Patent Description:
Aspects of wireless communication may comprise direct communication between devices, such as in V2X, V2V, and/or other D2D communication. The present disclosure provides improvements in V2X, V2V, and/or other D2D technology.

3GPP Discussion & Decision document <NPL>" discusses SSSB design and synchronization procedures in synchronization mechanisms for NR V2X. <CIT> discuses a method of synchronising devices in a V2X system, wherein a plurality of synchronization signals are transmitted, and one of them is selected based on a priority. <CIT> discusses the issues associated with the accuracy of synchronisation of a radio frame and frequency of a user apparatus with a base station when the apparatus is out of coverage of the base station.

Embodiments of the invention are outlined in the appended independent claims. Further detailed embodiments are provided by the dependent claims. The following description and the annexed drawings set forth in detail example illustrative features of the one or more aspects.

The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations <NUM>, UEs <NUM>, an Evolved Packet Core (EPC) <NUM>, and a Core Network (e.g., 5GC) <NUM>.

The base stations <NUM> configured for <NUM> LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC <NUM> through backhaul links <NUM> (e.g., S1 interface). The base stations <NUM> configured for NR (collectively referred to as Next Generation RAN (NG-RAN)) may interface with Core Network <NUM> through backhaul links <NUM>. The base stations <NUM> may communicate directly or indirectly (e.g., through the EPC <NUM> or Core Network <NUM>) with each other over backhaul links <NUM> (e.g., X2 interface).

A network that includes both small cell and macro cells may be known as a heterogeneous network. 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). Some UEs <NUM> may communicate with each other using device-to-device (D2D) communication link <NUM>.

A base station <NUM>, whether a small cell <NUM>' or a large cell (e.g., macro base station), may include an eNB, gNodeB (gNB), or other type of base station. Some base stations <NUM>, such as a gNB, may operate in a traditional sub <NUM> spectrum, in millimeter wave (mmW) frequencies, and/or near mmW frequencies in communication with the UE <NUM>. When the gNB operates in mmW or near mmW frequencies, the gNB may be referred to as an mmW base station. The mmW base station, e.g., the base station <NUM>, may utilize beamforming <NUM> with the UE <NUM> to compensate for the extremely high path loss and short range.

The Core Network <NUM> may include a Access and Mobility Management Function (AMF) <NUM>, other AMFs <NUM>, a Session Management Function (SMF) <NUM>, and a User Plane Function (UPF) <NUM>. The AMF <NUM> is the control node that processes the signaling between the UEs <NUM> and the Core Network <NUM>.

The base station <NUM> provides an access point to the EPC <NUM> or Core Network <NUM> for a UE <NUM>.

Referring again to <FIG>, in some aspects, communication may also be transmitted and received directly between UEs <NUM>, such as between a Vehicle User Equipment (VUE), Road Side Unit (RSU) <NUM>, or other UE. The communication may be based on V2V, V2X, or other D2D communication, such as Proximity Services (ProSe). Aspects of the communication may be based on PC5 or sidelink communication. Some wireless communication networks include vehicle-based communication devices that can communicate from vehicle-to-vehicle (V2V), e.g., as illustrated at <NUM>; vehicle-to-RSU, as illustrated at <NUM>; vehicle-to-infrastructure (V2I) (e.g., from the vehicle-based communication device to road infrastructure nodes <NUM>), as illustrated at <NUM>; vehicle-to-network (V2N) (e.g., from the vehicle-based communication device to one or more network nodes, such as a base station), e.g., as illustrated at <NUM>; or a combination thereof along with other devices, which can be collectively referred to as vehicle-to-anything (V2X) communication. V2X communication may include cellular-vehicle-to-everything (C-V2X) communication. Referring again to <FIG>, in some aspects, a UE <NUM>, e.g., a transmitting Vehicle User Equipment (VUE) or other UE, may be configured to transmit messages directly to another UE <NUM>. The communication may be based on V2X or other D2D communication, such as ProSe, etc. V2X communication or other D2D communication may also be transmitted and received by other transmitting and receiving devices, such as Road Side Unit (RSU) <NUM>, etc. Aspects of the communication may be based on PC5 or sidelink communication e.g., as described in connection with the example in <FIG>.

