Demand and response for sidelink synchronization signal block (S-SSB) transmissions

Abstract

A method of wireless communication by a user equipment receiving a sidelink includes detecting a lightweight sidelink synchronization signal (SL-SS) transmitted by a UE transmitting a sidelink. The lightweight SL-SS can have a pattern with a reduced number of physical sidelink broadcast channel (PSBCH) symbols. The method also includes transmitting, from the UE transmitting a sidelink, a request for additional SL-SS over an indicated resource. Another method includes receiving, from a UE receiving a sidelink, a request for additional sidelink synchronization signal (SL-SS). The method also includes transmitting the additional SL-SS in response to the request.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Patent Application No. 17 / 324,903, filed May 19, 2021, entitled “DEMAND AND RESPONSE FORSIDELINK SYNCHRONIZATION SIGNAL BLOCK (S-SSB) TRANSMISSION,” which claims the benefit of U.S. Provisional Patent Application No. 63 / 029,288, filed May 22, 2020, entitled “DEMAND AND RESPONSE FORSIDELINK SYNCHRONIZATION SIGNAL BLOCK (S-SSB) TRANSMISSION,” the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates generally to wireless communication, and more specifically to techniques and apparatus for the demand and response to side-link synchronization signal block (S-SSB) transmission. Background Technology

[0004] Wireless communication systems are widely deployed to provide a variety of telecommunications services, such as telephone, video, data, messaging, and broadcasting. Typical wireless communication systems employ multiple access technologies that can support communication with multiple users by sharing available system resources. Examples of such multiple access technologies include Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and Time Division Synchronous Code Division Multiple Access (TD-SCDMA).

[0005] These multiple access technologies have been adopted in various telecommunications standards to provide a common protocol enabling different wireless devices to communicate at the city, national, regional, and even global levels. An example telecommunications standard is fifth-generation (5G) New Radio (NR). 5G NR is part of the Continuous Mobile Broadband Evolution (CMB) program mandated by the 3rd Generation Partnership Project (3GPP) to meet new requirements related to latency, reliability, security, and scalability (e.g., the Internet of Things (IoT)), among others. 5G NR includes services related to enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). Some aspects of 5G NR can be based on the fourth-generation (4G) Long Term Evolution (LTE) standard. 5G NR technology requires further improvements. These improvements may also apply to other multiple access technologies and telecommunications standards that employ these technologies.

[0006] Wireless communication systems can include or support various types of communication systems, such as vehicle-to-everything (V2X) communication systems. Vehicles can use V2X communication systems to improve safety and help prevent collisions. Information about severe weather, nearby accidents, road conditions, and / or other information can be conveyed to the driver via V2X communication systems. In some cases, vehicles can communicate directly with each other using device-to-device (D2D) communication via a D2D wireless link.

[0007] With increasing demand for sidelink communication, different V2X communication systems compete for the same wireless communication resources. Furthermore, some sidelink user equipment (UEs) may be power-limited. Therefore, there is a need to improve the efficiency of sidelink wireless communication. Summary of the Invention

[0008] In various aspects of this disclosure, a method for wireless communication by a user equipment (UE) on a receiving side link includes detecting a side link synchronization signal (SL-SS) transmitted by the UE on a transmitting side link. The method also includes transmitting a request for additional SL-SS from the UE on the transmitting side link via an indicated resource.

[0009] In other aspects of this disclosure, a method for wireless communication by a user equipment (UE) on a transmitting sidelink includes receiving a request for an additional sidelink synchronization signal (SL-SS) from a UE on a receiving sidelink. The method also includes transmitting an additional SL-SS in response to the request.

[0010] Other aspects of this disclosure relate to an apparatus for wireless communication by a user equipment (UE), the apparatus having a processor, a memory coupled to the processor, and instructions stored in the memory. When the instructions are executed by the processor, the apparatus detects a sidelink synchronization signal (SL-SS) transmitted by the UE on the transmitting sidelink. The apparatus also transmits a request for additional SL-SS from the UE on the transmitting sidelink via indicated resources.

[0011] Other aspects of this disclosure relate to an apparatus for wireless communication by a user equipment (UE), the apparatus having a processor, a memory coupled to the processor, and instructions stored in the memory. When the instructions are executed by the processor, the apparatus receives a request for an additional sidelink synchronization signal (SL-SS) from the UE on the receiving sidelink. The apparatus also transmits the additional SL-SS in response to the request.

[0012] The aspects generally include, as described substantially with reference to the accompanying drawings and description, and as shown in the accompanying drawings and description, methods, apparatus, systems, computer program products, non-transitory computer-readable media, user equipment, base stations, wireless communication equipment, and processing systems.

[0013] The foregoing has provided a fairly broad overview of the features and technical advantages of the examples according to this disclosure in order to facilitate a better understanding of the following detailed description. Additional features and advantages will be described. The disclosed concepts and specific examples can be readily used as the basis for modifying or designing other structures for achieving the same purpose as this disclosure. Such equivalent structures do not depart from the scope of the appended claims. The characteristics of the disclosed concepts, their organization and operation, and related advantages will be better understood from the following description when considered in conjunction with the accompanying drawings. Each drawing is provided for illustrative and descriptive purposes and not as a limitation of the definitions in the claims. Attached Figure Description

[0014] To gain a more detailed understanding of the features described above, reference can be made to various aspects for a more specific description of the content briefly outlined above, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only certain typical aspects of the disclosure and should therefore not be considered as limiting its scope, as the description may allow for other equivalent aspects. The same reference numerals in different drawings can identify the same or similar elements.

[0015] Figure 1 This is a diagram illustrating an example of a wireless communication system and an access network.

[0016] Figure 2 Figures (A), (B), (C), and (D) in the figure illustrate examples of a first 5G New Radio (NR) frame, a downlink (DL) channel within a 5G NR subframe, a second 5G NR frame, and an uplink (UL) channel within a 5G NR subframe, respectively.

[0017] Figure 3 This is a diagram illustrating an example of a base station and user equipment (UE) in an access network.

[0018] Figure 4 This is a diagram illustrating an example of a vehicle-to-everything (V2X) system according to various aspects of this disclosure.

[0019] Figure 5 This is a block diagram illustrating an example of a vehicle-to-everything (V2X) system with a roadside unit (RSU) according to various aspects of this disclosure.

[0020] Figure 6 This is a diagram showing the symbol for a conventional side-link synchronization signal block (S-SSB).

[0021] Figure 7 This is a diagram illustrating the mode of a lightweight side-link synchronization signal block (S-SSB) according to various aspects of this disclosure.

[0022] Figure 8 This illustrates various aspects according to this disclosure. Figure 7 The graph shows a subset of the displayed patterns.

[0023] Figure 9 This is a timing diagram illustrating the requirements and responses of the Physical Side Link Broadcast Channel (PSBCH) according to various aspects of this disclosure.

[0024] Figure 10 This is a flowchart illustrating an example process performed, for example, by a user equipment (UE) on the receiving side link, according to various aspects of this disclosure.

[0025] Figure 11 This is a flowchart illustrating an example process performed, for example, by a user equipment (UE) transmitting a side link, according to various aspects of this disclosure. Detailed Implementation

[0026] Various aspects of this disclosure are described more fully below with reference to the accompanying drawings. However, this disclosure may be embodied in many different forms and should not be construed as limited to any particular structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be exhaustive and complete, and will fully convey the scope of this disclosure to those skilled in the art. Based on the teachings, those skilled in the art will understand that the scope of this disclosure is intended to cover any aspect of the disclosure, whether implemented independently of or in combination with any other aspect of this disclosure. For example, any number of the aspects set forth may be used to implement an apparatus or method. Furthermore, the scope of this disclosure is intended to cover an apparatus or method practiced using structures, functions, or structures and functions other than or related to the aspects set forth in this disclosure. It should be understood that any aspect of this disclosure may be embodied by one or more elements of the claims.

[0027] Several aspects of a telecommunications system will now be described with reference to various devices and techniques. These devices and techniques will be described in detail below and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively, “elements”). These elements may be implemented using hardware, software, or any combination thereof. Whether such an element is implemented as hardware or software depends on the specific application and the design constraints imposed on the entire system.

[0028] It should be noted that although the terms commonly associated with 5G and subsequent wireless technologies may be used to describe the aspects, the aspects of this disclosure may be applied to communication systems based on other generations, such as and including 3G and / or 4G technologies.

[0029] In cellular communication networks, wireless devices can communicate with each other via one or more network entities, such as base stations or scheduling entities. Some networks support device-to-device (D2D) communication, which enables the discovery and communication of nearby devices using direct links between devices (e.g., without going through a base station, relay, or another node). D2D communication can enable mesh networking and device-to-network relay functionality. Some examples of D2D technologies include Bluetooth pairing, Wi-Fi Direct, Miracast, and LTE-D. D2D communication can also be referred to as peer-to-peer (P2P) or sidelink communication.

[0030] D2D communication can be implemented using licensed or unlicensed frequency bands. Additionally, D2D communication can avoid the overhead of routing to and from base stations. Therefore, D2D communication can improve throughput, reduce latency, and / or improve energy efficiency. One type of D2D communication can include vehicle-to-everything (V2X) communication. V2X communication can assist autonomous vehicles in communicating with each other.

