Periodic resource reservation for aperiodic traffic over sidelink services

Abstract

Aspects presented herein can enable a wireless device to use periodic reserved resources to serve aperiodic traffic over a sidelink. In one aspect, a wireless device reserves a set of periodic resources for a sidelink transmission, where the reserved set of periodic resources includes reserved resources for SCI and reserved resources for data. The wireless device transmits, without a data transmission, the SCI in the periodic resources of the period. In another aspect, a first wireless device receives, from a second wireless device, a reservation of a set of periodic resources for a sidelink transmission. The first wireless device receives, from the second wireless device, a SCI in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 036,823, titled “PERIODIC RESOURCE RESERVATION FOR SERVING A PERIODIC TRAFFIC OVER SIDELINK,” filed June 9, 2020, and U.S. Patent Application No. 17 / 314,964, titled “PERIODIC RESOURCE RESERVATION FOR SERVING A PERIODIC TRAFFIC OVER SIDELINK,” filed May 7, 2021, which are expressly incorporated by reference herein in their entirety. BACKGROUND TECHNICAL FIELD

[0003] The present disclosure relates generally to communication systems, and more particularly, to sidelink-based wireless communications.

[0004] INTRODUCTION

[0005] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems can employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0006] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR). 5G NR is a set of enhancements implemented to the Aspects of wireless communication can include direct communication between devices, such as based on sidelink. There is a need for further improvements in sidelink communication technology. These improvements can also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies. SUMMARY

[0007] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0008] In an aspect of the disclosure, a method, a computer readable medium, and an apparatus for wireless communication at a wireless device are provided. The apparatus reserves a set of periodic resources for a sidelink transmission, where the reserved set of periodic resources includes reserved resources for sidelink control information (SCI) and reserved resources for data. The apparatus transmits the SCI in the periodic resources of a period without a data transmission.

[0009] In an aspect of the disclosure, a method, a computer readable medium, and an apparatus for wireless communication at a first wireless device are provided. The apparatus receives, from a second wireless device, a reservation of a set of periodic resources for a sidelink transmission. The apparatus receives, from the second wireless device, SCI in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission.

[0010] To the accomplishment of the foregoing and related aspects, one or more aspects comprise the features recited in the following description and the appended claims, and the following description and the appended claims together with the drawings make apparent to those skilled in the art the nature of the aspects. The description and drawings are illustrative only of the principles of the aspects. Other aspects, implementations, objects, features, and benefits will become apparent to the skilled artisan upon consideration of the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic diagram illustrating an example of a wireless communication system and an access network.

[0012] Figure 2 illustrates example aspects of a sidelink slot structure.

[0013] Figure 3 is a schematic diagram illustrating an example of a first device and a second device involved in sidelink-based wireless communication.

[0014] Figure 4 is a schematic diagram illustrating an example of sidelink communication.

[0015] Figure 5 is a schematic diagram illustrating an example resource reservation.

[0016] Figure 6is a diagram illustrating an example resource reservation.

[0017] Figure 7 is a diagram illustrating an example of two-stage PSCCH.

[0018] Figure 8A and Figure 8B is a diagram illustrating an example of a UE using a reserved resource.

[0019] Figure 9 is a diagram illustrating an example of resource reservation.

[0020] Figure 10 is a diagram illustrating an example of HARQ-ACK.

[0021] Figure 11 is a diagram illustrating an example of resource allocation mechanism.

[0022] Figure 12 is a communication flow between two UEs in accordance with aspects of the present disclosure.

[0023] Figure 13 is a flow diagram of a method of wireless communication.

[0024] Figure 14 is a diagram illustrating an example of a hardware implementation for an example apparatus.

[0025] Figure 15 is a flow diagram of a method of wireless communication.

[0026] Figure 16 is a diagram illustrating an example of a hardware implementation for an example apparatus. DETAILED DESCRIPTION

[0027] 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 can 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 can 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 the concepts being presented.

[0028] Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements”). These elements can be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends on the particular application and design constraints imposed on the overall system.

[0029] For example, an element, any part of an element, or any combination of elements can be implemented as a "processing system" including one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, system-on-a-chip (SoCs), baseband processors, field-programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functions described in this disclosure. One or more processors in a processing system can execute software. Whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise, software should be interpreted broadly as meaning instructions, instruction sets, code, code segments, program code, programs, subroutines, software components, applications, software applications, software packages, routines, subroutines, objects, executable programs, threads of execution, procedures, functions, etc.

[0030] Therefore, in one or more example embodiments, the described functionality can be implemented in hardware, software, or any combination thereof. If implemented in software, the functionality can be stored on a computer-readable medium or encoded as one or more instructions or code on a computer-readable medium. A computer-readable medium includes a computer storage medium. The storage medium can be any available medium that can be accessed by a computer. By way of example, and not limitation, such a computer-readable medium can include random access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of computer-readable media of the types described above, or any other medium that can be used to store computer-executable code in the form of computer-accessible instructions or data structures.

[0031] While aspects and embodiments are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases can come about in many different arrangements and scenarios. Innovations described herein can be implemented across many differing platform types, devices, systems, form factors, and so on. For example, implementations or use cases can be realized in and across the following categories: gaming consoles and systems; content creation and distribution; home and mobile entertainment; wireless multimedia devices and platforms; and so on. Also, the described innovations can be implemented in and across both hardware and software modules, and across different chipset platforms and operating systems. Some examples can be realized in standalone and / or integrated circuitry, and / or in embedded software. Although some examples can be primarily discussed with respect to a cellular telephone or mobile device, the described innovations can be implemented in and across any number of mobile platforms, devices, and systems including, for example, mobile phones, smart phones, tablets, gaming and media players, Internet of Things (IoT) devices, and so on. The described innovations can also be implemented in and across various types of chipsets and platforms, including, for example, application-specific integrated circuits (ASICs), System-on-a-Chip (SoC), etc. The described innovations can be implemented in and across various types of devices, chipsets, platforms, and so on, and can be realized in and across various types of end-user devices, including, for example, mobile phones, tablets, gaming and media players, Internet of Things (IoT) devices, and so on. Although some examples can be primarily discussed with respect to a cellular telephone or mobile device, the described innovations can be implemented in and across any number of mobile platforms, devices, and systems including, for example, mobile phones, smart phones, tablets, gaming and media players, Internet of Things (IoT) devices, and so on. The described innovations can also be implemented in and across various types of chipsets and platforms, including, for example, application-specific integrated circuits (ASICs), System-on-a-Chip (SoC), etc. The described innovations can be implemented in and across various types of devices, chipsets, platforms, and so on, and can be realized in and across various types of end-user devices, including, for example, mobile phones, tablets, gaming and media players, Internet of Things (IoT) devices, and so on. Although some examples can be primarily discussed with respect to a cellular telephone or mobile device, the described innovations can be implemented in and across any number of mobile platforms, devices, and systems including, for example, mobile phones, smart phones, tablets, gaming and media players, Internet of Things (IoT) devices, and so on. The described innovations can also be implemented in and across various types of chipsets and platforms, including, for example, application-specific integrated circuits (ASICs), System-on-a-Chip (SoC), etc. The described innovations can be implemented in and across various types of devices, chipsets, platforms, and so on, and can be realized in and across various types of end-user devices, including, for example, mobile phones, tablets, gaming and media players, Internet of Things (IoT) devices, and so on.

[0032] Figure 1 FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations 102, UEs 104, an Evolved Packet Core (EPC) 160, and a 5G Core (5GC) network 190. The base stations 102 can include macro cells (high power cellular base stations) and / or small cells (low power cellular base stations). The macro cells include base stations. The small cells include femtocells, picocells, and microcells.

[0033] Aspects presented herein can provide a periodic resource allocation mechanism that enables periodically reserved resources to be used for aperiodic traffic. Aspects presented herein can enable a UE to reserve periodic resources based on sensing or partial sensing techniques while also providing support for aperiodic traffic. When the UE chooses not to use the reserved resources in a transmission period, the UE can be configured to refrain from transmitting any data in that transmission period, enabling the UE to adjust resource reservations based on instantaneous traffic load. Thus, sidelink resources can be reserved by a UE in a periodic manner while still providing flexibility for aperiodic traffic.

[0034] In certain aspects, the UE 104 can include a resource reservation component 198 configured to reserve resources on a sidelink. The resource reservation component 198 can cause the UE to make a resource reservation on a sidelink and refrain from transmitting any data in the reserved resources when the UE determines that there is no data to transmit in a transmission window. The resource reservation component 198 can optionally cause the UE to release the reserved resources upon the UE stopping transmitting data in consecutive periods. In one configuration, the resource reservation component 198 can be configured to reserve a set of periodic resources for sidelink transmissions, where the reserved set of periodic resources includes reserved resources for SCI and reserved resources for data. In such a configuration, the resource reservation component 198 can transmit SCI in the periodic resources of a period without data transmission. In another configuration, the resource reservation component 198 can be configured to receive a reservation of a set of periodic resources for sidelink transmissions from a second wireless device. In such a configuration, the resource reservation component 198 can receive SCI from the second wireless device in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission.

[0035] Some examples of sidelink communications can include vehicle-based communications, such as vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) (e.g., from a vehicle-based communication device to a road infrastructure node, such as a roadside unit (RSU)), vehicle-to-network (V2N) (e.g., from a vehicle-based communication device to one or more network nodes, such as a base station), vehicle-to-pedestrian (V2P), cellular vehicle-to-everything (C-V2X), and / or combinations thereof and / or combinations with other devices (which can be collectively referred to as V2X communications). As an example, in Figure 1 V2X and / or D2D communications can also be transmitted and received by other transmitting and receiving devices, such as a roadside unit (RSU) 107, etc. Aspects of the communications can be based on PC5 or sidelink communications, for example, as described in connection with the examples in Figure 2 Although the following description can provide examples of V2X / D2D communications related to 5G NR, the concepts described herein can also be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

[0036] The base stations 102 configured for 4G LTE (collectively referred to as the Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) can interface with the EPC 160 through the first backhaul links 132 (e.g., S I interface). The base stations 102 configured for 5G R (collectively referred to as Next Generation RAN (NG-RAN)) can interface with the core network 190 through the second backhaul links 184. In addition to other functions, the base stations 102 can perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 can communicate directly or indirectly (e.g., through the EPC 160 or core network 190) with each other over the third backhaul links 134 (e.g., X2 interface). The first, second, and third backhaul links 132, 184, and 134 can be wired or wireless.