In an example, referring to the V2X or other D2D communication between the devices (e.g., over a sidelink channel of communication link <NUM>) may be based on 3GPP LTE. Although examples may be provided for V2X or other D2D communication in connection with LTE, the concepts described herein may be applicable to other technologies such as V2X or other D2D communication based on <NUM> NR, LTE-A, CDMA, GSM, and other wireless technologies. In one example, LTE may support V2X communications (which may be referred to as "LTE-V2X") for safety messages communicated between vehicles and/or from vehicles to infrastructure, among other uses. As another example, an NR communication, such as <NUM> NR, may also support V2X (which may be referred to as "NR-V2X") for communications related to autonomous driving, among other uses.

In V2X communications, communication devices can communicate with one another and/or with infrastructure devices over a sidelink channel. Support of synchronization using synchronization signal blocks (SSBs) within synchronization signal bursts may be provided in communication technologies over the Uu interface (e.g., from base station <NUM>/<NUM> to user equipment (UE) <NUM>). In this regard, the UE <NUM> may receive SSBs and synchronize with the base station <NUM>/<NUM> for network communication and for V2X communication. In V2X or other D2D communications, however, the UEs <NUM> may be out of range of a base station <NUM>/<NUM>. In some cases, sidelink communications may be synchronized with a global navigation satellite system (GNSS) <NUM>, which may be received in signal <NUM>. In other cases, UEs <NUM>, as well as RSUs <NUM>, may transmit an SLSS directly to other UEs, which the other UEs may use for synchronization. The SLSS may have a timing based on GNSS <NUM>, for example. At times, coverage from a GNSS may also be unavailable. Thus, a RSU <NUM>, or other RSSD, may comprise an SLSS component <NUM> configured to receive, from a first neighbor device, a first SLSS. The RSSD synchronizes in time/frequency with the first neighbor device, and transmits a second SLSS. The second SLSS may be based on a synchronized timing and a synchronized frequency with the first neighbor device. A group of such RSSD may be provided that synchronize with at least one neighbor RSSD in order to provide coordinated synchronization information via SLSS.

<FIG> illustrates an example diagram <NUM> illustrating a sidelink subframe within a frame structure that may be used for sidelink communication, e.g., between UEs <NUM>, between a UE and infrastructure, between a UE and an RSU, etc. The frame structure may be within an LTE frame structure. Although the following description may be focused on LTE, the concepts described herein may be applicable to other similar areas, such as <NUM> NR, LTE-A, CDMA, GSM, and other wireless technologies. This is merely one example, and other wireless communication technologies may have a different frame structure and/or different channels. Each subframe may include two slots. Each slot may include <NUM> SC-FDMA symbols. Although the diagram <NUM> illustrates a single RB subframe, the sidelink communication may include multiple RBs.

Each time slot may include a resource block (RB) (also referred to as physical RBs (PRBs)) that extends <NUM> consecutive subcarriers. As illustrated in <FIG>, some of the REs may include a reference signal, such as a demodulation RS (DMRS). At least one symbol may be used for feedback, as described herein. A symbol prior to and/or after the feedback may be used for turnaround between reception of data and transmission of the feedback. Another symbol, e.g., at the end of the subframe may be used as a guard symbol without transmission/reception. The guard enables a device to switch from operating as a transmitting device to prepare to operate as a receiving device, e.g., in the following subframe. Data or control may be transmitted in the remaining REs, as illustrated. For example, data may be carried in a PSSCH, and the control information may be carried in a PSCCH. The control information may comprise Sidelink Control Information (SCI). The position of any of the reference signals, control, and data may be different than the example illustrated in <FIG>.

