Group synchronization signaling for efficient communications in sidelink systems

Abstract

A set of user equipments (UEs) for sidelink communication includes a master UE and member UEs. Any of the UEs may measure one or more sidelink synchronization signal sources during a configured measurement gap within sidelink communications with a group of UEs. The member UE may send an alternative synchronization source report to the master UE indicating the detected synchronization source. A master UE is configured to determine to transition from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs. The primary UE is configured to transmit timing assistance information for synchronization with the second synchronization source to a group of UEs. The UE is configured to switch sidelink communications with a group of UEs to a second synchronization source.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. nonprovisional patent application No. 18 / 318,451, filed May 16, 2023, entitled “GROUP SYNCHRONIZATION SIGNALINGFOR EFFICIENT COMMUNICATIONS IN SIDELINK SYSTEMS,” the entire contents of which are incorporated herein by reference. Background Technology Technical Field

[0004] This disclosure relates to wireless communications including group synchronization signaling for sidelink systems.

[0005] introduction

[0006] Wireless communication systems are widely deployed to provide a variety of telecommunications services, such as telephone, video, data, messaging, and broadcasting. Typical wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple access technologies include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, Frequency Division Multiple Access (FDMA) systems, Orthogonal Frequency Division Multiple Access (OFDMA) systems, Single Carrier Frequency Division Multiple Access (SC-FDMA) systems, and Time Division Synchronous Code Division Multiple Access (TD-SCDMA) systems.

[0007] These multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different wireless devices to communicate at the city, national, regional, and even global levels. An example telecommunications standard is 5G New Radio (NR). 5G NR is part of the Continuous Evolution of Mobile Broadband (CEM) program issued by the 3rd Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with the Internet of Things (IoT),) and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). Some aspects of 5G NR can be based on the 4G Long Term Evolution (LTE) standard. Further improvements to 5G NR technology are needed. Furthermore, these improvements can also be applied to other multiple access technologies and telecommunications standards that adopt these technologies. Summary of the Invention

[0008] The following is a simplified outline of one or more aspects to provide a basic understanding of them. This outline is not a comprehensive overview of all anticipated aspects, nor is it intended to identify key or important elements of all aspects, nor to depict the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed descriptions that follow.

[0009] In some aspects, the technology described herein relates to a method for wireless communication at a user equipment (UE), the method comprising: determining a transition from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs; sending timing assistance information to the group of UEs for synchronization with the second synchronization source; and switching the sidelink communication with the group of UEs to the second synchronization source.

[0010] In some aspects, the technology described herein relates to a method for wireless communication at a user equipment (UE), the method comprising: receiving timing assistance information for synchronization with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source; and switching the sidelink communication with the group of UEs to the second synchronization source.

[0011] In some aspects, the technology described herein relates to an apparatus for wireless communication by a user equipment (UE), the apparatus comprising: a transceiver; a memory storing computer-executable instructions; and a processor coupled to the transceiver and the memory and configured to execute the computer-executable instructions to cause the UE to: determine to switch from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs; send timing assistance information to the group of UEs for synchronization with the second synchronization source; and switch sidelink communication with the group of UEs to the second synchronization source.

[0012] In some aspects, the technology described herein relates to an apparatus for wireless communication by a user equipment (UE), the apparatus comprising: a transceiver; a memory storing computer-executable instructions; and a processor coupled to the transceiver and the memory and configured to execute the computer-executable instructions to cause the apparatus to: receive timing auxiliary information for synchronization with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source; and switch sidelink communication with the group of UEs to the second synchronization source.

[0013] To achieve the foregoing and related objectives, one or more aspects include the features fully described below and specifically pointed out in the claims. The following description and drawings illustrate some exemplary features of one or more aspects in detail. However, these features indicate only some of the various ways in which the principles of the various aspects may be employed, and this description is intended to include all such aspects and their equivalents. Attached Figure Description

[0014] Figure 1 This is a diagram illustrating an example of a wireless communication system and an access network.

[0015] Figure 2A This is an example illustration of the first 5G NR frame.

[0016] Figure 2B This is a diagram illustrating an example of a downlink channel within a 5G NR subframe.

[0017] Figure 2C This is an example illustration of a second 5G NR frame.

[0018] Figure 2D This is a diagram illustrating an example of an uplink channel within a 5G NR subframe.

[0019] Figure 3 This is a diagram illustrating an example of communication between a first wireless communication device and a second wireless communication device.

[0020] Figure 4 This is a diagram illustrating an example of synchronization of side-link (SL) communication between a group of UEs.

[0021] Figure 5 This is a message diagram illustrating an example message used to switch synchronization sources for a group of UEs.

[0022] Figure 6 This is a message diagram illustrating an example message used to discover an alternative synchronization source for a group of UEs.

[0023] Figure 7 This is a conceptual data flow diagram illustrating the data flow between different parts / components in an example UE that includes an SL synchronization component.

[0024] Figure 8 This is a flowchart of an example method for operating a primary UE to switch synchronization sources for a group of UEs.

[0025] Figure 9 This is a flowchart of an example method for operating member UEs to switch synchronization sources for a group of UEs. Detailed Implementation

[0026] The detailed description below, illustrated with reference to the accompanying drawings, is intended as a description of various configurations and not as representing the only configuration in which the concepts described herein can be practiced. To provide a thorough understanding of the various concepts, the detailed description includes specific details. However, it will be apparent to those skilled in the art that these concepts can be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0027] The characteristics described generally relate to synchronization for sidelink communication, which can also be referred to as direct link communication. As used herein, a direct link refers to a direct wireless communication path from a first wireless device to a second wireless device. For example, in fifth-generation (5G) new radio (NR) communication technology, a direct link between two user equipment (UEs) can be referred to as a sidelink (SL), rather than through a Uu interface (e.g., communication from a gNB to a UE). Direct links can be utilized in D2D communication technologies, which can include vehicle-to-vehicle (V2V) communication, vehicle-to-infrastructure (V2I) communication (e.g., from a vehicle-based communication device to a road infrastructure node), vehicle-to-network (V2N) communication (e.g., from a vehicle-based communication device to one or more network nodes such as a base station), combinations thereof, and / or communication with other devices, which can be collectively referred to as vehicle-to-everything (V2X) communication. In V2X communication, vehicle-based communication devices can communicate with each other and / or with infrastructure devices via a direct link channel.

[0028] In one aspect, the described features relate to sidelink communication among a group of UEs when alternative synchronization sources may exist. In V2X communication, the synchronization process can address situations where a UE is within, partially within, or outside the coverage area of ​​a mobile network. For example, priorities for synchronization sources can be defined such that a higher-priority synchronization source, such as a base station (e.g., a gNB or eNB), is used within the coverage area, or, if available, a Global Navigation Satellite System (GNSS). A UE can transmit a Sidelink Synchronization Signal Block (SL-SSB) to propagate the established timing. A UE can synchronize based on an SL-SSB received from another UE. In some implementations, the priority of the SL-SSB can be based on received power (e.g., Reference Signal Received Power (RSRP)) or the number of hops from a higher-priority synchronization source. In cases where a UE is outside the coverage area of ​​a higher-priority synchronization source, the UE can generate its own SL-SSB to act as an independent synchronization source.

[0029] In some implementations, SL-SSBs can be transmitted periodically over a time period (e.g., 160 milliseconds (ms)). An SL-SSB can occupy 11 physical resource blocks (PRBs) over an entire time slot not used for data channel transmission. In some implementations, a UE transmitting an SL-SSB on one resource can receive an SL-SSB on another resource.

[0030] In some scenarios, a UE can communicate with a group of UEs via sidelink communication. For example, when a vehicle UE (vUE) and a passenger UE (pUE) are traveling together, the vUE can be associated with one or more pUEs. For instance, the vUE can use sidelink multicast communication to provide information to the passenger UE. In such scenarios, for example, if the vUE is outside the coverage area of ​​a higher-priority synchronization source, the vUE can act as an independent synchronization source by sending an SL-SSB. The SL-SSB can indicate the sidelink identity outside the coverage area.

