On-demand request and resource selection for sidelink synchronization signals

Abstract

In one embodiment, the UE identifies a resource pool that allows the transmission of sidelink synchronization signals, the resource pool including at least UE-specific resources, and sends sidelink synchronization signals to one or more peer sidelink UEs based on a subset of the resource pool. In another embodiment, the UE sends a synchronization request message to at least one peer sidelink UE, and in response to the sending, receives at least one sidelink synchronization signal from at least one peer sidelink UE.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Provisional Application No. 62 / 887,455, filed on August 15, 2019, entitled “RESOURCE SELECTION FOR SIDELINK SYNCHRONIZATION SIGNALS,” and U.S. Non-Provisional Application No. 16 / 994,141, filed on August 14, 2020, entitled “RESOURCE SELECTION AND ON-DEMAND REQUEST FOR SIDELINK SYNCHRONIZATION SIGNALS,” both of which are assigned to the assignee of this application and are hereby expressly incorporated herein by reference in their entirety. Technical Field

[0003]

[0013] Various aspects described herein generally relate to resource selection for a sidelink synchronization signal. Background Art

[0004] Wireless communication systems have evolved over many generations, including first generation analog wireless telephone service (1G), second generation (2G) digital wireless telephone service (including interim 2.5G and 2.75G networks), third generation (3G) high speed data, wireless service with Internet capabilities, and fourth generation (4G) service (e.g., Long Term Evolution (LTE) or WiMax). There are many different types of wireless communication systems in use today, including cellular and personal communications service (PCS) systems. Examples of known cellular systems include the cellular analog Advanced Mobile Phone System (AMPS), and digital cellular systems based on code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), global system for mobile access (GSM) variations of TDMA, and the like.

[0005] The fifth generation (5G) mobile standard requires higher data transfer speeds, a greater number of connections, and better coverage, among other improvements. According to the Next Generation Mobile Network Alliance, the 5G standard is designed to provide data rates of tens of megabits per second to each of tens of thousands of users and 1 gigabit per second to dozens of workers on an office floor. Hundreds of thousands of simultaneous connections should be supported to support large sensor deployments. Therefore, the spectrum efficiency of 5G mobile communications should be significantly enhanced compared to the current 4G standard. In addition, signaling efficiency should be enhanced and latency should be significantly reduced compared to the current standard.

[0006] Some wireless communication networks, such as 5G, support operation at very high or even extremely high frequency (EHF) bands, such as the millimeter wave (mmW) bands (typically, wavelengths of 1 mm to 10 mm or 30 to 300 GHz). These extremely high frequencies can support very high throughputs, such as up to six gigabits per second (Gbps). However, one of the challenges of wireless communication at very high or extremely high frequencies is that significant propagation losses may occur due to the high frequencies. As the frequency increases, the wavelength may decrease, and the propagation losses may also increase. At the mmW bands, the propagation losses may be severe. For example, the propagation losses may be on the order of 22 to 27 dB relative to the propagation losses observed in the 2.4 GHz or 5 GHz bands. Summary of the invention

[0007] One embodiment relates to a method of operating a user equipment (UE), comprising: identifying a resource pool that allows transmission of a sidelink synchronization signal, the resource pool including at least UE-specific resources, and sending a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the resource pool.

[0008] Another embodiment relates to a method of operating a user equipment (UE), comprising: sending a synchronization request message to at least one peer sidelink UE, and receiving at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the sending.

[0009] Another embodiment relates to a method of operating a user equipment (UE), comprising: receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool including at least UE-specific resources, and synchronizing a clock at the UE based at least in part on the sidelink synchronization signal.

[0010] Another embodiment relates to a user equipment (UE), comprising: a component for identifying a resource pool allowing transmission of a sidelink synchronization signal, the resource pool including at least UE-specific resources, and a component for sending a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the resource pool.

[0011] Another embodiment relates to a user equipment (UE), comprising: a component for receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool including at least UE-specific resources, and a component for synchronizing a clock at the UE based at least in part on the sidelink synchronization signal.

[0012] Another embodiment relates to a user equipment (UE) comprising: a component for sending a synchronization request message to at least one peer sidelink UE, and a component for receiving at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the sending.

[0013] Another embodiment is directed to a user equipment (UE) comprising means for receiving a synchronization request message from a peer sidelink UE, and means for sending at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message.

[0014] Another embodiment relates to a user equipment (UE) comprising a memory, at least one transceiver, and at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: identify a resource pool allowing transmission of a sidelink synchronization signal, the resource pool comprising at least UE-specific resources, and send a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the resource pool via at least one transceiver.

[0015] Another embodiment relates to a user equipment (UE) comprising a memory, at least one transceiver, and at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: receive a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool including at least UE-specific resources, and synchronize a clock at the UE at least in part based on the sidelink synchronization signal.

[0016] Another embodiment relates to a user equipment (UE) comprising a memory, at least one transceiver, and at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: send a synchronization request message to at least one peer sidelink UE via the at least one transceiver, and receive at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the sending.

[0017] Another embodiment relates to a user equipment (UE) comprising a memory, at least one transceiver, and at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: receive a synchronization request message from a peer sidelink UE, and send at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message.

[0018] Another embodiment relates to a non-transitory computer-readable medium comprising instructions stored thereon, which when executed by a user equipment (UE) causes the UE to perform actions, the instructions including at least one instruction configured to cause the UE to identify a resource pool that allows transmission of a sidelink synchronization signal, the resource pool comprising at least UE-specific resources, and at least one instruction configured to cause the UE to send a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the resource pool.

[0019] Another embodiment relates to a non-transitory computer-readable medium comprising instructions stored thereon, which, when executed by a user equipment (UE), cause the UE to perform actions, including: at least one instruction configured to cause the UE to receive a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool including at least UE-specific resources, and at least one instruction configured to cause the UE to synchronize a clock at the UE at least in part based on the sidelink synchronization signal.

[0020] Another embodiment relates to a non-transitory computer-readable medium comprising instructions stored thereon, which, when executed by a user equipment (UE), cause the UE to perform actions, including: at least one instruction configured to cause the UE to send a synchronization request message to at least one peer sidelink UE, and at least one instruction configured to cause the UE to receive at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the sending.

[0021] Another embodiment relates to a non-transitory computer-readable medium comprising instructions stored thereon, which, when executed by a user equipment (UE), cause the UE to perform actions, including: at least one instruction configured to cause the UE to receive a synchronization request message from a peer sidelink UE, and at least one instruction configured to cause the UE to send at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] A more complete understanding of the various aspects described herein and their many attendant advantages as they become better understood will be readily obtained by reference to the following detailed description when considered in conjunction with the accompanying drawings, which are presented for purposes of illustration only and not limitation, and in which:

[0023] Figure 1

[0013] An example wireless communication system in accordance with various aspects is shown.

[0024] Figure 2A and 2BExample wireless network structures in accordance with various aspects are shown.

[0025] Figure 3A An exemplary base station and an exemplary user equipment (UE) in an access network according to various aspects are shown.

[0026] Figure 3B Exemplary servers according to various aspects are shown.

[0027] Figure 4 An exemplary wireless communication system in accordance with various aspects of the present disclosure is shown.