<FIG> is a block diagram <NUM> of a first wireless communication device <NUM> in communication with a second wireless communication device <NUM>, e.g., via V2V/V2X/D2D communication. The device <NUM> may comprise a first device communicating directly with a second device, e.g., device <NUM>, via V2V/V2X/D2D communication. The communication may be based, e.g., on sidelink. The first device <NUM> may comprise a UE, an RSU, an RSSD, etc. The second device may similarly comprise a UE, an RSU, an RSSD, etc. Packets may be provided to a controller/processor <NUM> that implements layer <NUM> and layer <NUM> functionality.

At least one of the TX processor <NUM>, the RX processor <NUM>, or the controller/processor <NUM> of device <NUM> or the TX <NUM>, the RX processor <NUM>, or the controller/processor <NUM> may be configured to perform aspects described in connection with the SLSS component <NUM> of <FIG>.

V2X communication may enable UEs, such as vehicles, RSUs, and other UEs, to communicate with each other even in the absence of a connection to a cellular network. Such V2X communication may include C-V2X communication. The UEs may synchronize with a network in order to facilitate communication directly with each other. Among other potential synchronization sources, the devices may use a Global Navigation Satellite System (GNSS) signal may be used as a synchronization source by individual UEs. The GNSS may enable the UE to determine a timing and frequency for transmitting/receiving communication with other UEs, RSUs, etc. In some locations, the UE may not be able to reliably receive a GNSS. For example, in tunnels or other areas lacking GNSS coverage, the UE be unable to synchronize in order to participate in V2X communication. Aspects presented herein provide for a sidelink synchronization signal that is coordinated to provide synchronization information to UEs that are in areas lacking GNSS coverage.

<FIG> illustrates a resource diagram <NUM> showing example aspects of an SLSS that may be used to synchronize UEs that lack GNSS coverage, or other network coverage, to determine timing and frequency synchronization for V2X communication. The SLSS <NUM> may be transmitted by a UE <NUM>, a RSU <NUM>, etc. In an aspect, transmission of the SLSS <NUM>. Resources for the SLSS <NUM> may be scheduled or set aside in a periodic manner, e.g., using a spacing <NUM> between resources <NUM> for SLSS <NUM> transmission/reception. An offset, periodicity, etc. for SLSS resources may be preconfigured so that devices capable of V2X communication are aware of the resources set aside for the SLSS. The devices may avoid transmitting other V2X communication using the SLSS resources. Although the resources for the SLSS <NUM> are illustrated as being at the start of a period, the SLSS resources may be positioned at any designated time, e.g., with reference to a slot or frame. Within the SLSS resources, the UE or RSU may transmit zero, one, or multiple SLSS <NUM>. In other examples, the SLSS resource may correspond to a size of a single SLSS <NUM>. An SLSS may include multiple synchronization signal resources that a UE may use to transmit different signals comprised within an SLSS. For example, the illustrated SLSS resources includes fourteen synchronization signal resources, which may be referred to by indices <NUM>-<NUM>. The synchronization resources may each correspond to a single symbol. The SLSS <NUM> comprises a Primary Sidelink Synchronization Signal (PSSS) and a Secondary Sidelink Synchronization Signal (SSSS). Additionally, the SLSS may include Physical Sidelink Broadcast Channel (PSBCH) and Demodulation Reference Signal (DMRS). Additionally, a Master Information Block (MIB) may be transmitted in a same subframe in order to provide a System Frame Number (SFN) and other configuration information. It should be understood, however, that the SLSS <NUM> is one example of many different possible configurations of synchronization information that may be used in connection with the aspects of the present application.

