Physical sidelink feedback channel opportunity configuration for unlicensed sidelink communications

Abstract

Wireless communication systems, apparatuses, and methods are provided. A method of wireless communication performed by a first sidelink user equipment (UE) includes performing a listen before talk (LBT) procedure in an unlicensed band; and transmitting an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication to the second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities based on the LBT procedure being successful.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Greek Patent Application No. 20220100768, filed on September 20, 2022, the disclosure of which is incorporated herein by reference in its entirety as if fully set forth below and for all applicable purposes. Technical Field

[0003] The present application relates to wireless communication systems, and more particularly to physical sidelink feedback channel (PSFCH) opportunity configuration for unlicensed sidelink communications. Background Art

[0004] Wireless communication systems are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcast, etc. These systems may be capable of supporting communication with multiple users by sharing available system resources (e.g., time, frequency, and power). A wireless multiple-access communication system may include multiple base stations (BSs), each of which simultaneously supports communication for multiple communication devices, which may be otherwise referred to as user equipment (UE).

[0005] In order to meet the growing demand for extended mobile broadband connectivity, wireless communication technology is evolving from LTE technology to next-generation new radio (NR) technology. For example, compared to LTE, NR is designed to provide lower latency, higher bandwidth or throughput, and higher reliability. NR is designed to operate on a wide spectrum band array, for example, from low bands below about 1 MHz (GHz) and mid-bands from about 1 GHz to about 6 GHz to high bands such as millimeter wave (mmWave) bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed spectrum and shared spectrum. Spectrum sharing enables operators to have the opportunity to aggregate spectrum to dynamically support high-bandwidth services. Spectrum sharing can extend the benefits of NR technology to operating entities that may not have access to licensed spectrum.

[0006] NR can support various deployment scenarios to benefit from various spectrums in different frequency ranges, licensed and / or unlicensed, and / or coexistence of LTE and NR technologies. For example, NR can be deployed in standalone NR mode on licensed and / or unlicensed bands, or in dual connectivity mode with various combinations of NR and LTE on licensed and / or unlicensed bands.

[0007] In a wireless communication network, a BS can communicate with a UE in both the uplink and downlink directions. Sidelinks were introduced in LTE to allow a UE to transmit data to another UE (e.g., from one vehicle to another vehicle) without tunneling through the BS and / or associated core network. LTE sidelink technology has been extended to provide device-to-device (D2D) communications, vehicle-to-everything (V2X) communications, and / or cellular vehicle-to-everything (C-V2X) communications. Similarly, NR can be extended to support sidelink communications, D2D communications, V2X communications, and / or C-V2X on licensed and / or unlicensed bands (e.g., shared bands). Summary of the invention

[0008] The following summarizes some aspects of the present disclosure to provide a basic understanding of the technology discussed. This summary is not an exhaustive overview of all the expected features of the present disclosure, and is neither intended to identify the key or important elements of all aspects of the present disclosure, nor to delineate the scope of any or all aspects of the present disclosure. The sole purpose of this summary is to present some concepts of one or more aspects of the present disclosure in a summarized form as a prelude to more specific embodiments presented later.

[0009] In one aspect of the present disclosure, a method of wireless communication performed by a first sidelink user equipment (UE) may include: performing a listen-before-talk (LBT) procedure in an unlicensed band; and based on the success of the LBT procedure, sending an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication to a second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0010] In additional aspects of the present disclosure, a method of wireless communication performed by a first sidelink user equipment (UE) may include: sending sidelink communications to one or more sidelink UEs in an unlicensed band; and monitoring an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0011] In additional aspects of the present disclosure, a first sidelink user equipment (IE) may include: a memory; a transceiver; and at least one processor coupled to the memory and the transceiver, wherein the first sidelink UE is configured to: perform a listen-before-talk (LBT) procedure in an unlicensed band; and based on the success of the LBT procedure, send an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication to a second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0012] In additional aspects of the present disclosure, a first sidelink user equipment (IE) may include: a memory; a transceiver; and at least one processor coupled to the memory and the transceiver, wherein the first sidelink UE is configured to: send sidelink communications to one or more sidelink UEs in an unlicensed band; and monitor an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0013] After reading the description of the specific exemplary embodiments of the present invention below in conjunction with the accompanying drawings, other aspects, features and examples of the present invention will become apparent to those of ordinary skill in the art. Although the features of the present invention may be discussed below with respect to certain aspects and drawings, all examples of the present invention may include one or more of the advantageous features discussed herein. In other words, although one or more examples may be discussed as having certain advantageous features, one or more of such features may also be used according to the various examples of the present invention discussed herein. In a similar manner, although the exemplary aspects may be discussed below as device, system or method examples, it should be understood that such exemplary examples may be implemented in various devices, systems and methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A wireless communication network according to some aspects of the present disclosure is illustrated.

[0015] Figure 2 An example disaggregated base station architecture is illustrated in accordance with some aspects of the present disclosure.

[0016] Figure 3 Examples of resources associated with multiple PSFCH opportunities in accordance with some aspects of the present disclosure are illustrated.

[0017] Figure 4 A wireless communication network according to some aspects of the present disclosure is illustrated.

[0018] Figure 5 A signal flow diagram illustrating multiple PSFCH opportunities according to some aspects of the present disclosure.

[0019] Figure 6 is a block diagram of an exemplary user equipment (IE) according to some aspects of the present disclosure.

[0020] Figure 7 is a block diagram of an exemplary network element according to some aspects of the present disclosure.

[0021] Figure 8 is a flow chart of a communication method according to some aspects of the present disclosure.

[0022] Fig. 9 is a flow chart of a communication method according to some aspects of the present disclosure. DETAILED DESCRIPTION

[0023] The detailed description set forth below in conjunction with the accompanying drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. In order to provide a comprehensive understanding of the various concepts, the specific embodiments include specific details. However, it is apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, in order to avoid obscuring such concepts, well-known structures and components are shown in block diagram form.

[0024] The present disclosure as a whole relates to wireless communication systems, which are also referred to as wireless communication networks. In various instances, techniques and devices can be used for wireless communication networks, such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, 5th generation (5G) or new radio (NR) networks, and other communication networks. As described herein, the terms "network" and "system" can be used interchangeably.

[0025] OFDMA network can realize radio technology such as Evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM, etc. UTRA, E-UTRA and Global System for Mobile Communications (GSM) are parts of Universal Mobile Telecommunications System (IMTS). Specifically, Long Term Evolution (LTE) is a version of UMTS using E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided by an organization named "3rd Generation Partnership Project" (3GPP), and cdma2000 is described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). These radio technologies and standards are known or under development. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between telecommunication association groups with the goal of defining globally applicable third generation (3G) mobile phone specifications. 3GPP Long Term Evolution (LTE) is a 3GPP plan to improve the Universal Mobile Telecommunications System (IMTS) mobile phone standard. 3GPP may define specifications for next generation mobile networks, mobile systems, and mobile devices. The present disclosure relates to the evolution from LTE, 4G, 5G, NR and beyond wireless technologies, where access to the wireless spectrum is shared between networks using a range of new and different radio access technologies or radio air interfaces.

[0026] Specifically, 5G networks consider various deployments, various spectrums, and various services and devices that can be implemented using a unified air interface based on OFDM. To achieve these goals, in addition to developing new radio technologies for 5G NR networks, further enhancements to LTE and LTE-A are also considered. 5G NR will be able to scale to (1) provide coverage for the massive Internet of Things (IoT) with ultra-high density (e.g., approximately 1M nodes / km2), ultra-low complexity (e.g., approximately 10s of bits / second), ultra-low energy (e.g., approximately 10+ years of battery life), and provide deep coverage with the ability to reach challenging locations; (2) provide coverage including mission-critical control with strong security to protect sensitive personal, financial, or classified information, ultra-high reliability (e.g., approximately 99.9999% reliability), ultra-low latency (e.g., approximately 1 millisecond), and users with extensive mobility or lack of mobility; and (3) have enhanced mobile broadband, including extremely high capacity (e.g., approximately 10Tbps / km2), extremely high data rates (e.g., multi-Gbps rates, 100+Mbps user experienced rates), and deep awareness with advanced discovery and optimization capabilities.

[0027] 5G NR can be implemented using an optimized OFDM-based waveform with scalable parameter sets and transmission time intervals (TTIs); with a common, flexible framework to efficiently multiplex services and features using dynamic low-latency time division duplex (TDD) / frequency division duplex (FDD) designs; and with advanced wireless technologies such as massive multiple-input multiple-output (MIMO), robust millimeter wave (mmWave) transmission, advanced channel decoding, and device-centric mobility. The scalability of parameter sets in 5G NR and the scaling of subcarrier spacing can efficiently address various services operating across different spectrums and different deployments. For example, in various outdoor and macro coverage deployments of less than 3GHz FDD / TDD implementations, the subcarrier spacing may appear at 15kHz on bandwidths (BW) such as 5MHz, 10MHz, 20MHz, etc. For other various outdoor and small cell coverage deployments of TDD greater than 3GHz, the subcarrier spacing may appear at 30kHz on 80MHz / 100MHz BW. For various other indoor broadband implementations, using TDD on the unlicensed portion of the 5 GHz band, subcarrier spacing may occur at 60 kHz over 160 MHz BW. Finally, for various deployments transmitting with the mmWave component at 28 GHz TDD, subcarrier spacing may occur at 120 kHz over 500 MHz BW.

[0028] 5G NR's scalable parameter sets facilitate scalable TTIs for different latency and quality of service (QoS) requirements. For example, shorter TTIs can be used for low latency and high reliability, while longer TTIs can be used for higher spectral efficiency. Efficient multiplexing of long and short TTIs allows transmission to start on symbol boundaries. 5G NR also envisions a self-contained integrated subframe design with uplink / downlink scheduling information, data, and acknowledgment in the same subframe. The self-contained integrated subframe supports communications in unlicensed spectrum or contention-based shared spectrum, adaptive uplink / downlink, which can be flexibly configured on a per-cell basis to dynamically switch between uplink and downlink to meet current business needs.

[0029] The various other aspects and features of the present disclosure are further described below. It should be apparent that the teachings herein can be embodied in various forms, and any specific structure, function, or both disclosed herein are merely representative and not restrictive. Based on the teachings herein, it should be understood by those of ordinary skill in the art that the aspects disclosed herein can be implemented independently of any other aspects, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement a device or practice a method. In addition, such a device can be implemented or such a method can be practiced using other structures, functionality, or structures and functionality other than or different from one or more of the aspects set forth herein. For example, the method can be implemented as a part of a system, device, device, and / or as an instruction stored on a computer-readable medium for execution on a processor or computer. In addition, one aspect can include at least one element of a claim.

[0030] Deploying NR on unlicensed spectrum is called NR unlicensed (NR-U). The Federal Communications Commission (FCC) and the European Telecommunications Standards Institute (ETSI) are working to regulate 6 GHz as a new unlicensed band for wireless communications. The addition of the 6 GHz band allows hundreds of megahertz (MHz) of bandwidth (BW) to be used for unlicensed band communications. Additionally, NR-U can also be deployed on the 2.4 GHz unlicensed band, which is currently shared by various radio access technologies (RATs) such as IEEE 802.11 wireless local area networks (WLANs) or WiFi and / or license assisted access (LAA). Sidelink communications can benefit from utilizing the additional bandwidth available in unlicensed spectrum. However, channel access in a specific unlicensed spectrum can be managed by official agencies. For example, some unlicensed bands may impose restrictions on the power spectral density (PSD) and / or minimum occupied channel bandwidth (OCB) of transmissions in unlicensed bands. For example, the unlicensed national information infrastructure (UNII) radio band has a minimum OCB requirement of about at least 70%.

[0031] Some sidelink systems may operate on a 20 MHz bandwidth in an unlicensed band, e.g., for listen-before-talk (LBT) based channel access. The BS may configure a sidelink resource pool for sidelink communications on one or more 20 MHz LBT sub-bands. The sidelink resource pool is typically allocated with a plurality of frequency subchannels within a sidelink bandwidth part (SL-BWP), and the sidelink UE may select a sidelink resource (e.g., one or more subchannels in frequency and one or more time slots in time) for sidelink communications from the sidelink resource pool.

