TRANSMITTING A CONTROL SIGNAL SCHEDULING A DISCOVERY SIGNAL IN SIDELINK

Certain aspects of the present disclosure provide techniques for determining a relay capability configuration for using a control signal to schedule a physical sidelink shared channel (PSSCH) that carries information to organize sidelink connections. The control signal allows user equipments (UEs) to organize a sidelink network absent base station configurations or vendor configurations. For example, the control signal may schedule a discovery signal (DS) associated with a sidelink synchronization signal block (S-SSB). The control signal may be referred to as DS-physical sidelink control channel (DS-PSCCH), different from a normal PSCCH. The DS-PSCCH may have distinct structure and content to allow UEs to organize sidelink networks.

BACKGROUND

Field of the Disclosure

Aspects of present disclosure relate to wireless communications and, more particularly, to techniques for sidelink communication.

Description of Related Art

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. New radio (e.g., 5G NR) is an example of an emerging telecommunication standard. The NR is a set of enhancements to the LTE mobile standard promulgated by the 3GPP. The NR is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on a downlink (DL) and on an uplink (UL). To these ends, the NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in the NR and the LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this disclosure provide advantages that include improved techniques for organizing a sidelink network among user equipments (UEs) without a base station (BS). For example, one lead UE may transmit a sidelink synchronization signal block (S-SSB) for discovery by another UE. The lead UE may transmit and use a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the other UE.

Certain aspects of the subject matter described in this disclosure can be implemented in a method for wireless communication by a first UE. The method may include transmitting a sidelink synchronization signal block (S-SSB) for discovery by at least a second UE; and transmitting a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the second UE.

Certain aspects of the subject matter described in this disclosure can be implemented in a method for wireless communication by a second UE. The method may include receiving a sidelink synchronization signal block (S-SSB) transmitted by a first UE; receiving a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the second UE; and receiving the PSSCH from the first UE according to the control signal.

Aspects of the present disclosure provide means for, apparatus, processors, and computer-readable mediums for performing techniques and methods that may be complementary to the operations by the UE described herein, for example, by a transmitter UE.

DETAILED DESCRIPTION

Aspects of present disclosure provide apparatus, methods, processing systems, and computer readable mediums for scheduling a physical sidelink shared channel (PSSCH) that carries information to organize sidelink connections. The PSSCH may be scheduled using a control signal that may allow user equipments (UEs) to organize a sidelink network absent base station configurations or vendor configurations. For example, the control signal may schedule a discovery signal (DS) associated with a sidelink synchronization signal block (S-SSB). The control signal may be referred to as DS-physical sidelink control channel (DS-PSCCH), different from a normal PSCCH. The DS-PSCCH may have distinct structure and content to allow UEs to organize sidelink networks.

Sidelink communications among UEs (e.g., in vehicle-to-everything, or V2X applications) may take advantage of the wideband unlicensed channel and support enhanced-mobile-broadband (eMBB) and internet-of-things (IOT) use cases. In these use cases, a base station (gNodeB, or gNB) is generally not available, i.e., the UEs are out of coverage. Even if some UEs may be in coverage, the in-coverage UEs may not share a universal setting that allows the UEs naturally communicate with each other without further sensing or configuration/synchronization. Therefore, the UEs need to self-organize to form a sidelink network without expecting configurations from the gNB or UE vendor. The present disclosure provides techniques for one or more UEs to initiate sidelink network organization, such as by setting up resource pools, coordinating configurations, and the like.

The disclosed techniques thus enable deployment of UEs in sidelink eMBB use cases in various scenarios. For example, the UEs may not belong to the same operator or may not have a subscription. The UEs may not receive sidelink configuration from a base station or from a vendor (e.g., vendors may agree to a common configuration). The UEs may not have sufficient licensed spectrum for sidelink communications.

According to the present disclosure, UEs may detect and synchronize with each other to organize sidelink communications in these scenarios. At a high level, a discovery signal and the associated mechanism may enable a UE to initiate the organization of a sidelink network. For example, the discovery signal may include remaining minimum system information (RMSI) to provide node access information (e.g., different from the RMSI in a Uu interface).

According to aspects of the present disclosure, the RMSI may be carried by a PSSCH scheduled by a control signal. Using the control signal to schedule allows for flexibility for the PSSCH and does not require the PSSCH to carry the RMSI (although in some cases, the PSSCH may carry the RMSI, integrated with an S-SSB). This may avoid always sending the RMSI in the PSSCH in a limited number of available bits in the master information block (MIB). Examples of locations and sizes of resource allocated for DS-PSCCH are further discussed in the examples below.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with 3G, 4G, and/or new radio (e.g., 5G new radio (NR)) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

The NR access may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHz or beyond), millimeter wave (mmW) targeting high carrier frequency (e.g., e.g., 24 GHz to 53 GHz or beyond), massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC). These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTI) to meet respective quality of service (QOS) requirements. In addition, these services may co-exist in the same subframe. The NR supports beamforming and beam direction may be dynamically configured. Multiple-input multiple-output (MIMO) transmissions with precoding may also be supported. MIMO configurations in a downlink (DL) may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells.