[0031] In New Radio (NR) Vehicle-to-Everything (V2X) communication, the transmitting sidelink UE and the receiving sidelink UE must be synchronized to enable communication between them, for example, for demodulation of data reception. UEs can synchronize via a common base station or via a synchronized base station. When UEs are in different asynchronous cells or when one or both UEs are not within network coverage, UEs synchronize with each other via a sidelink synchronization signal (SL-SS).

[0032] The SL-SS is transmitted within the Sidelink Synchronization Signal Block (S-SSB). The signals carried in the S-SSB include the Sidelink Primary Synchronization Signal (S-PSS), the Sidelink Secondary Synchronization Signal (S-SSS), and the Physical Sidelink Broadcast Channel (PSBCH). Together, the S-PSS, S-SSS, and PSBCH carry information such as the source ID of the transmitting UE, as well as synchronization information.

[0033] S-SSB transmission is inefficient and power-intensive. According to various aspects of this disclosure, lightweight S-SSB (or lightweight SL-SS) achieves power savings and reduces the system overhead of S-SSB transmission. Lightweight SL-SS has a mode with S-PSS and / or S-SSS, but without any PSBCH or with a reduced number of PSBCHs. A receive (RX)-side link UE that detects lightweight SL-SS requires an additional SL-SS from a transmit (TX)-side link UE. For example, the additional SL-SS could be a PSBCH or SIB.

[0034] The receiving UE can receive a message identifying resources used to request additional SL-SS. In some aspects of this disclosure, the resources are pre-configured. In other aspects, the sending UE indicates the resources required for bearer operations. Still in other aspects, resources can be indicated through a combination of these techniques.

[0035] In various aspects of this disclosure, the request may carry information about the behavior of the receiving UE. This information may include, for example, whether the receiving UE is within or outside network coverage, the transmitting power of the receiving UE, the mobility level of the receiving UE, etc. The transmitting power of the request may be indicated by the transmitting UE or may be pre-configured. In other aspects, the receiving UE may be instructed to send the request only if certain conditions are met. Still in other aspects, multiple resources may be indicated or pre-configured for the receiving UE to issue the request.

[0036] According to various aspects of this disclosure, once the transmitting UE detects a request from the receiving UE, the transmitting UE begins transmitting the requested signal (e.g., PSBCH) from the next S-SSB timing. In some configurations, the transmitting UE follows an indicated or pre-configured offset.

[0037] In other aspects, once the transmitting UE sends the SL-SS, a timer is started. If the transmitting UE does not detect a request from any UE or any qualified UE before the timer expires, the transmitting UE can continue according to several options. In the first option, the transmitting UE increases its transmit power for the next transmission of the SL-SS. In the second option, the transmitting UE stops sending the SL-SS. In other aspects, combinations of options one and two may occur.

[0038] Figure 1This diagram illustrates an example of a wireless communication system and access network 100. The wireless communication system (also known as a wireless wide area network (WWAN)) includes a base station 102, a user interface unit (UE) 104, an evolved packet core (EPC) 160, and another core network 190 (e.g., a 5G core (5GC)). Base station 102 may include macro cells (high-power cellular base stations) and / or small cells 102' (low-power cellular base stations). The macro cell includes a base station. The small cell 102' includes femtocells, picocells, and microcells.

[0039] Base station 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) can interface with EPC 160 via backhaul link 132 (e.g., S1 interface). Base station 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN)) can interface with core network 190 via backhaul link 184. Among other functions, base station 102 can perform one or more of the following functions: transmission of user data, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection establishment and release, load balancing, distribution of non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and device tracking, RAN information management (RIM), paging, location, and delivery of warning messages. Base stations 102 can communicate with each other directly or indirectly (e.g., via EPC 160 or core network 190) via backhaul link 134 (e.g., X2 interface). The backhaul link 134 can be wired or wireless.

[0040] Base station 102 can communicate wirelessly with UE 104. Each base station 102 can provide communication coverage for a corresponding geographic coverage area 110. Overlapping geographic coverage areas 110 may exist. For example, a small cell 102' may have a coverage area 110' that overlaps with the coverage areas 110 of one or more macro base stations 102. A network that includes both small cells and macro cells can be referred to as a heterogeneous network. The heterogeneous network may also include evolved home nodes (eNBs) (HeNBs) that can provide services to restricted groups called closed subscriber groups (CSGs). The communication link 120 between base station 102 and UE 104 may include uplink (UL) (also known as reverse link) transmission from UE 104 to base station 102 and / or downlink (DL) (also known as forward link) transmission from base station 102 to UE 104. The communication link 120 may use multiple-input multiple-output (MIMO) antenna techniques, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link can be via one or more carriers. Base station 102 / UE 104 can allocate up to Y MHz (e.g., 5, 10, 15, 20, 100, 400 MHz, etc.) of spectrum bandwidth per carrier in carrier aggregation up to a total of Yx MHz (x component carriers) for transmission in each direction. Carriers can be adjacent to each other or not. Carrier allocation can be asymmetrical relative to DL and UL (e.g., more or fewer carriers can be allocated to DL compared to UL). Component carriers can comprise a primary component carrier and one or more secondary component carriers. The primary component carrier can be referred to as the primary cell (PCell), while the secondary component carrier can be referred to as the secondary cell (SCell).

[0041] Some UEs 104 can communicate with each other using device-to-device (D2D) communication link 158. D2D communication link 158 can use DL / UL WWAN spectrum. D2D communication link 158 can use one or more sidelink channels, such as Physical Sidelink Broadcast Channel (PSBCH), Physical Sidelink Discovery Channel (PSDCH), Physical Sidelink Shared Channel (PSSCH), and Physical Sidelink Control Channel (PSCCH). D2D communication can be performed through various wireless D2D communication systems, such as FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

[0042] The wireless communication system may further include a Wi-Fi access point (AP) 150 that communicates with a Wi-Fi station (STA) 152 via a communication link 154 in the 5 GHz unlicensed spectrum. When communicating in the unlicensed spectrum, the STA 152 / AP 150 may perform a free channel assessment (CCA) before communication to determine whether the channel is available.

[0043] Small cell 102' can operate in licensed and / or unlicensed spectrum. When operating in unlicensed spectrum, small cell 102' can employ NR and use the same 5 GHz unlicensed spectrum as Wi-FiAP 150. Using NR in unlicensed spectrum can increase coverage and / or capacity of the access network.

[0044] Base station 102, whether a small cell 102' or a large cell (e.g., a macro base station), may include an eNB, a gNodeB (gNB), or another type of base station. Some base stations, such as gNB 180, may operate in the conventional sub-6 GHz spectrum at millimeter-wave (mmWave) frequencies and / or communicate with UE 104 at near-mmWave frequencies. When gNB 180 operates at mmWave or near-mmWave frequencies, it may be referred to as an mmWave base station. Extremely high frequency (EHF) is a portion of the radio frequency (RF) spectrum in the electromagnetic spectrum. EHF has a range between 30 GHz and 300 GHz and wavelengths between 1 mm and 10 mm. Radio waves in this band may be referred to as millimeter waves. Near-mmW may extend down to 3 GHz frequencies with wavelengths of 100 mm. Ultra-high frequency (SHF) bands extend between 3 GHz and 30 GHz and are also known as centimeter waves. Communication using mmW / near mmW radio bands (e.g., 3 GHz–300 GHz) suffers from extremely high path loss and short range. mmWave base station 180, together with UE 104, can utilize beamforming 182 to compensate for the extremely high path loss and short range.

[0045] Base station 180 can transmit beamformed signals to UE 104 in one or more transmit directions 182'. UE 104 can receive beamformed signals from base station 180 in one or more receive directions 182'. UE 104 can also transmit beamformed signals to base station 180 in one or more transmit directions. Base station 180 can receive beamformed signals from UE 104 in one or more receive directions. Base station 180 / UE 104 can perform beam training to determine the optimal receive and transmit directions for each of base station 180 / UE 104. The transmit and receive directions of base station 180 can be the same or different. The transmit and receive directions of UE 104 can be the same or different.

[0046] EPC 160 may include Mobility Management Entity (MME) 162, other MMEs 164, Serving Gateway 166, Multimedia Broadcast Multicast Service (MBMS) Gateway 168, Broadcast Multicast Service Center (BM-SC) 170, and Packet Data Network (PDN) Gateway 172. MME 162 can communicate with Home Subscriber Server (HSS) 174. MME 162 is the control node that handles signaling between UE 104 and EPC 160. Typically, MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are transmitted through Serving Gateway 166, which is itself connected to PDN Gateway 172. PDN Gateway 172 provides UE IP address allocation and other functions. PDN Gateway 172 and BM-SC 170 are connected to IP Service 176. IP Service 176 may include the Internet, intranet, IP Multimedia Subsystem (IMS), PS streaming service, and / or other IP services. The BM-SC 170 provides functionality for MBMS user service provisioning and delivery. It can serve as an entry point for content provider MBMS transmissions, authorize and initiate MBMS bearer services within a Public Land Mobile Network (PLMN), and schedule MBMS transmissions. The MBMS gateway 168 can allocate MBMS traffic to base station 102 belonging to a Broadcast-Specific Service Multicast Single Frequency Network (MBSFN) area, and is responsible for session management (start / stop) and collecting billing information related to Evolved Multimedia Broadcast Multicast Service (eMBMS).