[0032] The deployment of a communication system such as a 5G New Radio (NR) system may be arranged with various components or constituent parts in a variety of ways. In a 5G NR system or network, a network node, a network entity, a mobility element of a network, a radio access network (RAN) node, a core network node, a network element or network equipment such as a base station (BS) or one or more units (or one or more components) performing base station functions may be implemented in an aggregated or decomposed architecture. For example, a BS such as a Node B (NB), an evolved NB (eNB), an NR BS, a 5G NB, an access point (AP), a transmit receive point (TRP) or a cell, etc. may be implemented as an aggregated base station (also referred to as an independent BS or a monolithic BS) or a decomposed base station.

[0033] A converged base station may be configured to utilize a radio protocol stack physically or logically integrated within a single RAN node. A decomposed base station may be configured to utilize a protocol stack physically or logically distributed between two or more units, such as one or more central or centralized units (CUs), one or more distributed units (DUs), or one or more radio units (RUs). In some aspects, a CU may be implemented within a RAN node, and one or more DUs may be co-located with the CU, or alternatively, may be geographically or virtually distributed in one or more other RAN nodes. A DU may be implemented to communicate with one or more RUs. Each of a CU, a DU, and a RU may also be implemented as a virtual unit, i.e., a virtual central unit (VCU), a virtual distributed unit (VDU), or a virtual radio unit (VRU).

[0034] Base station type operations or network designs may take into account the aggregated nature of base station functionality. For example, a disaggregated base station may be used in an integrated access backhaul (IAB) network, an open radio access network (O-RAN (network configurations such as those initiated by the O-RAN Alliance)), or a virtualized radio access network (vRAN, also known as a cloud radio access network (C-RAN)). Decomposition may include distributing functions across two or more units at various physical locations, as well as virtually distributing the functions of at least one unit, which may enable flexibility in network design. Various units of a disaggregated base station or disaggregated RAN architecture may be configured for wired or wireless communication with at least one other unit.

[0035] Figure 1 A wireless communication network 100 according to some aspects of the present disclosure is illustrated. The network 100 includes multiple base stations (BSs) 105 and other network entities. The BSs 105 may be stations that communicate with the UEs 115 and may also be referred to as evolved Node Bs (eNBs), next generation eNBs (gNBs), access points, etc. Each BS 105 may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" may refer to the particular geographic coverage area of ​​the BS 105 and / or the BS subsystem serving the coverage area, depending on the context in which the term is used.

[0036] The BS 105 may provide communication coverage for macro cells or small cells (such as pico cells or femto cells) and / or other types of cells. Macro cells generally cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with a network provider. Small cells (such as pico cells) will generally cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions with a network provider. Small cells (such as femto cells) will generally also cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs associated with the femto cells (e.g., UEs in a closed subscriber group (CSG), UEs of users in a home, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS, or a home BS. In Figure 1 In the example shown, BS105d and 105e may be conventional macro BSs, while BS105a to 105c may be macro BSs with one of three-dimensional (3D), full-dimensional (FD) or massive MIMO capabilities. BS105a to 105c may utilize their higher-dimensional MIMO capabilities to employ 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. BS105f may be a small cell BS, which may be a home node or a portable access point. BS105 may support one or more (e.g., two, three, four, etc.) cells.

[0037] Network 100 may support synchronous operation or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time.

[0038] UE 115 is dispersed throughout the wireless network 100, and each UE 115 can be stationary or mobile. UE 115 may also be referred to as a terminal, a mobile station, a subscriber unit, a station, etc. UE 115 may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, etc. In one aspect, UE 115 may be a device including a universal integrated circuit card (IICC). On the other hand, UE may be a device that does not include a UICC. In some aspects, UE 115 that does not include a UICC may also be referred to as an IoT device or an Internet of Everything (IoE) device. UE 115a-115d is an example of a mobile smart phone type device that accesses the network 100. UE 115 may also be a machine that is specifically configured for connected communications (including machine type communications (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT), etc.). UE 115e-115h are examples of various machines configured for communication to access network 100. UE 115i-115k are examples of vehicles equipped with wireless communication devices configured for communication to access network 100. UE 115 may be able to communicate with any type of BS (whether macro BS, small cell, etc.). Figure 1 , a lightning symbol (e.g., a communication link) indicates wireless transmission between UE 115 and a serving BS 105 (which is a BS designated to serve UE 115 on a downlink (DL) and / or uplink (UL)), desired transmission between BSs 105, backhaul transmission between BSs, or sidelink transmission between UE 115.

[0039] In operation, BS 105a-105c uses 3D beamforming and cooperative spatial techniques (such as coordinated multi-point (CoMP) or multiple connections) to serve UEs 115a and 115b. Macro BS 105d can perform backhaul communications with BS 105a to 105c and small cell BS 105f. Macro BS 105d can also send multicast services that UEs 115c and 115d subscribe to and receive. Such multicast services may include mobile TV or streaming video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

[0040] The BS 105 may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connections, and other access, routing, or mobility functions. At least some BSs 105 (e.g., the BS may be an example of an evolved Node B (eNB) or an access node controller (ANC)) may interface with the core network 130 via a backhaul link (e.g., S1, S2, etc.), and may perform radio configuration and scheduling to communicate with the UE 115. In various examples, the BSs 105 may communicate with each other directly or indirectly (e.g., via a core network) via a backhaul link (e.g., X1, X2, etc.), which may be a wired communication link or a wireless communication link.

[0041] The network 100 may also support mission-critical communications with ultra-reliable and redundant links for mission-critical devices such as UE 115e, which may be a vehicle (e.g., a car, truck, bus, autonomous vehicle, airplane, ship, etc.). The redundant communication links with UE 115e may include links from macro BSs 105d and 105e, and a link from a small cell BS 105f. Other machine-type devices such as UE 115f (e.g., a thermometer), UE 115g (e.g., a smart meter), and UE 115h (e.g., a wearable device) may communicate directly with a BS (such as small cell BS 105f and macro BS 105e) through the network 100, or in a multi-hop configuration by communicating with another user device that relays its information to the network (such as UE 115f communicating temperature measurement information to smart meter UE 115g, which is then reported to the network through small cell BS 105f). In some aspects, the UE 115h may harvest energy from the surrounding environment associated with the UE 115h. The network 100 may also provide additional network efficiency through dynamic, low-latency TDD / FDD communications such as vehicle-to-vehicle (V2V) communications between the UE 115i, 115j, or 115k and other UEs 115, vehicle-to-everything (V2X) communications, cellular vehicle-to-everything (C-V2X) communications, and / or vehicle-to-infrastructure (V2I) communications between the UE 115i, 115j, or 115k and the BS 105.

[0042] In some implementations, the network 100 utilizes an OFDM-based waveform for communication. An OFDM-based system may divide the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, frequency bins, etc. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may depend on the system BW. The system BW may also be divided into subbands. In other instances, the subcarrier spacing and / or the duration of the TTI may be scalable.

[0043] In some instances, BS 105 may assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RBs)) for downlink (DL) transmission and uplink (UL) transmission in network 100. DL refers to the transmission direction from BS 105 to UE 115, and UL refers to the transmission direction from UE 115 to BS 105. The communication may be in the form of a radio frame. A radio frame may be divided into a plurality of subframes, e.g., about 10. Each subframe may be divided into time slots, e.g., about 2. Each time slot may also be divided into micro-time slots. In FDD mode, simultaneous UL transmission and DL transmission may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In TDD mode, UL transmission and DL transmission occur in different time periods using the same frequency band. For example, a subframe subset (e.g., a DL subframe) in a radio frame may be used for DL ​​transmission, and another subframe subset (e.g., a UL subframe) in a radio frame may be used for UL transmission.

[0044] DL subframes and UL subframes may also be divided into several zones. For example, each DL subframe or UL subframe may have a predefined zone for the transmission of reference signals, control information, and data. A reference signal is a predetermined signal that facilitates communication between BS 105 and UE 115. For example, a reference signal may have a specific pilot pattern or structure, wherein a pilot tone may span an operational BW or frequency band, and each pilot tone is located at a predefined time and a predefined frequency. For example, BS 105 may send a cell-specific reference signal (CRS) and / or a channel state information-reference signal (CSI-RS) to enable UE 115 to estimate a DL channel. Similarly, UE 115 may send a sounding reference signal (SRS) to enable BS 105 to estimate an UL channel. Control information may include resource assignments and protocol control. Data may include protocol data and / or operational data. In some instances, BS 105 and UE 115 may communicate using a self-contained subframe. A self-contained subframe may include a portion for DL ​​communication and a portion for UL communication. A self-contained subframe may be DL-centric or UL-centric. A DL-centric subframe may include a DL communication duration that is longer than a UL communication duration. A UL-centric subframe may include a UL communication duration that is longer than a UL communication duration.

[0045] In some instances, network 100 may be an NR network deployed on a licensed spectrum. BS 105 may send synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)) in network 100 to facilitate synchronization. BS 105 may broadcast system information associated with network 100 (e.g., including a master information block (MIB), remaining minimum system information (RMSI), and other system information (OSI)) to facilitate initial network access. In some instances, BS 105 may broadcast PSS, SSS, and / or MIB in the form of a synchronization signal block (SSB) on a physical broadcast channel (PBCH), and may broadcast RMSI and / or OSI on a physical downlink shared channel (PDSCH).

[0046] In some examples, a UE 115 attempting to access the network 100 may perform an initial cell search by detecting the PSS from the BS 105. The PSS may enable synchronization of period timing and may indicate a physical layer identification value. The UE 115 may then receive the SSS. The SSS may enable radio frame synchronization and may provide a cell identification value that may be combined with the physical layer identification value to identify the cell. The SSS may also enable detection of duplex mode and cyclic prefix length. The PSS and SSS may be located in the center portion of the carrier or at any suitable frequency within the carrier.

[0047] After receiving the PSS and SSS, the UE 115 may receive the MIB. The MIB may include system information for initial network access and scheduling information for RMSI and / or OSI. After decoding the MIB, the UE 115 may receive the RMSI and / or OSI. The RMSI and / or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource sets (CORESET) for physical downlink control channel (PDCCH) monitoring, physical uplink control channel (PUCCH), physical uplink shared channel (PUSCH), power control, SRS, and cell barring.

[0048] After obtaining the MIB, RMSI, and / or OSI, the UE 115 may perform a random access procedure to establish a connection with the BS 105. For the random access procedure, the UE 115 may send a random access preamble, and the BS 105 may respond with a random access response. Upon receiving the random access response, the UE 115 may send a connection request to the BS 105, and the BS 105 may respond with a connection response (e.g., a contention resolution message).

[0049] After the connection is established, the UE 115 and the BS 105 may enter a normal operation phase in which operational data may be exchanged. For example, the BS 105 may schedule the UE 115 for UL communication and / or DL ​​communication. The BS 105 may send an UL scheduling grant and / or a DL scheduling grant to the UE 115 via the PDCCH. The BS 105 may send a DL communication signal to the UE 115 via the PDSCH according to the DL scheduling grant. The UE 115 may send an UL communication signal to the BS 105 via the PUSCH and / or the PUCCH according to the UL scheduling grant.

[0050] The network 100 may be designed to implement a wide range of use cases. Although in some examples, the network 100 may utilize a monolithic base station, there are a variety of other architectures that can be used to perform various aspects of the present disclosure. For example, the BS 105 may be separated into a remote radio head (RRH) and a baseband unit (BBU). The BBU may be concentrated in a BBU pool and connected to the RRH via a low latency and high bandwidth transmission link (such as an optical transmission link). The BBU pool may be a cloud-based resource. In some aspects, baseband processing is performed on a virtualized server running in a data center rather than co-located with the BS 105. In another example, the base station functionality may be split between a remote unit (RU), a distributed unit (DI), and a central unit (CI). The RU typically performs low physical layer functions, while the DU performs higher layer functions, which may include higher physical layer functions. The CU performs higher RAN functions, such as radio resource control (RRC).

