WO2023087137A1

WO2023087137A1 - Changing synchronization cases for vehicle-to-everything deployments

Info

Publication number: WO2023087137A1
Application number: PCT/CN2021/130912
Authority: WO
Inventors: Yi Qin; Cheol Hee Park; Xiaochen Chen; Jintao HOU; Zengyu Hao; Jianming Zhang; Hongjin GUO; Feng Chen; Lei ZOU; Hao Chen; Nan Zhang; Yi Ren; Boting WANG
Original assignee: Qualcomm Incorporated
Priority date: 2021-11-16
Filing date: 2021-11-16
Publication date: 2023-05-25

Abstract

Methods, systems, and devices for wireless communications are described. A sidelink UE may switch from one synchronization source to another synchronization source that has a higher synchronization priority level if one or more conditions or rules are satisfied. For instance, if a UE that is its own synchronization source (e.g., is utilizing a lower priority synchronization source) transmits SLSSs and does not receive any sidelink data transmission in response for a threshold amount of time, the UE may attempt to switch to a different synchronization source that has a higher synchronization priority level. For example, the UE may pause its SLSS transmissions and scan for SLSSs from other synchronization sources (e.g., that have higher synchronization priority levels).

Description

CHANGING SYNCHRONIZATION CASES FOR VEHICLE-TO-EVERYTHING DEPLOYMENTS

FIELD OF TECHNOLOGY

The following relates to wireless communications, including changing synchronization cases for vehicle-to-everything deployments.

BACKGROUND

Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power) . Examples of such multiple-access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal FDMA (OFDMA) , or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) . A wireless multiple-access communications system may include one or more base stations or one or more network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE) .

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support changing synchronization cases for vehicle-to-everything deployments. Generally, a sidelink UE may switch from one synchronization source to another synchronization source that has a higher synchronization priority level if one or more conditions or rules are satisfied. For instance, if a UE that is its own synchronization source (e.g., is utilizing a lower priority synchronization source) transmits sidelink synchronization signals (SLSSs) and does not receive any sidelink data transmission in response for a threshold amount of time, the UE may attempt to switch to a different synchronization source that has a higher synchronization priority level. For example, the UE may pause its SLSS transmissions and scan for SLSSs from other synchronization sources (e.g., that have higher synchronization priority levels) . The UE may synchronize with other synchronization sources that have higher synchronization priority levels, resulting in more efficient wireless communications, decreased latency, and improved user experience. In some examples, the threshold amount of time may be a multiple of a time period for periodically transmitting SLSSs. The new synchronization source having a higher synchronization priority level may be another UE, a global network satellite system (GNSS) satellite, a base station, or any combination thereof (e.g., an indirect connection) .

A method for wireless communications at a first user equipment (UE) is described. The method may include transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals, monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals, switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time, and receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

An apparatus for wireless communications at a first UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to transmit, according to a first synchronization priority level, one or more first sidelink synchronization signals, monitor for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals, switch from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time, and receive a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

Another apparatus for wireless communications at a first UE is described. The apparatus may include means for transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals, means for monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals, means for switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time, and means for receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

A non-transitory computer-readable medium storing code for wireless communications at a first UE is described. The code may include instructions executable by a processor to transmit, according to a first synchronization priority level, one or more first sidelink synchronization signals, monitor for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals, switch from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time, and receive a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the switching from the first synchronization priority level to the second synchronization priority level may include operations, features, means, or instructions for pausing transmission of the one or more first sidelink synchronization signals and scanning for the second sidelink synchronization signal, where receiving the second sidelink synchronization signal from the synchronization source may be based on scanning for the second sidelink synchronization signal.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, transmitting the one or more first sidelink synchronization signals may include operations, features, means, or instructions for transmitting the one or more first sidelink synchronization signals according to an internal clock of the first UE, where the first UE includes a second synchronization source associated with the first synchronization priority level.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the second synchronization priority level may be higher than the first synchronization priority level.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the synchronization source may include operations, features, means, or instructions for a satellite associated with a global navigation satellite system, a base station, a second UE, or any combination thereof.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, transmitting the one or more first sidelink synchronization signals may include operations, features, means, or instructions for transmitting the one or more first sidelink synchronization signals according to a first periodicity.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the threshold amount of time includes a multiple of a period of the first periodicity.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the first periodicity includes 160 milliseconds and the threshold amount of time includes 320 milliseconds.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for synchronizing with the synchronization source based on receiving the second sidelink synchronization signal and communicating with one or more UEs via a sidelink channel based on the synchronizing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a wireless communications system that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a wireless communications system that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

FIG. 3 illustrates an example of a process flow that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

FIGs. 4 and 5 show block diagrams of devices that support changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

FIG. 6 shows a block diagram of a communications manager that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

FIG. 7 shows a diagram of a system including a device that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

FIGs. 8 through 10 show flowcharts illustrating methods that support changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

A wireless communications system may support sidelink communications between one or more user equipments (UEs) on a sidelink channel. Sidelink communications between UEs may rely on time synchronization between sidelink UEs. For instance, a first UE may transmit one or more synchronization signals (e.g., sidelink synchronization signals (SLSSs) to a second UE. A synchronization source (e.g., the first UE) may transmit SLSSs, and a receiving device (e.g., the second UE) may synchronization with the synchronization source according to the received SLSSs. However, in some examples, some synchronization sources may be more reliable than others, or may otherwise have higher priorities. For instance, synchronizing with a global network satellite system (GNSS) satellite (e.g., directly, or indirectly via another sidelink UE that is synchronized directly with the GNSS satellite) may be a higher priority synchronization source than using a UEs own internal clock as a synchronization source (e.g., using a UE’s own internal clock may be a lowest priority synchronization source) .

When a UE cannot receive SLSSs from another UE or from higher priority synchronization sources, the UE may resort to utilizing its own internal clock as a synchronization source, and may transmit SLSSs (e.g., instead of monitoring for SLSSs from other synchronization sources) . However, if the UE changes its location, and is capable of receiving SLSSs from a higher priority synchronization source, the UE may be unable to do so because it is transmitting SLSSs instead of monitoring for SLSSs from other synchronization sources. This may lead to misaligned timing for the UE, a failure to connect with other synchronization sources, failed communications, increased latency, and decreased user experience.

A sidelink UE may switch from one synchronization source to another synchronization source that has a higher synchronization priority level if one or more conditions or rules are satisfied. For instance, if a UE that is its own synchronization source (e.g., is utilizing a lower priority synchronization source) transmits SLSSs and does not receive any sidelink data transmission in response for a threshold amount of time, the UE may attempt to switch to a different synchronization source that has a higher synchronization priority level. For example, the UE may pause its SLSS transmissions and scan for SLSSs from other synchronization sources (e.g., that have higher synchronization priority levels) . The UE may synchronize with other synchronization sources that have higher synchronization priority levels, resulting in more efficient wireless communications, decreased latency, and improved user experience. In some examples, the threshold amount of time may be a multiple of a time period for periodically transmitting SLSSs. The new synchronization source having a higher synchronization priority level may be another UE, a GNSS satellite, a base station, or any combination thereof (e.g., an indirect connection) .

Aspects of the disclosure are initially described in the context of wireless communications systems. Aspects of the disclosure are further illustrated by and described with reference to wireless communications systems and process flows. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to changing synchronization cases for vehicle-to-everything deployments.

