Reference timing determination based on sidelink propagation delay

In an embodiment, a UE establishes, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops. The UE determines estimates a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP) irrespective of whether the UE remains synchronized with respect to the network clock.

TECHNICAL FIELD

Various aspects described herein generally relate to reference timing determination based on sidelink propagation delay.

BACKGROUND

Some wireless communication networks, such as 5G, support operation at very high and even extremely-high frequency (EHF) bands, such as millimeter wave (mmW) frequency bands (generally, wavelengths of 1 mm to 10 mm, or 30 to 300 GHz). These extremely high frequencies may support very high throughput such as up to six gigabits per second (Gbps). One of the challenges for wireless communication at very high or extremely high frequencies, however, is that a significant propagation loss may occur due to the high frequency. As the frequency increases, the wavelength may decrease, and the propagation loss may increase as well. At mmW frequency bands, the propagation loss may be severe. For example, the propagation loss may be on the order of 22 to 27 dB, relative to that observed in either the 2.4 GHz, or 5 GHz bands.

SUMMARY

An embodiment is directed to a method of operating a user equipment (UE), comprising establishing, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, estimating, while the UE is synchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and determining, while the UE is synchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

Another embodiment is directed to a method of operating a user equipment (UE), comprising establishing, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, estimating, while the UE is unsynchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and determining, while the UE is unsynchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

Another embodiment is directed to a user equipment (UE), comprising means for establishing, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, means for estimating, while the UE is synchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and means for determining, while the UE is synchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

Another embodiment is directed to a user equipment (UE), comprising means for establishing, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, means for means for estimating, while the UE is unsynchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and means for determining, while the UE is unsynchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

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 the transceiver, the at least one processor configured to establish, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, estimate, while the UE is synchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and determine, while the UE is synchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

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 the transceiver, the at least one processor configured to establish, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, estimate, while the UE is unsynchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and determine, while the UE is unsynchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

Another embodiment is directed to a non-transitory computer-readable medium containing instructions stored thereon, which, when executed by a user equipment (UE), cause the UE to perform actions, the instructions comprising at least one instruction configure to cause the UE to establish, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, at least one instruction configure to cause the UE to estimate, while the UE is synchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and at least one instruction configure to cause the UE to determine, while the UE is synchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

Another embodiment is directed to a non-transitory computer-readable medium containing instructions stored thereon, which, when executed by a user equipment (UE), cause the UE to perform actions, the instructions comprising at least one instruction configure to cause the UE to establish, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops, at least one instruction configure to cause the UE to estimate, while the UE is unsynchronized with respect to a network clock, a propagation delay between the UE and the peer sidelink UE based in part upon a relationship between a propagation time, between the UE and the peer sidelink UE, and Reference Signal Received Power (RSRP), and at least one instruction configure to cause the UE to determine, while the UE is unsynchronized with respect to the network clock, a reference timing based on the estimated propagation delay.

DETAILED DESCRIPTION

Various aspects described herein generally relate to reference timing determination based on sidelink propagation delay.

These and other aspects are disclosed in the following description and related drawings to show specific examples relating to exemplary aspects. Alternate aspects will be apparent to those skilled in the pertinent art upon reading this disclosure, 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 so as to not obscure the relevant details of the aspects disclosed herein.

The terminology used herein describes particular aspects only and should not be construed to limit any aspects disclosed herein. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Those skilled in the art will further 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 preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Further, various aspects may be described in terms of sequences of actions to be performed by, for example, elements of a computing device. Those skilled in the art will recognize that various actions described herein can be performed by specific circuits (e.g., an application specific integrated circuit (ASIC)), by program instructions being executed by one or more processors, or by a combination of both. Additionally, these sequences of actions described herein can be considered to be embodied entirely within any form of non-transitory computer-readable medium having stored thereon a corresponding set of computer instructions that upon execution would cause an associated processor to perform the functionality described herein. Thus, the various aspects described herein may be embodied in a number of different forms, all of which have been contemplated to be within the scope of the claimed subject matter. In addition, for each of the aspects described herein, the corresponding form of any such aspects may be described herein as, for example, “logic configured to” and/or other structural components configured to perform the described action.

As used herein, the terms “user equipment” (or “UE”), “user device,” “user terminal,” “client device,” “communication device,” “wireless device,” “wireless communications device,” “handheld device,” “mobile device,” “mobile terminal,” “mobile station,” “handset,” “access terminal,” “subscriber device,” “subscriber terminal,” “subscriber station,” “terminal,” and variants thereof may interchangeably refer to any suitable mobile or stationary device that can receive wireless communication and/or navigation signals. These terms are also intended to include devices which communicate with another device that can receive wireless communication and/or navigation signals such as by short-range wireless, infrared, wireline connection, or other connection, regardless of whether satellite signal reception, assistance data reception, and/or position-related processing occurs at the device or at the other device. In addition, 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), and through the core network the UEs can be connected with external networks such as the Internet and with other UEs. Of course, other mechanisms of connecting to the core network and/or the Internet are also possible for the UEs, such as over a wired access network, a wireless local area network (WLAN) (e.g., based on IEEE 802.11, etc.) and so on. UEs can be embodied by any of a number of types of devices including but not limited to printed circuit (PC) cards, compact flash devices, external or internal modems, wireless or wireline phones, smartphones, tablets, tracking devices, asset tags, and so on. A communication link through which UEs can send signals to a RAN is called an uplink channel (e.g., a reverse traffic channel, a reverse control channel, an access channel, etc.). A communication link through which the RAN can send signals to UEs is called 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) can refer to either an uplink/reverse or downlink/forward traffic channel.

