Patent Publication Number: US-2023146161-A1

Title: Cyclic prefix (cp) extension in channel occupancy time (cot) sharing for sidelink communication

Description:
TECHNICAL FIELD 
     This application relates to wireless communication systems, and more particularly to cyclic prefix (CP) extensions in channel occupancy time (COT) sharing among sidelink user equipment devices (UEs). 
     INTRODUCTION 
     Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). A wireless multiple-access communications system may include a number of base stations (BSs), each simultaneously supporting communications for multiple communication devices, which may be otherwise known as user equipment (UE). 
     To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the long term evolution (LTE) technology to a next generation new radio (NR) technology, which may be referred to as 5 th  Generation (5G). For example, NR is designed to provide a lower latency, a higher bandwidth or a higher throughput, and a higher reliability than LTE. NR is designed to operate over a wide array of spectrum bands, for example, from low-frequency bands below about 1 gigahertz (GHz) and mid-frequency bands from about 1 GHz to about 6 GHz, to high-frequency bands such as millimeter wave (mmWave) bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed and shared spectrum. Spectrum sharing enables operators to opportunistically aggregate spectrums to dynamically support high-bandwidth services. Spectrum sharing can extend the benefit of NR technologies to operating entities that may not have access to a licensed spectrum. 
     In a wireless communication network, a BS may communicate with a UE in an uplink direction and a downlink direction. Sidelink was introduced in LTE to allow a UE to send data to another UE without tunneling through the BS and/or an associated core network. The LTE sidelink technology had been extended to provision for device-to-device (D2D) communications, vehicle-to-everything (V2X) communications, and/or cellular vehicle-to-everything (C-V2X) communications. Similarly, NR may be extended to support sidelink communications, D2D communications, V2X communications, and/or C-V2X over licensed bands and/or unlicensed bands. 
     BRIEF SUMMARY OF SOME EXAMPLES 
     The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later. 
     For example, in an aspect of the disclosure, a method of wireless communication performed by a first sidelink user equipment (UE), includes: detecting a first sidelink transmission in a channel occupancy time (COT), the COT for sharing with multiple sidelink UEs including the first sidelink UE; determining a cyclic prefix (CP) extension length for transmitting a second sidelink transmission after the first sidelink transmission, a gap duration between the first sidelink transmission and the second sidelink transmission satisfying a listen-before-talk (LBT) gap time threshold; applying a CP extension having the CP extension length to the second sidelink transmission; and transmitting, to a second sidelink UE, the second sidelink transmission with the CP extension. 
     In an additional aspect of the disclosure, a first user equipment (UE) includes a processor configured to: detect a first sidelink transmission in a channel occupancy time (COT), the COT for sharing with multiple sidelink UEs including the first sidelink UE; determine a cyclic prefix (CP) extension length for transmitting a second sidelink transmission after the first sidelink transmission, a gap duration between the first sidelink transmission and the second sidelink transmission satisfying a listen-before-talk (LBT) gap time threshold; and apply a CP extension having the CP extension length to the second sidelink transmission; and a transceiver configured to transmit, to a second sidelink UE, the second sidelink transmission with the CP extension. 
     In an additional aspect of the disclosure, a non-transitory computer-readable medium having program code recorded thereon, the program code including code for causing a first sidelink user equipment (UE) to detect a first sidelink transmission in a channel occupancy time (COT), the COT for sharing with multiple sidelink UEs including the first sidelink UE; code for causing the first sidelink UE to determine a cyclic prefix (CP) extension length for transmitting a second sidelink transmission after the first sidelink transmission, wherein a gap duration between the first sidelink transmission and the second sidelink transmission satisfies a listen-before-talk (LBT) gap time threshold; code for causing the first sidelink UE to apply a CP extension having the CP extension length to the second sidelink transmission; and code for causing the first sidelink UE to transmit, to a second sidelink UE, the second sidelink transmission with the CP extension. 
     In an additional aspect of the disclosure, a first user equipment (UE) includes means for detecting a first sidelink transmission in a channel occupancy time (COT), the COT for sharing with multiple sidelink UEs; means for determining a cyclic prefix (CP) extension length for transmitting a second sidelink transmission after the first sidelink transmission, a gap duration between the first sidelink transmission and the second sidelink transmission satisfying a listen-before-talk (LBT) gap time threshold; means for applying a CP extension having the CP extension length to the second sidelink transmission; and means for transmitting, to a second sidelink UE, the second sidelink transmission with the CP extension. 
     Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a wireless communication network according to one or more aspects of the present disclosure. 
         FIG.  2    illustrates a sidelink communication scheme that uses time division multiplex (TDM) COT sharing according to one or more aspects of the present disclosure. 
         FIG.  3    illustrates a sidelink communication scheme that uses frequency division multiplex (FDM) COT sharing according to one or more aspects of the present disclosure. 
         FIG.  4    is a block diagram of an example user equipment (UE) according to some aspects of the present disclosure. 
         FIG.  5    is a block diagram of an example base station (BS) according to one or more aspects of the present disclosure. 
         FIG.  6    illustrates a TDM sidelink channel occupancy time (COT) sharing scheme with active transmission according to one or more aspects of the present disclosure. 
         FIG.  7    illustrates an TDM sidelink COT sharing scheme with out-of-time span of initiating UE according to one or more aspects of the present disclosure. 
         FIG.  8    illustrates a TDM sidelink COT sharing scheme with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. 
         FIG.  9    illustrates a TDM sidelink COT sharing scheme with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. 
         FIG.  10    illustrates a TDM sidelink COT sharing scheme with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. 
         FIG.  11    illustrates a TDM sidelink COT sharing scheme with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. 
         FIG.  12    illustrates an FDM sidelink COT sharing scheme with a cyclic prefix (CP) extension according to one or more aspects of the present disclosure. 
         FIG.  13    illustrates a flow diagram of a communication method for transmitting a sidelink communication associated with a CP extension during a shared COT in accordance with one or more aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below, in connection with the appended 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. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
     This disclosure relates generally to wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may 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, Global System for Mobile Communications (GSM) networks, 5 th  Generation (5G) or new radio (NR) networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably. 
     An OFDMA network may implement a 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 and the like. UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS). In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from 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 various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project which was aimed at improving the UMTS mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. The present disclosure is concerned with the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces. 
     In particular, 5G networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of the new radio technology for 5G NR networks. The 5G NR will be capable of scaling to provide coverage (1) to a massive Internet of things (IoTs) with a ULtra-high density (e.g., ˜1 M nodes/km 2 ), ultra-low complexity (e.g., ˜10 s of bits/sec), ultra-low energy (e.g., ˜10+ years of battery life), and deep coverage with the capability to reach challenging locations; (2) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ˜99.9999% reliability), ultra-low latency (e.g., ˜1 ms), and users with wide ranges of mobility or lack thereof; and (3) with enhanced mobile broadband including extreme high capacity (e.g., ˜10 Tbps/km 2 ), extreme data rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates), and deep awareness with advanced discovery and optimizations. 
     The 5G NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI); having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD)/frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO), robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in 5G NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than 3 GHz FDD/TDD implementations, subcarrier spacing may occur with 15 kHz, for example over 5, 10, 20 MHz, and the like bandwidth (BW). For other various outdoor and small cell coverage deployments of TDD greater than 3 GHz, subcarrier spacing may occur with 30 kHz over 80/100 MHz BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the 5 GHz band, the subcarrier spacing may occur with 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting with mmWave components at a TDD of 28 GHz, subcarrier spacing may occur with 120 kHz over a 500 MHz BW. 
     The scalable numerology of the 5G NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. For example, shorter TTI may be used for low latency and high reliability, while longer TTI may be used for higher spectral efficiency. The efficient multiplexing of long and short TTIs to allow transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with UL/downlink scheduling information, data, and acknowledgement in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, adaptive UL/downlink that may be flexibly configured on a per-cell basis to dynamically switch between UL and downlink to meet the current traffic needs. 
     Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim. 
     NR technologies had been extended to operate over an unlicensed spectrum. The deployment of NR technologies over an unlicensed spectrum is referred to as NR-U. NR-U is targeted for operations over the 5 gigahertz (GHz) and 6 GHz bands, where there are well-defined channel access rules for sharing among operators of the same radio access technology (RAT) and/or of different RATs. When a BS operates over an unlicensed spectrum, the BS does not have ownership of the spectrum or control over the spectrum. Thus, the BS is required to contend for channel access in the spectrum, for example, via clear channel assessment (CCA) and/or listen-before-talk (LBT) procedures. 
     The provisioning of sidelink services, such as device-to-device (D2D), vehicle-to-vehicle (V2V), vehicle-to-everything (V2X), and/or cellular vehicle-to-everything (C-V2X) communications, over dedicated spectrum or licensed spectrum are relatively straight-forward as channel access in the dedicated spectrum or licensed spectrum is guaranteed. NR-U can bring benefit for sidelink services, for example, by offloading sidelink traffic to the unlicensed spectrum at no cost. However, channel access in a shared spectrum or an unlicensed spectrum is not guaranteed. Thus, to provision for sidelink services over a shared spectrum or unlicensed spectrum, sidelink user equipment devices (UEs) are required to contend for channel access in the spectrum, for example, via CCA and/or LBT procedures. 
     The present application describes mechanisms for sharing sidelink channel occupancy time (COT) for sidelink communications in a shared radio frequency band among sidelink UEs. For example, a first UE may contend for a COT in the shared radio frequency band for sidelink communication by performing a listen-before-talk (LBT) (e.g., a category 4 (CAT4) LBT) in the shared radio frequency band to acquire to a COT in the shared radio frequency band. After acquiring the COT, the first UE may transmit a sidelink data via a physical sidelink shared channel (PSSCH), a physical sidelink control channel (PSCCH), and/or a physical sidelink feedback channel (PSFCH) to another sidelink UE. The UE that acquires the COT may be referred to as an initiating UE and may transmit sidelink control information (SCI) indicating COT sharing information (e.g., a length of the initiating UE&#39;s transmission, a length of the remaining COT, whether the transmission supports frequency interlacing, and the like). A UE that monitors for the SCI may be referred to as a monitoring UE. Additionally, a UE that does not acquire the COT, but shares the COT acquired by another UE, may be referred to as a responding UE. 
     Certain frequency bands may have certain channel occupancy requirements. A channel occupancy may be defined by continuous transmissions in the channel. In slot-based transmissions, the initiating UE may continue to communicate during and share a COT as long as the initiating UE continues to occupy the channel. Because the initiating UE has already acquired the COT, the responding UE may perform a shorter LBT (e.g., CAT2 LBT or a CAT1 LBT) than the CAT4 LBT performed by the initiating UE to share the COT. Due to channel occupancy requirements, a UE may agree to surrender the channel if the UE has not occupied the channel for an LBT gap time threshold. Accordingly, if a slot structure has a gap duration that is longer than the LBT gap time threshold, the initiating UE will surrender the channel. In this example, the initiating UE may transmit once and then surrender the channel before a monitoring UE may take advantage of sharing the COT of the initiating UE. Instead of performing a CAT2 LBT or a CAT1 LBT to acquire the COT, the monitoring UE performs a CAT4 LBT to do so. Accordingly, if the gap duration exceeds an LBT gap time threshold (e.g., about 16 μs), the monitoring UE may be unable to take advantage of performing a shorter LBT to share the COT. 
     The present disclosure provides techniques for controlling one or more gap durations in a slot-based transmission. One way to create a transmission gap with a tight duration is to apply a CP extension to a transmission. In some examples, to control the gap duration for COT sharing, the responding UE may use a CP extension to create a gap duration between the initiating UE&#39;s transmission and the responding UE&#39;s transmission, where the gap duration satisfies an LBT gap time threshold (e.g., about 16 μs to about 25 μs). The responding UE may determine a CP extension length for transmitting a sidelink transmission after the initiating UE&#39;s sidelink transmission, where the gap duration between the responding UE&#39;s sidelink transmission and the initiating UE&#39;s sidelink transmission satisfies an LBT gap time threshold (e.g., about 16 μs or about 25 μs). Mechanisms for sidelink COT sharing using a CP extension are described in greater detail herein. 