FIG.1illustrates an example wireless communication network100in which aspects of the present disclosure may be performed. The wireless communication network100may include base stations (BSs)110a-z(each also individually referred to herein as BS110or collectively as BSs110). The wireless communication network100may further include user equipments (UEs)120a-y(each also individually referred to herein as UE120or collectively as UEs120). The UEs120aand120bmay each include a respective discovery signal manager122aand122b. Although the UEs120are illustrated to be within the coverage of the BSs110, the present disclosure is as well applicable to situations where one or more UEs120are outside of the coverage of the BSs110. For example, two or more UEs120that are outside of the coverage of the BSs110may nonetheless perform operations disclosed herein, to use discovery signals to initiate and organize sidelink networks.

As shown inFIG.1, the wireless communication network100may be an NR system (e.g., a 5G NR network) in communication with a core network132. The core network132may be in communication with the BSs110and/or the UEs120in the wireless communication network100via one or more interfaces.

The UEs120may be configured for a sidelink communication. Each UE120may be synchronized. As shown inFIG.1, a UE120amay be a transmitter UE, which may be synchronized to the core network132using a synchronization signal from one of the other UEs120. The UE120amay include a discovery signal manager122a. The discovery signal manager122amay transmit an S-SSB to be received by another UE and transmit a control signal associated with the S-SSB to schedule a PSSCH that conveys system information for the other UE. Also, as shown inFIG.1, a UE120bmay be a receiver UE, which may receive the S-SSB transmitted by the UE120a. The UE120bmay include another discovery signal manager122b. The discovery signal manager122bmay receive the S-SSB and a control signal associated with the S-SSB to schedule a PSSCH. The UE120bmay then receive the PSSCH from the UE120aaccording to the control signal. In aspects, the discovery signal managers122aand122bmay perform the operations800and900ofFIGS.8and9, as discussed below.

The BSs110may communicate with the UEs120in the wireless communication network100. The UEs120(e.g.,120x,120y, etc.) may be dispersed throughout the wireless communication network100, and each UE120may be stationary or mobile. The wireless communication network100may also include relay stations (e.g., a relay station110r), also referred to as relays or the like, that receive a transmission of data and/or other information from an upstream station (e.g., a BS110aor a UE120r) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE120or a BS110), or that relays transmissions between the UEs120, to facilitate communication between devices.

A network controller130may be in communication with a set of BSs110and provide coordination and control for these BSs110(e.g., via a backhaul). In aspects, the network controller130may be in communication with a core network132(e.g., a 5G Core Network (5GC)), which provides various network functions such as Access and Mobility Management, Session Management, User Plane Function, Policy Control Function, Authentication Server Function, Unified Data Management, Application Function, Network Exposure Function, Network Repository Function, Network Slice Selection Function, etc.

FIG.2illustrates example components of a BS110aand a UE120a(e.g., in the wireless communication network100ofFIG.1), which may be used to implement aspects of the present disclosure.

At the BS110a, a transmit processor220may receive data from a data source212and control information from a controller/processor240. The control information may be for a physical broadcast channel (PBCH), a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH), a physical downlink control channel (PDCCH), a group common PDCCH (GC PDCCH), etc. The data may be for a physical downlink shared channel (PDSCH), etc. A medium access control (MAC)-control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. The MAC-CE may be carried in a shared channel such as a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

The processor220may process (e.g., encode and symbol map) the data and the control information to obtain data symbols and control symbols, respectively. The transmit processor220may also generate reference symbols, such as for a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a PBCH demodulation reference signal (DMRS), and a channel state information reference signal (CSI-RS). A transmit (TX) MIMO processor230may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to modulators (MODs) in transceivers232a-232t. Each MOD in transceivers232a-232tmay process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each MOD in transceivers232a-232tmay further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. The downlink signals from the MODs in transceivers232a-232tmay be transmitted via the antennas in transceivers234a-234t, respectively.

The memories242and282may store data and program codes for the BS110aand the UE120a, respectively. A scheduler244may schedule UEs for data transmission on the downlink and/or the uplink.

Antennas252, processors266,258,264, and/or controller/processor280of the UE120aand/or antennas234, processors220,230,238, and/or controller/processor240of the BS110amay be used to perform the various techniques and methods described herein. For example, as shown inFIG.2, the controller/processor280of the UE120amay include a discovery signal manager122a. When UE120ais acting as a transmitter UE, the discovery signal manager122amay transmit an S-SSB to be received by at least a second UE. The discovery signal manager122amay further transmit a control signal associated with the S-SSB to schedule a PSSCH that conveys system information for the second UE. When UE120ais acting as a receiver UE, the discovery signal manager122amay also receive an S-SSB transmitted by another UE and receive a control signal associated with the S-SSB. The discovery signal manager122amay then receive a PSSCH according to the received control signal.

