Resource selection and on-demand request for sidelink synchronization signals

Abstract

To provide a method for resource selection for sidelink synchronization signals transmitted by peer UE belonging to a specific sidelink communication network.SOLUTION: In a method of resource selection for sidelink synchronization signals, user equipment (UE) includes identifying a pool of resources where transmission of sidelink synchronization signals is permitted. The pool of resources comprises at least UE-specific resources. The UE also includes selecting a subset of the pool of resources, and transmitting a sidelink synchronization signal to one or more peer sidelink UEs based on the selected subset of the pool of resources.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of U.S. Provisional Application No. 62 / 887,455, entitled "RESOURCE SELECTION FOR SIDELINK SYNCHRONIZATION SIGNALS," filed August 15, 2019, and U.S. Non-Provisional Application No. 16 / 994,141, entitled "RESOURCE SELECTION AND ON-DEMAND REQUEST FOR SIDELINK SYNCHRONIZATION SIGNALS," filed August 14, 2020, both of which are assigned to the assignee of the present application and are expressly incorporated herein by reference in their entireties.

[0002] BACKGROUND

[0002] Various aspects described herein generally relate to resource selection for a sidelink synchronization signal. [Background technology]

[0003] Wireless communication systems have evolved through various generations, including first-generation analog wireless telephone service (1G), second-generation (2G) digital wireless telephone service (including intermediate 2.5G and 2.75G networks), third-generation (3G) high-speed data, Internet-enabled wireless service, and fourth-generation (4G) service (e.g., Long Term Evolution (LTE) or WiMax). Currently, there are many different types of wireless communication systems in use, including cellular and personal communications services (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) variants of TDMA, and the like.

[0004]

[0004] Fifth-generation (5G) mobile standards require, among other improvements, higher data rates, a greater number of connections, and better coverage. The 5G standard from the Next Generation Mobile Network Alliance is designed to provide data rates of tens of megabits per second to each of tens of thousands of users, and data rates of one gigabit per second to dozens of workers on an office floor. To support large sensor deployments, hundreds of thousands of simultaneous connections should be supported. Therefore, the spectral efficiency of 5G mobile communications should be significantly enhanced compared to the current 4G standard. Furthermore, signaling efficiency should be enhanced and latency should be significantly reduced compared to current standards.

[0005]

[0005] Some wireless communication networks, such as 5G, support operation in the very high frequency (EHF) band, and even the millimeter wave (mmW) frequency band (generally wavelengths of 1 mm to 10 mm, or 30 to 300 GHz). These mmWaves can support very high throughput, such as up to 6 gigabits per second (Gbps). However, one of the challenges with wireless communication in the very high frequency or mmWave bands is that the high frequency can result in significant propagation loss. As the frequency increases, the wavelength can decrease, and propagation loss can increase as well. In the mmW frequency band, propagation loss can be severe. For example, propagation loss can be as much as 22 to 27 dB relative to the propagation loss observed in either the 2.4 GHz band or the 5 GHz band. Summary of the Invention

[0006]

[0006] One embodiment is directed to a method of operating a user equipment (UE), comprising: identifying a pool of resources allowed for transmission of a sidelink synchronization signal; and transmitting a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the pool of resources, the pool of resources comprising at least UE-specific resources.

[0007]

[0007] Another embodiment is directed to a method of operating a user equipment (UE), comprising: transmitting 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 transmitting.

[0008]

[0008] Another embodiment is directed 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 pool of resources allowed for transmission of the sidelink synchronization signal; and synchronizing a clock at the UE based at least in part on the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources.

[0009]

[0009] Another embodiment is directed to a user equipment (UE) comprising: means for identifying a pool of resources allowed for transmission of a sidelink synchronization signal; and means for transmitting a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the pool of resources, the pool of resources comprising at least UE-specific resources.

[0010]

[0010] Another embodiment is directed to a user equipment (UE) comprising: means for receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a pool of resources allowed to transmit the sidelink synchronization signal; and means for synchronizing a clock at the UE based at least in part on the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources.

[0011]

[0011] Another embodiment is directed to a user equipment (UE) comprising: means for transmitting a synchronization request message to at least one peer sidelink UE; and means for receiving at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the transmitting.

[0012]

[0012] 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 transmitting at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message.

[0013]

[0013] Another embodiment is directed 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, wherein the at least one processor is configured to: identify a pool of resources allowed for transmission of a sidelink synchronization signal; and transmit, via the at least one transceiver, a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the pool of resources, the pool of resources comprising at least UE-specific resources.

[0014]

[0014] Another embodiment is directed 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, wherein the at least one processor is configured to: receive a sidelink synchronization signal from a peer sidelink UE based on a subset of a pool of resources allowed for transmission of the sidelink synchronization signal; and synchronize a clock at the UE based at least in part on the sidelink synchronization signal, wherein the pool of resources comprises at least UE-specific resources.

[0015]

[0015] Another embodiment is directed 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, wherein the at least one processor is configured to: transmit 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 transmission.

[0016]

[0016] Another embodiment is directed 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, wherein the at least one processor is configured to receive a synchronization request message from a peer sidelink UE and to transmit at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message.

[0017]

[0017] Another embodiment is directed to a non-transitory computer-readable medium including instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising at least one instruction that configures the UE to identify a pool of resources allowed for transmission of a sidelink synchronization signal, and at least one instruction that configures the UE to transmit a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the pool of resources, the pool of resources comprising at least UE-specific resources.

[0018]

[0018] Another embodiment is directed to a non-transitory computer-readable medium including instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising at least one instruction to configure the UE to receive a sidelink synchronization signal from a peer sidelink UE based on a subset of a pool of resources allowed for transmission of the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources, and at least one instruction to configure the UE to synchronize a clock at the UE based at least in part on the sidelink synchronization signal.

[0019]

[0019] Another embodiment is directed to a non-transitory computer-readable medium including instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising at least one instruction that configures the UE to transmit a synchronization request message to at least one peer sidelink UE, and at least one instruction that configures the UE to receive at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the transmission.

[0020]

[0020] Another embodiment is directed to a non-transitory computer-readable medium including instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising at least one instruction that configures the UE to receive a synchronization request message from a peer sidelink UE, and at least one instruction that configures the UE to transmit at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message.