<FIG> illustrates an example <NUM> in which an SLSS <NUM> may be transmitted by a UE <NUM> that is within an area of cellular coverage <NUM> from a base station <NUM>. In <FIG>, the UE may receive synchronization information <NUM> from the base station <NUM>, and may transmit the SLSS <NUM> using a timing derived from the synchronization information <NUM> from the base station <NUM>. The UE <NUM> may transmit the SLSS <NUM> to a UE <NUM> that is outside the coverage <NUM> from the base station <NUM>. Therefore, the UE <NUM> is able to synchronize with the timing used by the UE <NUM> even though the UE <NUM> does not receive the synchronization information from the base station <NUM>. The SLSS <NUM> enables the UE <NUM> and the UE <NUM> to use a synchronized timing and frequency for V2X communication directly between the UE <NUM> and the UE <NUM>. <FIG> illustrates an example <NUM> in which an SLSS <NUM> may be transmitted by a UE <NUM> that is outside of cellular coverage of a base station. The example <NUM> may also apply to an in-coverage UE that is operating in an scheduling mode that is not under control of a base station or another mode that does not require synchronization with a base station or core network. In <FIG>, the UE <NUM> may receive synchronization information <NUM> from a GNSS <NUM>. The SLSS <NUM> transmitted to the UE <NUM> may use a timing derived from the synchronization information <NUM> from the GNSS <NUM>. The SLSS <NUM> enables the UEs <NUM> and <NUM> to use a synchronized timing and frequency for V2X communication directly between the UE <NUM> and the UE <NUM>.

There may be areas having limited GNSS coverage or limited network coverage in which UEs cannot reliably receive synchronization information from a GNSS or other network. For example, UEs in tunnels might not be able to use a GNSS in order to determining timing information in order to synchronize V2X communication with other UEs. Aspects presented herein provide a solution in which synchronization information may be provided within such areas of limited coverage using coordinated SLSS information. For example, road side synchronization devices (RSSDs) may be employed to coordinate SLSS transmission within such an area. An RSSD may comprise a RSU or may comprise other devices capable of communicating based on sidelink. The RSSDs may coordinate SLSS transmission with each other so that each RSSD may synchronize in time and frequency based on an SLSS from a source RSSD and may provide time and frequency information to another RSSD, e.g., in a neighbor RSSD in a different direction than the source RSSD, by transmitting an SLSS that uses timing and frequency synchronized with the source RSSD. A set of RSSDs may derive timing from a root RSSD that determines its timing from a GNSS or other network synchronization signal.

<FIG> illustrates an example <NUM> having a set of RSUs 602a-f located within an area <NUM> that has limited, or no, coverage by GNSS <NUM>. Although this example is described for a set of RSUs, the concept presented in <FIG> may be employed with other RSSDs, UEs, other V2X devices, or other sidelink devices. In <FIG>, a first RSU 602a may derive timing based on synchronization information from a GNSS <NUM>. The first RSU 602a transmits an SLSS 610a, using predefined SLSS resources, to the RSU 602b. The RSU 602b determines timing information, and also determines frequency information, based on the SLSS 610a. The RSU 602b determine a propagation delay based on a distance between the RSU 602a and the RSU 602b in order to compensate for the propagation delay in determining the timing and/or frequency. The RSU 602b transmits an SLSS 610b, using predefined SLSS resources, to the RSU 602c. The RSU 602c may then determine timing information, and may also determine frequency information, based on the SLSS 610b. The RSU 602c may determine a propagation delay based on a distance between the RSU 602b and the RSU 602c in order to compensate for the propagation delay in determining the timing and/or frequency. The RSU 602c may transmit an SLSS 610c, using predefined SLSS resources, to the RSU 602d. The RSU 602d may determine timing information, and may also determine frequency information, based on the SLSS 610c. The RSU 602d may determine a propagation delay based on a distance between the RSU 602c and the RSU 602d in order to compensate for the propagation delay in determining the timing and/or frequency. The RSU 602d may transmit an SLSS 610d, using predefined SLSS resources, to the RSU 602e. The RSU 602e may similarly determining timing information from SLSS 610d and transmit an SLSS to another neighbor RSU. In one example, there may be multiple RSUs within the set that are capable of receiving synchronization information from the GNSS. For example, the RSU 602a and the RSU 602f may be located near ends of a tunnel. Thus, the RSU 602f may be a source RSU that derives timing from the GNSS <NUM> and transmits the SLSS 610e based on that timing. As both the RSU 602a and the RSU 602f derive timing from the GNSS <NUM>, the RSU 602e may be able to derive related timing information from the SLSS 610d (that is received through a chain of RSUs, e.g., 602a, 602b, 602c, and 602d) and/or from the SLSS 610e that is received directly from a source RSU 602f. As a compensation is applied for the propagation delay each time an RSU receives the SLSS and before the RSU transmits its own SLSS, if the RSU 602d and the RSU 602f were equidistant from the RSU 602e, then the RSU 602e may receive the SLSS at the same time. However, if the RSU <NUM> and the RSU 602f are spaced at different distances from the RSU 602e, then the RSU 602e would be able to distinguish the SLSS 610d from the SLSS 610e as being different signals having different timing delays. Thus, each of the RSUs 602a-602f may be time and frequency synchronized to at least one of its neighboring RSUs. V2X communication, such as SLSS may be broadcast or groupcast and may be received by multiple receiving devices within range of a particular transmitting device, e.g., as illustrated at <NUM>. Thus, the SLSS 610a-e is received not just by adjacent RSUs, but also by UEs within range of the corresponding RSU. The receiving UE(s) <NUM> may use the SLSS to synchronize in time and/or frequency, for V2X communication.