FIG.3is a diagram showing an example of a frame format300for NR. The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 ms) and may be partitioned into 10 subframes, each of 1 ms, with indices of 0 through 9. Each subframe may include a variable number of slots (e.g., 1, 2, 4, 8, 16, . . . slots) depending on the SCS. Each slot may include a variable number of symbol periods (e.g., 7, 12, or 14 symbols) depending on the SCS. The symbol periods in each slot may be assigned indices. A mini-slot, which may be referred to as a sub-slot structure, refers to a transmit time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols). Each symbol in a slot may indicate a link direction (e.g., DL, UL, or flexible) for data transmission and the link direction for each subframe may be dynamically switched. The link directions may be based on the slot format. Each slot may include DL/UL data as well as DL/UL control information.

In NR, a synchronization signal block (SSB) is transmitted. In certain aspects, SSBs may be transmitted in a burst where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and/or beam refinement). The SSB includes a PSS, a SSS, and a two symbol PBCH. The SSB can be transmitted in a fixed slot location, such as the symbols 0-3 as shown inFIG.3. The PSS and SSS may be used by UEs for cell search and acquisition. The PSS may provide half-frame timing, the SS may provide the CP length and frame timing. The PSS and SSS may provide the cell identity. The PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frame, SS burst set periodicity, system frame number, etc. The SSBs may be organized into SS bursts to support beam sweeping. Further system information such as, remaining minimum system information (RMSI), system information blocks (SIBs), other system information (OSI) can be transmitted on a physical downlink shared channel (PDSCH) in certain subframes. The SSB can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmWave. The multiple transmissions of the SSB are referred to as a SS burst set. SSBs in an SS burst set may be transmitted in the same frequency region, while SSBs in different SS bursts sets can be transmitted at different frequency regions.

In some examples, the communication between the UEs120and BSs110is referred to as the access link. The access link may be provided via a Uu interface. Communication between devices may be referred as the sidelink.

Various sidelink channels may be used for sidelink communications, including a physical sidelink discovery channel (PSDCH), a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH may carry discovery expressions that enable proximal devices to discover each other. The PSCCH may carry control signaling such as sidelink resource configurations and other parameters used for data transmissions, and the PSSCH may carry the data transmissions. The PSFCH may carry feedback such as CSI related to a sidelink channel quality.

Example Sidelink Communication

FIG.4AandFIG.4Bshow diagrammatic representations of example vehicle to everything (V2X) systems, in accordance with some aspects of the present disclosure. Vehicles shown inFIG.4AandFIG.4Bmay communicate via sidelink channels and may perform control signal transmissions as described herein (e.g., in vehicle-to-vehicle, or V2V situations). In addition to the example application of sidelink communications in the V2X systems, implementations of the present disclosure is not limited to V2X systems, such as when no common vender or gNB configuration is available (e.g., when the vehicles402and404are out-of-coverage).

The V2X systems, provided inFIG.4AandFIG.4Bprovide two complementary transmission modes. A first transmission mode, shown by way of example inFIG.4A, involves direct communications (for example, also referred to as sidelink communications) between participants in proximity to one another in a local area. A second transmission mode, shown by way of example inFIG.4B, involves network communications through a network, which may be implemented over a Uu interface (for example, a wireless communication interface between a radio access network (RAN) and a UE).

Referring toFIG.4A, a V2X system400(for example, including vehicle to everything (V2X) communications) is illustrated with two vehicles402,404. The first transmission mode allows for direct communication between different participants in a given geographic location. As illustrated, a vehicle can have a wireless communication link406with an individual (V2P) (for example, via a UE) through a PC5 interface. Communications between the vehicles402and404may also occur through a PC5 interface408. In a like manner, communication may occur from a vehicle402to other highway components (for example, highway component401), such as a traffic signal or sign (V2I) through a PC5 interface412. With respect to each communication link illustrated inFIG.4A, two-way communication may take place between elements, therefore each element may be a transmitter and a receiver of information. The V2X system400may be a self-managed system implemented without assistance from a network entity. A self-managed system may enable improved spectral efficiency, reduced cost, and increased reliability as network service interruptions do not occur during handover operations for moving vehicles. The V2X system may be configured to operate in a licensed or unlicensed spectrum, thus any vehicle with an equipped system may access a common frequency and share information. Such harmonized/common spectrum operations allow for safe and reliable operation.

FIG.4Bshows a V2X system450for communication between a vehicle452and a vehicle454through a network entity456. These network communications may occur through discrete nodes, such as a BS (e.g., the BS110a), that sends and receives information to and from (for example, relays information between) vehicles452,454. The network communications through vehicle to network (V2N) links458and410may be used, for example, for long range communications between vehicles, such as for communicating the presence of a car accident a distance ahead along a road or highway. Other types of communications may be sent by the wireless node to vehicles, such as traffic flow conditions, road hazard warnings, environmental/weather reports, and service station availability, among other examples. Such data can be obtained from cloud-based sharing services.