According to various aspects,FIG. 1illustrates an exemplary wireless communications system100. The wireless communications system100(which may also be referred to as a wireless wide area network (WWAN)) may include various base stations102and various UEs104. The base stations102may include macro cells (high power cellular base stations) and/or small cells (low power cellular base stations), wherein the macro cells may include Evolved NodeBs (eNBs), where the wireless communications system100corresponds to an LTE network, or gNodeBs (gNBs), where the wireless communications system100corresponds to a 5G network or a combination of both, and the small cells may include femtocells, picocells, microcells, etc.

The base stations102may collectively form a Radio Access Network (RAN) and interface with an Evolved Packet Core (EPC) or Next Generation Core (NGC) through backhaul links. In addition to other functions, the base stations102may perform functions that relate to one or more of transferring user data, radio channel ciphering and deciphering, 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 service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations102may communicate with each other directly or indirectly (e.g., through the EPC/NGC) over backhaul links134, which may be wired or wireless.

The base stations102may wirelessly communicate with the UEs104. Each of the base stations102may provide communication coverage for a respective geographic coverage area110. In an aspect, although not shown inFIG. 1, geographic coverage areas110may be subdivided into a plurality of cells (e.g., three), or sectors, each cell corresponding to a single antenna or array of antennas of a base station102. As used herein, the term “cell” or “sector” may correspond to one of a plurality of cells of a base station102, or to the base station102itself, depending on the context.

While neighboring macro cell geographic coverage areas110may partially overlap (e.g., in a handover region), some of the geographic coverage areas110may be substantially overlapped by a larger geographic coverage area110. For example, a small cell base station102′ may have a geographic coverage area110′ that substantially overlaps with the geographic coverage area110of one or more macro cell base stations102. A network that includes both small cell and macro cells may be known as a heterogeneous network. A heterogeneous network may also include Home eNBs (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). The communication links120between the base stations102and the UEs104may include uplink (UL) (also referred to as reverse link) transmissions from a UE104to a base station102and/or downlink (DL) (also referred to as forward link) transmissions from a base station102to a UE104. The communication links120may use MIMO antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL).

The small cell base station102′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell base station102′ may employ LTE or 5G technology and use the same 5 GHz unlicensed frequency spectrum as used by the WLAN AP150. The small cell base station102′, employing LTE/5G in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network. LTE in an unlicensed spectrum may be referred to as LTE-unlicensed (LTE-U), licensed assisted access (LAA), or MulteFire.

According to various aspects,FIG. 2Aillustrates an example wireless network structure200. For example, an NGC210can be viewed functionally as control plane functions214(e.g., UE registration, authentication, network access, gateway selection, etc.), and user plane functions212(e.g., UE gateway function, access to data networks, Internet protocol (IP) routing, etc.), which operate cooperatively to form the core network. User plane interface (NG-U)213and control plane interface (NG-C)215connect the gNB222to the NGC210and specifically to the control plane functions214and user plane functions212. In an additional configuration, an eNB224may also be connected to the NGC210via NG-C215to the control plane functions214and NG-U213to user plane functions212. Further, eNB224may directly communicate with gNB222via a backhaul connection223. Accordingly, in some configurations, the New RAN220may only have one or more gNBs222, while other configurations include one or more of both eNBs224and gNBs222. Either gNB222or eNB224may communicate with UEs240(e.g., any of the UEs depicted inFIG. 1, such as UEs104, UE152, UE182, UE190, etc.). Another optional aspect may include a location server230that may be in communication with the NGC210to provide location assistance for UEs240. The location server230can be implemented as a plurality of structurally separate servers, or alternately may each correspond to a single server. The location server230can be configured to support one or more location services for UEs240that can connect to the location server230via the core network, NGC210, and/or via the Internet (not illustrated). Further, the location server230may be integrated into a component of the core network, or alternatively may be external to the core network.

According to various aspects,FIG. 2Billustrates another example wireless network structure250. For example, an NGC260can be viewed functionally as control plane functions, an access and mobility management function (AMF)264and user plane functions, and a session management function (SMF)262, which operate cooperatively to form the core network. User plane interface263and control plane interface265connect the eNB224to the NGC260and specifically to AMF264and SMF262. In an additional configuration, a gNB222may also be connected to the NGC260via control plane interface265to AMF264and user plane interface263to SMF262. Further, eNB224may directly communicate with gNB222via the backhaul connection223, with or without gNB direct connectivity to the NGC260. Accordingly, in some configurations, the New RAN220may only have one or more gNBs222, while other configurations include one or more of both eNBs224and gNBs222. Either gNB222or eNB224may communicate with UEs240(e.g., any of the UEs depicted inFIG. 1, such as UEs104, UE182, UE190, etc.). Another optional aspect may include a location management function (LMF)270, which may be in communication with the NGC260to provide location assistance for UEs240. The LMF270can be implemented as a plurality of separate servers (e.g., physically separate servers, different software modules on a single server, different software modules spread across multiple physical servers, etc.), or alternately may each correspond to a single server. The LMF270can be configured to support one or more location services for UEs240that can connect to the LMF270via the core network, NGC260, and/or via the Internet (not illustrated).