FIG. 1 illustrates an example of a wireless communications system 100 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The wireless communications system 100 may include one or more base stations 105, one or more UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-APro network, or a New Radio (NR) network. In some examples, the wireless communications system 100 may support enhanced broadband communications, ultra-reliable communications, low latency communications, communications with low-cost and low-complexity devices, or any combination thereof.

The base stations 105 may be dispersed throughout a geographic area to form the wireless communications system 100 and may be devices in different forms or having different capabilities. The base stations 105 and the UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which the UEs 115 and the base station 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 may support the communication of signals according to one or more radio access technologies.

The UEs 115 may be dispersed throughout a coverage area 110 of the wireless communications system 100, and each UE 115 may be stationary, or mobile, or both at different times. The UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, the base stations 105, or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or other network equipment) , as shown in FIG. 1.

The base stations 105 may communicate with the core network 130, or with one another, or both. For example, the base stations 105 may interface with the core network 130 through one or more backhaul links 120 (e.g., via an S1, N2, N3, or other interface) . The base stations 105 may communicate with one another over the backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105) , or indirectly (e.g., via core network 130) , or both. In some examples, the backhaul links 120 may be or include one or more wireless links.

One or more of the base stations 105 described herein may include or may be referred to by a person having ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB) , a next-generation NodeB or a giga-NodeB (either of which may be referred to as a gNB) , a Home NodeB, a Home eNodeB, or other suitable terminology.

A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA) , a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communications (MTC) device, among other examples, which may be implemented in various objects such as appliances, or vehicles, meters, among other examples.

The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as the base stations 105 and the network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, among other examples, as shown in FIG. 1.

The UEs 115 and the base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of one or more radio frequency spectrum resources having a defined physical layer structure for supporting the communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP) ) that is operated according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR) . Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information) , control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communications system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing (FDD) and time division duplexing (TDD) component carriers.

In some examples (e.g., in a carrier aggregation configuration) , a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers. A carrier may be associated with a frequency channel (e.g., an evolved universal mobile telecommunication system terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN) ) and may be positioned according to a channel raster for discovery by the UEs 115. A carrier may be operated in a standalone mode where initial acquisition and connection may be conducted by the UEs 115 via the carrier, or the carrier may be operated in a non-standalone mode where a connection is anchored using a different carrier (e.g., of the same or a different radio access technology) .

The communication links 125 shown in the wireless communications system 100 may include uplink transmissions from a UE 115 to a base station 105, or downlink transmissions from a base station 105 to a UE 115. Carriers may carry downlink or uplink communications (e.g., in an FDD mode) or may be configured to carry downlink and uplink communications (e.g., in a TDD mode) .

A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communications system 100. For example, the carrier bandwidth may be one of a number of determined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 megahertz (MHz) ) . Devices of the wireless communications system 100 (e.g., the base stations 105, the UEs 115, or both) may have hardware configurations that support communications over a particular carrier bandwidth or may be configurable to support communications over one of a set of one or more carrier bandwidths. In some examples, the wireless communications system 100 may include base stations 105 or UEs 115 that support simultaneous communications via carriers associated with multiple carrier bandwidths. In some examples, each served UE 115 may be configured for operating over portions (e.g., a sub-band, a BWP) or all of a carrier bandwidth.

Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM) ) . In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both) . Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams) , and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

One or more numerologies for a carrier may be supported, where a numerology may include a subcarrier spacing (Δf) and a cyclic prefix. A carrier may be divided into one or more BWPs having the same or different numerologies. In some examples, a UE 115 may be configured with multiple BWPs. In some examples, a single BWP for a carrier may be active at a given time and communications for the UE 115 may be restricted to one or more active BWPs.

The time intervals for the base stations 105 or the UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T _s=1/ (Δf _max·N _f) seconds, where Δf _max may represent the maximum supported subcarrier spacing, and N _f may represent the maximum supported discrete Fourier transform (DFT) size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms) ) . Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023) .

Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some examples, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period) . In some wireless communications systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., N _f) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communications system 100 and may be referred to as a transmission time interval (TTI) . In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally or alternatively, the smallest scheduling unit of the wireless communications system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs) ) .

Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using one or more of time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET) ) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of the UEs 115. For example, one or more of the UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs) ) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

Each base station 105 may provide communication coverage via one or more cells, for example a macro cell, a small cell, a hot spot, or other types of cells, or any combination thereof. The term “cell” may refer to a logical communication entity used for communication with a base station 105 (e.g., over a carrier) and may be associated with an identifier for distinguishing neighboring cells (e.g., a physical cell identifier (PCID) , a virtual cell identifier (VCID) , or others) . In some examples, a cell may also refer to a geographic coverage area 110 or a portion of a geographic coverage area 110 (e.g., a sector) over which the logical communication entity operates. Such cells may range from smaller areas (e.g., a structure, a subset of structure) to larger areas depending on various factors such as the capabilities of the base station 105. For example, a cell may be or include a building, a subset of a building, or exterior spaces between or overlapping with geographic coverage areas 110, among other examples.

A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by the UEs 115 with service subscriptions with the network provider supporting the macro cell. A small cell may be associated with a lower-powered base station 105, as compared with a macro cell, and a small cell may operate in the same or different (e.g., licensed, unlicensed) frequency bands as macro cells. Small cells may provide unrestricted access to the UEs 115 with service subscriptions with the network provider or may provide restricted access to the UEs 115 having an association with the small cell (e.g., the UEs 115 in a closed subscriber group (CSG) , the UEs 115 associated with users in a home or office) . A base station 105 may support one or multiple cells and may also support communications over the one or more cells using one or multiple component carriers.

In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., MTC, narrowband IoT (NB-IoT) , enhanced mobile broadband (eMBB) ) that may provide access for different types of devices.

In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, the overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous network in which different types of the base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

The wireless communications system 100 may support synchronous or asynchronous operation. For synchronous operation, the base stations 105 may have similar frame timings, and transmissions from different base stations 105 may be approximately aligned in time. For asynchronous operation, the base stations 105 may have different frame timings, and transmissions from different base stations 105 may, in some examples, not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations.

Some UEs 115, such as MTC or IoT devices, may be low cost or low complexity devices and may provide for automated communication between machines (e.g., via Machine-to-Machine (M2M) communication) . M2M communication or MTC may refer to data communication technologies that allow devices to communicate with one another or a base station 105 without human intervention. In some examples, M2M communication or MTC may include communications from devices that integrate sensors or meters to measure or capture information and relay such information to a central server or application program that makes use of the information or presents the information to humans interacting with the application program. Some UEs 115 may be designed to collect information or enable automated behavior of machines or other devices. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, healthcare monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business charging.

Some UEs 115 may be configured to employ operating modes that reduce power consumption, such as half-duplex communications (e.g., a mode that supports one-way communication via transmission or reception, but not transmission and reception simultaneously) . In some examples, half-duplex communications may be performed at a reduced peak rate. Other power conservation techniques for the UEs 115 include entering a power saving deep sleep mode when not engaging in active communications, operating over a limited bandwidth (e.g., according to narrowband communications) , or a combination of these techniques. For example, some UEs 115 may be configured for operation using a narrowband protocol type that is associated with a defined portion or range (e.g., set of subcarriers or resource blocks (RBs) ) within a carrier, within a guard-band of a carrier, or outside of a carrier.