[0031] On one hand, when a first vUE contacts a second UE (e.g., receives an SL-SSB from the second UE), if the second UE sends an SL-SSB indicating its sidelink identity within coverage, the first vUE may need to synchronize with the second UE. For example, if the second UE is synchronized with a base station or GNSS, its SL-SSB could be a higher-priority synchronization source. Several problems may arise in this scenario. First, communication may be interrupted when the first vUE changes its synchronization source from an independent SL-SSB to the second UE's SL-SSB. The pUEs in the group may no longer have a synchronization source. Second, pUEs may incur delays when discovering new synchronization sources. For example, the delay could be based on the periodicity of the new synchronization source's SL-SSB. Third, pUEs may generate redundant alternative synchronization sources. For example, if any pUE cannot receive an SL-SSB from the second vUE, the pUE may send an SL-SSB as an independent synchronization source. Ultimately, the first vUE may synchronize with the second vUE and send a new SL-SSB to propagate the second vUE's timing. The new SL-SSB can have a higher priority than an independent synchronization source, allowing the pUE to synchronize with the first vUE again. However, these multiple changes to the synchronization source may further prolong communication interruptions.

[0032] In one aspect, this disclosure provides techniques to enhance the distributed synchronization process for SL (Synchronization Reference UE) to avoid scenarios where a cluster's synchronization reference UE suddenly changes its reference synchronization source (e.g., from acting as an independent synchronization source to now following another synchronization reference UE). The UE acting as the synchronization reference UE (e.g., by sending an SL-SSB) can notify other UEs in the group of the second synchronization source before switching to it for sidelink communication. The UE can send timing assistance information for synchronizing with the second synchronization source, allowing all UEs in the group to switch to the second synchronization source simultaneously, thereby preventing communication interruptions between the group of UEs.

[0033] In some implementations, a group of UEs can be configured to assist in identifying a synchronization source for the group of UEs. The primary UE in the group can configure the other UEs to have alternative synchronization source measurement gaps, during which all UEs can measure the alternative synchronization source. The UEs can send an alternative synchronization source report to the primary UE containing information about the received synchronization signal (e.g., SL-SSB). The primary UE can then select a second synchronization source to switch to based on the alternative synchronization source report.

[0034] The disclosed SL-SSB-related signaling can provide switching of synchronization sources within a group of UEs in sidelink communication with reduced or eliminated communication interruptions. Furthermore, the signaling can allow UEs relying on a first synchronization source to quickly switch to a second synchronization source. In some implementations, alternative synchronization source reporting can allow a group of primary UEs to select a synchronization source acceptable to that group.

[0035] Various apparatuses and methods will now be used to present several aspects of a telecommunications system. These apparatuses and methods will be described in detail below and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively, “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether these elements are implemented as hardware or software depends on the specific application and the design constraints imposed on the system as a whole.

[0036] As an example, an element, any part of an element, or any combination of elements may be implemented as a "processing system" including one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, system-on-a-chip (SoCs), baseband processors, field-programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gate logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionalities described throughout this disclosure. One or more processors in the processing system can execute software. Whether referred to as software, firmware, middleware, microcode, hardware description language, or other names, software should be broadly interpreted as meaning instructions, instruction sets, code, code segments, program code, programs, subroutines, software components, applications, software applications, software packages, routines, subroutines, objects, executable files, threads of execution, procedures, functions, etc.

[0037] Therefore, in one or more example implementations, the functionality described herein can be implemented in hardware, software, or any combination thereof. If implemented in software, the functionality can be stored on a computer-readable medium or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media, which may be referred to as non-transitory computer-readable media. Non-transitory computer-readable media may not include transient signals. Storage media can be any available medium accessible to a computer. By way of example and not limitation, such computer-readable media may include random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of computer-readable media of the foregoing types, or any other medium capable of storing computer-executable code having instructions or data structures accessible to a computer.

[0038] Figure 1 This is an illustration of an example of a wireless communication system and access network 100. The wireless communication system (also referred to as a wireless wide area network (WWAN)) includes a base station 102, a user interface unit (UE) 104, an evolved packet core (EPC) 160, and another core network 190 (e.g., a 5G core (5GC)). The base station 102 may include macro cells (high-power cellular base stations) and / or small cells (low-power cellular base stations). Macro cells include base stations. Small cells include femtocells, picocells, and microcells.

[0039] In one aspect, one or more UEs in UE 104 may include an SL synchronization component 140 configured to determine a transition from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs. The SL synchronization component 140 may include a source component 142 configured to receive an indication of the frequency position of the SL-SSB within a bandwidth portion of a shared frequency band. The SL synchronization component 140 may include a timing assist component 144 configured to send timing assist information to the group of UEs for synchronization with the second synchronization source. The SL synchronization component 140 may include an SL handover component 146 configured to switch sidelink communication with the group of UEs to the second synchronization source.

[0040] In one aspect, one or more UEs in UE 104 (e.g., a second UE) may also include an SL synchronization component 140. The SL synchronization component 140 of the second UE 104 may be configured to receive timing assistance information for synchronization with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source. The SL synchronization component 140 of the second UE 104 may be configured to switch sidelink communication with the group of UEs to the second synchronization source.

[0041] In one aspect, one or more base stations in base station 102 may include a sidelink configuration component 120 configured to transmit a synchronization signal block that can be used as a synchronization source when the UE is within the coverage area of ​​base station 102. In some specific implementations, the sidelink configuration component 120 may transmit a synchronization source measurement gap configuration.

[0042] Base station 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) can interact with EPC 160 via a first backhaul link 132 (e.g., S1 interface), which can be a wired or wireless link. Base station 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN)) can interact with core network 190 via a second backhaul link 184, which can be wired or wireless. In addition to other functions, base station 102 may perform one or more of the following functions: user data transmission, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection establishment and release, load balancing, distribution of non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment tracking, RAN information management (RIM), paging, location, and delivery of warning messages. Base stations 102 may communicate directly or indirectly with each other via a third backhaul link 134 (e.g., an X2 interface) (e.g., via EPC 160 or core network 190). The third backhaul link 134 may be wired or wireless.

[0043] Base station 102 can wirelessly communicate with UE 104. Each base station in base station 102 can provide communication coverage for a corresponding geographic coverage area 110. Overlapping geographic coverage areas 110 may exist. For example, small cell 102' may have a coverage area 110' that overlaps with the coverage areas 110 of one or more macro base stations 102. A network that includes both small cells and macro cells can be referred to as a heterogeneous network. The heterogeneous network may also include evolved home node B (eNB) (HeNB), which can provide services to restricted groups referred to as closed subscriber groups (CSG). The communication link 112 between base station 102 and UE 104 may include uplink (UL) (also known as reverse link) transmission from UE 104 to base station 102 and / or downlink (DL) (also known as forward link) transmission from base station 102 to UE 104. Communication link 112 may use multiple-input multiple-output (MIMO) antenna technologies, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link may carry one or more carriers. For each carrier allocated in carrier aggregation for transmission in each direction, totaling up to Yx MHz (x component carriers), base station 102 / UE104 may use a spectrum with a bandwidth of up to Y MHz (e.g., 5MHz, 10MHz, 15MHz, 20MHz, 100MHz, 400MHz, etc.). Carriers may be adjacent to each other or may not be adjacent to each other. Carrier allocation may be asymmetric for DL ​​and UL (e.g., more or fewer carriers may be allocated to DL compared to UL). Component carriers may include primary component carriers and one or more secondary component carriers. The primary component carrier may be referred to as the primary cell (PCell) and the secondary component carrier may be referred to as the secondary cell (SCell).

[0044] Some UEs 104 can communicate with each other using device-to-device (D2D) communication link 158. D2D communication link 158 can use DL / UL WWAN spectrum. D2D communication link 158 can use one or more sidelink channels, such as Physical Sidelink Broadcast Channel (PSBCH), Physical Sidelink Discovery Channel (PSDCH), Physical Sidelink Shared Channel (PSSCH), and Physical Sidelink Control Channel (PSCCH). D2D communication can be conducted through various wireless D2D communication systems, such as FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR. In one aspect, D2D communication link 158 can be configured with direct link carrier aggregation for multiple component carriers.

[0045] The wireless communication system may also include a Wi-Fi access point (AP) 150 that communicates with a Wi-Fi station (STA) 152 via a communication link 154 in the 5 GHz unlicensed spectrum. When communicating in the unlicensed spectrum, the STA 152 / AP 150 may perform a free channel assessment (CCA) to determine the availability of a channel before communication.

[0046] Small cell 102' can operate in licensed and / or unlicensed spectrum. When operating in unlicensed spectrum, small cell 102' can employ NR, and uses the same 5 GHz unlicensed spectrum as the Wi-Fi AP 150. Small cell 102' employing NR in unlicensed spectrum can improve the coverage of the access network and / or increase the capacity of the access network.