[0047] Core network 190 may include Access and Mobility Management Functions (AMF) 192, other AMFs 193, Session Management Functions (SMF) 194, and User Plane Functions (UPF) 195. AMF 192 can communicate with Unified Data Management (UDM) 196. AMF 192 is the control node that handles signaling between UE 104 and core network 190. Typically, AMF 192 provides Quality of Service (QoS) streaming and session management. All user Internet Protocol (IP) packets are transmitted through UPF 195. UPF 195 provides UE IP address allocation and other functions. UPF 195 connects to IP service 197. IP service 197 may include the Internet, intranet, IP Multimedia Subsystem (IMS), PS streaming service, and / or other IP services.

[0048] Base station 102 may also be referred to as gNB, Node B, evolved Node B (eNB), access point, base transceiver, radio base station, radio transceiver, transceiver function, Basic Services Set (BSS), Extended Services Set (ESS), Transmitter Receiver Point (TRP), or other suitable terms. Base station 102 provides UE 104 with access to EPC 160 or core network 190. Examples of UE 104 include cellular phones, smartphones, Session Initiation Protocol (SIP) phones, laptops, personal digital assistants (PDAs), satellite radios, GPS devices, multimedia devices, video devices, digital audio players (e.g., MP3 players), cameras, game consoles, tablets, smart devices, wearable devices, vehicles, electricity meters, air pumps, large or small kitchen appliances, healthcare devices, implants, sensors / actuators, displays, or any other similar functional devices. Some UE 104 devices may be referred to as IoT devices (e.g., parking meters, air pumps, toasters, vehicles, heart monitors, etc.). UE 104 may also be referred to as a station, mobile station, subscriber station, mobile unit, subscriber unit, radio unit, remote unit, mobile device, radio device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, radio terminal, remote terminal, handheld device, user agent, mobile client, client, or some other suitable term.

[0049] Refer again Figure 1 In some respects, a sidelink UE (such as UE 104) can send or respond to SL-SS (Sidelink Synchronization Signal) requests. UE 104 may include an S-SSB request component 199 configured to send or receive requests.

[0050] Although the following description may focus on 5G NR, it can be applied to other similar areas such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

[0051] Figure 2 Figure 200 (A) shows an example of the first subframe within a 5G NR frame structure. Figure 2 Figure 230 (B) shows an example of a DL channel within a 5G NR subframe. Figure 2 Figure 250 (C) shows an example of a second subframe within a 5G NR frame structure. Figure 2 Figure 280 (D) illustrates an example of a UL channel within a 5G NR subframe. The 5G NR frame structure can be Frequency Division Duplex (FDD), where subframes within a specific set of subcarriers (carrier system bandwidth) are dedicated to either DL or UL, or the 5G NR frame structure can be Time Division Duplex (TDD), where subframes within a specific set of subcarriers (carrier system bandwidth) are dedicated to both DL and UL. Figure 2 (A) and Figure 2 In the example provided in (C), it is assumed that the 5G NR frame structure is TDD, where subframe 4 is configured with slot format 28 (primarily DL), where D is DL, U is UL, and X is flexibly used between DL / UL, and subframe 3 is configured with slot format 34 (mostly UL). Although subframe 3 is shown with slot format 34 and subframe 4 with slot format 28 respectively, any particular subframe can be configured with any of the various available slot formats 0-61. Slot formats 0 and 1 are both DL and UL, respectively. Other slot formats 2-61 include a mixture of DL, UL, and flexible symbols. The slot format is configured for the UE via the received Slot Format Indicator (SFI) (dynamically via DL Control Information (DCI) or semi-statically / statically via Radio Resource Control (RRC) signaling). Note that the following description also applies to the TDD 5G NR frame structure.

[0052] Other wireless communication technologies may have different frame structures and / or different channels. A frame (10 ms) can be divided into 10 equal-sized subframes (1 ms). Each subframe may include one or more time slots. Subframes may also include mini-time slots, which may contain 7, 4, or 2 symbols. Each time slot may contain 7 or 14 symbols, depending on the time slot configuration. For time slot configuration 0, each time slot may contain 14 symbols, and for time slot configuration 1, each time slot may contain 7 symbols. Symbols on the DL can be Cyclic Prefix (CP) Orthogonal Frequency Division Multiplexing (OFDM) (CP-OFDM) symbols. Symbols on the UL can be CP-OFDM symbols (for high-throughput scenarios) or Discrete Fourier Transform (DFT) Extended OFDM (DFT-S-OFDM) symbols (also known as Single Carrier Frequency Division Multiple Access (SC-FDMA) symbols) (for power-constrained scenarios; limited to single-stream transmission). The number of time slots within a subframe is based on the time slot configuration and numbering. For slot configuration 0, different digital parameters μ0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots per subframe, respectively. For slot configuration 1, different digital parameters 0 to 2 allow for 2, 4, and 8 slots per subframe, respectively. Therefore, for slot configuration 0 and digital parameter μ, each slot has 14 symbols, and each subframe has 2μ slots. Subcarrier spacing and symbol length / duration are functions of the digital parameters. The subcarrier spacing can be equal to 2^μ * 15 kHz, where μ is a digital parameter from 0 to 5. Similarly, digital parameter μ = 0 has a subcarrier spacing of 15 kHz, and digital parameter μ = 5 has a subcarrier spacing of 480 kHz. Symbol length / duration is inversely proportional to the subcarrier spacing. Figure 2 (A) to Figure 2 Example (D) is provided for slot configuration 0, where each slot has 14 symbols, and for the number μ = 0, each subframe has 1 slot. The subcarrier spacing is 15 kHz, and the symbol duration is approximately 66.7 μs.

[0053] A resource grid can represent the frame structure. Each time slot contains a resource block (RB) that extends 12 consecutive subcarriers (also known as a physical RB (PRB)). The resource grid is divided into multiple resource elements (REs). The number of bits carried by each RE depends on the modulation scheme.

[0054] like Figure 2As illustrated in (A), some REs carry reference (pilot) signals (RS) for the UE. The RS may include a demodulation RS (DM-RS) (indicated as Rx for a specific configuration, where 100x is the port number, but other DM-RS configurations are possible) and a channel state information reference signal (CSI-RS) for channel estimation at the UE. The RS may also include a beam measurement RS (BRS), a beam refinement RS (BRRS), and a phase tracking RS (PT-RS).

[0055] Figure 2 (B) shows examples of various DL channels within a subframe of a frame. The Physical Downlink Control Channel (PDCCH) carries the DCI in one or more Control Channel Elements (CCEs), each CCE containing nine RE Groups (REGs), each REG containing four consecutive REs in an OFDM symbol. The Primary Synchronization Signal (PSS) can be within symbol 2 of a specific subframe of the frame. UE104 uses the PSS to determine subframe / symbol timing and the Physical Layer Identifier. The Secondary Synchronization Signal (SSS) can be within symbol 4 of a specific subframe of the frame. The UE uses the SSS to determine the Physical Layer Cell Identifier Group Number and the radio frame timing. Based on the Physical Layer Identifier and the Physical Layer Cell Identifier Group Number, the UE can determine the Physical Cell Identifier (PCI). Based on this PCI, the UE can determine the location of the aforementioned DM-RS. The Physical Broadcast Channel (PBCH) carrying the Primary Information Block (MIB) can be logically grouped with the PSS and SSS to form a Synchronization Signal (SS) / PBCH block. The MIB provides numerous RBs within the system bandwidth and system frame number (SFN). The Physical Downlink Shared Channel (PDSCH) carries user data and broadcast system information not transmitted via the PBCH, such as System Information Blocks (SIBs) and paging messages.

[0056] like Figure 2 As illustrated in (C), some REs carry DM-RS for channel estimation at the base station (indicated as R for a particular configuration, but other DM-RS configurations are also possible). The UE can transmit DM-RS for the Physical Uplink Control Channel (PUCCH) and DM-RS for the Physical Uplink Shared Channel (PUSCH). The PUSCH DM-RS can be transmitted in the first one or two symbols preceding the PUSCH. The PUCCH DM-RS can be transmitted in different configurations depending on whether a short or long PUCCH is transmitted and depending on the specific PUCCH format used. Although not shown, the UE can transmit a Sounding Reference Signal (SRS). The base station can use the SRS for channel quality estimation to enable frequency-dependent scheduling on the UL.

[0057] Figure 2(D) shows examples of various UL channels within a subframe of a frame. The PUCCH can be positioned as indicated in one configuration. The PUCCH carries uplink control information (UCI), such as scheduling requests, channel quality indicators (CQI), pre-decoding matrix indicators (PMI), rank indicators (RI), and hybrid automatic repeat request (HARQ) acknowledgment / negative acknowledgment (ACK / NACK) feedback. The PUCCH carries data and can additionally be used to carry buffer status reports (BSR), power headroom reports (PHR), and / or UCI.

[0058] Figure 3 This is a block diagram of base station 310 communicating with UE 350 in the access network. In the DL, IP packets from EPC 160 can be provided to controller / processor 375. Controller / processor 375 implements Layer 3 and Layer 2 functions. Layer 3 includes the Radio Resource Control (RRC) layer, and Layer 2 includes the Service Data Adaptation Protocol (SDAP) layer, Packet Data Convergence Protocol (PDCP) layer, Radio Link Control (RLC) layer, and Media Access Control (MAC) layer. The controller / processor 375 provides RRC layer functions associated with broadcasting system information (e.g., MIB and SIB), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-Radio Access Technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functions associated with header compression / decompression, security (encryption, decryption, integrity protection, integrity verification), and handover support functions; RLC layer functions associated with upper-layer packet data unit (PDU) transmission, error correction via ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functions associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs to transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority processing, and logical channel prioritization.