According to various aspects,FIG. 3Aillustrates an exemplary base station (BS)310(e.g., an eNB, a gNB, a small cell AP, a WLAN AP, etc.) in communication with an exemplary UE350(e.g., any of the UEs depicted inFIG. 1, such as UEs104, UE152, UE182, UE190, etc.) in a wireless network. In the DL, IP packets from the core network (NGC210/EPC260) may be provided to a controller/processor375. The controller/processor375implements 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/processor375provides RRC layer functionality associated with broadcasting of system information (e.g., master information block (MIB), system information blocks (SIBs)), 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 functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), 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 functionality associated with mapping between logical channels and transport channels, scheduling information reporting, error correction, priority handling, and logical channel prioritization.

The processing system359can be associated with a memory360that stores program codes and data. The memory360may be referred to as a non-transitory computer-readable medium. In the UL, the processing system359provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the core network. The processing system359is also responsible for error detection.

Channel estimates derived by the channel estimator358from a reference signal or feedback transmitted by the base station310may be used by the TX processor368to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor368may be provided to different antenna352via separate transmitters354. Each transmitter354may modulate an RF carrier with a respective spatial stream for transmission. In an aspect, the transmitters354and the receivers354may be one or more transceivers, one or more discrete transmitters, one or more discrete receivers, or any combination thereof.

The UL transmission is processed at the base station310in a manner similar to that described in connection with the receiver function at the UE350. Each receiver318receives a signal through its respective antenna320. Each receiver318recovers information modulated onto an RF carrier and provides the information to a RX processor370. In an aspect, the transmitters318and the receivers318may be one or more transceivers, one or more discrete transmitters, one or more discrete receivers, or any combination thereof.

The processing system375can be associated with a memory376that stores program codes and data. The memory376may be referred to as a non-transitory computer-readable medium. In the UL, the processing system375provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE350. IP packets from the processing system375may be provided to the core network. The processing system375is also responsible for error detection.

FIG. 3Billustrates an exemplary server300B. In an example, the server300B may correspond to one example configuration of the location server230described above. InFIG. 3B, the server300B includes a processor301B coupled to volatile memory302B and a large capacity nonvolatile memory, such as a disk drive303B. The server300B may also include a floppy disc drive, compact disc (CD) or DVD disc drive306B coupled to the processor301B. The server300B may also include network access ports304B coupled to the processor301B for establishing data connections with a network307B, such as a local area network coupled to other broadcast system computers and servers or to the Internet.

FIG. 4illustrates an exemplary wireless communications system400according to various aspects of the disclosure. In the example ofFIG. 4, a UE404, which may correspond to any of the UEs described above with respect toFIG. 1(e.g., UEs104, UE182, UE190, etc.), is attempting to calculate an estimate of its position, or assist another entity (e.g., a base station or core network component, another UE, a location server, a third party application, etc.) to calculate an estimate of its position. The UE404may communicate wirelessly with a plurality of base stations402a-d(collectively, base stations402), which may correspond to any combination of base stations102or180and/or WLAN AP150inFIG. 1, using RF signals and standardized protocols for the modulation of the RF signals and the exchange of information packets. By extracting different types of information from the exchanged RF signals, and utilizing the layout of the wireless communications system400(i.e., the base stations locations, geometry, etc.), the UE404may determine its position, or assist in the determination of its position, in a predefined reference coordinate system. In an aspect, the UE404may specify its position using a two-dimensional coordinate system; however, the aspects disclosed herein are not so limited, and may also be applicable to determining positions using a three-dimensional coordinate system, if the extra dimension is desired. Additionally, whileFIG. 4illustrates one UE404and four base stations402, as will be appreciated, there may be more UEs404and more or fewer base stations402.

To support position estimates, the base stations402may be configured to broadcast reference RF signals (e.g., Positioning Reference Signals (PRS), Cell-specific Reference Signals (CRS), Channel State Information Reference Signals (CSI-RS), synchronization signals, etc.) to UEs404in their coverage areas to enable a UE404to measure reference RF signal timing differences (e.g., OTDOA or RSTD) between pairs of network nodes and/or to identify the beam that best excite the LOS or shortest radio path between the UE404and the transmitting base stations402. Identifying the LOS/shortest path beam(s) is of interest not only because these beams can subsequently be used for OTDOA measurements between a pair of base stations402, but also because identifying these beams can directly provide some positioning information based on the beam direction. Moreover, these beams can subsequently be used for other position estimation methods that require precise ToA, such as round-trip time estimation based methods.

As used herein, a “network node” may be a base station402, a cell of a base station402, a remote radio head, an antenna of a base station402, where the locations of the antennas of a base station402are distinct from the location of the base station402itself, or any other network entity capable of transmitting reference signals. Further, as used herein, a “node” may refer to either a network node or a UE.