[0021]

[0021] A more complete appreciation of the various aspects described herein and their many attendant advantages will be readily obtained when better understood by reference to the following detailed description of the invention, taken in conjunction with the accompanying drawings, which are presented for purposes of illustration only and not limitation, in which: [Brief explanation of the drawings]

[0022] [Figure 1]

[0022] FIG. 1 illustrates an exemplary wireless communication system, in accordance with various aspects. [Figure 2A]

[0023] FIG. 1 illustrates an example wireless network structure, in accordance with various aspects. [Figure 2B] FIG. 1 illustrates an example wireless network structure, in accordance with various aspects. [Figure 3A]

[0024] 1 illustrates an example base station and example user equipment (UE) in an access network, in accordance with various aspects. [Figure 3B]

[0025] 1 illustrates an exemplary server, in accordance with various aspects. [Figure 4]

[0026] FIG. 1 illustrates an example wireless communication system in accordance with various aspects of the present disclosure. [Figure 5]

[0027] 5 illustrates a sidelink communications network 500 according to one embodiment of the present disclosure. [Figure 6]

[0028] FIG. 1 illustrates a sidelink communication network according to another embodiment of the present disclosure. [Figure 7]

[0029] FIG. 1 illustrates successively higher timing errors along hops of a sidelink communication network in accordance with an embodiment of the present disclosure. [Figure 8]

[0030] FIG. 1 illustrates an example frame structure supporting sidelink synchronization signals according to one embodiment of the present disclosure. [Figure 9]

[0031] FIG. 10 illustrates an example process for selecting resources for a sidelink synchronization signal according to another aspect of the present disclosure. [Figure 10]

[0032] FIG. 10 illustrates an example process for selecting resources for a sidelink synchronization signal according to another aspect of the present disclosure. [Figure 11]

[0033] FIG. 10 illustrates an example process for selecting resources for a sidelink synchronization signal according to another aspect of the present disclosure. [Figure 12]

[0034] FIG. 10 illustrates an example process for requesting a sidelink synchronization signal according to another aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0023]

[0035] Various aspects described herein generally relate to resource selection and / or on-demand request for sidelink synchronization signals.

[0024]

[0036] These and other aspects are disclosed in the following description and related drawings to show specific examples related to exemplary aspects. Alternative aspects will become apparent to those skilled in the art upon reading this disclosure and may be constructed and implemented without departing from the scope or spirit of the present disclosure. Additionally, well-known elements may not be described in detail or may be omitted so as not to obscure the relevant details of the aspects disclosed herein.

[0025]

[0037] 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 "aspect" does not require that all aspects include the discussed feature, advantage or mode of operation.

[0026]

[0038] The terms used herein are merely descriptive of particular aspects and should not be construed as limiting the aspects disclosed herein. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. Furthermore, those skilled in the art will understand that the terms "comprises," "comprising," "includes," 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.

[0027]

[0039] Further, various aspects may be described in terms of a sequence of actions to be performed by, for example, elements of a computing device. Those skilled in the art will recognize that the various actions described herein may be performed by particular circuitry (e.g., an application-specific integrated circuit (ASIC)), by program instructions executed by one or more processors, or a combination of both. Furthermore, these sequences of actions described herein may be considered to be embodied as a whole in any form of non-transitory computer-readable medium storing a corresponding set of computer instructions that, when executed, cause an associated processor to perform the functions described herein. Accordingly, the various aspects described herein may be embodied in several different forms, all of which are contemplated to be within the scope of the claimed subject matter. Furthermore, for each aspect 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.

[0028]

[0040] 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 variations thereof may interchangeably refer to any suitable mobile or fixed device capable of receiving wireless communication and / or navigation signals. These terms also include devices that communicate with other devices capable of receiving wireless communication and / or navigation signals, such as by short-range wireless, infrared, wireline, or other connections, regardless of whether satellite signal reception, assistance data reception, and / or position-related processing occurs in the device or in other devices. Furthermore, these terms are intended to include all devices, including wireless and wireline communication devices, that can communicate with a core network via a Radio Access Network (RAN), through which the UE may be connected 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 possible for the UE, such as via a wired access network, a wireless local area network (WLAN) (e.g., based on IEEE 802.11, etc.), etc. The UE may be embodied by any of several 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 wireline phone, a smartphone, a tablet, a tracking device, an asset tag, etc. The communication link through which the UE can send signals to the RAN is called an uplink channel (e.g., a reverse traffic channel, a reverse control channel, an access channel, etc.).The communication links through which the RAN may send signals to the UEs are called downlink or forward link channels (e.g., paging channels, control channels, broadcast channels, forward traffic channels, etc.). As used herein, the term traffic channel (TCH) can refer to either an uplink / reverse traffic channel or a downlink / forward traffic channel.

[0029]

[0041] 1 illustrates an exemplary wireless communication system 100. The wireless communication system 100 (sometimes 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 macrocells (high-power cellular base stations) and / or small cells (low-power cellular base stations), where the macrocells may include evolved Node Bs (eNBs) where the wireless communication system 100 corresponds to an LTE network, or gNode Bs (gNBs) where the wireless communication system 100 corresponds to a 5G network, or a combination of both, and the small cells may include femtocells, picocells, microcells, etc.

[0030]

[0042] The base stations 102 collectively form a radio access network (RAN) and may interface with an evolved packet core (EPC) or next generation core (NGC) through backhaul links. In addition to other functions, the base stations 102 may perform functions related to one or more of: forwarding user data, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, RAN sharing, multimedia broadcast multicast services (MBMS), subscriber and equipment tracing, RAN information management (RIM), paging, positioning, and delivery of alert messages. The base stations 102 may communicate with each other directly or indirectly (e.g., through the EPC / NGC) via backhaul links 134, which may be wired or wireless.

[0031]

[0043] The base stations 102 may communicate wirelessly with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. In one aspect, although not shown in FIG. 1 , the geographic coverage area 110 may be subdivided into multiple cells (e.g., three), or sectors, with each cell corresponding to a single antenna or array of antennas 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.

[0032]

[0044] Neighboring macrocell geographic coverage areas 110 may partially overlap (e.g., in handover regions), but some of the geographic coverage areas 110 may be significantly overlapped by larger geographic coverage areas 110. For example, a small cell base station 102' may have a geographic coverage area 110' that significantly 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 known as a heterogeneous network. A heterogeneous network may also include a Home eNB (HeNB) that may serve a restricted group known as a Closed Subscriber Group (CSG). The communication link 120 between the base station 102 and the UE 104 may include uplink (UL) transmissions (also called reverse link) from the UE 104 to the base station 102 and / or downlink (DL) transmissions (also called forward link) from the base station 102 to the UE 104. The communication link 120 may use MIMO antenna techniques, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link may be over one or more carriers. The allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL ​​than for UL).