[0037] The base stations 102 can wirelessly communicate with the UEs 104. Each of the base stations 102 can provide communication coverage for a respective geographic coverage area 110. There can be overlapping geographic coverage areas 110. For example, a small cell 102' can have a coverage area 110' that overlaps with one or more macrocells 102. A network that includes both small cell and macrocells can be known as a heterogeneous network. A heterogeneous network can also include Home Evolved NodeBs (eNBs) (HeNBs), which can provide service to a restricted group known as a closed subscriber group (CSG). The communication links 120 between the base stations 102 and the UEs 104 can include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and / or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 can use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and / or transmit diversity. The communication links can be through one or more carriers, and each carrier can be a band of frequency waves having a predetermined width and can be used to transmit data between base stations 102 and UEs 104. The base stations 102 / UEs 104 can use spectrum up to Y MHz (e.g., 5 MHz, 10 MHz, 15 MHz, 20 MHz, 100 MHz, 400 MHz, etc.) bandwidth per carrier allocated in the UL and / or DL. The carriers can or can not be adjacent to each other. The allocation of carriers can be asymmetric with respect to DL and UL (e.g., more or less carriers can be allocated for DL than for UL). The carriers can be

[0038] Some UEs 104 can communicate using device-to-device (D2D) communication link 158. The D2D communication link 158 can use a DL / UL WWAN spectrum. The D2D communication link 158 can use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). D2D communication can be through a variety of wireless D2D communications systems, such as for example, WiMedia, Bluetooth, ZigBee, Wi-Fi based on Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, LTE, or NR.

[0039] The wireless communications system can also include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154, e.g., in a 5 GHz unlicensed frequency spectrum or the like. When communicating in an unlicensed frequency spectrum, the STAs 152 / AP 150 can perform a clear channel assessment (CCA) prior to communicating, to determine whether the channel is available for use.

[0040] The small cells 102' can operate in a licensed and / or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cells 102' can employ NR and use the same unlicensed frequency spectrum as used by the Wi-Fi AP 150 (e.g., 5 GHz, etc.). The small cells 102' employing NR in an unlicensed frequency spectrum can boost coverage and / or increase capacity for access networks.

[0041] The electromagnetic spectrum is often subdivided based on frequency / wavelength into various classes, bands, channels, etc. In 5G NR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz - 7. 125 GHz) and FR2 (24.25 GHz - 52.6 GHz). Despite a portion of FR1 being above 6 GHz, FR1 is often referred to as a “sub-6 GHz” band in various documents and articles. A similar nomenclature issue sometimes occurs with regard to FR2, which is often referred to as a “millimeter wave” band in various documents and articles, despite being different from the extremely high frequency (EHF) band (30 GHz - 300 GHz) which is designated by the International Telecommunications Union (ITU) as a “millimeter wave” band.

[0042] The frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Recent 5G NR studies have identified operating bands for these mid-band frequencies as frequency range designation FR3 (7. 125 GHz - 24.25 GHz). Bands falling into FR3 can inherit FR1 characteristics and / or FR2 characteristics, and thus can effectively extend features of FR1 and / or FR2 to mid-band frequencies. Moreover, even higher bands are currently under exploration to extend 5G NR operation beyond 52.6 GHz. For example, three higher operating bands have been identified as frequency range designations FR4-a or FR4-1 (52.6 GHz - 71 GHz), FR4 (52.6 GHz - 114.25 GHz), and FR5 (114.25 GHz - 300 GHz). Each of these higher bands fall into the EHF band.

[0043] With the above in mind, unless specifically stated otherwise, it should be appreciated that the term “sub-6 GHz” or the like, if used herein, can broadly represent frequencies that can be less than 6 GHz, can be within FR1, or can include mid-band frequencies. Further, unless specifically stated otherwise, it should be appreciated that the term “millimeter wave” or the like, if used herein, can broadly represent frequencies that can include mid-band frequencies, frequencies that can be within FR2, FR4, FR4-a, or FR4-1, and / or FR5, or frequencies that can be within the EHF frequency band.

[0044] The base stations 102, whether small cell 102' or large cell (e.g., macro base station), can include and / or be referred to as an eNB, gNodeB (gNB), gNodeB (gNB), or another type of base station. Some base stations, such as gNB 180 can operate in a traditional sub-6 GHz spectrum, in millimeter wave frequencies, and / or near millimeter wave frequencies in communications with the UEs 104. When the gNB 180 operates in millimeter wave or near millimeter wave frequencies, the gNB 180 can be referred to as a millimeter wave base station. The millimeter wave base station gNB 180 can utilize beamforming 182 with the UEs 104 to compensate for the path loss and short range. The base station 180 and the UE 104 can each include a plurality of antennas, such as antenna elements, antenna panels, and / or antenna arrays to facilitate beamforming.

[0045] The base station 180 can transmit a beamformed signal to the UE 104 in one or more transmit directions 182'. The UE 104 can receive the beamformed signal from the base station 180 in one or more receive directions 182". The UE 104 can also transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 can receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180 / UE 104 can perform beam training to determine the best receive and transmit directions for each of the base station 180 / UE 104. The transmit and receive directions for the base station 180 can or can not be the same. The transmit and receive directions for the UE 104 can or can not be the same.

[0046] The EPC 160 can include a mobility management entity (MME) 162, other MMEs 164, a serving gateway 166, a multimedia broadcast multicast service (MBMS) gateway 168, a broadcast multicast service center (BM-SC) 170, and a packet data network (PDN) gateway 172. The MME 162 can be in communication with a home subscriber server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the serving gateway 166, which itself is connected to the PDN gateway 172. The PDN gateway 172 provides UE IP address allocation as well as other functions. The PDN gateway 172 and the BM-SC 170 are connected to the IP services 176. The IP services 176 can include the Internet, an intranet, an IP multimedia subsystem (IMS), a PS streaming service, and / or other IP services. The BM-SC 170 can provide functions for MBMS user service provisioning and delivery. The BM-SC 170 can serve as an entry point for content provider MBMS transmission, can be used to authorize and initiate MBMS Bearer Services, and can be used to schedule MBMS transmissions. The MBMS gateway 168 can be used to

[0047] The core network 190 can include an access and mobility management function (AMF) 192, other AMFs 193, a session management function (SMF) 194, and a user plane function (UPF) 195. The AMF 192 can be in communication with a unified data management (UDM) 196. The AMF 192 is the control node that processes the signaling between the UEs 104 and the core network 190. Generally, the AMF 192 provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF 195. The UPF 195 provides UE IP address allocation as well as other functions. The UPF 195 is connected to the IP services 197. The IP services 197 can include the Internet, an intranet, an IP multimedia subsystem (IMS), a packet switched (PS) streaming (PSS) service, and / or other IP services.

[0048] A base station can include and / or be referred to as a gNB, NodeB, eNB, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), a transmit reception point (TRP), or some other suitable terminology. A base station 102 provides an access point to the EPC 160 or core network 190 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitch appliance, a healthcare device, an implant, a sensor / actuator, a display, or any other similar functional device. Some of the UEs 104 can be referred to as IoT devices (e.g., a parking meter, gas pump, toaster, vehicle, heart monitor, etc.). The UE 104 can also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communication device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

[0049] Figure 2 FIGs. 200 and 210 illustrate example diagrams that illustrate non-limiting aspects of a slot structure that can be used for sidelink communications. In some examples, the slot structure can be within a 5G / NR frame structure. In other examples, the slot structure can be within a LTE frame structure or frame structure. Aspects can also apply within slot structures of different radio access technologies. Although the following description can focus on 5G NR, the concepts described herein can also be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies. Figure 2The example slot structure in FIG. 200 is merely one example, and other sidelink communications can have different frame structures and / or different channels used for sidelink communications. A frame (10 ms) can be divided into 10 equally sized subframes (1 ms). Each subframe can include one or more slots. A subframe can also include mini-slots, which can include 7, 4, or 2 symbols. Each slot can include 7 or 14 symbols, depending on the slot configuration. For a slot configuration 0, each slot can include 14 symbols, and for a slot configuration 1, each slot can include 7 symbols. FIG. 200 illustrates a single resource block of a single slot transmission, which can correspond to a 0.5 mm transmission time interval (TTI), for example. A physical sidelink control channel can be configured to occupy multiple physical resource blocks (PRBs), for example, 10, 12, 15, 20, or 25 PRBs. The PSCCH can be limited to a single subchannel. For example, the PSCCH duration can be configured to be 2 symbols or 3 symbols. For example, a subchannel can include 10, 15, 20, 25, 50, 75, or 100 PRBs. Resources for sidelink transmissions can be selected from a resource pool including one or more subchannels. As a non-limiting example, a resource pool can include 1 to 27 subchannels. A PSCCH size can be established for a resource pool, for example, between 10% to 100% of one subchannel for a duration of 2 symbols or 3 symbols. Figure 2 FIG. 210 in FIG. 200 illustrates an example where the PSCCH occupies about 50% of a subchannel, as one example to illustrate the concept of the PSCCH occupying a portion of a subchannel length. A physical sidelink shared channel (PSSCH) occupies at least one subchannel. The PSCCH can include a first portion of sidelink control information (SCI), and in some examples, the PSSCH can include a second portion of the SCI.

[0050] A resource grid can be used to represent the frame structure. Each time slot can include a resource block (RB) (also referred to as a physical RB (PRB)) that extends 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs). The number of bits carried by each RE depends on the modulation scheme. As Figure 2 As shown, some of the REs can include control information in the PSCCH, and some REs can include a demodulation RS (DMRS). At least one symbol can be used for feedback. Figure 2An example is illustrated with two symbols for a physical sidelink feedback channel (PSFCH) with adjacent gap symbols. The symbols before and / or after the feedback can be used for transition between data reception and feedback transmission. The gap enables the device to switch from operating as a transmitting device to preparing to operate as a receiving device, e.g., in the next slot. As shown, data can be transmitted in the remaining REs. The data can include a data message as described herein. The location of any of the data, DMRS, SCI, feedback gap symbols, and / or LBT symbols can be different in the example shown. In some aspects, multiple slots can be aggregated together. Figure 2 The example shown is different. In some aspects, multiple slots can be aggregated together.

[0051] Figure 3 is a block diagram 300 of a first wireless communication device 310 in communication with a second wireless communication device 350. The communication can be based on sidelink, e.g., using a PC5 interface. In some examples, the devices 310 and 350 can communicate based on V2X or other D2D communication. The devices 310 and 350 can include UEs, RSUs, base stations, etc. In some examples, the device 310 can be a UE and the device 350 can be a UE. Packets can be provided to a controller / processor 375 implementing layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer.

[0052] The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, can include error detection on the transport channels, forward error correction (FEC) coding / decoding of the transport channels, interleaving, rate matching, mapping to physical channels, modulation / demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols are then split into parallel streams. Each stream can then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and / or frequency domain, and then combined together using an inverse fast Fourier transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 374 can be used to determine the beamforming

[0053] At the device 350, each receiver 354RX receives a signal through its respective antenna 352. Each receiver 354RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functionality associated with various signal processing functions. The RX processor 356 can perform spatial processing on the information to recover any spatial streams destined for the device 350. If multiple spatial streams are destined for the device 350, they can be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then converts the OFDM symbol stream from the time-domain to the frequency domain using a fast Fourier transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the device 310. These soft decisions can be based on channel estimates computed by the channel estimator 358. The soft decisions are then decoded and de-interleaved to recover the data and control signals that were originally transmitted by the device 310 on the physical channel. The data and control signals are then provided to the controller / processor 359, which implements layer 3 and layer 2 functionality.