[0047] The electromagnetic spectrum is typically subdivided into various categories, bands, channels, etc., based on frequency / wavelength. In 5G NR, two initial operating bands have been designated as frequency ranges FR1 (410MHz to 7.125GHz) and FR2 (24.25GHz to 52.6GHz). The frequencies between FR1 and FR2 are generally referred to as the mid-band frequencies. Although a portion of FR1 is greater than 6GHz, in various documents and articles, FR1 is often (interchangeably) referred to as the "sub-6GHz" band. Similar naming issues sometimes arise regarding FR2, although it is different from the extremely high frequency (EHF) band (30GHz to 300GHz) which the International Telecommunication Union (ITU) defines as the "millimeter wave" (mmW) band, it is often (interchangeably) referred to as the "millimeter wave" band in various documents and articles.

[0048] Considering the above aspects, unless otherwise specifically stated, it should be understood that, as used herein, the term "below 6 GHz" and the like can broadly refer to frequencies less than 6 GHz, within FR1, or including intermediate frequency band frequencies. Furthermore, unless otherwise specifically stated, it should be understood that, as used herein, the term "millimeter wave" and the like can broadly refer to frequencies including intermediate frequency band frequencies, within FR2, or within the EHF band. Communication using the mmW radio frequency band has extremely high path loss and short range. The mmW base station 180 can utilize beamforming 182 with the UE 104 to compensate for path loss and short range.

[0049] Base station 180 may transmit beamformed signals to UE 104 in one or more transmit directions 182'. UE 104 may receive beamformed signals from base station 180 in one or more receive directions 182''. UE 104 may also transmit beamformed signals to base station 180 in one or more transmit directions. Base station 180 may receive beamformed signals from UE 104 in one or more receive directions. Base station 180 / UE 104 may perform beam training to determine the optimal receive and transmit directions for each of base station 180 / UE 104. The transmit and receive directions of base station 180 may be the same or different. The transmit and receive directions of UE 104 may be the same or different.

[0050] EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. MME 162 can communicate with the Home Subscriber Server (HSS) 174. MME 162 is the control node that handles signaling between UE 104 and EPC 160. Generally, MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are delivered through the Serving Gateway 166, which is itself connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation and other functions. The PDN Gateway 172 and BM-SC 170 are connected to the IP Service 176. The IP Service 176 may include the Internet, intranets, IP Multimedia Subsystem (IMS), PS streaming service, and / or other IP services. The BM-SC 170 provides functions for MBMS user service dispatch and delivery. The BM-SC 170 can act as an entry point for content provider MBMS transmission, authorize and initiate MBMS bearer services in a Public Land Mobile Network (PLMN), and schedule MBMS transmissions. The MBMS gateway 168 can allocate MBMS services to base station 102 belonging to a Broadcast-Specific Service Multicast Single Frequency Network (MBSFN) area, and is responsible for session management (start / stop) and collecting eMBMS-related billing information.

[0051] The core network 190 may include Access and Mobility Management Functions (AMF) 192, other AMFs 193, Session Management Functions (SMF) 194, and User Plane Functions (UPF) 195. AMF 192 can communicate with Unified Data Management (UDM) 196. AMF 192 is the control node that handles signaling between UE 104 and the core network 190. Generally, AMF 192 provides QoS flow and session management. All user Internet Protocol (IP) packets are delivered through UPF 195. UPF 195 provides UE IP address allocation and other functions. UPF 195 connects to IP services 197. IP services 197 may include the Internet, intranets, IP Multimedia Subsystem (IMS), PS streaming services, and / or other IP services.

[0052] Base stations may include and / or be referred to as gNB, Node B, eNB, access point, base transceiver, radio base station, radio transceiver, transceiver function, Basic Service Set (BSS), Extended Service Set (ESS), Transmit-Receive Point (TRP), or some other suitable terminology. Base station 102 provides access to EPC 160 or core network 190 for UE 104. Examples of UE 104 include cellular phones, smartphones, Session Initiation Protocol (SIP) phones, laptops, personal digital assistants (PDAs), satellite radios, GPS devices, multimedia devices, video devices, digital audio players (e.g., MP3 players), cameras, game consoles, tablet devices, smart devices, wearable devices, vehicles, electricity meters, air pumps, large or small kitchen appliances, healthcare devices, implants, sensors / actuators, displays, or any other similarly functional devices. Some UEs in UE 104 may be referred to as IoT devices (e.g., parking timers, air pumps, toasters, vehicles, heart monitors, etc.). UE 104 may also be referred to as a station, mobile station, subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, mobile phone, user agent, mobile client, client, or some other suitable term.

[0053] While the following description may focus on 5G NR, the concepts described herein may be applicable to other similar areas such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

[0054] Figure 2A Figure 200 illustrates an example of the first subframe within a 5G NR frame structure. Figure 2B Figure 230 illustrates an example of a DL channel within a 5G NR subframe. Figure 2CFigure 250 is an example of a second subframe within a 5G NR frame structure. Figure 2D Figure 280 illustrates an example of a UL channel within a 5G NR subframe. This 5G / NR frame structure can be either Frequency Division Duplex (FDD) or Time Division Duplex (TDD). In FDD, for a specific set of subcarriers (carrier system bandwidth), subframes within that set are dedicated to either DL or UL. In TDD, for a specific set of subcarriers (carrier system bandwidth), subframes within that set are dedicated to both DL and UL. Figure 2A , Figure 2C In the provided example, the 5G NR frame structure is assumed to be TDD, where subframe 4 is configured with slot format 28 (mostly DL), where D is DL, U is UL, and X can be flexibly used between DL / UL, and subframe 3 is configured with slot format 34 (mostly UL). Although subframes 3 and 4 are shown as having slot formats 34 and 28 respectively, any particular subframe can be configured with any of the various available slot formats 0-61. Slot formats 0 and 1 are both DL and UL, respectively. Other slot formats 2-61 include a mixture of DL, UL, and flexible symbols. The UE is configured using the slot format via the received Slot Format Indicator (SFI) (dynamically configured via DL Control Information (DCI) or semi-statically / statically configured via Radio Resource Control (RRC) signaling). Note that the following description also applies to the 5G NR frame structure as TDD.

[0055] Other wireless communication technologies may have different frame structures and / or different channels. A frame (10 ms) can be divided into 10 equal-sized subframes (1 ms). Each subframe may include one or more time slots. Subframes may also include micro-time slots, which may include 7, 4, or 2 symbols. Each time slot may include 7 or 14 symbols, depending on the time slot configuration. For time slot configuration 0, each time slot may include 14 symbols, and for time slot configuration 1, each time slot may include 7 symbols. Symbols on the DL can be Cyclic Prefix (CP) OFDM (CP-OFDM) symbols. Symbols on the UL can be CP-OFDM symbols (for high-throughput scenarios) or Discrete Fourier Transform (DFT) Extended OFDM (DFT-s-OFDM) symbols (also known as Single Carrier Frequency Division Multiple Access (SC-FDMA) symbols) (for power-constrained scenarios; limited to single-stream transmission). The number of time slots within a subframe is based on the time slot configuration and parameter set (numerology). For slot configuration 0, different parameter sets µ 0 through 5 allow each subframe to have 1, 2, 4, 8, 16, and 32 slots, respectively. For slot configuration 1, different parameter sets 0 through 2 allow each subframe to have 2, 4, and 8 slots, respectively. Accordingly, for slot configuration 0 and parameter set µ, there are 14 symbols per slot and 2 per subframe. µ Each time slot. Subcarrier spacing and symbol length / duration are functions of the parameter set. Subcarrier spacing can be equal to... ,in The parameter sets are 0 to 5. Therefore, the subcarrier spacing is 15 kHz for parameter set µ=0 and 480 kHz for parameter set µ=5. The symbol length / duration is negatively correlated with the subcarrier spacing. Figures 2A to 2D Examples are provided for slot configuration 0 with 14 symbols per slot and parameter set µ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs.

[0056] A resource grid can be used to represent the frame structure. Each time slot consists of a resource block (RB) extending for 12 consecutive subcarriers (also known as a physical RB (PRB)). The resource grid is divided into multiple resource elements (REs). The number of bits carried by each RE depends on the modulation scheme.

[0057] like Figure 2A As illustrated, some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include a demodulated RS (DM-RS) for channel estimation at the UE (indicated as R for a particular configuration). x(where 100x is the port number, but other DM-RS configurations are possible) and Channel State Information Reference Signal (CSI-RS). RS may also include Beam Measurement RS (BRS), Beam Refinement RS (BRRS), and Phase Tracking RS (PT-RS).