Roadside units (RSUs) may be utilized. An RSU may be used for V2I communications. In some examples, an RSU may act as a forwarding node to extend coverage for a UE. In some examples, an RSU may be co-located with a BS or may be standalone. RSUs can have different classifications. For example, RSUs can be classified into UE-type RSUs and Micro NodeB-type RSUs. Micro NB-type RSUs have similar functionality as the Macro eNB/gNB. The Micro NB-type RSUs can utilize the Uu interface. UE-type RSUs can be used for meeting tight quality-of-service (QOS) requirements by minimizing collisions and improving reliability. UE-type RSUs may use centralized resource allocation mechanisms to allow for efficient resource utilization. Critical information (e.g., such as traffic conditions, weather conditions, congestion statistics, sensor data, etc.) can be broadcast to UEs in the coverage area. Relays can re-broadcasts critical information received from some UEs. UE-type RSUs may be a reliable synchronization source.

In some cases, vehicles (e.g., UEs) within a V2X system may have a relay capability and operate as relay UEs (e.g., in-coverage UEs).FIGS.5A-5Billustrate example V2X systems500,502in which certain UEs may operate as relay UEs. As shown, the V2X systems500,502illustrated inFIGS.5A-5Bmay include a base station (e.g., gNB), a first vehicle (e.g., a transmitter UE) and a second vehicle (e.g., second UE). In some cases, the V2X systems500,502may be an example of the V2X/V2X systems400,450described above with reference toFIGS.4A and4B.

In some cases, the transmitter UE may communicate directly with the gNB via a Uu interface or indirectly with the gNB via the relay UE via a PC5 interface. For example, as illustrated inFIG.5A, the transmitter UE may communicate directly with the gNB using the Uu interface or may communicate with the gNB indirectly via the relay UE using a PC5 interface. In other cases, as illustrated inFIG.5B, the transmitter UE may only indirectly communicate with the gNB via the relay UE using the PC5 interface. For example, in some cases, the transmitter UE may communicate with the relay UE via a PC5 interface to send a message. Thereafter, the relay UE may forward this message to the gNB via the Uu interface. Similarly, the gNB may communicate with the transmitter UE via the relay UE.

In some cases, relay UEs within the V2X systems500,502illustrated inFIGS.5A-5Bmay have or be associated with different relay capabilities. For example, in some cases, the relay capabilities may include or may be associated with a discontinuous reception (DRX) cycle of the relay UE, traffic on a Uu link and/or PC5 link associated with the relay UE, a channel quality associated with a sidelink (e.g., PC5 link), a number of other UEs that the relay UE is connected to, a time source of the relay UE, and/or channel state information (CSI) associated with a Uu link of the relay UE.

Example Sidelink Synchronization

When a base station (e.g., a gNB) is available, UEs that are in coverage are expected to follow the same timing reference as the base station. If none available, the timing references of the deployed UEs are desired to be aligned with each other. Both may be achieved via synchronization procedures, such as global navigation satellite system (GNSS) based and gNB based synchronization procedures, for example. When a UE powers on, the UE may search for synchronization signal block (SSB) signals available (e.g., provided by the GNSS or gNB). The SSB signals may be directly provided by the GNSS or gNB, or indirectly provided by another UE within the coverage of the GNSS or gNB. When none available, sidelink SSB (S-SSB) may still be provided for synchronization, according to aspects of the present disclosure.

An example of synchronizing within the V2X system is illustrated inFIG.6. For example,FIG.6shows an example V2X system600implementing aspects ofFIGS.4A-4B and5A-5B. As shown, in one example, the V2X system600illustrated inFIG.6may include a first UE (e.g., a UE-1), a second UE (e.g., a UE-2), a third UE (e.g., a UE-3), and a fourth UE (e.g., a UE-4). The V2X system may further include a base station (BS) (e.g., a gNB).

In an example, nodes of the V2X system600, such as the UEs and the BS may be synchronized. The nodes may be synchronized using multiple synchronization techniques. One technique is Global Navigation Satellite System (GNSS) based synchronization, which prioritizes GNSS signals for synchronization. Another technique is gNB/eNB based synchronization, which prioritizes eNB/gNB SSB signal for synchronization. In another example, sidelink UEs (e.g., UE-3) out-of-coverage may use S-SSB for synchronization.

In some cases, each node in the V2X system600may receive synchronization signals from different synchronization sources. For example, in some cases, UE-1 may receive the synchronization signals directly from the gNB. In other cases, the nodes may receive the synchronization signals from the GNSS (not shown). In either case, each node may synchronize to the V2X system/network600using a synchronization signal received from a synchronization source based on a priority associated with that synchronization source and/or synchronization signal, as explained below. In some cases, UE-2 or UE-4 may receive the SSB from UE-1, thus indirectly receiving the SSB from the gNB or GNSS. In some cases, UE-4 may receive S-SSB from UE-3, which is outside of the coverage by the gNB or UE-1 to receive SSB directly or indirectly from the gNB.