The wireless communications system 100 may be configured to support ultra-reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communications system 100 may be configured to support ultra-reliable low-latency communications (URLLC) . The UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions. Ultra-reliable communications may include private communication or group communication and may be supported by one or more services such as push-to-talk, video, or data. Support for ultra-reliable, low-latency functions may include prioritization of services, and such services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, and ultra-reliable low-latency may be used interchangeably herein.

In some examples, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol) . One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some examples, groups of the UEs 115 communicating via D2D communications may utilize a one-to-many (1: M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between the UEs 115 without the involvement of a base station 105.

In some systems, the D2D communication link 135 may be an example of a communication channel, such as a sidelink communication channel, between vehicles (e.g., UEs 115) . In some examples, vehicles may communicate using vehicle-to-everything (V2X) communications, vehicle-to-vehicle (V2V) communications, or some combination of these. A vehicle may signal information related to traffic conditions, signal scheduling, weather, safety, emergencies, or any other information relevant to a V2X system. In some examples, vehicles in a V2X system may communicate with roadside infrastructure, such as roadside units, or with the network via one or more network nodes (e.g., base stations 105) using vehicle-to-network (V2N) communications, or with both.

The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC) , which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management function (AMF) ) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a Packet Data Network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for the UEs 115 served by the base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to IP services 150 for one or more network operators. The IP services 150 may include access to the Internet, Intranet (s) , an IP Multimedia Subsystem (IMS) , or a Packet-Switched Streaming Service.

Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC) . Each access network entity 140 may communicate with the UEs 115 through one or more other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs) . Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105) .

The wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz) . Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately one decimeter to one meter in length. The UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to the UEs 115 located indoors. The transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

The wireless communications system 100 may also operate in a super high frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also known as the centimeter band, or in an extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz) , also known as the millimeter band. In some examples, the wireless communications system 100 may support millimeter wave (mmW) communications between the UEs 115 and the base stations 105, and EHF antennas of the respective devices may be smaller and more closely spaced than UHF antennas. In some examples, this may facilitate use of antenna arrays within a device. The propagation of EHF transmissions, however, may be subject to even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. The techniques disclosed herein may be employed across transmissions that use one or more different frequency regions, and designated use of bands across these frequency regions may differ by country or regulating body.

The wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communications system 100 may employ License Assisted Access (LAA) , LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as the base stations 105 and the UEs 115 may employ carrier sensing for collision detection and avoidance. In some examples, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA) . Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among other examples.

A base station 105 or a UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port.

The base stations 105 or the UEs 115 may use MIMO communications to exploit multipath signal propagation and increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers. Such techniques may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams (e.g., different codewords) . Different spatial layers may be associated with different antenna ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO) , where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO) , where multiple spatial layers are transmitted to multiple devices.

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

A base station 105 or a UE 115 may use beam sweeping techniques as part of beam forming operations. For example, a base station 105 may use multiple antennas or antenna arrays (e.g., antenna panels) to conduct beamforming operations for directional communications with a UE 115. Some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station 105 multiple times in different directions. For example, the base station 105 may transmit a signal according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by a transmitting device, such as a base station 105, or by a receiving device, such as a UE 115) a beam direction for later transmission or reception by the base station 105.

Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station 105 in a single beam direction (e.g., a direction associated with the receiving device, such as a UE 115) . In some examples, the beam direction associated with transmissions along a single beam direction may be determined based on a signal that was transmitted in one or more beam directions. For example, a UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions and may report to the base station 105 an indication of the signal that the UE 115 received with a highest signal quality or an otherwise acceptable signal quality.

In some examples, transmissions by a device (e.g., by a base station 105 or a UE 115) may be performed using multiple beam directions, and the device may use a combination of digital precoding or radio frequency beamforming to generate a combined beam for transmission (e.g., from a base station 105 to a UE 115) . The UE 115 may report feedback that indicates precoding weights for one or more beam directions, and the feedback may correspond to a configured number of beams across a system bandwidth or one or more sub-bands. The base station 105 may transmit a reference signal (e.g., a cell-specific reference signal (CRS) , a channel state information reference signal (CSI-RS) ) , which may be precoded or unprecoded. The UE 115 may provide feedback for beam selection, which may be a precoding matrix indicator (PMI) or codebook-based feedback (e.g., a multi-panel type codebook, a linear combination type codebook, a port selection type codebook) . Although these techniques are described with reference to signals transmitted in one or more directions by a base station 105, a UE 115 may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE 115) or for transmitting a signal in a single direction (e.g., for transmitting data to a receiving device) .

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

The wireless communications system 100 may be a packet-based network that operates 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. A Radio Link Control (RLC) layer may 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 error detection techniques, error correction techniques, or both to support retransmissions 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 UE 115 and a base station 105 or a core network 130 supporting radio bearers for user plane data. At the physical layer, transport channels may be mapped to physical channels.

The UEs 115 and the base stations 105 may support retransmissions of data to increase the likelihood that data is received successfully. Hybrid automatic repeat request (HARQ) feedback is one technique for increasing the likelihood that data is received correctly over a communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC) ) , forward error correction (FEC) , and retransmission (e.g., automatic repeat request (ARQ) ) . HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., low signal-to-noise conditions) . In some examples, a device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval.

A sidelink UE 115 may switch from one synchronization source to a higher priority synchronization source if one or more conditions or rules are satisfied. For instance, if a UE 115 that is its own synchronization source (e.g., is utilizing a lower priority synchronization source) transmits SLSSs and does not receive any sidelink data transmission in response for a threshold amount of time, the UE 115 may attempt to switch to a higher priority synchronization source. For example, the UE 115 may pause its SLSS transmissions and scan for SLSSs from other synchronization sources (e.g., that have higher priority levels) . The UE 115 may synchronize with other synchronization sources that have higher priority levels, resulting in more efficient wireless communications, decreased latency, and improved user experience. In some examples, the threshold amount of time may be a multiple of a period for transmitting SLSSs. The new synchronization source having a higher priority level may be another UE 115, a GNSS satellite, a base station, or any combination thereof (e.g., an indirect connection) .

FIG. 2 illustrates an example of a wireless communications system 200 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. Wireless communications system may include a satellite 205, a UE 115-a, a UE 115-b, a UE 115-c, and a UE 115-d. In some examples, the UEs 115 may be sidelink UEs (e.g., V2X UEs, smart devices, wearable devices, or the like) . The satellite 205 may serve wireless devices (e.g., UEs 115) that are located within coverage area 210.

In some examples, a UE 115 may derive its own timing from one or more synchronization sources. For instance, a UE 115 may derive its own synchronization from a GNSS, a base station 105, another UE 115 (e.g., another UE 115 transmitting a SLSS) , or its own internal clock. In some examples, a UE 115 may perform synchronization most accurately via higher priority synchronization sources (e.g., a GNSS satellite 205 or a base station 105) , may perform synchronization less accurately via lower priority synchronization sources (e.g., UEs 115) ; and may perform synchronization least accurately via its own internal clock (e.g., a synchronization source having a lowest synchronization priority level) .