     Aspects of the present disclosure can provide several benefits. For example, applying the CP extension having the CP extension length to the responding UE&#39;s sidelink transmission may enable the responding UE to take advantage of performing a shorter LBT (e.g., performing an CAT2 LBT or a CAT1 LBT instead of a CAT4 LBT). Thus, the disclosed examples can consume less time and fewer resources. 
       FIG.  1    illustrates a wireless communication network  100  according to one or more aspects of the present disclosure. The network  100  may be a 5G network. The network  100  includes a number of base stations (BSs)  105  (individually labeled as  105   a,    105   b,    105   c,    105   d,    105   e,  and  105   f ) and other network entities. A BS  105  may be a station that communicates with UEs  115  and may also be referred to as an evolved node B (eNB), a next generation eNB (gNB), an access point, and the like. Each BS  105  may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS  105  and/or a BS subsystem serving the coverage area, depending on the context in which the term is used. 
     A BS  105  may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a pico cell, would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a femto cell, would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). 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 the example shown in  FIG.  1   , the BSs  105   d  and  105   e  may be regular macro BSs, while the BSs  105   a - 105   c  may be macro BSs enabled with one of three dimension (3D), full dimension (FD), or massive MIMO. The BSs  105   a - 105   c  may take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS  105   f  may be a small cell BS which may be a home node or portable access point. A BS  105  may support one or multiple (e.g., two, three, four, and the like) cells. 
     The network  100  may support synchronous 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. 
     The UEs  115  are dispersed throughout the wireless network  100 , and each UE  115  may be stationary or mobile. A UE  115  may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A 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, or the like. In one aspect, a UE  115  may be a device that includes a Universal Integrated Circuit Card (UICC). In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs  115  that do not include UICCs may also be referred to as IoT devices or internet of everything (IoE) devices. The UEs  115   a - 115   d  are examples of mobile smart phone-type devices accessing network  100 . A UE  115  may also be a machine specifically configured for connected communication, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. The UEs  115   e - 115   h  are examples of various machines configured for communication that access the network  100 . The UEs  115   i - 115   k  are examples of vehicles equipped with wireless communication devices configured for communication that access the network  100 . A UE  115  may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In  FIG.  1   , a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE  115  and a serving BS  105 , which is a BS designated to serve the UE  115  on the downlink (DL) and/or uplink (UL), desired transmission between BSs  105 , backhaul transmissions between BSs, or sidelink transmissions between UEs  115 . 
     In operation, the BSs  105   a - 105   c  may serve the UEs  115   a  and  115   b  using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS  105   d  may perform backhaul communications with the BSs  105   a - 105   c,  as well as small cell, the BS  105   f.  The macro BS  105   d  may also transmits multicast services which are subscribed to and received by the UEs  115   c  and  115   d.  Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts. 
     The BSs  105  may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs  105  (e.g., which may be an example of a gNB or an access node controller (ANC)) may interface with the core network through backhaul links (e.g., NG-C, NG-U, etc.) and may perform radio configuration and scheduling for communication with the UEs  115 . In various examples, the BSs  105  may communicate, either directly or indirectly (e.g., through core network), with each other over backhaul links (e.g., X1, X2, etc.), which may be wired or wireless communication links. 
     The network  100  may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE  115   e,  which may be a drone. Redundant communication links with the UE  115   e  may include links from the macro BSs  105   d  and  105   e,  as well as links from the small cell BS  105   f.  Other machine type devices, such as the UE  115   f  (e.g., a thermometer), the UE  115   g  (e.g., smart meter), and UE  115   h  (e.g., wearable device) may communicate through the network  100  either directly with BSs, such as the small cell BS  105   f,  and the macro BS  105   e,  or in multi-step-size configurations by communicating with another user device which relays its information to the network, such as the UE  115   f  communicating temperature measurement information to the smart meter, the UE  115   g,  which is then reported to the network through the small cell BS  105   f.  The network  100  may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as V2V, V2X, C-V2X communications between a UE  115   i,    115   j,  or  115   k  and other UEs  115 , and/or vehicle-to-infrastructure (V2I) communications between a UE  115   i,    115   j,  or  115   k  and a BS  105 . 
     In some implementations, the network  100  utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. 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 be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable. 
     In some aspects, the BSs  105  can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB)) for downlink (DL) and uplink (UL) transmissions in the network  100 . DL refers to the transmission direction from a BS  105  to a UE  115 , whereas UL refers to the transmission direction from a UE  115  to a BS  105 . The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes or slots, for example, about 10. Each slot may be further divided into mini-slots. In a FDD mode, simultaneous UL and DL transmissions 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 a TDD mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions. 
     The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs  105  and the UEs  115 . For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS  105  may transmit cell specific reference signals (CRSs) and/or channel state information—reference signals (CSI-RSs) to enable a UE  115  to estimate a DL channel. Similarly, a UE  115  may transmit sounding reference signals (SRSs) to enable a BS  105  to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some aspects, the BSs  105  and the UEs  115  may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for DL communication. 
     In some aspects, the network  100  may be an NR network deployed over a licensed spectrum. The BSs  105  can transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)) in the network  100  to facilitate synchronization. The BSs  105  can broadcast system information associated with the network  100  (e.g., including a master information block (MIB), remaining system information (RMSI), and other system information (OSI)) to facilitate initial network access. In some instances, the BSs  105  may broadcast the PSS, the SSS, and/or the MIB in the form of synchronization signal block (SSBs) over a physical broadcast channel (PBCH) and may broadcast the RMSI and/or the OSI over a physical downlink shared channel (PDSCH). 
     In some aspects, a UE  115  attempting to access the network  100  may perform an initial cell search by detecting a PSS from a BS  105 . The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE  115  may then receive a SSS. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier. 
     After receiving the PSS and SSS, the UE  115  may receive a 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 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 set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical UL control channel (PUCCH), physical UL shared channel (PUSCH), power control, and SRS. 
     After obtaining the MIB, the RMSI and/or the OSI, the UE  115  can perform a random access procedure to establish a connection with the BS  105 . In some examples, the random access procedure may be a four-step random access procedure. For example, the UE  115  may transmit a random access preamble and the BS  105  may respond with a random access response. The random access response (RAR) may include a detected random access preamble identifier (ID) corresponding to the random access preamble, timing advance (TA) information, a UL grant, a temporary cell-radio network temporary identifier (C-RNTI), and/or a backoff indicator. Upon receiving the random access response, the UE  115  may transmit a connection request to the BS  105  and the BS  105  may respond with a connection response. The connection response may indicate a contention resolution. In some examples, the random access preamble, the RAR, the connection request, and the connection response can be referred to as message 1 (MSG1), message 2 (MSG2), message 3 (MSG3), and message 4 (MSG4), respectively. In some examples, the random access procedure may be a two-step random access procedure, where the UE  115  may transmit a random access preamble and a connection request in a single transmission and the BS  105  may respond by transmitting a random access response and a connection response in a single transmission. 
     After establishing a connection, the UE  115  and the BS  105  can enter a normal operation stage, where operational data may be exchanged. For example, the BS  105  may schedule the UE  115  for UL and/or DL communications. The BS  105  may transmit UL and/or DL scheduling grants to the UE  115  via a PDCCH. The scheduling grants may be transmitted in the form of DL control information (DCI). The BS  105  may transmit a DL communication signal (e.g., carrying data) to the UE  115  via a PDSCH according to a DL scheduling grant. The UE  115  may transmit a UL communication signal to the BS  105  via a PUSCH and/or PUCCH according to a UL scheduling grant. 
     In some aspects, the BS  105  may communicate with a UE  115  using HARQ techniques to improve communication reliability, for example, to provide a URLLC service. The BS  105  may schedule a UE  115  for a PDSCH communication by transmitting a DL grant in a PDCCH. The BS  105  may transmit a DL data packet to the UE  115  according to the schedule in the PDSCH. The DL data packet may be transmitted in the form of a transport block (TB). If the UE  115  receives the DL data packet successfully, the UE  115  may transmit a HARQ ACK to the BS  105 . Conversely, if the UE  115  fails to receive the DL transmission successfully, the UE  115  may transmit a HARQ NACK to the BS  105 . Upon receiving a HARQ NACK from the UE  115 , the BS  105  may retransmit the DL data packet to the UE  115 . The retransmission may include the same coded version of DL data as the initial transmission. Alternatively, the retransmission may include a different coded version of the DL data than the initial transmission. The UE  115  may apply soft-combining to combine the encoded data received from the initial transmission and the retransmission for decoding. The BS  105  and the UE  115  may also apply HARQ for UL communications using substantially similar mechanisms as the DL HARQ. 
     In some aspects, the network  100  may operate over a system BW or a component carrier (CC) BW. The network  100  may partition the system BW into multiple BWPs (e.g., portions). A BS  105  may dynamically assign a UE  115  to operate over a certain BWP (e.g., a certain portion of the system BW). The assigned BWP may be referred to as the active BWP. The UE  115  may monitor the active BWP for signaling information from the BS  105 . The BS  105  may schedule the UE  115  for UL or DL communications in the active BWP. In some aspects, a BS  105  may assign a pair of BWPs within the CC to a UE  115  for UL and DL communications. For example, the BWP pair may include one BWP for UL communications and one BWP for DL communications. 
     In some aspects, the network  100  may operate over a shared channel, which may include shared frequency bands or unlicensed frequency bands. For example, the network  100  may be an NR-unlicensed (NR-U) network operating over an unlicensed frequency band. In such an aspect, the BSs  105  and the UEs  115  may be operated by multiple network operating entities. To avoid collisions, the BSs  105  and the UEs  115  may employ an LBT procedure to monitor for transmission opportunities (TXOPs) in the shared channel. A wireless communication device may perform an LBT in the shared channel. LBT is a channel access scheme that may be used in the unlicensed spectrum. When the LBT results in an LBT pass (the wireless communication device wins contention for the wireless medium), the wireless communication device may access the shared medium to transmit and/or receive data. For example, a transmitting node (e.g., a BS  105  or a UE  115 ) may perform an LBT prior to transmitting in the channel. When the LBT passes, the transmitting node may proceed with the transmission. When the LBT fails, the transmitting node may refrain from transmitting in the channel. In an example, the LBT may be based on energy detection. For example, the LBT results in a pass when signal energy measured from the channel is below a threshold. Conversely, the LBT results in a failure when signal energy measured from the channel exceeds the threshold. In another example, the LBT may be based on signal detection. For example, the LBT results in a pass when a channel reservation signal (e.g., a predetermined preamble signal) is not detected in the channel. A TXOP may also be referred to as channel occupancy time (COT). 
     Sidelink communications refers to the communications among UEs without tunneling through a BS and/or a core network. Sidelink communication can be communicated over a physical sidelink control channel (PSCCH) and a physical sidelink shared channel (PSSCH). The PSCCH and PSSCH are analogous to a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) in downlink (DL) communication between a BS and a UE. For instance, the PSCCH may carry sidelink control information (SCI) and the PSSCH may carry SCI and/or sidelink data (e.g., user data). Each PSCCH is associated with a corresponding PSSCH, where SCI in a PSCCH may carry reservation and/or scheduling information for sidelink data transmission in the associated PSSCH. In some examples, a UE may transmit PSSCH carrying SCI, which may be indicated in two stages. In a first stage control (SCI-1), the UE may transmit PSCCH carrying information for resource allocation and decoding a second stage control. The first stage SCI may include at least one of a priority, PSSCH resource assignment, resource reservation period (if enabled), PSSCH DMRS pattern (if more than one pattern is configured), a second-stage SCI format (e.g., size of 2nd SCI), an amount of resources for the second-stage SCI, a number of PSSCH demodulation reference signal (DMRS) port(s), a modulation and coding scheme (MCS), etc. In a second stage control (SCI-2), the UE may transmit PSCCH carrying information for decoding the PSSCH. The second stage SCI may include a -bit L1 destination identifier (ID), an 8-bit L1 source ID, a HARQ process ID, a new data indicator (NDI), a redundancy version (RV), etc. Sidelink communication can also be communicated over a physical sidelink feedback control channel (PSFCH), which indicates an acknowledgement(ACK)-negative acknowledgement (NACK) for a previously transmitted PSSCH. Use cases for sidelink communication may include vehicle-to-everything (V2X), industrial IoT (IIoT), and/or NR-lite. 