[0033]

[0045] The wireless communication system 100 may further include a wireless local area network (WLAN) access point (AP) 150 communicating with a WLAN station (STA) 152 via a communication link 154 in an unlicensed frequency spectrum (e.g., 5 GHz). When communicating in the unlicensed frequency spectrum, the WLAN STA 152 and / or the WLAN AP 150 may perform clear channel assessment (CCA) prior to communicating to determine whether a channel is available.

[0034]

[0046] The small cell base station 102' may operate in licensed and / or unlicensed frequency spectrum. When operating in the unlicensed frequency spectrum, the small cell base station 102' may employ LTE or 5G technology and use the same 5 GHz unlicensed frequency spectrum used by the WLAN AP 150. A small cell base station 102' employing LTE / 5G in the unlicensed frequency spectrum may boost coverage to and / or increase capacity of the access network. LTE in the unlicensed spectrum is sometimes referred to as LTE-unlicensed (LTE-U), licensed assisted access (LAA), or MultiFire.

[0035]

[0047] The wireless communication system 100 may further include an mmW base station 180 that may operate in mmW and / or near-mmW frequencies and that is in communication with the UE 182. Extremely high frequency (EHF) is a portion of RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 and 10 millimeters. Radio waves in this band are sometimes referred to as millimeter waves. Near-mmW may extend down to frequencies of 3 GHz, with wavelengths of 100 millimeters. The super high frequency (SHF) band, also referred to as centimeter wave, extends between 3 GHz and 30 GHz. Communications using the mmW / near-mmW radio frequency bands have high path loss and relatively short range. The mmW base station 180 may utilize beamforming 184 with the UE 182 to compensate for the extremely high path loss and short range. Furthermore, it will be appreciated that in alternative configurations, one or more base stations 102 may also transmit using mmW or near mmW and beamforming. Accordingly, it will be appreciated that the above description is by way of example only and should not be construed as limiting various aspects disclosed herein.

[0036]

[0048] The wireless communication system 100 may further include one or more UEs, such as a UE 190, that indirectly connect to one or more communication networks via one or more device-to-device (D2D) peer-to-peer (P2P) links. In the embodiment of FIG. 1, the UE 190 has a D2D P2P link 192 with one of the UEs 104 connected to one of the base stations 102 (e.g., through which the UE 190 may indirectly obtain cellular connectivity) and a D2D P2P link 194 with a WLAN STA 152 connected to a WLAN AP 150 (through which the UE 190 may indirectly obtain WLAN-based Internet connectivity). In one example, the D2D P2P links 192-194 may be supported using any well-known D2D radio access technology (RAT), such as LTE Direct (LTE-D), WiFi Direct (WiFi-D), Bluetooth, etc.

[0037]

[0049] According to various aspects, FIG. 2A illustrates an exemplary wireless network structure 200. For example, the NGC 210 may be functionally considered to have 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, data network access, Internet Protocol (IP) routing, etc.) that operate cooperatively 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, specifically to the control plane function 214 and the user plane function 212. In an additional configuration, the eNB 224 may also be connected to the NGC 210 via the NG-C 215 to the control plane function 214 and the NG-U 213 to the user plane function 212. Additionally, the eNB 224 may communicate directly with the gNB 222 via a backhaul connection 223. Thus, in some configurations, the new RAN 220 may have only one or more gNBs 222, while other configurations include one or more of both the eNB 224 and the gNB 222. Either the gNB 222 or the eNB 224 may communicate with the UE 240 (e.g., any of the UEs shown in FIG. 1, such as the UE 104, the UE 152, the UE 182, the UE 190, etc.). Another optional aspect may include a location server 230, which may be in communication with the NGC 210 to provide location assistance to the UE 240. The location servers 230 may be implemented as multiple 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 the UE 240 that can connect to the location server 230 via the core network NGC 210 and / or via the Internet (not shown). Furthermore, the location server 230 may be incorporated into a component of the core network or, alternatively, may be external to the core network.

[0038]

[0050] According to various aspects, FIG. 2B illustrates another exemplary wireless network structure 250. For example, the NGC 260 may be functionally considered a control plane function, an Access and Mobility Management Function (AMF) 264, and a user plane function, a Session Management Function (SMF) 262, which operate cooperatively to form a core network. A user plane interface 263 and a control plane interface 265 connect the eNB 224 to the NGC 260, specifically to the AMF 264 and the SMF 262. In an additional configuration, the gNB 222 may also be connected to the NGC 260 via the control plane interface 265 to the AMF 264 and the user plane interface 263 to the SMF 262. Additionally, the eNB 224 may communicate directly with the gNB 222 via the backhaul connection 223, with or without gNB direct connectivity to the NGC 260. Thus, 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. Either the gNBs 222 or the eNBs 224 may communicate with the UEs 240 (e.g., any of the UEs shown in FIG. 1, 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 the NGC 260 to provide location assistance to the UEs 240. The LMF 270 may be implemented as multiple separate servers (e.g., physically separate servers, different software modules on a single server, different software modules spread across multiple physical servers, etc.), or alternatively, may each correspond to a single server. The LMF 270 may be configured to support one or more location services for the UEs 240 that can connect to the LMF 270 via the core network, the NGC 260, and / or the Internet (not shown).

[0039]

[0051] 3A illustrates an exemplary base station (BS) 310 (e.g., eNB, gNB, small cell AP, WLAN AP, etc.) in communication with an exemplary UE 350 (e.g., UE 104, UE 152, UE 182, UE 190, etc., any of the UEs shown in FIG. 1) in a wireless network. In the DL, IP packets from the core network (NGC 210 / EPC 260) may be provided to a controller / processor 375. The controller / processor 375 implements functionality 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 related to 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 related to header compression / decompression, security (encryption, decryption, integrity protection, integrity verification), and handover support functions; RLC layer functions related to transfer of upper layer packet data units (PDUs), error correction via 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 related to mapping between logical channels and transport channels, scheduling information reporting, error correction, priority handling, and logical channel prioritization.

[0040]

[0052] The transmit (TX) processor 316 and receive (RX) processor 370 implement Layer 1 functions related to various signal processing functions. Layer 1, including the physical (PHY) layer, may include error detection on transport channels, forward error correction (FEC) coding / decoding of transport channels, interleaving, rate matching, mapping onto physical channels, modulation / demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), M-phase shift keying (M-PSK), multi-level quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to a time-domain orthogonal frequency division multiplexing (OFDM) subcarrier, multiplexed with a reference signal (e.g., a pilot) in the time and / or frequency domain, and then combined with each other using an inverse fast Fourier transform (IFFT) to generate a physical channel carrying a time-domain OFDM symbol stream. The OFDM streams are spatially precoded to generate multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine coding and modulation schemes and for spatial processing. The channel estimates may be derived from a reference signal and / or channel condition feedback transmitted 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 the respective spatial stream for transmission.