[0028] Figure 5 A sidelink communication network 500 is shown in accordance with an embodiment of the present disclosure.

[0029] Figure 6 A sidelink communication network according to another embodiment of the present disclosure is shown.

[0030] Figure 7 Successively higher timing errors are shown along hops of the sidelink communication network in accordance with an embodiment of the present disclosure.

[0031] Figure 8 An example frame structure supporting a sidelink synchronization signal according to an embodiment of the present disclosure is shown.

[0032] Fig. 9 An exemplary process for selecting resources for a sidelink synchronization signal according to another aspect of the present disclosure is shown.

[0033] Fig.10 An exemplary process for selecting resources for a sidelink synchronization signal according to another aspect of the present disclosure is shown.

[0034] Fig.11 An exemplary process for selecting resources for a sidelink synchronization signal according to another aspect of the present disclosure is shown.

[0035] Fig.12 An exemplary process of requesting a sidelink synchronization signal according to another aspect of the present disclosure is shown. DETAILED DESCRIPTION

[0036] Various aspects described herein generally relate to resource selection and / or on-demand requests for sidelink synchronization signals.

[0037] These and other aspects are disclosed in the following description and related drawings to illustrate specific examples related to the exemplary aspects. Upon reading this disclosure, alternative aspects will be apparent to those skilled in the relevant art and may be constructed and practiced without departing from the scope or spirit of the disclosure. Additionally, well-known elements will not be described in detail or may be omitted to avoid obscuring the relevant details of the aspects shown herein.

[0038] 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 advantageous over other aspects. Likewise, the term "aspects" does not require that all aspects include the discussed feature, advantage, or mode of operation.

[0039] The terms used herein describe only specific aspects and should not be construed as limiting any aspect disclosed herein. As used herein, the singular forms "a", "an" and "the" are intended to also include plural forms, unless the context clearly indicates otherwise. It will be further understood by those skilled in the art that the terms "comprising" and / or "including" as used herein specify the presence of stated features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0040] In addition, various aspects may be described in terms of a sequence of actions to be performed by, for example, an element of a computing device. Those skilled in the art will recognize that the various actions described herein may be performed by a dedicated circuit (e.g., an application specific integrated circuit (ASIC)), by program instructions being executed by one or more processors, or by a combination of the two. In addition, these action sequences described herein may be considered to be fully embodied in any form of non-transitory computer-readable medium having a corresponding computer instruction set stored thereon, which, when executed, will cause the associated processor to perform the functions described herein. Therefore, the various aspects described herein may be embodied in a variety of different forms, all of which are contemplated to be within the scope of the claimed subject matter. In addition, for each of the various aspects described herein, the corresponding form of any such aspect may be described herein as, for example, "logic configured to perform the described actions" and / or other structural components configured to perform the described actions.

[0041] As used herein, the terms "user equipment" (or "UE"), "user device", "user terminal", "client device", "communication device", "wireless device", "wireless communication device", "handheld device", "mobile device", "mobile terminal", "mobile station", "handset", "access terminal", "subscriber device", "subscriber terminal", "subscriber station", "terminal" and their variants may interchangeably refer to any suitable mobile or fixed device that can receive wireless communication and / or navigation signals. These terms are also intended to include a device that communicates with another device, which may receive wireless communication and / or navigation signals, for example, via short-range wireless, infrared, wired connection or other connection, regardless of whether satellite signal reception, auxiliary data reception and / or location-related processing occurs at the device or at another device. In addition, these terms are intended to include all devices that can communicate with a core network via a radio access network (RAN), including wireless and wired communication devices, and through the core network, the UE can connect to external networks such as the Internet and other UEs. Of course, other mechanisms for connecting to the core network and / or the Internet are also possible for the UE, such as through a wired access network, a wireless local area network (WLAN) (e.g., based on IEEE802.11, etc.), etc. The UE may be embodied by any of a variety of types of devices, including but not limited to a printed circuit (PC) card, a compact flash device, an external or internal modem, a wireless or wired phone, a smart phone, a tablet computer, a tracking device, an asset tag, etc. The communication link through which the UE may send signals to the RAN is referred to as an uplink channel (e.g., a reverse traffic channel, a reverse control channel, an access channel, etc.). The communication link through which the RAN may send signals to the UE is referred to as a downlink or forward link channel (e.g., a paging channel, a control channel, a broadcast channel, a forward traffic channel, etc.). As used herein, the term traffic channel (TCH) may refer to an uplink / reverse or downlink / forward traffic channel.

[0042] According to various aspects, Figure 1 An exemplary wireless communication system 100 is shown. The wireless communication system 100 (which may also be referred to as a wireless wide area network (WWAN)) may include various base stations 102 and various UEs 104. The base stations 102 may include macro cells (high-power cellular base stations) and / or small cells (low-power cellular base stations), wherein the macro cells may include evolved Node Bs (eNBs) in which the wireless communication system 100 corresponds to an LTE network, or gNodeBs (gNBs) in which the wireless communication system 100 corresponds to a 5G network, or a combination of both, and the small cells may include femto cells, pico cells, micro cells, etc.

[0043] The base stations 102 may form a radio access network (RAN) together and interface with an evolved packet core (EPC) or a next generation core (NGC) via a backhaul link. In addition to other functions, the base stations 102 may also perform functions related to one or more of the following: transmitting user data, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., switching, dual connectivity), inter-cell interference coordination, connection establishment and release, load balancing, distribution of non-access stratum (NAS) messages, NAS node selection, synchronization, RAN sharing, multimedia broadcast multicast service (MBMS), user and device tracking, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 may communicate with each other directly or indirectly (e.g., via EPC / NGC) via a backhaul link 134, which may be wired or wireless.

[0044] Base stations 102 may communicate wirelessly with UEs 104. Each of base stations 102 may provide communication coverage for a corresponding geographic coverage area 110. Figure 1 1, but the geographic coverage area 110 may be subdivided into multiple cells (e.g., three) or sectors, each cell corresponding to a single antenna or antenna array of the base station 102. As used herein, the term "cell" or "sector" may correspond to one of the multiple cells of the base station 102, or to the base station 102 itself, depending on the context.

[0045] Although adjacent macrocell geographic coverage areas 110 may partially overlap (e.g., in a handover region), some geographic coverage areas 110 may be substantially overlapped by larger geographic coverage areas 110. For example, a small cell base station 102' may have a geographic coverage area 110' that substantially overlaps with the geographic coverage area 110 of one or more macrocell base stations 102. A network including both small cells and macrocells may be referred to as a heterogeneous network. A heterogeneous network may also include a home eNB (HeNB), which may provide services to a restricted group referred to as a closed subscriber group (CSG). The communication link 120 between the base station 102 and the UE 104 may include an uplink (UL) (also referred to as a reverse link) transmission from the UE 104 to the base station 102 and / or a downlink (DL) (also referred to as a forward link) transmission from the base station 102 to the UE 104. The communication link 120 may use MIMO antenna technology, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link may be through one or more carriers. The allocation of carriers may be asymmetric with respect to DL and UL (eg, more or fewer carriers may be allocated to DL than to UL).