[0059] Transmit (TX) processor 316 and receive (RX) processor 370 implement Layer 1 functions associated with various signal processing functions. Layer 1, including the physical (PHY) layer, may include error detection on the transport channel, forward error correction (FEC) encoding / decoding of the transport channel, interleaving, rate matching, mapping to the physical channel, modulation / demodulation of the physical channel, and MIMO antenna processing. TX processor 316 processes the mapping to the signal constellation based on various modulation schemes (e.g., binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), M-phase shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The encoded and modulated symbols can then be divided into parallel streams. Each stream can then be mapped to OFDM subcarriers, multiplexed with a reference signal (e.g., pilot) in the time and / or frequency domains, and then combined using inverse fast Fourier transform (IFFT) to produce a physical channel carrying the time-domain OFDM symbol stream. The OFDM streams are spatially pre-decoded to produce multiple spatial streams. The channel estimate from channel estimator 374 can be used to determine the decoding and modulation scheme, as well as for spatial processing. The channel estimate can be derived from the reference signal and / or channel condition feedback transmitted by UE 350. Each spatial stream can then be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX can use the corresponding spatial stream to modulate an RF carrier for transmission.

[0060] At UE 350, each receiver 354RX receives signals via its respective antenna 352. Each receiver 354RX recovers the information modulated onto the RF carrier and provides this information to the receive (RX) processor 356. The TX processor 368 and RX processor 356 implement Layer 1 functions associated with various signal processing functions. The RX processor 356 can perform spatial processing on the information to recover any spatial streams leading to UE 350. If multiple spatial streams are leading to UE 350, they can be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then uses a Fast Fourier Transform (FFT) to convert the OFDM symbol stream from the time domain to the frequency domain. The frequency domain signal consists of a separate OFDM symbol stream for each subcarrier of the OFDM signal. By determining the most probable signal constellation points transmitted by the base station 310, the symbols on each subcarrier and the reference signal are recovered and demodulated. These soft decisions can be based on a channel estimate calculated by the channel estimator 358. The soft decision is then decoded and deinterleaved to recover the data and control signals originally transmitted by base station 310 on the physical channel. The data and control signals are then provided to controller / processor 359, which implements Layer 3 and Layer 2 functions.

[0061] The controller / processor 359 may be associated with a memory 360 that stores program code and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller / processor 359 provides demultiplexing, packet reassembly, decryption, header decompression, and control signal processing between transport and logical channels to recover IP packets from the EPC 160. The controller / processor 359 is also responsible for error detection using ACK and / or NACK protocols to support HARQ operation.

[0062] Similar to the functions described in the DL transmission combined with base station 310, controller / processor 359 provides RRC layer functions associated with system information (e.g., MIB and SIB) acquisition, RRC connectivity, and measurement reporting; PDCP layer functions associated with header compression / decompression and security (encryption, decryption, integrity protection, and integrity verification); RLC layer functions associated with upper-layer PDU transmission, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functions associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs to TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority processing, and logical channel priority.

[0063] The channel estimate derived by the channel estimator 358 from the reference signal or feedback transmitted from the base station 310 can be used by the TX processor 368 to select an appropriate decoding and modulation scheme and facilitate spatial processing. The spatial stream generated by the TX processor 368 can be provided to different antennas 352 via individual transmitters 354TX. Each transmitter 354TX can use the corresponding spatial stream to modulate an RF carrier for transmission.

[0064] The UL transmission is processed at base station 310 in a manner similar to that described in conjunction with the receiver function at UE 350. Each receiver 318RX receives the signal via its respective antenna 320. Each receiver 318RX recovers the information modulated onto the RF carrier and provides this information to RX processor 370.

[0065] The controller / processor 375 may be associated with a memory 376 that stores program code and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller / processor 375 provides demultiplexing, packet reassembly, decryption, header decompression, and control signal processing between transport and logical channels to recover IP packets from the UE 350. IP packets from the controller / processor 375 may be provided to the EPC 160. The controller / processor 375 is also responsible for error detection using ACK and / or NACK protocols to support HARQ operation.

[0066] At least one of the TX processor 368, RX processor 356, and controller / processor 359 can be configured to perform operations related to... Figure 1 The S-SSB requirement component 199 relates to various aspects. Additionally, at least one of the TX processor 316, RX processor 370, and controller / processor 375 can be configured to perform actions related to... Figure 1 The S-SSB requirement component 199 is related to various aspects.

[0067] In some aspects, the user equipment 350 of the receiving-side link and the user equipment 350 of the transmitting-side link may include components for detection, components for transmitting, components for receiving, components for initiation, components for incrementing, components for stopping, and / or components for selection. Such components may include combinations of... Figure 3 One or more components of the UE 350 described.

[0068] Figure 4 This diagram illustrates a device-to-device (D2D) communication system 400 including V2X communication according to various aspects of this disclosure. For example, the D2D communication system 400 may include V2X communication (e.g., a first UE 450 communicating with a second UE 451). In some aspects, the first UE 450 and / or the second UE 451 may be configured to communicate in licensed and / or shared radio spectrum. The shared radio spectrum may be unlicensed, and thus a variety of different technologies can be used for communication in the shared radio spectrum, including New Radio (NR), LTE, Advanced LTE, Licensed Assisted Access (LAA), Dedicated Short Range Communication (DSRC), MuLTEFire, 4G, etc. The above list of technologies is for illustrative purposes only and is not exhaustive.

[0069] The D2D communication system 400 can use NR radio access technology. Of course, other radio access technologies, such as LTE radio access technology, can also be used. In D2D communication (e.g., V2X communication or vehicle-to-vehicle (V2V) communication), UEs 450 and 451 can operate on the networks of different mobile network operators (MNOs). Each network can operate in its own radio spectrum. For example, the air interface to the first UE 450 (e.g., the Uu interface) can be on one or more frequency bands different from the air interface to the second UE 451. The first UE 450 and the second UE 451 can communicate via sidelink component carriers (e.g., via the PC5 interface). In some examples, the MNO can schedule sidelink communication between or among UEs 450 and 451 in licensed and / or shared radio spectrum (e.g., the 5 GHz radio spectrum band).

[0070] The shared radio spectrum may be unlicensed, so different technologies may use the shared radio spectrum for communication. In some respects, the MNO does not schedule D2D communication (e.g., sidelink communication) between or among UEs 450 and 451. The D2D communication system 400 may also include a third UE 452.

[0071] For example, the third UE 452 can operate in the first network 410 (e.g., the first MNO) or another network. The third UE 452 can perform D2D communication with the first UE 450 and / or the second UE 451. The first base station 420 (e.g., gNB) can communicate with the third UE 452 via downlink (DL) carrier 432 and / or uplink (UL) carrier 442. DL communication can utilize various DL resources (e.g., DL subframes). Figure 2 (A) and / or DL ​​channel ( Figure 2 (B)). Various UL resources can be used (e.g., UL subframes). Figure 2 (C) and UL channel ( Figure 2 UL communication is performed via UL carrier 442.

[0072] The first network 410 operates in the first spectrum and includes, for example, a first base station 420 (e.g., a gNB) that communicates with at least the first UE 450. Figure 1-3 As described above. The first base station 420 (e.g., gNB) can communicate with the first UE 450 via DL carrier 430 and / or UL carrier 440. DL communication can utilize various DL resources (e.g., DL subframes). Figure 2 (A) and / or DL ​​channel ( Figure 2 (B)). Various UL resources can be used (e.g., UL subframes). Figure 2 (C) and UL channel ( Figure 2 UL communication is performed via UL carrier 440.

[0073] In some respects, the second UE 451 may be on a different network than the first UE 450. In some respects, the second UE 451 may be on a second network 411 (e.g., of a second MNO). The second network 411 may operate in a second spectrum (e.g., a second spectrum different from the first spectrum) and may include, for example, a second base station 421 (e.g., a gNB) communicating with the second UE 451. Figure 1-3 As described in [the text].

[0074] The second base station 421 can communicate with the second UE 451 via DL carrier 431 and UL carrier 441. Various DL resources (e.g., DL subframes) can be used. Figure 2 (A) and DL channel ( Figure 2 (B))) performs DL communication via DL carrier 431. Various UL resources (e.g., UL subframes) are used. Figure 2 (C) and / or UL channel ( Figure 2 UL communication is performed via UL carrier 441.

[0075] In a conventional system, the first base station 420 and / or the second base station 421 allocate resources to the UE for device-to-device (D2D) communication (e.g., V2X and / or V2V communication). For example, the resources may be a UL resource pool, which may be orthogonal (e.g., one or more FDM channels) or non-orthogonal (e.g., Code Division Multiplexing (CDM) / Resource Extended Multiple Access (RSMA) in each channel). The first base station 420 and / or the second base station 421 may configure the resources via PDCCH (e.g., a faster method) or RRC (e.g., a slower method).