[0054] The controller / processor 359 is also coupled to the shared data memory 346 and can be responsible for managing the reception and / or transmission of data by the modem 350 using the communication subsystem 340 via the RF transceiver 342 and / or the wireless interface 344. The controller / processor 359, in one example, controls dynamic allocation of resources between the modem 350 and the wireless local area network (WLAN) subsystem 348. For example, the controller / processor 359 can allocate resources based on one or more criteria such as network conditions, battery power levels, and / or user preferences.

[0055] Similar to the functionality described in connection with the transmission by the device 310, the controller / processor 359 can provide RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression / decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transmission channels, multiplexing / de-multiplexing of MAC SDUs onto TBs, demultiplexing of TBs to MAC SDUs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

[0056] Channel estimates derived by the channel estimator 358 from a reference signal or feedback transmitted by the device 310 can be used by the TX processor 368 to select the appropriate coding and modulation schemes to be used by the device 310. The spatial streams generated by the TX processor 368 can be provided to different antenna 352 via separate transmitters 354TX. Each transmitter 354TX can modulate an RF carrier with a respective spatial stream for transmission.

[0057] The transmission is processed at the device 310 in a manner similar to that described in connection with the receiver function at the device 350. Each receiver 318RX receives a signal through its respective antenna 320. Each receiver 318RX recovers information modulated onto an RF carrier and provides the information to the RX processor 370.

[0058] The controller / processor 375 is also coupled to the shared data memory 376 and can be responsible for managing the receiver and / or transmitter functions of the device 350. The controller / processor 375, in one example, controls dynamic allocation of resources between the modem 350 and the WLAN subsystem 348. For example, the controller / processor 375 can allocate resources based on one or more criteria such as network conditions, battery power levels, and / or user preferences.

[0059] At least one of the TX processor 368, RX processor 356, or controller / processor 359 of device 350, or the TX processor 316, RX processor 370, or controller / processor 375, can be configured to perform combined operations. Figure 1 The resource reservation component 198 in the document describes various aspects.

[0060] Figure 4 This is a schematic diagram 400 illustrating an example of sidelink communication between wireless devices. Communication can be based on, among other things... Figure 2 The description of the time slot structure from various aspects, or the link structure on the other side. Although Figure 4 The examples described are for UEs 402, 404, 406, and 408, but aspects can be applied to other wireless devices configured for sidelink-based communication, such as RSUs, IAB nodes, etc. Figure 4 As shown, transmitting UE 402 can transmit transmission 414 including control information (e.g., sidelink control information (SCI)) and / or corresponding data channels that can be received by receiving UEs 404, 406, and 408. The SCI may include information for decoding the corresponding data and can also be used by the receiving device to prevent interference by avoiding transmission on occupied resources during data transmission. For example, the SCI may reserve resources for sidelink communication. The number of TTIs and the RBs to be occupied by the data transmission can be indicated in the SCI from the transmitting device. In addition to operating as receiving devices, UEs 402, 404, 406, and 408 may also be able to operate as transmitting devices. Therefore, UEs 406 and 408 are exemplified as transmitting transmissions 416 and 420. Transmissions 414, 416, or 420 can be broadcast or multicast to nearby devices. For example, UE 402 can transmit communications intended to be received by other UEs within a range 401 of UE 402. In other examples, transmissions 414, 416, or 420 may be multicast to nearby devices that are group members. In other examples, transmissions 414, 416, or 420 may be unicast from one UE to another. Additionally or alternatively, RSU 407 may receive communications from UEs 402, 404, 406, and 408 and / or send communications 418 to UEs 402, 404, 406, and 408.

[0061] Resource allocation can refer to how resources (e.g., time and / or frequency resources) are allocated to transmitting devices for transmitting packets. In sidelink communications, resource allocation can be performed in a centralized manner (which can be referred to herein as “mode 1”) or a distributed manner (which can be referred to herein as “mode 2”). When operating using mode 1, resource allocation for sidelink communications can be determined by a network entity, such as a base station. For example, a base station can transmit an indication to a UE indicating resources allocated to the UE for transmitting sidelink communications (e.g., for transmitting sidelink data packets to other UEs). When operating using mode 2, resource allocation for sidelink communications is determined by the communicating UEs, e.g., each UE autonomously determines resources for sidelink transmissions. For example, a transmitting UE can autonomously determine resource allocation for transmitting sidelink control and data to one or more receiving UEs. To coordinate selection of sidelink resources by various UEs, each UE can use sensing techniques to monitor resource reservations by other sidelink UEs, and can select resources for sidelink transmissions from unreserved resources. Devices communicating over a sidelink can determine one or more radio resources in the time and frequency domain used by other devices, selecting transmission resources that avoid collisions with other devices.

[0062] For example, as part of a sensing mechanism for resource allocation mode 2, a UE can determine (e.g., sense) whether a selected sidelink resource has been reserved by other UEs before selecting the sidelink resource for data transmission. If the UE determines that the sidelink resource has not been reserved by other UEs, the UE can use the selected sidelink resource for transmitting data, e.g., in a PSSCH transmission. The UE can estimate or determine which radio resources (e.g., sidelink resources) can be in use and / or reserved by other UEs by detecting and decoding sidelink control information (SCI) transmitted by other UEs. The UE can use a sensing-based resource selection algorithm to estimate or determine which radio resources are in use and / or reserved by other UEs. The UE can receive SCI from another UE that includes reservation information based on a resource reservation field included in the SCI. The UE can continuously monitor (e.g., sense) and decode SCI from peer UEs. The SCI can include reservation information, e.g., indicating time slots and RBs that a particular UE has selected for future transmissions. The UE can exclude resources used and / or reserved by other UEs from a candidate resource set for a sidelink transmission by the UE, and the UE can select / reserve resources for the sidelink transmission from resources that are not in use and thus form the candidate resource set. The UE can continuously perform sensing on SCI with resource reservations, thereby maintaining a candidate resource set from which the UE can select one or more resources for a sidelink transmission. Once the UE selects a candidate resource, the UE can transmit SCI indicating its own reservation of the resource for a sidelink transmission. The number of resources (e.g., sub-channels per subframe) reserved by the UE can depend on the size of data to be transmitted by the UE. Although this example is described with respect to a UE receiving reservations from another UE, reservations can also be received from RSUs or other devices that communicate based on sidelinks.

[0063] When operating using mode 2 (e.g., in a distributed manner), a transmitting UE can determine resources for communication from a resource pool. A resource pool can refer to a set of time and / or frequency resources on which sidelink communication can occur. Figure 5 An example of time and frequency resources that can be used for sidelink communication is illustrated. A resource pool can be preconfigured (e.g., preloaded on a UE), configured by a base station, or otherwise determined by a UE. In some examples, a transmitting UE can randomly select resources from a resource pool for transmission. In such examples, a receiving UE can continuously monitor candidate resources to receive communications, e.g., SCI indicating resource reservations. In some examples, collisions or interference can occur if nearby UEs randomly select the same resources.

[0064] In some examples, a UE can use historical resource utilization of other UEs to predict future activity. For example, by identifying that a first UE transmits periodically and what resources the first UE uses when transmitting, a second UE can determine where future transmissions by the first UE are likely to occur and when these transmissions are likely to occur. Figure 5 An example of periodic resources 550 that can be reserved by a UE for sidelink communications is illustrated. Thus, by “listening” to past other UE activity (e.g., historical resource utilization), a second UE can predict future activity of other UEs and can select resources for transmissions that are less likely to result in collisions and / or interference.

[0065] However, it can be appreciated that for a second UE to identify historical resource utilization, the second UE can operate in an “always on” mode to facilitate sensing or reception of transmissions by other UEs. The continuous monitoring by the second UE increases power consumption or processing resources to identify historical resource utilization and predict future activity.

[0066] In some examples, a UE can perform partial sensing to determine historical resource utilization of other UEs. When performing partial sensing, a UE can selectively sense a subset of resources, thus reducing power consumption as compared to monitoring a set of resources. However, partial sensing can be ineffective when transmissions by other UEs are not periodic. For example, a UE employing partial sensing can miss information about aperiodic transmissions and thus can not accurately predict future activity of other UEs based on determined historical resource utilization.

[0067] Radio resource allocation for sidelink communications can be based on resource reservation. For example, when a UE is preparing to transmit data on a sidelink, the UE can first determine whether resources are reserved by other UEs. The UE can then reserve resources from the remaining unreserved resources that are available. Figure 5 A diagram 500 illustrating an example of resource reservation for sidelink transmissions is shown. Resource allocation for each UE can be in units of one or more subchannels (e.g., subchannels SC 1-SC 4) in the frequency domain and can be based on one time slot in the time domain. A UE can also use resources in a current time slot for an initial transmission and can reserve resources in future time slots for retransmissions. In this example, UEs (e.g., UE1 and UE2) can reserve up to two different future time slots for retransmissions. Resource reservations can be limited in a window of pre-defined time slots and subchannels. For example, as shown in the diagram 500 in FIG. 5, a UE can reserve resources in a window of eight (8) time slots by four (4) subchannels. Figure 5 As shown in the diagram 500 in FIG. 5, resource reservation can include a window of eight (8) time slots by four (4) subchannels, which can provide a total number of thirty-two (32) available resource blocks. This resource reservation window can also be referred to as a resource selection window. Each resource block in the resource selection window can be used by a transmitting device to transmit data and control information.

[0068] In one example, a first UE (“UE1”) can reserve a subchannel (e.g., SC 4) in a current slot (e.g., slot 1) for its initial data transmission and can reserve additional future slots (e.g., 504 and 506) within a window for data retransmissions. For example, UE1 can reserve subchannel SC 2 in slot 3 and SC 3 in slot 4 for future retransmissions, as shown. UE1 can then transmit information about which resources it is using and / or reserving to other UEs, for example, by including the reservation information in the reserved resources field of SCI (e.g., first stage SCI). A UE can be configured to reserve one, two, or three transmissions using SCI. The maximum number of reservations allowed for a UE can be preconfigured for the UE. For example, a UE can reserve up to three transmissions within a resource selection window. Figure 5

[0069] As shown in FIG. 6, a second UE (“UE2”) can also reserve resources in subchannels SC 1 and SC 2 in slot 1 for its current data transmission and can reserve a first data retransmission using subchannels SC 1 and SC 2 in slot 4 and a second data retransmission using subchannels SC 3 and SC 4 in slot 7, as shown. Figure 5 Figure 5 Similarly, UE2 can subsequently transmit resource usage and reservation information to other UEs, such as using the reserved resources field in SCI. A UE can also be configured to use the same number of subchannels (e.g., bandwidth) for all reservations. For example, resources 502, 504, and 506 reserved by UE1 can have the same number of subchannels (e.g., 1), and resources 508, 510, and 512 reserved by UE 2 can also have the same number of subchannels (e.g., 2). However, the starting subchannel of each reserved resource can be different. For example, resource 502 can start at SC 4, resource 504 can start at SC 2, and resource 506 can start at SC 3, etc.