     Some of the UEs  115  may communicate with each other in peer-to-peer communications. For example, a first UE may communicate with a second UE over a sidelink. In some instances, the sidelink may be a unicast bidirectional link, each between a pair of UEs. In some other instances, the sidelink may be multicast links supporting multicast sidelink services among the UEs. For instance, the first UE may transmit multicast data to the second UE over sidelinks. In some aspects, some of the UEs are associated with vehicles (e.g., similar to the UEs  115   i - k  in  FIG.  1   ) and the communications over the sidelinks may be C-V2X communications. C-V2X communications may refer to communications between vehicles and any other wireless communication devices in a cellular network. 
     NR supports two modes of radio resource allocations (RRA), a mode-1 RRA and a mode-2 RRA, for sidelink over a licensed spectrum. The mode-1 RRA supports network controlled RRA that can be used for in-coverage sidelink communication. For instance, a serving BS may determine a radio resource on behalf of a sidelink UE and transmit an indication of the radio resource to the sidelink UE. The serving BS may provide a dynamic grant or may activate a configured sidelink grant for sidelink communications. Sidelink feedback can be reported back to the BS by the transmitting UE. The mode-2 RRA supports autonomous RRA for sidelink UEs to perform autonomous sidelink communications over a shared radio frequency band (e.g., in a shared radio spectrum or an unlicensed spectrum). In some aspects, the shared radio frequency band may be partitioned into multiple subchannels or frequency subbands. A sidelink UE may be configured to operate in a mode-2 RRA. For instance, the sidelink UE may be configured with a resource pool in the shared radio frequency band. Additionally, the channel access may be in units of sidelink communication frames in time. Each sidelink communication frame may include an LBT gap duration followed by a sidelink resource. A sidelink UE intending to transmit in a frequency subband may perform an LBT in the LBT gap duration. If the LBT is successful, the sidelink UE may proceed to transmit SCI and/or sidelink data in the following sidelink resource. 
     The present disclosure provides techniques for UEs to share sidelink COT resources. A plurality of UEs may communicate the sidelink communication using COT sharing. For example, a UE may acquire a COT and share the COT with one or more other UEs. The UE that acquires the COT may be referred to as an initiating UE. A UE that does not acquire the COT, but shares the COT acquired by another UE, may be referred to as a responding UE. The initiating UE and the responding UE may each perform an LBT before acquiring or sharing the COT for communicating sidelink transmissions. An LBT may be in a variety of modes. An LBT mode may be, for example, a category 4 (CAT4) LBT, a category 2 (CAT2) LBT, or a category 1 (CAT1) LBT. A CAT1 LBT is referred to a no LBT mode, where no LBT is to be performed prior to a transmission. A CAT2 LBT refers to an LBT without a random backoff period. For instance, a transmitting node may determine a channel measurement in a time interval and determine whether the channel is available or not based on a comparison of the channel measurement against a ED threshold. A CAT4 LBT refers to an LBT with a random backoff and a variable contention window (CW). 
     The initiating UE may perform a CAT4 LBT to acquire the COT. After the initiating UE acquires the COT, the initiating UE may transmit PSCCH carrying SCI indicating COT sharing information (e.g., a length of the initiating UE&#39;s transmission, a length of the remaining COT, whether the transmission supports frequency interlacing, and the like). A sidelink UE initiating a COT may indicate information about unused or available time and/or frequency domain resources in the COT that may be shared with other sidelink UEs. 
     A monitoring sidelink UE (e.g., the responding UE) may monitor for the COT sharing information and opportunistically join the COT and utilize the unused or available resources in the COT based on the detected COT sharing information. When a monitoring UE shares a COT acquired by the initiating UE, the monitoring UE may be referred to as a responding UE. The responding UE may perform an LBT prior to transmitting in the initiating UE&#39;s COT. The LBT mode of the LBT performed by the responding UE may depend on a gap duration between the initiating UE&#39;s sidelink transmission and the responding UE&#39;s sidelink transmission. For example, the responding UE may perform, depending on the gap duration, a CAT2 LBT or a CAT1 LBT to acquire or share the COT. 
     Certain frequency bands may have certain channel occupancy requirements. A channel occupancy may be defined by continuous transmissions in the channel. In slot-based transmissions, the initiating UE may continue to communicate during and share a COT as long as the initiating UE continues to occupy the channel. Because the initiating UE has already acquired the COT, the responding UE may perform a shorter LBT (e.g., CAT2 LBT or a CAT1 LBT) than the CAT4 LBT performed by the initiating UE to share the COT. In some examples, a transmission slot may include a gap duration. The initiating UE agrees to surrender the channel if the UE has not occupied the channel for an LBT gap time threshold. Accordingly, if the slot structure has a gap duration that is longer than the LBT gap time threshold, the initiating UE will surrender the channel. If the LBT gap time threshold is 16 microseconds (μs) and a subcarrier spans about 15, 30, or 60 kHz in frequency, the gap duration in a slot structure (e.g., V2X PSCCH/PSSCH) may span about one symbol, which has a duration longer than 16 μs. In this example, the initiating UE may transmit once and then surrender the channel before a monitoring UE may take advantage of sharing the COT of the initiating UE. Instead of performing a CAT2 LBT or a CAT1 LBT to acquire the COT, the monitoring UE performs a CAT4 LBT to do so. Accordingly, if the gap duration exceeds an LBT gap time threshold (e.g., about 16 μs), the monitoring UE may be unable to take advantage of performing a shorter LBT to share the COT. 
     The present disclosure provides techniques for controlling one or more gap durations in a slot-based transmission. One way to create a transmission gap with a tight duration is to apply a CP extension to a transmission. In some examples, to control the gap duration for COT sharing, the responding UE may use a CP extension to create a gap duration between the initiating UE&#39;s transmission and the responding UE&#39;s transmission, where the gap duration satisfies an LBT gap time threshold (e.g., about 16 μs to about 25 μs). For instance, a communication signal may include one or more OFDM symbols and a CP extension can be prepended or attached to a beginning symbol of the one or more OFDM symbols to reduce a gap between a previous communication signal and the communication. For example, in an NR V2X waveform, the last symbol of a slot may be a gap, and the responding UE may use a CP extension to occupy a later portion of this symbol to shorten the gap duration such that the initiating UE does not surrender the COT and the responding UE is able to share the COT, without performing the longer CAT4 LBT. The responding UE may be responsible for maintaining the proper length gap from the previous transmission for COT sharing. The proper length gap depends on where the responding UE&#39;s transmission occurs relative to the end of the transmission burst of the initiating UE. The responding UE may determine a CP extension length for transmitting a sidelink transmission after the initiating UE&#39;s sidelink transmission, where a gap duration between the initiating UE&#39;s sidelink transmission and the responding UE&#39;s sidelink transmission satisfies the LBT gap time. 
     In some examples, the responding UE may select a length for the CP extension to provide a tight transmission gap for a certain LBT to be performed. In an example, the responding UE may select a length for the CP extension such that the gap duration may have a duration less than about 16 μs for no LBT to be performed prior to the responding UE&#39;s UL transmission. In another example, the responding UE may select a length for the CP extension such that the gap duration may have a duration of about 25 μs for a CAT2 LBT to be performed prior to the responding UE&#39;s UL transmission. A symbol duration may vary depending on an SCS and a number of subcarriers in a symbol, and thus a maximum CP extension length may be dependent on the SCS and the number of subcarriers in a symbol. Mechanisms for applying a CP extension to a sidelink communication transmitted during a shared COT are described in greater detail herein. 
       FIG.  2    illustrates a sidelink communication scheme  200  that uses time division multiplex (TDM) COT sharing according to one or more aspects of the present disclosure. The scheme  200  may be employed by a UE  215 . The UE  215  may correspond to a UE  115  in a network such as the network  100 . In particular, the UE  215  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. The network may support TDM COT sharing between sidelink UEs. 
     In  FIG.  2   , a frequency band  202  may be a shared radio frequency band or an unlicensed band shared by a plurality of network operating entities. The frequency band  202  may, for example, have a BW of about 10 megahertz (MHz) or about 20 MHz and a subcarrier spacing (SCS) of about 15 kilohertz (kHz), about 20 kHz, or about 60 kHz. The frequency band  202  may be located at any suitable frequencies. In some aspects, the frequency band  202  may be located at about 2.5 GHz, 6 GHz, or 20 GHz. 
     A UE  215  may contend for a COT  202  in a frequency band  202 , which may be a shared radio frequency band and/or an unlicensed band, for sidelink communication with another UE (e.g., the UE  217 ) over a sidelink. To communicate sidelink communication over the frequency band  202 , the UE  215  may perform an LBT  230  to contend for the COT  220  in the frequency band  202 . LBT may refer to a channel sensing mechanism used by devices (e.g., UE  215 ) to determine the presence of other signals in the channel prior to transmission and to avoid collisions with other transmissions. A device may sense the medium for a period of time. In an example, the UE  215  may perform a CAT4 to contend for the COT  220 . If the LBT  230  fails, the UE  215  may refrain from transmitting in the frequency band  202 . However, if the LBT  230  is successful, the UE  215  may proceed to use the COT  220  for sidelink communication. In the illustrated example of  FIG.  2   , the LBT  230  is successful as shown by the checkmark. Thus, the UE  215  may communicate sidelink communication with the UE  217  in the frequency band  202  during the COT  220 . For example, the UE  215  may acquire the COT  220  and transmit a sidelink communication  232  including PSSCH (indicated by the patterned box corresponding to sidelink transmission  232 ) and/or PSCCH (indicated by the two white boxes corresponding to sidelink transmission  232 ). The PSCCH may indicate SCI, which may carry information indicating when the sidelink communication  232  will end and the length of the remaining COT  220 . 
     The UE  215  may share the COT  220  with one or more other UEs. The UE  215  may have acquired a COT  220  with a duration longer that what is required for transmitting the UE  215 &#39;s sidelink communication  232 . Thus, there may be unused time domain resources in the COT  220 . The UE  217  may monitor PSCCH from other UEs (including the UE  215 ) and recover COT sharing information from the SCI. The UE  217  may desire to share the COT  220  that was acquired by the initiating UE  215  and transmit a sidelink communication  240  (e.g., PSCCH and/or PSSCH) during the shared COT  222 . The responding UE  217  may compute a length  234  for a CP extension  238  such that a gap duration  237  between the sidelink transmission  232  and the sidelink transmission  240  satisfies an LBT gap time threshold (e.g., 16 μs or 25 μs). In an example, the gap duration  237  satisfies the LBT gap time threshold if the gap duration  237  is not greater than the LBT gap time threshold. For example, if the gap duration  237  satisfies an LBT gap time threshold for a CAT2 LBT, then the LBT  236  may be a CAT 2 LBT. The UE  217  may apply the CP extension  238  with the length  234  to the sidelink transmission  240  and perform the LBT  236 . If the LBT  236  is successful, the responding UE  217  may transmit the sidelink communication  240  with the CP extension  238 . If the LBT  236  fails, the responding UE  217  refrains from transmitting the sidelink communication  240 . In another example, if the gap duration  237  satisfies a LBT gap time threshold for a CAT1 LBT (no LBT), then the LBT  236  may be a CAT1 LBT. The UE  215  may apply the CP extension  238  with the length  234  to the sidelink transmission  240  and transmit without an LBT. 
