or a UE115as described herein. The device1005may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager1010, an I/O controller1015, a transceiver1020, an antenna1025, memory1030, and a processor1040. These components may be in electronic communication via one or more buses (e.g., bus1045).

The communications manager1010, when at a first UE that transmits sidelink synchronization signals, may identify a set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE, the set of sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, transmit the set of sidelink synchronization signals based on the identifying, receive, from the second UE, a sidelink connection request based on the transmitted set of sidelink synchronization signals, and establish the sidelink communications link with the second UE responsive to the sidelink connection request.

The communications manager1010, when at a second UE that receives sidelink synchronization signals, may also identify a set of resources to monitor for sidelink synchronization signals for synchronizing a sidelink communications link between a first UE and the second UE, the sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, receive the first sidelink synchronization signal from the first UE on the set of resources, determine, based on the first sidelink synchronization signal, a coarse timing for the second sidelink synchronization signal, receive, based on the coarse timing, the second sidelink synchronization signal, determine, based on the second sidelink synchronization signal, a fine timing for synchronizing communications with the first UE and the identifier of the first UE, and transmit, to the first UE, a sidelink connection request based on the fine timing and the identifier of the first UE.

The I/O controller1015may manage input and output signals for the device1005. The I/O controller1015may also manage peripherals not integrated into the device1005. In some cases, the I/O controller1015may represent a physical connection or port to an external peripheral. In some cases, the I/O controller1015may utilize an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operating system. In other cases, the I/O controller1015may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller1015may be implemented as part of a processor. In some cases, a user may interact with the device1005via the I/O controller1015or via hardware components controlled by the I/O controller1015.

In some cases, the wireless device may include a single antenna1025. However, in some cases, the device may have more than one antenna1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The code1035may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code1035may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code1035may not be directly executable by the processor1040but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

The communications manager1115may identify at least a first UE that is to provide a sidelink communications link with one or more other UEs, transmit configuration information to at least the first UE that indicates the set of sidelink synchronization signals, and determine, based on one or more channel parameters associated with the first UE, a set of sidelink synchronization signals for synchronizing the sidelink communications link between the first UE and the one or more other UEs, where the set of sidelink synchronization signals include first sidelink synchronization signal that provides coarse synchronization and a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE. The communications manager1115may be an example of aspects of the communications manager1410described herein. The actions performed by the communications manager1115as described herein may be implemented to realize one or more potential advantages. One implementation may allow a UE115in communication with a base station105to save power and increase battery life by providing synchronization configuration information so the UE115may efficiently determine synchronization of sidelink communications. Additionally or alternatively, the base station may further reduce complexity by providing signals or signal formats that are used for communications between base stations and UEs. Another implementation may provide improved quality and reliability of service at the UE115, as latency and the number of separate resources allocated to the UE115may be reduced.

The receiver1210may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to device-to-device synchronization in wireless communications, etc.). Information may be passed on to other components of the device1205. The receiver1210may be an example of aspects of the transceiver1420described with reference toFIG.14. The receiver1210may utilize a single antenna or a set of antennas.

The communications manager1215may be an example of aspects of the communications manager1115as described herein. The communications manager1215may include a sidelink configuration manager1220and a sidelink synchronization manager1225. The communications manager1215may be an example of aspects of the communications manager1410described herein.

The sidelink configuration manager1220may identify at least a first UE that is to provide a sidelink communications link with one or more other UEs and transmit configuration information to at least the first UE that indicates the set of sidelink synchronization signals.

The sidelink synchronization manager1225may determine, based on one or more channel parameters associated with the first UE, a set of sidelink synchronization signals for synchronizing the sidelink communications link between the first UE and the one or more other UEs, where the set of sidelink synchronization signals include first sidelink synchronization signal that provides coarse synchronization and a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE.

The transmitter1230may transmit signals generated by other components of the device1205. In some examples, the transmitter1230may be collocated with a receiver1210in a transceiver module. For example, the transmitter1230may be an example of aspects of the transceiver1420described with reference toFIG.14. The transmitter1230may utilize a single antenna or a set of antennas.