The RSUs 602a-602f may be arranged such that each RSU is able to receive signals from its immediate neighboring RSU(s). As well, each RSU may be arranged with equal distance such that the propagation delay from multiple neighbor RSUs are the same. For example, the RSU 602b, 602c, and 602d may be positioned with an equal distance between RSUs so that the RSU 602c receives both the SLSS 610b and the SLSS 610d at the same time, or in an overlapping manner.

Additionally or alternatively, the SLSS resources may be divided into multiple sets, and the different sets may be used in an alternating pattern by the RSUs 602a-602f. For example, the SLSS subframes may be divided into two sets: Set <NUM> {S0, S2, S4,. } and Set <NUM> {S1, S3, S5,. A particular RSU may transmit its SLSS using Set <NUM> and receive SLSS using Set <NUM>. For example, the RSUs 602a, 602c, 602e may transmit SLSS using Set <NUM>, and the RSUs 602b, 602d, 602f may transmit SLSS using Set <NUM>. UE(s) <NUM> may receive both sets of the SLSSs as a single synchronization source. As one example, the RSUs within the set may be numbered, and even numbered RSUs may transmit in even numbered SLSS subframes while odd numbered RSUs may transmit SLSS in odd numbered SLSS subframes. <FIG> illustrates an example <NUM> of a first set of SLSS resources for a first set of RSUs (set A) and a second set of SLSS resources for a second set of RSUs (set B). The RSUs may be divided into the different sets in an alternating pattern. In the example of <FIG>, the RSUs 602a, 602c, 602e may be comprised in Set A, while the RSUs 602b, 602d, 602f may be comprised in Set B.

<FIG> illustrates an example communication flow <NUM> between a group of RSSDs 802a-c that synchronize in time and/or frequency with at least one neighbor RSSD and that transmit SLSS in order to provide synchronization information for V2X communication. The RSSD 802a may receive synchronization information <NUM> directly from a GNSS. The RSSD 802a may use the synchronization information <NUM> to determine, at <NUM>, a timing for the SLSS <NUM>. At <NUM>, the RSSD 802a may generate an SLSS having timing derive from the GNSS, and having frequency information. Then, the RSSD 802a may transmit the SLSS <NUM>. The SLSS <NUM> may be transmitted, e.g., via sidelink based broadcast, multicast, or groupcast in a manner that it can be received by at least one neighboring RSSD 802b. The RSSD 802b may be an immediate neighbor, or an adjacent neighbor, of the RSSD 802a.