[0051] For simplicity of discussion, the present disclosure refers to the methods of the present disclosure being performed by a base station or more generally by a network entity, while the functionality may be performed by various architectures other than a monolithic base station. In addition to a disaggregated base station, various aspects of the present disclosure may also be performed by a centralized unit (CU), a distributed unit (DU), a radio unit (RU), a near real-time (near RT) RAN intelligent controller (RIC), a non-real-time (non-RT) RIC, an integrated access and backhaul (IAB) node, a relay node, a sidelink node, etc.

[0052] In some aspects, UE 115a may perform a listen-before-talk (LBT) procedure in an unlicensed band. UE 115a may send an acknowledgement / negative acknowledgement (ACK / NACK) to UE 115a based on the LBT procedure being successful. The ACK / NACK may be associated with the sidelink communication received from UE 115b. UE 115a may send the ACK / NACK in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0053] Figure 2 A diagram illustrating an example decomposed base station 200 architecture is shown. The decomposed base station 200 architecture may include one or more central units (CUs) 210 that may communicate directly with a core network 220 via a backhaul link, or indirectly with the core network 220 through one or more decomposed base station units, such as a near real-time (near-RT) RAN intelligent controller (RIC) 225 via an E2 link, or a non-real-time (non-RT) RIC 215 associated with a service management and orchestration (SMO) framework 205, or both. The CU 210 may communicate with one or more distributed units (DUs) 230 via respective midhaul links, such as an F1 interface. The DU 230 may communicate with one or more radio units (RUs) 240 via respective fronthaul links. The RU 240 may communicate with respective UEs 115 via one or more radio frequency (RF) access links. In some implementations, a UE 115 may be served simultaneously by multiple RUs 240.

[0054] Each of the units (i.e., CU 210, DU 230, RU 240, and near-RT RIC 225, non-RT RIC 215, and SMO framework 205) may include or be coupled to one or more interfaces configured to receive or send signals, data, or information (collectively referred to as signals) via a wired or wireless transmission medium. Each of the units or an associated processor or controller that provides instructions to the communication interface of these units may be configured to communicate with one or more of the other units via a transmission medium. For example, these units may include a wired interface configured to receive or send signals to one or more of the other units via a wired transmission medium. In addition, the unit may include a wireless interface that may include a receiver, a transmitter, or a transceiver (such as a radio frequency (RF) transceiver) that is configured to receive or send signals, or both, to one or more of the other units via a wireless transmission medium.

[0055] In some aspects, CU 210 may host one or more higher layer control functions. Such control functions may include radio resource control (RRC), packet data convergence protocol (PDCP), service data adaptation protocol (SDAP), etc. Each control function may be implemented using an interface that is configured to communicate signals with other control functions hosted by CU 210. CU 210 may be configured to handle user plane functionality (i.e., central unit-user plane (CU-UP)), control plane functionality (i.e., central unit-control plane (CU-CP)), or a combination thereof. In some specific implementations, CU 210 may be logically split into one or more CU-UP units and one or more CU-CP units. When implemented in an O-RAN configuration, the CU-UP unit may communicate bidirectionally with the CU-CP unit via an interface (such as an E1 interface). As needed, CU 210 may be implemented to communicate with DU 230 for network control and signaling.

[0056] DU 230 may correspond to a logical unit that includes one or more base station functions for controlling the operation of one or more RUs 240. In some aspects, DU 230 may host one or more of a radio link control (RLC) layer, a medium access control (MAC) layer, and one or more high physical (PHY) layers (such as modules for forward error correction (FEC) encoding and decoding, scrambling, modulation and demodulation, etc.) at least in part according to a functional split such as those defined by the 3rd Generation Partnership Project (3GPP). In some aspects, DU 230 may also host one or more low PHY layers. Each layer (or module) may be implemented using an interface that is configured to communicate signals with other layers (and modules) hosted by DU 230 or with control functions hosted by CU 210.

[0057] The lower layer functionality may be implemented by one or more RUs 240. In some deployments, the RU 240 controlled by the DU 230 may correspond to a logical node that hosts RF processing functions or low PHY layer functions (such as performing fast Fourier transform (FFT), inverse FFT (iFFT), digital beamforming, physical random access channel (PRACH) extraction and filtering, etc.), or both, based at least in part on functional splitting (such as lower layer functional splitting). In such an architecture, the RU 240 may be implemented to handle over-the-air (OTA) communications with one or more UEs 115. In some specific implementations, real-time and non-real-time aspects of control plane communications and user plane communications with the RU 240 may be controlled by the corresponding DU 230. In some scenarios, this configuration may enable the implementation of the DU 230 and the CU 210 in a cloud-based RAN architecture (such as a vRAN architecture).

[0058] The SMO framework 205 may be configured to support RAN deployment and provisioning of non-virtualized network elements and virtualized network elements. For non-virtualized network elements, the SMO framework 205 may be configured to support the deployment of dedicated physical resources for RAN coverage requirements, which may be managed via an operation and maintenance interface (such as an O1 interface). For virtualized network elements, the SMO framework 205 may be configured to interact with a cloud computing platform (such as an open cloud (O-Cloud) 290) to perform network element lifecycle management (such as to instantiate virtualized network elements) via a cloud computing platform interface (such as an O2 interface). Such virtualized network elements may include, but are not limited to, CU 210, DU 230, RU 240, and near-RT RIC 225. In some specific implementations, the SMO framework 205 may communicate with hardware aspects of the 4G RAN (such as an open eNB (O-eNB) 211) via the O1 interface. Additionally, in some specific implementations, the SMO framework 205 may communicate directly with one or more RUs 240 via the O1 interface. The SMO framework 205 may also include a non-RT RIC 215 configured to support the functionality of the SMO framework 205 .

[0059] The non-RT RIC 215 may be configured to include logic functions that enable non-real-time control and optimization of RAN elements and resources, artificial intelligence / machine learning (AI / ML) workflows including model training and updating, or policy-based guidance of applications / features in the near-RT RIC 225. The non-RT RIC 215 may be coupled to or in communication with the near-RT RIC 225 (such as via an A1 interface). The near-RT RIC 225 may be configured to include logic functions that enable near-real-time control and optimization of RAN elements and resources via data collection and actions through an interface (such as via an E2 interface) that connects one or more CUs 210, one or more DUs 230, or both, and the O-eNB with the near-RT RIC 225.

[0060] In some implementations, in order to generate an AI / ML model to be deployed in the near-RT RIC 225, the non-RT RIC 215 may receive parameters or external enrichment information from an external server. Such information may be utilized by the near-RT RIC 225 and may be received from a non-network data source or from a network function at the SMO framework 205 or the non-RT RIC 215. In some examples, the non-RT RIC 215 or the near-RT RIC 225 may be configured to tune RAN behavior or performance. For example, the non-RT RIC 215 may monitor long-term trends and patterns of performance and employ AI / ML models to perform corrective actions through the SMO framework 205 (such as via reconfiguration of O1) or via the creation of RAN management policies (such as A1 policies).

[0061] In some aspects, the first UE 115 may perform a listen-before-talk (LBT) procedure in an unlicensed band. The first UE 115 may send an acknowledgement / negative acknowledgement (ACK / NACK) to the second UE 115 based on the LBT procedure being successful. The ACK / NACK may be associated with the sidelink communication received from the second UE 115. The first UE 115 may send the ACK / NACK in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0062] Figure 3 A wireless communication network 300 is illustrated in accordance with some aspects of the present disclosure. Figure 3 An example of a wireless communication system 300 supporting techniques for configuring multiple PSFCH opportunities for sidelink feedback in accordance with various aspects of the present disclosure is illustrated. The wireless communication system 300 illustrates communication between UE 115a and UE 115b, which may be corresponding devices described herein (including as described in reference Figure 1 and Figure 2 15a) described herein. In some aspects, UE 115a and UE 115b can communicate within a geographic coverage area and communicate with each other via communication link 305 and communication link 310 operating in sidelink mode. In some implementations, UE 115b can receive a configuration of multiple PSFCH opportunities 325 on multiple LBT subbands 330 and symbols corresponding to PSSCH 315.

[0063] The wireless communication system 300 (which may be an example of an NR system supporting NR sidelink communication (such as V2X communication)) may support sending feedback (such as HARQ feedback) over the PSFCH 320 to achieve higher reliability for both unicast transmission and multicast transmission. For example, the UE 115a or the UE 115b or both may send a HARQ response (such as ACK or NACK) on the PSFCH opportunity 325 in response to the sidelink communication between the UE 115a and the UE 115b, and the PSFCH may be arranged or otherwise configured as a global resource pool with a predetermined (e.g., preconfigured) mapping or assignment. In other words, in some cases, there may be multiple PSFCH opportunities 325 for one PSSCH. Such examples where there may be multiple PSFCH opportunities 325 for one PSSCH may include an example of a unicast HARQ response (such that one UE 115 receives a data transmission and sends feedback via the PSFCH in response to the data transmission) and an example of a groupcast HARQ response option 2 (such that multiple UEs 115 receive a data transmission and each send or refrain from sending a PSFCH 320 in response to the data transmission).

[0064] In some aspects, one or more PSFCH opportunities 325 are mapped or assigned to one PSSCH 315, and where UE 115a transmits a data transmission on the PSSCH 315 to UE 115b, UE 115b may determine the PSFCH opportunity 325 mapped or assigned to the PSSCH 315 on which UE 115a transmits the data transmission, and UE 115b may accordingly transmit ACK / NACK feedback in response to the data transmission on the one or more PSFCH opportunities 325. In some cases, such mapping or assignment may be preconfigured for each PSSCH 315 resource over which UE 115 may transmit.

[0065] In some aspects, each PSSCH 315 may be mapped to multiple PSFCH opportunities 325, and each different PSFCH opportunity 325 may correspond to a different set of physical resource blocks (PRBs) in a symbol period (such as a PSFCH symbol period). In some cases, each PRB set in a PSFCH symbol period may include a configurable number of PRBs.

[0066] In some aspects, UE 115a and UE 115b can communicate on an unlicensed radio frequency spectrum band. In such cases where UE 115a and UE 115b communicate on an unlicensed radio frequency spectrum band, UE 115a and UE 115b can perform LBT (e.g., LBT procedure or channel access procedure) before sending to support coexistence with other radio access technologies (RATs). In some aspects, UE 115b can perform LBT before sending ACK / NACK feedback (e.g., HARQ response) on one or more PSFCH opportunities 325. However, in some cases, PSFCH opportunity 325 may be occupied or otherwise unavailable, so that LBT for PSFCH opportunity 325 may fail. As a result, UE 115b may not be able to obtain channel access for PSFCH opportunity 325, and may not be able to send ACK / NACK to UE 115a on PSFCH opportunity 325. UE 115a that fails to receive ACK / NACK feedback corresponding to (e.g., mapped or assigned to) a PSSCH 315 carrying a data transmission from UE 115b on a PSFCH opportunity 325 may determine or otherwise assume that UE 115b failed to successfully receive the data transmission. Therefore, UE 115a may resend the data transmission to UE 115b on a second PSSCH 315, which may be unnecessary if UE 115b successfully received the initial data transmission and experienced an LBT failure when attempting to send the associated ACK / NACK feedback. Various aspects of the present disclosure provide multiple PSFCH opportunities 325 in the time domain and / or frequency domain to increase the probability of LBT going through and PSFCH being sent to UE 115a.

[0067] In some aspects, UE 115b may receive a configuration of multiple PSFCH opportunities 325 (such as PSFCH opportunity 325a, PSFCH opportunity 325b, and PSFCH opportunity 325c) on multiple LBT subbands 330 (such as on LBT subband 330a and LBT subband 330b). In other words, one PSSCH on which UE 115a may send data transmissions (and request HARQ responses) to UE 115b may correspond to multiple PSFCH opportunities 325 on multiple LBT subbands 330 and / or multiple symbols.

[0068] For example, UE 115a may send a data transmission on PSSCH 315 corresponding to a plurality of PSFCH opportunities 325, the plurality of PSFCH opportunities including PSFCH opportunity 325a located in LBT subband 330a and in a first PSFCH symbol, PSFCH opportunity 325b located in LBT subband 330b and in a first PSFCH symbol, and PSFCH opportunity 325c located in LBT subband 330b and in a second PSFCH symbol. Thus, UE 115b may perform an LBT procedure on one or more of the PSFCH opportunities 325 to determine which of the plurality of PSFCH opportunities 325 are available (e.g., which of the plurality of PSFCH opportunities 325 pass LBT). In some aspects, UE 115b may determine that one or more of the plurality of PSFCH opportunities 325 are available (e.g., pass LBT), and may send an ACK / NACK associated with the data transmission on at least one of the available one or more PSFCH opportunities 325.