FIG.13shows a block diagram1300of a communications manager1305that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The communications manager1305may be an example of aspects of a communications manager1115, a communications manager1215, or a communications manager1410described herein. The communications manager1305may include a sidelink configuration manager1310, a sidelink synchronization manager1315, and a sidelink resource manager1320. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

The sidelink configuration manager1310may identify at least a first UE that is to provide a sidelink communications link with one or more other UEs. In some examples, the sidelink configuration manager1310may transmit configuration information to at least the first UE that indicates the set of sidelink synchronization signals. In some cases, the set of sidelink synchronization signals further include a physical broadcast channel transmission that provides system information for the sidelink communications link, such as one or more of random access resources to be used by the second UE for transmission of the sidelink connection request, or beam information for the sidelink communications link.

In some cases, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization. In some cases, the first reference signal sequence is selected from a first subset of available reference signal sequences that provide the coarse synchronization, and the second reference signal sequence is selected from a second subset of available reference signal sequences, and where the first reference signal sequence is associated with a range of cell identifications configured for sidelink communications, and the second reference signal sequence is associated with a specific cell identification within the range of cell identifications.

In some cases, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal. In some cases, the set of sidelink synchronization signals include one or more of a sounding reference signal, a primary synchronization signal, a secondary synchronization signal, a physical broadcast channel signal, a channel state information reference signal, or a control channel signal.

In some cases, the configuration information provides beam index information that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and where the set of sidelink synchronization signals are associated with synchronization signals of the subset of transmission beams. In some cases, the beam index information is provided in a bit mask that indicates the subset of transmission beams or in a synchronization raster that indicates the subset of transmission beams. In some cases, the configuration information provides an indication of a time window for device discovery and measurement, and where the set of sidelink synchronization signals is determined based on the time window. In some cases, the one or more channel parameters include one or more of a mobility state of the first UE, a direction of movement of the first UE, a transmit timing of the base station and the first UE, or a number of UEs that are enabled to establish a sidelink communications link.

The sidelink synchronization manager1315may determine, based on one or more channel parameters associated with the first UE, a set of sidelink synchronization signals for synchronizing the sidelink communications link between the first UE and the one or more other UEs, where the set of sidelink synchronization signals include first sidelink synchronization signal that provides coarse synchronization and a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE.

In some examples, the sidelink synchronization manager1315may receive, from the first UE, updated channel information. In some examples, the sidelink synchronization manager1315may determine, based on the updated channel information, updated beam index information.

The sidelink resource manager1320may identify resources and configurations associated with sidelink communications. In some cases, the primary synchronization signal is associated with a range of cell identifications configured for sidelink communications, and the secondary synchronization signal is associated with a specific cell identification within the range of cell identifications. In some cases, the configuration information provides a signal structure that indicates physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals, and where the set of sidelink synchronization signals are determined based on the indicated physical resources. In some cases, the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information. In some cases, beam index information is provided in an indication of random access resources that are available for sidelink connection requests used to establish the sidelink communications link. In some cases, the random access resources include a set of random access resources that each have an associated beam.

FIG.14shows a diagram of a system1400including a device1405that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The device1405may be an example of or include the components of device1105, device1205, or a base station105as described herein. The device1405may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager1410, a network communications manager1415, a transceiver1420, an antenna1425, memory1430, a processor1440, and an inter-station communications manager1445. These components may be in electronic communication via one or more buses (e.g., bus1450).

The communications manager1410may identify at least a first UE that is to provide a sidelink communications link with one or more other UEs, transmit configuration information to at least the first UE that indicates the set of sidelink synchronization signals, and determine, based on one or more channel parameters associated with the first UE, a set of sidelink synchronization signals for synchronizing the sidelink communications link between the first UE and the one or more other UEs, where the set of sidelink synchronization signals include first sidelink synchronization signal that provides coarse synchronization and a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE.

In some cases, the wireless device may include a single antenna1425. However, in some cases, the device may have more than one antenna1425, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory1430may include RAM, ROM, or a combination thereof. The memory1430may store computer-readable code1435including instructions that, when executed by a processor (e.g., the processor1440) cause the device to perform various functions described herein. In some cases, the memory1430may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The code1435may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code1435may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code1435may not be directly executable by the processor1440but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG.15shows a flowchart illustrating a method1500that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The operations of method1500may be implemented by a UE115or its components as described herein. For example, the operations of method1500may be performed by a communications manager as described with reference toFIGS.7through10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

Optionally, at1505, the UE may receive, from a serving base station of the first UE, configuration information that indicates the set of sidelink synchronization signals. The operations of1505may be performed according to the methods described herein. In some examples, aspects of the operations of1505may be performed by a sidelink configuration manager as described with reference toFIGS.7through10.