[0058] Figure 2B Examples of various DL channels within a subframe of a frame are illustrated. The Physical Downlink Control Channel (PDCCH) carries the DCI within one or more Control Channel Elements (CCEs), each CCE comprising nine RE Groups (REGs), each REG comprising four consecutive REs in an OFDM symbol. The Primary Synchronization Signal (PSS) is located within symbol 2 of a specific subframe of the frame. The PSS is used by the UE 104 to determine subframe / symbol timing and physical layer identification. The Secondary Synchronization Signal (SSS) is located within symbol 4 of a specific subframe of the frame. The SSS is used by the UE to determine the Physical Layer Cell Identifier Group Number and radio frame timing. Based on the Physical Layer Identifier and Physical Layer Cell Identifier Group Number, the UE can determine the Physical Cell Identifier (PCI). Based on the PCI, the UE can determine the location of the aforementioned DM-RS. The Physical Broadcast Channel (PBCH) carrying the Primary Information Block (MIB) can be logically grouped with the PSS and SSS to form a Synchronization Signal (SS) / PBCH block. The MIB provides the System Frame Number (SFN) and the number of Restricted Blocks (RBs) in the system bandwidth. The Physical Downlink Shared Channel (PDSCH) carries user data, broadcast system information (such as System Information Blocks (SIBs)) not transmitted via the PBCH, and paging messages.

[0059] like Figure 2C As illustrated, some REs in the REs carry DM-RS (indicated as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE can transmit DM-RS for the Physical Uplink Control Channel (PUCCH) and DM-RS for the Physical Uplink Shared Channel (PUSCH). The PUSCH DM-RS can be transmitted in the first or first two symbols of the PUSCH. Depending on whether a short or long PUCCH is transmitted and depending on the specific PUCCH format used, the PUCCH DM-RS can be transmitted in different configurations. The UE can transmit a Sounding Reference Signal (SRS). The SRS can be transmitted in the last symbol of a subframe. The SRS can have a comb structure, and the UE can transmit the SRS on one of the comb teeth. The SRS can be used by the base station for channel quality estimation to enable frequency-dependent scheduling of the UL.

[0060] Figure 2DExamples of various UL channels within a subframe of a frame are illustrated. The PUCCH can be located as indicated in one configuration. The PUCCH carries uplink control information (UCI), such as scheduling requests, channel quality indicators (CQI), pre-decoding matrix indicators (PMI), rank indicators (RI), and HARQ ACK / NACK feedback. The PUSCH carries data and may additionally be used to carry buffer status reports (BSR), power clearance reports (PHR), and / or UCI.

[0061] Figure 3 This is a block diagram 300 showing a first wireless communication device 310 communicating with a second wireless communication device 350, for example, via V2V / V2X / D2D communication. Device 310 may include a transmitting device communicating with a receiving device (e.g., device 350) via V2V / V2X / D2D communication. Communication may be, for example, based on a sidelink. Transmitting device 310 may include a UE, RSU, etc. Receiving device may include a UE, RSU, etc. Packets may be provided to a controller / processor 375 implementing Layer 3 and Layer 2 functionality. Layer 3 includes the RRC layer, and Layer 2 includes the Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, and Media Access Control (MAC) layer.

[0062] Transmit (TX) processor 316 and receive (RX) processor 370 implement Layer 1 functionality associated with various signal processing functions. Layer 1 (which includes the physical (PHY) layer) may include error detection on the transport channel, forward error correction (FEC) decoding / decoding of the transport channel, interleaving, rate matching, mapping to the physical channel, modulation / demodulation of the physical channel, and MIMO antenna processing. TX processor 316 processes the mapping to the signal constellation based on various modulation schemes (e.g., binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), M-order phase shift keying (M-PSK), M-order quadrature amplitude modulation (M-QAM)). The decoded and modulated symbols can then be divided into parallel streams. Each stream can then be mapped to OFDM subcarriers, multiplexed with a reference signal (e.g., a pilot) in the time and / or frequency domains, and then combined using inverse fast Fourier transform (IFFT) to produce a physical channel carrying a stream of time-domain OFDM symbols. The OFDM stream is spatially pre-decoded to generate multiple spatial streams. Channel estimates from channel estimator 374 can be used to determine the decoding and modulation scheme, as well as for spatial processing. The channel estimates can be derived from a reference signal transmitted by device 350 and / or channel condition feedback. Each spatial stream can then be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX can modulate an RF carrier with the corresponding spatial stream for transmission.

[0063] At device 350, each receiver 354RX receives a signal via its corresponding antenna 352. Each receiver 354RX recovers the information modulated onto the RF carrier and provides that information to the receive (RX) processor 356. The TX processor 368 and RX processor 356 implement Layer 1 functionality associated with various signal processing functions. The RX processor 356 can perform spatial processing on the information to recover any spatial stream destined for device 350. If multiple spatial streams are destined for device 350, the RX processor 356 can combine them into a single OFDM symbol stream. The RX processor 356 then uses a Fast Fourier Transform (FFT) to transform the OFDM symbol stream from the time domain to the frequency domain. The frequency domain signal consists of a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, along with the reference signal, are recovered and demodulated by determining the signal constellation points most likely to be transmitted by device 310. These soft decisions can be based on a channel estimate calculated by the channel estimator 358. The soft decision is then decoded and deinterleaved to recover the data and control signals originally transmitted by device 310 on the physical channel. The data and control signals are then provided to controller / processor 359, which implements layer 3 and layer 2 functionality.

[0064] The controller / processor 359 may be coupled to a memory 360 that stores program code and data. The memory 360 may be referred to as a computer-readable medium. The controller / processor 359 provides demultiplexing, packet reassembly, decryption, header decompression, and control signal processing between the transport channel and the logical channel. The controller / processor 359 is also responsible for error detection using ACK and / or NACK protocols to support HARQ operation.

[0065] Similar to the functions described in conjunction with the transmissions performed by device 310, controller / processor 359 can provide RRC layer functionality associated with system information (e.g., MIB, SIB) acquisition, RRC connectivity, and measurement reporting; PDCP layer functionality associated with header compression / decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functionality associated with the transmission of upper-layer PDUs, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority handling, and logical channel priority ordering.

[0066] The channel estimate derived by the channel estimator 358 from the reference signal or feedback transmitted by the device 310 can be used by the TX processor 368 to select an appropriate decoding and modulation scheme, as well as to facilitate spatial processing. The spatial stream generated by the TX processor 368 can be provided to different antennas 352 via individual transmitters 354TX. Each transmitter 354TX can modulate an RF carrier with the corresponding spatial stream for transmission.

[0067] Transmission is processed at device 310 in a manner similar to that described for the receiver function at device 350. Each receiver 318RX receives the signal via its corresponding antenna 320. Each receiver 318RX recovers the information modulated onto the RF carrier and provides that information to the RX processor 370.

[0068] The controller / processor 375 may be coupled to a memory 376 that stores program code and data. The memory 376 may be referred to as a computer-readable medium. The controller / processor 375 provides demultiplexing, packet reassembly, decryption, header decompression, and control signal processing between the transport channel and the logical channel. The controller / processor 375 is also responsible for error detection using ACK and / or NACK protocols to support HARQ operation.

[0069] At least one of the TX processor 368, RX processor 356, and controller / processor 359 can be configured to combine Figure 1 The SL synchronization component 140 is used to perform various aspects. Similarly, at least one of the TX processor 316, RX processor 370, and controller / processor 375 can be configured to combine Figure 1 The SL synchronization component 140 is used to perform various aspects.

[0070] Figure 4Figure 400 illustrates an example of synchronization for SL communication between a group of UEs 410. The group of UEs 410 may include, for example, a vehicle UE (vUE) 420 (e.g., vUE1) and one or more passenger UEs (pUEs) 430 (e.g., pUE1 430a, pUE2 430b, pUE3 430c, and pUE4 430d). In some implementations, vUE 420 may be the primary UE among the group of UEs 410. For example, where vUE 420 is integrated into the vehicle and pUE 430 is located inside the vehicle, vUE 420 may be better able to receive external signals and serve as a synchronization source for pUE 430. However, it should be understood that a group of UEs 410 may not necessarily include different types of UEs, and any member UE may be selected as the primary UE of the group of UEs 410. In some implementations, the primary UE may serve as an independent synchronization source for the group of UEs 410. For example, when vUE 420 is disconnected from any base station or GNSS service, vUE 420 can generate a standalone SL-SSB for pUE 430 for sidelink communication.