A location server (e.g., location server230) may send assistance data to the UE404that includes an identification of one or more neighbor cells of base stations402and configuration information for reference RF signals transmitted by each neighbor cell. Alternatively, the assistance data can originate directly from the base stations402themselves (e.g., in periodically broadcasted overhead messages, etc.). Alternatively, the UE404can detect neighbor cells of base stations402itself without the use of assistance data. The UE404(e.g., based in part on the assistance data, if provided) can measure and (optionally) report the OTDOA from individual network nodes and/or RSTDs between reference RF signals received from pairs of network nodes. Using these measurements and the known locations of the measured network nodes (i.e., the base station(s)402or antenna(s) that transmitted the reference RF signals that the UE404measured), the UE404or the location server can determine the distance between the UE404and the measured network nodes and thereby calculate the location of the UE404.

The term “position estimate” is used herein to refer to an estimate of a position for a UE404, which may be geographic (e.g., may comprise a latitude, longitude, and possibly altitude) or civic (e.g., may comprise a street address, building designation, or precise point or area within or nearby to a building or street address, such as a particular entrance to a building, a particular room or suite in a building, or a landmark such as a town square). A position estimate may also be referred to as a “location,” a “position,” a “fix,” a “position fix,” a “location fix,” a “location estimate,” a “fix estimate,” or by some other term. The means of obtaining a location estimate may be referred to generically as “positioning,” “locating,” or “position fixing.” A particular solution for obtaining a position estimate may be referred to as a “position solution.” A particular method for obtaining a position estimate as part of a position solution may be referred to as a “position method” or as a “positioning method.”

The term “base station” may refer to a single physical transmission point or to multiple physical transmission points that may or may not be co-located. For example, where the term “base station” refers to a single physical transmission point, the physical transmission point may be an antenna of the base station (e.g., base station402) corresponding to a cell of the base station. Where the term “base station” refers to multiple co-located physical transmission points, the physical transmission points may be an array of antennas (e.g., as in a MIMO system or where the base station employs beamforming) of the base station. Where the term “base station” refers to multiple non-co-located physical transmission points, the physical transmission points may be a Distributed Antenna System (DAS) (a network of spatially separated antennas connected to a common source via a transport medium) or a Remote Radio Head (RRH) (a remote base station connected to a serving base station). Alternatively, the non-co-located physical transmission points may be the serving base station receiving the measurement report from the UE (e.g., UE404) and a neighbor base station whose reference RF signals the UE is measuring. Thus,FIG. 4illustrates an aspect in which base stations402aand402bform a DAS/RRH420. For example, the base station402amay be the serving base station of the UE404and the base station402bmay be a neighbor base station of the UE404. As such, the base station402bmay be the RRH of the base station402a.The base stations402aand402bmay communicate with each other over a wired or wireless link422.

To accurately determine the position of the UE404using the OTDOAs and/or RSTDs between RF signals received from pairs of network nodes, the UE404needs to measure the reference RF signals received over the LOS path (or the shortest NLOS path where an LOS path is not available), between the UE404and a network node (e.g., base station402, antenna). However, RF signals travel not only by the LOS/shortest path between the transmitter and receiver, but also over a number of other paths as the RF signals spread out from the transmitter and reflect off other objects such as hills, buildings, water, and the like on their way to the receiver. Thus,FIG. 4illustrates a number of LOS paths410and a number of NLOS paths412between the base stations402and the UE404. Specifically,FIG. 4illustrates base station402atransmitting over an LOS path410aand an NLOS path412a,base station402btransmitting over an LOS path410band two NLOS paths412b,base station402ctransmitting over an LOS path410cand an NLOS path412c,and base station402dtransmitting over two NLOS paths412d.As illustrated inFIG. 4, each NLOS path412reflects off some object430(e.g., a building). As will be appreciated, each LOS path410and NLOS path412transmitted by a base station402may be transmitted by different antennas of the base station402(e.g., as in a MIMO system), or may be transmitted by the same antenna of a base station402(thereby illustrating the propagation of an RF signal). Further, as used herein, the term “LOS path” refers to the shortest path between a transmitter and receiver, and may not be an actual LOS path, but rather, the shortest NLOS path.

In an aspect, one or more of base stations402may be configured to use beamforming to transmit RF signals. In that case, some of the available beams may focus the transmitted RF signal along the LOS paths410(e.g., the beams produce highest antenna gain along the LOS paths) while other available beams may focus the transmitted RF signal along the NLOS paths412. A beam that has high gain along a certain path and thus focuses the RF signal along that path may still have some RF signal propagating along other paths; the strength of that RF signal naturally depends on the beam gain along those other paths. An “RF signal” comprises an electromagnetic wave that transports information through the space between the transmitter and the receiver. As used herein, a transmitter may transmit a single “RF signal” or multiple “RF signals” to a receiver. However, as described further below, the receiver may receive multiple “RF signals” corresponding to each transmitted RF signal due to the propagation characteristics of RF signals through multipath channels.

Where a base station402uses beamforming to transmit RF signals, the beams of interest for data communication between the base station402and the UE404will be the beams carrying RF signals that arrive at UE404with the highest signal strength (as indicated by, e.g., the Received Signal Received Power (RSRP) or SINR in the presence of a directional interfering signal), whereas the beams of interest for position estimation will be the beams carrying RF signals that excite the shortest path or LOS path (e.g., an LOS path410). In some frequency bands and for antenna systems typically used, these will be the same beams. However, in other frequency bands, such as mmW, where typically a large number of antenna elements can be used to create narrow transmit beams, they may not be the same beams.

Sidelink communications relate to peer-to-peer communications between UEs in accordance with 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 UE). Generally, the peer UEs that belong to a particular sidelink communications network attempt to maintain a common reference time to facilitate sidelink communications among the peer UEs.