[0041]

[0053] In the UE 350, each receiver 354a receives a signal through its respective antenna 352. Each receiver 354a recovers information modulated onto an RF carrier and provides the information to the RX processor 356. The TX processor 368 and the RX processor 356 implement Layer 1 functionality related to various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover the spatial streams destined for the UE 350. If multiple spatial streams are destined for the UE 350, they may be combined into a single OFDM symbol stream by the RX processor 356. The RX processor 356 then converts the OFDM symbol stream from the time domain to the frequency domain using a fast Fourier transform (FFT). The frequency-domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier and the reference signal are recovered and demodulated by determining the most likely signal constellation point transmitted by the base station 310. These soft decisions may be based on channel estimates calculated by a channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to a processing system 359 that implements Layer 3 and Layer 2 functions.

[0042]

[0054] 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 and logical channels, packet reassembly, decryption, header recovery, and control signal processing to recover IP packets from the core network. The processing system 359 is also responsible for error detection.

[0043]

[0055] Similar to the functionality described with respect to DL transmission by base station 310, processing system 359 provides RRC layer functionality related to system information (e.g., MIB, SIB) acquisition, RRC connection, and measurement reporting; PDCP layer functionality related to header compression / decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functionality related to transfer of upper layer PDUs, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality related to 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 via hybrid automatic repeat request (HARQ), priority handling, and logical channel prioritization.

[0044]

[0056] Channel estimates derived by the channel estimator 358 from a reference signal or feedback transmitted by the base station 310 may be used by the TX processor 368 to select an appropriate coding and modulation scheme and to enable 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 respective spatial stream for transmission. In an aspect, the transmitter 354b and receiver 354a may be one or more transceivers, one or more individual transmitters, one or more individual receivers, or any combination thereof.

[0045]

[0057] UL transmissions are processed at the base station 310 in a manner similar to that described with respect to the receiver functions at the UE 350. Each receiver 318b receives signals 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 receiver 318b may be one or more transceivers, one or more individual transmitters, one or more individual receivers, or any combination thereof.

[0046]

[0058] 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 recovery, and 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.

[0047]

[0059] 3B illustrates an exemplary server 300B. In one example, server 300B may correspond to one exemplary configuration of location server 230 described above. In FIG. 3B, server 300B includes a processor 301B coupled to volatile memory 302B and mass non-volatile memory, such as a disk drive 303B. Server 300B may also include a floppy disk drive, compact disk (CD), or DVD disk drive 306B coupled to processor 301B. Server 300B may also include a network access port 304B coupled to 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 to the Internet.

[0048]

[0060] FIG. 4 illustrates an exemplary wireless communications system 400 in accordance with various aspects of the present disclosure. In the example of FIG. 4, a UE 404, which may correspond to any of the UEs described above with respect to FIG. 1 (e.g., UE 104, UE 182, UE 190, etc.), is attempting to calculate an estimate of its location or assist another entity (e.g., a base station or core network component, another UE, a location server, a third-party application, etc.) in calculating an estimate of its location. The UE 404 may communicate wirelessly with multiple base stations 402a-d (collectively, base stations 402), which may correspond to any combination of base stations 102 or 180 and / or WLAN AP 150 in FIG. 1, using RF signals and standardized protocols for modulation of RF signals and exchange of information packets. By extracting different types of information from the exchanged RF signals and utilizing the layout of the wireless communications system 400 (i.e., base station locations, geometry, etc.), the UE 404 may determine, or assist in determining, its location in a predefined reference frame. In one aspect, the UE 404 may specify its location using a two-dimensional coordinate system, although the aspects disclosed herein are not so limited and may be applicable to determining location using a three-dimensional coordinate system if additional dimensions are desired. Additionally, while FIG. 4 shows one UE 404 and four base stations 402, it will be appreciated that there may be more UEs 404 and more or fewer base stations 402.

[0049]

[0061] Sidelink communication relates to peer-to-peer communication between UEs via 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 achieved whereby one or more UEs act as a synchronization source (referred to as SyncRef UEs). Generally, peer UEs belonging to a particular sidelink communication network attempt to maintain a common reference time to enable sidelink communication between peer UEs.

[0050]

[0062] 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 are not required to designate one another as a synchronization source for deriving their respective time and frequency resources. In some designs, some system-wide resources are designated or reserved for sidelink synchronization signaling in an SFN-based manner (e.g., in 3GPP Rel. 12, two resources are reserved for sidelink synchronization signaling in each synchronization period). In such implementations, there is no beam management functionality carried over from sidelink synchronization to sidelink communication (e.g., because sidelink synchronization signaling is transported via an SFN-based manner).

[0051]

[0063] 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 shown below with reference to FIG. 5. In other designs, the SyncRef UE may be indirectly connected to a base station or GNSS (e.g., more than one hop away via one or more peer UEs in a sidelink communication network). In yet other designs, the SyncRef UE may act as an independent synchronization source without a direct or indirect connection to a base station or GNSS.

[0052]

[0064] FIG. 5 illustrates a sidelink communication network 500 according to one embodiment of the present disclosure. Referring to FIG. 5, the sidelink communication network 500 includes a GNSS satellite 502 and UEs 504, 506, 508, and 510. The UE 504 is synchronized with the network clock of the GNSS satellite 502 based on reception of various GNSS signals. The UE 504 is connected to the UE 506 via a sidelink communication link 512, which is connected to the UE 508 via a sidelink communication link 514, which is connected to the UE 510 via a sidelink communication link 516. Although not shown, one or more of the UEs 504-510 may also be connected to a terrestrial communication network. In FIG. 5, the UE 504 corresponds to a SyncRef UE. Also, although not shown, the UE 510 may be further connected to another peer UE via a sidelink communication link 518, and so on.

[0053]

[0065] As mentioned above, some networks reserve two resources for sidelink synchronization signaling. In one example of such a system, sidelink synchronization signaling over sidelink communication links 512-516 may be configured as shown in Table 1, as follows:

[0054] [Table 1]

[0055]

[0066] As shown in Table 1, since there are only two available resources for SLSS transmission, the subframes used for SLSS transmission alternate at each hop in the sidelink communications network 500 between resource 1 and resource 2.