In the V2X system600, when the UEs turn on, each UE may search for a nearby NR network. For example, in some cases, while searching for a nearby NR network, the UEs (e.g., UE-1) may receive the synchronization signals from the gNB. However, in other cases, the UEs in the V2X system600(e.g., the UE-2, the UE-3, the UE-4) may not receive the synchronization signals from the gNB, but may instead search for and receive the synchronization signals (i.e., sidelink synchronization signals) from other UEs in the V2X system600.

For example, as shown, when UE-1 turns on, UE-1 may search for the nearby NR network and may discover the gNB, which belongs to the NR network. To assist with discovery and synchronization with the gNB, the gNB may transmit a synchronization signal block (SSB) that includes, for example, a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH) (e.g., including a master information block (MIB)) periodically in different transmit directions (e.g., beams). Accordingly, UE-1 may receive the SSB from the gNB and may synchronize to the NR network based on the received SSB. In this case, the gNB may function as UE-1's synchronization source. Thereafter, once UE-1 is synchronized, the UE-1 may perform an attach procedure with the BS and begin camping on a cell associated with the gNB.

While UE-1 may receive the synchronization signals from the gNB and use the gNB as a synchronization source, UE-2 may instead receive SSBs from other UEs, such as UE-1, and may use UE-1 as a synchronization source. For example, when UE-2 turn on, UE-2 may search for the nearby NR network. However, in this case, UE-2 may instead discover the UE-1, which belongs to the NR network. As with the gNB, UE-1 may transmit SSBs periodically in different transmit directions. UE-2 may receive the SSBs from the UE-1 and may synchronize to the NR network based on the received SSBs. Here, UE-1 may function as a synchronization source for UE-2. Thereafter, in some cases, UE-2 may perform an attach procedure with UE-1 to access the NR network.

In some cases, a UE may discover multiple other UEs when searching for the nearby NR network. For example, in some cases, when the UE-4 turns on, the UE-4 may search for the nearby NR network and may discover UE-1 and UE-2 belonging to the NR network. UE-1 and UE-2 may transmit the SSB periodically in different transmit directions, which may be received by UE-4. In such cases, when the UE-4 receives multiple SSBs from multiple other UEs, the UE-4 may be configured to select, and synchronize to, the SSB according to a priority associated with the SSB. In some cases, the priority of each SSB may be indicated within each SSB itself. In some cases, the UE-4 may determine priority information associated with each received SSB based on one or more predetermined tables, which define different priorities of synchronization signals (e.g., SSBs) based on, for example, where the synchronization signals are coming from and the type of synchronization technique preferred (e.g., GNSS-based synchronization vs. eNB/gNB-based synchronization).

For example, as shown below, for GNSS-based synchronization, a synchronization signal received from another UE that is directly synchronized to GNSS may have a highest priority (e.g., P1) while synchronization signals received from UEs that are indirectly synchronized to a gNB/eNB may have a lower priority (e.g., P5).

TABLE 1GNSS-Based Synchronization PrioritiesGNSS based synchronizationP1UE directly synchronized to GNSSP2UE indirectly synchronized to the GNSSP3eNB/gNBP4UE directly synchronized to eNB/gNBP5UE indirectly synchronized to gNB/eNBP6Remaining UEs

As shown in Table 2, below, for gNB/eNB-based synchronization, a synchronization signal received from another UE that is directly synchronized to a gNB/eNB may have a highest priority (e.g., P1) while synchronization signals received from UEs that are indirectly synchronized to GNSS may have a lower priority (e.g., P5).

TABLE 2gNB/eNB-Based Synchronization PrioritiesgNB/eNB based synchronizationP1UE directly synchronized to gNB/eNBP2UE indirectly synchronized to gNB/eNBP3GNSSP4UE directly synchronized to GNSSP5UE indirectly synchronized to GNSSP6Remaining UEs

In certain cases, in response to receiving SSBs from UE-1 and UE-2, the UE-4 may evaluate information associated with each SSB to determine which SSB has a highest priority. For example, in some cases, if the V2X system600is gNB/eNB-synchronization based, the UE-4 may determine that the SSB received from the UE-1 has a higher priority (e.g., P1) than the SSB received from the UE-2 (e.g., P2) and the SSB received from the UE-3 (e.g., P2), since the UE-1 is directly synchronized to the BS while UE-2 are indirectly synchronized to the BS via UE-1. Accordingly, in this case, the UE-4 may select the SSB from the UE-1 having the highest priority for synchronization.