     To meet a BW occupancy requirement and/or a PSD requirement in a frequency band, a UE may transmit a sidelink communication using a frequency interlaced waveform, as shown in  FIG.  3   . Certain frequency bands may have certain BW occupancy requirements and/or a maximum allowable power spectral density (PSD). To meet BW occupancy requirements and/or boost transmit power under certain PSD limitations, sidelink transmissions in the network (e.g., network  100 ) may use a frequency-interlaced waveform. For example, an unlicensed band may be partitioned into a plurality of frequency interlaces and sidelink communications can be transmitted over one or more frequency interlaces. 
       FIG.  3    illustrates a sidelink communication scheme  300  that uses frequency division multiplex (FDM) COT sharing according to one or more aspects of the present disclosure. The scheme  300  may be employed by a UE  315 . The UE  315  may correspond to a UE  115  in a network such as the network  100 . In particular, the UE  315  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. The network may support frequency interlace-based COT sharing between sidelink UEs. 
     In  FIG.  3   , a frequency band  302  is partitioned into a plurality of frequency interlaces  308  shown as  308   I(0)  to  308   (M-1) , where M is a positive integer. Each frequency interlace  308   I(i)  may include K plurality of RBs  310  evenly spaced over the frequency band  302 , where K is a positive integer and i may vary between 0 to M-1. In other words, the RBs  310  in a particular frequency interlace  308   I(i)  are spaced apart from each other by at least one other RB  310 . The frequency interlace  308   I(0)  as shown by the pattern filled boxes includes RBs  310  from clusters  304   C(0)  to  304   C(K-1) . The values of K and M may vary based on several factors, such as the bandwidth, the SCS, and/or the PSD limitation of the frequency band  302 . 
     In an aspect, the frequency band  302  may have a bandwidth of about 20 MHz and each subcarrier  312  may span about 15 kHz in frequency. In such an aspect, the frequency band  302  may include about ten frequency interlaces  308  (e.g., M=10). For example, an allocation may include one frequency interlace  308  having ten distributed or equally spaced RBs  310 . Compared to an allocation with a single RB or ten localized RBs, the interlaced allocation with the ten distributed RBs  310  allows a UE to transmit with a higher BW occupancy. In another aspect, the frequency band  302  may have a bandwidth of about 20 MHz and each subcarrier  312  may span about 30 kHz in frequency. In such an aspect, the frequency band  302  may include about five frequency interlaces  308  (e.g., M=5). Similarly, an allocation may include one frequency interlace  308  having ten distributed RBs  310 . The interlaced allocation with the ten distributed RBs may allow for a wider BW occupancy than an allocation with a single RB or ten localized RBs. 
     A group of M localized RBs  310  forms a cluster  304 . As shown, the frequency interlaces  308   I(0)  to  308   (M-1)  form K clusters  304   C(0)  to  304   C(K-1) . Each RB  310  may span about twelve contiguous subcarriers  312  in frequency and a time period  314 . The subcarriers  312  are indexed from 0 to 11. The subcarriers  312  are also referred to as resource elements (REs). The time period  314  may span any suitable number of OFDM symbols  306 . In some aspects, the time period  314  may correspond to one TTI, which may include about fourteen OFDM symbols  306 . 
     While  FIG.  3    illustrates the frequency interlaces  308  spanning one slot or one RB  310  duration (e.g., the time period  314 ), the frequency interlaces  308  can span a longer duration, for example, 2, 3, or more slots or any suitable number of symbol  306  durations. In some aspects, the RBs  310  are physical resource blocks (PRBs) and each frequency interlace  308  may include PRBs uniformly spaced in the frequency band  302 . 
     In the scheme  300 , an initiating UE  315  may select one or more frequency interlaces  308  for sidelink communication with another UE in a COT  320 . As an example, the initiating UE  315  selects the frequency interlace  308   I(0)  for sidelink communication with a sidelink UE in the COT  320 . In some other examples, the initiating UE  315  may select a different frequency interlace  308   I(m) , where m may be between 1 and M-1, for the sidelink communication. Additionally, the UE  315  may use any suitable number of frequency interlaces  308  for the sidelink communication, for example, between 1 to M number of frequency interlaces  308 . The sidelink communication over the frequency interlace  308   I(0)  may include sidelink data and SCI. The sidelink data may be communicated via a PSSCH. The SCI may be communicated via a PSCCH. The SCI may carry information or parameters related to the transmission of the PSSCH. In some examples, the SCI carries information needed to support interlace-based COT sharing. In interlace-based transmission, short transmission gaps may be introduced to allow other UEs to join in other interlaces. As discussed further below, the responding UE may use a CP extension to meet the short transmission gaps. 
     The initiating UE  315  may occupy frequency interlace  308   I(0)  for sidelink communication and may share the COT with a responding UE, which will occupy another frequency interlace  308  in the frequency band  302  for sidelink communication. In some examples, the initiating UE  315  may acquire the COT  320  and may not require all frequency interlaces  308  in the frequency band  302  for each sidelink communication. Thus, there may be unused frequency interlaces  308  or frequency domain resources in the COT. The responding UE  317  may take advantage of the initiating UE  315 &#39;s channel access after acquiring the COT  320  and may perform an LBT to occupy frequency interlace  308   I(1)  for sidelink communication. The frequency interlace occupied by the initiating UE  315  is different from the frequency interlace occupied by the responding UE  317 . 
     The responding UE  317  may monitor PSCCH from other UEs (including the UE  315 ) and recover COT sharing information from the SCI. For example, the UE  317  may determine, based on the SCI, that the interlace-based transmission is supported. The responding UE  317  may perform an LBT  336  to share the COT  320  and transmit in the frequency interlace  308   I(1) . The responding UE  317  may compute a length  334  for a CP extension  338  such that a gap duration  337  between the initiating UE&#39;s sidelink transmission (e.g., PSSCH/PSCCH) corresponding to the frequency interlace  308   I(0)  and the responding UE&#39;s sidelink transmission (e.g., PSSCH/PSCCH) corresponding to the frequency interlace  308   I(1)  satisfies an LBT gap time threshold (e.g., 16 μs or 25 μs). In an example, the gap duration  337  satisfies the LBT gap time threshold if the gap duration  337  is not greater than the LBT gap time threshold. For example, if the gap duration  337  satisfies a LBT gap time threshold for a CAT2 LBT, then the LBT  336  may be a CAT 2 LBT. The UE  317  may apply the CP extension  338  with the length  334  to the responding UE&#39;s sidelink transmission. If the LBT  336  is successful, the responding UE  317  may transmit the sidelink communication with the CP extension  338  in the frequency interlace  308   I(1) . If the LBT  336  fails, the responding UE  317  refrains from transmitting the sidelink communication. In another example, if the gap duration  337  satisfies a LBT gap time threshold for a CAT1 LBT (no LBT), then the LBT  336  may be a CAT1 LBT. The UE  317  may apply the CP extension  338  with the length  334  to the sidelink transmission and transmit the sidelink transmission in the frequency interlace  308   I(1)  without an LBT. 
       FIG.  4    is a block diagram of an example UE  400  according to one or more aspects of the present disclosure. The UE  400  may be a UE  115  discussed above in  FIG.  1   , a UE  215  discussed above in  FIG.  2   , and/or a UE  315  discussed above in  FIG.  3   . As shown, the UE  400  may include a processor  402 , a memory  404 , a COT sharing module  408 , a sidelink communication module  409 , a transceiver  410  including a modem subsystem  412  and a radio frequency (RF) unit  414 , and one or more antennas  416 . These elements may be in direct or indirect communication with each other, for example via one or more buses. 
     The processor  402  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  402  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. 
     The memory  404  may include a cache memory (e.g., a cache memory of the processor  402 ), 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 device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In an aspect, the memory  404  includes a non-transitory computer-readable medium. The memory  404  may store, or have recorded thereon, instructions  406 . The instructions  406  may include instructions that, when executed by the processor  402 , cause the processor  402  to perform the operations described herein with reference to the UEs  115 ,  215 , and/or  315  in connection with aspects of the present disclosure, for example, aspects of  FIGS.  2 ,  3   , and  6 - 13 . Instructions  406  may also be referred to as program code. The program code may be for causing a wireless communication device to perform these operations, for example by causing one or more processors (such as processor  402 ) to control or command the wireless communication device to do so. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements. 
     The COT sharing module  408  and/or the sidelink communication module  409  may be implemented via hardware, software, or combinations thereof. For example, the COT sharing module  408  and/or the sidelink communication module  409  may be implemented as a processor, circuit, and/or instructions  406  stored in the memory  404  and executed by the processor  402 . In some instances, the COT sharing module  408  and/or the sidelink communication module  409  can be integrated within the modem subsystem  412 . For example, the COT sharing module  408  and/or the sidelink communication module  409  can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem  412 . 
     The COT sharing module  408  and/or the sidelink communication module  409  may be used for various aspects of the present disclosure, for example, aspects of  FIGS.  2 ,  3 , and  6 - 13   . In some aspects, the COT sharing module  408  may be configured to detect a first sidelink transmission in a COT, the COT for sharing with multiple sidelink UEs including the UE  400 . The UE  400  may share the COT with an initiating UE, and the first sidelink transmission may include PSSCH and/or PSCCH communications. For example, the COT sharing module  408  may detect COT sharing SCI in a PSSCH communication to enable the UE  400  to opportunistically join the COT and utilize any time and/or frequency resource not occupied by the initiating UE&#39;s sidelink communication. 
     The COT sharing module  408  may be configured to determine a CP extension length for transmitting a second sidelink transmission after the first sidelink transmission, where a gap duration between the first sidelink transmission and the second sidelink transmission satisfies an LBT gap time threshold (e.g., 16 μs or 25 μs). The COT sharing module  408  may be configured to apply a CP extension having the CP extension length to the second sidelink transmission. In some aspects, the sidelink communication module  409  may be configured to transmit, to the second sidelink UE, the second sidelink transmission with the CP extension. 
     As shown, the transceiver  410  may include the modem subsystem  412  and the RF unit  414 . The transceiver  410  can be configured to communicate bi-directionally with other devices, such as the BSs  105 . The modem subsystem  412  may be configured to modulate and/or encode the data from the memory  404 , the COT sharing module  408 , and/or the sidelink communication module  409  according to an MCS, e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit  414  may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data (e.g., PSSCH data and/or PSCCH control information, PSFCH ACK/NACK feedbacks, COT sharing SCI, HARQ ACK/NACK) from the modem subsystem  412  (on outbound transmissions) or of transmissions originating from another source such as a UE  115  or a BS  105 . The RF unit  414  may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver  410 , the modem subsystem  412  and the RF unit  414  may be separate devices that are coupled together at the UE  115  to enable the UE  115  to communicate with other devices. 
     The RF unit  414  may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas  416  for transmission to one or more other devices. The antennas  416  may further receive data messages transmitted from other devices. The antennas  416  may provide the received data messages for processing and/or demodulation at the transceiver  410 . The transceiver  410  may provide the demodulated and decoded data (e.g., PSSCH data and/or PSCCH control information, PSFCH ACK/NACK feedbacks, COT sharing SCI, HARQ ACK/NACK) to the COT sharing module  408  and/or the sidelink communication module  409  for processing. The antennas  416  may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit  414  may configure the antennas  416 . 