[0056]

[0067] FIG. 6 illustrates a sidelink communications network 600 in accordance with another embodiment of the present disclosure. In FIG. 6, UE 506 and UE 508 lose their connection to each other, as shown at 602. Thus, UE 508 and UE 510 disconnect from the GNSS-synchronized UE 504, which served as the SyncRef UE in the sidelink communications network 500 of FIG. 5. The UEs 508-510 thereby form a new GNSS-independent sidelink communications network. In one example, assume that UE 508 becomes the SyncRef UE for the new GNSS-independent sidelink communications network. Also, although not shown, UE 510 may be further connected to yet another peer UE via sidelink communications link 606, and so on.

[0057]

[0068] In this case, in a system where two resources are reserved for sidelink synchronization signaling, the sidelink synchronization signaling over the sidelink communication links 604-606 may be configured as shown in Table 2, as follows:

[0058] [Table 2]

[0059]

[0069] For a UE that derives its synchronization from the SyncRef UE, the reference timing is the “receive timing” of the SyncRef UE’s synchronization signal (e.g., SFNed) 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 transmitted 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, propagation delay along each hop in the sidelink communication network contributes to a timing error between the SyncRef UE and each successive UE at each hop in the sidelink communication network. This timing error depends on the propagation distance along each hop as well as the number of hops from the original synchronization source (e.g., a GNSS satellite 502 or a terrestrial base station, or, in the case of an unsynchronized network, from the SyncRef UE itself).

[0060]

[0070] 7 illustrates successively higher timing errors along hops of the sidelink communication network 500, in accordance with one embodiment of the present disclosure. In particular, the timing errors are shown in FIG. 7 for a particular radio frame, denoted as radio frame X. Referring to FIG. 7, the timing of the UE 504 is set to the GNSS timing, and the timing of the UE 506 is set to the timing of the UE 504 plus a propagation delay t p1 and the timing of the UE 508 is set to the timing of the UE 506 plus the propagation delay t p2 and the timing of the UE 510 is set to the timing of the UE 508 plus the propagation delay t p3 , and so on. Thus, the further in hops a peer UE is from the SyncRef UE, the larger the timing error. Moreover, although Figure 7 is described with respect to the GNSS-synchronized sidelink communication network 500 of Figure 5, the same problem occurs in sidelink communication networks that lack synchronization with the network clock.

[0061]

[0071] FIG. 8 illustrates an example frame structure 800 supporting a sidelink synchronization signal in accordance with one embodiment of the present disclosure. As shown in FIG. 8, the frame structure 800 includes 14 subframes, with subframes 2 and 5 allocated to a sidelink secondary synchronization signal (S-SSS), subframes 3-4 allocated to a sidelink primary synchronization signal (S-PSS), subframes 6-13 allocated to a PSBCH, and subframe 14 serving as a gap. In some designs, the sidelink synchronization signal block (S-SSB, which comprises S-PSS and S-SSS) periodicity may be 160 ms, although this period may be configurable. In some designs, the frame structure 800 may be used to support vehicle-based communications, such as NR vehicle-to-everything (V2X) communications. In particular, the frame structure 800 may be used for sidelink communication-related functions, including resource selection, S-SSB ID determination, SyncRef UE selection and / or reselection, etc.

[0062]

[0072] Some 5G NR sidelink designs target more generalized use cases and do not target specific UE types or specific sidelink scenarios. For example, some UE types, such as wearable devices and IoT devices, may prioritize power consumption higher than other UE types, such as plug-in devices or phones. In a further example, wearable devices and IoT devices may lack the capability to directly connect to a GNSS or terrestrial network and may therefore require synchronization from a primary device (e.g., a GNSS-enabled or network-enabled device). In a further example, in mmW sidelink, where beam management is central to 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 transmitting or receiving sidelink synchronization signals. In a further example, sidelink relay, in which a 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 preferable.

[0063]

[0073] Embodiments of the present disclosure are directed to mechanisms by which resources for transmission of sidelink synchronization signals are identified. In particular, a pool of resources (e.g., time and frequency resources) may be defined from which a subset of resources for the sidelink synchronization signal is identified.

[0064]

[0074] 9 shows an example process 900 for selecting resources for a sidelink synchronization signal according to one aspect of the present disclosure. The process 900 of FIG. 9 is performed by a UE 905, which may correspond to any of the UEs described above (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 900 of FIG. 9 may be performed while the UE 905 is directly or indirectly synchronized with respect to a network clock, while in other designs, the process 900 of FIG. 9 may be performed while the UE 905 is not synchronized with respect to a network clock.

[0065]

[0075] At 902, the UE 905 (e.g., the controller / processor 359) identifies a pool of resources allowed for transmission of sidelink synchronization signals, the pool of resources comprising at least UE-specific resources. In one example, the UE-specific resources may be assigned to the UE 905 by a base station (e.g., a gNB). The UE-specific resources may be distinguished from system-wide resources reserved for sidelink synchronization signals as described above (e.g., two resources are system-widely reserved for sidelink synchronization signaling in each synchronization period). Thus, by including the UE-specific resources in the pool, the UE 905 is not limited to using the reserved system-wide resources.

[0066]

[0076] In some designs, some or all of the reserved system-wide resources for sidelink synchronization signaling may also be included in the pool at 902, although this is not strictly required. For example, the reserved system-wide resources for sidelink synchronization signaling may be omitted from the pool in some designs for use by legacy devices that do not consider UE-specific resources for sidelink synchronization signaling.

[0067]

[0077] At 904, the UE 905 (e.g., the controller / processor 359) optionally selects a subset of the pool of resources. Alternatively, the selection at 904 may be made via an external entity and then communicated to the UE 905. Regardless of the entity making the selection at 904, the selection at 904 may be implemented in various manners. For example, the UE 905 may monitor which resources are being used for sidelink synchronization signaling by other peer UEs and then select the subset at 904 to not conflict with the resources detected as being used by these peer UEs. In some designs, UE-specific resources may be selected as part of the subset at 904 such that 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 to include a combination of both UE-specific resources and reserved system-wide resources (e.g., SFNed resources). In this case, the configured or pre-configured periodic resources configured for SFNed synchronization signal transmissions (e.g., reserved system-wide synchronization signal resources) may be supplemented by additional resources that the UE may acquire for non-SFNed synchronization signal transmissions.