At1510, the UE may identify a set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE, the set of sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE. The operations of1510may be performed according to the methods described herein. In some examples, aspects of the operations of1510may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10. In some cases, the set of sidelink synchronization signals may also include a physical broadcast channel transmission that provides system information for the sidelink communications link, such as one or more of random access resources to be used by the second UE for transmission of the sidelink connection request, beam information for the sidelink communications link, and the like.

In some cases, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization. In some cases, the first reference signal sequence is selected from a first subset of available reference signal sequences that provide the coarse synchronization, and the second reference signal sequence is selected from a second subset of available reference signal sequences, and where the first reference signal sequence is associated with a range of cell identifications configured for sidelink communications, and the second reference signal sequence is associated with a specific cell identification within the range of cell identifications.

In some cases, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal. In some cases, the primary synchronization signal is associated with a range of cell identifications configured for sidelink communications, and the secondary synchronization signal is associated with a specific cell identification within the range of cell identifications.

In some cases, physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals may be provided in a signal structure configured by a serving base station, and where the first sidelink synchronization signal and the second sidelink synchronization signal are determined based on the indicated physical resources. In some cases, the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information. In some cases, the UE may receive, from a serving base station, an indication of a time window for device discovery and measurement, and where the set of sidelink synchronization signals is determined based on the time window.

At1520, the UE may transmit the set of sidelink synchronization signals based on the identifying. The operations of1520may be performed according to the methods described herein. In some examples, aspects of the operations of1520may be performed by a sidelink transmission manager as described with reference toFIGS.7through10.

At1525, the UE may receive, from the second UE, a sidelink connection request based on the transmitted set of sidelink synchronization signals. The operations of1525may be performed according to the methods described herein. In some examples, aspects of the operations of1525may be performed by a sidelink random access manager as described with reference toFIGS.7through10.

At1530, the UE may establish the sidelink communications link with the second UE responsive to the sidelink connection request. The operations of1530may be performed according to the methods described herein. In some examples, aspects of the operations of1530may be performed by a sidelink connection establishment manager as described with reference toFIGS.7through10.

At1605, the UE may receive beam index information from a serving base station that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and where the set of sidelink synchronization signals are associated with predefined synchronization signals of the subset of transmission beams. The operations of1605may be performed according to the methods described herein. In some examples, aspects of the operations of1605may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10. In some cases, the beam index information is provided in a bit mask that indicates the subset of transmission beams or in a synchronization raster that indicates the subset of transmission beams.

At1610, the UE may identify, based on the beam index information, the set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE. The operations of1610may be performed according to the methods described herein. In some examples, aspects of the operations of1610may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10.

At1615, the UE may transmit the set of sidelink synchronization signals based on the identifying. The operations of1615may be performed according to the methods described herein. In some examples, aspects of the operations of1615may be performed by a sidelink transmission manager as described with reference toFIGS.7through10.

At1620, the UE may receive, from the second UE, a sidelink connection request based on the transmitted set of sidelink synchronization signals. The operations of1620may be performed according to the methods described herein. In some examples, aspects of the operations of1620may be performed by a sidelink random access manager as described with reference toFIGS.7through10.

At1625, the UE may establish the sidelink communications link with the second UE responsive to the sidelink connection request. The operations of1625may be performed according to the methods described herein. In some examples, aspects of the operations of1625may be performed by a sidelink connection establishment manager as described with reference toFIGS.7through10.

At1630, the UE may receive updated beam index information. The operations of1630may be performed according to the methods described herein. In some examples, aspects of the operations of1630may be performed by a sidelink configuration manager as described with reference toFIGS.7through10.

At1635, the UE may update the set of sidelink synchronization signals based on the updated beam index information. The operations of1635may be performed according to the methods described herein. In some examples, aspects of the operations of1635may be performed by a sidelink configuration manager as described with reference toFIGS.7through10.