     In an example, the transceiver  410  is configured to receive sidelink transmissions, PSCCH SCI, PSFCH ACK/NACK feedbacks from another UE, and/or sidelink COT sharing SCI, for example, by coordinating with the COT sharing module  408 . In an example, the transceiver  410  is configured to transmit PSSCH data, PSFCH ACK/NACK feedbacks to another UE and/or receive PSSCH data, for example, by coordinating with the COT sharing module  408 . 
     In an aspect, the UE  400  can include multiple transceivers  410  implementing different RATs (e.g., NR and LTE). In an aspect, the UE  400  can include a single transceiver  410  implementing multiple RATs (e.g., NR and LTE). In an aspect, the transceiver  410  can include various components, where different combinations of components can implement different RATs. 
       FIG.  5    is a block diagram of an example BS  500  according to one or more aspects of the present disclosure. The BS  500  may be a BS  105  in the network  100  as discussed above in  FIG.  1   . A shown, the BS  500  may include a processor  502 , a memory  504 , a transceiver  510  including a modem subsystem  512  and a RF unit  514 , and one or more antennas  516 . These elements may be in direct or indirect communication with each other, for example via one or more buses. 
     The processor  502  may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor  502  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. 
     The memory  504  may include a cache memory (e.g., a cache memory of the processor  502 ), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid state memory device, 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 aspects, the memory  504  may include a non-transitory computer-readable medium. The memory  504  may store instructions  506 . The instructions  506  may include instructions that, when executed by the processor  502 , cause the processor  502  to perform operations described herein, for example, aspects of  FIG.  1   . Instructions  506  may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement(s) as discussed above with respect to  FIG.  4   . 
     As shown, the transceiver  510  may include the modem subsystem  512  and the RF unit  514 . The transceiver  510  can be configured to communicate bi-directionally with other devices, such as the UEs  115 ,  215 ,  315 , and/or  400  and/or another core network element. The modem subsystem  512  may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit  514  may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data (e.g., a sidelink resource configuration, sidelink COT sharing configuration) from the modem subsystem  512  (on outbound transmissions) or of transmissions originating from another source such as a UE  115 ,  215 ,  315 , and/or  400 . The RF unit  514  may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver  510 , the modem subsystem  512  and/or the RF unit  514  may be separate devices that are coupled together at the BS  105  to enable the BS  105  to communicate with other devices. 
     The RF unit  514  may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas  516  for transmission to one or more other devices. This may include, for example, transmission of information to complete attachment to a network and communication with a camped UE  115 ,  215 ,  315 , or  400  according to some aspects of the present disclosure. The antennas  516  may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver  510 . The transceiver  510  may provide the demodulated and decoded data to any modules of the BS  500  for processing. The antennas  516  may include multiple antennas of similar or different designs in order to sustain multiple transmission links. 
     In an aspect, the BS  500  can include multiple transceivers  510  implementing different RATs (e.g., NR and LTE). In an aspect, the BS  500  can include a single transceiver  510  implementing multiple RATs (e.g., NR and LTE). In an aspect, the transceiver  510  can include various components, where different combinations of components can implement different RATs. 
       FIGS.  6 - 12    illustrate various mechanisms for a responding UE (e.g., the UEs  115 ,  215 ,  315  and/or  400 ) to share a COT acquired by an initiating UE for sidelink communication. In  FIGS.  6 - 12   , the schemes  600 - 1200  may be employed by a UE such as the UEs  115 ,  215 ,  315  and/or  400  in a network such as the network  100 . In particular, the UE may acquire a COT and provide COT sharing information to allow other UEs to join the COT and/or or monitor for COT sharing information from another sidelink UE and join the other UE&#39;s COT as shown in the schemes  600 - 1200 . 
     In some examples, the responding UE may be responsible for determining a length of the CP extension. The CP extension length may be based on where the initiating UE&#39;s sidelink transmission occurs (e.g., within the duration of the shared COT for FDM sidelink COT sharing, within the duration of the shared COT for TDM sidelink COT sharing, or outside the duration of the shared COT for TDM sidelink COT sharing) and/or where the responding UE&#39;s sidelink transmission occurs. 
       FIG.  6    illustrates a TDM sidelink COT sharing scheme  600  with active transmission according to one or more aspects of the present disclosure. The scheme  600  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using TDM sidelink sharing. The scheme  600  is described using a similar TDM structure as in the scheme  200 . The scheme  600  may be employed by an initiating UE  602 , a UE  604 , and a UE  606 . The UE  602 ,  604 , or  606  may correspond to a UE  115  in a network such as the network  100 . In particular, any of the UEs  602 ,  604 , or  606  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. 
     In the scheme  600 , an initiating UE  602  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) may initiate or contend for the COT  608  in a frequency band  610  by performing an LBT  612  in the frequency band  610 . The UE  602  may monitor SCI, which may be transmitted at some predetermined resources in each slot. The SCI may provide COT information (e.g., the duration of the COT, whether other sidelink UEs can share the COT, etc.). The LBT  612  may be a CAT4 LBT similar to the LBT  230  in  FIG.  2   . The LBT  612  is a pass as shown by the checkmark indicating that the UE  602  acquired the COT  608 . After acquiring the COT  608 , the UE  602  may transmit a sidelink communication  614  to a second sidelink UE (e.g., UE  604 , UE  606 , or other UE) during the symbols 1-9 of slot 0 (as just one example). The transmission of communications during any particular symbols, slots, etc., as discussed in the present disclosure, may be provided to provide examples and are not intended to be limiting. 
     The initiating UE  602  may transmit a sidelink transmission in a portion of a COT  608  while leaving some gap durations for other UE&#39;s to transmit sidelink communications. The initiating UE  602  may support TDM COT sharing within the active transmission. For example, a UE  604  may share the COT  608  of the initiating UE  602  and transmit PSFCH to the initiating UE  602 . In another example, a UE  606  may share the COT  608  of the initiating UE  602  and transmit PSCCH/PSSCH to the initiating UE  602 . In some examples, the initiating UE  602  may transmit SCI including COT sharing information. The COT sharing information may indicate that other sidelink UEs can share the COT and/or time duration of the COT. In some examples, a monitoring UE may monitor for SCI, detect SCI, read the COT sharing information, and decide to use the COT if the monitoring UE has data to transmit. 
     The COT  608  may include three transmission slots, slot 0, slot 1, and slot 2, with each slot including fourteen symbols. In each of the slots, symbol 0 may be a repetition of symbol 1. Additionally, a portion of symbol 13 in slot 0 and in slot 1 may include a CP extension that controls a gap duration between the initiating UE  602 &#39;s sidelink transmission and the responding UE&#39;s sidelink transmission such that the gap duration satisfies an LBT gap time threshold. The responding UE that is sharing the initiating UE  602 &#39;s COT may be responsible for determining, based on a starting and/or ending point of the initiating UE  602 &#39;s sidelink transmission  614 , a duration of the shared COT  608 , and/or a remainder of the duration of the shared COT  608  after the sidelink transmission  614 , a length of the CP extension. In an example, the responding UE may determine the remainder duration of the shared COT  608  by determining a difference between the ending point of the initiating UE  602 &#39;s sidelink transmission and the duration of the COT. In another example, the responding UE determines a length of the initiating UE  602 &#39;s transmission based on the starting and ending points of the initiating UE  602 &#39;s sidelink transmission and subtracts the length from the COT duration. 
     In an example, the UE  604  may detect the sidelink transmission  614  in the COT  608  shared by multiple UEs (e.g., the initiating UE  602 , the UE  604 , and/or the UE  606 ). The UE  604  may perform an LBT to contend for the shared COT  608 . To reduce a gap duration such that it satisfies the LBT gap time threshold, the UE  604  may determine a CP extension length for transmitting a sidelink transmission and apply the CP extension having the length to a sidelink transmission. For example, the UE  604  may transmit a PSFCH transmission  616 , which may include a sidelink ACK/NACK feedback in symbol 12 of slot 0, with the symbol 11 of slot 0 being a repetition of symbol 12 of slot 0, to the initiating UE  602 . If the gap duration during symbol 10 of slot 0 satisfies the LBT gap time threshold, the UE  604  may perform a CAT2 LBT or a CAT1 LBT instead of a CAT4 LBT. 
     To transmit the PSFCH transmission  616  within the same slot (e.g., slot 0) and the same COT  608  as was used by the initiating UE  602  to transmit the sidelink transmission  614 , the UE  604  may compute a length of the CP extension in accordance with equation (1): 
       CP extension length=T symbol —LBT Gap time threshold,  (1)
 
     where T symbol  represents a symbol duration or symbol length. In an example, the LBT gap time threshold is 16 μs. The UE  604  may apply the CP extension having the CP extension length to the PSFCH transmission  616  and perform an LBT prior to the PSFCH transmission  616 . For example, the UE  604  may perform an LBT (e.g., CAT2 LBT or CAT1 LBT) during a gap duration in symbol 10 in slot 0 created by the application of the CP extension. If the LBT is successful, the UE  604  may transmit the PSFCH transmission  616  with the CP extension. Accordingly, if the LBT gap time threshold is 16 μs and a responding UE (e.g., UE  604 ) shares a COT with an initiating UE (e.g.,  602 ) and transmits PSFCH in the shared COT, the responding UE may determine a CP extension length of T symbol —16 μs to generate a gap duration of 16 μs in the last symbol of the previous slot (e.g., the slot including the sidelink transmission  614  of the initiating UE  602 ). In an example, T symbol  represents a symbol duration or symbol length of symbol 10 of slot 0. 
     In another example, the UE  606  may detect the sidelink transmission  614  in the COT  608  shared by multiple UEs (e.g., the initiating UE  602 , the UE  604 , and/or the UE  606 ). The COT  608  may be for sharing with the multiple sidelink UEs. The UE  606  may perform LBT to contend for the shared COT  608 . To reduce a gap duration such that it satisfies the LBT gap time threshold, the UE  606  may determine a CP extension length for transmitting a sidelink transmission and apply the CP extension having the length to a sidelink transmission. For example, the UE  606  may transmit a PSCCH/PSSCH transmission  618 , which may include a sidelink PSCCH/PSSCH transmission in symbols 1-12 of slot 1, with the symbol 0 of slot 1 being a repetition of symbol 1 of slot 1, to the initiating UE  602 . If the gap duration during symbol 13 of slot 0 satisfies the LBT gap time threshold, the UE  606  may perform a CAT2 LBT or a CAT1 LBT instead of a CAT4 LBT. 
     To transmit the PSCCH/PSSCH transmission  618  within slot 1 during the shared COT  608 , which was used by the initiating UE  602  to transmit the sidelink transmission  614 , the UE  606  may compute a length of the CP extension in accordance with equation (2): 
       CP extension length=T symbol —LBT Gap time threshold,  (2)
 
     where T symbol  represents a symbol duration or symbol length. In an example, the LBT gap time threshold is 16 μs. The UE  606  may apply the CP extension having the CP extension length to the PSCCH/PSSCH transmission  618  and perform an LBT prior to the PSCCH/PSSCH transmission  618 . For example, the UE  606  may perform an LBT (e.g., CAT2 LBT or CAT1 LBT) during a gap duration of symbol 13 in slot 0. If the LBT is successful, the UE  606  may transmit the PSCCH/PSSCH transmission  618  with the CP extension. Accordingly, if the LBT gap time threshold is 16 μs and a responding UE (e.g., UE  606 ) shares a COT with an initiating UE (e.g.,  602 ) and transmits PSCCH/PSSCH in a succeeding slot of the slot in which the initiating UE transmitted in, the responding UE may determine a CP extension length of T symbol —16 μs to generate a gap duration of 16 μs in the last symbol of the previous slot (e.g., the slot including the sidelink transmission  614  of the initiating UE  602 ). In an example, T symbol  represents a symbol duration or symbol length of symbol 13 of slot 0. 