[0068]

[0078] 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., whether RSRP to a synchronization source (e.g., a gNB or another UE) is below a threshold). For example, assume the pool of resources is set A and the selected subset of resources at 904 is set B. Set B is the union of sets B1 and B2, whereby set B1 is an SFNed resource set (e.g., reserved system-wide resources) and set B2 is a non-SFNed resource set (e.g., UE-specific resources). In this case, the trigger for B1 (e.g., RSRP threshold) and the trigger for B2 may be configured differently (e.g., such trigger or threshold may be preconfigured in the UE 905).

[0069]

[0079] At 906, the UE 905 (e.g., the controller / processor 359, the antenna(s) 352, the transmitter(s) 354, and / or the TX processor 368) transmits a sidelink synchronization signal to one or more peer sidelink UEs based on the selected subset of resources.

[0070]

[0080] 10 shows an example process 1000 for transporting a sidelink synchronization signal on selected resources according to one aspect of the present disclosure. The process 1000 of FIG. 10 is performed by a UE 1005, which may correspond to any of the UEs described above (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 1000 of FIG. 10 may be performed while the UE 1005 is directly or indirectly synchronized with respect to a network clock, while in other designs, the process 1000 of FIG. 10 may be performed while the UE 1005 is not synchronized with respect to a network clock.

[0071]

[0081] At 1002, a 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 pool of resources permitted for transmitting the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources. For example, the sidelink synchronization signal received at 1002 may correspond to the sidelink synchronization signal transmitted by the UE 905 at 906. In one example, the UE-specific resources may be assigned to the peer sidelink UE (e.g., the UE 905) by a base station (e.g., a gNB). The UE-specific resources may be distinguished from the system-wide resources reserved for sidelink synchronization signals as described above (e.g., two resources are system-widely reserved for sidelink synchronization signaling in 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 subset of resources for the sidelink synchronization signal and / or the pool of resources associated with the sidelink synchronization signal may be configured and / or selected similarly as described above with respect to FIG. 9.

[0072]

[0082] 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 is out of sync with respect to the network clock.

[0073]

[0083] 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 a wearable device). In this case, the selected resource(s) may comprise sidelink communication resources (e.g., typically used for data traffic), in which case the sidelink synchronization signal need not be periodic.

[0074]

[0084] In other designs, the selection of 904 and the transmission of 906 or 1002 may be performed in an opportunistic manner. For example, the UE 905 may detect that the selected resource(s) do not conflict with a peer sidelink UE or gNB and may then transmit a sidelink communication signal at 906 in response to this detection.

[0075]

[0085] In other designs, the selection of 904 and the transmission of 906 or 1002 may be performed in a periodic manner. For example, the selected resource(s) may comprise only some or all of the reserved system-wide resources, even though UE-specific resources may have been selected from a pool at 904.

[0076]

[0086] 9-10 , in some designs, the transmission at 906 or 1002 may occur one or more times. In some designs, the transmission at 906 or 1002 may repeat periodically, which may comprise multiple transmission periods (or intervals). For example, a first set of sidelink synchronization signals may repeat at a lower periodicity (e.g., 160 ms) indefinitely (e.g., until a new periodicity is determined), and a second set of sidelink synchronization signals may repeat at a higher periodicity (e.g., 5 ms) for a certain duration (e.g., 10 times). In some designs, the first set of sidelink synchronization signals repeating at a lower periodicity may be transported using SFNed (or reserved system-wide) synchronization resources, and the second set of sidelink synchronization signals repeating at a higher periodicity may be transported using non-SFNed (or UE-specific) synchronization resources. In this case, the first set of sidelink synchronization signals may provide coarse timing / frequency synchronization, and the second set of sidelink synchronization signals repeat at a higher periodicity (e.g., 5 ms) for a certain duration (e.g., 10 times). Ned (e.g., UE-specific, such as unicast) may be used for finer timing / frequency synchronization. In some designs, sidelink synchronization signal transmission on SFNed resources (or reserved system-wide resources) may be performed periodically based on one or more self-triggering conditions (e.g., turning on periodic sidelink synchronization signal transmission when RSRP from the synchronization source falls below a threshold), while transmission on non-SFNed resources (or UE-specific resources) may be performed in response to a request (e.g., on-demand or event-based trigger) from a peer sidelink UE. SFNed and non-SFNed synchronization resources may thereby, in some designs, be used together with each other to improve overall synchronization.

[0077]

[0087] 9-10 , in some designs, the UE 905 may transmit an indication signal indicating the selected resource(s) from 904 to one or more peer sidelink UEs (e.g., including the UE 1005), such as a peer sidelink UE that requested transmission of a sidelink synchronization signal. For example, the indication signal may inform the one or more peer sidelink UEs of a potential sidelink synchronization signal on those selected resource(s), so that the one or more peer sidelink UEs can scan or search for a sidelink synchronization signal within the selected resource(s). For example, the indication signal may comprise two bits to indicate one of a plurality of transmission window opportunities, such as the next 0-40 ms, 40-80 ms, 80-120 ms, or 120-160 ms. The 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 time-aligned with the corresponding sidelink synchronization signal (e.g., the indication may be transmitted 5 ms to 10 ms earlier than the sidelink synchronization signal). In this case, 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 include fewer bits than the sidelink synchronization signal.

[0078]

[0088] 11 shows an example process 1100 for requesting a sidelink synchronization signal according to one aspect of the present disclosure. The process 1100 of FIG. 11 is performed by a UE 1105, which may correspond to any of the UEs described above (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 1100 of FIG. 11 may be performed while the UE 1105 is directly or indirectly synchronized with respect to a network clock, while in other designs, the process 1100 of FIG. 11 may be performed while the UE 1105 is not synchronized with respect to a network clock.

[0079]

[0089] At 1102, the UE 1105 (e.g., the controller / processor 359, the antenna(s) 352, the transmitter(s) 354, and / or the TX processor 368) transmits a synchronization request message to at least one peer sidelink UE. At 1104, the UE (e.g., the controller / processor 359, the antenna(s) 352, the receiver(s) 354, the RX processor 356) receives at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the transmission of 1102.

[0080]

[0090] 12 shows an example process 1200 for transmitting an on-demand sidelink synchronization signal according to one aspect of the present disclosure. The process 1200 of FIG. 12 is performed by a UE 1205, which may correspond to any of the UEs described above (e.g., UEs 240, 350, 504, 506, 508, 510, etc.). In some designs, the process 1200 of FIG. 12 may be performed while the UE 1205 is directly or indirectly synchronized with respect to a network clock, while in other designs, the process 1200 of FIG. 12 may be performed while the UE 1205 is not synchronized with respect to a network clock.

[0081]

[0091] At 1202, the UE 1205 (e.g., the controller / processor 359, the antenna(s) 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(s) 352, the transmitter(s) 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.