[0069] Figure 4A wireless communication network 400 according to some aspects of the present disclosure is illustrated. The wireless communication network 400 may include a network element 105, a UE 115a, and a UE 115b. In some aspects, the UE 115a may send a sidelink communication 425 to the UE 115b. In response, the UE 115b may send an ACK / NACK to the UE 115a on one or more PSFCH opportunities 420. The ACK / NACK may indicate whether the sidelink communication is successfully received by the UE 115b. The UE 115b may perform a listen-before-talk (LBT) procedure in an unlicensed band before sending the ACK / NACK. The UE 115b may perform an LBT procedure or other clear channel assessment (CCA) on one or more sidelink communication channels. In some instances, the UE 115b may perform an LBT procedure or other CCA to obtain access to a channel occupancy time (COT) in an unlicensed (e.g., shared) spectrum. For example, UE 115b may perform category 1 LBT, category 2 LBT, category 3 LBT and / or category 4 LBT to obtain access to COT in unlicensed spectrum. In some aspects, UE 115b may perform LBT in one or more time resources, space resources and / or frequency resources to obtain access to the channel in one or more PSFCH opportunities 420. These frequency resources may include spectrum, frequency band, frequency sub-band, frequency sub-channel, resource element, resource block and / or frequency interleaving. These time resources may include time slot, sub-time slot, symbol, subframe or any other suitable time resource. In some aspects, UE 115b may perform LBT on one or more directional beams (e.g., beams in the direction of UE 115a to which UE 115b intends to send ACK / NACK).

[0070] In some aspects, UE 115b may send ACK / NACK to UE 115a in the earliest PSFCH opportunity 420a of the multiple PSFCH opportunities 420 in which LBT is successful. UE 115b may send ACK / NACK in the earliest PSFCH opportunity 420a to reduce the latency of sending feedback to UE 115a (e.g., a UE that sends PSSCH 425 to UE 115b). In some aspects, if UE 115a does not receive an ACK associated with PSSCH communication 425 from UE 115b, UE 115a may have multiple opportunities (e.g., up to two opportunities or more) to resend PSSCH communication 425. For example, UE 115a may send an initial PSSCH communication in PSSCH 425a. PSSCH 425b and 425c may be opportunities to resend PSSCH communication. Based on the LBT performed by UE 115b being unsuccessful, UE 115b sending a NACK to UE 115a (e.g., sending a NACK in PSFCH opportunities 420a and 420b), and / or the ACK / NACK sent by UE 115b not being correctly received and decoded by UE 115a, UE 115a may not receive an ACK associated with PSSCH communication 425 from UE 115b. In some aspects, multiple PSFCH opportunities 420 may increase the probability that UE 115a receives an ACK / NACK. For example, UE 115b may send an ACK / NACK in the earliest PSFCH opportunity (e.g., PSFCH opportunity 420a) through LBT and in the next (e.g., subsequent) PSFCH opportunity (e.g., PSFCH opportunity 420b) through LBT. Additionally or alternatively, UE 115b may send an ACK / NACK in multiple subbands (e.g., subchannels) of an unlicensed band through LBT. A subband may refer to or include a frequency bandwidth over which UE 115b may perform LBT procedures. For example, in an example where UE 115b and UE 115a communicate via a 5 GHz unlicensed radio frequency spectrum band, a subband may refer to or include a 20 MHz frequency range or other suitable frequency range.

[0071] In some aspects, UE 115b may send ACK / NACK to UE 115a in all PSFCH opportunities 420 in which UE 115b performed successful LBT. UE 115b may increase the probability that UE 115a successfully receives and decodes the ACK / NACK based on sending the ACK / NACK in all PSFCH opportunities 420 through LBT. In some aspects, UE 115a may combine multiple ACK / NACK transmissions from UE 115b to successfully decode the ACK / NACK.

[0072] In some aspects, UE 115b may receive a configuration indicating parameters associated with multiple PSFCH opportunities. UE 115b may receive the configuration from UE 115a and / or network element 105. The configuration may indicate the number of PSFCH opportunities 420, time resources associated with multiple PSFCH opportunities 420, frequency resources associated with multiple PSFCH opportunities 420, and other suitable parameters associated with multiple PSFCH opportunities 420. In this regard, UE 115b may receive the configuration from UE 115a via at least one of a radio resource control (RRC) message, a medium access control control element (MAC-CE), a sidelink control information (SCI), or other suitable communications. Additionally or alternatively, UE 115b may receive the configuration from network element 105 via at least one of a radio resource control (RRC) message, a downlink control information (DCI) 410, a medium access control control element (MAC-CE), or other suitable communications.

[0073] In some aspects, the configuration may include a default configuration indicating parameters associated with the plurality of PSFCH opportunities 420. The default configuration may be adjusted (e.g., updated over time) based on parameters including, but not limited to, an LBT procedure success rate, an interference level associated with an unlicensed band, a buffer status report (BSR) associated with the UE 115a, a data type associated with the sidelink PSSCH communication 425, a priority level associated with the sidelink PSSCH communication 425, or other suitable parameters.

[0074] In some aspects, UE 115b may receive an indicator indicating a subset of the number of multiple PSFCH opportunities 420. UE 115b may receive the indicator from UE 115a and / or network element 105. The default configuration may include a default number of PSFCH opportunities 420 and their associated time / frequency resources. UE 115b may then receive an indicator indicating a subset of PSFCH opportunities 420. UE 115b may send ACK / NACK in a subset of PSFCH opportunities 420. The subset may be based on the above parameters. For example, UE 115b may measure an LBT success rate. The LBT success rate may indicate the number of times the attempted LBT is successful within a certain period of time. The LBT success rate may reflect the level of interference / activity in an unlicensed band. UE 115b may send an LBT success rate indicator to UE 115a and / or network element 105. UE 115a and / or network element 105 may send the subset of PSFCH opportunities 420 and their associated time / frequency resources to UE 115b via at least one of an RRC message, a MAC-CE message, DCI 410, SCI, or other suitable communication.

[0075] In some aspects, the subset of PSFCH opportunities 420 may be based on a data type associated with the PSSCH communication 425. The data type associated with the PSSCH communication 425 may include enhanced mobile broadband data, V2X data, massive machine type communication (mMTC) data, ultra-reliable low latency communication (URLLC) data, and / or other types of data. The UE 115a may send the data type associated with the PSSCH communication 425 to the network element 105. The network element 105 may send the subset of PSFCH opportunities 420 and their associated time / frequency resources to the UE 115a via at least one of an RRC message, a MAC-CE message, a DCI 410, or other suitable communication based on the data type. The UE 115a may send the subset of PSFCH opportunities 420 and their associated time / frequency resources to the UE 115b via at least one of an RRC message, a MAC-CE message, an SCI, or other suitable communication.

[0076] In some aspects, the subset of PSFCH opportunities 420 may be based on a priority level associated with the PSSCH communication 425. The priority level associated with the PSSCH communication 425 may be based on a latency requirement and / or a reliability requirement associated with the PSSCH communication 425. The UE 115a may send the priority level associated with the PSSCH communication 425 to the network element 105. The network element may send the subset of PSFCH opportunities 420 and an indicator of their associated time / frequency resources to the UE 115a based on the priority level via at least one of an RRC message, a MAC-CE message, a DCI 410, or other suitable communication. The UE 115a may send the indicator of the subset of PSFCH opportunities 420 and their associated time / frequency resources to the UE 115b via at least one of an RRC message, a MAC-CE message, a SCI, or other suitable communication.

[0077] In some aspects, UE 115b may receive and decode PSSCH communication 425a from UE 115a in the first time slot. UE 115b may perform an unsuccessful LBT at the next PSFCH opportunity 420a after decoding PSSCH communication 425a, thereby preventing UE 115b from sending an ACK to UE 115a. In response to not receiving an ACK from UE 115b during PSFCH opportunity 420a, UE 115a may resend PSSCH communication 425b to UE 115b. UE 115b may identify PSSCH communication 425b as a retransmission and refrain from decoding the retransmitted PSSCH communication 425b, thereby reducing power consumption and computing resources. UE 115b may perform LBT at the next PSFCH opportunity 420b after the retransmission of PSSCH communication 425b. If the LBT succeeds at the next PSFCH opportunity 420b, UE 115b may send an ACK to UE 115a. If UE 115a successfully decodes the ACK, UE 115a may refrain from retransmitting the PSSCH again in PSSCH 425c. If UE 115a does not successfully decode the ACK, UE 115a may retransmit the PSSCH communication again in PSSCH 425c.

[0078] In some aspects, UE 115b may receive an ACK / NACK from UE 115a in one or more of the PSFCH opportunities 420. Then, in an uplink communication 430, UE 115b may send the ACK / NACK to the network element 105 in a HARQ process. In some aspects, UE 115b may send the ACK / NACK to the network element 105 in the uplink communication 430 after a last PSFCH opportunity 420c in the plurality of PSFCH opportunities 420. In some aspects, UE 115b may send the ACK / NACK to the network element 105 after a time period (e.g., a HARQ process time period) after an earliest PSFCH opportunity 420a in the plurality of PSFCH opportunities 420.

[0079] In some aspects, UE 115a can send sidelink communication as a group of sidelink UEs including UE 115b as a groupcast sidelink communication. In this case, UE 115b in the group of sidelink UEs can be configured to send NACK to UE 115a only when UE 115b does not successfully decode the sidelink communication. If UE 115b successfully decodes the sidelink communication, UE 115b can suppress sending ACK. In this way, UE 115a can know that the group of sidelink UEs has successfully decoded the sidelink communication based on not receiving any NACK. When UE 115b does not receive NACK from any sidelink UE in the groupcast, UE 115b can send ACK to network element 105 in uplink communication 430.

[0080] Figure 5 6 is a signaling diagram of a wireless communication method 500 according to some aspects of the present disclosure. The actions of the communication method 500 may be performed by a computing device (e.g., a processor, a processing circuit, and / or other suitable components) of a communication device or other suitable means for performing the actions. For example, a wireless communication device (such as UE 115 or UE 600) may utilize one or more components (such as a processor 602, a memory 604, a PSFCH opportunity module 608, a transceiver 610, a modem 612, and one or more antennas 616) to perform various aspects of the method 500. A wireless communication device (such as a network unit 105 or 700) may utilize one or more components (such as a processor 702, a memory 704, a PSFCH opportunity module 708, a transceiver 710, a modem 712, and one or more antennas 716) to perform various aspects of the method 500.

[0081] At action 502, the network element 105 may send a PSFCH opportunity configuration to the UE 115a. In this regard, the network element 105 may send the configuration of the PSFCH opportunities and their associated time / frequency resources to the UE 115a via at least one of an RRC message, a MAC-CE message, a DCI, or other suitable communication.

[0082] At action 504, UE 115a may send the configuration of PSFCH opportunities and their associated time / frequency resources to UE 115b via at least one of an RRC message, a MAC-CE message, an SCI, or other suitable communication.

[0083] At action 506, UE 115a may send at least one of the following to the network unit 105 via uplink control information (UCI), PUCCH communication, PUSCH communication, or other suitable communication: LBT procedure success rate, interference level associated with the unlicensed band, buffer status report (BSR) associated with UE 115a, data type associated with side link communication, priority level associated with side link communication, or other suitable parameters.

[0084] At action 508, the network element 105 may send an indicator of a subset of PSFCH opportunities to the UE 115a. In this regard, the network element 105 may send the subset of PSFCH opportunities and their associated time / frequency resources to the UE 115a via at least one of an RRC message, a MAC-CE message, a DCI, or other suitable communication. The subset of PSFCH opportunities may be based on the LBT procedure success rate sent to the network element 105 at action 506, the interference level associated with the unlicensed band, a buffer status report (BSR) associated with the UE 115a, a data type associated with the sidelink communication, a priority level associated with the sidelink communication, or other suitable parameters.