In some cases, UE-3 illustrates UEs that are out of coverage of the gNB and other in-coverage UEs. Although UE-1, UE-2, and UE-4 are shown to be directly or indirectly in coverage of the gNB inFIG.6, UE-1, UE-2, and UE-4 may be out of the gNB coverage along with UE-3 and still organize a sidelink network, according to aspects of the present disclosure. In such cases, sidelink configuration may not be expected from the gNB. Similarly, the out-of-coverage UEs may not belong to the same operator. Some of the UEs may not have subscription. Accordingly, there is a need for a technique that allows the out-of-coverage UEs to organize sidelink communications absent external configurations. In accordance with certain aspects of the present disclosure, UE-3 may transmit an S-SSB to UE-4 for synchronization. An example slot structure700for the S-SSB is provided inFIG.7.

As shown inFIG.7, the S-SSB structure in one slot includes physical sidelink broadcast channel (PBCH), sidelink primary synchronization signal (SPSS), and sidelink secondary synchronization signal (SSSS). The PBCH carries information for supporting synchronization in the sidelink, including demodulation reference signal (DMRS). For example, PBCH provides system-wide information (e.g., time division duplex (TDD) configuration, frame number, slot index, network/GNSS coverage, etc.) and synchronization information required by a UE for establishing a sidelink connection. The SPSS and SSSS are used by a receiver UE to synchronize to the transmitter of the S-SSB, and may jointly be referred to as the sidelink synchronization signal (SLSS) for time and frequency synchronization. The S-SSB may use the same numerology as the PSCCH or PSSCH.

In some cases, for a normal or extended cyclic prefix (CP), the PBCH, SPSS, and SSSS are carried in the first 11 or 13 symbols of the S-SSB slot, leaving a gap or guard symbol at the end. The S-SSB may not often be transmitted in the slots of a resource pool (i.e., not multiplexed with other sidelink physical channel within the SL BWP). The frequency location of an S-SSB is often pre-configured within a sidelink BWP, such that a receiver UE needs not perform blind detection in the frequency domain to discover an S-SSB.

By detecting the SPSS and SSSS sent by a transmitter UE, a receiver UE (e.g., UE-4 ofFIG.6) may be able to synchronize to the transmitter UE (e.g., UE-3 ofFIG.6) and estimate the beginning of the frame and carrier frequency offsets. Because the transmitter UE may have already been using a common sidelink timing reference with other UEs in a sidelink network, the receiver UE may receiving sidelink communications from the other UEs after synchronizing with the transmitter UE. As such, not all UEs in the sidelink network needs to transmit the S-SSB. According to aspects of the present disclosure, a control signal may be transmitted to schedule the PSSCH that carries the discovery signal. Transmitting the control signal may provide more flexibility for the PSSCH by allowing for more available bits in the master information block (MIB) than without transmitting the control signal.

Example Discovery Signal Transmission for Sidelink Synchronization

Aspects of present disclosure provide techniques for scheduling a physical sidelink shared channel (PSSCH) that conveys system information (SI) for another UE. For example, the PSSCH may be scheduled via a control signal associated with an S-SSB that enables out-of-coverage UEs to initiate and organize sidelink networks without external configurations.

In aspects, the PSSCH conveys remaining minimum system information (RMSI) that serves as a discovery signal (DS). The DS may be scheduled by a physical sidelink control channel (PSCCH). In aspects, the control signal may include the DS scheduled by the PSCCH via a demodulation reference signal DMRS. The DS may be specified at a location with respect to the S-SSB for the receiver UE to identify.

FIG.8is a flow diagram illustrating example operations800for wireless communication by a first UE (e.g., a transmitter UE that transmits S-SSBs). In one non-limiting example, operations800may be performed by the UE120ain the wireless communication network100ofFIG.1.

Operations800begin, at802, by transmitting an S-SSB to be received by at least a second UE. The S-SSB may include system and synchronization information. For example, the S-SSB may have a structure similar to the S-SSB slot shown inFIG.7.

At804, the transmitter UE transmits a control signal associated with the S-SSB to schedule a PSSCH that conveys SI for the second UE. For example, the PSSCH may convey remaining minimum system information (RMSI) as a discovery signal (DS).

In aspects, the control signal may be a PSCCH that schedules a PSSCH that includes the DS. In some cases, the transmitter UE may indicate that the PSSCH includes the DS via a demodulation reference signal (DMRS) pattern.

FIG.9is a flow diagram illustrating example operations900that may be considered complementary to the operations800ofFIG.8. For example, operations900may be performed by a receiver UE monitoring for S-SSBs from a transmitter UE (performing operations800ofFIG.8).

Operations900begin, at902, by receiving an S-SSB transmitted by a first UE, such as the transmitter UE of operations800. For example, the S-SSB may have a structure similar to the S-SSB slot shown inFIG.7.

At904, the second UE receives a control signal associated with the S-SSB to schedule a PSSCH that conveys system information (SI) for the second UE. For example, the PSSCH may convey remaining minimum system information (RMSI) as a discovery signal (DS). The DS may be conveyed by the PSSCH. In some cases, the PSSCH (including the DS) is scheduled by a PSCCH. To distinguish the scheduling PSCCH from normal sidelink PSCCH, the specific DS scheduling channel with the control signal may be referred to as the DS-PSCCH.