[0076] In some systems, each UE 450, 451 autonomously selects resources for D2D communication. For example, each UE 450, 451 can sense and analyze channel occupancy during a sensing window. UE 450, 451 can use the sensing information to select resources from the sensing window. As discussed, one UE 451 can assist another UE 450 in performing resource selection. The assisting UE 451 can be referred to as the receiver UE or partner UE, which can potentially notify the transmitter UE 450. The transmitter UE 450 can send information to the receiver UE 451 via sidelink communication.

[0077] D2D communication (e.g., V2X and / or V2V communication) can be performed via one or more sidelink carriers 470, 480. For example, one or more sidelink carriers 470, 480 may include one or more channels such as the Physical Sidelink Broadcast Channel (PSBCH), Physical Sidelink Discovery Channel (PSDCH), Physical Sidelink Shared Channel (PSSCH), and Physical Sidelink Control Channel (PSCCH).

[0078] In some examples, sidelink carriers 470 and 480 can operate using the PC5 interface. The first UE 450 can transmit to one or more (e.g., multiple) devices via the first sidelink carrier 470, including to the second UE 451. The second UE 451 can transmit to one or more (e.g., multiple) devices via the second sidelink carrier 480, including to the first UE 450.

[0079] In some respects, UL carrier 440 and first sidelink carrier 470 can be aggregated to increase bandwidth. In some respects, first sidelink carrier 470 and / or second sidelink carrier 480 can share a first spectrum (with first network 410) and / or share a second spectrum (with second network 411). In some respects, sidelink carriers 470, 480 can operate in unlicensed / shared radio spectrum.

[0080] In some aspects, sidelink communication on a sidelink carrier can occur between a first UE 450 and a second UE 451. In one aspect, the first UE 450 can perform sidelink communication with one or more (e.g., multiple) devices, including the second UE 451, via a first sidelink carrier 470. For example, the first UE 450 can send broadcast transmissions to multiple devices (e.g., the second UE 451 and the third UE 452) via the first sidelink carrier 470. The second UE 451 (e.g., among other UEs) can receive such broadcast transmissions. Additionally or alternatively, the first UE 450 can send multicast transmissions to multiple devices (e.g., the second and third UEs 451, 452) via the first sidelink carrier 470. The second UE 451 and / or the third UE 452 (e.g., among other UEs) can receive such multicast transmissions. Multicast transmissions can be connectionless or connection-oriented. Multicast transmissions can also be referred to as multicast transmissions.

[0081] Furthermore, the first UE 450 may send unicast transmissions to devices (such as the second UE 451) via a first sidelink carrier 470. The second UE 451 (e.g., among other UEs) may receive such unicast transmissions. Additionally or alternatively, the second UE 451 may perform sidelink communication with one or more (e.g., multiple) devices, including the first UE 450, via a second sidelink carrier 480. For example, the second UE 451 may send broadcast transmissions to multiple devices via the second sidelink carrier 480. The first UE 450 (e.g., among other UEs) may receive such broadcast transmissions.

[0082] In another example, the second UE 451 can send multicast transmissions to multiple devices (e.g., the first and third UEs 450, 452) via the second sidelink carrier 480. The first UE 450 and / or the third UE 452 (e.g., among other UEs) can receive such multicast transmissions. Furthermore, the second UE 451 can send unicast transmissions to devices (such as the first UE 450) via the second sidelink carrier 480. The first UE 450 (e.g., among other UEs) can receive such unicast transmissions. The third UE 452 can communicate in a similar manner.

[0083] In some respects, such sidelink communication may occur on a sidelink carrier between the first UE 450 and the second UE 451, for example, in the absence of an MNO allocating resources for such communication (e.g., one or more portions of resource blocks (RBs), time slots, frequency bands, and / or channels associated with sidelink carriers 470 and 480) and / or without scheduling such communication. Sidelink communication may include service communication (e.g., data communication, control communication, paging communication, and / or system information communication). Furthermore, sidelink communication may include sidelink feedback communication associated with service communication (e.g., transmission of feedback information for previously received service communication). Sidelink communication may employ at least one sidelink communication structure having at least one feedback symbol. The feedback symbol of the sidelink communication structure may be assigned any sidelink feedback information that can be propagated in a device-to-device (D2D) communication system 400 between devices (e.g., the first UE 450, the second UE 451, and / or the third UE 452). As discussed, a UE can be a vehicle (e.g., UE 450, 451), a mobile device (e.g., 452), or another type of device. In some cases, a UE can be a special type of UE, such as a roadside unit (RSU).

[0084] Figure 5 An example of a V2X system 500 with an RSU 510 according to various aspects of this disclosure is shown. Figure 5 As shown, transmitter UE 504 transmits data to RSU 510 and receiving UE 502 via sidelink transmission 512. Additionally or alternatively, RSU 510 may transmit data to transmitter UE 504 via sidelink transmission 512. RSU 510 may forward data received from transmitter UE 504 to cellular network (e.g., gNB) 508 via UL transmission 514. gNB 508 may transmit data received from RSU 510 to other UEs 506 via DL transmission 516. RSU 510 may be integrated with traffic infrastructure (e.g., traffic lights, light poles, etc.). For example, as... Figure 5 As shown, RSU 510 is a traffic signal located on one side of road 520. Alternatively, RSU 510 may be a standalone unit.

[0085] In New Radio (NR) Vehicle-to-Everything (V2X) communications, the user equipment (UE) transmitting the sidelink and the UE receiving the sidelink must synchronize to enable communication between them, such as demodulation for receiving data. UEs can synchronize via a common base station or via a synchronized base station. When UEs are in different asynchronous cells or when one or both UEs are not within network coverage, UEs synchronize with each other via a sidelink synchronization signal (SL-SS). The SL-SS is transmitted within the sidelink synchronization signal block (S-SSB). The signals carried in the S-SSB include the sidelink primary synchronization signal (S-PSS), the sidelink secondary synchronization signal (S-SSS), and the physical sidelink broadcast channel (PSBCH). The S-PSS, S-SSS, and PSBCH together carry information such as the source ID of the transmitting UE and synchronization information.

[0086] The S-SSB bandwidth is eleven resource blocks (RBs) within the bandwidth of the pre-configured sidelink bandwidth portion (SL-BWP). The UE assumes that the digital parameters of the SL-SS and PSBCH are the same as the digital parameters of the SL-BWP received by the SL-SS / PSBCH block. The frequency location of the S-SSB is pre-configured. The UE assumes the frequency location corresponding to the subcarrier at index 66 in the SL-SS / PSBCH block, which is provided by the parameter absoluteFrequencySSB-SL. Therefore, the UE does not perform assumption detection on the frequency location of the S-SSB for a given frequency band. In other words, the UE knows where to look for the S-SSB. The UE assumes that the subcarrier at index 0 in the SL-SS / PSBCH block is aligned with the subcarrier at index 0 in the SL-BWP. Note that the potential pre-configured frequency locations may be limited.

[0087] For all subcarrier spacings (SCS), the S-SSB periodicity can be 160ms. S-SSB resources in the time domain are pre-configured. S-SSBs within a 160ms period are distributed at equal intervals and have the following pre-configured parameters: the offset from the start of the S-SSB period to the first S-SSB; and the spacing between adjacent S-SSBs. For frequency 1 (FR1-sub-6GHz), the number of S-SSB transmissions within one S-SSB period can be configured as: 15kHz SCS, {1}, 30kHz SCS, {1 or 2}, 60kHz SCS, {1, 2 or 4}; for frequency 2 (FR2-mmWave), the number of S-SSB transmissions within one S-SSB period can be configured as: 60kHz SCS, {1, 2, 4, 8, 16 or 32} and 120kHz SCS, {1, 2, 4, 8, 16, 32 or 64}.

[0088] Figure 6This is a diagram illustrating the orthogonal frequency division multiplexing (OFDM) symbols of a conventional side-link synchronization signal block (S-SSB). Specifically, the NR S-SSB structure with a normal cyclic prefix is ​​shown below. Figure 6 As shown. The first symbol is used for PSBCH. The second and third symbols are used for S-PSS. The fourth and fifth symbols are used for S-SSS. All symbols except the last one are used for PSBCH. The last symbol is empty, forming a gap. No specific symbols are reserved for Automatic Gain Control (AGC) tuning. For the case of extended cyclic prefixes, the structure is the same except that the number of PSBCH symbols after S-SSS is only 6.

[0089] The two symbols of the side-link master synchronization signal (S-PSS) can use the same sequence. The M-sequence of length 127 in the S-PSS uses the same polynomial (e.g., x...). 7 +x 4 +1) and the same initial value, but different from the cyclic shift {22, 65} of the NR downlink primary synchronization signal (DL-PSS). Additionally, the two symbols of the sidelink secondary synchronization signal (S-SSS) can use the same sequence. The 127-length Gold sequence of the S-SSS repeats the same polynomial, initial value, and cyclic shift as the Gold sequence of the NR downlink secondary synchronization signal (DL-SSS). The UE assumes that the S-PSS symbols, S-SSS symbols, PSBCH demodulation reference signal (DM-RS), and PSBCH symbol data all have the same transmission power.