[0085] At action 510, UE 115a may send an indicator of the subset of PSFCH opportunities to UE 115b. In this regard, UE 115a may send the indicator of the subset of PSFCH opportunities to UE 115b via at least one of a radio resource control (RRC) message, a medium access control control element (MAC-CE), a sidelink control information (SCI), or other suitable communication.

[0086] At act 512, UE 115a may send a PSSCH communication to UE 115b. The PSSCH communication may be associated with a HARQ process in which UE 115a monitors ACK / NACK feedback from UE 115b.

[0087] At act 514 , UE 115b may successfully decode the PSSCH sent by UE 115a at act 512 .

[0088] At act 516 , UE 115b may perform an unsuccessful LBT. UE 115b may perform an LBT in an attempt to send ACK / NACK feedback to UE 115a. UE 115b may perform an unsuccessful LBT in the PSFCH of a subset of the PSFCH opportunities received at act 510 .

[0089] At act 518, UE 115b may perform a successful LBT. After the LBT failed at act 516, UE 115b may perform LBT in an attempt to send ACK / NACK feedback to UE 115a. UE 115b may perform LBT in the next PSFCH of the subset of PSFCH opportunities after the PSFCH opportunity at act 516.

[0090] At act 520, UE 115b may send an ACK to UE 115a indicating successful decoding of the PSSCH communication sent to UE 115b at act 512. UE 115b may send an ACK to UE 115a based on the successful LBT at act 518.

[0091] At act 522, UE 115b may perform another successful LBT. UE 115b may perform LBT to attempt to resend ACK / NACK feedback to UE 115a. UE 115b may perform LBT in the next PSFCH of the subset of PSFCH opportunities following the PSFCH opportunity at act 518.

[0092] At act 524, UE 115b may resend an ACK to UE 115a indicating successful decoding of the PSSCH communication sent to UE 115b at act 512. UE 115b may resend the ACK to UE 115a in order to increase the probability that UE 115a successfully decodes the ACK.

[0093] At act 526, UE 115a may send HARQ feedback indicating an ACK to network element 105. In some aspects, UE 115a may send HARQ feedback to network element 105 after the last PSFCH opportunity.

[0094] Figure 66 is a block diagram of an exemplary UE 600 according to some aspects of the present disclosure. UE 600 may be UE 115 in network 100, 200, or 300 as discussed above. As shown, UE 600 may include a processor 602, a memory 604, a PSFCH opportunity module 608, a transceiver 610 (including a modem subsystem 612 and a radio frequency (RF) unit 614), and one or more antennas 616. These elements may be coupled to each other, for example, via one or more buses and communicate with each other directly or indirectly.

[0095] The processor 602 may include a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 602 may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or any other such configuration.

[0096] Memory 604 may include cache memory (e.g., cache memory of processor 602), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory, solid-state memory devices, hard drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some examples, memory 604 includes non-transitory computer-readable media. Memory 604 may store instructions 606. Instructions 606 may include instructions that, when executed by processor 602, cause processor 602 to perform various aspects of the present disclosure (e.g., Figure 3 , Figure 4 A and Figure 4 B). Instructions 606 may also be referred to as code. The terms "instructions" and "code" should be broadly interpreted to include any type of computer-readable statements. For example, the terms "instructions" and "code" may refer to one or more programs, routines, subroutines, functions, procedures, etc. "Instructions" and "code" may include a single computer-readable statement or multiple computer-readable statements.

[0097] The PSFCH opportunity module 608 may be implemented via hardware, software, or a combination thereof. For example, the PSFCH opportunity module 608 may be implemented as a processor, circuit, and / or instructions 606 stored in the memory 604 and executed by the processor 602. In some aspects, the PSFCH opportunity module 608 may be implemented Figures 3 to 5, Figure 8 and Fig. 9 For example, the PSFCH opportunity module 608 can perform a listen-before-talk (LBT) procedure in an unlicensed band and, based on the LBT procedure being successful, send an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication to a second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0098] As shown, the transceiver 610 may include a modem subsystem 612 and an RF unit 614. The transceiver 610 may be configured to communicate bidirectionally with other devices, such as the BS 105 and / or the UE 115. The modem subsystem 612 may be configured to modulate and / or encode data from the memory 604 according to a modulation and coding scheme (MCS) (e.g., a low-density parity check (LDPC) decoding scheme, a turbo decoding scheme, a convolutional decoding scheme, a digital beamforming scheme, etc.). The RF unit 614 may be configured to process (e.g., perform analog-to-digital conversion or digital-to-analog conversion, etc.) the modulated / encoded data from the modem subsystem 612 (for outbound transmissions) or transmissions originating from another source, such as the UE 115 or the BS 105. The RF unit 614 may be further configured to perform analog beamforming in conjunction with digital beamforming. Although shown as being integrated together in the transceiver 610, the modem subsystem 612 and the RF unit 614 may be separate devices that are coupled together to enable the UE 600 to communicate with other devices.

[0099] The RF unit 614 may provide modulated and / or processed data, such as a data packet (or more generally, a data message that may contain one or more data packets and other information), to the antenna 616 for transmission to one or more other devices. The antenna 616 may also receive data messages sent from other devices. The antenna 616 may provide the received data message for processing and / or demodulation at the transceiver 610. The antenna 616 may include multiple antennas of similar or different designs to maintain multiple transmission links. The RF unit 614 may configure the antenna 616.

[0100] In some examples, the UE 600 may include multiple transceivers 610 that implement different RATs (e.g., NR and LTE). In some examples, the UE 600 may include a single transceiver 610 that implements multiple RATs (e.g., NR and LTE). In some examples, the transceiver 610 may include various components, where different combinations of the components may implement the RATs.

[0101] Figure 77 is a block diagram of an exemplary network unit 700 according to some aspects of the present disclosure. The network unit 700 may be a BS 105, a CU 210, a DU 230, or a RU 240 as discussed above. As shown, the network unit 700 may include a processor 702, a memory 704, a PSFCH opportunity module 708, a transceiver 710 (including a modem subsystem 712 and an RF unit 714), and one or more antennas 716. These elements may be coupled to each other, for example, via one or more buses and communicate with each other directly or indirectly.

[0102] The processor 702 may have various features that are specific types of processors. For example, these features may include a CPU, a DSP, an ASIC, a controller, an FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 702 may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

[0103] Memory 704 may include cache memory (e.g., cache memory of processor 702), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, solid-state memory devices, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some examples, memory 704 may include non-transitory computer-readable media. Memory 704 may store instructions 706. Instructions 706 may include instructions that, when executed by processor 702, cause processor 702 to perform the operations described herein (e.g., Figures 3 to 5 Instructions 706 may also be referred to as codes, which may be broadly interpreted to include any type of computer-readable statements.

[0104] The PSFCH opportunities module 708 may be implemented via hardware, software, or a combination thereof. For example, the PSFCH opportunities module 708 may be implemented as a processor, circuit, and / or instructions 706 stored in the memory 704 and executed by the processor 702.

[0105] In some aspects, the PSFCH opportunity module 708 can implement Figures 3 to 5 , Figure 8 and Fig. 9For example, the PSFCH opportunity module 708 can send a configuration associated with multiple PSFCH opportunities to the sidelink UE. Additionally or alternatively, the PSFCH opportunity module 708 can be implemented in any combination of hardware and software, and in some specific implementations can involve, for example, the processor 702, the memory 704, the instructions 706, the transceiver 710 and / or the modem 712.

[0106] As shown, the transceiver 710 may include a modem subsystem 712 and an RF unit 714. The transceiver 710 may be configured to communicate bidirectionally with other devices, such as the UE 115 and / or the UE 600. The modem subsystem 712 may be configured to modulate and / or encode data according to an MCS (e.g., an LDPC decoding scheme, a turbo decoding scheme, a convolutional decoding scheme, a digital beamforming scheme, etc.). The RF unit 714 may be configured to process (e.g., perform analog-to-digital conversion or digital-to-analog conversion, etc.) the modulated / encoded data from the modem subsystem 712 (for outbound transmissions) or from another source, such as the UE 115 or the UE 600. The RF unit 714 may be further configured to perform analog beamforming in conjunction with digital beamforming. Although shown as being integrated together in the transceiver 710, the modem subsystem 712 and / or the RF unit 714 may be separate devices that are coupled together at the network unit 700 to enable the network unit 700 to communicate with other devices.

[0107] The RF unit 714 may provide modulated and / or processed data, such as data packets (or more generally, data messages that may include one or more data packets and other information), to the antenna 716 for transmission to one or more other devices. For example, according to aspects of the present disclosure, this may include a configuration indicating multiple sub-slots within a time slot. The antenna 716 may also receive data messages sent from other devices and provide the received data messages for processing and / or demodulation at the transceiver 710. The antenna 716 may include multiple antennas of similar design or different design to maintain multiple transmission links.

[0108] In some examples, the network unit 700 may include multiple transceivers 710 that implement different RATs (e.g., NR and LTE). In some examples, the network unit 700 may include a single transceiver 710 that implements multiple RATs (e.g., NR and LTE). In some examples, the transceiver 710 may include various components, where different combinations of components may implement the RATs.

[0109] Figure 8800 is a flow chart of a communication method 800 according to some aspects of the present disclosure. Various aspects of the method 800 may be performed by a computing device (e.g., a processor, processing circuitry, and / or other suitable components) of a wireless communication device or other suitable means for performing such actions. For example, a wireless communication device (such as UE 115 or UE 600) may utilize one or more components (such as processor 602, memory 604, PSFCH opportunity module 608, transceiver 610, modem 612, and one or more antennas 616) to perform various aspects of the method 800. The method 800 may employ mechanisms similar to those in networks 100 and 200 and with respect to Figures 3 to 5 As shown, method 800 includes multiple enumerated actions, but method 800 may include additional actions before, after, and between these enumerated actions. In some aspects, one or more of these enumerated actions may be omitted or performed in a different order.

[0110] At action 810, method 800 includes a first side link UE (e.g., UE 115 or UE 600) performing a listen-before-talk (LBT) procedure in an unlicensed band. The first side link UE may perform an LBT procedure or other clear channel assessment (CCA) on one or more side link communication channels. In some instances, the first side link UE may perform an LBT procedure or other CCA to obtain access to a channel occupancy time (COT) in an unlicensed (e.g., shared) spectrum. For example, the first side link UE may perform a category 1 LBT, a category 2 LBT, a category 3 LBT, and / or a category 4 LBT to obtain access to a COT in an unlicensed spectrum. In some aspects, the first side link UE may perform LBT in one or more time resources, space resources, and / or frequency resources to obtain access to a channel within one or more PSFCH opportunities. These frequency resources may include spectrum, frequency band, frequency subband, frequency subchannel, resource element, resource block, and / or frequency interleaving. These time resources may include time slots, subslots, symbols, subframes, or any other suitable time resources. In some aspects, a first sidelink UE may perform LBT on one or more directional beams (e.g., a beam in the direction of a second sidelink UE to which the first sidelink UE intends to send an acknowledgement / negative acknowledgement (ACK / NACK)).

[0111] At act 820, method 800 includes the first sidelink UE sending an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication. The first sidelink UE may send an ACK / NACK to the second sidelink UE based on the LBT procedure success at act 810. When the first sidelink UE successfully receives (e.g., decodes) the sidelink communication, the first sidelink UE may send an acknowledgement (ACK) to the second sidelink UE. When the first sidelink UE does not successfully receive (e.g., decode) the sidelink communication, the first sidelink UE may send a negative acknowledgement (NACK) to the second sidelink UE.

[0112] In some aspects, the first side link UE may send an ACK / NACK in at least one of a plurality of physical side link feedback channel (PSFCH) opportunities. In some aspects, the first side link UE may send an ACK / NACK after a successful LBT. However, in some aspects, the first side link UE may refrain from sending an ACK / NACK when an LBT fails. In order to increase the probability that the first side link UE performs a successful LBT and sends an ACK / NACK, aspects of the present disclosure provide a plurality of PSFCH opportunities in which the first side link UE may contend for a channel and send an ACK / NACK.