[0071] A group of UEs 410 can participate in a communication session. For example, vUE 420 can send unicast or multicast messages to pUE 430 via sidelink physical channels (e.g., PSCCH and PSSCH). In some implementations, higher-layer applications can facilitate message sending, voice, video, or data communication among a group of UEs 410.

[0072] On one hand, the primary UE (e.g., vUE 420) can communicate with a second UE 450 (e.g., vUE2). For example, the second UE 450 can send the SL-SSB 452 received at vUE 420. In some specific implementations, one or more pUEs in pUE 430 can receive the SL-SSB 452. According to some synchronization rules (e.g., 3GPP Release 16), the SL-SSB 452 can have a higher priority than an independent SL-SSB generated by vUE 420. For example, the second UE 450 can generate the SL-SSB 452 based on synchronization signals from base station 460 or from GNSS. For example, UE 450 can be associated with a different mobile network, can monitor different frequency bands, can be located in different coverage areas, or can receive better signals than vUE 420. Due to the higher priority of the SL-SSB 452 as a synchronization source, vUE 420 can decide to switch to the SL-SSB 452 as the new synchronization source.

[0073] If vUE 420 immediately switches to SL-SSB 452 as its synchronization source, pUE 430 may lose its synchronization source. That is, vUE 420 may no longer send independent SL-SSBs. pUE 430b may lose synchronization with a group of UEs 410, and the communication session may be interrupted. In some implementations, each pUE in pUE 430 can search for a new synchronization source. If pUE 430a, for example, does not receive SL-SSB 452, pUE 430a can generate a new independent SL-SSB to act as a synchronization source (e.g., for communication with pUE 430b). Thus, one or more subgroups of UEs that do not include the entire group of UEs 410 can be formed. Ultimately, vUE 420 can generate an SL-SSB based on SL-SSB 452, which can be received by pUE 430 and has a higher priority. However, generating a new independent SL-SSB by pUE 430 may be considered redundant and / or wasteful. This disclosure provides techniques for timing the handover synchronization of a set of UEs 410.

[0074] Figure 5 This is a message diagram 500 illustrating an example message for switching synchronization sources for a group of UEs 410. The group of UEs 410 may include a first synchronization source 520, which may be, for example, vUE 420. The group of UEs 410 may include one or more member UEs 530, such as pUE 430 (e.g., pUE1 430a and pUE2 430b). The group of UEs 410 may participate in a communication session 512.

[0075] The second synchronization source 550 may not be part of a group of UEs 410. For example, the second synchronization source 550 may be a second UE 450. The second synchronization source 550 may send an SL-SSB 552. At block 560, the first synchronization source 520 may receive the SL-SSB 552 and measure synchronization parameters. For example, the first synchronization source may determine the sidelink identifier of the second synchronization source 550 and may determine whether the second synchronization source 550 is within or outside coverage. In some implementations, the first synchronization source 520 may determine that the second synchronization source 550 has a higher priority than the first synchronization source based on the sidelink identifier and / or the status of being within or outside coverage. Due to the higher priority, the first synchronization source may determine to switch from the first synchronization source (e.g., an independent SL-SSB of the first synchronization source 520) to the second synchronization source for sidelink communication with a group of UEs 410.

[0076] The first synchronization source 520 may send auxiliary information 570 to a group of UEs 410 for synchronization with the second synchronization source 550. For example, the auxiliary information 570 may include an offset 572 between a first timing of the first synchronization source and a second timing of the second synchronization source; the number of time slots 574 or subframes that differ between the second timing and the first timing; or the number of fractional time slots 576 representing the timing difference between the first timing and the second timing. For example, the auxiliary information 570 may be sent as a Radio Resource Control (RRC), V2X, or application layer message communicated via unicast or multicast on a sidelink channel.

[0077] In some implementations, the first synchronization source 520 may optionally send a synchronization source handover message 580 to a group of UEs 410. The synchronization source handover message 580 may indicate the selection of a second synchronization source (e.g., a new synchronization source 582) and the timing of the handover (e.g., handover time 584). For example, the new synchronization source 582 may be indicated as a sidelink identifier. The handover time 584 may be, for example, a time slot or subframe boundary. The synchronization source handover message 580 may be a lower-level message, such as a physical layer signal (e.g., sidelink control information) or a Media Access Control (MAC) control element (CE). In some implementations, the synchronization source handover message 580 may be an RRC message indicating a configuration change of the SL-SSB.

[0078] At block 590, a group of UEs 410 and a second synchronization source 550 can derive timing based on the second synchronization source 550. That is, a group of UEs 410 can switch the timing used for sidelink communication based on the timing of SL-SSB 552 and / or the timing indicated by auxiliary information 570. In one respect, because each member of the group of UEs 410 changes the timing simultaneously (e.g., at time slot boundaries), the communication session 512 can continue without significant interruption.

[0079] Figure 6 This is a message diagram 600 illustrating an example message used to discover an alternative synchronization source for a group of UEs 410. The group of UEs 410 may include a primary UE 620 and member UEs 530, such as pUE 430 (e.g., pUE1 430a and pUE2 430b). The group of UEs 410 may participate in a communication session 512.

[0080] On one hand, the primary UE 620 (e.g., vUE 420) can send a synchronization source measurement gap configuration 640. The synchronization source measurement gap configuration 640 can be sent to each of the other UEs (e.g., pUE 430) as, for example, a unicast or multicast RRC message or an application layer message. The synchronization source measurement gap configuration 640 defines the measurement gap in communication session 512 for measuring one or more sidelink synchronization sources. For example, the sidelink synchronization sources can be on different resources. In some implementations, the synchronization source measurement gap configuration 640 defines the measurement gap by a measurement gap period 642, a gap offset 644 within a time slot or subframe, and a gap length 646.

[0081] At box 650, each of the group of UEs 410 can measure an alternative synchronization source. For example, each pUE 430 can attempt to receive an SL-SSB. Each pUE 430 can measure RSRP 664 corresponding to the SL-SSB of the alternative synchronization source.

[0082] Each pUE 430 may then send an alternative synchronization source report 660 to the primary UE 620 and / or the entire group of UEs 410. The alternative synchronization source report 660 may include, for example, a list of synchronization sources 662. For each synchronization source 662, the alternative synchronization source report 660 may include auxiliary information 570 and RSRP 664.

[0083] At block 670, the primary UE 620 can select a synchronization source. In some implementations, the primary UE 620 can select a second synchronization source 550 in response to all UEs in a group of UEs 410 indicating that a second synchronization source 550 has an RSRP 664 threshold met. In some implementations, if one or more UEs do not report that the second synchronization source 550 meets the threshold, the primary UE 620 may not select an alternative synchronization source. That is, the primary UE 620 and / or the first synchronization source 520 may continue to act as the synchronization source. In some implementations, the primary UE 620 may select a synchronization source based on priority, for example, indicating an SL-SSB within the coverage area.

[0084] The primary UE 620 can send a synchronization source switching message 580 to indicate the new synchronization source 582 and the switching time 584.

[0085] Figure 7 This is a conceptual data flow diagram 700 illustrating the data flow between different parts / components in example UE 704, which could be an example of UE 104 including SL synchronization component 140. SL synchronization component 140 includes the components described above for... Figure 1The source component 142, timing auxiliary component 144, and SL switching component 146 are discussed. In some specific implementations, the SL synchronization component 140 may include a configuration component 720, an SL-SSB receiving component 730, and / or a reporting component 740.

[0086] UE 704 may also include a receiver component 710 and a transmitter component 712. The receiver component 710 may include, for example, an RF receiver for receiving the signals described herein. The transmitter component 712 may include, for example, an RF transmitter for transmitting the signals described herein. In some embodiments, the receiver component 710 and the transmitter component 712 may be co-located at a transceiver (such as...). Figure 3 In Tx / Rx 354).

[0087] Receiver component 710 can receive downlink or sidelink signals, such as SL-SSB 552, auxiliary information 570, synchronization source switching message 580, synchronization source measurement gap configuration 640, and alternative synchronization source report 660. Receiver component 710 can deliver SL-SSB to SL-SSB receiving component 730. Receiver component 710 can deliver auxiliary information 570 and / or synchronization source switching message 580 to SL switching component 146. Receiver component 710 can deliver synchronization source measurement gap configuration 640 to configuration component 720. Receiver component 710 can deliver alternative synchronization source report 660 to reporting component 740.