Additionally, when performing synchronization via another UE 115, the UE 115 may perform synchronization more accurately by synchronization with another UE 115 that is directly synchronized with GNSS or a base station 105, as compared to the other UE 115 being indirectly synchronized (e.g., being synchronized via a third UE 115 that may in turn be directly synchronized or indirectly synchronized) . For instance, the UE 115-a may synchronize directly with the GNSS via the satellite 205. The satellite 205 may communicate with the UE 115-a via communication link 225. The UE 115-a may synchronize to the satellite 205 to align transmission time interval (TTI) boundaries for transmitting and receiving sidelink communications. In some examples, the satellite 205 may transmit, via the communication link 225, one or more synchronization signals to the UE 115-a, based on which the UE 115-a may synchronize to the GNSS. Although described and illustrated with reference to satellite 205, a UE 115-a may similarly synchronize with a base station 105 based on signaling from the base station 105 received via a communication link.

A UE 115-b may synchronize to the GNSS indirectly via the UE 115-a. For example, the UE 115-a may transmit a synchronization signal 215-a (e.g., an SLSS) , a master information block (MIB) , sidelink synchronization signal block (S-SSB, or the like) , to the UE 115-b, and the UE 115-b may synchronize its sidelink communications according to a timing based on synchronization signal 215-a. Although the UE 115-b is not synchronized directly to the GNSS satellite 205, the UE 115-b may still benefit from synchronization with the GNSS.

In some examples, a UE 115 may synchronize to its own internal clock. For example, the UE 115-c may be located outside the coverage area 210 served by the satellite 205. Additionally, when located at position P1, the UE 115-c may be outside the range of the UE 115-a (e.g., and may thus be located too far away from the UE 115-a to synchronize indirectly with the GNSS via the UE 115-a) . In such examples, the UE 115-c may synchronize to its own internal clock. Instead of monitoring for synchronization signals 215 (e.g., synchronization signal 215-b from the UE 115-a) , the UE 115-c may transmit synchronization signal 215-c according to its own internal clock. Upon receiving the synchronization signal 215-c, the UE 115-d may communicate with the UE 115-c (e.g., may transmit sidelink data to the UE 115-c) according to a timing associated with the synchronization signal 215-c.

In some examples, a UE 115 may identify a set of priorities (e.g., synchronization priorities) among the synchronization references and search for the synchronization reference with the highest synchronization priority level. For instance, S-SSB transmissions from UEs 115 that have direct synchronization may have a highest synchronization priority level; UEs 115 that have indirect synchronization via another UE 115 with direct synchronization may have a lower synchronization priority level than for direct synchronization; and UEs 115 that have indirect synchronization via another UE 115 with indirect synchronization may have a lower synchronization priority level than for indirect synchronization where the other UE 115 has direct synchronization. For instance, the UE 115-a may synchronize with the satellite 205 (e.g., a highest synchronization priority level) , the UE 115-b may synchronize with the GNSS via the UE 115-a (e.g., a synchronization priority level that is lower than direct synchronization) , and the UE 115-c (e.g., while located at position P1) may synchronize with its own internal clock (e.g., a lowest synchronization priority level) .

An example table is provided below for different sets of synchronization priority levels:

Table 1: Examples of Sets of Synchronization Priorities

In Table 1, P0 may represent the highest priority and P4 (for Case 1) or P7 (for cases 2 and 3) may represent the lowest priority of a set of synchronization priority levels. Additional examples of sets of synchronization priorities may be possible without deviating from the scope of the present disclosure.

As described herein, if a UE 115 (e.g., the UE 115-c) is not within a threshold distance of other synchronization sources (e.g., if the UE 115-c is not within a threshold distance of the UE 115-a) , then the UE 115-c may transmit synchronization signals 215-c according to its own internal clock. That is, because the UE 115-c (e.g., located at position P1) is not within range of any synchronization sources having a higher synchronization priority level, the UE 115-c may resort to a lower priority synchronization source (e.g., its own internal clock) , and may instead transmit synchronization signals 215-c. However, the UE 115-c may be mobile (e.g., may be a V2X UE) , and may travel (e.g., along path 220) from position P1 to Position P2. In such examples, the UE 115-c may be within range of the UE 115-a, and may be capable of synchronizing with the GNSS via the UE 115-a. However, the UE 115-c may be unable to receive and decode the synchronization signal 215-b transmitted by the UE 115-aaccording to the synchronization source of the satellite 205. For instance, the UE 115-amay transmit synchronization signal 215-a, synchronization signal 215-b, or both, according to single timing associated with the synchronization source of the satellite 205.

The UE 115-a may transmit synchronization signals 215-a and 215-b (e.g., SLSSs having SLSS ID=0) , according to an internal clock (e.g., internal clock=1) . However, internal clocks for the UE 115-b and the UE 115-c, respectively, may not be aligned with the internal clock of the UE 115-a. For instance, the UE 115-b may receive the synchronization signal 215-a (e.g., having SLSS ID-0) , and may thus synchronize with the UE 115-a, despite having an internal clock=0. However, the UE 115-c may also be misaligned in time with the UE 115-a (e.g., having an internal clock=0) .

Additionally, or alternatively, the UE 115-a may transmit synchronization signal (e.g., SLSS ID=252) to the UE 115-d. The UE 115-c may be transmitting, according to its own internal clock, synchronization signal 215-c to the UE 115-d, and may therefore not be monitoring for synchronization signal 215-b from the UE 115-a. For instance, the UE 115-b may be half duplex limited, and may therefore be incapable of receiving the synchronization signal 215-b from the UE 115-a when it is transmitting the synchronization signal 215-c to the UE 115-d. Additionally, or alternatively, the UE 115-a may not be able to perform sidelink communications with the UE 115-a (e.g., receive or transmit data signaling from or to the UE 115-a) due to timing misalignment with the UE 115-a. For instance, upon moving from P1 to P2, the UE 115-c may be located close enough to the UE 115-a to perform sidelink communications. But the UE 115-c may not be able to decode the synchronization signal 215-b because the timing of the UE 115-a and the timing of the UE 115-b may not align.

Thus, because the UE 115-c may not receive or successfully decode the synchronization signal 215-b, the UE 115-a may incorrectly determine that it is the only synchronization reference UE (e.g., syncRefUE) . The UE 115-c may continue to transmit SLSSs (e.g., synchronization signals 215-c) , but may receive no responsive sidelink data signaling. For example, the UE 115-c may not receive any sidelink data signaling from the UE 115-d, which is no longer located close enough to the UE 115-c to receive the synchronization signals 215-c. in some examples, the UE 115-c may not receive any sidelink data signaling form other proxime or neighbor UEs (e.g., the UE 115-a, the UE 115-b, or the like) , because other proximate or neighbor UEs are synchronized to a synchronization source that has a higher synchronization priority level (e.g., the GNSS via the satellite 205) . The UE 115-a may continue to transmit synchronization signals 215-c, despite being located at position P2 which it could receive synchronization signals 215-b from the UE 115-a. In such examples, the UE 115-a may be unable to synchronize to a synchronization source that has a higher synchronization priority level (e.g., the GNSS directly or indirectly via the UE 115-a) . This may result in the UE 115-c being unable to synchronize with and communicate with other sidelink UEs 115, failed sidelink communications, increased system latency, traffic delays or safety issues (e.g., if V2X UEs 115 do not synchronize with and communicate with other V2X devices) , or the like.