[0113] In some aspects, the multiple PSFCH opportunities may include multiple PSFCH opportunities in the time domain. For example, the multiple PSFCH opportunities may be scheduled in multiple time slots, sub-time slots, symbols, or other suitable time periods. In some aspects, the multiple PSFCH opportunities may include multiple PSFCH opportunities in the frequency domain. For example, the multiple PSFCH opportunities may be scheduled in multiple frequency sub-bands, frequency ranges, and / or frequency sub-channels. For example, referring to Figure 3, UE 115a may send data transmissions on PSSCH 315 corresponding to multiple PSFCH opportunities 325, the multiple PSFCH opportunities including PSFCH opportunity 325a located in LBT subband 330a and in a first PSFCH symbol, PSFCH opportunity 325b located in LBT subband 330b and in a first PSFCH symbol, and PSFCH opportunity 325c located in LBT subband 330b and in a second PSFCH symbol. Thus, UE 115b may perform an LBT procedure on one or more PSFCH opportunities in PSFCH opportunities 325 to determine which PSFCH opportunities in the multiple PSFCH opportunities 325 are available (e.g., which PSFCH opportunities in the multiple PSFCH opportunities 325 pass LBT). In some aspects, the UE 115a may determine that one or more of multiple PSFCH opportunities 325 are available (e.g., via LBT) and may send ACK / NACK feedback in a PSFCH 320 associated with the PSSCH communication 315 on at least one of the available multiple PSFCH opportunities 325.

[0114] In some aspects, the first side link UE may send an ACK / NACK to the second side link UE in the earliest PSFCH opportunity among multiple PSFCH opportunities in which the LBT is successful. The first side link UE may send an ACK / NACK in the earliest PSFCH opportunity to reduce the latency of sending feedback to the second side link UE (e.g., a UE that sends a PSSCH to the first side link UE). In some aspects, if the second side link UE does not receive an ACK associated with the PSSCH communication from the first side link UE, the second side link UE may have multiple opportunities (e.g., up to two opportunities or more) to resend the PSSCH communication. Based on the unsuccessful LBT performed by the first side link UE, the first side link UE sending a NACK to the second side link UE, and / or the ACK / NACK sent by the first side link UE not being correctly received and decoded by the second side link UE, the second side link UE may not receive an ACK associated with the PSSCH communication from the first side link UE. In some aspects, multiple PSFCH opportunities may increase the probability of the second side link UE receiving an ACK / NACK. For example, the first side link UE may send ACK / NACK in the earliest PSFCH opportunity through LBT and in the next (e.g., subsequent) PSFCH opportunity through LBT. Additionally or alternatively, the first side link UE may send ACK / NACK in multiple subbands (e.g., subchannels) of an unlicensed band through LBT. A subband may refer to or include a frequency bandwidth on which the first side link UE may perform an LBT procedure. For example, in an example in which the first side link UE and the second side link UE communicate through a 5 GHz unlicensed radio frequency spectrum band, the subband may refer to or include a 20 MHz frequency range or other suitable frequency range.

[0115] In some aspects, the first sidelink UE may send ACK / NACK to the second sidelink UE in all PSFCH opportunities of multiple PSFCH opportunities in which the first sidelink UE performs a successful LBT. The first sidelink UE may increase the probability of the second sidelink UE successfully receiving and decoding the ACK / NACK based on sending the ACK / NACK in all PSFCH opportunities through the LBT. In some aspects, the second sidelink UE may combine multiple ACK / NACK transmissions from the first sidelink UE to successfully decode the ACK / NACK.

[0116] In some aspects, a first side link UE may receive a configuration indicating parameters associated with multiple PSFCH opportunities. The first side link UE may receive the configuration from a second side link UE and / or a network unit (e.g., BS105, RU 240, DU 230, CU 210, and / or network unit 700). The configuration may indicate the number of PSFCH opportunities, time resources associated with multiple PSFCH opportunities, frequency resources associated with multiple PSFCH opportunities, and other suitable parameters associated with multiple PSFCH opportunities. In this regard, the first side link UE may receive the configuration from the second side link UE via at least one of a radio resource control (RRC) message, a medium access control control element (MAC-CE), a side link control information (SCI), or other suitable communications. Additionally or alternatively, the first side link UE may receive the configuration from the network unit via at least one of a radio resource control (RRC) message, a downlink control information (DCI), a medium access control control element (MAC-CE), or other suitable communications.

[0117] In some aspects, the configuration may include a default configuration indicating parameters associated with the plurality of PSFCH opportunities. The default configuration may be adjusted (e.g., updated over time) based on parameters including, but not limited to, a LBT procedure success rate, an interference level associated with an unlicensed band, a buffer status report (BSR) associated with a second sidelink UE, a data type associated with the sidelink communication, a priority level associated with the sidelink communication, or other suitable parameters.

[0118] In some aspects, the first side link UE may receive an indicator indicating a subset of the number of multiple PSFCH opportunities. The first side link UE may receive the indicator from the second side link UE and / or the network unit. The default configuration may include a default number of PSFCH opportunities and their associated time / frequency resources. The first side link UE may then receive an indicator indicating a subset of P SFCH opportunities. The first side link UE may send ACK / NACK in a subset of P SFCH opportunities. The subset may be based on the above parameters. For example, the first side link UE may measure the LBT success rate. The LBT success rate may indicate the number of times the attempted LBT is successful within a certain period of time. The LBT success rate may reflect the level of interference / activity in the unlicensed band. The first side link UE may send an LBT success rate indicator to the second side link UE and / or the network unit. The second side link UE and / or the network unit may send a subset of PSFCH opportunities and their associated time / frequency resources to the first side link UE via at least one of an RRC message, a MAC-CE message, a DCI, an SCI, or other suitable communications.

[0119] In some aspects, a subset of PSFCH opportunities may be based on a data type associated with a PSSCH communication. The data type associated with a PSSCH communication may include enhanced mobile broadband data, V2X data, massive machine type communication (mMTC) data, ultra-reliable low latency communication (URLLC) data, and / or other types of data. The second side link UE may send the data type associated with the PSSCH communication to the network unit. The network unit may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the second side link UE based on the data type via at least one of an RRC message, a MAC-CE message, a DCI, or other suitable communications. The second side link UE may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the first side link UE via at least one of an RRC message, a MAC-CE message, a SCI, or other suitable communications.

[0120] In some aspects, the subset of PSFCH opportunities may be based on a priority level associated with PSSCH communications. The priority level associated with PSSCH communications may be based on latency requirements and / or reliability requirements associated with PSSCH communications. The second side link UE may send a priority level associated with PSSCH communications to the network unit. The network unit may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the second side link UE based on the priority level via at least one of an RRC message, a MAC-CE message, a DCI, or other suitable communications. The second side link UE may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the first side link UE via at least one of an RRC message, a MAC-CE message, a SCI, or other suitable communications.

[0121] In some aspects, the first side link UE may receive and decode a PSSCH communication from a second side link UE in a first time slot. The first side link UE may perform an unsuccessful LBT at the next PSFCH opportunity after decoding the PSSCH communication, thereby preventing the first side link UE from sending an ACK to the second side link UE. In response to not receiving an ACK from the first side link UE, the second side link UE may resend the PSSCH communication to the first side link UE. The first side link UE may identify the PSSCH communication as a retransmission and suppress decoding of the retransmitted PSSCH communication, thereby reducing power consumption and computing resources. The first side link UE may perform an LBT at the next PSFCH opportunity after the retransmission of the PSSCH communication. If the LBT is successful at the next PSFCH opportunity, the first side link UE may send an ACK to the second side link UE. If the second side link UE successfully decodes the ACK, the second side link UE may suppress retransmitting the P SCH again. If the second side link does not successfully decode the ACK, the second side link UE may retransmit the PSSCH communication again.

[0122] Fig. 9 900 is a flow chart of a communication method 900 according to some aspects of the present disclosure. Various aspects of the method 900 may be performed by a computing device (e.g., a processor, processing circuitry, and / or other suitable components) of a wireless communication device or other suitable means for performing such actions. For example, a wireless communication device (such as UE 115 or UE 600) may utilize one or more components (such as a processor 602, a memory 604, a PSFCH opportunity module 608, a transceiver 610, a modem 612, and one or more antennas 616) to perform various aspects of the method 900. The method 900 may employ mechanisms similar to those in networks 100 and 200 and with respect to Figures 3 to 5 As shown, method 900 includes multiple enumerated actions, but method 900 may include additional actions before, after, and between these enumerated actions. In some aspects, one or more of these enumerated actions may be omitted or performed in a different order.

[0123] At action 910, method 900 includes a first sidelink UE (e.g., UE 115 or UE 600) sending a sidelink communication to one or more sidelink UEs in an unlicensed band. In this regard, the first sidelink UE may send a PSSCH, a PSCCH, or other suitable sidelink communication to the one or more sidelink UEs. In some aspects, the first sidelink UE may perform a listen-before-talk (LBT) procedure in the unlicensed band to obtain access to the channel before sending the sidelink communication. The first sidelink UE may perform an LBT procedure or other clear channel assessment (CCA) on one or more sidelink communication channels. In some instances, the first sidelink UE may perform an LBT procedure or other CCA to obtain access to a channel occupancy time (COT) in an unlicensed (e.g., shared) spectrum. For example, the first sidelink UE may perform a category 1 LBT, a category 2 LBT, a category 3 LBT, and / or a category 4 LBT to obtain access to the COT in the unlicensed spectrum. These frequency resources may include spectrum, frequency band, frequency sub-band, frequency sub-channel, resource element, resource block and / or frequency interlace. These time resources may include time slot, sub-time slot, symbol, subframe or any other suitable time resource. In some aspects, the first side link UE may perform LBT on one or more directional beams (e.g., a beam in the direction of a second side link UE to which the first side link UE intends to send an acknowledgement / negative acknowledgement (ACK / NACK)).

[0124] At act 920, method 900 includes the first sidelink UE monitoring, in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities, an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication.

[0125] The first sidelink UE may receive ACK / NACK from the second sidelink UE and / or other sidelink UEs. When the second sidelink UE successfully receives (e.g., decodes) the sidelink communication, the second sidelink UE may send an acknowledgment (ACK) to the first sidelink UE. When the second sidelink UE does not successfully receive (e.g., decode) the sidelink communication, the second sidelink UE may send a negative acknowledgment (NACK) to the first sidelink UE.

[0126] In some aspects, the first side link UE may receive an ACK / NACK in at least one of a plurality of physical side link feedback channel (PSFCH) opportunities based on monitoring. In some aspects, the first side link UE may receive an ACK / NACK after the second side link UE performs a successful LBT. However, in some aspects, the second side link UE may refrain from sending an ACK / NACK when the LBT fails. In order to increase the probability that the second side link UE performs a successful LBT and sends an ACK / NACK, aspects of the present disclosure provide a plurality of PSFCH opportunities in which the second side link UE may contend for a channel and send an ACK / NACK.

[0127] In some aspects, the multiple PSFCH opportunities may include multiple PSFCH opportunities in the time domain. For example, the multiple PSFCH opportunities may be scheduled in multiple time slots, sub-time slots, symbols, or other suitable time periods. In some aspects, the multiple PSFCH opportunities may include multiple PSFCH opportunities in the frequency domain. For example, the multiple PSFCH opportunities may be scheduled in multiple frequency sub-bands, frequency ranges, and / or frequency sub-channels. For example, referring to Figure 3 , UE 115a may send data transmissions on PSSCH 315 corresponding to multiple PSFCH opportunities 325, the multiple PSFCH opportunities including PSFCH opportunity 325a located in LBT subband 330a and in a first PSFCH symbol, PSFCH opportunity 325b located in LBT subband 330b and in a first PSFCH symbol, and PSFCH opportunity 325c located in LBT subband 330b and in a second PSFCH symbol. Thus, UE 115b may perform an LBT procedure on one or more PSFCH opportunities in PSFCH opportunities 325 to determine which PSFCH opportunities in the multiple PSFCH opportunities 325 are available (e.g., which PSFCH opportunities in the multiple PSFCH opportunities 325 pass LBT). In some aspects, the UE 115a may determine that one or more of multiple PSFCH opportunities 325 are available (e.g., via LBT) and may send ACK / NACK feedback in a PSFCH 320 associated with the PSSCH communication 315 on at least one of the available multiple PSFCH opportunities 325.