[0046] The wireless communication system 100 may also include a wireless local area network (WLAN) access point (AP) 150 in communication with a WLAN station (STA) 152 via a communication link 154 in an unlicensed spectrum (e.g., 5 GHz). When communicating in the unlicensed spectrum, the WLAN STA 152 and / or the WLAN AP 150 may perform a clear channel assessment (CCA) prior to communication to determine whether the channel is available.

[0047] The small cell base station 102' can operate in licensed and / or unlicensed spectrum. When operating in the unlicensed spectrum, the small cell base station 102' can adopt LTE or 5G technology and use the same 5 GHz unlicensed spectrum as the 5 GHz unlicensed spectrum used by the WLAN AP 150. The small cell base station 102' using LTE / 5G in the unlicensed spectrum can improve the coverage of the access network and / or increase the capacity of the access network. LTE in the unlicensed spectrum can be referred to as LTE-Unlicensed (LTE-U), Licensed Assisted Access (LAA), or MulteFire.

[0048] The wireless communication system 100 may also include a mmW base station 180, which may operate in mmW frequencies and / or near mmW frequencies to communicate with UE 182. Extremely high frequency (EHF) is part of RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 mm and 10 mm. The radio waves in this band may be referred to as millimeter waves. Near mmW may extend downward to a frequency of 3 GHz with a wavelength of 100 mm. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also known as centimeter waves. Communications using mmW / near mmW radio frequency bands have high path loss and relatively short distances. The mmW base station 180 may utilize beamforming 184 with UE 182 to compensate for extremely high path loss and short distances. In addition, it should be understood that in alternative configurations, one or more base stations 102 may also transmit using mmW or near mmW and beamforming. Therefore, it should be understood that the foregoing description is merely an example and should not be construed as limiting the various aspects disclosed herein.

[0049] The wireless communication system 100 may also include one or more UEs (such as UE 190) indirectly connected to one or more communication networks via one or more device-to-device (D2D) peer-to-peer (P2P) links. Figure 1In an embodiment of the present invention, the UE 190 has a D2D P2P link 192 in which one of the UEs 104 is connected to one of the base stations 102 (e.g., the UE 190 can indirectly obtain cellular connectivity through the D2D P2P link 192), and a D2D P2P link 194 in which the WLAN STA 152 is connected to the WLAN AP 150 (the UE 190 can indirectly obtain WLAN-based Internet connectivity through the D2D P2P link 194). In an example, the D2D P2P links 192-194 can be supported by any well-known D2D radio access technology (RAT) (such as LTE Direct (LTE-D), WiFi Direct (WiFi-D), Bluetooth, etc.).

[0050] According to various aspects, Figure 2A An example wireless network architecture 200 is shown. For example, the NGC 210 can be functionally viewed as a control plane function 214 (e.g., UE registration, authentication, network access, gateway selection, etc.) and a user plane function 212 (e.g., UE gateway function, access to data networks, Internet Protocol (IP) routing, etc.), which operate in collaboration to form a core network. A user plane interface (NG-U) 213 and a control plane interface (NG-C) 215 connect the gNB 222 to the NGC 210, and specifically to the control plane function 214 and the user plane function 212. In another configuration, the eNB 224 can also be connected to the NGC 210 via the NG-C 215 to the control plane function 214 and to the user plane function 212 via the NG-U 213. In addition, the eNB 224 can communicate directly with the gNB 222 via the backhaul connection 223. Accordingly, in some configurations, the new RAN 220 may have only one or more gNBs 222, while other configurations include one or more of both eNBs 224 and gNBs 222. The gNB 222 or the eNB 224 may communicate with the UE 240 (e.g., Figure 1 2, such as UE 104, UE 152, UE 182, UE 190, etc.). Another optional aspect may include a location server 230, which may communicate with the NGC 210 to provide location assistance to the UE 240. The location server 230 may be implemented as a plurality of structurally separate servers, or alternatively may each correspond to a single server. The location server 230 may be configured to support one or more location services for a UE 240 that may be connected to the location server 230 via the core network, the NGC 210, and / or via the Internet (not shown). In addition, the location server 230 may be integrated into a component of the core network, or alternatively may be external to the core network.

[0051] According to various aspects, Figure 2B Another example wireless network structure 250 is shown. For example, the NGC 260 can be functionally viewed as a control plane function, an access and mobility management function (AMF) 264 and a user plane function, and a session management function (SMF) 262, which operate in collaboration to form a core network. The user plane interface 263 and the control plane interface 265 connect the eNB 224 to the NGC 260, and specifically to the AMF 264 and the SMF 262. In another configuration, the gNB 222 can also be connected to the NGC 260 via a control plane interface 265 to the AMF 264 and a user plane interface 263 to the SMF 262. In addition, the eNB 224 can communicate directly with the gNB 222 via a backhaul connection 223 with or without a gNB direct connection to the NGC 260. Accordingly, in some configurations, the new RAN 220 may have only one or more gNBs 222, while other configurations include one or more of both eNBs 224 and gNBs 222. The gNB 222 or the eNB 224 may communicate with a UE 240 (e.g., Figure 1 240, such as any UE depicted in the core network, such as UE 104, UE 182, UE 190, etc.). Another optional aspect may include a location management function (LMF) 270, which may be in communication with NGC 260 to provide location assistance to UE 240. LMF 270 may be implemented as multiple separate servers (e.g., physically separate servers, different software modules on a single server, different software modules distributed on multiple physical servers, etc.), or alternatively may each correspond to a single server. LMF 270 may be configured to support one or more location services for UE 240 that may be connected to LMF 270 via the core network, NGC 260, and / or via the Internet (not shown).

[0052] According to various aspects, Figure 3A FIG. 1 shows a wireless network with an exemplary UE 350 (eg, Figure 1104, UE 152, UE 182, UE 190, etc.) is in communication with an exemplary base station (BS) 310 (e.g., eNB, gNB, small cell AP, WLAN AP, etc.). In the DL, IP packets from the core network (NGC 210 / EPC 260) may be provided to the controller / processor 375. The controller / processor 375 implements functions for a radio resource control (RRC) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller / processor 375 provides: RRC layer functions associated with broadcasting of system information (e.g., master information block (MIB), system information block (SIB)), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-RAT mobility, and measurement configuration for UE measurement reporting; PDCP layer functions associated with header compression / decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functions associated with upper layer packet data unit (PDU) transmission, error correction through automatic repeat request (ARQ), concatenation, segmentation and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functions associated with mapping between logical channels and transport channels, scheduling information reporting, error correction, priority handling, and logical channel prioritization.

[0053] The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functions associated with various signal processing functions. Layer 1 including the physical (PHY) layer may include error detection on the transmission channel, forward error correction (FEC) encoding / decoding of the transmission channel, interleaving, rate matching, mapping to the physical channel, modulation / demodulation of the physical channel, and MIMO antenna processing. The 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-phase shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols can then be divided into parallel streams. Each stream can then be mapped to an orthogonal frequency division multiplexing (OFDM) subcarrier, multiplexed with a reference signal (e.g., pilot) in the time domain and / or frequency domain, and then combined together using an inverse fast Fourier transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to generate multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation schemes and for spatial processing. Channel estimates may be derived based on reference signals and / or channel condition feedback sent by the UE 350. Each spatial stream may then be provided to one or more different antennas 320 via a separate transmitter 318a. Each transmitter 318a may modulate an RF carrier with a corresponding spatial stream for transmission.