     In another example, the initiating UE  602  may desire to transmit a sidelink PSCCH/PSSCH transmission  620  during the COT  608 . The initiating UE  602  may perform LBT to contend for the shared COT  608 . To reduce a gap duration such that it satisfies the LBT gap time threshold, the initiating UE  602  may determine a CP extension length for transmitting a sidelink transmission and apply the CP extension having the length to a sidelink transmission. For example, the initiating UE  602  may transmit a PSCCH/PSSCH transmission  620 , which may include a sidelink PSCCH/PSSCH transmission in symbols 1-12 of slot 2, with the symbol 0 of slot 1 being a repetition of symbol 1 of slot 1, to another sidelink UE. If the gap duration within symbol 13 of slot 1 satisfies the LBT gap time threshold, the initiating UE  602  may perform a CAT2 LBT or a CAT1 LBT instead of a CAT4 LBT. 
     To transmit the PSCCH/PSSCH transmission  620  within slot 2 during the shared COT  608 , which was used by the initiating UE  602  to transmit the sidelink transmission  614 , the initiating UE  602  may compute a length of the CP extension in accordance with equation (3): 
       CP extension length=T symbol —LBT Gap time threhsold,  (3)
 
     where T symbol  represents a symbol duration or symbol length. In an example, the LBT gap time threshold is 16 μs. The initiating UE  602  may apply the CP extension having the CP extension length to the PSCCH/PSSCH transmission  620  and perform an LBT prior to the PSCCH/PSSCH transmission  620 . For example, the initiating UE  602  may perform an LBT (e.g., CAT2 LBT or CAT1 LBT) during a gap duration of symbol 13 in slot 1. If the LBT is successful, the initiating UE  602  may transmit the PSCCH/PSSCH transmission  620  with the CP extension. Accordingly, if the LBT gap time threshold is 16 μs and the initiating UE  602  transmits PSCCH/PSSCH in a slot different from the first slot 0 in the shared COT  608 , the initiating UE  606  may determine a CP extension length of T symbol —16 μs to generate a gap duration of 16 μs in the last symbol of the previous slot (e.g., the slot including the PSCCH/PSSCH transmission  618  of the UE  606 ). In an example, T symbol  represents a symbol duration or symbol length of symbol 13 of slot 1. The initiating UE  602 &#39;s sidelink transmission (e.g., PSCCH/PSSCH transmission  620 ) may follow a transmission from the same UE of PSCCH/PSFCH, may follow a PSFCH from another UE, or follow a PSCCH/PSCCH from another UE (sharing the COT  608 ). Equation (3) may be used in any of these examples. 
       FIG.  7    illustrates an TDM sidelink COT sharing scheme  700  with out-of-time span of initiating UE according to one or more aspects of the present disclosure. The scheme  700  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using TDM sidelink sharing. The scheme  700  is described using a similar TDM structure as in the scheme  200 . The scheme  700  may be employed by an initiating UE  602 , a UE  604 , and a UE  706 . The UE  602 ,  604 , or  706  may correspond to a UE  115  in a network such as the network  100 . In particular, any of the UEs  602 ,  604 , or  706  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. 
     Aspects of the scheme  700  may overlap with aspects of the scheme  600  in  FIG.  6   . In the scheme  700 , the initiating UE  602  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) may initiate or contend for a COT  708  in the frequency band  610  by performing the LBT  612  in the frequency band  610 . The initiating UE  602  may transmit the sidelink transmission  614  in a portion of the COT  708  while leaving some gap durations for other UE&#39;s to transmit sidelink communications. The initiating UE  602  may support TDM COT sharing outside the active transmission. For example, a UE  604  may share the COT  708  of the initiating UE  602  and transmit PSFCH to the initiating UE  602 . In another example, a UE  706  may share the COT  708  of the initiating UE  602  and transmit PSCCH/PSSCH to the initiating UE  602 . 
     The COT  708  may include three transmission slots, slot 0, slot 1, and slot 2, with each slot including fourteen symbols. In each of the slots, symbol 0 may be a repetition of symbol 1. Additionally, a portion of symbol 13 in slot 0 and in slot 1 may include a CP extension that controls a gap duration between the initiating UE  602 &#39;s sidelink transmission and the responding UE&#39;s sidelink transmission such that the gap duration satisfies an LBT gap time threshold. The responding UE that is sharing the initiating UE  602 &#39;s COT may be responsible for determining, based on a starting and/or ending point of the initiating UE  602 &#39;s sidelink transmission, a duration of the shared COT  708 , and/or a remainder of the duration of the shared COT  708  after the initiating UE  602 &#39;s sidelink transmission, a length of the CP extension. As discussed in relation to  FIG.  6   , the UE  604  may perform an LBT during the gap duration in symbol 10 of slot 0 and transmit the PSFCH transmission  616 . 
     After the UE  604  transmits the PSFCH transmission  616 , the initiating UE  602  may perform an LBT during a gap duration in symbol 13 of slot 0. If the LBT is successful, then the initiating UE  602  may transmit a PSCCH/PSSCH transmission  718  in symbol 1-12 of slot 1, with the symbol 0 of slot 1 being a repetition of symbol 1 of slot 1, to a sidelink UE. 
     In an example, the UE  706  may detect the sidelink transmission (e.g., PSCCH/PSSCH transmission  718 ) in the COT  708  shared by multiple UEs (e.g., the initiating UE  602 , the UE  604 , and/or the UE  706 ). The UE  706  may perform an LBT to contend for the shared COT  708 . To reduce a gap duration such that it satisfies the LBT gap time threshold, the UE  706  may determine a CP extension length for transmitting a sidelink transmission and apply the CP extension having the length to a sidelink transmission. For example, the UE  706  may transmit a PSCCH/PSSCH transmission  720  in symbols 1-12 of slot 2, with the symbol 0 of slot 2 being a repetition of symbol 1 of slot 2, to the initiating UE  602 . If the gap duration during symbol 13 of slot 1 satisfies the LBT gap time threshold, the UE  706  may perform a CAT2 LBT or a CAT1 LBT instead of a CAT4 LBT. 
     To transmit the PSCCH/PSSCH transmission  720  within slot 2 during the shared COT  708 , which was used by the initiating UE  602  to transmit the sidelink (e.g., PSCCH/PSSCH) transmission  714 , the UE  706  may compute a length of the CP extension in accordance with equation (4): 
       CP extension length=T symbol —LBT Gap time threhsold,  (4)
 
     where T symbol  represents a symbol duration or symbol length. In an example, the LBT gap time threshold is 16 μs. The UE  706  may apply the CP extension having the CP extension length to the PSCCH/PSSCH transmission  720  and perform an LBT prior to the PSCCH/PSSCH transmission  720 . For example, the UE  706  may perform an LBT (e.g., CAT2 LBT or CAT1 LBT) during a gap duration of symbol 13 in slot 1. If the LBT is successful, the UE  706  may transmit the PSCCH/PSSCH transmission  720  with the CP extension. In this example, the responding UE  706  may generate a gap duration of 16 μs in the last symbol of the previous slot (e.g., the slot including the sidelink transmission  718  of the initiating UE  602 ). In an example, T symbol  represents a symbol duration or symbol length of symbol 13 of slot 1. In some examples, if the UE  706  intends to transmit a transmission with a transmission length or duration that is short limited (e.g., up to 0.584 milliseconds), the UE  706  may transmit the transmission without performing an LBT. 
       FIG.  8    illustrates a TDM sidelink COT sharing scheme  800  with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. The scheme  800  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using TDM sidelink sharing. The scheme  800  is described using a similar TDM structure as in the scheme  200 . The scheme  800  may be employed by an initiating UE  802 , a UE  803 , a UE  804 , and a UE  806 . The UEs  802 ,  803 ,  804 , or  806  may correspond to a UE  115  in a network such as the network  100 . In particular, any of the UEs  802 ,  803 ,  804 , or  806  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. 
     In the scheme  800 , an initiating UE  802  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) may initiate or contend for a COT  808  in a frequency band  810  by performing an LBT  812  in the frequency band  810 . The LBT  812  may be a CAT4 LBT similar to the LBT  230  in  FIG.  2   . The LBT  812  is a pass as shown by the checkmark indicating that the UE  802  acquired the COT  808 . The COT  808  may include three transmission slots, slot 0, slot 1, and slot 2, with each slot including fourteen symbols. In each of the slots, symbol 0 may be a repetition of symbol 1. Additionally, a portion of symbol 13 in slot 0 and in slot 1 may include a CP extension that controls a gap duration between the initiating UE  802 &#39;s sidelink transmission and the responding UE&#39;s sidelink transmission such that the gap duration satisfies an LBT gap time threshold. The responding UE that is sharing the initiating UE  802 &#39;s COT may be responsible for determining, based on a starting and/or ending point of the initiating UE  802 &#39;s sidelink transmission, a duration of the shared COT  808 , and/or a remainder of the duration of the shared COT  808  after the initiating UE  802 &#39;s sidelink transmission, a length of the CP extension. 
     After acquiring the COT  808 , the UE  802  may transmit a sidelink communication  814  to a second sidelink UE (e.g., UE  803 , UE  804 , UE  806 , or other UE) during the symbols 1-9 in slot 0 of the COT  808 . The initiating UE  802  may transmit the sidelink transmission  814  in a portion of the COT  808  while leaving some gap durations for other UE&#39;s to transmit sidelink communications. The initiating UE  802  may support TDM COT sharing outside the active transmission. For example, a UE  803  may share the COT  808  of the initiating UE  802  and transmit a PSFCH transmission  840  to the initiating UE  802  in slot 0 of the COT. In another example, a UE  804  may share the COT  808  of the initiating UE  802  and transmit a PSSCH/PSSCH transmission  818  to the initiating UE  802  in slot 1 of the COT. In another example, a UE  806  may share the COT  808  of the initiating UE  802  and transmit a PSCCH/PSSCH transmission  820  to the initiating UE  802  in slot 2 of the COT 
     The UE  803  may perform an LBT during the gap duration in symbol 10 of slot 0 and transmit the PSFCH transmission  840 . The UE  803  may generate a gap duration of 16 μs in the symbol 10 in slot 0 of COT  808  and perform LBT during the gap duration. The UE  803  may determine a CP extension length for transmitting the PSFCH transmission  840 , with the LBT gap time threshold being 16 μs, and apply a CP extension having the CP extension length to the PSFCH transmission  840 . The UE  803  may transmit the PSFCH transmission  840  during the symbol 12 of the slot 0 in the COT  808 , with the symbol 11 being a repetition of symbol 12, to the initiating UE  802 . 
     Additionally, the scheme  800  may apply to SCS of 15 KHz or 30 KHz in a scenario in which a sidelink transmission by the initiating UE does not immediately precede a sidelink transmission by a responding UE (e.g., UE  804  or  806 ). For example, the initiating UE  802 &#39;s sidelink transmission  814  immediately precedes the UE  803 &#39;s PSFCH transmission  840  because no other UE has transmitted between the initiating UE  802 &#39;s sidelink transmission  814  and the  803 &#39;s PSFCH transmission  840 . Conversely, the initiating UE  802 &#39;s sidelink transmission  814  does not immediately precede the UE  804 &#39;s PSCCH/PSSCH transmission  818  because the UE  803  has transmitted a sidelink communication (e.g., PSFCH transmission  840 ) between the initiating UE  802 &#39;s sidelink transmission  814  and the UE  804 &#39;s PSCCH/PSSCH transmission  818 . Similarly, the initiating UE  802 &#39;s sidelink transmission  814  does not immediately precede the UE  806 &#39;s PSCCH/PSSCH transmission  820  because the UE  803  has transmitted a sidelink communication (e.g., PSFCH transmission  840 ) between the initiating UE  802 &#39;s sidelink transmission  814  and the UE  806 &#39;s PSCCH/PSSCH transmission  820 . 