[0088] Configuration component 720 can be configured to send or receive synchronization source measurement gap configuration 640. For example, when UE 704 is configured as the primary UE 620, configuration component 720 can generate the measurement gap configuration. Configuration component 720 can send synchronization source measurement gap configuration 640 via transmitter component 712. When UE 704 is configured as a member of a group of UEs 410, configuration component 720 can receive synchronization source measurement gap configuration 640 via receiver component 710.

[0089] SL-SSB receiving component 730 is configured to receive SL-SSB 552 from a second synchronization source 550. For example, SL-SSB receiving component 730 can monitor resources configured to carry SL-SSB 552. In some implementations, SL-SSB receiving component 730 can measure synchronization parameters of SL-SSB 552. For example, SL-SSB receiving component 730 can decode SL-SSB 552 to determine a sidelink identifier and / or in-coverage or out-of-coverage status. SL-SSB receiving component 730 can also measure the timing difference between the current synchronization source and the second synchronization source 550. When UE 704 is configured as the primary UE 620, SL-SSB receiving component 730 can provide the measured synchronization parameters to source component 142. When UE 704 is configured as a member of a group of UEs 410, SL-SSB receiving component 730 can provide the measured synchronization parameters to reporting component 740.

[0090] Reporting component 740 is configured to receive or transmit alternative synchronization source report 660. For example, when UE 704 is configured as primary UE 620, reporting component 740 can decode the received alternative synchronization source report 660. Reporting component 740 can provide synchronization source parameters to source component 142, such as auxiliary information 570 and RSRP 664 for each synchronization source included in alternative synchronization source report 660. When UE 704 is configured as a member of a group of UEs 410, reporting component 740 can generate alternative synchronization source report 660 based on measurements from SL-SSB receiving component 730. Reporting component 740 can transmit SL-SSB receiving component 730 via transmitter component 712.

[0091] Source component 142 is configured to determine whether to switch from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs. Source component 142 may receive synchronization parameters from SL-SSB receiving component 730 and / or reporting component 740. Source component 142 may select a synchronization source. In some implementations, source component 142 selects a synchronization source based on priority. In some implementations, source component 142 selects a synchronization source in response to a reported RSRP satisfaction threshold for the synchronization source at each of the group of UEs 410. In some implementations, source component 142 selects the current synchronization source and does not change the synchronization source. Source component 142 may output the selected synchronization source and corresponding synchronization parameters to timing auxiliary component 144.

[0092] Timing assistance component 144 is configured to send timing assistance information for synchronization with a second synchronization source to a group of UEs. For example, timing assistance component 144 may send assistance information 570 via transmitter component 712. For example, timing assistance component 144 may include synchronization parameters for the selected synchronization source in timing assistance information 570. In some implementations, timing assistance component 144 may send a synchronization source handover message 580 via transmitter component 712. For example, timing assistance component 144 may include a sidelink identifier for the new synchronization source 582 and a handover time 584 in the synchronization source handover message 580.

[0093] The SL handover component 146 is configured to switch sidelink communication with a group of UEs to a second synchronization source. For example, the SL handover component 146 may provide timing information to the receiver component 710 and the transmitter component 712, such as defining the time slots and symbols of RF resources. In a specific implementation where UE 704 sends or receives the synchronization source handover message 580, the SL handover component 146 may switch the synchronization source at handover time 584.

[0094] Figure 8 This is a flowchart of an example method 800 for operating UE 104 (e.g., the first UE 104) to change the synchronization source used for sidelink communication between a group of UEs. Method 800 can be performed by a UE (such as UE 104, which may include memory 360 and may be the entire UE 104 or a component of UE 104 such as SL synchronization component 140, TX processor 368, RX processor 356, or controller / processor 359). Method 800 can be performed by an SL synchronization component 140 communicating with the sidelink configuration component 120 of base station 102 and / or the SL synchronization component 140 of the second UE 104. For example, UE 104 can perform method 800 while acting as the primary UE 620.

[0095] At block 810, method 800 can optionally include measuring one or more sidelink synchronization sources during a configured measurement gap within sidelink communication with a group of UEs. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 can implement SL synchronization component 140 and / or SL-SSB receiver component 730 to measure one or more sidelink synchronization sources (e.g., a second synchronization source 550) during a configured measurement gap 652 within sidelink communication with a group of UEs 410 (e.g., communication session 512). Therefore, UE 104, RX processor 356, and / or controller / processor 359 implementing SL synchronization component 140, receiver component 710, and / or SL-SSB receiver component 730 can provide components for measuring one or more sidelink synchronization sources during a configured measurement gap within sidelink communication with a group of UEs.

[0096] At block 820, method 800 includes determining a transition from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 may execute SL synchronization component 140 and / or source component 142 to determine a transition from a first synchronization source 520 to a second synchronization source 550 for sidelink communication with a group of UEs 410. In some embodiments, at sub-block 822, block 820 may optionally include receiving a synchronization signal (e.g., SL-SSB 552) from the second synchronization source 550. At sub-block 824, block 820 may optionally include determining that the second synchronization source 550 has a higher priority than the first synchronization source 520. In some embodiments, at sub-block 826, block 820 may optionally include receiving an alternative synchronization source report 660 indicating a detected synchronization source from one or more pUEs of pUE 430 in the group of UEs 410. At sub-block 828, block 820 may optionally include selecting a second synchronization source 550 from the detected synchronization sources. Therefore, the UE 104, RX processor 356, and / or controller / processor 359 performing SL synchronization component 140 and / or source component 142 may provide components for determining a transition from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs.

[0097] At block 830, method 800 includes sending timing assistance information to a group of UEs for synchronization with a second synchronization source. In one aspect, for example, UE 104, TX processor 368, and / or controller / processor 359 may execute SL synchronization component 140 and / or SL switching component 146 to send timing assistance information 570 to a group of UEs 410 for synchronization with a second synchronization source 550. Therefore, UE 104, TX processor 368, and / or controller / processor 359 executing SL synchronization component 140 and / or SL switching component 146 may provide components for sending timing assistance information to a group of UEs for synchronization with a second synchronization source.

[0098] At block 840, method 800 may optionally include sending a message to a group of UEs indicating the selection and switching time of a second synchronization source. In one aspect, for example, UE 104, TX processor 368, and / or controller / processor 359 may execute SL synchronization component 140 and / or SL switching component 146 to send a message 580 to a group of UEs 410 indicating a switching time 584 for the selection and switching of a second synchronization source (e.g., a new synchronization source 582). Therefore, UE 104, TX processor 368, and / or controller / processor 359 executing SL synchronization component 140 and / or SL switching component 146 may provide components for sending a message to a group of UEs indicating the selection and switching time of a second synchronization source.

[0099] At block 850, method 800 includes switching sidelink communication with a group of UEs to a second synchronization source. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 may execute SL synchronization component 140 and / or SL switching component 146 to switch sidelink communication with a group of UEs 410 to a second synchronization source 550. Therefore, UE 104, RX processor 356, and / or controller / processor 359 executing SL synchronization component 140 and / or SL switching component 146 may provide components for switching sidelink communication with a group of UEs to a second synchronization source.

[0100] Figure 9This is a flowchart of an example method 900 for operating UE 104 (e.g., the first UE 104) to change the synchronization source used for sidelink communication among a group of UEs. Method 900 can be performed by a UE (such as UE 104, which may include memory 360 and may be the entire UE 104 or a component of UE 104 such as SL synchronization component 140, TX processor 368, RX processor 356, or controller / processor 359). Method 900 can be performed by an SL synchronization component 140 communicating with the sidelink configuration component 120 of base station 102 and / or the SL synchronization component 140 of the second UE 104. For example, UE 104 can perform method 900 while acting as a member UE (e.g., pUE 430) of a group of UEs 410.

[0101] At block 910, method 900 may optionally include receiving an SL-SSB from a second synchronization source. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 may execute SL synchronization component 140 and / or SL-SSB receiving component 730 to receive an SL-SSB 552 from a second synchronization source 550. Therefore, UE 104, RX processor 356, and / or controller / processor 359 executing SL synchronization component 140, receiver component 710, and / or SL-SSB receiving component 730 may provide components for receiving an SL-SSB from a second synchronization source.

[0102] At block 920, method 900 can optionally include measuring one or more sidelink synchronization sources during a configured measurement gap within sidelink communication with a group of UEs. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 can implement SL synchronization component 140 and / or SL-SSB receiver component 730 to measure one or more sidelink synchronization sources (e.g., a second synchronization source 550) during a configured measurement gap 652 within sidelink communication with a group of UEs 410 (e.g., communication session 512). Therefore, UE 104, RX processor 356, and / or controller / processor 359 implementing SL synchronization component 140, receiver component 710, and / or SL-SSB receiver component 730 can provide components for measuring one or more sidelink synchronization sources during a configured measurement gap within sidelink communication with a group of UEs.