[0054] At the UE 350, each receiver 354a receives a signal through its respective antenna 352. Each receiver 354a recovers the information modulated onto the RF carrier and provides the information to the RX processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functions associated with various signal processing functions. The RX processor 356 can perform spatial processing on the information to recover any spatial stream destined for the UE 350. If multiple spatial streams are destined for the UE 350, the RX processor 356 can combine them into a single OFDM symbol stream. Subsequently, the RX processor 356 converts the OFDM symbol stream from the time domain to the frequency domain using a fast Fourier transform (FFT). The frequency domain signal includes a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols and reference signals on each subcarrier are recovered and demodulated by determining the most likely signal constellation point sent by the base station 310. These soft decisions can be based on channel estimates calculated by the channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals originally sent on the physical channel by base station 310. The data and control signals are then provided to processing system 359, which implements layer 3 and layer 2 functions.

[0055] The processing system 359 may be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a non-transitory computer readable medium. In the UL, the processing system 359 provides demultiplexing between transport channels and logical channels, packet reassembly, decryption, header decompression, and control signal processing to recover IP packets from the core network. The processing system 359 is also responsible for error detection.

[0056] Similar to the functions described in conjunction with DL transmissions performed by the base station 310, the processing system 359 provides: RRC layer functions associated with system information (e.g., MIB, SIB) acquisition, RRC connection, and measurement reporting; PDCP layer functions associated with header compression / decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functions associated with upper layer PDU transmission, error correction through ARQ, concatenation, segmentation and reassembly of RLC SDUs, resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functions associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through hybrid automatic repeat request (HARQ), priority handling, and logical channel prioritization.

[0057] The TX processor 368 may use channel estimates derived by the channel estimator 358 from a reference signal or feedback sent by the base station 310 to select the appropriate codec and modulation scheme, as well as to facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antennas 352 via separate transmitters 354b. Each transmitter 354b may modulate an RF carrier with a corresponding spatial stream for transmission. In one aspect, the transmitter 354b and the receiver 354a may be one or more transceivers, one or more discrete transmitters, one or more discrete receivers, or any combination thereof.

[0058] The UL transmission is processed at the base station 310 in a manner similar to that described in conjunction with the receiver functionality at the UE 350. Each receiver 318b receives a signal through its respective antenna 320. Each receiver 318b recovers information modulated onto an RF carrier and provides the information to the RX processor 370. In an aspect, the transmitter 318a and the receiver 318b may be one or more transceivers, one or more separate transmitters, one or more separate receivers, or any combination thereof.

[0059] The processing system 375 may be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a non-transitory computer readable medium. In the UL, the processing system 375 provides demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, control signal processing to recover IP packets from the UE 350. The IP packets from the processing system 375 may be provided to the core network. The processing system 375 is also responsible for error detection.

[0060] Figure 3B An exemplary server 300B is shown. In an example, server 300B may correspond to one example configuration of location server 230 described above. Figure 3B In the embodiment, the server 300B includes a processor 301B coupled to a volatile memory 302B and a large capacity non-volatile memory such as a disk drive 303B. The server 300B may also include a floppy disk drive, a compact disk (CD) or a DVD optical disk drive 306B coupled to the processor 301B. The server 300B may also include a network access port 304B coupled to the processor 301B for establishing a data connection with a network 307B, such as a local area network coupled to other broadcast system computers and servers or coupled to the Internet.

[0061] Figure 4 An exemplary wireless communication system 400 is shown in accordance with various aspects of the present disclosure. Figure 4 In the example of Figure 1 Any of the described UEs (e.g., UE 104, UE 182, UE 190, etc.) is attempting to compute an estimate of its location, or assisting another entity (e.g., a base station or core network component, another UE, a location server, a third-party application, etc.) in computing an estimate of its location. UE 404 may communicate with multiple base stations 402a-d (collectively, base stations 402) (which may correspond to Figure 1 102 or 180 and / or WLAN AP 150 in the wireless communication system 400 for wireless communication. By extracting different types of information from the exchanged RF signals and utilizing the layout of the wireless communication system 400 (i.e., base station locations, geometry, etc.), the UE 404 can determine its position in a predefined reference coordinate system, or assist in determining its position. In one aspect, the UE 404 can use a two-dimensional coordinate system to specify its position; however, the aspects disclosed herein are not limited thereto and may also be applicable to determining position using a three-dimensional coordinate system if additional dimensions are required. Additionally, although Figure 4One UE 404 and four base stations 402 are shown, but it should be understood that there may be more UEs 404 and more or fewer base stations 402.

[0062] Sidelink communications involve peer-to-peer communications between UEs according to a device-to-device (D2D) protocol (e.g., V2V, V2X, LTE-D, WiFi Direct, etc.). In some designs, synchronization (e.g., time and frequency synchronization) is implemented whereby one or more UEs act as synchronization sources (referred to as SyncRef UEs). Typically, peer UEs belonging to a particular sidelink communication network attempt to maintain a common reference time to facilitate sidelink communications between peer UEs.

[0063] In some designs, the sidelink communication link is decoupled from the sidelink synchronization link. For example, two peer UEs participating in sidelink communication with each other do not need to designate one or the other as a synchronization source for deriving their respective time and frequency resources. In some designs, certain system-wide resources are designated or reserved for sidelink synchronization signaling in an SFN-based manner (e.g., in 3GPP Rel.12, 2 resources are reserved for sidelink synchronization signaling in each synchronization period). In such an implementation, there is no beam management functionality to proceed from sidelink synchronization to sidelink communication (e.g., because the sidelink synchronization signaling is transmitted via an SFN-based manner).

[0064] In some designs, the SyncRef UE may be directly connected to a base station (e.g., a gNB) or a global navigation satellite system (GNSS), as described below with respect to Figure 5 In other designs, the SyncRef UE may be indirectly connected to the base station or GNSS (e.g., via one or more peer UEs in the sidelink communication network over one hop). In still other designs, the SyncRef UE may act as an independent synchronization source without any direct or indirect connection to the base station or GNSS.

[0065] Figure 5 A sidelink communication network 500 is shown according to an embodiment of the present disclosure. Figure 5 , sidelink communication network 500 includes GNSS satellite 502 and UEs 504, 506, 508, and 510. UE 504 is synchronized with the network clock of GNSS satellite 502 based on receiving various GNSS signals. UE 504 is connected to UE 506 via sidelink communication link 512, UE 506 is connected to UE 508 via sidelink communication link 514, and UE 508 is connected to UE 510 via sidelink communication link 516. Although not shown, one or more of UEs 504-510 may also be connected to a terrestrial communication network. Figure 5, UE 504 corresponds to a SyncRef UE. In addition, although not shown, UE 510 may also be connected to another peer UE via a sidelink communication link 518 or the like.

[0066] As mentioned above, some networks reserve 2 resources for sidelink synchronization signaling. In an example of such a system, the sidelink synchronization signaling on the sidelink communication links 512-516 can be configured as shown in Table 1 as follows:

[0067]

[0068]

[0069] Table 1

[0070] As shown in Table 1, the subframes used for SLSS transmissions alternate between resources 1 and 2 at each hop in the sidelink communication network 500 because there are only two resources available for SLSS transmissions.