[0090] Different types of synchronization references can be used. Example synchronization types include GNSS-based synchronization and gNB / eNB-based synchronization. Each type of synchronization reference has its own synchronization priority, which is pre-configured. For the side-link (SL) synchronization procedure, the UE selects the synchronization reference with the highest priority as the reference to derive its transmission timing. When two or more UE synchronization sources have the same priority, the UE selects the S-SSB with the highest Reference Signal Received Power (RSRP) as the synchronization source. The NR side-link (SL) procedure for signaling, identifying the priority of one or more synchronization references, and selecting the synchronization reference is similar to the Long Term Evolution (LTE) procedure.

[0091] In NRV2X communication, the triggering of S-SSB transmissions reuses a process from LTE V2X. That is, the gNB can instruct a UE within coverage area to become a synchronization reference and send a sidelink synchronization signal (SL-SS) to allow synchronization with other UEs. For example, the gNB can configure a threshold such that when the downlink RSRP drops below a configured threshold, the UE becomes a synchronization source and sends an SL-SS. A UE outside coverage area can also become a synchronization reference when it has data to transmit. In this case, for example, when the RSRP from the current synchronization reference (e.g., another SL UE) drops below a pre-configured RSRP threshold, the UE sends an SL-SS. For example, a UE outside coverage area can become a synchronization reference once it has not received a synchronization signal.

[0092] S-SSB transmission can be resource inefficient and may also increase power consumption. For example, the described resource and power issues may occur if the side-link (SL) UE transmitting the SL-SS is in deep coverage, if the SL UE transmitting the SL-SS moves rapidly, or if there is no nearby UE responding. The described resource and power issues may also occur during beam management when the UE transmits the SL-SS on FR2 (frequency range 2, e.g., mmWave), where multiple S-SSB blocks are specified every 160ms for different beam directions. That is, there are more S-SSB opportunities because each S-SSB can be transmitted on a different beam.

[0093] According to various aspects of this disclosure, lightweight S-SSB (lite S-SSB) (or lightweight SL-SS (lite SL-SS)) achieves power savings and reduces system overhead for S-SSB transmission.

[0094] In some respects, the transmitting (TX) UE sends a lightweight SL-SS (or a lightweight S-SSB). A lightweight SL-SS consists only of an S-PSS and / or S-SSS with a reduced number of Physical Side Link Broadcast Channel (PSBCH) symbols, e.g., no PSBCH. This is similar to the situation described above regarding normal CP (Cyclic Prefix) S-SSBs. Figure 6 As mentioned, the PSBCH exists on 9 out of 14 symbols in each S-SSB. Therefore, omitting the PSBCH reduces transmission power. In some configurations, the transmitting UE can be a power-constrained sidelink UE, which can benefit from power savings.

[0095] Figure 7This is a diagram illustrating modes of lightweight sidelink synchronization signal blocks (S-SSBs) according to various aspects of this disclosure. As shown in modes 1-8, no PSBCH is transmitted. In mode 1, there are two S-PSS symbols and two S-SSS symbols. In other aspects, as shown in modes 2, 3, and 4, the sidelink UE transmitting SL-SS transmits S-PSS and S-SSS only once for each S-SSB (instead of transmitting S-PSS and S-SSS twice for each S-SSB as in mode 1). Still in other aspects, the sidelink UE transmits only S-PSS or S-SSS, as shown in modes 5, 6, 7, and 8.

[0096] In a further aspect of this disclosure, the sidelink UE can use the SL-SS mode based on instructions received from the gNB (e.g., for scenarios within coverage) or pre-configuration (e.g., for scenarios outside coverage). Alternatively, for example, when outside network coverage, the sidelink UE can select the SL-SS mode itself. When the UE selects the mode itself, the receiving sidelink UE should know which mode has been selected.

[0097] According to various aspects of this disclosure, the SL-SS mode can implicitly indicate (or be based on) information related to UE behavior. For example, the SL-SS mode can implicitly indicate UE transmit power, UE mobility level, whether the UE is within or outside coverage area, etc. Figure 8 This illustrates various aspects according to this disclosure. Figure 7 A graph showing a subset of patterns. For example, as... Figure 8 As shown, Mode 1 can indicate that the sidelink UE transmitting SL-SS is a high-mobility UE. That is, the symbol is repeated in Mode 1 to help the receiving sidelink UE detect the signal while overcoming the Doppler effect. In this example, other modes indicate that the transmitting sidelink UE is a low-mobility and / or low-power UE. In other examples, Modes 2-4 can further indicate that the transmitting sidelink UE is within network coverage (e.g., directly or indirectly) or outside network coverage. Based on mode detection, the receiving sidelink UE can learn more about the transmitting UE and therefore decide whether to synchronize with it.

[0098] In other aspects of this disclosure, the SL-SS mode explicitly indicates information about the transmitting UE. For example, the SL-SS may explicitly indicate UE transmit power, mobility level, whether the UE is within coverage, etc. Currently, for NR V2X communication, the S-PSS and S-SSS together indicate 672 SL-SSIDs (Sidelink Service Set Identifiers). For example, SL-SSID {0, 1, ..., 335} may indicate that the transmitting UE is within coverage or is receiving synchronization signals from a UE within coverage. SL-SSID {336, 337, ..., 671} may indicate that the transmitting UE has no connection with a UE within coverage. The PSBCH may include a flag indicating whether the UE transmitting the S-SSB itself is within the cell's coverage.

[0099] According to various aspects of this disclosure, as described above, SL-SSIDs are partitioned. Then, within each set of SL-SSIDs, it is further partitioned into subsets indicating UE transmit power and / or mobility and / or coverage status (e.g., whether within coverage area). For example, the set may indicate UE transmit power, and the subset may indicate coverage status. In these respects, there are two sets of SL-SSIDs, and numerous additional subsets are created.

[0100] In other aspects, SL-SSIDs have undergone entirely new divisions. For example, three SL-SSID sets can be created by dividing SSIDs into different sets and mapping SL-SSIDs based on UE transmit power, mobility, coverage status, etc. For example, in this aspect, SL-SSIDs carry X+Y+Z bits, where the X bits indicate UE transmit power, the Y bits indicate mobility, and the Z bits indicate coverage status.

[0101] Explicit and implicit signaling can be combined. For example, the selected mode can implicitly indicate transmit power, while SL-SSID indicates whether the UE is within coverage area.

[0102] From the perspective of the UE on the receiving side link, a lightweight SL-SS can have the same mode as a conventional SL-SS (e.g., mode 1). Alternatively, at the cost of higher receiver complexity, a lightweight SL-SS can be transmitted at different frequency locations in different modes (e.g., modes 2-8), with different (e.g., reserved) SL-SSIDs, and / or with different timing offsets. In some aspects of this disclosure, the UE on the receiving side link searches for a lightweight SL-SS on a frequency indicated by the gNB or pre-configured (absoluteFrequencySSB-SL). The frequency can be the same as or different from the frequency of a conventional SL-SS. Of course, the UE on the transmitting side link transmits on that frequency. In these aspects, the indication (e.g., reserved SL-SSID and / or different frequency) indicates to the receiving UE whether a lightweight SL-SS or a conventional SL-SS has been transmitted, helping the receiving UE decide whether to participate in the S-SSB.

[0103] In a further aspect, the transmitting sidelink UE can transmit a lightweight SL-SS at a time offset indicated by the gNB or a pre-configured time offset (timeOffsetSSB-SL). This time offset can be different from or the same as the traditional SL-SS time offset. A different time offset can reduce interference from neighboring UEs on lightweight SL-SS transmitted by a power-limited UE.

[0104] According to various aspects of this disclosure, a receive (RX)-side link UE that detects a lightweight SL-SS requires an additional SL-SS from a transmit (TX)-side link UE. For example, the additional SL-SS could be a PSBCH or SIB.

[0105] Figure 9 This is a timing diagram 900 showing the PSBCH demand and response explicitly according to various aspects of this disclosure. At time t1, UE 902 on the transmitting side transmits a lightweight SL-SS to UE 904 on the receiving side. UE 904 on the receiving side detects the lightweight SL-SS transmission request for PSBCH at time t2. At time t3, UE 902 on the transmitting side sends a PSBCH to UE 904 on the receiving side in response to this request.

[0106] The UE 904 on the receiving side link can receive messages that identify one or more resources used to request additional SL-SS. These resources identify where and when the request is made, the subcarrier spacing (SCS) used to transmit the request, and the transmit power used to transmit the request.

[0107] In all aspects of this disclosure, resources are pre-configured. For example, the UE 904 on the receiving side link may transmit a pre-configured preamble for a period of time (e.g., N time slots or N ms (e.g., N=1)) after detecting a signal such as an S-SSSS. The preamble can be any pre-configured sequence. In some configurations, the preamble is a lightweight SL-SS with a pre-configured (or reserved) SL-SSID or the same SL-SSID as the UE 902 on the transmitting side link. Resource block (RB) allocation, SCS, transmit power, etc., may also be pre-configured.

[0108] In other aspects of this disclosure, the transmitting sidelink UE 902 indicates the resource carrying the request. For example, the SL-SSID may indicate when the request should be sent. The transmitting sidelink UE 902 may indicate, relative to a signal (such as S-SSSS), when the transmitting sidelink UE 902 expects the receiving sidelink UE 904 to send the request. In this example, the transmitting sidelink UE 902 indicates that the resource is the same set of RBs and the same SCS as the SL-SS.