FIG.17shows a flowchart illustrating a method1700that supports device-to-device synchronization in wireless communications in accordance with aspects of the present disclosure. The operations of method1700may be implemented by a UE115or its components as described herein. For example, the operations of method1700may be performed by a communications manager as described with reference toFIGS.7through10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At1705, the UE may identify a set of resources to monitor for sidelink synchronization signals for synchronizing a sidelink communications link between a first UE and the second UE, the sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE. The operations of1705may be performed according to the methods described herein. In some examples, aspects of the operations of1705may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10.

At1710, the UE may receive the first sidelink synchronization signal from the first UE on the set of resources. The operations of1710may be performed according to the methods described herein. In some examples, aspects of the operations of1710may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10.

At1715, the UE may determine, based on the first sidelink synchronization signal, a coarse timing for the second sidelink synchronization signal. The operations of1715may be performed according to the methods described herein. In some examples, aspects of the operations of1715may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10.

At1720, the UE may receive, based on the coarse timing, the second sidelink synchronization signal. The operations of1720may be performed according to the methods described herein. In some examples, aspects of the operations of1720may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10.

At1725, the UE may determine, based on the second sidelink synchronization signal, a fine timing for synchronizing communications with the first UE and the identifier of the first UE. The operations of1725may be performed according to the methods described herein. In some examples, aspects of the operations of1725may be performed by a sidelink synchronization manager as described with reference toFIGS.7through10.

At1730, the UE may transmit, to the first UE, a sidelink connection request based on the fine timing and the identifier of the first UE. The operations of1730may be performed according to the methods described herein. In some examples, aspects of the operations of1730may be performed by a sidelink random access manager as described with reference toFIGS.7through10.

At1805, the base station may identify at least a first UE that is to provide a sidelink communications link with one or more other UEs. The operations of1805may be performed according to the methods described herein. In some examples, aspects of the operations of1805may be performed by a sidelink configuration manager as described with reference toFIGS.11through14.

At1810, the base station may determine, based on one or more channel parameters associated with the first UE, a set of sidelink synchronization signals for synchronizing the sidelink communications link between the first UE and the one or more other UEs, where the set of sidelink synchronization signals include first sidelink synchronization signal that provides coarse synchronization and a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE. The operations of1810may be performed according to the methods described herein. In some examples, aspects of the operations of1810may be performed by a sidelink synchronization manager as described with reference toFIGS.11through14.

At1815, the base station may transmit configuration information to at least the first UE that indicates the set of sidelink synchronization signals. The operations of1815may be performed according to the methods described herein. In some examples, aspects of the operations of1815may be performed by a sidelink configuration manager as described with reference toFIGS.11through14.

Aspects of the following examples may be combined with any of the previous examples or aspects described herein. Thus, example 1 is a method for wireless communication at a first UE including: identifying a set of sidelink synchronization signals for transmission to at least a second UE for synchronizing a sidelink communications link between the first UE and at least the second UE, the set of sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, transmitting the set of sidelink synchronization signals based at least in part on the identifying, receiving, from the second UE, a sidelink connection request based at least in part on the transmitted set of sidelink synchronization signals, and establishing the sidelink communications link with the second UE responsive to the sidelink connection request.

In example 2, the method of example 1 may include: receiving, from a serving base station of the first UE, configuration information that indicates the set of sidelink synchronization signals. In example 3, in the method of examples 1-2 the set of sidelink synchronization signals further include a physical broadcast channel transmission that provides system information for the sidelink communications link.

In example 4, in the method of examples 1-3, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization. In example 5, in the method of example 4, the first reference signal sequence is selected from a first subset of available reference signal sequences that provide the coarse synchronization, and the second reference signal sequence is selected from a second subset of available reference signal sequences, and where the first reference signal sequence is associated with a range of cell identifications configured for sidelink communications, and the second reference signal sequence is associated with a specific cell identification within the range of cell identifications.

In example 6, in the method of examples 1-3, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal. In example 7, in the method of example 6, wherein the primary synchronization signal is associated with a range of cell identifications configured for sidelink communications, and the secondary synchronization signal is associated with a specific cell identification within the range of cell identifications.