At906, the second UE receives the PSSCH from the first UE according to the control signal.

In one aspect, the resource used for the control signal may be predefined at a constant or fixed location relative to the S-SSB. For example, the DS-PSCCH may occupy a fixed resource location with respect to the S-SSB. This way, the receiver UE, when discovering the S-SSB, would know where to find the PSCCH, by deriving its location based on the S-SSB location. Based on the scheduling information in the PSCCH, the receiver UE may then receive the PSSCH carrying the discovery signal (e.g., RMSI) and establish sidelink communications with the transmitter UE. In some cases, the S-SSB may additionally provide information on the control signal, such as whether one has been transmitted with the S-SSB. If the S-SSB does not indicate that the control signal has been transmitted, the receiver UE may proceed with blind detection of the control signal.

For example, the S-SSB may provide additional information of the control signal, such as using one bit in MIB to indicate whether the control signal (DS-PSCCH) is accompanying the S-SSB. In other cases, the S-SSB indicates on/off information (not the location information), such as in case some S-SSB transmitting nodes do not want to transmit discovery signal.

Examples of the fixed location of the control signal are illustrated inFIGS.10-13. As shown inFIGS.10and11, the control signal (i.e., the “predefined control channel”) aligns with the S-SSB in the time domain. As to the frequency domain, the number of resource blocks (RBs) for the control signal may be fixed or constant. For example, the control signal may occupy four, eight, or twelve RBs. Different frequency locations may be used. In a first option, as shown inFIG.10, the control signal may be next to the S-SSB in the frequency domain, leaving the remaining resources to be filled with DS transmission. In a second option, as shown inFIG.11, the control signal may be located on the opposite edge of the frequency band. For example, when the sidelink S-SSB is for unlicensed band and is located near one edge of the 20 MHz channel, then the control signal may occupy the other edge of the 20 MHz channel.

In another example illustrated inFIG.12, the control signal may share a common starting location in the time domain with the S-SSB but may not occupy the same duration as the S-SSB. In some cases, the control signal may occupy a fixed or constant number of symbols, such as one, two, or three symbols. In the frequency domain, the control signal may use the remaining portion of the subband that is not occupied by the S-SSB. Alternatively, the control signal may occupy a fixed number of RBs, such as twelve RBs for example.

In yet another example illustrated inFIG.13, the control signal and the S-SSB may have the same time and frequency location but may be offset by a time period. As shown, the control signal (i.e., the “predefined control channel”) may occupy the same time and frequency resources as the S-SSB. In this case, the transmitter UE transmits the control signal at a different time, after a period of time offset, than the S-SSB.

In another aspect, the location of the control signal may be indicated instead of being fixed relative to the S-SSB. For example, the MIB of the S-SSB may provide information on RBs used for the control signal to inform the receiver UE about the location of the control signal. As such, the receiver UE may find the control signal based on the S-SSB, with greater flexibility than the fixed-location situation with the tradeoff being potentially using more resources in the MIB for the indication.

In some cases, the location and size of resource allocations (and any combination thereof) for the control signal may be pre-defined. The MIB may need indicate which one of a set of pre-defined configurations has been utilized (i.e., without repeating the detailed resource allocation information of the location and size). For example, a first pre-defined configuration may indicate a first symbol size and location and a first subcarrier size and location used for the control signal transmission; a second pre-defined configuration may indicate a second symbol size and location and a second subcarrier size and location used for the control signal transmission. The MIB may indicate which one of the first or the second pre-defined configuration of the control signal is transmitted. This allows for an aggregation level control, similar to the aggregation level control for a Uu PDCCH. Techniques described above may be used to indicate whether the control signal is transmitted with the S-SSB (e.g., using one bit in the MIB to indicate whether such control signal is transmitted along with the S-SSB).

In certain aspects, the control signal (DS-PSCCH) may have a distinct set of structure and content different from other sidelink channels, such as normal PSCCH, PSSCH, PBCH, and PSFCH. The structure and content may be related to coding, modulation, reference signals, and resource allocations, among others. For example, the structure of the control signal may include a fixed information size of 24 bits cyclic redundancy check (CRC). The modulation of the control signal may be quadrature phase shift keying (QPSK). The content of the control signal may include the resource allocation for the PSSCH that carries system information, such as the RMSI.

In some cases, if the PSSCH carrying the RMSI is aligned with the control signal in time, then the control signal may need to provide the frequency domain resource allocation (FDRA) only. For example, when the receiver UE attempts to establish a sidelink with the transmitter UE, the receiver UE may not have a proper sidelink configuration. The control signal from the transmitter UE may then provide the basic FDRA unit (i.e., an RB) and use the FDRA to indicate the starting RB and the length of occupied RBs, with respect to the control signal location.