In some examples, a UE 115 may transition to a higher priority synchronization priority level if one or more conditions are satisfied. The UE 115-c may transmit synchronization signals (e.g., SLSSs) periodically according to its own internal clock (e.g., when it is synchronized to its own internal clock) . However, if the UE 115-c does not receive any sidelink data for a threshold amount of time, then the UE 115-c may exit a current synchronize (e.g., P7 according to table 1) , and may monitor for synchronization signals 215 to determine if any synchronization source having a higher synchronization priority level is available for scanning and synchronization. For example, the UE 115-c may stop transmitting synchronization signals 215-c according to the internal clock of the UE 115-c, and may start monitoring for other SLSS sources. Based on the monitoring, the UE 115-c may receive synchronization signals from other synchronization sources (e.g., synchronization signal 215-b) , and my synchronize with another synchronization source that has higher synchronization priority level (e.g., may synchronize indirectly with the GNSS via the UE 115-a) .

In some examples, a threshold amount of time after which the UE 115-c is to transition to a different synchronization source may be based at least in art on a periodicity at which synchronization signals are transmitted. For instance, if the UE 115-c transmits SLSSs according to a first periodicity (e.g., a period of 160 ms) , then the threshold amount of time may be equal to or a multiple of the period (e.g., 320 ms) . In some examples, the threshold amount of time may be preconfigured, or may be indicated by another device (e.g., a sidelink UE 115, a base station 105, or the like) , or may be included in one or more standards documents, or any combination thereof.

FIG. 3 illustrates an example of a process flow 300 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. Process flow 300 may include a synchronization source 305 (e.g., a UE 115, a base station 105, a satellite 205, or the like) , a UE 115-e and a UE 115-f (e.g., a V2X UE, a sidelink UE, or the like) , which may be examples of corresponding devices described with reference to FIGs. 1-2.

At 310, the synchronization source 305 may transmit one or more SLSSs. The synchronization source may be base station, a satellite of a GNSS, or another UE that is connected to (e.g., synchronized with) a base station or a GNSS. The synchronization source 305 may transmit SLSSs periodically (e.g., every period 320, which may be, for example, 160 ms) .

At 315, the UE 115-e may transmit SLSSs. The UE 115-e may operate according to a first synchronization priority level. For instance, the UE 115-e may act as its own synchronization source, and may transmit SLSSs periodically to another wireless device (e.g., the UE 115-f) . In some examples, the UE 115-e may not be within a threshold distance of the synchronization source 305. The UE 115-e may be an example of the UE 115-c as described with reference to FIG. 2. The UE 115-e may therefore transmit SLSSs to another UE 115-f. If the UE 115-e and the UE 115-f are located within a threshold distance of each other, then the UE 115-f may synchronize to a timing of the UE 115-e. In response to receiving the SLSS at 315-a, the UE 115-f may transmit a sidelink data message to the UE 115-e at 325. However, if the UE 115-e changes its position, it may be close enough to the synchronization source 305 to receive SLSSs transmitted at 310. However, the UE 115-e may continue to operate according to the first synchronization priority source (e.g., the internal clock of the UE 115-e) . Thus, the UE 115-e may continue to transmit SLSSs (e.g., at 315-b, 315-c, and 315-d) . However, the UE 115-f may not receive the SLSSs (e.g., because it is not located close to the UE 115-e) . Thus, the UE 115-f may not transmit any sidelink data message responsive to SLSSs transmitted at 315-b, 315-c, and 315-d, etc. ) .

Additionally, or alternatively, the UE 115-e may not receive SLSSs transmitted by the synchronization source 305 (e.g., at 310-a, 310-b, and 310-c, etc. ) . This may occur because the UE 115-e is operating according to the first synchronization priority level, while the synchronization source 305 is operating according to a second synchronization priority level. The second synchronization priority level may be higher than the first synchronization priority level. Additionally, or alternatively, the UE 115-e may operate at a timing that is different (e.g., not aligned) from a timing at which the synchronization source 305 is operating. In some examples, the UE 115-e may fail to receive the SLSSs transmitted by the synchronization source 305 at 310 because the UE 115-e is operating in a half-duplex mode, and is not able to receive SLSSs at 310 while transmitting SLSSs at 315.

In some examples, the UE 115-e may monitor for data transmissions responsive to SLSSs (e.g., transmitted at 315-b) . If the UE 115-e does not receive sidelink data transmissions during a threshold amount of time (e.g., time period 330) , then the UE 115-e may switch from the first synchronization priority level to a second synchronization priority level at 335. For instance, the UE 115-e may transmit the SLSS at 315-b, and may monitor for data response. After time period 330, the UE 115-e may transmit another SLSS at 315-c, and may monitor for a sidelink data transmission from another UE 115. If no such signaling is received (e.g., within time period 330) , the UE 115-e may switch from the first synchronization priority level to another (e.g., a second) synchronization priority level. The time period 330 may be a multiple of the period 320. For instance, the period 320 may be 160 ms, while the threshold amount of time (e.g., time period 330) , may be 320 ms (twice the period 320) . In other examples, the threshold amount of time may not be related to the period 320, or may be standardized, or may be indicated by a synchronization source 305, a base station, another wireless device, or the like.

At 335, the UE 115-e may switch synchronization priority levels by pausing transmission of SLSSs, and instead scanning for SLSSs. Based on the scanning, the UE 115-e may receive SLSSs (e.g., at 310-d) from the synchronization source 305 (e.g., having a higher synchronization priority level than the UE 115-e) . In such examples, at 340, the UE 115-e may synchronize with the synchronization source 305, and may communicate with the synchronization source 305 based on the synchronization (e.g., according to a timing established via the synchronization) .

FIG. 4 shows a block diagram 400 of a device 405 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The device 405 may be an example of aspects of a UE 115 as described herein. The device 405 may include a receiver 410, a transmitter 415, and a communications manager 420. The device 405 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 410 may provide a means for receiving information such as packets, user data, control information, or any combination thereof associated with various information channels (e.g., control channels, data channels, information channels related to changing synchronization cases for vehicle-to-everything deployments) . Information may be passed on to other components of the device 405. The receiver 410 may utilize a single antenna or a set of multiple antennas.

The transmitter 415 may provide a means for transmitting signals generated by other components of the device 405. For example, the transmitter 415 may transmit information such as packets, user data, control information, or any combination thereof associated with various information channels (e.g., control channels, data channels, information channels related to changing synchronization cases for vehicle-to-everything deployments) . In some examples, the transmitter 415 may be co-located with a receiver 410 in a transceiver module. The transmitter 415 may utilize a single antenna or a set of multiple antennas.

The communications manager 420, the receiver 410, the transmitter 415, or various combinations thereof or various components thereof may be examples of means for performing various aspects of changing synchronization cases for vehicle-to-everything deployments as described herein. For example, the communications manager 420, the receiver 410, the transmitter 415, or various combinations or components thereof may support a method for performing one or more of the functions described herein.

In some examples, the communications manager 420, the receiver 410, the transmitter 415, or various combinations or components thereof may be implemented in hardware (e.g., in communications management circuitry) . The hardware may include a processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure. In some examples, a processor and memory coupled with the processor may be configured to perform one or more of the functions described herein (e.g., by executing, by the processor, instructions stored in the memory) .

Additionally or alternatively, in some examples, the communications manager 420, the receiver 410, the transmitter 415, or various combinations or components thereof may be implemented in code (e.g., as communications management software or firmware) executed by a processor. If implemented in code executed by a processor, the functions of the communications manager 420, the receiver 410, the transmitter 415, or various combinations or components thereof may be performed by a general-purpose processor, a DSP, a central processing unit (CPU) , an ASIC, an FPGA, or any combination of these or other programmable logic devices (e.g., configured as or otherwise supporting a means for performing the functions described in the present disclosure) .