[0071] Figure 6 FIG. 6 shows a sidelink communication network 600 according to another embodiment of the present disclosure. Figure 6 , UE 506 and UE 508 lose their connection with each other, as shown at 602. As a result, UE 508 and 510 are disconnected from GNSS synchronized UE 504, which is in Figure 5 508-510 thus form a new sidelink communication network independent of GNSS. In the example, it is assumed that UE 508 becomes the SyncRef UE of the new sidelink communication network independent of GNSS. In addition, although not shown, UE 510 can also be connected to another peer UE via a sidelink communication link 606, etc.

[0072] In this case, in a system that reserves 2 resources for sidelink synchronization signaling, the sidelink synchronization signaling on the sidelink communication links 604-606 may be configured as shown in Table 2 as follows:

[0073]

[0074] Table 2

[0075] For a UE that derives its synchronization from a SyncRef UE, the reference timing is the “receive timing” of the synchronization signal (e.g., SFNed) of the SyncRef UE at the receiver (e.g., an unsynchronized UE), in a manner similar to downlink timing synchronization with respect to a base station. Sidelink physical channels and signals (for communication) may be sent based on this reference timing. In some designs, the sidelink communication network does not support timing advance (TA) as in the case of a UE to gNB uplink. In such a sidelink communication network, the propagation delay along each hop in the sidelink communication network results in a timing error between the SyncRef UE and each successive UE at each hop of the sidelink communication network. The timing error depends on the propagation distance along each hop and the number of hops from the original synchronization source (e.g., hops from a GNSS satellite 502 or a ground base station, or hops from the SyncRef UE itself in the case of an unsynchronized network).

[0076] Figure 7 5 shows successively higher timing errors along the jumps of the sidelink communication network 500 according to an embodiment of the present disclosure. Figure 7 The timing error relative to a particular radio frame denoted as radio frame X is shown in FIG. Figure 7 , the timing of UE 504 is set to the GNSS timing, and the timing of UE 506 is set to the timing of UE 504 plus the propagation delay t p1 , the timing of UE 508 is set to the timing of UE 506 plus the propagation delay t p2 , the timing of UE 510 is set to the timing of UE 508 plus the propagation delay t p3 , and so on. Therefore, the further the peer UE is from the SyncRef UE in terms of hopping, the larger the timing error. Figure 5 The GNSS synchronized sidelink communication network 500 describes Figure 7 , but the same problem occurs in sidelink communication networks that lack synchronization with the network clock.

[0077] Figure 8 FIG. 8 shows an example frame structure 800 supporting a sidelink synchronization signal according to an embodiment of the present disclosure. Figure 8As shown, frame structure 800 includes 14 subframes, where subframes 2 and 5 are allocated to the sidelink secondary synchronization signal (S-SSS), subframes 3-4 are allocated to the sidelink primary synchronization signal (S-PSS), subframes 6-13 are allocated to the PSBCH, and subframe 14 is used as a gap. In some designs, the sidelink synchronization signal block (S-SSB, which includes S-PSS and S-SSS) period can be 160ms, although the period can be configurable. In some designs, frame structure 800 can be used to support vehicle-based communications, such as NR vehicle-to-everything (V2X) communications. In particular, frame structure 800 can be used for functions related to sidelink communications, including resource selection, S-SSB ID determination, SyncRef UE selection and / or reselection, etc.

[0078] Some 5G NR sidelink designs target more general use cases rather than specific UE types or specific sidelink scenarios. For example, some UE types (such as wearables and IoT devices) may prioritize power consumption more than other UE types (such as plug-in devices or phones). In another example, wearables and IoT devices may lack the ability to connect directly to GNSS or terrestrial networks and may thereby require synchronization from a master device (e.g., a GNSS-capable or network-capable device). In another example, in a mmW sidelink where beam management is critical for sidelink data communications, it may be desirable to derive at least a portion of the initial transmit / receive beam information based on the beam used for transmission or reception of sidelink synchronization signals. In another example, a sidelink relay where the UE derives synchronization from a base station (e.g., a gNB) may suffer from intermittent gNB coverage loss, in which case a request-response based synchronization mechanism may be preferred.

[0079] Embodiments of the present disclosure relate to mechanisms for identifying resources for transmission of sidelink synchronization signals. Specifically, a pool of resources (eg, time and frequency resources) may be defined from which resources for a subset of sidelink synchronization signals may be identified.

[0080] Fig. 9 An example process 900 for selecting resources for a sidelink synchronization signal is shown according to an aspect of the present disclosure. Fig. 9 The process 900 is performed by a UE 905, which may correspond to any of the above-mentioned UEs (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 900 may be performed when the UE 905 is directly or indirectly synchronized with respect to a network clock. Fig. 9 In other designs, the process 900 may be performed when the UE 905 is not synchronized with the network clock. Fig. 9 Process 900.

[0081] At 902, UE 905 (e.g., controller / processor 359) identifies a resource pool that allows transmission of a sidelink synchronization signal, the resource pool including at least UE-specific resources. In an example, the UE-specific resources may be allocated to UE 905 by a base station (e.g., gNB). The UE-specific resources may be distinguished from the system-wide resources reserved for the sidelink synchronization signal as described above (e.g., 2 resources are reserved for sidelink synchronization signaling at each synchronization period). Accordingly, by including the UE-specific resources in the pool, UE 905 is not limited to using the reserved system-wide resources.

[0082] In some designs, some or all of the system-wide resources reserved for sidelink synchronization signaling may also be included in the pool at 902. However, this is not strictly required. For example, in some designs, the system-wide resources reserved for sidelink synchronization signaling may be omitted from the pool for use by legacy devices that do not consider UE-specific resources for sidelink synchronization signaling.

[0083] At 904, the UE 905 (e.g., the controller / processor 359) optionally selects a subset of the resource pool. Alternatively, the selection at 904 may occur via an external entity and then be communicated to the UE 905. Regardless of the entity making the selection at 904, the selection at 904 may be performed in various ways. For example, the UE 905 may monitor which resources are being used by other peer UEs for sidelink synchronization signaling, and then select a subset at 904 so as not to conflict with resources detected as being used by these peer UEs. In some designs, UE-specific resources may be selected at 904 as part of the subset so that the reserved system-wide resources for sidelink synchronization signaling remain available for use by legacy devices. In some designs, the subset may be selected at 904 so as to include a combination of both UE-specific resources and reserved system-wide resources (e.g., resources via SFN). In this case, the configured or preconfigured periodic resources configured for synchronization signal transmission of SFN (eg, reserved system-wide synchronization signal resources) may be supplemented by additional resources that the UE may obtain for synchronization signal transmission of non-SFN.

[0084] In some designs, the selection at 904 may select between UE-specific resources or reserved system-wide resources based on a trigger condition (e.g., if the RSRP to a synchronization source (e.g., a gNB or another UE) is below a threshold). For example, assume that the resource pool is set A and the resources of the selected subset at 904 are set B. Set B is the union of sets B1 and B2, whereby set B1 is a set of resources for SFN (e.g., reserved system-wide resources) and set B2 is a set of resources for non-SFN (e.g., UE-specific resources). In this case, the triggers (e.g., RSRP thresholds) for B1 and B2 may be configured differently (e.g., such triggers or thresholds may be preconfigured at UE 905).