[0128] In some aspects, the first side link UE may receive an ACK / NACK from the second side link UE in the earliest PSFCH opportunity among multiple PSFCH opportunities in which the second side link UE successfully performs LBT. The first side link UE may receive an ACK / NACK in the earliest PSFCH opportunity to reduce the latency of receiving feedback from the second side link UE. In some aspects, if the first side link UE does not receive an ACK associated with a PSSCH communication from the second side link UE, the first side link UE may have multiple opportunities (e.g., up to two opportunities or more opportunities) to resend the PSSCH communication. Based on the unsuccessful LBT performed by the second side link UE, the first side link UE receiving a NACK from the second side link UE, and / or the ACK / NACK sent by the second side link UE not being correctly received and decoded by the first side link UE, the first side link UE may not receive an ACK associated with a PSSCH communication from the second side link UE. In some aspects, multiple PSFCH opportunities may increase the probability of the first side link UE receiving an ACK / NACK. For example, the first side link may receive ACK / NACK in the earliest PSFCH opportunity of the second side link UE through LBT and in the next (e.g., subsequent) PSFCH opportunity of the second side link UE through LBT. Additionally or alternatively, the first side link UE may receive ACK / NACK in multiple subbands (e.g., subchannels) of an unlicensed band through LBT. A subband may refer to or include a frequency bandwidth on which the second side link UE may perform an LBT procedure. For example, in an example in which the first side link UE and the second side link UE communicate through a 5 GHz unlicensed radio frequency spectrum band, the subband may refer to or include a 20 MHz frequency range or other suitable frequency range.

[0129] In some aspects, the first side link UE may receive ACK / NACK from the second side link UE in all PSFCH opportunities of multiple PSFCH opportunities in which the second side link UE performs a successful LBT. The first side link UE may monitor all P SFCH opportunities for ACK / NACK. The second side link UE may increase the probability of the first side link UE successfully receiving and decoding the ACK / NACK based on sending the ACK / NACK in all PSFCH opportunities through the LBT. In some aspects, the first side link UE may combine multiple ACK / NACK transmissions from the second side link UE to successfully decode the ACK / NACK.

[0130] In some aspects, the first side link UE may receive an ACK / NACK from the second side link UE in one or more of the PSFCH opportunities. The first side link UE may then send an ACK / NACK to a network element (e.g., BS 105, RU 240, DU 230, CU 210, and / or network element 700) in a HARQ process. In some aspects, the first side link UE may send an ACK / NACK to the network element after the last PSFCH opportunity in the plurality of PSFCH opportunities. In some aspects, the first side link UE may send an ACK / NACK to the network element after a time period (e.g., a processing time period) after the earliest PSFCH opportunity in the plurality of PSFCH opportunities.

[0131] In some aspects, a first sidelink UE may send a sidelink communication to a group of sidelink UEs including a second sidelink UE as a groupcast sidelink communication. In this case, a second sidelink UE in the group of sidelink UEs may be configured to send a NACK to the first sidelink UE only if the second sidelink UE does not successfully decode the sidelink communication, and to refrain from sending an ACK if the second sidelink UE successfully decodes the sidelink communication. In this manner, the first sidelink UE may know that the group of sidelink UEs has successfully decoded the sidelink communication. When the first sidelink UE does not receive a NACK from any sidelink UE in the groupcast, the first sidelink UE may send an ACK to the network element.

[0132] In some aspects, a first sidelink UE may send a configuration indicating parameters associated with multiple PSFCH opportunities to one or more sidelink UEs including a second sidelink UE. The first sidelink UE may receive the configuration from a network unit (e.g., BS105, RU 240, DU 230, CU 210, and / or network unit 700) and forward the configuration to the second sidelink UE. The configuration may indicate the number of PSFCH opportunities, time resources associated with multiple PSFCH opportunities, frequency resources associated with multiple PSFCH opportunities, and other suitable parameters associated with multiple PSFCH opportunities. In this regard, the first sidelink UE may send the configuration to the second sidelink UE via at least one of a radio resource control (RRC) message, a medium access control control element (MAC-CE), a sidelink control information (SCI), or other suitable communications. Additionally or alternatively, the first sidelink UE may receive the configuration from the network unit via at least one of a radio resource control (RRC) message, a downlink control information (DCI), a medium access control control element (MAC-CE), or other suitable communications.

[0133] In some aspects, the configuration may include a default configuration indicating parameters associated with the plurality of PSFCH opportunities. The default configuration may be adjusted (e.g., updated over time) based on parameters including, but not limited to, a LBT procedure success rate, an interference level associated with an unlicensed band, a buffer status report (BSR) associated with the first sidelink UE, a data type associated with the sidelink communication, a priority level associated with the sidelink communication, or other suitable parameters.

[0134] In some aspects, the first side link UE may send an indicator indicating a subset of the number of multiple PSFCH opportunities to the second side link UE. The first side link UE may receive the indicator from the network unit. The default configuration may include a default number of PSFCH opportunities and their associated time / frequency resources. The first side link UE may then send an indicator indicating a subset of PSFCH opportunities. The first side link UE may receive ACK / NACK from the second side link UE in a subset of PSFCH opportunities. The subset may be based on the above parameters. For example, the second side link UE may measure an LBT success rate. The LBT success rate may indicate the number of times the attempted LBT is successful within a certain period of time. The LBT success rate may reflect the level of interference / activity in the unlicensed band. The first side link UE may receive an LBT success rate indicator from the second side link UE. The first side link UE and / or the network unit may send a subset of PSFCH opportunities and their associated time / frequency resources to the second side link UE via at least one of an RRC message, a MAC-CE message, a DCI, an SCI, or other suitable communications.

[0135] In some aspects, a subset of PSFCH opportunities may be based on a data type associated with a sidelink communication (e.g., PSSCH). The data type associated with the PSSCH communication may include enhanced mobile broadband data, V2X data, massive machine type communication (mMTC) data, ultra-reliable low latency communication (IRLLC) data, and / or other types of data. The first sidelink UE may send the data type associated with the PSSCH communication to the network unit. The network unit may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the first sidelink UE via at least one of an RRC message, a MAC-CE message, a DCI, or other suitable communication based on the data type. The first sidelink UE may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the second sidelink UE via at least one of an RRC message, a MAC-CE message, an SCI, or other suitable communication.

[0136] In some aspects, a subset of PSFCH opportunities may be based on a priority level associated with PSSCH communications. The priority level associated with PSSCH communications may be based on latency requirements and / or reliability requirements associated with PSSCH communications. The first side link UE may send a priority level associated with PSSCH communications to the network unit. The network unit may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the first side link UE via at least one of an RRC message, a MAC-CE message, a DCI, or other suitable communications based on the priority level. The first side link UE may send a subset of PSFCH opportunities and an indicator of their associated time / frequency resources to the second side link UE via at least one of an RRC message, a MAC-CE message, a SCI, or other suitable communications.

[0137] In some aspects, the second side link UE may receive and decode PSSCH communications from the first side link UE in the first time slot. The second side link UE may perform an unsuccessful LBT at the next PSFCH opportunity after decoding the PSSCH communication, thereby preventing the second side link UE from sending an ACK to the first side link UE. In response to not receiving an ACK from the second side link UE, the first side link UE may resend the PSSCH communication to the second side link UE. The second side link UE may identify the PSSCH communication as a retransmission and suppress decoding of the retransmitted PSSCH communication, thereby reducing power consumption and computing resources. The second side link UE may perform LBT at the next PSFCH opportunity after the retransmission of the PSSCH communication. If the LBT is successful at the next PSFCH opportunity, the second side link UE may send an ACK to the first side link UE. If the first side link UE successfully decodes the ACK, the first side link UE may suppress retransmitting the P SCH again. If the first side link does not successfully decode the ACK, the first side link UE may retransmit the PSSCH communication again.

[0138] Other aspects of the present disclosure include the following:

[0139] Aspect 1 includes a method of wireless communication performed by a first sidelink user equipment (IE), the method comprising: performing a listen-before-talk (LBT) procedure in an unlicensed band; and based on the success of the LBT procedure, sending an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication to a second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0140] Aspect 2 includes the method according to aspect 1, wherein the multiple PSFCH opportunities include multiple PSFCH opportunities in the time domain.

[0141] Aspect 3 includes a method according to any one of aspects 1 to 2, wherein the multiple PSFCH opportunities include multiple PSFCH opportunities in the frequency domain.

[0142] Aspect 4 includes the method according to any one of aspects 1 to 3, wherein sending the ACK / NACK includes sending the ACK / NACK in an earliest PSFCH opportunity among the multiple PSFCH opportunities.

[0143] Aspect 5 includes the method according to any one of aspects 1 to 4, further comprising resending the ACK / NACK in a next PSFCH opportunity after the earliest PSFCH opportunity.

[0144] Aspect 6 includes the method of any one of aspects 1 to 5, wherein sending the ACK / NACK includes sending the ACK / NACK in a plurality of subbands of the unlicensed frequency band.

[0145] Aspect 7 includes the method according to any one of aspects 1 to 6, wherein sending the ACK / NACK includes sending the ACK / NACK in all PSFCH opportunities of the plurality of PSFCH opportunities.

[0146] Aspect 8 includes a method according to any one of Aspects 1 to 7, the method also including receiving a configuration indicating at least one of the following: the number of the multiple PSFCH opportunities; the time resources associated with the multiple PSFCH opportunities; or the frequency resources associated with the multiple PSFCH opportunities.

[0147] Aspect 9 includes a method according to any one of aspects 1 to 8, the method also comprising receiving an indicator indicating a subset of the multiple PSFCH opportunities, wherein sending the ACK / NACK includes sending the ACK / NACK in the subset of the multiple PSFCH opportunities.

[0148] Aspect 10 includes a method according to any one of Aspects 1 to 9, the method also comprising sending an indicator indicating a success rate of an LBT procedure, wherein the indicator indicating the subset of the multiple PSFCH opportunities is based on the LBT procedure success rate.

[0149] Aspect 11 includes a method according to any one of Aspects 1 to 10, the method also comprising sending an indicator indicating at least one of a data type associated with the sidelink communication or a priority level associated with the sidelink communication, wherein the indicator indicating the subset of the multiple PSFCH opportunities is based on at least one of the data type or the priority level.

[0150] Aspect 12 includes a method according to any one of Aspects 1 to 11, wherein receiving the indicator indicating the subset of the multiple PSFCH opportunities includes receiving the indicator via at least one of a radio resource control (RRC) message, downlink control information (DCI), a medium access control control element (MAC-CE), or sidelink control information (SCI).

[0151] Aspect 13 includes a method according to any one of aspects 1 to 12, wherein receiving the indicator indicating the subset of the plurality of PSFCH opportunities comprises receiving the indicator from at least one of a network element or the second sidelink UE.

[0152] Aspect 14 includes a method according to any one of Aspects 1 to 13, the method further comprising: receiving the side link communication from the second side link UE in a first time slot; and suppressing decoding of retransmission of the side link communication in a second time slot, wherein the second time slot is after the first time slot; and sending the ACK / NACK includes sending ACK after the second time slot.

[0153] Aspect 15 includes a method of wireless communication performed by a first sidelink user equipment (IE), the method comprising: sending sidelink communications to one or more sidelink UEs in an unlicensed band; and monitoring an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

[0154] Aspect 16 includes a method according to Aspect 15, the method further comprising: receiving an ACK / NACK from a second side link UE based on the monitoring, wherein the one or more side link UEs include the second side link UE; and sending the ACK / NACK to a network unit after the last PSFCH of the multiple PSFCH opportunities.

[0155] Aspect 17 includes a method according to any one of Aspects 15 to 16, the method further comprising: receiving an ACK / NACK from a second side link UE based on the monitoring, wherein the one or more side link UEs include the second side link UE; and sending the ACK / NACK to a network unit after a time period after the earliest PSFCH of the multiple PSFCH opportunities.

[0156] Aspect 18 includes the method of any one of aspects 15 to 17, further comprising sending an ACK to a network element based on not receiving a NACK from the one or more sidelink UEs during the monitoring.