In some designs, sidelink communication links are decoupled from sidelink synchronization links. For example, two peer UEs participating in sidelink communication with each other are not required 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 at each synchronization period). In such an implementation, there is no beam management functionality that carries over from sidelink synchronization to sidelink communication (e.g., because the sidelink synchronization signaling is transported via an SFN-based manner).

In some designs, SyncRef UEs can be connected directly to a base station (e.g., gNB) or Global Navigation Satellite System (GNSS), as shown below with respect toFIG. 5. In other designs, SyncRef UEs can be indirectly connected to the base station or GNSS (e.g., more than one hop away via one or more peer UEs in the sidelink communications network). In yet other designs, SyncRef UEs can act as independent synchronization sources without any direct or indirect connection to a base station or GNSS.

FIG. 5illustrates a sidelink communications network500in accordance with an embodiment of the disclosure. Referring toFIG. 5, the sidelink communications network500comprises a GNSS satellite502and UEs504,506,508and510. UE504is synchronized with a network clock of the GNSS satellite502based on receipt of various GNSS signals. UE504is connected to UE506via a sidelink communications link512, UE506is connected to UE508via a sidelink communications link514, and UE508is connected to UE510via a sidelink communications link516. While not shown, one or more of UEs504-510may also be connected to a terrestrial communications network. InFIG. 5, UE504corresponds to the SyncRef UE. Also, while not shown, UE510may be further connected to yet another peer UE over a sidelink communications link518, and so on.

As noted above, certain networks reserve2resources for sidelink synchronization signaling. In an example of such a system, the sidelink synchronization signaling over the sidelink communications links512-516may be configured as shown in Table 1 (in Table 1, INC corresponds to in-coverage indicator, which indicates if the UE is directly synchronized either to GNSS or eNB), as follows:

As shown in Table 1, the Subframe used for the SLSS transmission alternates at each hop in the sidelink communications network500between Resources 1 and 2 because there are only two available resources for the SLSS transmissions.

FIG. 6illustrates a sidelink communications network600in accordance with another embodiment of the disclosure. InFIG. 6, UE506and UE508lose their connection to each other as shown at602. Hence, UEs508and510are disconnected from the GNSS-synchronized UE504which was acting as the SyncRef UE in the sidelink communications network500ofFIG. 5. UEs508-510thereby form a new GNSS-independent sidelink communications network. In an example, assume that UE508becomes the SyncRef UE for the new GNSS-independent sidelink communications network. Also, while not shown, UE510may be further connected to yet another peer UE over a sidelink communications link606, and so on.

In this case, in a system whereby 2 resources are reserved for sidelink synchronization signaling, the sidelink synchronization signaling over sidelink communications links604-606may be configured as shown in Table 2, as follows:

For a UE that derives its synchronization from a SyncRef UE, a reference timing is the ‘received timing’ of the SyncRef UE's synchronization signals (e.g., SFNed) at the receiver (e.g., unsynchronized UE), in a manner that is analogous 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, sidelink communications networks do not support a timing advance (TA) as in the case of UE-to-gNB uplink. In such sidelink communications networks, the propagation delay along each hop in the sidelink communications network contributes to a timing error between the SyncRef UE and each successive UE at each hop of the sidelink communications 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., hops from GNSS satellite502or terrestrial base station, or the SyncRef UE itself in the case of an unsynchronized network).

FIG. 7illustrates successively higher timing errors along hops of the sidelink communications network500in accordance with an embodiment of the disclosure. In particular, timing errors are shown inFIG. 7relative to a particular radio frame denoted as radio frame X. Referring toFIG. 7, UE504's timing is set to the GNSS timing, UE506's timing is set to UE504's timing plus a propagation delay tp1, UE508's timing is set to UE506's timing plus a propagation delay tp2, UE510's timing is set to UE508's timing plus a propagation delay tp3, and so on. Accordingly, the further away a peer UE from the SyncRef UE in terms of hops, the greater the timing error. Moreover, whileFIG. 7is described with respect to the GNSS-synchronized sidelink communications network500ofFIG. 5, the same problem occurs in sidelink communications networks which lack synchronization with a network clock.

FIG. 8illustrates an example frame structure800that supports sidelink synchronization signals in accordance with an embodiment of the disclosure. As shown inFIG. 8, the frame structure800includes 14 subframes, with subframes2and5allocated to sidelink secondary synchronization signals (S-SSS), subframes3-4allocated to sidelink primary synchronization signals (S-PSS), subframes6-13allocated to PSBCH and subframe14functioning as a gap. In some designs, the sidelink sync signal block (S-SSB, which comprises S-PSS and S-SSS) periodicity may be 160 ms, although this period may be configurable. The periodicity in this context refers to how often the frame structure800is repeated (e.g., every 160 ms). In some designs, the frame structure800may be used to support vehicle-based communications, such as NR vehicle-to-everything (V2X) communications. Among other things, the frame structure800may be used for sidelink communication-related functionality, including resource selection, S-SSB ID determination, SyncRef UE selection and/or re-selection, and so on.