[0085] At 906, the UE 905 (e.g., controller / processor 359, antenna 352, transmitter 354, and / or TX processor 368) sends a sidelink synchronization signal to one or more peer sidelink UEs based on the resources of the selected subset.

[0086] Fig.10 An example process 1000 for transmitting a sidelink synchronization signal on selected resources according to an aspect of the present disclosure is shown. Fig.10 The process 1000 is performed by a UE 1005, which may correspond to any of the above-mentioned UEs (e.g., UE 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 1000 may be performed when the UE 1005 is directly or indirectly synchronized with respect to a network clock. Fig.10 In other designs, the process 1000 may be performed when the UE 1005 is not synchronized with the network clock. Fig.10 of process 1000.

[0087] At 1002, UE 1005 (e.g., antenna 342, demodulator 354, receive processor 356, etc.) receives a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool including at least UE-specific resources. For example, the sidelink synchronization signal received at 1002 may correspond to the sidelink synchronization signal sent by UE 905 at 906. In one example, the UE-specific resources may be allocated to the peer sidelink UE (e.g., UE 905) by a base station (e.g., a gNB). The UE-specific resources may be distinguished from the system-wide resources reserved for the sidelink synchronization signal as described above (e.g., 2 system-wide resources are reserved for sidelink synchronization signaling at each synchronization period). Thus, by including the UE-specific resources in the pool, the peer sidelink UE is not limited to using the reserved system-wide resources. The resources of the subset in which the sidelink synchronization signal is located and / or the resource pool associated with the sidelink synchronization signal may be similarly configured and / or selected, as described above with respect to Fig. 9 as described.

[0088] At 1004, the UE 1005 (e.g., the controller / processor 359) synchronizes a clock at the UE based at least in part on the sidelink synchronization signal. In some designs, such synchronization may provide various technical advantages, such as clock synchronization for sidelink communications in scenarios where the UE 1005 has lost synchronization with respect to a network clock.

[0089] In some designs, the selection of 904 and the transmission of 906 or 1002 may be performed in an on-demand manner (e.g., in response to a request from one or more peer UEs (such as wearable devices)). In this case, the selected resources may include sidelink communication resources (e.g., for normal data traffic), in which case the sidelink synchronization signal need not be periodic.

[0090] In other designs, the selection at 904 and the transmission at 906 or 1002 may be performed in an opportunistic manner. For example, UE 905 may detect that the selected resources do not conflict with a peer sidelink UE or gNB and may then send a sidelink communication signal at 906 in response to the detection.

[0091] In other designs, the selection at 904 and the transmission at 906 or 1002 may be performed in a periodic manner. For example, the selected resources may include only some or all of the reserved system-wide resources, even though UE-specific resources may have been selected from the pool at 904.

[0092] Reference Figure 9-10In some designs, the transmission at 906 or 1002 may occur once or multiple times. In some designs, the transmission at 906 or 1002 may be repeated on a periodic basis, which may include multiple transmission periods (or intervals). For example, a first set of sidelink synchronization signals may be repeated indefinitely (e.g., until a new period is determined, etc.) with a lower period (e.g., 160), while a second set of sidelink synchronization signals may be repeated for a certain duration (e.g., 10 times) with a higher period (e.g., 5 ms). In some designs, a first set of sidelink synchronization signals repeated with a low period may be transmitted using SFN (or reserved system-wide) synchronization resources, while a second set of sidelink synchronization signals repeated with a higher period may be transmitted using non-SFN (or UE-specific) synchronization resources. In this case, the first set of sidelink synchronization signals may provide coarse timing / frequency synchronization, while non-SFN (e.g., UE-specific, such as unicast) may be used for finer timing / frequency synchronization. In some designs, transmission of the sidelink synchronization signal on SFN resources (or reserved system-wide resources) may be performed periodically based on a self-triggering condition (e.g., when the RSRP from the synchronization source is below a threshold, periodic sidelink synchronization signal transmission is turned on, etc.), while transmission on non-SFN resources (or UE-specific resources) may be performed in response to a request from a peer sidelink UE (e.g., on-demand or event-based triggering). The SFN and non-SFN synchronization resources may thus be used in conjunction with each other to improve overall synchronization in some designs.

[0093] Reference Figure 9-10In some designs, UE 905 may send an indication signal indicating the selected resources from 904 to one or more peer sidelink UEs (e.g., including UE 1005) (e.g., a peer sidelink UE requesting transmission of a sidelink synchronization signal). For example, the indication signal may alert one or more peer sidelink UEs to potential sidelink synchronization signals on those selected resources so that one or more peer sidelink UEs may scan or search for the sidelink synchronization signal within the selected resources. For example, the indication signal may include two bits to indicate one of a plurality of transmission window opportunities, such as the next 0-40ms, 40-80ms, 80-120ms, or 120-160ms. One or more peer sidelink UEs may then monitor the designated transmission window opportunity to receive the sidelink synchronization signal. In some designs, the indication signal may be associated in time with the corresponding sidelink synchronization signal (e.g., indicating that it is sent only 5ms to 10ms earlier than the sidelink synchronization signal). In this case, the two bits of the indication signal may be used to indicate multiple transmission window opportunities, such as the next 5-10 ms, 45-50 ms, 85-90 ms, or 125-130 ms. In some designs, the indication signal may contain fewer bits than the sidelink synchronization signal.

[0094] Fig.11 An example process 1100 for requesting a sidelink synchronization signal is shown according to an aspect of the present disclosure. Fig.11 The process 1100 is performed by a UE 1105, which may correspond to any of the above-mentioned UEs (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 1100 may be performed when the UE 1105 is directly or indirectly synchronized with respect to a network clock. Fig.11 In other designs, the process 1100 may be performed when the UE 1105 is not synchronized with respect to the network clock. Fig.11 Process 1100.

[0095] At 1102, UE 1105 (e.g., controller / processor 359, antenna 352, transmitter 354, and / or TX processor 368) transmits a synchronization request message to at least one peer sidelink UE. At 1104, UE (e.g., controller / processor 359, antenna 352, receiver 354, RX processor 356) receives at least one sidelink synchronization signal from at least one peer sidelink UE in response to the transmission of 1102.

[0096] Fig.12 An example process 1200 for sending an on-demand sidelink synchronization signal is shown according to one aspect of the present disclosure. Fig.12The process 1200 is performed by a UE 1205, which may correspond to any of the above-mentioned UEs (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 1200 may be performed when the UE 1205 is directly or indirectly synchronized with respect to a network clock. Fig.12 In other designs, the process 1200 may be performed when the UE 1205 is not synchronized with the network clock. Fig.12 Process 1200.

[0097] At 1202, the UE 1205 (e.g., the controller / processor 359, the antenna 342, the demodulator 354, the receive processor 356, etc.) receives a synchronization request message from a peer sidelink UE. At 1204, the UE 1205 (e.g., the controller / processor 359, the antenna 352, the transmitter 354, and / or the TX processor 368) transmits at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message.