In some examples, the communications manager 420 may be configured to perform various operations (e.g., receiving, monitoring, transmitting) using or otherwise in cooperation with the receiver 410, the transmitter 415, or both. For example, the communications manager 420 may receive information from the receiver 410, send information to the transmitter 415, or be integrated in combination with the receiver 410, the transmitter 415, or both to receive information, transmit information, or perform various other operations as described herein.

The communications manager 420 may support wireless communications at a first UE in accordance with examples as disclosed herein. For example, the communications manager 420 may be configured as or otherwise support a means for transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The communications manager 420 may be configured as or otherwise support a means for monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The communications manager 420 may be configured as or otherwise support a means for switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The communications manager 420 may be configured as or otherwise support a means for receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

By including or configuring the communications manager 420 in accordance with examples as described herein, the device 405 (e.g., a processor controlling or otherwise coupled to the receiver 410, the transmitter 415, the communications manager 420, or a combination thereof) may support techniques for synchronization for sidelink devices that result in improved reliability of communications, reduced system latency, more efficient utilization of available system resources, and improved user experience.

FIG. 5 shows a block diagram 500 of a device 505 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The device 505 may be an example of aspects of a device 405 or a UE 115 as described herein. The device 505 may include a receiver 510, a transmitter 515, and a communications manager 520. The device 505 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 510 may provide a means for receiving information such as packets, user data, control information, or any combination thereof associated with various information channels (e. g., control channels, data channels, information channels related to changing synchronization cases for vehicle-to-everything deployments) . Information may be passed on to other components of the device 505. The receiver 510 may utilize a single antenna or a set of multiple antennas.

The transmitter 515 may provide a means for transmitting signals generated by other components of the device 505. For example, the transmitter 515 may transmit information such as packets, user data, control information, or any combination thereof associated with various information channels (e.g., control channels, data channels, information channels related to changing synchronization cases for vehicle-to-everything deployments) . In some examples, the transmitter 515 may be co-located with a receiver 510 in a transceiver module. The transmitter 515 may utilize a single antenna or a set of multiple antennas.

The device 505, or various components thereof, may be an example of means for performing various aspects of changing synchronization cases for vehicle-to-everything deployments as described herein. For example, the communications manager 520 may include an SLSS transmission manager 525, a Data manager 530, a synchronization priority level manager 535, an SLSS reception manager 540, or any combination thereof. The communications manager 520 may be an example of aspects of a communications manager 420 as described herein. In some examples, the communications manager 520, or various components thereof, may be configured to perform various operations (e.g., receiving, monitoring, transmitting) using or otherwise in cooperation with the receiver 510, the transmitter 515, or both. For example, the communications manager 520 may receive information from the receiver 510, send information to the transmitter 515, or be integrated in combination with the receiver 510, the transmitter 515, or both to receive information, transmit information, or perform various other operations as described herein.

The communications manager 520 may support wireless communications at a first UE in accordance with examples as disclosed herein. The SLSS transmission manager 525 may be configured as or otherwise support a means for transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The Data manager 530 may be configured as or otherwise support a means for monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The synchronization priority level manager 535 may be configured as or otherwise support a means for switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The SLSS reception manager 540 may be configured as or otherwise support a means for receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

FIG. 6 shows a block diagram 600 of a communications manager 620 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The communications manager 620 may be an example of aspects of a communications manager 420, a communications manager 520, or both, as described herein. The communications manager 620, or various components thereof, may be an example of means for performing various aspects of changing synchronization cases for vehicle-to-everything deployments as described herein. For example, the communications manager 620 may include an SLSS transmission manager 625, a Data manager 630, a synchronization priority level manager 635, an SLSS reception manager 640, a synchronization priority level switching manager 645, an SLSS periodicity manager 650, a synchronization manager 655, or any combination thereof. Each of these components may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The communications manager 620 may support wireless communications at a first UE in accordance with examples as disclosed herein. The SLSS transmission manager 625 may be configured as or otherwise support a means for transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The Data manager 630 may be configured as or otherwise support a means for monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The synchronization priority level manager 635 may be configured as or otherwise support a means for switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The SLSS reception manager 640 may be configured as or otherwise support a means for receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

In some examples, to support switching from the first synchronization priority level to the second synchronization priority level, the synchronization priority level switching manager 645 may be configured as or otherwise support a means for pausing transmission of the first sidelink synchronization signals. In some examples, to support switching from the first synchronization priority level to the second synchronization priority level, the synchronization priority level switching manager 645 may be configured as or otherwise support a means for scanning for the second sidelink synchronization signal, where receiving the second sidelink synchronization signal from the synchronization source is based on scanning for the second sidelink synchronization signal.

In some examples, to support transmitting the one or more first sidelink synchronization signals, the SLSS transmission manager 625 may be configured as or otherwise support a means for transmitting the one or more first sidelink synchronization signals according to an internal clock of the first UE, where the first UE includes a second synchronization source associated with the first synchronization priority level.

In some examples, the second synchronization priority level is higher than the first synchronization priority level.

In some examples, to support synchronization source, the SLSS reception manager 640 may be configured as or otherwise support a means for a satellite associated with a global navigation satellite system, a base station, a second UE, or any combination thereof.

In some examples, to support transmitting the one or more first sidelink synchronization signals, the SLSS periodicity manager 650 may be configured as or otherwise support a means for transmitting the one or more first sidelink synchronization signals according to a first periodicity.

In some examples, the threshold amount of time includes a multiple of a period of the first periodicity.

In some examples, the first periodicity includes 160 milliseconds. In some examples, the threshold amount of time includes 320 milliseconds.

In some examples, the synchronization manager 655 may be configured as or otherwise support a means for synchronizing with the synchronization source based on receiving the second sidelink synchronization signal. In some examples, the synchronization manager 655 may be configured as or otherwise support a means for communicating with one or more UEs via a sidelink channel based on the synchronizing.

FIG. 7 shows a diagram of a system 700 including a device 705 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The device 705 may be an example of or include the components of a device 405, a device 505, or a UE 115 as described herein. The device 705 may communicate wirelessly with one or more base stations 105, UEs 115, or any combination thereof. The device 705 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, such as a communications manager 720, an input/output (I/O) controller 710, a transceiver 715, an antenna 725, a memory 730, code 735, and a processor 740. These components may be in electronic communication or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more buses (e.g., a bus 745) .

The I/O controller 710 may manage input and output signals for the device 705. The I/O controller 710 may also manage peripherals not integrated into the device 705. In some cases, the I/O controller 710 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 710 may utilize an operating system such as

or another known operating system. Additionally or alternatively, the I/O controller 710 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 710 may be implemented as part of a processor, such as the processor 740. In some cases, a user may interact with the device 705 via the I/O controller 710 or via hardware components controlled by the I/O controller 710.

In some cases, the device 705 may include a single antenna 725. However, in some other cases, the device 705 may have more than one antenna 725, which may be capable of concurrently transmitting or receiving multiple wireless transmissions. The transceiver 715 may communicate bi-directionally, via the one or more antennas 725, wired, or wireless links as described herein. For example, the transceiver 715 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 715 may also include a modem to modulate the packets, to provide the modulated packets to one or more antennas 725 for transmission, and to demodulate packets received from the one or more antennas 725. The transceiver 715, or the transceiver 715 and one or more antennas 725, may be an example of a transmitter 415, a transmitter 515, a receiver 410, a receiver 510, or any combination thereof or component thereof, as described herein.