[0103] At block 930, method 900 may optionally include sending an alternative synchronization source report indicating a detected synchronization source to the primary UE based on the received SL-SSB. In one aspect, for example, UE 104, TX processor 368, and / or controller / processor 359 may execute SL synchronization component 140 and / or reporting component 740 to send an alternative synchronization source report 660 indicating a detected synchronization source to the primary UE 620 based on the received SL-SSB 552. Therefore, UE 104, TX processor 368, and / or controller / processor 359 executing SL synchronization component 140 and / or SL switching component 146 may provide components for sending an alternative synchronization source report indicating a detected synchronization source to the primary UE based on the received SL-SSB.

[0104] At block 940, method 900 includes receiving timing assistance information for synchronization with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 may execute SL synchronization component 140 and / or timing assistance component 144 to receive timing assistance information 570 for synchronization with a second synchronization source 550 from a primary UE 620 in sidelink communication with a group of UEs 410 using a first synchronization source 520. Therefore, UE 104, RX processor 356, and / or controller / processor 359 executing SL synchronization component 140, receiver component 710, and / or timing assistance component 144 may provide components for receiving timing assistance information for synchronization with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source.

[0105] At block 950, method 900 may optionally include receiving a message sent to a group of UEs indicating the time of selection and handover of a second synchronization source. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 may execute SL synchronization component 140 and / or timing auxiliary component 144 to receive the message sent to a group of UEs indicating the time of selection and handover of a second synchronization source. Therefore, UE 104, RX processor 356, and / or controller / processor 359 executing SL synchronization component 140, receiver component 710, and / or timing auxiliary component 144 may provide components for receiving the message sent to a group of UEs indicating the time of selection and handover of a second synchronization source.

[0106] At block 960, method 900 includes switching sidelink communication with a group of UEs to a second synchronization source. In one aspect, for example, UE 104, RX processor 356, and / or controller / processor 359 may execute SL synchronization component 140 and / or SL switching component 146 to switch sidelink communication with a group of UEs 410 to a second synchronization source 550. Therefore, UE 104, RX processor 356, and / or controller / processor 359 executing SL synchronization component 140 and / or SL switching component 146 may provide components for switching sidelink communication with a group of UEs to a second synchronization source.

[0107] Some further example terms

[0108] Specific implementation examples are described in the following numbered clauses:

[0109] Clause 1. A method for wireless communication at a user equipment (UE), the method comprising: determining a transition from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs; sending timing assistance information to the group of UEs for synchronization with the second synchronization source; and switching sidelink communication with the group of UEs to the second synchronization source.

[0110] Clause 2. The method according to Clause 1, wherein the timing auxiliary information includes one or more of the following: the offset between the first timing of the first synchronization source and the second timing of the second synchronization source; the number of time slots or subframes that differ between the second timing and the first timing; or the number of fractional time slots of the timing difference between the first timing and the second timing.

[0111] Clause 3. The method according to Clause 1 or 2, wherein determining the transition from the first synchronization source to the second synchronization source comprises: receiving a synchronization signal from the second synchronization source; and determining that the second synchronization source has a higher priority than the first synchronization source.

[0112] Clause 4. The method according to Clause 1 or 2, wherein determining the transition from the first synchronization source to the second synchronization source comprises: receiving from one or more of the UEs in the group of UEs an alternative synchronization source report indicating the detected synchronization source; and selecting the second synchronization source from the detected synchronization source.

[0113] Clause 5. The method according to Clause 4, wherein the alternative synchronization source report includes timing assistance information and the reference signal received power (RSRP) of the second synchronization source measured at the corresponding UE in the set of UEs.

[0114] Clause 6. The method according to Clause 5, wherein the second synchronization source is selected in response to all UEs in the group of UEs indicating that the RSRP satisfies the threshold of the second synchronization source.

[0115] Clause 7. The method according to any one of Clauses 1 to 6, the method further comprising sending a message to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

[0116] Clause 8. The method described in Clause 7, wherein the message is a physical layer signal or a Media Access Control (MAC) control element (CE).

[0117] Clause 9. The method according to any one of Clauses 1 to 8, the method further comprising measuring one or more sidelink synchronization signal sources during a configured measurement gap within the sidelink communication with the group of UEs.

[0118] Clause 10. The method according to Clause 9, wherein the configured measurement gap is defined by the measurement gap period, the gap offset within a time slot or subframe, and the gap length.

[0119] Clause 11. The method according to Clause 9 or 10, wherein the configuration of the measurement gap is provided by the first synchronization source or the primary UE in the group of UEs.

[0120] Clause 12. A method for wireless communication at a user equipment (UE), the method comprising: receiving timing assistance information for synchronizing with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source; and switching the sidelink communication with the group of UEs to the second synchronization source.

[0121] Clause 13. The method according to Clause 12, wherein the timing assistance information includes one or more of the following: the offset between a first timing of the first synchronization source and a second timing of the second synchronization source; the number of time slots or subframes that differ between the second timing and the first timing; or the number of fractional time slots representing the timing difference between the first timing and the second timing.

[0122] Clause 14. The method according to Clause 12 or 13, the method further comprising: receiving a side-link synchronization block (SL-SSB) from the second synchronization source; and sending an alternative synchronization source report indicating the detected synchronization source to the primary UE based on the received SL-SSB.

[0123] Clause 15. The method according to Clause 14, wherein the alternative synchronization source report includes timing assistance information and the reference signal received power (RSRP) of the second synchronization source measured at the corresponding UE in the set of UEs.

[0124] Clause 16. The method according to Clause 14 or 14, the method further comprising receiving a message sent to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

[0125] Clause 17. The method described in Clause 16, wherein the message is a physical layer signal or a Media Access Control (MAC) control element (CE).

[0126] Clause 18. The method according to any one of Clauses 14 to 17, wherein receiving the SL-SSB is performed during a configured measurement gap within the sidelink communication with the group of UEs.

[0127] Clause 19. The method according to Clause 18, wherein the configured measurement gap is defined by the measurement gap period, the gap offset within a time slot or subframe, and the gap length.

[0128] Clause 20. The method according to Clause 18 or 19, wherein the configuration of the measurement gap is provided by the first synchronization source or the primary UE in the group of UEs.

[0129] Clause 21. An apparatus for wireless communication by a user equipment (UE), the apparatus comprising: a transceiver; a memory storing computer-executable instructions; and a processor coupled to the transceiver and the memory and configured to execute the computer-executable instructions to cause the UE to: determine to switch from a first synchronization source to a second synchronization source for sidelink communication with a group of UEs; send timing assistance information to the group of UEs for synchronization with the second synchronization source; and switch sidelink communication with the group of UEs to the second synchronization source.

[0130] Clause 22. The apparatus according to Clause 21, wherein the timing assistance information includes one or more of the following: an offset between a first timing of the first synchronization source and a second timing of the second synchronization source; the number of time slots or subframes that differ between the second timing and the first timing; or the number of fractional time slots representing the timing difference between the first timing and the second timing.

[0131] Clause 23. The apparatus according to Clause 21 or 22, wherein, in order to determine a transition from the first synchronization source to the second synchronization source, the processor is configured to execute the instructions to cause the apparatus to: receive a synchronization signal from the second synchronization source; and determine that the second synchronization source has a higher priority than the first synchronization source.

[0132] Clause 24. The apparatus according to Clause 21 or 22, wherein, in order to determine a transition from the first synchronization source to the second synchronization source, the processor is configured to execute the instructions to cause the apparatus to: receive from one or more of the UEs in the group of UEs an alternative synchronization source report indicating a detected synchronization source; and select the second synchronization source from the detected synchronization source.

[0133] Clause 25. The apparatus according to Clause 24, wherein the alternative synchronization source report includes timing assistance information and the reference signal received power (RSRP) of the second synchronization source measured at the respective UE in the group of UEs.

[0134] Clause 26. The apparatus according to any one of Clauses 21 to 25, wherein the processor is configured to execute the instructions to cause the apparatus to send a message to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

[0135] Clause 27. The apparatus according to any one of Clauses 21 to 25, wherein the processor is configured to execute the instructions to cause the apparatus to measure one or more sidelink synchronization signal sources during a configured measurement gap within the sidelink communication with the group of UEs.