[0098] Reference Figure 11-12 In some designs, the transmission of 1102 or 1202 is triggered in response to a synchronization failure of UE 1105 (e.g., UE 1105 becomes unsynchronized with respect to the network clock). In a specific example, assume that 1105 loses GNSS-based synchronization. In this case, UE 1105 may still be able to transmit for a few seconds because its oscillator will not drift beyond the critical point associated with excessive transmission rate errors. Therefore, UE 1105 can use these few seconds to perform the transmission of 1102 or 1202 and then attempt to switch its synchronization source to a SyncRef UE (which itself may or may not be synchronized to an external network such as GNSS) using the sidelink synchronization signal received at 1104 or 1204. In some designs, the transmission of 1102 or 1202 is triggered in response to detecting that the quality of the current synchronization source (e.g., RSRP) has dropped below a threshold.

[0099] Reference Figure 11-12 In one example, the synchronization request message may be sent on a sidelink communication channel (e.g., as a medium access control (MAC) control element (CE)). In another example, the synchronization request message may be sent via unicast (e.g., to a specific sidelink peer UE acting as a relay UE). In another example, the synchronization request message may be sent via multicast or broadcast (e.g., to any nearby UEs in the vicinity (similar to SOS)). Reference Figure 11-12 In some designs, the transmission of 1102 or 1202 may trigger Fig. 9 Selection and transmission of 904-906.

[0100] In further design, the above Figure 9-12 The various operations described may be implemented via various “means” such as specific hardware components of the associated UEs 905 and 1105. For example, means for receiving and transmitting various aspects of UEs 906 and 1102-1104 may correspond to transceiver-related circuits on the respective UEs (e.g., Figure 3A Any combination of antenna 352, receiver 354, RX processor 356, transmitter 354, TX processor 368, etc. of the UE 350. In another example, the means for determining and selecting aspects of 902-904 may correspond to processor-related circuits (such as Figure 3A Any combination of the controller / processor 359 of the UE350).

[0101] Although some embodiments are described above with respect to a particular parameter set (e.g., 15kHz SCS), other embodiments may involve implementations using different parameter sets (e.g., 30kHz SCS, 60kHz SCS, 120kHz SCS, 240kHz SCS, 480kHz SCS, etc.).

[0102] Those skilled in the art will appreciate that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be mentioned throughout the above description may be represented by voltage, current, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, or any combination thereof.

[0103] In addition, those skilled in the art will appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the various aspects disclosed herein can be implemented as electronic hardware, computer software, or a combination of the two. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been generally described above with respect to their functions. Whether this functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the entire system. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be interpreted as departing from the scope of the various aspects described herein.

[0104] The various illustrative logical blocks, modules, and circuits described in conjunction with the aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, a combination of one or more microprocessors and a DSP core, or other such configurations).

[0105] The methods, sequences and / or algorithms described in conjunction with the various aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM, flash memory, ROM, EPROM, EEPROM, registers, hard disks, removable disks, CD-ROMs, or any other form of non-transitory computer-readable medium known in the art. An exemplary non-transitory computer-readable medium may be coupled to a processor so that the processor can read information from and write information to the non-transitory computer-readable medium. In an alternative, the non-transitory computer-readable medium may be integrated into a processor. The processor and the non-transitory computer-readable medium may reside in an ASIC. The ASIC may reside in a user device (e.g., UE) or a base station. In an alternative, the processor and the non-transitory computer-readable medium may be discrete components in a user device or a base station.

[0106] In one or more exemplary aspects, the functions described herein can be implemented with hardware, software, firmware, or any combination thereof. If implemented with software, the function can be stored as one or more instructions or codes on a non-transitory computer-readable medium or sent by a non-transitory computer-readable medium. Computer-readable media may include storage media and / or communication media, including any non-transitory media that can facilitate the transfer of a computer program from one place to another. Storage media can be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media may include RAM, ROM, EEPROM, CD-ROM, or other optical disk storage, disk storage, or other magnetic storage devices, or any other medium that can be used to carry or store the desired program code in the form of an instruction or data structure and can be accessed by a computer. In addition, any connection is appropriately referred to as a computer-readable medium. For example, if software is sent from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves, coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwaves are included in the definition of the medium. The terms disk and disc, which are used interchangeably herein, include CD, laser disc, optical disc, DVD, floppy disk and Blu-ray disc, which typically reproduce data magnetically and / or optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0107] Although the foregoing disclosure shows illustrative aspects, those skilled in the art will appreciate that various changes and modifications may be made herein without departing from the scope of the present disclosure as defined by the appended claims. In addition, based on the various illustrative aspects described herein, those skilled in the art will appreciate that the functions, steps and / or actions in any method described above and / or recited in any method claim attached hereto need not be performed in any particular order. In addition, to the extent that any element is described above or recited in the appended claims in the singular, those skilled in the art will appreciate that the singular also contemplates the plural unless expressly limited to the singular.

Claims

1. A method for operating a user equipment UE, comprising: identifying a resource pool that allows transmission of a sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for transmission of the sidelink synchronization signal, and the UE-specific resources are allocated by the base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as A sidelink synchronization signal is sent to one or more peer sidelink UEs based on the subset of the resource pool.

2. The method according to claim 1, wherein: The resource pool also includes: the system-wide resources reserved for sidelink synchronization signal transmission.

3. The method according to claim 1, in, The subset of resources includes at least a portion of the UE-specific resources, or wherein the subset of resources includes at least a portion of the reserved system-wide resources, or Any combination of them.

4. The method according to claim 1, wherein: The subset of resources includes at least a portion of the UE-specific resources.

5. The method according to claim 1, wherein: The sending is in response to a request from at least one of the one or more peer sidelink UEs to send the sidelink synchronization signal in an on-demand manner.

6. The method according to claim 1, further comprising: determining that the subset of resources will not interfere with the one or more peer sidelink UEs and / or base stations, wherein the sending is performed in an opportunistic manner in response to the determining.

7. The method according to claim 1, wherein: The sending is repeated periodically.

8. The method according to claim 7, wherein: The periodic transmission includes: sending a first group of synchronization signals according to a first period, and A second group of synchronization signals is sent according to a second period.

9. The method according to claim 8, in, The first period is higher than the second period, wherein the first set of synchronization signals is transmitted on a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmission, and The second set of synchronization signals is sent on a second portion of the subset of resources corresponding to at least a portion of the UE-specific resources.

10. The method according to claim 7, wherein: The periodic transmission includes: sending a first group of synchronization signals according to a first period, and A second set of synchronization signals is sent on demand.

11. The method according to claim 10, in, The first set of synchronization signals is transmitted on a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmission, and The second set of synchronization signals is sent on a second portion of the subset of resources corresponding to at least a portion of the UE-specific resources.

12. The method according to claim 10, wherein: The second set of synchronization signals is sent in response to a synchronization request received from another peer sidelink UE or synchronization quality falling below a threshold.

13. The method according to claim 1, wherein: The resource pool and the subset of resources each include resources defined according to a combination of time and frequency.

14. The method according to claim 1, further comprising: An indication signal indicative of the subset of the resource pool is sent to the one or more peer sidelink UEs.