In some cases, if the PSSCH carrying the RMSI is aligned with the control signal in frequency, then the control signal may need to provide the time domain resource allocation (TDRA) only. For example, the basic unit for TDRA is a slot. When the receiver UE attempts to establish a sidelink with the transmitter UE, the receiver UE may be provided the starting slot and the duration of occupied slots with respect to the control signal location, indicated by the TDRA from the transmitter UE.

In some cases, when the PSSCH carrying the RMSI does not align with the control signal in either time or frequency, then both FDRA and TDRA are provided in the control signal.

In some cases, the control signal may further indicate the modulation and coding scheme (MCS), such as polar coding. The control signal may further indicate a time pattern and number of ports of PSSCH DMRS, and/or a DMRS pattern.

In some cases, in order to avoid unnecessary discovery/decoding attempts, the control signal may further include UE identity information to allow the receiver UE to decide whether a sidelink connection is desirable. The control signal may also provide information on the service provided by the transmitter UE, so that the receiver UE and other nodes may selectively connect to the transmitter UE. For example, the transmitter UE may indicate that the transmitter UE has the capability to connect to certain public land mobile network (PLMN), so that the transmitter UE may serve as a relay UE to the receiver UE and other nodes. In some cases, the control signal may provide information on the destination UE (e.g., in a unicast use case) or information of groupcast. In some cases, the identify information, service information, unicast or group cast information may be included in the RMSI when the control signal does not include such information.

FIG.14illustrates a communications device1400that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for techniques disclosed herein, such as operations illustrated inFIG.8. The communications device1400includes a processing system1402coupled to a transceiver1408(e.g., a transmitter and/or a receiver). The transceiver1408is configured to transmit and receive signals for the communications device1400via an antenna1410. The processing system1402may be configured to perform processing functions for the communications device1400, including processing signals received and/or to be transmitted by the communications device1400.

The processing system1402includes a processor1404coupled to a computer-readable medium/memory1415via a bus1406. The computer-readable medium/memory1415is configured to store instructions (e.g., computer-executable code) that when executed by the processor1404, cause the processor1404to perform the operations illustrated inFIG.8.

The computer-readable medium/memory1412stores code1414for transmitting a sidelink synchronization signal block (S-SSB) for discovery by at least a second UE, and code1416for transmitting a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the second UE. The processing system1402includes circuitry1422for transmitting a sidelink synchronization signal block (S-SSB) for discovery by at least a second UE, and circuitry1424for transmitting a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the second UE.

Means for transmitting may include a processor (e.g., the controller/processor280), one or more antennas (e.g., the antennas242or the antenna1410), and/or circuitry for transmitting (e.g., the circuitry1422or1424for transmitting). Means for scheduling a PSSCH may include a processor (e.g., the controller/processor280). Means for synchronizing may include a processor (e.g., the controller/processor280) and/or circuitry for synchronizing (e.g., the discovery signal manager122a). In certain aspects, various processors and/or various circuitry may include a circuit, a CPU, a GPU, a DSP, an ASIC, a FPGA, or other PLD, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described here.

FIG.15illustrates a communications device1500that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for techniques disclosed herein, such as operations illustrated inFIG.9. The communications device1500includes a processing system1502coupled to a transceiver1508(e.g., a transmitter and/or a receiver). The transceiver1508is configured to transmit and receive signals for the communications device1500via an antenna1510. The processing system1502may be configured to perform processing functions for the communications device1500, including processing signals received and/or to be transmitted by the communications device1500.

The processing system1502includes a processor1504coupled to a computer-readable medium/memory1512via a bus1506. The computer-readable medium/memory1512is configured to store instructions (e.g., computer-executable code) that when executed by the processor1504, cause the processor1504to perform the operations illustrated inFIG.9.

The computer-readable medium/memory1512stores code1514for receiving a sidelink synchronization signal block (S-SSB) transmitted by a first UE, code1516for receiving a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the second UE, and code1518for receiving the PSSCH from the first UE according to the control signal. The processing system1502includes circuitry1522for receiving a sidelink synchronization signal block (S-SSB) transmitted by a first UE, circuitry1524for receiving a control signal associated with the S-SSB to schedule a physical sidelink shared channel (PSSCH) that conveys system information (SI) for the second UE, and circuitry1526for receiving the PSSCH from the first UE according to the control signal.

Means for receiving may include a processor (e.g., the controller/processor280), one or more antennas (e.g., the antennas242or the antenna1510), and/or circuitry for receiving (e.g., the circuitry1522,1524, or1526for receiving). Means for scheduling a PSSCH may include a processor (e.g., the controller/processor280). Means for synchronizing may include a processor (e.g., the controller/processor280) and/or circuitry for synchronizing (e.g., the discovery signal manager122b). In certain aspects, various processors and/or various circuitry may include a circuit, a CPU, a GPU, a DSP, an ASIC, a FPGA, or other PLD, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described here.

Additional Considerations