[0070] Figure 6 is a diagram 600 illustrating an example of resource reservation. If a UE (e.g., a sidelink transmitting UE) reserves resources in a periodic manner, such as every slot, the UE can reserve resources in a slot (e.g., slot 1) for an initial data transmission and can reserve resources in a future slot (e.g., slot 2) for a data retransmission, as shown. Figure 5 ​​If the time slot i in the illustrated period 552 uses the first resource 602 for transmission, the UE can reserve two other resources within the same period, such as the second resource 604 in time slot i+x and the third resource 606 in time slot i+y. Each of the reserved resources 602, 604, and 606 can have a number of z sub-channels. For example, if the period has thirty-two (32) time slots (e.g., with time slot indices from #0 to #31), the UE can transmit the first resource 602 with z sub-channels in time slot 0, and the UE can reserve the second resource 604 with z sub-channels in time slot i+x, where x can be greater than zero (0) and less than or equal to thirty-one (31) (e.g., 0 < x ≤ 31), and the UE can also reserve the third resource 606 with z sub-channels in time slot i+y, where y can be greater than x and less than or equal to thirty-one (31) (e.g., x < y ≤ 31). Table 1 below is an example reservation signaled by the UE's SCI in time slot i corresponding to Figure 6 The corresponding example reservation signaled by the UE's SCI in time slot i.

[0071]

[0072] Table 1

[0073] The UE can use the second resource 604 and / or the third resource 606 for retransmission of the first resource 602, such as when the transmission of the first resource 602 fails. The UE can also use the second resource 604 and / or the third resource 606 for other purposes other than retransmission.

[0074] The transmitting UE using the reserved resources for transmission can request feedback from one or more receiving UEs or the base station for the transmission. Based on the feedback from one or more receiving UEs or the base station, the transmitting UE can choose not to use the reserved resources. For example, referring again to Figure 6 , the transmitting UE can use the first resource 602 for data transmission and can request the base station or the receiving UE that receives the data transmission to provide feedback to the transmitting UE. If the transmitting UE receives feedback from the receiving UE or the base station confirming the reception / decoding of the data transmission, the transmitting UE can choose not to use the second resource 604 and / or the third resource 606, which may initially be configured or reserved for retransmission of the data transmission.

[0075] The sidelink resource reservation can be periodic or aperiodic. For example, the UE can periodically reserve one or more sidelink resources, such as by including in the SCI or in a part of the SCI (e.g., in as Figure 7The reservation period is indicated in SCI-1 of the two-stage SCI discussed in detail). Thus, when periodic resource reservations are enabled for a UE, the reservation in SCI can signal the periodic repetition. In some examples, the reservation period for periodic resource reservations can be configured through signaling in SCI to a value between 0 ms and 1000 ms, and periodic resource reservations can also be disabled through (pre-)configuration. In other examples, each resource reservation can be associated with a priority indicated in SCI. Resource reservations associated with higher priorities can preempt resource reservations associated with lower priorities.

[0076] In some examples, resource reservations can be indicated by a transmitting UE in multiple SCI parts, where the SCI can indicate resources in which the UE is using for a sidelink transmission. For example, a UE can transmit a first part of a reservation in a physical sidelink control channel (PSCCH) and can transmit a second part of the reservation in a physical sidelink shared channel (PSSCH). In other words, a first stage of control information (e.g., SCI-1) can be transmitted on the PSCCH and contain resource allocation and information related to decoding of a second stage of control information (e.g., SCI-2), and the second stage of control information can be transmitted on the corresponding PSSCH and can contain information for decoding data (SCH) in the PSSCH. Thus, multiple resources can be indicated or reserved through a combination of a first SCI part indicated in a PSCCH region and a second SCI part in a PSSCH region. For example, the first SCI part in the PSCCH can reserve resources for the UE in the PSSCH, and the first SCI part can also indicate to a receiving UE that there is a second SCI part or more SCI parts (e.g., two-stage SCI) in the PSSCH. The second SCI part can reserve other resources or provide signaling and / or information to the UE that can be unrelated to the resources reserved in the first part SCI.

[0077] Figure 7is a diagram 700 illustrating an example of two-stage SCI. To reduce control overhead and improve processing timeline, SCI for sidelink grant can be split into two or more parts. For example, a first SCI part 702 can be transmitted within a control region (e.g., PSCCH region 708), and a second SCI part 704 can be transmitted within a downlink traffic region (e.g., PSSCH region 710). The PSCCH region 708 and the PSSCH region 710 can together form one slot. The first SCI part 702 can include initial control information about the sidelink transmission, such as resource allocation (RA) or other resource reservation information for sidelink allocation in SCH 706, rank and modulation order, etc. In addition, the first SCI part 702 can also include control information about the second SCI part 704. In some examples, the control information can indicate the number (size) and code rate of the resource elements of the second SCI part 704. The control information can also indicate the location (e.g., starting resource element) and code rate of the second SCI part 704. The second SCI part 704 can include remaining control information about the sidelink allocation. For example, the remaining control information can include non-time critical control information or other resource allocation for data transmission in SCH 706, such as source ID and destination ID for data transmission. In one aspect, the first SCI part 702 (e.g., SCI-1) format can include one or more of the following: priority (QoS value), PSSCH resource allocation (e.g., frequency / time resources for PSSCH), resource reservation period (e.g., if enabled), PSSCH DMRS pattern (e.g., if more than one pattern is configured), second SCI format (e.g., information about the size of the second SCI), 2-bit beta offset for second stage control resource allocation, number of PSSCH DMRS ports (e.g., 1 or 2), 5-bit MCS, and / or reserved bits, etc.

[0078] As discussed in connection with Figure 5 and Figure 6The discussed, sensing and / or partial sensing based resource allocation mechanisms can be configured to be periodic in that periodic resource reservations can enable sidelink transmitting UEs to identify and predict the activities of other transmitting UEs based on their past activities (e.g., their usage of reserved resources, etc.). Thus, the resource allocation mechanisms can reduce resource collisions among different transmitting UEs. However, the sensing or partial sensing mechanisms can not be as effective for aperiodic traffic or aperiodic resource allocation because the activities of other transmitting UEs can be more unpredictable. Moreover, periodic resource allocation can not be flexible enough to accommodate aperiodic traffic. For example, because periodic resource allocation can have a fixed resource allocation within each period, the resource allocation within a resource selection window can be fully reserved for retransmissions by multiple UEs, leaving fewer available resource options for aperiodic traffic within the resource selection window. Moreover, a transmitting UE can reserve resources and choose not to use the reserved resources, which can result in a waste of resources and reduce the flexibility for other UEs to reuse the resources.

[0079] Aspects presented herein can provide a periodic resource allocation mechanism that enables periodically reserved resources to be used for aperiodic sidelink traffic, which can enable UEs to periodically reserve resources based on sensing or partial sensing techniques while also providing support for aperiodic traffic. In one aspect, the resource reservations among one or more transmitting UEs can be periodic, enabling or facilitating sensing activities by other transmitting UEs, such as described in connection with Figure 5 If a UE chooses not to use the reserved resources in a transmission period, the UE can be configured to refrain from transmitting any data (e.g., padding data) in the reserved resources within the transmission period, enabling the UE to adjust the resource reservations based on the instantaneous traffic load. Thus, sidelink resources can be reserved by UEs in a periodic manner while still providing flexibility for aperiodic traffic.

[0080] When a UE does not have any data transmission in a given period, the UE can remain idle and not transmit SCI and / or data. For example, the UE can skip transmission for the given period. While this can save power for the UE, if the UE does not transmit in a certain period, the UE can lose the resources (e.g., periodic time and frequency resources) that it periodically reserves for the sidelink channel. For example, as described in connection with Figure 5 and Figure 6As described, when a transmitting UE reserves resources for transmission, the UE can reserve additional resources for future transmissions. However, when the UE does not transmit (e.g., in a currently reserved slot), the UE can not reserve additional future slots. For example, each periodic resource can indicate the next periodic resource. If the UE does not transmit within the periodic resource, the next periodic resource can not be indicated. Thus, resources within the sidelink channel can be reserved and occupied by other UEs and / or base stations, and if the sidelink channel is fully occupied, the UE can not be able to reserve any resources in the future. On the other hand, to maintain periodic resource reservation, the UE can continue to transmit both data (e.g., SCH 606) and control information (e.g., SCI) using the reserved resources, where the data can be padding data (i.e., data padded with bits). While this can enable the UE to maintain resource reservation within the channel, this can be a waste of power for the UE and a waste of resources that can be used by other UEs.

[0081] Figure 8A and Figure 8B are a diagram 800A and a diagram 800B illustrating examples of a UE making and using reserved resources in accordance with aspects of the present disclosure. In one aspect, a transmitting UE can reserve a set of periodic resources within a transmission period, such as described in connection with Figure 5 and Figure 6 . The transmission period can be based on the periodic resource reservation, such as the period between periodic resources. In some examples, the transmission period can be based on a resource selection window. When sidelink data is ready to be transmitted by the transmitting UE (e.g., before the transmission period begins), the transmitting UE can transmit the data using the periodically reserved resources. For example, as shown in Figure 8A , the transmitting UE can reserve resources 802, 804, and 806 within a transmission period 812 (e.g., a resource window). If data 808 arrives at the transmitting UE before the transmission period 812 begins, the transmitting UE can transmit and / or retransmit the data 808 and its corresponding SCI 810 using the reserved resources 802, 804, and / or 806. On the other hand, as shown in Figure 8B , if the transmitting UE determines that there is no data to transmit in the transmission period 812, the transmitting UE can be configured to transmit the SCI 810 without data (e.g., without padding data) in the reserved resources 802, 804, and / or 806. Transmitting SCI without data when there is no data to transmit can enable the transmitting UE to not occupy the data region (e.g., the PSSCH region) of the sidelink channel, which can enable other UEs to transmit data in the data region. Figure 7In one aspect, the transmitting UE can indicate in the SCI whether there is an associated data transmission from the transmitting UE. For example, the transmitting UE can use one or more bits of the SCI or can add one or more bits to the SCI (e.g., to the SL_SCH field) to indicate whether there is data associated with its transmission. In another example, the UE can include a single bit in the SCI to indicate whether there is a data transmission associated with the SCI. In such an example, when there is no associated data transmission, the transmitting UE can indicate a zero (0) in the bit indication field of the SCI. The UE can then use the reserved resources to transmit the SCI and skip transmission of data. In response, a receiving UE can receive the SCI, determine that there is no accompanying data transmission, and skip attempting to monitor for or receive data, which can save power consumption of the receiving UE. In such an example, when there is a data transmission, the transmitting UE can indicate a one (1) in the bit field of the SCI. The UE can then use the reserved resources to transmit both the SCI and the data. A UE receiving the SCI can determine that there is an accompanying data transmission and can determine information for the data transmission and attempt to receive the data transmission.