Embodiments of the disclosure are directed to mechanisms by which a reference timing can be determined in a sidelink communications network that takes the propagation delay over one or more hops into account. In some designs, the reference timing can be calculated in this manner while a SyncRef UE is synchronized with respect to a network clock (e.g., GNSS clock or terrestrial network clock), while in other designs, the reference timing can be calculated in this manner while a SyncRef UE IS unsynchronized with respect to the network clock.

FIG. 9illustrates an exemplary process900of determining a reference timing according to an aspect of the disclosure. The process900ofFIG. 9is performed by a UE, which may correspond to any of the above-noted UEs (e.g., UE240,350,504,506,508,510, etc.). At902, the UE (e.g., controller/processor359, antenna(s)352, receiver(s)354, RX processor356, transmitter(s)354, and/or TX processor368) establishes, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops.

At904, the UE (e.g., controller/processor359, antenna(s)352, receiver(s)354, RX processor356, transmitter(s)354, and/or TX processor368) optionally determines while the UE is synchronized with respect to a network clock (e.g., a GNSS clock, a terrestrial network clock, etc.), a propagation delay parameter between the UE and a peer sidelink UE. In some designs, the determination performed by the UE at904is optional because the propagation delay parameter can instead be obtained at least in part via crowdsourcing from one or more other UEs. For example, the propagation delay parameter can be determined by another UE that is (or was previously) located in proximity to the UE's current location, and then forwarded to the UE (e.g., either directly or indirectly). In another example, the propagation delay parameter may be averaged from propagation delay parameters determined by a plurality of such UEs (e.g., a weighted average, whereby more recently determined propagation delay parameters or propagation delay parameters determined in closer proximity to the UE's current location are prioritized more highly than other propagation delay parameters, etc.). In a further example, the propagation delay parameter may be determined by the UE at904and then may itself be averaged or weighted based on one or more crowdsourced propagation delay parameter(s). In some designs, irrespective of whether the UE or some other UE or combination of UEs determines the propagation delay parameter, each UE whose measurements contribute to the propagation delay parameter in some manner is synchronized with respect to the network clock when such measurements are made. In one embodiment, the crowdsource information may be collated and averaged at a server, a network edge and/or road-side unit (RSU), and thereafter provided to the UE.

With respect to904, the network clock synchronization can either be direct or indirect. For example, in context withFIG. 5, UE504is directly synchronized with the GNSS clock of GNSS satellite502, whereas UEs506-510are indirectly synchronized with the GNSS clock of GNSS satellite502via their respective sidelink hops to UE504. In context withFIG. 6, UE504is directly synchronized with the GNSS clock of GNSS satellite502, UE506is indirectly synchronized with the GNSS clock of GNSS satellite502via its respective sidelink hop to UE504, and UEs508-508are unsynchronized with the GNSS clock of GNSS satellite502.

At906, the UE (e.g., controller/processor359) estimates, while the UE is synchronized with respect to the network clock, a propagation delay between the UE and the peer sidelink UE based in part upon the propagation delay parameter. As will be described below in more detail, the propagation delay parameter can correspond to a calculated propagation delay between the UE and the peer sidelink UE. In this case, the estimating of906simply reuses the propagation delay that was determined at904. Alternatively, the propagation delay parameter can correspond to a relationship between various metrics by which the propagation delay (or propagation time) can be estimated. In this case, the estimating of906may involve determining these metrics and then estimating the propagation delay (or propagation time) as a function of the determined relationship. The relationship may be determined locally at the UE, or may be crowdsourced from one or more other UEs, or a combination thereof. These aspects will be explained in more detail below.

At908, the UE (e.g., controller/processor359) determines, while the UE is synchronized with respect to the network clock, a reference timing based on the estimated propagation delay. In an example, the reference timing determination908may be performed with respect to Radio Frame X as inFIG. 7, except a respective UE at each hop compensates for the propagation delay on that hop (tp1, tp2, or tp3) such that the Radio Frame X does not drift as the hop count increases as shown inFIG. 7.

FIG. 10illustrates an exemplary process1000of determining a reference timing according to another aspect of the disclosure. The process1000ofFIG. 10is performed by a UE, which may correspond to any of the above-noted UEs (e.g., UE240,350,504,506,508,510, etc.). At1002, the UE (e.g., controller/processor359, antenna(s)352, receiver(s)354, RX processor356, transmitter(s)354, and/or TX processor368) establishes, with a peer sidelink UE, at least one sidelink communications link that each comprises one or more hops.

At1004, the UE (e.g., controller/processor359, antenna(s)352, receiver(s)354, RX processor356, transmitter(s)354, and/or TX processor368) determines while the UE is synchronized with respect to a network clock (e.g., a GNSS clock, a terrestrial network clock, etc.), a propagation delay parameter between the UE and a peer sidelink UE. In an example,1002-1004may correspond to902-904ofFIG. 9. In some designs, the determination performed by the UE at1004is optional because the propagation delay parameter can instead be obtained at least in part via crowdsourcing from one or more other UEs. For example, the propagation delay parameter can be determined by another UE that is (or was previously) located in proximity to the UE's current location, and then forwarded to the UE (e.g., either directly or indirectly). In another example, the propagation delay parameter may be averaged from propagation delay parameters determined by a plurality of such UEs (e.g., a weighted average, whereby more recently determined propagation delay parameters or propagation delay parameters determined in closer proximity to the UE's current location are prioritized more highly than other propagation delay parameters, etc.). In a further example, the propagation delay parameter may be determined by the UE at1004and then may itself be averaged or weighted based on one or more crowdsourced propagation delay parameter(s). In some designs, irrespective of whether the UE or some other UE or combination of UEs determines the propagation delay parameter, each UE whose measurements contribute to the propagation delay parameter in some manner is synchronized with respect to the network clock when such measurements are made. In one embodiment, the crowdsource information may be collated and averaged at a server, a network edge and/or RSU and thereafter provided to the UE.