In example 8, in the method of examples 1-7, physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals are provided in a signal structure configured by a serving base station, and wherein the first sidelink synchronization signal and the second sidelink synchronization signal are determined based at least in part on the indicated physical resources. In example 9, in the method of example 8 the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information.

In example 10, in the method of examples 1-9, the identifying may include receiving beam index information from a serving base station that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and wherein the set of sidelink synchronization signals are associated with predefined synchronization signals of the subset of transmission beams. In example 11, in the method of example 10, the beam index information is provided in a bit mask that indicates the subset of transmission beams or in a synchronization raster that indicates the subset of transmission beams. In example 12, in the method of examples 10-11, the identifying may further include: receiving updated beam index information, and updating the set of sidelink synchronization signals based at least in part on the updated beam index information. In example 13, in the method of examples 10-12, the beam index information is provided in an indication of random access resources that are available for the sidelink connection request that each have an associated beam.

In example 14, in the method of examples 1-13, the identifying may include: receiving, from a serving base station, an indication of a time window for device discovery and measurement, and wherein the set of sidelink synchronization signals is determined based at least in part on the time window. In example 15, the method of examples 1-14 may further include: determining that an updated set of sidelink synchronization signals are to be transmitted based at least in part on one or more updated QCL parameters of the first UE, and transmitting an indication of the updated set of sidelink synchronization signals to at least one of the second UE or a base station. In example 16, the method of examples 1-16 may further include: determining, at the first UE, a mobility state of the first UE, wherein the set of synchronization signals is based at least in part on the mobility state, and transmitting an indication of the mobility state to one or more of the second UE or a base station.

Example 17 is a method for wireless communication at a second UE, including: identifying a set of resources to monitor for sidelink synchronization signals for synchronizing a sidelink communications link between a first UE and the second UE, the sidelink synchronization signals including one or more of a first sidelink synchronization signal that provides coarse synchronization or a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, receiving the first sidelink synchronization signal from the first UE on the set of resources, determining, based at least in part on the first sidelink synchronization signal, a coarse timing for the second sidelink synchronization signal, receiving, based at least in part on the coarse timing, the second sidelink synchronization signal, determining, based at least in part on the second sidelink synchronization signal, a fine timing for synchronizing communications with the first UE and the identifier of the first UE, and transmitting, to the first UE, a sidelink connection request based at least in part on the fine timing and the identifier of the first UE.

In example 18, in the method of example 17, the identifying may include: receiving, from a serving base station of the first UE, configuration information that indicates a configuration of the sidelink synchronization signals. In example 19, in the method of examples 17-18, the sidelink synchronization signals further include a physical broadcast channel transmission that provides system information for the sidelink communications link.

In example 20, in the method of examples 17-19, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization.

In example 21, in the method of examples 17-19, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal. In example 22, in the method of example 21, the primary synchronization signal is associated with a range of cell identifications configured for sidelink communications, and the secondary synchronization signal is associated with a specific cell identification within the range of cell identifications.

In example 23, in the method of examples 17-22, physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals are provided in a signal structure configured by a serving base station, and where the set of resources is determined based at least in part on the indicated physical resources. In example 24, in the method of example 23, the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information.

In example 25, in the method of examples 17-24, the identifying may include: receiving beam index information from a serving base station that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and where the sidelink synchronization signals are associated with predefined synchronization signals of the subset of transmission beams. In example 26, in the method of example 25, the beam index information is provided in a bit mask that indicates the subset of transmission beams or in a synchronization raster that indicates the subset of transmission beams. In example 27, in the method of examples 25-26, the identifying may further include: receiving updated beam index information, and updating the set of sidelink synchronization signals based at least in part on the updated beam index information. In example 28, in the method of examples 25-27, the beam index information is provided in an indication of random access resources that are available for the sidelink connection request that each have an associated beam.

In example 29, in the method of examples 17-28, the identifying may include: receiving, from a serving base station, an indication of a time window for device discovery and measurement, and where the set of resources is determined based at least in part on the time window. In example 30, the method of examples 17-29 may further include: receiving, from the first UE or a base station, an indication that an updated set of sidelink synchronization signals are to be transmitted based at least in part on one or more updated QCL parameters of the first UE, and updating the set of resources based at least in part on the updated set of sidelink synchronization signals. In example 31, the method of examples 17-30 may further include: receiving, from the first UE or a base station, an indication of a mobility state of the first UE, and determining the set of resources to monitor for sidelink synchronization signals based at least in part on the mobility state.