[0082] While the transmitting UE can choose not to transmit any data in the PSSCH, the transmitting UE can still indicate its PSSCH resource allocation (e.g., via the SCI) such that the transmitting UE can continue to reserve time and / or frequency domain resources associated with PSSCH (i.e., data) transmission. In other words, the transmitting can continue to perform PSSCH resource reservation or allocation (e.g., frequency or time resources for PSSCH) as if there is data to transmit, but can choose not to transmit any data in the reserved or allocated resources. Thus, the transmitting UE can continue to reserve resources by indicating the reserved resources in the SCI on the data channel. Thus, other UEs decoding the SCI (i.e., SCI-1) can still be able to know what time / frequency domain resources the transmitting UE is reserving / using.

[0083] In one aspect of the disclosure, for a transmitting UE to inform other UEs or other devices (such as a base station) that the transmitting UE will not transmit any data in one or more reserved resources within a transmission period, such as described in connection with Figure 8B In one aspect of the disclosure, for a transmitting UE to inform other UEs or other devices (such as a base station) that the transmitting UE will not transmit any data in one or more reserved resources within a transmission period, such as described in connection with

[0084] As described in connection with Figure 7The SCI for sidelink grant can include two parts, where a first SCI part (e.g., SCI-1) can be transmitted within a control region (e.g., PSCCH) and a second SCI part (e.g., SCI-2) can be transmitted within a downlink traffic region (e.g., PSSCH). In one aspect (e.g., Option 1), an indication of whether the transmitting UE will transmit data in the reserved resources of the period can be included in SCI-1. The transmitting UE can transmit SCI-1 in the reserved resources without transmitting data, or transmit SCI-2 when there is no data transmission. In another aspect (e.g., Option 2), an indication of whether the transmitting UE is transmitting any data in the reserved resources can be included in SCI-2, and the transmitting UE can transmit both SCI-1 and SCI-2 in the reserved resources without transmitting data when there is no data transmission. If a receiving device receives an indication that the transmitting UE is not transmitting data associated with the SCI (such as by an indication in SCI-1 or SCI-2), the receiving device can skip attempting to decode or monitor for data.

[0085] In some examples, transmitting the indication in SCI-2 (e.g., Option 2) can be more suitable for unicast services, where SCI-2 can be directed to one receiving device. Since SCI-2 can contain a source ID and a destination ID, the receiving device can be able to determine whether SCI-2 is targeted to the receiving device. For example, the transmitting UE can include an indication in SCI-2 of whether there is accompanying data along with the source ID and destination ID, and the receiving device can look at the destination ID along with the indication in SCI-2 to determine whether there is a data transmission intended for the receiving device. If SCI-2 indicates no data transmission, the receiving device can skip decoding for data or the receiving device would not expect any data to decode. On the other hand, transmitting the indication in SCI-1 of whether there is accompanying data (e.g., Option 1) can be more suitable or more useful for groupcast / broadcast where there is a group of receiving devices that can receive the SCI.

[0086] As discussed in connection with Figure 5 and Figure 6 In addition to the reservation in the next transmission period (e.g., 502, 508, 602 for periodic resource reservation in the next transmission), the transmitting UE can use one SCI to reserve up to two additional resources (e.g., 504, 506, 510, 512, 604, 606) in the current transmission period. In one aspect of the disclosure, if the transmitting UE indicates no data transmission associated with the current SCI, the transmitting UE can not reserve other resources in the current transmission period, such as discussed in connection with Figure 8BThe above. For example, the UE can refrain from reserving resources in the current transmission period. However, the transmitting UE can still indicate a reservation in the next transmission period, e.g., by indicating a period in SCI-1. For example, as Figure 9 As shown in diagram 900 in FIG. 9, when the transmitting UE indicates in the current SCI 910 (e.g., SCI-1) that the UE will not transmit any associated data in the current transmission period 912, the transmitting UE can use the resources 902 within the current transmission period 912 to transmit the SCI 910, but the transmitting UE can not reserve or can skip reserving other resources within the current transmission period 912, such as resources 904 and 906, etc. However, the transmitting UE can still make a resource reservation for the next transmission period 914, e.g., resource 908. Since other resources (e.g., 904, 906) in the same period can be used for retransmission, the transmitting UE can not have data to retransmit if there is no data transmission in the current transmission period.

[0087] In another aspect of the disclosure, the transmitting UE can be configured to release the periodic reservation. For example, if the transmitting UE does not have data to transmit for K consecutive periods, the transmitting UE can determine to release its reserved resources. The value K can be an integer defined at the transmitting UE or indicated / configured for the transmitting UE, such as by the base station. If the transmitting UE has data to transmit after releasing its reserved resources, the transmitting UE can select or reserve new resources. For example, if the transmitting UE does not transmit data for a period of time, it is likely that the transmitting UE has completed the transmission and can not have data to transmit. Thus, the transmitting UE can be configured to release its reserved resources. The release of the periodic resources can enable more resources to be used by other devices.

[0088] In one example, after K consecutive periods of no data transmission is reached, the transmitting UE can explicitly release the reservation (e.g., the periodic resource reservation). For example, the transmitting UE can indicate the release by setting the reservation period indicated in SCI-1 to a certain codepoint associated with the release of the resource reservation. For example, there can be an indication field of the resource reservation period in SCI-1 that the transmitting UE can use to indicate the time (e.g., 10 ms, 100 ms, etc.) at which its next reservation can occur. If this resource reservation period field in SCI-1 is enabled, other UEs or the base station can determine that the transmitting UE has another transmission after the current transmission. The time or period at which the next reservation transmission occurs can be based on the periodicity of the resource reservation. Thus, the transmitting UE can explicitly release its reserved resources by setting the resource reservation period field in SCI-1 to a certain codepoint, such as all zeros, etc. Other UEs receiving the SCI-1 from the transmitting UE can determine that the transmitting UE has explicitly released its reserved resources and can select to use the released resources.

[0089] Figure 11 is a diagram 1100 illustrating an example of a resource allocation mechanism according to some aspects of the present disclosure. A transmitting UE can periodically reserve multiple resources 1114 in multiple transmission periods (e.g., 1102, 1104, 1106, 1108, 1110, and 1112, etc.). When a data packet 1116 arrives before the transmission period 1102 or transmission occasion, the transmitting UE can use the resources 1114 for transmitting SCI 1118 and the data packet 1116 in the transmission period 1102, and the transmitting UE can also make resource reservation for the next transmission period 1104 using the transmitted SCI 1118 in the transmission period. In the transmission period 1104, if the transmitting UE has no data for transmission, the transmitting UE can transmit SCI 1118 without data in the transmission period 1104. However, the UE can still indicate the resource reservation for the next transmission period 1106 by indicating the periodic resources in the SCI 1118. For example, the transmitting UE can still indicate the reserved resources (i.e., the dashed resources 1114 in Figure 11 SCI (i.e., SCI-1) on the data channel (e.g., PSSCH), but the transmitting UE can not transmit any transmission on the indicated resources, as the purpose of the transmitting UE indicating the resources for data transmission is to reserve the resources, and can not be used for actual data transmission. Thus, other UEs decoding the SCI (i.e., SCI-1) can still be able to know what time / frequency domain resources the transmitting UE is reserving.

[0090] The UE can perform / apply the same actions in the transmission periods 1106, 1108, 1110, etc. However, if there is no data transmission after a number of consecutive periods (e.g., 3), the transmitting UE can be configured to release the resource reservation, e.g., after the transmission period 1108. Thus, in the transmission period 1110, the UE can still transmit the SCI 1118 reserved in the transmission period 1108, but the SCI 1118 in the transmission period 1110 can contain an indication (e.g., by setting the periodicity to a certain codepoint) that the transmitting UE has released its reserved resources. The transmitting UE can stop using the subsequent instances of the periodic resource reservation, e.g., in the reserved period 1112. If the UE has data to transmit after releasing the periodic resources, the UE can perform a new resource determination and reservation. Based on the codepoint in the SCI, other UEs or the base station can determine that the transmitting UE has released its reserved resources in the transmission period 1112, and they can instead use the resources.

[0091] As combined with Figure 6The transmitting UE that transmits using the reserved resources can request feedback from the receiving device. In response, the receiving device can transmit a hybrid automatic repeat request (HARQ)-ACK feedback if the transmission is successfully received, and / or a HARQ-NACK feedback if the transmission fails (e.g., the transmission is not received after a certain time period or if the received transmission cannot be decoded, etc.). In one aspect, the receiving device can still transmit a HARQ-ACK feedback to the transmitting UE when the transmitting UE indicates that there is no data transmission associated with the transmission. For example, in the case of unicast, the receiving UE can still transmit a HARQ-ACK feedback when the receiving UE is expected to decode the SCI of the transmitting UE and determine that there is no data transmission associated with the SCI. This HARQ-ACK feedback can indicate whether the SCI is received correctly. This feedback information can be used by the transmitting UE for link adjustment and measurement.

[0092] In another aspect, the receiving UE or base station can skip the HARQ-ACK or NACK feedback for a current transmission period in which the transmitting UE indicates that there is no data transmission associated with the current transmission period. For example, in the case of groupcast where there can be a NACK-only transmission, the receiving UE can not feedback a NACK if the receiving UE determines that there is no data associated with the transmission. In other words, if the receiving UE receives a SCI from the transmitting UE in the groupcast, the receiving UE can not send a HARQ-ACK feedback to the transmitting UE. However, if the receiving UE does not receive a SCI from the transmitting UE, the receiving UE can request the transmitting UE to retransmit the SCI by sending a NACK feedback.