[0082]

[0092] 11-12 , in some designs, transmission of 1102 or 1202 is triggered in response to a synchronization failure by UE 1105 (e.g., UE 1105 becoming unsynchronized with respect to the network clock). In a particular example, assume 1105 loses GNSS-based synchronization. In this case, UE 1105 can still transmit for several seconds because its oscillator will not drift beyond a critical point associated with excessive transmission rate error. Thus, UE 1105 can utilize these several seconds to perform transmission of 1102 or 1202 and then attempt to use the sidelink synchronization signal(s) received at 1104 or 1204 to switch its synchronization source to SyncRef UE (which may or may not itself be synchronized to an external network, such as GNSS). In some designs, transmission of 1102 or 1202 is triggered in response to detecting the quality of the current synchronization source (e.g., RSRP) below a threshold.

[0083]

[0093] 11-12, in one example, the synchronization request message may be transmitted via a sidelink communications channel (e.g., as a Medium Access Control (MAC) Control Element (CE)). In another example, the synchronization request message may be transmitted via unicast (e.g., to a specific sidelink peer UE acting as a relay UE). In another example, the synchronization request message may be transmitted via multicast or broadcast (e.g., to any nearby UEs in proximity, like an SOS). Referring to FIGS. 11-12, in some designs, the transmission of 1102 or 1202 may trigger the selection and transmission of 904-906 in FIG. 9.

[0084]

[0094] 9-12 may be implemented via different “means,” such as specific hardware components of the associated UEs 905 and 1105. For example, the means for receiving and transmitting aspects of 906 and 1102-1104 may correspond to any combination of transceiver-related circuitry on the respective UE, such as the antenna(s) 352, the receiver(s) 354, the RX processor 356, the transmitter(s) 354, and the Tx processor 368 of the UE 350 of FIG. 3A. In a further example, the means for determining and selecting aspects of 902-904 may correspond to any combination of processor-related circuitry on the respective UE, such as the controller / processor 359 of the UE 350 of FIG. 3A.

[0085]

[0095] Although some of the embodiments are described above with respect to a particular numerology (e.g., 15 kHz SCS), other embodiments may be directed to implementations in which different numerologies are used (e.g., 30 kHz SCS, 60 kHz SCS, 120 kHz SCS, 240 kHz SCS, 480 kHz SCS, etc.).

[0086]

[0096] 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, the data, instructions, commands, information, signals, bits, symbols, and chips that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0087]

[0097] Furthermore, those skilled in the art will appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the particular application and design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the various aspects described herein.

[0088]

[0098] The various example logic blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed using 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 alternatively, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or other such configuration).

[0089]

[0099] The methods, sequences, and / or algorithms described in connection with the aspects disclosed herein may be embodied directly in hardware, in software modules executed by a processor, or in a combination of the two. The software modules may reside in RAM, flash memory, ROM, EPROM, EEPROM, registers, hard disk, removable disk, CD-ROM, 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 such that the processor can read information from and write information to the non-transitory computer-readable medium. Alternatively, the non-transitory computer-readable medium may be integral to the 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., a UE) or a base station. Alternatively, the processor and the non-transitory computer-readable medium may be discrete components in the user device or base station.

[0090]

[0100] In one or more exemplary aspects, the functions described herein may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a non-transitory computer-readable medium. Computer-readable media may include storage and / or communication media, including any non-transitory medium that may enable a computer program to be transferred from one place to another. Storage media may be any available medium that can be accessed by a computer. By way of example, and not limitation, such computer-readable media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if software is transmitted 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 microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. The terms disk and disc, which may be used interchangeably herein, include CDs, laser discs, optical discs, DVDs, floppy disks, and Blu-ray discs, which typically reproduce data magnetically and / or optically with a laser. Combinations of the above should also be included within the scope of computer-readable media.

[0091]

[0101] While the above disclosure sets forth exemplary embodiments, those skilled in the art will appreciate that various changes and modifications can be made herein without departing from the scope of the present disclosure, as defined by the appended claims. Furthermore, those skilled in the art will appreciate that, in accordance with the various exemplary embodiments described herein, the functions, steps, and / or actions in any method described above and / or recited in any method claims appended hereto need not be performed in any particular order. Furthermore, those skilled in the art will appreciate that, to the extent any element is described above or recited in the appended claims in the singular, the singular(s) also contemplates the plural, unless limitation to the singular(s) is expressly stated.

Claims

1. 1. A method of operating a user equipment (UE), comprising: identifying a pool of resources allowed for transmission of a sidelink synchronization signal, said pool of resources comprising at least UE-specific resources; transmitting a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of said pool of resources; A method comprising:

2. 2. The method of claim 1, wherein the pool of resources further comprises system-wide resources reserved for sidelink synchronization signal transmissions.

3. the subset of resources comprises at least a portion of the UE-specific resources; or the subset of resources comprises at least a portion of the reserved system-wide resources; or Any combination thereof, The method of claim 1.

4. The method of claim 1 , wherein the subset of resources comprises at least a portion of the UE-specific resources.

5. 2. The method of claim 1, wherein the transmitting comprises transmitting the sidelink synchronization signal in an on-demand manner in response to a request from at least one of the one or more peer sidelink UEs.

6. determining that the subset of resources does not interfere with the one or more peer sidelink UEs and / or base stations. Furthermore, wherein the transmitting is performed in response to detecting in an opportunistic manner. The method of claim 1.

7. The method of claim 1 , wherein the transmitting repeats periodically.

8. the periodic transmitting transmitting a first set of synchronization signals according to a first periodicity; transmitting a second set of synchronization signals according to a second periodicity; and The method of claim 7, comprising:

9. the first periodicity is higher than the second periodicity; the first set of synchronization signals are transmitted on a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmissions; the second set of synchronization signals are transmitted on a second portion of the subset of resources corresponding to at least a portion of the UE-specific resources. The method of claim 8.

10. the periodic transmitting transmitting a first set of synchronization signals according to a first periodicity; transmitting a second set of synchronization signals in an on-demand manner; The method of claim 7, comprising:

11. the first set of synchronization signals are transmitted on a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmissions; the second set of synchronization signals are transmitted on a second portion of the subset of resources corresponding to at least a portion of the UE-specific resources. The method of claim 10.

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

13. The method of claim 1 , wherein the pool of resources and the subset of resources each comprise resources defined in terms of a combination of time and frequency.