[0157] Aspect 19 includes a method according to any one of Aspects 15 to 18, the method also comprising receiving a configuration from a network unit indicating at least one of: the number of the multiple PSFCH opportunities; the time resources associated with the multiple PSFCH opportunities; or the frequency resources associated with the multiple PSFCH opportunities.

[0158] Aspect 20 includes a method according to any one of aspects 15 to 19, the method also comprising receiving an indicator indicating a subset of the multiple PSFCH opportunities from the network element, wherein monitoring the ACK / NACK includes monitoring the ACK / NACK in the subset of the multiple PSFCH opportunities.

[0159] Aspect 21 includes a method according to any one of Aspects 15 to 20, the method also comprising sending an indicator indicating at least one of a buffer status report (BSR) or a LBT procedure success rate to the network unit, wherein the subset of the multiple PSFCH opportunities is based on at least one of the BSR or the LBT procedure success rate.

[0160] Aspect 22 includes a method according to any one of Aspects 15 to 21, the method also comprising sending an indicator to the network unit indicating a data type associated with the sidelink communication or at least one of a priority level associated with the sidelink communication, wherein the subset of the multiple PSFCH opportunities is based on at least one of the data type or the priority level.

[0161] Aspect 23 includes a method according to any one of aspects 15 to 22, wherein receiving the indicator includes receiving the indicator via at least one of a radio resource control (RRC) message, a medium access control control element (MAC-CE), or downlink control information (DCI).

[0162] Aspect 24 includes a method according to any one of Aspects 16 to 23, the method also comprising sending the indicator indicating the subset of the multiple PSFCH opportunities to the one or more sidelink UEs via at least one of an RRC message, a MAC-CE, or sidelink control information (SCI).

[0163] Aspect 25 includes a method according to any one of Aspects 16 to 24, wherein sending the sidelink communication to the one or more sidelink UEs includes sending sidelink multicast communication to multiple sidelink UEs among the one or more sidelink UEs; and monitoring the ACK / NACK includes monitoring the ACK / NACK in all PSFCH opportunities.

[0164] Aspect 26 includes a non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions including one or more instructions that, when executed by one or more processors of a UE, cause the UE to perform any of aspects 1 to 14.

[0165] Aspect 27 includes a non-transitory computer-readable medium storing one or more instructions for wireless communication, the one or more instructions including one or more instructions that, when executed by one or more processors of a network element, cause the network element to perform any of Aspects 15 to 25.

[0166] Aspect 28 includes a user equipment (IE) comprising one or more components for performing any one or more of aspects 1-14.

[0167] Aspect 29 includes a network element comprising one or more components for performing any one or more of aspects 15-25.

[0168] Aspect 30 includes a user equipment (IE), the user equipment (UE) comprising: a memory; a transceiver; and at least one processor, the at least one processor coupled to the memory and the transceiver, wherein the UE is configured to perform any one or more of aspects 1 to 14.

[0169] Aspect 31 includes a network unit comprising: a memory; a transceiver; and at least one processor coupled to the memory and the transceiver, wherein the network unit is configured to perform any one or more of aspects 15 to 25.

[0170] Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be mentioned throughout the above description may be represented by voltage, current, electromagnetic waves, magnetic fields or magnetic particles, optical fields or optical particles, or any combination thereof.

[0171] The various illustrative blocks and modules described in conjunction with the disclosure herein may be implemented or executed using a general purpose processor, DSP, ASIC, FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration).

[0172] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored as one or more instructions or codes on a computer-readable medium, or sent via a computer-readable medium. Other examples and specific implementations are within the scope of the present disclosure and the appended claims. For example, due to the nature of software, the functions described above may be implemented using software, hardware, firmware, hard wiring, or any combination thereof executed by a processor. The features that implement the functions may also be physically located at different locations, including being distributed so that the various parts of the functions are implemented at different physical locations. In addition, as used herein (including in the claims), as used in an item enumeration (e.g., followed by an item enumeration such as "at least one of" or "one or more of"), "or" indicates an inclusive enumeration, such that, for example, an enumeration of [at least one of A, B, or C] means: A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

[0173] As those skilled in the art will understand by now and depending on the specific application at hand, many modifications, substitutions and changes may be made to the materials, devices, configurations and methods of use of the apparatus of the present disclosure without departing from the spirit and scope of the present disclosure. In view of this, the scope of the present disclosure should not be limited to the scope of the specific examples illustrated and described herein (because they are only some examples thereof), but should be fully equivalent to the claims attached hereto and their functional equivalents.

Claims

1. A method of wireless communication performed by a first sidelink user equipment (IE), the method comprising: Implementing Listen Before Talk (LBT) procedures in unlicensed bands; as well as Based on the LBT procedure being successful, an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication is sent to a second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

2. The method of claim 1, wherein the plurality of PSFCH opportunities comprises a plurality of PSFCH opportunities in at least one of a time domain or a frequency domain.

3. The method of claim 1, wherein sending the ACK / NACK comprises sending the ACK / NACK in an earliest PSFCH opportunity among the multiple PSFCH opportunities, and the method further comprises resending the ACK / NACK in a next PSFCH opportunity after the earliest PSFCH opportunity.

4. The method according to claim 1, further comprising: Receiving a configuration indicating at least one of the following: the number of the plurality of PSFCH opportunities; time resources associated with the plurality of PSFCH opportunities; or Frequency resources associated with the plurality of PSFCH opportunities.

5. The method according to claim 4, further comprising: An indicator is received that indicates a subset of the plurality of PSFCH opportunities, wherein sending the ACK / NACK comprises sending the ACK / NACK in the subset of the plurality of PSFCH opportunities.

6. The method according to claim 5, further comprising: An indicator is sent indicating a success rate of an LBT procedure, wherein the indicator indicating the subset of the plurality of PSFCH opportunities is based on the LBT procedure success rate.

7. The method according to claim 5, further comprising: An indicator is sent that indicates at least one of a data type associated with the sidelink communication or a priority level associated with the sidelink communication, wherein the indicator that indicates the subset of the plurality of PSFCH opportunities is based on at least one of the data type or the priority level.

8. A method of wireless communication performed by a first sidelink user equipment (IE), the method comprising: transmitting sidelink communications to one or more sidelink UEs in an unlicensed frequency band; as well as An acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication is monitored in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

9. The method according to claim 8, further comprising: receiving an ACK / NACK from a second sidelink UE based on the monitoring, wherein the one or more sidelink UEs include the second sidelink UE; as well as The ACK / NACK is sent to a network element after a last PSFCH opportunity of the plurality of PSFCH opportunities.

10. The method according to claim 8, further comprising: receiving an ACK / NACK from a second sidelink UE based on the monitoring, wherein the one or more sidelink UEs include the second sidelink UE; as well as The ACK / NACK is sent to the network element after a time period after an earliest PSFCH opportunity among the plurality of PSFCH opportunities.

11. The method according to claim 8, further comprising: An ACK is sent to a network element based on not receiving a NACK from the one or more sidelink UEs during the monitoring period.

12. The method according to claim 8, further comprising: Receiving, from a network element, a configuration indicating at least one of: the number of the plurality of PSFCH opportunities; time resources associated with the plurality of PSFCH opportunities; or Frequency resources associated with the plurality of PSFCH opportunities.

13. The method according to claim 12, further comprising: An indicator is received from the network element indicating a subset of the plurality of PSFCH opportunities, wherein monitoring the ACK / NACK comprises monitoring the ACK / NACK in the subset of the plurality of PSFCH opportunities.

14. The method according to claim 13, further comprising: An indicator indicating at least one of a buffer status report (BSR) or a LBT procedure success rate is sent to the network element, wherein the subset of the multiple PSFCH opportunities is based on at least one of the BSR or the LBT procedure success rate.

15. The method according to claim 13, further comprising: An indicator is sent to the network element indicating at least one of a data type associated with the sidelink communication or a priority level associated with the sidelink communication, wherein the subset of the plurality of PSFCH opportunities is based on at least one of the data type or the priority level.

16. A first sidelink user equipment (UE), the first sidelink user equipment (UE) comprising: Memory; Transceiver v and at least one processor coupled to the memory and the transceiver, wherein the first sidelink UE is configured to: Implementing Listen Before Talk (LBT) procedures in unlicensed bands; as well as Based on the LBT procedure being successful, an acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication is sent to the second sidelink UE in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

17. The first sidelink UE of claim 16, wherein the plurality of PSFCH opportunities comprises a plurality of PSFCH opportunities in at least one of a time domain or a frequency domain.

18. The first sidelink UE according to claim 16, wherein the first sidelink UE is further configured to: sending the ACK / NACK in an earliest PSFCH opportunity among the plurality of PSFCH opportunities; and The ACK / NACK is resent in a next PSFCH opportunity after the earliest PSFCH opportunity.

19. The first sidelink UE according to claim 16, wherein the first sidelink UE is further configured to: Receiving a configuration indicating at least one of the following: the number of the plurality of PSFCH opportunities; time resources associated with the plurality of PSFCH opportunities; or Frequency resources associated with the plurality of PSFCH opportunities.

20. The first sidelink UE of claim 19, wherein the first sidelink UE is further configured to: An indicator is received that indicates a subset of the plurality of PSFCH opportunities, wherein sending the ACK / NACK comprises sending the ACK / NACK in the subset of the plurality of PSFCH opportunities.

21. The first sidelink UE according to claim 20, wherein the first sidelink UE is further configured to: An indicator is sent indicating a success rate of an LBT procedure, wherein the indicator indicating the subset of the plurality of PSFCH opportunities is based on the LBT procedure success rate.

22. The first sidelink UE of claim 20, wherein the first sidelink UE is further configured to: An indicator is sent that indicates at least one of a data type associated with the sidelink communication or a priority level associated with the sidelink communication, wherein the indicator that indicates the subset of the plurality of PSFCH opportunities is based on at least one of the data type or the priority level.

23. A first sidelink user equipment (UE), the first sidelink user equipment (UE) comprising: Memory; Transceiver; as well as at least one processor coupled to the memory and the transceiver, wherein the first sidelink UE is configured to: transmitting sidelink communications to one or more sidelink UEs in an unlicensed band; and An acknowledgement / negative acknowledgement (ACK / NACK) associated with the sidelink communication is monitored in at least one of a plurality of physical sidelink feedback channel (PSFCH) opportunities.

24. The first sidelink UE of claim 23, wherein the first sidelink UE is further configured to: receiving an ACK / NACK from a second sidelink UE based on the monitoring, wherein the one or more sidelink UEs include the second sidelink UE; and The ACK / NACK is sent to a network element after a last PSFCH opportunity of the plurality of PSFCH opportunities.

25. The first sidelink UE of claim 23, wherein the first sidelink UE is further configured to: receiving an ACK / NACK from a second sidelink UE based on the monitoring, wherein the one or more sidelink UEs include the second sidelink UE; and The ACK / NACK is sent to the network element after a time period after an earliest PSFCH opportunity among the plurality of PSFCH opportunities.

26. The first sidelink UE of claim 23, wherein the first sidelink UE is further configured to: An ACK is sent to a network element based on not receiving a NACK from the one or more sidelink UEs during the monitoring period.

27. The first sidelink UE of claim 23, wherein the first sidelink UE is further configured to: Receiving, from a network element, a configuration indicating at least one of: the number of the plurality of PSFCH opportunities; time resources associated with the plurality of PSFCH opportunities; or Frequency resources associated with the plurality of PSFCH opportunities.

28. The first sidelink UE of claim 27, wherein the first sidelink UE is further configured to: An indicator is received from the network element indicating a subset of the plurality of PSFCH opportunities, wherein monitoring the ACK / NACK comprises monitoring the ACK / NACK in the subset of the plurality of PSFCH opportunities.

29. The first sidelink UE of claim 28, wherein the first sidelink UE is further configured to: An indicator indicating at least one of a buffer status report (BSR) or a LBT procedure success rate is sent to the network element, wherein the subset of the multiple PSFCH opportunities is based on at least one of the BSR or the LBT procedure success rate.

30. The first sidelink UE of claim 28, wherein the first sidelink UE is further configured to: An indicator is sent to the network element indicating at least one of a data type associated with the sidelink communication or a priority level associated with the sidelink communication, wherein the subset of the plurality of PSFCH opportunities is based on at least one of the data type or the priority level.

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