[0093] The transmitting UE can use the mapping between the PSCCH and the physical sidelink feedback channel (PSFCH) to determine the HARQ-ACK resource. As shown in the diagram 1000 in FIG. 10, the starting subchannel of the PSSCH (i.e., the data channel) can be used to determine the HARQ-ACK resource (i.e., the PSFCH). Thus, the transmitting UE can receive the HARQ feedback in the PSFCH based on one or more of the following: the starting subchannel of the PSCCH in which the SCI is transmitted (e.g., SCI-1 or SCI, if present), the slot that includes the PSCCH (e.g., SCI-1 or SCI, if present), the source identifier, and / or the destination identifier of the transmission, etc. For example, when there is a transmitted SCI without a data transmission associated with the SCI, the UE can change its reliance on the data channel to the control channel. Thus, the UE can determine the HARQ-ACK feedback resource based on the subchannel of the PSCCH and the slot index of the PSCCH. In other words, the subchannel and slot of the data transmission can be changed to the subchannel and slot of the control transmission to determine the feedback resource. Figure 10 As shown in the diagram 1000 in FIG. 10, the starting subchannel of the PSSCH (i.e., the data channel) can be used to determine the HARQ-ACK resource (i.e., the PSFCH). Thus, the transmitting UE can receive the HARQ feedback in the PSFCH based on one or more of the following: the starting subchannel of the PSCCH in which the SCI is transmitted (e.g., SCI-1 or SCI, if present), the slot that includes the PSCCH (e.g., SCI-1 or SCI, if present), the source identifier, and / or the destination identifier of the transmission, etc. For example, when there is a transmitted SCI without a data transmission associated with the SCI, the UE can change its reliance on the data channel to the control channel. Thus, the UE can determine the HARQ-ACK feedback resource based on the subchannel of the PSCCH and the slot index of the PSCCH. In other words, the subchannel and slot of the data transmission can be changed to the subchannel and slot of the control transmission to determine the feedback resource.

[0094] Additionally or alternatively, when the receiving UE receives the SCI indicating no data transmission from the transmitting UE, the receiving UE can determine whether to transmit the HARQ-ACK / NACK feedback based on whether the receiving UE receives the associated SCI-2. For example, if the receiving UE does not receive the SCI-2 (such as if the SL_SCH field is contained in the SCI-1), the receiving UE can choose not to transmit the HARQ-ACK feedback. On the other hand, if the SL_SCH field is contained in the SCI-2 and received by the receiving UE, the receiving UE can transmit the HARQ-ACK feedback to the transmitting UE.

[0095] Figure 12 is a communication flow 1200 between a first UE and a second UE in accordance with aspects of the present disclosure. Aspects presented herein can enable a UE to reserve periodic resources based on sensing or partial sensing, and when the UE chooses not to use the reserved resources in a transmission period, the UE can be configured to refrain from transmitting any data in the transmission period, thereby enabling the UE to adjust resource reservation based on instantaneous traffic load.

[0096] At 1206, the first UE 1202 can reserve a set of periodic resources for sidelink transmissions, where the reserved set of periodic resources can include reserved resources for SCI and reserved resources for data, such as described in connection with Figure 5 and Figure 6 .

[0097] At 1208, after the first UE 1202 reserves the set of periodic resources, the first UE 1202 can indicate its reserved resources in SCI and can transmit the SCI to other UEs, such as the second UE 1204. Thus, the second UE 1204 can receive the resource reservation information for the set of periodic resources for sidelink transmissions from the first UE 1202.

[0098] At 1210, the first UE 1202 can determine not to transmit data in the period. For example, the first UE 1202 can have completed data transmission in a previous transmission occasion and can not have additional data for transmission in the current transmission occasion. Thus, the first UE 1202 can determine not to transmit data in the period based on no data for transmission at the first UE 1202 in the period.

[0099] At 1212, after determining not to transmit data in the period, the first UE 1202 can transmit the SCI to the second UE 1204 without transmitting data in the periodic resources of the period, such as described in connection with Figure 8B , Figure 9 and Figure 11 .

[0100] In some examples, the SCI can include an indication that the SCI is not associated with a data transmission. In one example, as described in connection with Figure 7 the first part of the SCI transmitted on the PSCCH (e.g., for two-stage SCI) and / or can be included / transmitted in the second part of the SCI transmitted on the PSSCH. In another example, as described in connection with Figure 9 the SCI not associated with a data transmission in a period can not reserve resources within the period, but can indicate a periodic reservation in a next period.

[0101] At 1214, if the second UE 1204 is configured to transmit HARQ feedback for SCI without data, the first UE 1202 can receive HARQ feedback for the SCI transmitted without data (e.g., for the SCI transmitted at 1212). For example, the first UE 1202 can receive (or the second UE 1204 can transmit) the HARQ feedback in a physical sidelink feedback channel (PSFCH) based on a starting subchannel of a PSCCH in which the SCI is transmitted, a slot in which the PSCCH including the SCI is transmitted, a source identifier, and / or a destination identifier, among other examples. In another example, the first UE 1202 can receive (or the second UE 1204 can transmit) the HARQ feedback based on the SCI being unicast. In another example, the first UE 1202 can receive (or the second UE 1204 can transmit) the HARQ feedback based on the second part of the SCI being transmitted in a PSSCH.

[0102] At 1216, as described in connection with Figure 11 if the first UE 1202 determines that it has no data to transmit in a threshold number of consecutive periods, the first UE 1202 can release one or more remaining periodic resources in the set of periodic resources.

[0103] At 1218, the first UE 1202 can indicate to the second UE 1204 a release regarding the periodic resource reservation. For example, the first UE 1202 can transmit an indication to the second UE 1204 based on a codepoint corresponding to a release of a periodic reservation transmitted in SCI. For example, there can be an indication field of a resource reservation period in SCI-1 that can be used by the first UE 1202 to indicate a time at which its next reservation can occur (e.g., 10 ms, 100 ms, etc.). If this resource reservation period field in SCI-1 is enabled, the second UE 1204 can determine that the first UE 1202 has another transmission after the current transmission. Thus, the first UE 1202 can explicitly release its reserved resources by setting the resource reservation period field in SCI-1 to a certain codepoint (e.g., all zeros, etc.). In response, the second UE 1204 receiving the SCI-1 from the first UE 1202 can determine that the first UE 1202 has explicitly released its reserved resources, and the second UE 1204 can choose to use the released resources.

[0104] In some examples, as shown at 1220, the second UE 1204 can measure a RSRP of a PSCCH carrying the SCI (e.g., the SCI received at 1212) (e.g., measure a DMRS of the PSCCH containing the SCI), and the second UE 1204 can determine whether to reserve the resources associated with the SCI based on the indication and the measured RSRP. For example, the second UE 1204 (which can not be in communication with the first UE 1202) can monitor for one or more SCIs transmitted by one or more UEs located in its vicinity (e.g., within its reception range), and if the second UE 1204 detects that the SCI contains an indication that the SCI is not associated with a data transmission, and if the measured RSRP of the PSCCH carrying the SCI is above a threshold, the second UE 1204 can determine that the resources in the next period can be reserved by at least one other UE. For example, when a sensing UE (e.g., a transmitting UE that is transmitting a transmission to a receiving UE) detects an SCI from another (reserving) UE indicating a reservation of resources, the sensing UE can measure how strong the signal from the reserving UE is, such as based on measuring a RSRP of the channel. This can enable the sensing UE to determine how strong the interference that the receiver of the sensing UE (e.g., the receiving UE) can experience in case the sensing UE is to transmit a packet in the corresponding resources. Thus, if the measured RSRP is large (e.g., above a threshold), this can indicate that the interference experienced by the receiver of the sensing UE can be large, and thus the sensing UE can determine that this resource can not be used for transmission, and can skip using the resource. On the other hand, if the measured RSRP is small (e.g., below a threshold), this can indicate that the interference experienced by the receiver of the sensing UE can be small, and thus the sensing UE can determine to use this resource for transmission. In other words, in both cases, the resource can be reserved by another UE based on transmitting the SCI. But if the measured interference is small, the sensing UE can still use the resource for communication (e.g., as if the resource was not reserved). Thus, in some examples, the sensing UE can determine whether a resource is available based on the measured RSRP (rather than determining whether the resource is reserved).

[0105] Figure 13 FIG. 13 is a flow diagram of a method of wireless communication, in accordance with some examples. The method can be performed by a wireless device or a component of a wireless device (e.g., the UE 104, 1202; the RSU 107; the device 310 or 350; the apparatus 1402; the processing system, which can include the memory 360 and which can be the device 350 or a component of the device 350, such as the TX processor 368, the RX processor 356, and / or the controller / processor 359). The method can enable a UE to serve aperiodic traffic using periodically reserved resources. The method can improve the use of wireless resources in sidelink communications.

[0106] At 1302, the wireless device can reserve a set of periodic resources for a sidelink transmission, where the reserved set of periodic resources can include reserved resources for SCI and reserved resources for data, such as described in connection with Figure 5 , Figure 6 , Figure 11 and Figure 12 . For example, at 1206, the first UE 1202 can reserve a set of periodic resources for a sidelink transmission that includes reserved resources for SCI and data. The reservation of the set of periodic resources for the sidelink transmission can be performed, e.g., by the resource reservation component 1440 of the apparatus 1402 in Figure 14 .

[0107] At 1304, the wireless device can determine not to transmit data in the period, such as described in connection with Figure 8A , Figure 8B , Figure 9 , Figure 11 and Figure 12 . For example, at 1210, the first UE 1202 can determine not to transmit data in the period. The determination not to transmit data can be performed, e.g., by the data transmission determination component 1442 of the apparatus 1402 in Figure 14 . Thus, the wireless device can determine not to transmit data in the period based on there being no data for transmission at the wireless device in the period.

[0108] At 1306, the wireless device can transmit SCI in the periodic resources of the period without data transmission, such as described in connection with Figure 8A , Figure 9 , Figure 11 and Figure 12 . For example, at 1212, the first UE 1202 can transmit SCI to the second UE 1204 without transmitting data. The transmission of the SCI without data can be performed, e.g., by the SCI processing component 1444 and / or the transmission component 1434 of the apparatus 1402 in Figure 14 . In one example, the SCI can include an indication that there is no data transmission associated with the SCI. In such an example, a two-stage SCI can be used such that the indication can be included in a first part of the SCI (e.g., SCI-1) transmitted on the PSCCH. In another example, the indication can be included in a second part of the SCI (e.g., SCI-2) transmitted on the PSSCH, such as described in connection with Figure 7 , Figure 8A , Figure 8B , Figure 9 , Figure 11 and Figure 12As described. In another example, when there is no data to transmit in a period, the SCI can not reserve resources in the period and can indicate a periodic reservation in a next period. Thus, the wireless device can transmit the SCI in the period without data transmission based on an absence of data for transmission at the wireless device in the period.