The RSSD 802b may use the synchronization information in the SLSS <NUM> to determine, at <NUM>, to synchronize timing/frequency with the RSSD 802a. In order to accurately synchronize timing/frequency with the RSSD 802a, the RSSD 802b may compensate for a propagation delay, at <NUM>. The RSSD 802b may use a known distance between the RSSD 802a and the RSSD 802b to determine a delay between transmission of the SLSS <NUM> from the RSSD 802a and reception of the SLSS <NUM> at the RSSD 802b. For example, the RSSD 802b may calculate Tb=Ta-Tpropagation, where Tb corresponds to a start time of a subframe, and Ta corresponds to a start time of the same subframe detected from the SLSS <NUM> from the RSSD 802a. Tpropagation = distanceab/c, where distanceab corresponds to a distance between the RSSD 802a and the RSSD 802b and c corresponds to the speed of light. An RSSD may know a distance, or be provided with information about a distance, to the other RSSD in the group. In another example, an RSSD may know or be provided distance information for the RSSD's immediate neighbors in the group, e.g., with which the RSSD will exchange the SLSS. The RSSD 802b may remove the propagation delay, or otherwise compensate for the propagation delay, in generating an SLSS, at <NUM>, using synchronized time/frequency with the RSU 802a. The RSSD 802b may transmit the SLSS <NUM> to the RSSD 802c. The SLSS <NUM> may be transmitted, e.g., via sidelink based broadcast, multicast, or groupcast in a manner that it can be received by at least one neighboring RSSD 802c. The RSSD 802c may be an immediate neighbor, or an adjacent neighbor, of the RSSD 802b.

Similar to the description of the RSSD 802b, the RSSD 802c may receive the SLSS <NUM>, compensate for a propagation delay at <NUM>, synchronize in time/frequency with the RSSD 802b at <NUM>, generate an SLSS at <NUM>, and transmit the SLSS <NUM>. Although this example, illustrates three RSSDs, an area may be covered by any number of RSSDs in order to provide synchronization information via SLSS when a GNSS, or other network synchronization information, is not available. A UE in limited coverage, such as a vehicle traveling through a tunnel, may receive an SLSS from any of the RSSD 802a, 802b, or 802c. While the UE <NUM> is illustrated as receiving the SLSS <NUM>, the UE <NUM> may receive any of the SLSSs <NUM>, <NUM>, or <NUM> for which the UE <NUM> is within range of the transmitting RSSD. At <NUM>, the UE <NUM> may use the SLSS <NUM> to determine time and frequency synchronization, e.g., for use in transmitting and receiving other V2X communication. The UE <NUM> may synchronize in time/frequency based on the received SLSS in order transmit or receive communication with other UEs, with RSUs, etc..

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by an RSSD or a component of an RSSD, e.g., by an RSU or other such device capable of communicating using sidelink, or V2X based communication (e.g., RSU <NUM>, device <NUM> or <NUM>, RSU 602a-f, RSSD 802a-c, the apparatus <NUM>, <NUM>'; the processing system <NUM>, etc.). Optional aspects are presented with a dashed line. The method improves synchronization, e.g., for V2X communication, even in areas in which UEs have limited ability to synchronize with a GNSS or other network synchronization information.

At <NUM>, the RSSD receives, from a first neighbor device, a first SLSS. The reception may be performed, e.g., by the reception component and/or the first SLSS component <NUM> of the apparatus <NUM> in <FIG>. <FIG> illustrates aspects of an example, SLSS may that be received from the first neighbor device. The first neighbor device may correspond to one of RSU 602a-f or any of RSSD 802a or 802b.

As illustrated at <NUM>, the RSSD may remove a propagation delay from the first SLSS to synchronize the timing and the frequency with the first neighbor device. The removal may be performed, e.g., by the propagation delay component <NUM> of the apparatus <NUM> in <FIG>. The propagation delay may be removed from a transmit timing of the first SLSS or the second SLSS based on a distance from the RSSD to at least the first neighbor device or a second neighbor device. Example aspects of removal of a propagation delay are described in connection with <NUM> in <FIG>.