15. A method for operating a user equipment UE, comprising: receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that is allowed to transmit the sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission and the UE-specific resources are allocated by the base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as A clock is synchronized at the UE based at least in part on the sidelink synchronization signal.

16. The method according to claim 15, wherein: The resource pool also includes: the system-wide resources reserved for sidelink synchronization signal transmission.

17. The method according to claim 15, in, The subset of resources includes at least a portion of the UE-specific resources, or wherein the subset of resources includes at least a portion of the reserved system-wide resources, or Any combination of them.

18. The method according to claim 15, wherein: The subset of resources includes at least a portion of the UE-specific resources.

19. The method according to claim 15, further comprising: sending a request for the sidelink synchronization signal to the peer sidelink UE, Wherein, the sidelink synchronization signal is received on-demand in response to the request.

20. The method according to claim 15, wherein: The receiving is repeated periodically.

21. The method according to claim 20, wherein: The periodic reception: receiving a first group of synchronization signals according to a first period, and A second group of synchronization signals is received according to a second period.

22. The method according to claim 21, in, The first period is higher than the second period, wherein the first set of synchronization signals is received over a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmission, and The second set of synchronization signals is received on a second portion of the subset of resources corresponding to at least a portion of the UE-specific resources.

23. The method according to claim 20, wherein: The periodic receiving includes: receiving a first group of synchronization signals according to a first period, and A second set of synchronization signals is received in an on-demand manner.

24. The method according to claim 23, in, The first set of synchronization signals is received over a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmission, and The second set of synchronization signals is received on a second portion of the subset of resources corresponding to at least a portion of the UE-specific resources.

25. The method of claim 15, wherein: The resource pool and the subset of resources each include resources defined according to a combination of time and frequency.

26. The method of claim 15, further comprising: An indication signal is received from the peer sidelink UE indicating the subset of the resource pool.

27. A method of operating a user equipment UE, comprising: sending a synchronization request message to at least one peer sidelink UE; as well as In response to sending the synchronization request message, at least one sidelink synchronization signal is received from the at least one peer sidelink UE on one or more UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

28. The method according to claim 27, wherein: The sending sends the synchronization request message as a medium access control MAC control element CE through a sidelink communication channel.

29. The method according to claim 27, wherein: The sending sends the synchronization request message via unicast, multicast, or broadcast.

30. The method of claim 27, further comprising: determining that the UE has changed from being synchronized with respect to a network clock to being out of synchronization with respect to the network clock, Wherein, the sending is performed in response to the determining.

31. The method of claim 27, further comprising: determining that a quality associated with a synchronization source of the UE has dropped below a threshold, Wherein, the sending is performed in response to the determining.

32. A method of operating a user equipment UE, comprising: receiving a synchronization request message from a peer sidelink UE; as well as In response to the synchronization request message, at least one sidelink synchronization signal is sent to the peer sidelink UE on one or more UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

33. The method of claim 32, wherein: The receiving receives the synchronization request message as a medium access control MAC control element CE on a sidelink communication channel.

34. The method of claim 32, wherein: The receiving receives the synchronization request message via unicast, multicast or broadcast.

35. A user equipment UE, comprising: means for identifying a resource pool for which transmission of a sidelink synchronization signal is allowed, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for transmission of the sidelink synchronization signal and the UE-specific resources are allocated by the base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as Means for sending a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the resource pool.

36. A user equipment UE, comprising: means for receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool allowed to transmit the sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission and the UE-specific resources are allocated by the base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as Means for synchronizing a clock at the UE based at least in part on the sidelink synchronization signal.

37. A user equipment UE, comprising: means for sending a synchronization request message to at least one peer sidelink UE; as well as A component for receiving at least one sidelink synchronization signal from at least one peer sidelink UE on one or more UE-specific resources in response to sending the synchronization request message, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

38. A user equipment UE, comprising: means for receiving a synchronization request message from a peer sidelink UE; as well as A component for sending at least one sidelink synchronization signal to the peer sidelink UE on one or more UE-specific resources in response to the synchronization request message, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

39. A user equipment UE, comprising: Memory; at least one transceiver; as well as at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: identifying a resource pool that allows transmission of a sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for transmission of the sidelink synchronization signal, and the UE-specific resources are allocated by the base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as A sidelink synchronization signal is transmitted via the at least one transceiver to one or more peer sidelink UEs based on the subset of the resource pool.

40. A user equipment UE, comprising: Memory; at least one transceiver; as well as at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein The UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as A clock is synchronized at the UE based at least in part on the sidelink synchronization signal.

41. A user equipment UE, comprising: Memory; at least one transceiver; as well as at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: sending, via the at least one transceiver, a synchronization request message to at least one peer sidelink UE; and In response to sending the synchronization request message, at least one sidelink synchronization signal is received from the at least one peer sidelink UE on one or more UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

42. A user equipment UE, comprising: Memory; at least one transceiver; as well as at least one processor coupled to the memory and the at least one transceiver, and the at least one processor is configured to: receiving a synchronization request message from a peer sidelink UE; as well as In response to the synchronization request message, at least one sidelink synchronization signal is sent to the peer sidelink UE on one or more UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

43. A non-transitory computer-readable medium comprising instructions stored thereon, the instructions, when executed by a user equipment (UE), causing the UE to perform actions, the instructions comprising: at least one instruction configured to cause the UE to: identify a resource pool that allows transmission of a sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by a base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as At least one instruction configured to cause the UE to send a sidelink synchronization signal to one or more peer sidelink UEs based on the subset of the resource pool.

44. A non-transitory computer-readable medium comprising instructions stored thereon, the instructions, when executed by a user equipment (UE), causing the UE to perform actions, the instructions comprising: at least one instruction configured to cause the UE to: receive a sidelink synchronization signal from a peer sidelink UE based on a subset of a resource pool that allows transmission of the sidelink synchronization signal, the resource pool comprising at least UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by a base station to a specific UE, the specific UE having a reference timing independent of a network clock; as well as At least one instruction configured to cause the UE to synchronize a clock at the UE based at least in part on the sidelink synchronization signal.

45. A non-transitory computer-readable medium comprising instructions stored thereon, the instructions, when executed by a user equipment (UE), causing the UE to perform actions, the instructions comprising: at least one instruction configured to cause the UE to: send a synchronization request message to at least one peer sidelink UE; as well as At least one instruction configured to cause the UE to perform the following operations: in response to sending the synchronization request message, receive at least one sidelink synchronization signal from the at least one peer sidelink UE on one or more UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

46. ​​A non-transitory computer-readable medium comprising instructions stored thereon, the instructions, when executed by a user equipment (UE), causing the UE to perform actions, the instructions comprising: at least one instruction configured to cause the UE to: receive a synchronization request message from a peer sidelink UE; as well as At least one instruction configured to cause the UE to perform the following operations: in response to the synchronization request message, send at least one sidelink synchronization signal to the peer sidelink UE on one or more UE-specific resources, wherein the UE-specific resources are distinguished from system-wide resources reserved for sidelink synchronization signal transmission, and the UE-specific resources are allocated by the base station to a specific UE, and the specific UE has a reference timing independent of the network clock.

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