14. transmitting an indication signal to the one or more peer sidelink UEs to indicate the subset of the pool of resources. The method of claim 1 further comprising:

15. 1. 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 pool of resources allowed for transmission of the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources. synchronizing a clock at the UE based at least in part on the sidelink synchronization signal; and A method comprising:

16. 16. The method of claim 15, wherein the pool of resources further comprises system-wide resources reserved for sidelink synchronization signal transmissions.

17. the subset of resources comprises at least a portion of the UE-specific resources; or the subset of resources comprises at least a portion of the reserved system-wide resources; or Any combination thereof, 16. The method of claim 15.

18. The method of claim 15 , wherein the subset of resources comprises at least a portion of the UE-specific resources.

19. sending a request for the sidelink synchronization signal to the peer sidelink UE; 16. The method of claim 15, wherein the sidelink synchronization signal is received in an on-demand manner in response to the request.

20. The method of claim 15 , wherein the receiving repeats periodically.

21. said periodic receiving; receiving a first set of synchronization signals according to a first periodicity; receiving a second set of synchronization signals according to a second periodicity; 21. The method of claim 20.

22. the first periodicity is higher than the second periodicity; the first set of synchronization signals is received on a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmission; 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.

22. The method of claim 21.

23. the periodic transmitting receiving a first set of synchronization signals according to a first periodicity; receiving a second set of synchronization signals in an on-demand manner; 21. The method of claim 20, comprising:

24. the first set of synchronization signals is received on a first portion of the subset of resources corresponding to system-wide resources reserved for sidelink synchronization signal transmission; 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.

24. The method of claim 23.

25. 16. The method of claim 15, wherein the pool of resources and the subset of resources each comprise resources defined in terms of a combination of time and frequency.

26. receiving an indication signal from the peer sidelink UE indicating the subset of the pool of resources; The method of claim 15 further comprising:

27. 1. A method of operating a user equipment (UE), comprising: sending a synchronization request message to at least one peer sidelink UE; receiving at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the transmitting; and A method comprising:

28. 28. The method of claim 27, wherein the transmitting comprises transmitting the synchronization request message on a sidelink communication channel as a Medium Access Control (MAC) Command Element (CE).

29. 28. The method of claim 27, wherein said transmitting comprises transmitting the synchronization request message as via unicast, multicast or broadcast.

30. determining that the UE has transitioned from being synchronized with respect to a network clock to being not synchronized with respect to the network clock; the transmitting is performed in response to the determining.

28. The method of claim 27.

31. determining that a quality associated with a synchronization source of the UE has fallen below a threshold; the transmitting is performed in response to the determining.

28. The method of claim 27.

32. 1. A method of operating a user equipment (UE), comprising: receiving a synchronization request message from a peer sidelink UE; transmitting at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message; A method comprising:

33. 33. The method of claim 32, wherein the receiving receives the synchronization request message on a sidelink communication channel as a Medium Access Control (MAC) Command Element (CE).

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

35. A user equipment (UE), means for identifying a pool of resources on which sidelink synchronization signals are allowed to be transmitted, said pool of resources comprising at least UE-specific resources. means for transmitting a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of said pool of resources; A user equipment (UE) comprising:

36. A user equipment (UE), means for receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a pool of resources allowed for transmission of the sidelink synchronization signal, said pool of resources comprising at least UE-specific resources. means for synchronizing a clock at the UE based at least in part on the sidelink synchronization signal; and A user equipment (UE) comprising:

37. A user equipment (UE), means for transmitting a synchronization request message to at least one peer sidelink UE; means for receiving at least one sidelink synchronization signal from the at least one peer sidelink UE in response to said transmitting; and A user equipment (UE) comprising:

38. A user equipment (UE), means for receiving a synchronization request message from a peer sidelink UE; means for transmitting at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message; A user equipment (UE) comprising:

39. A user equipment (UE), Memory and at least one transceiver; at least one processor coupled to the memory and the at least one transceiver; wherein the at least one processor identifying a pool of resources allowed for transmission of a sidelink synchronization signal, said pool of resources comprising at least UE-specific resources; transmitting, via the at least one transceiver, a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the pool of resources; and A user equipment (UE) configured to:

40. A user equipment (UE), Memory and at least one transceiver; at least one processor coupled to the memory and the at least one transceiver; wherein the at least one processor receiving a sidelink synchronization signal from a peer sidelink UE based on a subset of a pool of resources allowed for transmission of the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources. synchronizing a clock at the UE based at least in part on the sidelink synchronization signal; and A user equipment (UE) configured to:

41. A user equipment (UE), Memory and at least one transceiver; at least one processor coupled to the memory and the at least one transceiver; wherein the at least one processor: transmitting a synchronization request message to at least one peer sidelink UE via the at least one transceiver; receiving at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the transmission; and A user equipment (UE) configured to:

42. A user equipment (UE), Memory and at least one transceiver; at least one processor coupled to the memory and the at least one transceiver; wherein the at least one processor: receiving a synchronization request message from a peer sidelink UE; transmitting at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message; A user equipment (UE) configured to:

43. 1. A non-transitory computer-readable medium containing instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising: at least one instruction for configuring the UE to identify a pool of resources on which sidelink synchronization signals are allowed to be transmitted, the pool of resources comprising at least UE-specific resources. at least one instruction for configuring the UE to transmit a sidelink synchronization signal to one or more peer sidelink UEs based on a subset of the pool of resources; 1. A non-transitory computer-readable medium comprising:

44. 1. A non-transitory computer-readable medium containing instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising: at least one instruction for configuring the UE to receive a sidelink synchronization signal from a peer sidelink UE based on a subset of a pool of resources allowed for transmission of the sidelink synchronization signal, the pool of resources comprising at least UE-specific resources. at least one instruction configuring the UE to synchronize a clock at the UE based at least in part on the sidelink synchronization signal; 1. A non-transitory computer-readable medium comprising:

45. 1. A non-transitory computer-readable medium containing instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising: at least one instruction configuring the UE to send a synchronization request message to at least one peer sidelink UE; at least one instruction configuring the UE to receive at least one sidelink synchronization signal from the at least one peer sidelink UE in response to the transmission; 1. A non-transitory computer-readable medium comprising:

46. 1. A non-transitory computer-readable medium containing instructions stored thereon that, when executed by a user equipment (UE), cause the UE to perform an action, the instructions comprising: at least one instruction for configuring the UE to receive a synchronization request message from a peer sidelink UE; and at least one instruction configuring the UE to transmit at least one sidelink synchronization signal to the peer sidelink UE in response to the synchronization request message; 1. A non-transitory computer-readable medium comprising:

Images