At some point after1004, assume that the UE becomes unsynchronized with respect to the network clock (e.g., as shown inFIG. 6with respect to UEs508and510). With respect to1006, the UE (e.g., controller/processor359) estimates, while the UE is unsynchronized with respect to the network clock, a propagation delay (or propagation time) between the UE and the peer sidelink UE based in part upon the propagation delay parameter that was determined while the UE was synchronized with respect to the network clock. Hence, even though the propagation delay parameter may be somewhat out-of-date, the propagation delay parameter is leveraged for some period of time. As will be appreciated described in more detail below, if the propagation delay parameter comprises a relationship between metrics, up-to-date values of those metrics can be ascertained and then applied to the predetermined relationship to derive an estimate of the propagation delay. Alternatively, if the propagation delay parameter corresponds to an earlier calculated propagation delay, that earlier calculated propagation delay (from when the UE1005was synchronized) can simply be used as the estimated propagation delay. The relationship may be determined locally at the UE, or may be crowdsourced from one or more other UEs, or a combination thereof.

At1008, the UE (e.g., controller/processor359) determines, while the UE is unsynchronized with respect to the network clock, a reference timing based on the estimated propagation delay. In an example, the reference timing determination1008may be performed with respect to Radio Frame X as inFIG. 7, except a respective UE at each hop compensates for the propagation delay on that hop (tp1, tp2, or tp3) such that the Radio Frame X does not drift as the hop count increases as shown inFIG. 7.

FIG. 11illustrates an example implementation of the processes900-1000in accordance with an embodiment of the disclosure. The exemplary process ofFIG. 11is described with respect to the embodiment whereby UE1and/or UE2determine their own respective propagation delay parameter(s) (e.g., propagation time to RSRP relationship). However, in other embodiments, the determination of the propagation delay parameter(s) may be at least partially crowdsourced.

At1102, a network (e.g., GNSS satellite502, base station310, etc.) transmits timing signal(s) that are based on a network clock, and UE2receives the timing signals at1104. At1106, UE2synchronizes with the network clock based on the received timing signal(s). At1108, UEs1and2establish a sidelink communications link (e.g., as in902ofFIG. 9 or 1002ofFIG. 10). At1110, UE1and/or UE2determine a propagation delay parameter between UEs1and2(e.g., as in904ofFIGS. 9 and 1004ofFIG. 10). At this point, UE2(and possibly UE1as well) is synchronized with respect to the network clock. At1112, UE1and/or UE2estimate a propagation delay based on the propagation delay parameter (e.g., as in906ofFIG. 9). At1114, UE1and/or UE2determine a reference timing based on the estimated propagation delay from1112(e.g., as in908ofFIG. 9).

Referring toFIG. 11, at1116, the network transmits timing signal(s) that are based on the network clock, but the timing signal(s) are lost at1118(i.e., not successfully received by UE2). At1120, both UEs1and2are unsynchronized with the network clock due to the loss of the timing signal(s). At1122, UE1and/or UE2estimate the propagation delay based on the propagation delay parameter determined at1110(e.g., as in1006ofFIG. 10). At1124, UE1and/or UE2determine a reference timing based on the estimated propagation delay from1122(e.g., as in908ofFIG. 9).

In some designs, the propagation delay parameter described above with respect toFIGS. 8-11may comprise a relationship between a propagation time and Reference Signal Received Power (RSRP). The RSRP is typically environmentally dependent so the above-noted relationship cannot be applied globally between peer UEs. However, a propagation-to-RSRP relationship may generally be reliable for some threshold period of time depending on the stability of the environment and UE mobility. In an example, the relationship can be computed while a SyncRef UE is synchronized with the network clock with a known location. At this time, RSRP is measured and parameters that characterize the propagation-to-RSRP relationship are calculated. One example propagation-to-RSRP relationship (or function f( )) is as follows:
RSRP=const*(distance)−alpha;
f(RSRP)=(RSRP/a)b,
whereby the parameters ‘a’ and ‘b’ can later be reused to estimate the propagation delay while the respective UEs are unsynchronized, const is a constant value based on the well known free-space path loss (FSPL) formula which derives from the Friis transmission formula, and alpha is a path-loss value (e.g., in free space alpha=2, in an environment with reflections such as multi-path alpha may range between 2.5 to 4, etc.).

In an example, sidelink synchronization signals can be used to derive the propagation-to-RSRP relationship. However, this is not strictly necessary, and other sidelink signals can also be used. For example, a DMRS over a sidelink communication channel can be used to derive the propagation-to-RSRP relationship (e.g., so long as the sidelink communication includes the synchronization status of the transmitting UE). Hence, any reference signal (e.g., DMRS, CSI-RS, etc.) or synchronization signals (SSB) from a transmitting UE that it itself synchronized (so that its Tx timing is accurate up to allowed limits) can be used to facilitate the determination of the propagation-to-RSRP relationship. Later, when the respective UEs lose their network clock synchronization, the RSRP (e.g., of sidelink synchronization signals) can be measured while unsynchronized with the predetermined propagation-to-RSRP relationship being used to estimate the propagation time (while unsynchronized).