The memory 730 may include random access memory (RAM) and read-only memory (ROM) . The memory 730 may store computer-readable, computer-executable code 735 including instructions that, when executed by the processor 740, cause the device 705 to perform various functions described herein. The code 735 may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. In some cases, the code 735 may not be directly executable by the processor 740 but may cause a computer (e.g., when compiled and executed) to perform functions described herein. In some cases, the memory 730 may contain, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 740 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 740 may be configured to operate a memory array using a memory controller. In some other cases, a memory controller may be integrated into the processor 740. The processor 740 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 730) to cause the device 705 to perform various functions (e.g., functions or tasks supporting changing synchronization cases for vehicle-to-everything deployments) . For example, the device 705 or a component of the device 705 may include a processor 740 and memory 730 coupled to the processor 740, the processor 740 and memory 730 configured to perform various functions described herein.

The communications manager 720 may support wireless communications at a first UE in accordance with examples as disclosed herein. For example, the communications manager 720 may be configured as or otherwise support a means for transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The communications manager 720 may be configured as or otherwise support a means for monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The communications manager 720 may be configured as or otherwise support a means for switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The communications manager 720 may be configured as or otherwise support a means for receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching.

By including or configuring the communications manager 720 in accordance with examples as described herein, the device 705 may support techniques for synchronization for sidelink devices that result in improved reliability of communications, reduced system latency, more efficient utilization of available system resources, and improved user experience.

In some examples, the communications manager 720 may be configured to perform various operations (e.g., receiving, monitoring, transmitting) using or otherwise in cooperation with the transceiver 715, the one or more antennas 725, or any combination thereof. Although the communications manager 720 is illustrated as a separate component, in some examples, one or more functions described with reference to the communications manager 720 may be supported by or performed by the processor 740, the memory 730, the code 735, or any combination thereof. For example, the code 735 may include instructions executable by the processor 740 to cause the device 705 to perform various aspects of changing synchronization cases for vehicle-to-everything deployments as described herein, or the processor 740 and the memory 730 may be otherwise configured to perform or support such operations.

FIG. 8 shows a flowchart illustrating a method 800 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The operations of the method 800 may be implemented by a UE or its components as described herein. For example, the operations of the method 800 may be performed by a UE 115 as described with reference to FIGs. 1 through 7. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may perform aspects of the described functions using special-purpose hardware.

At 805, the method may include transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The operations of 805 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 805 may be performed by an SLSS transmission manager 625 as described with reference to FIG. 6.

At 810, the method may include monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The operations of 810 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 810 may be performed by a Data manager 630 as described with reference to FIG. 6.

At 815, the method may include switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The operations of 815 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 815 may be performed by a synchronization priority level manager 635 as described with reference to FIG. 6.

At 820, the method may include receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching. The operations of 820 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 820 may be performed by an SLSS reception manager 640 as described with reference to FIG. 6.

FIG. 9 shows a flowchart illustrating a method 900 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The operations of the method 900 may be implemented by a UE or its components as described herein. For example, the operations of the method 900 may be performed by a UE 115 as described with reference to FIGs. 1 through 7. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may perform aspects of the described functions using special-purpose hardware.

At 905, the method may include transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The operations of 905 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 905 may be performed by an SLSS transmission manager 625 as described with reference to FIG. 6.

At 910, the method may include monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The operations of 910 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 910 may be performed by a Data manager 630 as described with reference to FIG. 6.

At 915, the method may include switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The operations of 915 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 915 may be performed by a synchronization priority level manager 635 as described with reference to FIG. 6.

At 920, the method may include pausing transmission of the first sidelink synchronization signals. The operations of 920 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 920 may be performed by a synchronization priority level switching manager 645 as described with reference to FIG. 6.

At 925, the method may include scanning for the second sidelink synchronization signal, where receiving the second sidelink synchronization signal from the synchronization source is based on scanning for the second sidelink synchronization signal. The operations of 925 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 925 may be performed by a synchronization priority level switching manager 645 as described with reference to FIG. 6.

At 930, the method may include receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching. The operations of 930 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 930 may be performed by an SLSS reception manager 640 as described with reference to FIG. 6.

FIG. 10 shows a flowchart illustrating a method 1000 that supports changing synchronization cases for vehicle-to-everything deployments in accordance with aspects of the present disclosure. The operations of the method 1000 may be implemented by a UE or its components as described herein. For example, the operations of the method 1000 may be performed by a UE 115 as described with reference to FIGs. 1 through 7. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the described functions. Additionally or alternatively, the UE may perform aspects of the described functions using special-purpose hardware.

At 1005, the method may include transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals. The operations of 1005 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 1005 may be performed by an SLSS transmission manager 625 as described with reference to FIG. 6.

At 1010, the method may include monitoring for sidelink data transmissions based on transmitting the one or more first sidelink synchronization signals. The operations of 1010 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 1010 may be performed by a Data manager 630 as described with reference to FIG. 6.

At 1015, the method may include switching from the first synchronization priority level to a second synchronization priority level based on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time. The operations of 1015 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 1015 may be performed by a synchronization priority level manager 635 as described with reference to FIG. 6.

At 1020, the method may include receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based on the switching. The operations of 1020 may be performed in accordance with examples as disclosed herein. In some examples, aspects of the operations of 1020 may be performed by an SLSS reception manager 640 as described with reference to FIG. 6.

The following provides an overview of aspects of the present disclosure:

Aspect 1: A method for wireless communications at a first UE, comprising: transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals; monitoring for sidelink data transmissions based at least in part on transmitting the one or more first sidelink synchronization signals; switching from the first synchronization priority level to a second synchronization priority level based at least in part on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time; and receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based at least in part on the switching.

Aspect 2: The method of aspect 1, wherein the switching from the first synchronization priority level to the second synchronization priority level comprises: pausing transmission of the one or more first sidelink synchronization signals; and scanning for the second sidelink synchronization signal, wherein receiving the second sidelink synchronization signal from the synchronization source is based at least in part on scanning for the second sidelink synchronization signal.

Aspect 3: The method of any of aspects 1 through 2, wherein transmitting the one or more first sidelink synchronization signals comprises: transmitting the one or more first sidelink synchronization signals according to an internal clock of the first UE, wherein the first UE comprises a second synchronization source associated with the first synchronization priority level.

Aspect 4: The method of any of aspects 1 through 3, wherein the second synchronization priority level is higher than the first synchronization priority level.

Aspect 5: The method of any of aspects 1 through 4, wherein the synchronization source comprises: a satellite associated with a global navigation satellite system, a base station, a second UE, or any combination thereof.

Aspect 6: The method of any of aspects 1 through 5, wherein transmitting the one or more first sidelink synchronization signals comprises: transmitting the one or more first sidelink synchronization signals according to a first periodicity.

Aspect 7: The method of aspect 6, wherein the threshold amount of time comprises a multiple of a period of the first periodicity.

Aspect 8: The method of any of aspects 6 through 7, wherein the first periodicity comprises 160 milliseconds; and the threshold amount of time comprises 320 milliseconds.