     If a responding UE  804 ,  806  does not transmit a sidelink transmission immediately after the initiating UE  802 , then the responding UE  804 ,  806  may perform an LBT during a gap duration to access the channel with a CP extension of T symbol —25 μs to generate a gap duration of 25 μs in the last symbol (e.g., symbol 13) in the previous slot. If the LBT is successful, the UE  804  shares the COT  808  of the initiating UE  802  and transmits the PSCCH/PSSCH transmission  818  in slot 1 in the COT  808 . Similarly, if the LBT is successful, the UE  806  shares the COT  808  of the initiating UE  802  and transmits the PSCCH/PSSCH transmission  820  in slot 2 in the COT  808 . 
       FIG.  9    illustrates a TDM sidelink COT sharing scheme  900  with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. The scheme  900  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using TDM sidelink sharing. The scheme  900  is described using a similar TDM structure as in the scheme  200 . The scheme  900  may be employed by the initiating UE  802  and the initiating UE  804 . The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. Additionally, the scheme  900  may apply to SCS of 15 KHz or 30 KHz in a scenario in which a responding UE transmits in multiple continuous slots. 
     Similar to the scheme  800  in  FIG.  8   , in the scheme  900 , the initiating UE  802  may acquire a COT  908  including three transmission slots, slot 0, slot 1, and slot 2, with each slot including fourteen symbols. In each of the slots, symbol 0 may be a repetition of symbol 1. Additionally, the UE  803  may perform an LBT during a gap duration of 16 μs in symbol 10 in slot 0 of the COT  908  to access the channel with a CP extension of T symbol —16 The UE  804  may perform an LBT during a gap duration of 25 μs in last symbol (e.g., symbol 13) in slot 0 of the COT  908  to access the channel with a CP extension of T symbol —25 μs. Based on successful LBTs, the initiating UE  802  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) transmits the sidelink transmission  804 , the UE  803  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) transmits the PSFCH transmission  840 , and the UE  804  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) transmits the PSCCH/PSSCH transmission  818 . 
     In the scheme  900 , if the UE  804  transmits in multiple continuous slots, for slots other than the first slot in the COT  908  (e.g., slot 0 in the COT  908 ), the UE  804  may use a CP extension length of T symbol —16 μs to generate a gap of 16 μs in the last symbol (e.g., symbol 13) in the previous slot (e.g., the slot in which the PSCCH/PSSCH transmission  818  was transmitted in slot 1 by itself). A portion of symbol 13 in slot 1 in the COT  908  may include a CP extension that controls a gap duration between the UE  804 &#39;s sidelink transmission (e.g., PSCCH/PSSCH transmission  818 ) and the UE  804 &#39;s sidelink transmission (e.g., PSCCH/PSSCH transmission  920 ), which are transmitted in continuous slots by the same UE, such that the gap duration satisfies an LBT gap time threshold. If the LBT is successful, the UE  804  transmits the PSCCH/PSSCH transmission  920  during the COT  908 . 
     In some examples, if the gap duration is shorter than a critical threshold compared to another UE attempting to share the COT within the initiating UE, then the CP extension may stop the other UE from sharing the COT. Accordingly, a collision may be avoided. In an example, the critical threshold may be about 9 μs. 
     In the examples illustrated in  FIGS.  8  and  9   , the schemes  800  and  900  corresponded to SCS of about 15 KHz or about 30 KHz, which provide for symbol lengths that are greater than 25 μs. In  FIGS.  10  and  11   , the schemes  1000  and  1100  correspond to SCS of about 60 KHz, which provides for symbol lengths that are less than 25 μs. Accordingly, it may not be possible for a responding UE to create a 25 μs gap using a CP extension. In this example, the responding UE may use the full symbol gap in the last symbol and puncture part of symbol 0 as well (which is a repetition of symbol 1) in a slot. 
       FIG.  10    illustrates a TDM sidelink COT sharing scheme  1000  with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. The scheme  1000  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using TDM sidelink sharing. The scheme  1000  is described using a similar TDM structure as in the scheme  200 . The scheme  1000  may be employed by an initiating UE  802 , a UE  803 , a UE  1004 , and a UE  1006 . The UEs  802 ,  803 ,  1004 , or  1006  may correspond to a UE  115  in a network such as the network  100 . In particular, any of the UEs  802 ,  803 ,  1004 , or  1006  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. 
     Aspects of the scheme  800  in  FIG.  8    may correspond to aspects of the scheme  1000 . For example, the initiating UE  802  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) may initiate or contend for a COT  1008  in the frequency band  810  by performing the LBT  812  in the frequency band  810 . The LBT  812  may be a CAT4 LBT similar to the LBT  230  in  FIG.  2   . The LBT  812  is a pass as shown by the checkmark indicating that the UE  802  acquired the COT  1008 . The COT  1008  may include three transmission slots, slot 0, slot 1, and slot 2, with each slot including fourteen symbols. In slot 0, symbol 0 may be a repetition of symbol 1. As discussed in relation to  FIG.  8   , the UE  802  transmits the sidelink transmission  814 , and the UE  803  transmits the PSFCH transmission  840 . 
     The initiating UE  802  may transmit the sidelink transmission  814  in a portion of the COT  1008  while leaving some gap durations for other UE&#39;s to transmit sidelink communications. The initiating UE  802  may support TDM COT sharing outside the active transmission. For example, UE  1004  may share the COT  1008  of the initiating UE  802  and transmit a PSSCH/PSSCH transmission  1018  to the initiating UE  802  in slot 1 of the COT. In another example, a UE  1006  may share the COT  1008  of the initiating UE  802  and transmit a PSCCH/PSSCH transmission  1020  to the initiating UE  802  in slot 2 of the COT. 
     As discussed, the scheme  1000  may apply to SCS of about 60 KHz in a scenario in which a sidelink transmission by the initiating UE does not immediately precede a sidelink transmission by a responding UE (e.g., UE  1004  or  1006 ). For example, the initiating UE  802 &#39;s sidelink transmission  814  immediately precedes the UE  803 &#39;s PSFCH transmission  840  because no other UE has transmitted between the initiating UE  802 &#39;s sidelink transmission  814  and the  803 &#39;s PSFCH transmission  840 . Conversely, the initiating UE  802 &#39;s sidelink transmission  814  does not immediately precede the UE  1004 &#39;s PSCCH/PSSCH transmission  1018  because the UE  803  has transmitted a sidelink communication (e.g., PSFCH transmission  840 ) between the initiating UE  802 &#39;s sidelink transmission  814  and the UE  1004 &#39;s PSCCH/PSSCH transmission  1018 . Similarly, the initiating UE  802 &#39;s sidelink transmission  814  does not immediately precede the UE  1006 &#39;s PSCCH/PSSCH transmission  1020  because the UE  803  has transmitted a sidelink communication (e.g., PSFCH transmission  840 ) between the initiating UE  802 &#39;s sidelink transmission  814  and the UE  1006 &#39;s PSCCH/PSSCH transmission  1020 . 
     If the SCS of about 60 KHz, the symbol length may be shorter than 25 μs. Accordingly, the responding UE  1004  may maintain the gap duration in symbol 13 in slot 0 in COT  1008  and puncture symbol 0 in the next slot (e.g., slot 1) in the COT  1008  to extend the gap duration to the punctured symbol. For example, the UE  1004  may use a 25 μs LBT to access the channel with a puncturing of symbol 0 by extension of 25 μs—T symbol  to generate a gap of 25 μs in the last symbol in the previous slot (e.g., slot 0) and the first symbol (e.g., symbol 0) in a current slot (e.g., the slot 1). In other words, rather than apply a CP extension as discussed in relation to  FIG.  8    or  FIG.  9   , the UE  1004  may puncture symbol 0 in slot 1 to generate the gap duration of 25 μs by combining the gap duration in symbol 13 of the previous slot 0 and part of symbol 0 in slot 1. The UE  1004  may perform LBT during the 25 μs gap duration. If the LBT is successful, the UE  1004  may transmit the PSCCH/PSSCH transmission  1018  during symbols 1-12 in slot 1 during the COT  1008 . Additionally, the UE  1004  may transmit a portion of a repetition of symbol 1 in symbol 0 in the slot 1. 
     The UE  1006  may perform similar actions as those discussed in relation to  1004  to transmit a PSCCH/PSSCH transmission  1020  in slot 2 during the COT  1008 . For example, the UE  1006  may use a 25 μs LBT to access the channel with a puncturing of symbol 0 by extension of 25 μs—T symbol  to generate a gap of 25 μs in the last symbol in the previous slot (e.g., slot 1) and the first symbol (e.g., symbol 0) in a current slot (e.g., the slot 2). The UE  1006  may perform LBT during the 25 μs gap duration. If the LBT is successful, the UE  1006  may transmit the PSCCH/PSSCH transmission  1020  during symbols 1-12 in slot 2 during the COT  1008 . Additionally, the UE  1006  may transmit a portion of a repetition of symbol 1 in symbol 0 in the slot 2. 
       FIG.  11    illustrates a TDM sidelink COT sharing scheme  1100  with out-of-time span of initiating UE in accordance with one or more aspects of the present disclosure. The scheme  1100  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using TDM sidelink sharing. The scheme  1100  is described using a similar TDM structure as in the scheme  200 . The scheme  1100  may be employed by the initiating UE  802 , the UE  803 , and the UE  1104 . The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. 
     Similar to the scheme  900  in  FIG.  9   , in the scheme  1100 , the initiating UE  802  may acquire a COT  1108  including three transmission slots, slot 0, slot 1, and slot 2, with each slot including fourteen symbols. In slot 0, symbol 0 may be a repetition of symbol 1. Additionally, the UE  803  may perform an LBT during a gap duration of 16 μs in symbol 10 in slot 0 of the COT  1108  to access the channel with a CP extension of T symbol —16 μs. 
     If the SCS of about 60 KHz, the symbol length may be shorter than 25 μs. Similar to the scheme  1000  in  FIG.  10   , in the scheme  1100 , a UE  1104  may maintain the gap duration in symbol 13 in slot 0 in COT  1108  and puncture symbol 0 in the next slot (e.g., slot 1) in the COT  1108  to extend the gap duration to the punctured symbol. For example, the UE  1104  may use a 25 μs LBT to access the channel with a puncturing of symbol 0 by extension of 25 μs—T symbol  to generate a gap of 25 μs in the last symbol in the previous slot (e.g., slot 0) and the first symbol (e.g., symbol 0) in a current slot (e.g., the slot 1). In other words, rather than apply a CP extension as discussed in relation to  FIG.  8    or  FIG.  9   , the UE  1104  may puncture symbol 0 in slot 1 to generate the gap duration of 25 μs by combining the gap duration in symbol 13 of the previous slot 0 and part of symbol 0 in slot 1. The UE  1104  may perform LBT during the 25 μs gap duration. If the LBT is successful, the UE  1104  may transmit the PSCCH/PSSCH transmission  1018  during symbols 1-12 in slot 1 during the COT  1108 . Additionally, the UE  1104  may transmit a portion of a repetition of symbol 1 in symbol 0 in the slot 1. 
     In the scheme  1100 , if the UE  1104  transmits in multiple continuous slots, for slots other than the first slot in the COT  1108  (e.g., slot 0 in the COT  1108 ), the UE  1104  may use a CP extension length of T symbol —16 μs to generate a gap of 16 μs in the last symbol (e.g., symbol 13) in the previous slot (e.g., the slot in which the PSCCH/PSSCH transmission  1018  was transmitted in slot 1 by itself). A portion of symbol 13 in slot 1 in the COT  1108  may include a CP extension that controls a gap duration between the UE  1104 &#39;s sidelink transmission (e.g., PSCCH/PSSCH transmission  1018 ) and the UE  1004 &#39;s sidelink transmission (e.g., PSCCH/PSSCH transmission  1120 ), which are transmitted in continuous slots by the same UE, such that the gap duration satisfies an LBT gap time threshold. If the LBT is successful, the UE  1104  transmits the PSCCH/PSSCH transmission  1120  during the COT  1108 . 