At <NUM>, the RSSD synchronizes a timing and a frequency with the first neighbor device. The synchronization may be performed, e.g., by the synchronization component <NUM> of the apparatus <NUM> in <FIG>. The timing of the first SLSS may derived from a GNSS signal. The timing of the first SLSS may be derived from a GNSS signal that is received, e.g., directly, by the first neighbor device. For example, the RDSD may correspond to RSSD 802b and the first neighbor device may correspond to RSSD 802a. Thus, the timing of the first SLSS may be derived from a third SLSS having the timing based on the GNSS signal. For example, the RSSD may correspond to RSU 602c, 602d, 602e, which receives an SLSS that is based on at least one SLSS from other RSU's having a root SLSS 610a that is based directly on a GNSS signal.

At <NUM>, the RSSD transmits a second SLSS, wherein the second SLSS is based on a synchronized timing and a synchronized frequency with the first neighbor device. The transmission may be performed, e.g., by the second SLSS component and/or the transmission component <NUM> of the apparatus <NUM> in <FIG>. The RSSD may transmit the SLSS to a second neighbor device, e.g., as part of a coordinated group of RSSD. The SLSS may be broadcast, multicast, groupcast, etc. so that the SLSS may be received by neighboring RSSD and/or UEs.

As illustrated at <NUM>, the RSSD may select a transmission power to transmit the second SLSS for reception by a first adjacent neighbor device. The selection may be performed, e.g., by the transmission power component <NUM> of the apparatus <NUM> in <FIG>. The transmission power may be selected so that the SLSS is received by adjacent/immediate neighbors and so that an RSSD beyond the immediate/adjacent neighbor would receive a significantly stronger signal from its own immediate neighbor RSSD in comparison to an RSSD that is not an adjacent/immediate neighbor RSSD.

Preconfigured SLSS subframes are divided into at least a first set of SLSS subframes and a second set of SLSS subframes. The RSSD receives SLSS signals in the first set of SLSS subframes transmitted by at least one immediate neighbor RSSD and transmits the second SLSS in the second set of SLSS subframes. <FIG> illustrates an example of SLSS resources divided into two sets.

The RSSD may be comprised in a group of RSSDs, e.g., as described in connection with <FIG> and <FIG>, using the synchronized timing and the synchronized frequency based on SLSS communicated between adjacent neighbor RSSDs comprised in the group of RSSDs. The group of RSSDs may comprise an alternating pattern of RSSDs in first set of RSSDs and a second set of RSSDs. The preconfigured SLSS subframes may be divided into at least a first set of SLSS subframes and a second set of SLSS subframes based on the alternating pattern of RSSDs, and the first set of RSSDs may transmit the first SLSS using the first set of SLSS subframes and the second set of RSSDs may transmit the second SLSS using the second set of SLSS subframes. <FIG> illustrates an example of SLSS resources divided into two sets.

<FIG> is a conceptual data flow diagram <NUM> illustrating the data flow between different means/components in an example apparatus <NUM>. The apparatus may be an RSSD or a component of an RSSD. An example of an RSSD may include an RSU, for example. The apparatus includes a reception component <NUM> that receives wireless communication, e.g., including communication based on sidelink, a transmission component <NUM> that transmits wireless communication, e.g., including communication based on sidelink. The apparatus may include a first SLSS component <NUM> configured to receive, from a first neighbor device <NUM>, a first SLSS, e.g. as described in connection with <NUM>. The apparatus may include a synchronization component <NUM> configured to synchronize a timing and a frequency with the first neighbor device <NUM>, e.g. as described in connection with <NUM>. The apparatus may include a second SLSS component <NUM> configured to transmitting a second SLSS, wherein the second SLSS is based on a synchronized timing and a synchronized frequency with the first neighbor device, e.g. as described in connection with <NUM>. The second SLSS may be received by another neighbor device <NUM> and/or a UE <NUM>. The apparatus may include a transmission power component <NUM> configured to select a transmission power to transmit the second SLSS for reception by a first adjacent neighbor device <NUM>, e.g. as described in connection with <NUM>. The apparatus may include a propagation delay component <NUM> configured to remove a propagation delay from the first SLSS to synchronize the timing and the frequency with the first neighbor device, e.g. as described in connection with <NUM>.