More specifically, in some designs, when unsynchronized, the reference timing can be derived using a sidelink synchronization signal transmitted by a peer UE based on a function of the received timing of the synchronization signal from the peer UE, the RSRP of the sidelink synchronization signal, and an estimate of the propagation time using the predetermined propagation-to-RSRP relationship (f( )).

In one example, the timing reference determination at908or1008comprises:Estimating a first reference time (t1) as the time of reception of a synchronization signal transmitted by a SyncRef UE,Estimating the RSRP of the synchronization signal,Estimating a second reference time (t2) as the t2=t1−f−1(RSRP),Using the second reference time (t2) as the timing reference for transmission of sidelink physical signals and waveforms to one or more peer UE(s).

In another example, the determination of the propagation-to-RSRP relationship (f( )) may comprise determining a propagation time (tpd) estimate based on a location of UE and a location of the peer UE (e.g., while synchronized). In one case, where the location of the peer UE is known at the UE using location information included as part of a sidelink transmission from the peer UE. Such a transmission may occur at a time prior to the transmission of the synchronization signal, or at the same time (e.g., as part of a sidelink data channel). A RSRP estimate of the received sidelink signal is then determined. One or more parameters of a propagation-to-RSRP relationship (f( )) are then determined which equate (or map) the measured RSRP with the propagation time (tpd) estimate. In one example, where RSRP=f(tpd), f( ) has the parametric form f(tpd)=a*(tpd)b.

In another example, when synchronized, a quality of the synchronization between the peer UEs may be ascertained. In one example, the quality can be indicated (e.g., in sidelink synchronization signals) as a level between 0 and 1. For example, 1 can be used to designate high quality GNSS synchronization, where an expected timing error is small (e.g., less than 3 Ts, etc.). In another example, 0.5 can be used to designate lower quality GNSS synchronization, where an expected timing error is larger (e.g., less than 12 Ts, etc.). In some designs, the synchronization quality can be used as a weighting coefficient in the propagation-to-RSRP relationship (f( )).

In some designs, the propagation-to-RSRP relationship (f( )) may depend on the receive beam (e.g., spatial configuration of the receive beam). In this case, when synchronized, the propagation-to-RSRP relationship (f( )) is determined specific to a particular receive beam of the UE. Then, when unsynchronized, the propagation-to-RSRP relationship (f( )) is likewise used to determine the reference timing for that specific receive beam. For example, parameters (a,b) in the propagation-to-RSRP relationship (f( )) may be different based on whether a particular receive beam is LOS or NLOS. Specific recognition of whether a beam is LOS or NLOS is possible but not expressly required.

In some designs, the propagation delay parameter need not include the propagation-to-RSRP relationship (f( )) as described above. For example, when synchronized, a UE can estimate an arrival time of a sidelink synchronization signal from a SyncRef UE to determine a one-way propagation delay between the two UEs. It will be appreciated that there can sometimes be multiple SyncRef UEs, in which case the propagation delay can be estimated with respect to multiple SyncRef UEs. Then, when unsynchronized, the UE continues to receive the sidelink synchronization signals from the SyncRef UE(s) (e.g., some of which may stop transmitting the sidelink synchronization signal if out of coverage) and use the previously recorded propagation delay(s) to estimate the current propagation delay(s). So, while the above-noted propagation-to-RSRP relationship (f( )) relies upon a combination of old data and new data (e.g., the current RSRP), in this embodiment the ‘old’ propagation delay is simply re-used.

In further designs, the various operations described above with respect toFIGS. 9-10may be implemented via various “means”, such as particular hardware components of the associated UEs905and1005. For example, means for performing the establishing aspects of502,504,802and804may correspond to any combination of transceiver-related circuitry on the respective UEs, such as antenna(s)352, receiver(s)354, RX processor356, transmitter(s)354, Tx processor368, etc. of UE350ofFIG. 3A. In a further example, means for performing the determining and estimating aspects of904-908and1004-1008may corresponding to any combination of processor-related circuitry on the respective UEs, such as controller/processor359of UE350ofFIG. 3A.

While some of the embodiments are described above with respect to EN-DC mode, the various embodiments of the disclosure are also applicable with respect to other types of dual connectivity modes, such as such as NR-NR NR-LTE, etc. Moreover, while some of the embodiments are described with respect to specific numerologies (e.g., 15 kHz SCS), other embodiments may be directed to implementations whereby different numerologies are used (e.g., 30 kHz SCS, 60 kHz SCS, 120 kHz SCS, 240 kHz SCS, 480 kHz SCS, etc.).

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

While the foregoing disclosure shows illustrative aspects, those skilled in the art will appreciate that various changes and modifications could be made herein without departing from the scope of the disclosure as defined by the appended claims. Furthermore, in accordance with the various illustrative aspects described herein, those skilled in the art will appreciate that the functions, steps, and/or actions in any methods described above and/or recited in any method claims appended hereto need not be performed in any particular order. Further still, to the extent that any elements are described above or recited in the appended claims in a singular form, those skilled in the art will appreciate that singular form(s) contemplate the plural as well unless limitation to the singular form(s) is explicitly stated.