[0109] In other respects, resources can be indicated through a combination of the techniques described above. For example, the offset can be indicated by the UE 902 on the transmitting side link, but RB allocation and / or transmit power can be pre-configured.

[0110] In other aspects of this disclosure, the requirements may carry information about the behavior of UE 904 on the receiving side link. This information may include, for example, whether UE 904 on the receiving side link is within or outside network coverage, the transmit power of UE 904 on the receiving side link, the mobility level of UE 904 on the receiving side link, etc. For example, this information may be useful when UE 902 on the transmitting side link prefers to join a static UE rather than a mobile UE.

[0111] The required transmission power can be indicated by the transmitting side link UE 902, or it can be pre-configured as described above. If the transmission power of the UE requesting the PSBCH is known at the UE initiating the SL-SS, the transmitting side link UE 902 can better estimate its path loss (PL) and determine whether sidelink communication with the receiving side link UE 904 is beneficial. For example, if the path loss is high, the transmitting side link UE 902 can decide not to communicate with UE 904 joining that particular receiving sidelink.

[0112] In other respects, the UE 904 on the receiving side link can only be instructed to send the request if certain conditions are met. For example, if the UE's transmit power is greater than a threshold, the UE 904 on the receiving side link is within cell coverage, or the UE on the receiving side link has low mobility, then the UE can only send the request. These conditions can originate from the UE 902 on the transmitting side link or the gNB, or they can be pre-configured. Therefore, for example, the UE 902 on the transmitting side link knows whether the request was received from a low-power UE or a UE with low mobility.

[0113] In other aspects, multiple resources can be indicated or pre-configured for the receiving-side link UE 904 to issue the request. These multiple resources can be based on the receiving-side link UE 904's transmit power, mobility, coverage, etc. For example, there may be two demand timings: five time slots after S-SSS and seven time slots after S-SSS. If the receiving-side link UE 904 is a low-mobility UE, it transmits in the five time slots after S-SSS. If the receiving-side link UE 904 is a high-mobility UE, it transmits in the seven time slots after S-SSS. For communication in frequency range 2 (FR2-mmWave), multiple resources can be specified so that the UE initiating SL-SS can scan different receive beams to obtain the demand signal from the receiving-side link UE 904.

[0114] According to various aspects of this disclosure, once the transmitting UE detects a request from the receiving UE, the transmitting UE begins transmitting the requested signal (e.g., PSBCH) from the next S-SSB timing. In some configurations, the transmitting UE follows an indicated or pre-configured offset.

[0115] In other aspects, once the transmitting UE sends an SL-SS, a timer is started. If the transmitting UE does not detect a demand from any UE or any eligible UE before the timer expires, the transmitting UE has several options. In the first option, the transmitting UE increases its transmit power for the next SL-SS transmission. If the UE is at maximum transmit power, the UE will continue to transmit at maximum power. In the second option, the transmitting UE will stop sending SL-SS. The transmitting UE restarts the lightweight SL-SS process after a period of time, which can be random, indicated by the gNB, or pre-configured. In some aspects, stopping can be conditional on the transmit power being at a maximum level. In a further aspect, a combination of options one and two can occur. That is, each time the timer expires, the transmit power continues to increase for subsequent transmissions. Once the maximum power is reached, transmission stops.

[0116] As mentioned above, Figure 6-9This is provided as an example only. Other examples may differ from those provided. Figure 6-9 The example described.

[0117] Figure 10 This is a flowchart illustrating an example procedure 1000 performed, for example, by a user equipment (UE) on the receiving side link, according to various aspects of this disclosure. Procedure 1000 is an example of the requirement for side link synchronization signal block (S-SSB) transmission.

[0118] like Figure 10 As shown, in some aspects, process 1000 may include detecting a sidelink synchronization signal (SL-SS) transmitted by a UE transmitting the sidelink (block 1002). The SL-SS may have a mode with a reduced number of Physical Sidelink Broadcast Channel (PSBCH) symbols (block 1002). For example, the UE (e.g., using antenna 352, RX / TX 354, RX processor 356, controller / processor 359, and / or memory 360) may detect the SL-SS without a PSBCH.

[0119] like Figure 10 As shown, in some aspects, process 1000 may include sending a request for an additional SL-SS from a UE on the transmitting side link via an indicated resource (block 1004). For example, a UE (e.g., using antenna 352, RX / TX 354, TX processor 368, controller / processor 359, and / or memory 360) may send a request for an additional SL-SS. The additional SL-SS may be a PSBCH and / or a System Information Block (SIB). The indicated resource may be a pre-configured resource or may be indicated by the UE on the transmitting side link. The request may indicate the coverage status of the UE on the receiving side link, the transmit power of the UE on the receiving side link, and / or the mobility level of the UE on the receiving side link.

[0120] Figure 11 This is a flowchart illustrating an example procedure 1100 performed, for example, by a user equipment (UE) transmitting a sidelink, according to various aspects of this disclosure. Procedure 1100 is an example of a request and response to a sidelink synchronization signal block (S-SSB) transmission.

[0121] like Figure 11 As shown, in some aspects, process 1100 may include receiving a request for an additional sidelink synchronization signal (SL-SS) from the UE on the receiving sidelink (block 1102). For example, the UE (e.g., using antenna 352, RX / TX 354, RX processor 356, controller / processor 359, and / or memory 360) may receive a request for an additional SL-SS.

[0122] like Figure 11As shown, in some aspects, process 1100 may include sending an additional SL-SS in response to the request (block 1104). For example, the UE (e.g., using antenna 352, RX / TX 354, TX processor 368, controller / processor 359, and / or memory 360) may send the additional SL-SS during the next sidelink synchronization signal block (S-SSB) timing or after a time offset. The time offset may be indicated by the base station or pre-configured.

[0123] Examples of implementation methods are described in the following numbered clauses.

[0124] 1. A method for wireless communication by a user equipment (UE) via a receiving-side link, comprising:

[0125] Detect the sidelink synchronization signal (SL-SS) sent by the UE on the transmitting sidelink; and

[0126] The UE sends a request for additional SL-SS from the transmitting side link using the indicated resources.

[0127] 2. The method according to Clause 1, wherein the additional SL-SS includes the PSBCH and / or the System Information Block (SIB).

[0128] 3. The method according to Clause 1 or 2, wherein the indicated resource includes pre-configured resources.

[0129] 4. The method according to any one of the preceding clauses further includes sending a preamble on a pre-configured resource.

[0130] 5. The method according to any one of the preceding clauses, wherein the preamble includes a response SL-SS with a reserved sidelink service set identifier (SL-SSID).

[0131] 6. The method according to any one of the preceding clauses, wherein the reserved SL-SSID is pre-configured.

[0132] 7. The method according to any one of the preceding clauses, wherein the reserved SL-SSID is the SL-SSID of the UE on the transmitting side link.

[0133] 8. The method according to any one of the preceding clauses, wherein the pre-configured resources appear within a period of time after the sidelink secondary synchronization signal (S-SSS).

[0134] 9. The method according to any one of the preceding clauses, wherein the indicated resource is indicated by the UE of the transmitting side link.

[0135] 10. The method according to any one of the preceding clauses, wherein the indicated resource is indicated by the UE of the transmitting side link using an SL-SSID, the SL-SSID defining an offset relative to a signal, after which the UE of the transmitting side link expects to receive the request.

[0136] 11. The method according to any one of the preceding clauses, wherein the indicated resource further includes pre-configured resources, the pre-configured resources defining resource block allocation and / or transmission power for the required resources.

[0137] 12. The method according to any one of the preceding clauses, wherein the requirement indicates the coverage status of the UE on the receiving side link, the transmit power of the UE on the receiving side link, and / or the mobility level of the UE on the receiving side link.

[0138] 13. The method according to any one of the preceding clauses, wherein the transmission power is indicated by the UE of the transmitting side link.

[0139] 14. The method according to any one of the preceding clauses, wherein the transmission power is pre-configured.

[0140] 15. The method according to any one of the preceding clauses further includes a transmission requirement when the transmit power of the UE on the receiving side link is higher than a threshold.

[0141] 16. The method according to any one of the preceding clauses, wherein the threshold is defined by the UE of the transmitting side link.

[0142] 17. The method according to any one of the preceding clauses, wherein the threshold is pre-configured.

[0143] 18. The method according to any one of the preceding clauses further includes selecting resources for transmission needs based on the coverage status of the UE on the receiving side link, the transmit power of the UE on the receiving side link, and / or the mobility level of the UE on the receiving side link.

[0144] 19. The method according to any one of the preceding clauses, wherein the SL-SS has a mode with a reduced number of Physical Side Link Broadcast Channel (PSBCH) symbols.

[0145] 20. A method for wireless communication by a user equipment (UE) via a transmitting sidelink, comprising:

[0146] The UE receives the additional sidelink synchronization signal (SL-SS) from the receiving sidelink; and

[0147] Send an additional SL-SS in response to the request.

[0148] 21. The method according to Clause 20, wherein the transmission occurs during the timing of the next side link synchronization signal block (S-SSB).

[0149] 22. The method according to Clause 20, wherein the transmission occurs after a time offset.

[0150] 23. The method according to any one of Clauses 20 or 22, wherein the time offset is indicated by the base station or pre-configured.