[0109] At 1308, the wireless device can receive HARQ feedback in response to the SCI, such as described in connection with Figure 6 , Figure 10 and Figure 12 At 1214, the first UE 1202 can receive, from the second UE 1204, HARQ feedback for the SCI transmitted without data. The reception of the HARQ feedback can be performed, for example, by the HARQ feedback processing component 1446 and / or the reception component 1430 of the apparatus 1402 in Figure 14 In one example, the wireless device can receive the HARQ feedback in the PSFCH based on one or more of: a starting subchannel of the PSCCH in which the SCI is transmitted, a slot comprising the PSCCH in which the SCI is transmitted, a source identifier, or a destination identifier. In another example, the wireless device can receive the HARQ feedback based on the SCI being unicast. In another example, the HARQ feedback can be received based on the second portion of the SCI being transmitted in the PSSCH, such as described in connection with Figure 6 and Figure 10

[0110] At 1310, the wireless device can release remaining periodic resources of the set of periodic resources based on determining that the wireless device has no data to transmit in a threshold number of consecutive periods, such as described in connection with Figure 11 and Figure 12 For example, at 1216, if the first UE 1202 has no data to transmit in a threshold number of consecutive periods, the first UE 1202 can release the remaining periodic resources of the set of periodic resources. The release of the remaining periodic resources can be performed, for example, by the reserved resource release component 1448 of the apparatus 1402 in Figure 14 For example, the wireless device can release the remaining periodic resources based on a codepoint corresponding to a release of the periodic reservation transmitted in the SCI.

[0111] Figure 14 ​is a diagram 1400 illustrating an example of a hardware implementation for an apparatus 1402. The apparatus 1402 is a wireless device that supports sidelink communications. In some aspects, the apparatus 1402 can be a transmitting UE or a component of a transmitting UE. The apparatus can include a baseband processor 1404 (also referred to as a modem) coupled to a RF transceiver 1422. In some aspects, the baseband processor 1404 can be a cellular baseband processor, and the RF transceiver can be a cellular RF transceiver. In some aspects, the apparatus 1402 can also include one or more subscriber identity modules (SIM) cards 1420, an application processor 1406 coupled to a secure digital (SD) card 1408 and a screen 1410, a Bluetooth module 1412, a wireless local area network (WLAN) module 1414, a Global Positioning System (GPS) module 1416, and / or a power supply 1418. The baseband processor 1404 communicates with the wireless device 104 and / or BS 102 / 180 by the RF transceiver 1422. The baseband processor 1404 can include a computer- readable medium / memory. The baseband processor 1404 is responsible for the general processing of the apparatus 1402 including the execution of software stored on the computer-readable medium / memory. The software, when executed by the baseband processor 1404, causes the baseband processor 1404 to perform the various functions described supra. The computer-readable medium / memory can also be used for storing data that is manipulated by the baseband processor 1404 when executing software. The baseband processor 1404 further includes a reception component 1430, a communication manager 1432, and a transmission component 1434. The communication manager 1432 includes the one or more illustrated components. The components of the communication manager 1432 can be stored in the computer-readable medium / memory and / or configured as hardware within the baseband processor 1404. The baseband processor 1404 can be a component of the wireless device 350 and can include the memory 360 and / or at least one of the TX processor 368, the RX processor 356, and the controller / processor 359. In one configuration, the apparatus 1402 can be a modem chip and include only the baseband processor 1404, and in another configuration, the apparatus 1402 can be an entire wireless device (e.g., see 350 of FIG. 13) and include the additional modules of the apparatus 1402. Figure 3

[0112] The communication manager 1432 includes a resource reservation component 1440 configured to reserve a set of periodic resources for a sidelink transmission, e.g., as described in connection with 1302 of FIG. 13. The communication manager 1432 further includes a data transmission determination component 1442 configured to determine not to transmit data in the period, e.g., as described in connection with 1304 of FIG. 13. The communication manager 1432 further includes an SCI processing component 1444 configured to transmit SCI in the periodic resources of the period without a data transmission, e.g., as described in connection with 1306 of FIG. 13. Figure 13 Figure 13 The communication manager 1432 includes a resource reservation component 1440 configured to reserve a set of periodic resources for a sidelink transmission, e.g., as described in connection with 1302 of FIG. 13. The communication manager 1432 further includes a data transmission determination component 1442 configured to determine not to transmit data in the period, e.g., as described in connection with 1304 of FIG. 13. The communication manager 1432 further includes an SCI processing component 1444 configured to transmit SCI in the periodic resources of the period without a data transmission, e.g., as described in connection with 1306 of FIG. 13.​​Figure 13 as described above in connection with 1306. The communications manager 1432 also includes a HARQ feedback handling component 1446 configured to receive HARQ feedback in response to the SCI, e.g., as described above in connection with 1308. The communications manager 1432 also includes a reserved resource release component 1448 configured to release remaining periodic resources of the set of periodic resources based on a determination that the wireless device has no data to transmit in a threshold number of consecutive periods, e.g., as described above in connection with 1310. Figure 13 Figure 13

[0113] The apparatus can include additional components that perform each of the blocks of the algorithm in the flowchart of FIG. 13. As such, each block in the flowchart of FIG. 13 can be performed by a component and the apparatus can include one or more of those components. The components can be one or more hardware components specifically configured to carry out the stated processes / algorithm, implemented by a processor configured to perform the stated processes / algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof. Figure 13 Figure 13 The apparatus of FIG. 13 can be a processor or other component that carries out the processes / algorithm described above. As such, each block in the flowchart of FIG. 13 can be performed by a component and the apparatus can include one or more of those components. The components can be one or more hardware components specifically configured to carry out the stated processes / algorithm, implemented by a processor configured to perform the stated processes / algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

[0114] In one configuration, the apparatus 1402, and in particular the baseband processor 1404, includes means for reserving a set of periodic resources for sidelink transmissions (e.g., resource reservation component 1440). The apparatus 1402 includes means for determining that no data is transmitted in a period (e.g., data transmission determination component 1442). The apparatus 1402 includes means for transmitting a SCI in the periodic resources of the period without data transmission (e.g., SCI handling component 1444 and / or transmission component 1434). The apparatus 1402 includes means for receiving HARQ feedback in response to the SCI (e.g., HARQ feedback handling component 1446 and / or reception component 1430). The apparatus 1402 includes means for releasing remaining periodic resources of the set of periodic resources based on a determination that the wireless device has no data to transmit in a threshold number of consecutive periods (e.g., reserved resource release component 1448).

[0115] The means can be one or more of the components of the apparatus 1402 configured to perform the functions recited by the means. As described above, the apparatus 1402 can include the TX processor 368, the RX processor 356, and the controller / processor 359. As such, in one configuration, the means can be the TX processor 368, the RX processor 356, and the controller / processor 359 configured to perform the functions recited by the means.

[0116] Figure 15 ​​​is a flowchart 1500 of a method of wireless communication. The method can be performed by a first wireless device or a component of a first wireless device (e.g., the UE 104, 1204; the RSU 107; the device 310 or 350; the apparatus 1602; the processing system, which can include the memory 360 and which can be the device 350 or a component of the device 350, e.g., the TX processor 368, the RX processor 356, and / or the controller / processor 359). The method can enable the first wireless device to monitor for receiving SCI without data, such that the first wireless device can skip monitoring for data in a sidelink transmission to conserve power. The method can improve the use of wireless resources in sidelink communications.

[0117] At 1502, the first wireless device can receive, from a second wireless device, a reservation of a set of periodic resources for a sidelink transmission, such as described in connection with Figure 5 、 Figure 6 and Figure 12 . For example, at 1208, the second UE 1204 can receive, from the first UE 1202, a reservation of a set of periodic resources for a sidelink transmission. The reception of the reservation can be performed, for example, by the sidelink reservation processing component 1640 and / or the reception component 1630 of the apparatus 1602 in Figure 16

[0118] At 1504, the first wireless device can receive, from the second wireless device, SCI in a period of the periodic resources, the SCI can include an indication that the SCI is not associated with a data transmission, such as described in connection with Figure 8A 、 Figure 8B 、 Figure 9 and Figure 11 . For example, at 1212, the second UE 1204 can receive, from the first UE 1202, SCI in a period, where the SCI can include an indication that the SCI is not associated with a data transmission. The reception of the SCI can be performed, for example, by the sidelink transmission processing component 1642 and / or the reception component 1630 of the apparatus 1602 in Figure 16

[0119] In one example, the indication can be included in a first part (e.g., SCI-1) of the SCI received in the PSCCH. In such an example, the first wireless device can refrain from attempting to decode a second part of the SCI and the data transmission in response to receiving the indication in the first part of the SCI. In another example, the indication can be included in a second part (e.g., SCI-2) of the SCI received in the PSSCH, such as described in connection with Figure 7 、 Figure 8A 、 Figure 8B and Figure 11 ​​As described. In such an example, the first wireless device can refrain from attempting to decode the data transmission in response to receiving the indication in the second portion of the SCI. In another example, the SCI can not reserve resources in the period when the SCI indicates that it is not associated with data, but can indicate a periodic reservation in a next period.

[0120] At 1506, the first wireless device can receive a release of remaining periodic resources of the set of periodic resources, the release based on a codepoint in the SCI corresponding to a release of the periodic reservation, such as described in connection with Figure 11 As described. For example, at 1218, the second UE 1204 can receive, from the first UE 1202, a release of remaining periodic resources of the set of periodic resources. The reception of the release can be performed, for example, by the release reception component 1630 and / or the reservation release processing component 1644 of the apparatus 1602 in FIG. 13. Figure 16 As described. For example, at 1218, the second UE 1204 can receive, from the first UE 1202, a release of remaining periodic resources of the set of periodic resources. The reception of the release can be performed, for example, by the release reception component 1630 and / or the reservation release processing component 1644 of the apparatus 1602 in FIG. 13.

[0121] At 1508, the first wireless device can transmit, to the second wireless device, HARQ feedback in response to the SCI, such as described in connection with Figure 6 and Figure 10 As described. For example, at 1214, the second UE 1204 can transmit, to the first UE 1202, HARQ feedback in response to the SCI. The transmission of the HARQ feedback can be performed, for example, by the HARQ feedback component 1646 and / or the transmission component 1634 of the apparatus 1602 in FIG. 13. Figure 16 As described. For example, at 1214, the second UE 1204 can transmit, to the first UE 1202, HARQ feedback in response to the SCI. The transmission of the HARQ feedback can be performed, for example, by the HARQ feedback component 1646 and / or the transmission component 1634 of the apparatus 1602 in FIG. 13.

[0122] In one example, the HARQ feedback can be transmitted in the PSFCH based on one or more of a starting subchannel of a PSCCH in which the SCI is transmitted, a slot in which the PSCCH in which the SCI is transmitted is included, a source identifier, or a destination identifier. In another example, the HARQ feedback can be transmitted based on the SCI being unicast. In another example, the HARQ feedback can be transmitted based on the second portion of the SCI being transmitted in a PSSCH.

[0123] In other examples, the first wireless device can refrain from transmitting the HARQ feedback to the second wireless device in response to the SCI. In one example, the first wireless device can refrain from transmitting the HARQ feedback based on the SCI being groupcast or broadcast. In another example, the first wireless device can refrain from transmitting the HARQ feedback based on the indication being received in the first portion of the SCI received in a PSCCH, such as described in connection with Figure 6 and Figure 10 As described. For example, at 1214, the second UE 1204 can transmit, to the first UE 1202, HARQ feedback in response to the SCI. The transmission of the HARQ feedback can be performed, for example, by the HARQ feedback component 1646 and / or the transmission component 1634 of the apparatus 1602 in FIG. 13.