Example 32 is a method for wireless communication at a base station, including: identifying at least a first UE that is to provide a sidelink communications link with one or more other UEs, determining, based at least in part on one or more channel parameters associated with the first UE, a set of sidelink synchronization signals for synchronizing the sidelink communications link between the first UE and the one or more other UEs, where the set of sidelink synchronization signals include first sidelink synchronization signal that provides coarse synchronization and a second sidelink synchronization signal that provides fine synchronization and an identifier of the first UE, and transmitting configuration information to at least the first UE that indicates the set of sidelink synchronization signals.

In example 33, in the method of example 32, the set of sidelink synchronization signals further include a physical broadcast channel transmission that provides system information for the sidelink communications link.

In example 34, in the method of examples 32-33, the first sidelink synchronization signal is a first sounding reference signal having a first reference signal sequence that provides the coarse synchronization, and the second sidelink synchronization signal is a second reference signal having a second reference signal sequence that is selected from a set of available sounding reference signal sequences to provide the identifier of the first UE and to provide the fine synchronization. In example 35, in the method of example 34, the first reference signal sequence is selected from a first subset of available reference signal sequences that provide the coarse synchronization, and the second reference signal sequence is selected from a second subset of available reference signal sequences, and where the first reference signal sequence is associated with a range of cell identifications configured for sidelink communications, and the second reference signal sequence is associated with a specific cell identification within the range of cell identifications.

In example 36, in the method of examples 32-33, the first sidelink synchronization signal is a primary synchronization signal and the second sidelink synchronization signal is a secondary synchronization signal. In example 37, in the method of example 36, the primary synchronization signal is associated with a range of cell identifications configured for sidelink communications, and the secondary synchronization signal is associated with a specific cell identification within the range of cell identifications.

In example 38, in the method of examples 32-37, the configuration information provides a signal structure that indicates physical resources to be used at the first UE for transmission of the set of sidelink synchronization signals, and where the set of sidelink synchronization signals are determined based at least in part on the indicated physical resources. In example 39, in the method of example 38, the physical resources indicated in the configuration information include an indication of symbols for transmission of the first sidelink synchronization signal, the second sidelink synchronization signal, and physical broadcast channel information.

In example 40, in the method of examples 32-39, the set of sidelink synchronization signals include one or more of a sounding reference signal, a primary synchronization signal, a secondary synchronization signal, a physical broadcast channel signal, a channel state information reference signal, or a control channel signal.

In example 41, in the method of examples 32-40, the configuration information provides beam index information that indicates a subset of a set of transmission beams that are available for transmissions of the sidelink communications link, and where the set of sidelink synchronization signals are associated with synchronization signals of the subset of transmission beams. In example 42, in the method of example 41, the beam index information is provided in a bit mask that indicates the subset of transmission beams or in a synchronization raster that indicates the subset of transmission beams. In example 43, the method of examples 41-42 may further include: receiving, from the first UE, updated channel information, determining, based at least in part on the updated channel information, updated beam index information, and transmitting the updated beam index information to at least the first UE. In example 44, in the method of examples 41-43, the beam index information is provided in an indication of random access resources that are available for sidelink connection requests used to establish the sidelink communications link. In example 45, in the method of example 44, the random access resources include a plurality of random access resources that each have an associated beam.

In example 46, in the method of examples 32-45, the configuration information provides an indication of a time window for device discovery and measurement, and where the set of sidelink synchronization signals is determined based at least in part on the time window. In example 47, in the method of examples 32-46, the one or more channel parameters include one or more of a mobility state of the first UE, a direction of movement of the first UE, a transmit timing of the base station and the first UE, or a number of UEs that are enabled to establish a sidelink communications link.

Example 48 is a system or apparatus including means for implementing a method or realizing an apparatus as in any of examples 1-47.

Example 49 is a non-transitory computer-readable medium storing instructions executable by one or more processors to cause the one or more processors to implement a method as in any of examples 1-47.

Aspects of these examples may be combined with aspects or embodiments disclosed in other implementations.