Aspect 9: The method of any of aspects 1 through 8, further comprising: synchronizing with the synchronization source based at least in part on receiving the second sidelink synchronization signal; and communicating with one or more UEs via a sidelink channel based at least in part on the synchronizing.

Aspect 10: An apparatus for wireless communications at a first UE, comprising a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of aspects 1 through 9.

Aspect 11: An apparatus for wireless communications at a first UE, comprising at least one means for performing a method of any of aspects 1 through 9.

Aspect 12: A non-transitory computer-readable medium storing code for wireless communications at a first UE, the code comprising instructions executable by a processor to perform a method of any of aspects 1 through 9.

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

Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communications systems such as Ultra Mobile Broadband (UMB) , Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

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

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

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

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

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

The term “determine” or “determining” encompasses a wide variety of actions and, therefore, “determining” can include calculating, computing, processing, deriving, investigating, looking up (such as via looking up in a table, a database, or another data structure) , ascertaining and the like. Also, “determining” can include receiving (such as receiving information) , accessing (such as accessing data in a memory) and the like. Also, “determining” can include resolving, selecting, choosing, establishing and other such similar actions.

In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration, ” and not “preferred” or “advantageous over other examples. ” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

An apparatus for wireless communications at a first user equipment (UE) , comprising:

a processor;

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

transmit, according to a first synchronization priority level, one or more first sidelink synchronization signals;

monitor for sidelink data transmissions based at least in part on transmitting the one or more first sidelink synchronization signals;

switch from the first synchronization priority level to a second synchronization priority level based at least in part on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time; and

receive a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based at least in part on the switching.
The apparatus of claim 1, wherein the instructions to switch from the first synchronization priority level to the second synchronization priority level are executable by the processor to cause the apparatus to:

pause transmission of the one or more first sidelink synchronization signals; and

scan for the second sidelink synchronization signal, wherein receiving the second sidelink synchronization signal from the synchronization source is based at least in part on scanning for the second sidelink synchronization signal.
The apparatus of claim 1, wherein the instructions to transmit the one or more first sidelink synchronization signals are executable by the processor to cause the apparatus to:

transmit the one or more first sidelink synchronization signals according to an internal clock of the first UE, wherein the first UE comprises a second synchronization source associated with the first synchronization priority level.
The apparatus of claim 1, wherein the second synchronization priority level is higher than the first synchronization priority level.
The apparatus of claim 1, wherein the synchronization source comprises a satellite associated with a global navigation satellite system, a base station, a second UE, or any combination thereof.
The apparatus of claim 1, wherein the instructions to transmit the one or more first sidelink synchronization signals are executable by the processor to cause the apparatus to:

transmit the one or more first sidelink synchronization signals according to a first periodicity.
The apparatus of claim 6, wherein the threshold amount of time comprises a multiple of a period of the first periodicity.
The apparatus of claim 6, wherein:

the first periodicity comprises 160 milliseconds; and

the threshold amount of time comprises 320 milliseconds.
The apparatus of claim 1, wherein the instructions are further executable by the processor to cause the apparatus to:

synchronize with the synchronization source based at least in part on receiving the second sidelink synchronization signal; and

communicate with one or more UEs via a sidelink channel based at least in part on the synchronizing.
A method for wireless communications at a first user equipment (UE) , comprising:

transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals;

monitoring for sidelink data transmissions based at least in part on transmitting the one or more first sidelink synchronization signals;

switching from the first synchronization priority level to a second synchronization priority level based at least in part on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time; and

receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based at least in part on the switching.
The method of claim 10, wherein the switching from the first synchronization priority level to the second synchronization priority level comprises:

pausing transmission of the one or more first sidelink synchronization signals; and

scanning for the second sidelink synchronization signal, wherein receiving the second sidelink synchronization signal from the synchronization source is based at least in part on scanning for the second sidelink synchronization signal.
The method of claim 10, wherein transmitting the one or more first sidelink synchronization signals comprises:

transmitting the one or more first sidelink synchronization signals according to an internal clock of the first UE, wherein the first UE comprises a second synchronization source associated with the first synchronization priority level.
The method of claim 10, wherein the second synchronization priority level is higher than the first synchronization priority level.
The method of claim 10, wherein the synchronization source comprises:

a satellite associated with a global navigation satellite system, a base station, a second UE, or any combination thereof.
The method of claim 10, wherein transmitting the one or more first sidelink synchronization signals comprises:

transmitting the one or more first sidelink synchronization signals according to a first periodicity.
The method of claim 15, wherein the threshold amount of time comprises a multiple of a period of the first periodicity.
The method of claim 15, wherein:

the first periodicity comprises 160 milliseconds; and

the threshold amount of time comprises 320 milliseconds.
The method of claim 10, further comprising:

synchronizing with the synchronization source based at least in part on receiving the second sidelink synchronization signal; and

communicating with one or more UEs via a sidelink channel based at least in part on the synchronizing.
An apparatus for wireless communications at a first user equipment (UE) , comprising:

means for transmitting, according to a first synchronization priority level, one or more first sidelink synchronization signals;

means for monitoring for sidelink data transmissions based at least in part on transmitting the one or more first sidelink synchronization signals;

means for switching from the first synchronization priority level to a second synchronization priority level based at least in part on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time; and

means for receiving a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based at least in part on the switching.
The apparatus of claim 19, wherein the means for the switching from the first synchronization priority level to the second synchronization priority level comprise:

means for pausing transmission of the one or more first sidelink synchronization signals; and

means for scanning for the second sidelink synchronization signal, wherein receiving the second sidelink synchronization signal from the synchronization source is based at least in part on scanning for the second sidelink synchronization signal.
The apparatus of claim 19, wherein the means for transmitting the one or more first sidelink synchronization signals comprise:

means for transmitting the one or more first sidelink synchronization signals according to an internal clock of the first UE, wherein the first UE comprises a second synchronization source associated with the first synchronization priority level.
The apparatus of claim 19, wherein the second synchronization priority level is higher than the first synchronization priority level.
The apparatus of claim 19, wherein the means for the synchronization source comprise:

means for a satellite associated with a global navigation satellite system, a base station, a second UE, or any combination thereof.
The apparatus of claim 19, wherein the means for transmitting the one or more first sidelink synchronization signals comprise:

means for transmitting the one or more first sidelink synchronization signals according to a first periodicity.
The apparatus of claim 24, wherein the threshold amount of time comprises a multiple of a period of the first periodicity.
The apparatus of claim 24, wherein:

the first periodicity comprises 160 milliseconds; and

the threshold amount of time comprises 320 milliseconds.
The apparatus of claim 19, further comprising:

means for synchronizing with the synchronization source based at least in part on receiving the second sidelink synchronization signal; and

means for communicating with one or more UEs via a sidelink channel based at least in part on the synchronizing.
A non-transitory computer-readable medium storing code for wireless communications at a first user equipment (UE) , the code comprising instructions executable by a processor to:

transmit, according to a first synchronization priority level, one or more first sidelink synchronization signals;

monitor for sidelink data transmissions based at least in part on transmitting the one or more first sidelink synchronization signals;

switch from the first synchronization priority level to a second synchronization priority level based at least in part on the monitoring and an absence of received sidelink data transmissions for a threshold amount of time; and

receive a second sidelink synchronization signal from a synchronization source associated with the second synchronization priority level based at least in part on the switching.