[0136] Clause 28. An apparatus for wireless communication by a user equipment (UE), the apparatus comprising: a transceiver; a memory storing computer-executable instructions; and a processor coupled to the transceiver and the memory and configured to execute the computer-executable instructions to cause the apparatus to: receive timing assistance information for synchronization with a second synchronization source from a primary UE in sidelink communication with a group of UEs using a first synchronization source; and switch sidelink communication with the group of UEs to the second synchronization source.

[0137] Clause 29. The apparatus according to Clause 28, wherein the processor is configured to execute the instructions to cause the apparatus to: receive a side-link synchronization block (SL-SSB) from the second synchronization source; and send an alternative synchronization source report indicating the detected synchronization source to the primary UE based on the received SL-SSB.

[0138] Clause 30. The apparatus according to Clause 28 or 29, wherein the processor is configured to execute the instructions to cause the apparatus to receive a message sent to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

[0139] It should be understood that the specific order or hierarchy of the boxes in the disclosed process / flowcharts is merely an example of the exemplary method. It should be understood that the specific order or hierarchy of the boxes in the process / flowcharts may be rearranged based on design preferences. Furthermore, some boxes may be combined or omitted. The appended method claims present the elements of various boxes in a sample order, but this does not imply limitation to the given specific order or hierarchy.

[0140] The foregoing description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects. Therefore, the claims are not intended to be limited to the aspects shown herein, but are to be consistent with the full scope of the language claims, wherein elements referred to in the singular are not intended to mean “one and only one”, but rather “one or more” unless specifically stated otherwise. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or superior to other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and / or C, which may include multiple A, multiple B, or multiple C. Specifically, combinations such as "at least one of A, B, or C", "one or more of A, B, or C", "at least one of A, B, and C", "one or more of A, B, and C", and "A, B, C, or any combination thereof" can be A only, B only, C only, A and B, A and C, B and C, or A and B and C, wherein any such combination may include one or more members of A, B, or C. All structural and functional equivalents of the elements throughout the various aspects described herein that are known to a person of ordinary skill in the art or will later be known are expressly incorporated herein by reference and are intended to be covered by the claims. Furthermore, nothing disclosed herein is intended to be offered to the public, whether or not such disclosure is expressly stated in the claims. Terms such as "module", "mechanism", "element", and "device" may not replace the word "part". Therefore, no claim element will be construed as a part plus function unless the element is expressly stated using the phrase "part for...".

Claims

1. A method for conducting wireless communication at a user equipment (UE), the method comprising: The system determines to switch from the first synchronization source to the second synchronization source for sidelink communication with a group of UEs. Send timing assistance information for synchronization with the second synchronization source to the group of UEs; and The sidelink communication with the group of UEs will be switched to the second synchronization source.

2. The method according to claim 1, wherein the timing auxiliary information includes one or more of the following: The offset between the first timing of the first synchronization source and the second timing of the second synchronization source; The number of time slots or subframes that differ between the second timing and the first timing; or The number of fractional time slots representing the timing difference between the first timing and the second timing.

3. The method of claim 1, wherein determining the transition from the first synchronization source to the second synchronization source comprises: Receive synchronization signal from the second synchronization source; as well as The second synchronization source is determined to have a higher priority than the first synchronization source.

4. The method of claim 1, wherein determining the transition from the first synchronization source to the second synchronization source comprises: Receive an alternative synchronization source report indicating the detected synchronization source from one or more of the UEs in the group of UEs; as well as Select the second synchronization source from the detected synchronization sources.

5. The method of claim 4, wherein the alternative synchronization source report includes timing assistance information and the reference signal received power (RSRP) of the second synchronization source measured at the corresponding UE in the group of UEs.

6. The method of claim 5, wherein the second synchronization source is selected in response to all UEs in the group of UEs indicating that the RSRP of the second synchronization source meets the threshold.

7. The method of claim 1, further comprising sending a message to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

8. The method of claim 7, wherein the message is a physical layer signal or a Media Access Control (MAC) control element (CE).

9. The method of claim 1, further comprising measuring one or more sidelink synchronization signal sources during a configured measurement gap within the sidelink communication with the group of UEs.

10. The method of claim 9, wherein the configured measurement gap is defined by the measurement gap period, the gap offset within a time slot or subframe, and the gap length.

11. The method of claim 9, wherein the configuration of the measurement gap is provided by the first synchronization source or the primary UE in the group of UEs.

12. A method for conducting wireless communication at a user equipment (UE), the method comprising: The primary UE in sidelink communication with a group of UEs using the first synchronization source receives timing auxiliary information for synchronization with the second synchronization source. as well as The sidelink communication with the group of UEs will be switched to the second synchronization source.

13. The method of claim 12, wherein the timing assistance information includes one or more of the following: The offset between the first timing of the first synchronization source and the second timing of the second synchronization source; The number of time slots or subframes that differ between the second timing and the first timing; or The number of fractional time slots representing the timing difference between the first timing and the second timing.

14. The method according to claim 12, further comprising: Receive the side link synchronization block (SL-SSB) from the second synchronization source; as well as Based on the received SL-SSB, the primary UE is sent a report indicating an alternative synchronization source for the detected synchronization source.

15. The method of claim 14, wherein the alternative synchronization source report includes timing assistance information and the reference signal received power (RSRP) of the second synchronization source measured at a corresponding UE in the group of UEs.

16. The method of claim 14, further comprising receiving a message sent to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

17. The method of claim 16, wherein the message is a physical layer signal or a Media Access Control (MAC) control element (CE).

18. The method of claim 14, wherein receiving the SL-SSB is performed during a configured measurement gap within the sidelink communication with the group of UEs.

19. The method of claim 18, wherein the configured measurement gap is defined by the measurement gap period, the gap offset within a time slot or subframe, and the gap length.

20. The method of claim 18, wherein the configuration of the measurement gap is provided by the first synchronization source or the primary UE in the group of UEs.

21. An apparatus for wireless communication by a user equipment (UE), the apparatus comprising: transceiver; Memory, the memory storing computer-executable instructions; and A processor, coupled to the transceiver and the memory, and configured to execute computer-executable instructions to cause the UE to: The system determines to switch from the first synchronization source to the second synchronization source for sidelink communication with a group of UEs. Send timing assistance information for synchronization with the second synchronization source to the group of UEs; and The sidelink communication with the group of UEs will be switched to the second synchronization source.

22. The apparatus of claim 21, wherein the timing assistance information includes one or more of the following: The offset between the first timing of the first synchronization source and the second timing of the second synchronization source; The number of time slots or subframes that differ between the second timing and the first timing; or The number of fractional time slots representing the timing difference between the first timing and the second timing.

23. The apparatus of claim 21, wherein, in order to determine a transition from the first synchronization source to the second synchronization source, the processor is configured to execute the instructions to cause the apparatus to: Receive synchronization signal from the second synchronization source; and The second synchronization source is determined to have a higher priority than the first synchronization source.

24. The apparatus of claim 21, wherein, in order to determine a transition from the first synchronization source to the second synchronization source, the processor is configured to execute the instructions to cause the apparatus to: Receive, from one or more of the UEs in the group of UEs, an alternative synchronization source report indicating the detected synchronization source; and Select the second synchronization source from the detected synchronization sources.

25. The apparatus of claim 24, wherein the alternative synchronization source report includes timing assistance information and the reference signal received power (RSRP) of the second synchronization source measured at a corresponding UE in the group of UEs.

26. The apparatus of claim 21, wherein the processor is configured to execute the instructions to cause the apparatus to send a message to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

27. The apparatus of claim 21, wherein the processor is configured to execute the instructions to cause the apparatus to measure one or more sidelink synchronization signal sources during a configured measurement gap within the sidelink communication with the group of UEs.

28. An apparatus for wireless communication by a user equipment (UE), the apparatus comprising: transceiver; Memory, the memory storing computer-executable instructions; and A processor, coupled to the transceiver and the memory, and configured to execute the computer-executable instructions to cause the device to: The primary UE in sidelink communication with a group of UEs using the first synchronization source receives timing auxiliary information for synchronization with the second synchronization source. as well as The sidelink communication with the group of UEs will be switched to the second synchronization source.

29. The apparatus of claim 28, wherein the processor is configured to execute the instructions to cause the apparatus to: Receive the side link synchronization block (SL-SSB) from the second synchronization source; and Based on the received SL-SSB, the primary UE is sent a report indicating an alternative synchronization source for the detected synchronization source.

30. The apparatus of claim 28, wherein the processor is configured to execute the instructions to cause the apparatus to receive a message sent to the group of UEs indicating the selection of the second synchronization source and the time of the handover.

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