     In some examples, if the gap duration is shorter than a critical threshold compared to another UE attempting to share the COT within the initiating UE, then the CP extension may stop the other UE from sharing the COT. Accordingly, a collision may be avoided. In an example, the critical threshold may be about 11 μs. 
       FIG.  12    illustrates an FDM sidelink COT sharing scheme  1200  with a CP extension according to one or more aspects of the present disclosure. The scheme  1200  provisions for COT sharing among sidelink UEs (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) using FDM sidelink sharing. The scheme  1200  is described using a similar FDM structure as in the scheme  300 . The scheme  1200  may be employed by an initiating UE  1202 , a UE  1204 , and a UE  1206 . The UE  1202 ,  1204 , or  1206  may correspond to a UE  115  in a network such as the network  100 . In particular, any of the UEs  1202 ,  1204 , or  1206  may communicate with one or more other UEs over a sidelink. The x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. 
     In the scheme  1200 , an initiating UE  1202  (e.g., the UEs  115 ,  215 ,  315 , and/or  400 ) may initiate or contend for a COT  1208  in a frequency band  1210  by performing an LBT  1212  in the frequency band  1210 . The LBT  1212  may be a CAT4 LBT similar to the LBT  330  in  FIG.  3   . The LBT  1212  is a pass as shown by the checkmark indicating that the UE  1202  acquired the COT  1208 . After acquiring the COT  1208 , the UE  1202  may transmit a sidelink communication  1214  to a UE  1204  during the symbols 1-9 of slot 0 in a frequency interlace 0. The initiating UE  1202  may transmit a sidelink transmission  1214  in a portion of the COT  1208  while leaving some frequency interlaces for other UE&#39;s to transmit sidelink communications. The initiating UE  1202  may support FDM COT sharing with CP extension. 
     The frequency band  1210  may include one or more frequency interlaces. Although two frequency interlaces (e.g., frequency interlace 0 and frequency interlace 1) are shown, it should be understood that the frequency band  1210  may include more than two frequency interlaces. The UEs  1204  and  1206  may monitor for SCI carrying COT sharing information indicating one or more frequency interlaces used by and/or not used by the initiating UE  1202  during the COT  1208 . 
     A UE  1204  may detect the sidelink transmission  1214  in the COT  1208  shared by multiple sidelink UEs including the UE  1204 . The UE  1204  may determine a CP extension length for transmitting a PSFCH transmission  1216  after the sidelink transmission  1214 , where a gap duration between the sidelink transmission  1214  and the PSFCH transmission  1216  satisfies an LBT gap time threshold. In an example, the LBT gap time threshold is 16 μs. The UE  1204  may determine CP extension length of T symbol —16 μs to generate a gap duration of 16 μs in symbol 10 in slot 0 of COT  1208 . In an example, T symbol  represents a symbol duration or symbol length of symbol 10 in slot 0. The UE  1204  may apply the CP extension having the CP extension length to the PSFCH transmission  1216  and perform an LBT prior to the PSFCH transmission  1216 . For example, the UE  1204  may perform an LBT (e.g., CAT2 LBT or CAT1 LBT) during a gap duration of symbol 10 in slot 0 in frequency interlace 0. If the LBT is successful, the UE  1204  may transmit the PSFCH transmission  1216  with the CP extension. 
     The initiating UE  1202  may perform similar actions as discussed in relation to UE  1204  to perform an LBT during a gap duration of 16 μs in symbol 13 in slot 0 of COT  1208 . If the LBT is successful, the initiating UE  1202  may transmit a sidelink transmission  1218  in symbols 1-12 in frequency interlace 0 in a slot 1 during the COT  1208 . 
     The UE  1206  may detect the sidelink transmission  1216  in the COT  1208  shared by multiple sidelink UEs including the UE  1206 . The UE  1206  may determine a CP extension length for transmitting a sidelink transmission  1220  (e.g., PSSCH/PSCCH transmission) in the frequency interlace 1 during the COT  1208 , where a gap duration between the sidelink transmission  1216  and the sidelink transmission  1220  satisfies an LBT gap time threshold. In an example, the LBT gap time threshold is 16 μs. The UE  1206  may determine CP extension length of T symbol —16 μs to generate a gap duration of 16 μs in symbol 10 in slot 1 in the frequency interlace 1 of COT  1208 . In an example, T symbol  represents a symbol duration or symbol length of symbol 13 in slot 0. The UE  1206  may apply the CP extension having the CP extension length to the sidelink transmission  1220  and perform an LBT prior to the sidelink transmission  1220 . For example, the UE  1206  may perform an LBT (e.g., CAT2 LBT or CAT1 LBT) during a gap duration of symbol 13 in slot 0 in frequency interlace 1. If the LBT is successful, the UE  1206  may transmit the sidelink transmission  1220  with the CP extension in the frequency interlace 1. 
     The initiating UE  1202  may stop its sidelink transmission temporarily to avoid blocking the other UEs&#39; (e.g., UE  1204  or UE  1206 ) CAT2 LBTs. It may be desirable for the initiating UE  1202  to not stop for too long (e.g., longer than 16 μs), or the COT  1208  is surrendered by the UE  1202  (e.g., based on channel occupancy requirements). In an example, the initiating UE  1202  may resume transmission using the CP extension of T symbol —16 μs for the symbol 13 in slot 0. In this example, the UE  1202  may perform a CAT1 LBT to resume sidelink transmissions in frequency interlace 0 in the COT  1208 . 
     In some examples, if the LBT gap time threshold is 16 μs, the initiating UE  602  may use a CP extension length of T symbol —16 μs for a first symbol to generate a gap duration of 16 μs in the last symbol of the previous slot (e.g., the slot including the sidelink transmission  1218  of the initiating UE  1202 ) and may perform a CAT2 LBT (e.g., 16 μs) before transmitting the CP extension in symbol 13 of slot 0. In an example, T symbol  represents a symbol duration or symbol length of symbol 13 of slot 0. The initiating UE  1202  may apply the CP extension having the CP extension length to the sidelink transmission  1218  and perform an LBT prior to the sidelink transmission  1218 . If the LBT is successful, the UE  1202  may transmit the sidelink transmission  1218  with the CP extension in the frequency interlace 0. 
       FIG.  13    illustrates a flow diagram of a communication method  1300  for transmitting a sidelink communication associated with a CP extension during a shared COT in accordance with one or more aspects of the present disclosure. Blocks of the method  1300  can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device. In some aspects, the wireless communication device is a UE (e.g., UEs  115 ,  215 ,  315 , and/or UE  400 ) that may utilize one or more components, such as the processor  402 , the memory  404 , the COT sharing module  408 , the sidelink communication module  409 , the transceiver  410 , and/or the antennas  416  to execute the blocks of the method  1300 . The method  1300  may employ similar aspects as in the scheme  200  in  FIG.  2   , the scheme  300  in  FIG.  3   , the scheme  500  in  FIG.  5   , the scheme  600  in  FIG.  6   , the scheme  700  in  FIG.  7   , the scheme  800  in  FIG.  8   , the scheme  900  in  FIG.  9   , the scheme  1000  in  FIG.  10   , the scheme  1100  in  FIG.  11   , and/or the scheme  1200  in  FIG.  2   . As illustrated, the method  1300  includes a number of enumerated blocks, but aspects of the method  1300  may include additional blocks before, after, and/or in between the enumerated blocks. In some aspects, one or more of the enumerated blocks may be omitted or performed in a different order. 
     At block  1310 , the method  1300  includes detecting a first sidelink transmission in a channel occupancy time (COT), the COT for sharing with multiple sidelink UEs including a first sidelink UE. In some examples, the first sidelink UE may detect the first sidelink transmission in the COT. The first sidelink UE may detect the first sidelink transmission by monitoring for SCI indicating COT sharing information on the COT. The first sidelink transmission may include the SCI. 
     At block  1320 , the method  1300  includes determining a cyclic prefix (CP) extension length for transmitting a second sidelink transmission after the first sidelink transmission, a gap duration between the first sidelink transmission and the second sidelink transmission satisfying a listen-before-talk (LBT) gap time threshold. In some examples, the first sidelink UE may determine the CP extension length. In an example, the LBT gap time threshold is 16 microseconds (as just one example of a numeric value). In another example, the LBT gap time threshold is 16 microseconds (as just one example of another numeric value). 
     At block  1330 , the method  1300  includes applying a CP extension having the CP extension length to the second sidelink transmission. In some examples, the first sidelink UE may apply the CP extension having the CP extension length to the second sidelink transmission. In an example, to apply a CP extension to a signal including symbols 0 to K, the first sidelink UE may generate the CP extension and attach the CP extension to a beginning of the signal. For example, if the signal includes symbols 0 to K, the first sidelink UE may generate the CP extension by copying an ending portion of symbol 0. After generating the CP extension, the first sidelink UE may attach the CP extension to the beginning of the symbol 0. 
     At block  1340 , the method  1300  includes transmitting, to a second sidelink UE, the second sidelink transmission with the CP extension. In some examples, the first sidelink UE may transmit the second sidelink transmission with the CP extension. 
     In some examples, the first sidelink UE may detect the first sidelink transmission from a third sidelink UE, where the first sidelink transmission includes COT sharing information. The second sidelink UE may be the same as or different from the third sidelink UE. In some examples, the first sidelink UE may perform an LBT during the gap duration and transmit the second sidelink transmission if the LBT is successful. The second sidelink transmission may include PSFCH, PSCCH, and/or PSSCH. In some examples, the gap duration may occur before the first sidelink UE transmits the second sidelink transmission. 
     In some examples, the first sidelink transmission is included in a first frequency interlace in the COT, and the second sidelink transmission is included in a second frequency interface in the COT. In some examples, the first sidelink UE may transmit the second sidelink transmission starting at a first symbol and then apply the CP extension to a second symbol preceding the first symbol. In some examples, the first sidelink UE detects the first sidelink transmission in a first slot in the COT and transmits the second sidelink transmission in a second slot in the COT. The first slot may be the same as or different from the second slot. 
     In some examples, the first sidelink UE may detect the first sidelink transmission in a first slot in the COT. The first sidelink transmission may end at a first symbol in the first slot, and the first slot may be devoid of PSFCH. The first sidelink UE may transmit the second sidelink transmission in a next slot after the first slot, and the LBT gap time threshold may be 16 μs. In some examples, the first sidelink UE may perform a category 2 (CAT2) LBT and acquire the COT if the CAT2 LBT is successful. In some examples, the first sidelink UE may perform a CAT1 LBT to transmit the second sidelink transmission with the CP extension. 
     In some examples, the first sidelink UE may determine a third sidelink transmission that is transmitted between the first and second sidelink transmissions in the COT, and the multiple sidelink UEs may include a third sidelink UE that transmitted the third sidelink transmission. The LBT gap time threshold may be 25 μs. In an example, the first sidelink UE may determine the third sidelink transmission based on the COT configuration (e.g., if there is a PSFCH opportunity configured at the end of the slot). In another example, the first sidelink UE may determine the first sidelink transmission based on COT sharing information (if the first SL transmission ended already). 
     In some examples, the first sidelink UE may determine a second CP extension length for transmitting a third sidelink transmission. The first sidelink UE may transmit the second sidelink transmission in a first slot, and the first CP extension length may be different from the second CP extension length. The first sidelink UE may transmit the third sidelink transmission in a second slot, where the first and second slots are continuous slots. In some examples, the first sidelink UE may puncture a first symbol in a first slot in the COT. The first gap duration may include the punctured portion of the first symbol and a second gap duration, and the second gap duration may occur in a second symbol immediately preceding the first symbol. Additionally, the LBT gap time threshold may be 25 μs. 
     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 referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, an 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 the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). 
     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 on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list 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). 
     As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.