[0151] 24. The method according to any one of clauses 20-23 further comprises:

[0152] A timer is started after one of the additional sidelink synchronization signals (SL-SS) is transmitted within the sidelink synchronization signal block (S-SSB). The SL-SS has a mode with a reduced number of Physical Sidelink Broadcast Channel (PSBCH) symbols; and

[0153] When the timer expires before receiving a request, the transmit power is increased for the next SL-SS transmission.

[0154] 25. The method according to any one of clauses 20-24, further comprising:

[0155] After one of the additional side link synchronization signals (SL-SS) is sent within the side link synchronization signal block (S-SSB), a timer is started. The SL-SS has a mode with a reduced number of physical side link broadcast channel (PSBCH) symbols.

[0156] When the timer expires before receiving a request and the UE transmit power is at a threshold level, the next SL-SS transmission is stopped; and

[0157] Send future SL-SS messages within the time period following the stop.

[0158] 26. The method according to any one of Clauses 20-25, wherein the time period is an arbitrary time period, indicated by the base station or pre-configured.

[0159] 27. An apparatus for wireless communication by a user equipment (UE), comprising:

[0160] processor;

[0161] Memory coupled to the processor; and

[0162] Instructions stored in memory and operable, which, when executed by a processor, cause the device to:

[0163] Detect the sidelink synchronization signal (SL-SS) sent by the UE on the transmitting sidelink; and

[0164] The UE sends a request for additional SL-SS from the transmitting side link using the indicated resources.

[0165] 28. The apparatus according to Clause 27, wherein the additional SL-SS includes the PSBCH and / or the System Information Block (SIB).

[0166] 29. The apparatus according to clause 27 or 28, wherein the indicated resources include pre-configured resources.

[0167] The foregoing disclosure provides illustrations and descriptions, but is not intended to consume or limit the aspects to the precise form disclosed. Modifications and variations can be made based on the foregoing disclosure, or can be derived from practice in the aspects.

[0168] As used, the term "component" is intended to be interpreted broadly as hardware, firmware, or a combination of hardware and software. As used, a processor is implemented as hardware, firmware, and / or a combination of hardware and software.

[0169] Several aspects are described in conjunction with thresholds. As used, depending on the context, satisfying a threshold can refer to a value that is greater than, greater than or equal to, less than, less than or equal to, equal to, or not equal to the threshold.

[0170] Clearly, the described systems and / or methods can be implemented in various forms of hardware, firmware, and / or combinations of hardware and software. The actual dedicated control hardware or software code used to implement these systems and / or methods does not limit these aspects. Therefore, there is no reference to specific software code to describe the operation and behavior of the systems and / or methods—it should be understood that software and hardware can be designed to implement the systems and / or methods, at least in part, based on this description.

[0171] Although specific combinations of features are recited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of the aspects. In fact, many of these features can be combined in ways not specifically stated in the claims and / or disclosed in the specification. Although each dependent claim listed below may be directly subordinated to only one claim, the disclosure of an aspect includes every dependent claim in combination with every other claim in the claim set. The phrase “at least one of” in the list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination having multiple identical elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other order of a, b, and c).

[0172] Unless explicitly stated otherwise, no element, action, or instruction used should be construed as essential or necessary. Furthermore, as used, the articles “a” and “an” are intended to include one or more items and are interchangeable with “one or more.” Additionally, as used, the terms “set” and “group” are intended to include one or more items (e.g., related items, unrelated items, combinations of related and unrelated items, etc.) and are interchangeable with “one or more.” If only one item is intended to be used, the phrase “only one” or similar language is used. Additionally, as used, the terms “has,” “have,” “having,” and / or similar are identified as open-ended terms. Furthermore, the phrase “based on” is intended to mean “based, at least in part, on,” unless explicitly stated otherwise.

Claims

1. A method of wireless communication by a user equipment (UE) receiving a sidelink, comprising: detecting a lightweight sidelink synchronization signal (SL-SS) transmitted by a UE transmitting a sidelink, the lightweight SL-SS being devoid of a physical sidelink broadcast channel (PSBCH); and in response to detecting the lightweight SL-SS being devoid of a physical sidelink broadcast channel (PSBCH), transmitting a request for a supplemental SL-SS including a PSBCH from the UE transmitting the sidelink over an indicated resource.

2. The method of claim 1, wherein, the supplemental SL-SS includes a system information block (SIB).

3. The method of claim 1, wherein, the indicated resource includes a preconfigured resource.

4. The method of claim 3, further comprising transmitting a preamble over the preconfigured resource.

5. The method of claim 4, wherein, the preamble includes a reply SL-SS having a reserved sidelink service set identifier (SL-SSID).

6. The method of claim 5, wherein, the reserved SL-SSID is preconfigured.

7. The method of claim 6, wherein, the reserved SL-SSID is a SL-SSID of the UE transmitting the sidelink.

8. The method of claim 4, wherein, the preconfigured resource occurs within a time period after a sidelink secondary synchronization signal (S-SSS).

9. The method of claim 1, wherein, the indicated resource is indicated by the UE transmitting the sidelink.

10. The method of claim 9, wherein, the indicated resource is indicated by the UE transmitting the sidelink with a SL-SSID defining an offset from a signal after which the UE transmitting the sidelink expects to receive the request.

11. The method of claim 9, wherein, the indicated resource further includes a preconfigured resource defining a resource block allocation and / or a transmit power for the request.

12. The method of claim 1, wherein, the request indicates a coverage status of the UE receiving the sidelink, a transmit power of the UE receiving the sidelink, and / or a mobility level of the UE receiving the sidelink.

13. The method of claim 12, wherein, the transmit power is indicated by the UE transmitting the sidelink.

14. The method of claim 12, wherein, the transmit power is preconfigured.

15. The method of claim 1, further comprising transmitting the request when a transmit power of the UE receiving the sidelink is above a threshold.

16. The method of claim 15, wherein, the threshold is defined by the UE transmitting the sidelink.

17. The method of claim 15, wherein, the threshold is preconfigured.

18. The method of claim 1, further comprising selecting a resource for transmitting the request based on a coverage status of the UE receiving the sidelink, a transmit power of the UE receiving the sidelink, and / or a mobility level of the UE receiving the sidelink.

19. A method of wireless communication by a user equipment (UE) transmitting a sidelink, comprising: transmitting a lightweight sidelink synchronization signal (SL-SS), the lightweight SL-SS being devoid of a physical sidelink broadcast channel (PSBCH); receiving a request for a supplemental sidelink synchronization signal (SL-SS) from a UE receiving a sidelink; and transmitting the supplemental SL-SS in response to the request, the supplemental SL-SS including a PSBCH.

20. The method of claim 19, wherein, the transmitting the supplemental SL-SS occurs during a next sidelink synchronization signal block (S-SSB) occasion.

21. The method of claim 19, wherein, the transmitting the supplemental SL-SS occurs after a time offset.

22. The method of claim 21, wherein, the time offset is indicated by a base station or is preconfigured.

23. The method of claim 19, further comprising: starting a timer after transmitting one of the supplemental sidelink synchronization signals (SL-SSs) within a sidelink synchronization signal block (S-SSB); and when the timer expires before receiving the demand, increasing a transmit power for a next SL-SS transmission.

24. The method of claim 19, further comprising: starting a timer after transmitting one of the supplemental sidelink synchronization signals (SL-SSs) within a sidelink synchronization signal block (S-SSB); when the timer expires before receiving the demand and a UE transmit power is at a threshold level, stopping a next SL-SS transmission; and transmitting a future SL-SS within a time period after the stopping.

25. The method of claim 24, wherein, the time period is an arbitrary time period, indicated by a base station, or preconfigured.

26. An apparatus for wireless communication by a user equipment (UE), comprising: a processor; a memory coupled with the processor; and instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to: detect a lightweight sidelink synchronization signal (SL-SS) transmitted by a transmitting UE of a sidelink, the lightweight SL-SS being devoid of a physical sidelink broadcast channel (PSBCH); and in response to detecting the lightweight SL-SS being devoid of a physical sidelink broadcast channel (PSBCH), transmit a demand from the transmitting UE of the sidelink for a supplemental SL-SS including a PSBCH over an indicated resource.

27. The apparatus of claim 26, wherein, the supplemental SL-SS includes a system information block (SIB).

28. The apparatus of claim 26, wherein, the indicated resource includes a preconfigured resource.

29. An apparatus for wireless communication by a user equipment (UE), comprising: a processor; a memory coupled with the processor; and instructions stored in the memory and operable, when executed by the processor, to cause the apparatus to: transmit a lightweight sidelink synchronization signal (SL-SS), the lightweight SL-SS being devoid of a physical sidelink broadcast channel (PSBCH); receive a demand for a supplemental sidelink synchronization signal (SL-SS) from a receiving UE of a sidelink; and in response to the demand, transmit the supplemental SL-SS including a PSBCH.

30. An apparatus for performing wireless communication at a user equipment (UE), the apparatus comprising means for performing the method of any of claims 1-18.

31. An apparatus for performing wireless communication at a user equipment (UE), the apparatus comprising means for performing the method of any of claims 19-25.

32. A computer readable medium having program code recorded thereon, wherein, the program code is executable by one or more processors of a user equipment (UE) to cause the processors to perform the method of any of claims 1-18.

33. A computer readable medium having program code recorded thereon, wherein, the program code is executable by one or more processors of a user equipment (UE) to cause the processors to perform the method of any of claims 19-25.

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