<FIG> is a diagram <NUM> illustrating an example of a hardware implementation for an apparatus <NUM>' employing a processing system <NUM>. The processing system <NUM> may be implemented with a bus architecture, represented generally by the bus <NUM>. The bus <NUM> may include any number of interconnecting buses and bridges depending on the specific application of the processing system <NUM> and the overall design constraints. The bus <NUM> links together various circuits including one or more processors and/or hardware components, represented by the processor <NUM>, the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and the computer-readable medium / memory <NUM>. The bus <NUM> may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

The processing system <NUM> may be coupled to a transceiver <NUM>. The transceiver <NUM> is coupled to one or more antennas <NUM>. The transceiver <NUM> provides a means for communicating with various other apparatus over a transmission medium. The transceiver <NUM> receives a signal from the one or more antennas <NUM>, extracts information from the received signal, and provides the extracted information to the processing system <NUM>, specifically the reception component <NUM>. In addition, the transceiver <NUM> receives information from the processing system <NUM>, specifically the transmission component <NUM>, and based on the received information, generates a signal to be applied to the one or more antennas <NUM>. The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium / memory <NUM>. The processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory <NUM>. The software, when executed by the processor <NUM>, causes the processing system <NUM> to perform the various functions described supra for any particular apparatus. The computer-readable medium / memory <NUM> may also be used for storing data that is manipulated by the processor <NUM> when executing software. The processing system <NUM> further includes at least one of the components <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. The components may be software components running in the processor <NUM>, resident/stored in the computer readable medium / memory <NUM>, one or more hardware components coupled to the processor <NUM>, or some combination thereof. The processing system <NUM> may be a component of the device <NUM> or the device <NUM> and may include the memory <NUM>, <NUM> and/or at least one of the TX processor <NUM>, <NUM>, the RX processor <NUM>, <NUM>, and the controller/processor <NUM>, <NUM>.

In one configuration, the apparatus <NUM>/<NUM>' for wireless communication includes means for receiving, from a first neighbor device, a first SLSS; means for synchronizing a timing and a frequency with the first neighbor device; means for transmitting a second SLSS, wherein the second SLSS is based on a synchronized timing and a synchronized frequency with the first neighbor device; means for selecting a transmission power to transmit the second SLSS for reception by a first adjacent neighbor device; and means for removing a propagation delay from the first SLSS to synchronize the timing and the frequency with the first neighbor device. As described supra, the processing system <NUM> may include the TX processor <NUM>, <NUM>, the RX processor <NUM>, <NUM>, and the controller/processor <NUM>, <NUM>. As such, in one configuration, the aforementioned means may be the TX processor <NUM>, <NUM>, the RX processor <NUM>, <NUM>, and the controller/processor <NUM>, <NUM> configured to perform the functions recited by the aforementioned means.

Claim 1:
A method of wireless communication at a Road Side Synchronization Device, RSSD, (602b) with a user equipment, UE, (<NUM>), wherein the RSSD and the UE are out of range of a synchronization source from GNSS or other network, the method comprising:
receiving (<NUM>), by the RSSD (602b), from a first neighbor device (602a), a first Sidelink Synchronization Signal, SLSS, (<NUM>);
synchronizing (<NUM>) a timing and a frequency with the first neighbor device (602a); and
transmitting (<NUM>), to a second neighbor device (602c) and the UE (<NUM>), a second SLSS (<NUM>, <NUM>), wherein the second SLSS is based on a synchronized timing and a synchronized frequency with the first neighbor device (602a), characterized in that:
preconfigured SLSS subframes are divided into at least a first set of SLSS subframes and a second set of SLSS subframes, and wherein the RSSD (602b) receives the first SLSS signal in the first set of SLSS subframes transmitted by the first neighbor device (602a) and transmits the second SLSS to the second neighbor device (602c) in the second set of SLSS subframes.