[0124] In another example, as shown at 1510, the first wireless device can measure the RSRP of the PSCCH carrying the SCI (e.g., measure the DMRS of the PSCCH containing the SCI), and the first wireless device can determine whether to reserve the resources associated with the SCI based on the indication and the measured RSRP. For example, the first wireless device (which can not be in communication with the second UE) can monitor one or more SCIs transmitted by one or more UEs located in its vicinity (e.g., reception range), and if the first wireless device detects that the SCI contains an indication that the SCI is not associated with a data transmission, and if the measured RSRP of the PSCCH carrying the SCI is above a threshold, the first wireless device can determine that the resources in the next period can be reserved by at least one UE.

[0125] Figure 16is a diagram 1600 illustrating an example of a hardware implementation for an apparatus 1602. The apparatus 1602 can be a wireless device that supports sidelink communications. In some aspects, the apparatus 1602 can be a UE, or a component of a UE. The apparatus can include a baseband processor 1604 (also referred to as a modem) coupled to a RF transceiver 1622. In some aspects, the baseband processor 1604 and the RF transceiver 1622 can be a cellular baseband processor and a cellular RF transceiver. In some aspects, the apparatus 1602 can also include one or more subscriber identity modules (SIM) cards 1620, an application processor 1606 coupled to a secure digital (SD) card 1608 and a screen 1610, a Bluetooth module 1612, a wireless local area network (WLAN) module 1614, a Global Positioning System (GPS) module 1616, and / or a power supply 1618. The baseband processor 1604 communicates with the UE 104 and / or BS 102 / 180 through the RF transceiver 1622. The baseband processor 1604 can include a computer- readable medium / memory. The baseband processor 1604 is responsible for general processing, including the execution of software stored on the computer-readable medium / memory. The software, when executed by the baseband processor 1604, causes the baseband processor 1604 to perform the various functions described supra. The computer-readable medium / memory can also be used for storing data that is manipulated by the baseband processor 1604 when executing software. The baseband processor 1604 further includes a reception component 1630, a communication manager 1632, and a transmission component 1634. The communication manager 1632 includes the one or more illustrated components. The components of the communication manager 1632 can be stored in the computer-readable medium / memory and / or configured as hardware within the baseband processor 1604. The baseband processor 1604 can be a component of the device 350 and can include the memory 360 and / or at least one of the TX processor 368, the RX processor 356, and the controller / processor 359. In one configuration, the apparatus 1602 can be a modem chip and include only the baseband processor 1604, and in another configuration, the apparatus 1602 can be an entire UE (e.g., see 350 of FIG. 1) and include the additional modules of the apparatus 1602. Figure 3

[0126] The communication manager 1632 includes a sidelink reservation processing component 1640 that is configured to receive, from a second wireless device, a reservation of a set of periodic resources for a sidelink transmission, e.g., as described in connection with 1502 of FIG. 15. The communication manager 1632 further includes a sidelink transmission processing component 1642 that is configured to receive, from the second wireless device in a period of the periodic resources, a SCI including an indication that the SCI is not associated with a data transmission, e.g., as described in connection with 1504 of FIG. 15. Figure 15 Figure 15 ​​described above. The communication manager 1632 further includes a reservation release processing component 1644 that is configured to receive a release of remaining periodic resources of the set of periodic resources, the release being based on a codepoint in the SCI corresponding to a release of a periodic reservation, e.g., as described above in connection with Figure 15 The communication manager 1632 further includes a HARQ feedback component 1646 that is configured to transmit, to the second wireless device, HARQ feedback in response to the SCI, e.g., as described above in connection with Figure 15

[0127] The apparatus can include additional components that perform each of the blocks of the algorithm in the flowchart of Figure 15 The apparatus can include additional components that perform each of the blocks of the algorithm in the flowchart of Figure 15 Figure 15 Each block in the flowchart of FIG. 10 can be performed by a component and the apparatus can include one or more of those components. Components can be one or more hardware components specifically configured to carry out the stated processes / algorithm, implemented by a processor specifically configured to carry out the stated processes / algorithm, configured by a processor to carry out the stated processes / algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

[0128] In one configuration, the apparatus 1602 (and in particular the baseband processor 1604) includes means for receiving, from a second wireless device, a reservation of a set of periodic resources for a sidelink transmission (e.g., the sidelink reservation processing component 1640 and / or the reception component 1630). The apparatus 1602 includes means for receiving, from the second wireless device in a period of the periodic resources, a SCI including an indication that the SCI is not associated with a data transmission (e.g., the sidelink transmission processing component 1642 and / or the reception component 1630). The apparatus 1602 includes means for receiving a release of remaining periodic resources of the set of periodic resources (e.g., the reservation release processing component 1644 and / or the reception component 1630), the release being based on a codepoint in the SCI corresponding to a release of a periodic reservation. The apparatus 1602 includes means for transmitting, to the second wireless device, HARQ feedback in response to the SCI (e.g., the HARQ feedback component 1646 and / or the transmission component 1634).

[0129] The means can be one or more components of the apparatus 1602 configured to perform the functions recited by the means. As described above, the apparatus 1602 can include the TX processor 368, the RX processor 356, and the controller / processor 359. Accordingly, in one configuration, the means can be the TX processor 368, the RX processor 356, and the controller / processor 359 configured to perform the functions recited by the means.

[0130] ​The following examples are illustrative only and can be combined with aspects of the other embodiments or teachings described herein without limitation.

[0131] Aspect 1 is a method of wireless communication at a wireless device, comprising: reserving a set of periodic resources for a sidelink transmission, wherein the reserved set of periodic resources includes reserved resources for SCI and reserved resources for data; and transmitting the SCI without a data transmission in the periodic resources of a period.

[0132] In Aspect 2, the method of Aspect 1 further includes the wireless device transmitting the SCI without a data transmission in the period based on there being no data for transmission at the wireless device in the period.

[0133] In Aspect 3, the method of Aspect 1 or Aspect 2 further includes the SCI including an indication that there is no data transmission associated with the SCI.

[0134] In Aspect 4, the method of any of aspects 1-3 further includes the indication being included in a first portion of the SCI transmitted on a PSCCH.

[0135] In Aspect 5, the method of any of aspects 1-4 further includes the indication being included in a second portion of the SCI transmitted on a PSSCH.

[0136] In Aspect 6, the method of any of aspects 1-5 further includes the SCI not reserving resources within the period and indicating a periodic reservation in a next period.

[0137] In Aspect 7, the method of any of aspects 1-6 further includes receiving HARQ feedback in response to the SCI.

[0138] In Aspect 8, the method of any of aspects 1-7 further includes receiving the HARQ feedback in a PSFCH based on one or more of a starting subchannel of a PSCCH in which the SCI is transmitted, a slot including the PSCCH in which the SCI is transmitted, a source identifier, or a destination identifier.

[0139] In Aspect 9, the method of any of aspects 1-8 further includes receiving the HARQ feedback based on the SCI being unicast.

[0140] In Aspect 10, the method of any of aspects 1-9 further includes receiving the HARQ feedback based on a second portion of the SCI being transmitted in a PSSCH.

[0141] In aspect 11, the method of any of aspects 1-10 further includes releasing remaining periodic resources of the set of periodic resources based on a determination that the wireless device does not have the data to transmit in a threshold number of consecutive periods.

[0142] In aspect 12, the method of any of aspects 1-11 further includes the wireless device releasing the remaining periodic resources based on a codepoint corresponding to a release of a periodic reservation transmitted in the SCI.

[0143] In aspect 13, the method of any of aspects 1-12 further includes determining not to transmit data in the period.

[0144] Aspect 14 is an apparatus for wireless communication that includes at least one processor coupled to a memory and configured to implement a method as in any of aspects 1-13.

[0145] Aspect 15 is an apparatus for wireless communication that includes means for implementing a method as in any of aspects 1-13.

[0146] Aspect 16 is a non-transitory computer-readable medium storing computer-executable code, where the code, when executed by a processor, causes the processor to implement a method as in any of aspects 1-13.

[0147] Aspect 17 is a method of wireless communication at a first wireless device, comprising: receiving, from a second wireless device, a reservation of a set of periodic resources for sidelink transmissions; and receiving, from the second wireless device, a SCI in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission.

[0148] In aspect 18, the method of aspect 17 further includes the indication being included in a first portion of the SCI received in a PSCCH.

[0149] In aspect 19, the method of aspect 17 or aspect 18 further includes the first wireless device refraining from attempting to decode a second portion of the SCI and the data transmission in response to receiving the indication in the first portion of the SCI.

[0150] In aspect 20, the method of any of aspects 17-19 further includes the indication being included in a second portion of the SCI received in a PSSCH.

[0151] In aspect 21, the method of any of aspects 17-20 further includes the first wireless device refraining from attempting to decode the data transmission in response to receiving the indication in the second portion of the SCI.

[0152] In aspect 22, the method of any of aspects 17-21 further includes that the SCI does not reserve resources within the period and indicates a periodic reservation in a next period.

[0153] In aspect 23, the method of any of aspects 17-22 further includes receiving a release of remaining periodic resources of the set of periodic resources, the release based on a codepoint in the SCI corresponding to a release of a periodic reservation.

[0154] In aspect 24, the method of any of aspects 17-23 further includes transmitting HARQ feedback to the second wireless device in response to the SCI.

[0155] In aspect 25, the method of any of aspects 17-24 further includes transmitting the HARQ feedback in a PSFCH based on one or more of a starting subchannel of the PSCCH in which the SCI is transmitted, a slot in which the PSCCH in which the SCI is transmitted is included, a source identifier, or a destination identifier.

[0156] In aspect 26, the method of any of aspects 17-25 further includes transmitting the HARQ feedback based on the SCI being unicast.

[0157] In aspect 27, the method of any of aspects 17-26 further includes transmitting the HARQ feedback based on a second portion of the SCI being transmitted in a PSSCH.

[0158] In aspect 28, the method of any of aspects 17-27 further includes refraining from transmitting HARQ feedback to the second wireless device in response to the SCI.

[0159] In aspect 29, the method of any of aspects 17-28 further includes that the first wireless device refrains from transmitting the HARQ feedback based on the SCI being groupcast or broadcast.

[0160] In aspect 30, the method of any of aspects 17-29 further includes that the first wireless device refrains from transmitting the HARQ feedback based on receiving the indication in a first portion of the SCI received in a PSCCH.

[0161] In aspect 31, the method of any of aspects 17-30 further includes measuring an RSRP of a PSCCH carrying the SCI and determining whether to reserve resources associated with the SCI based on the indication and the measured RSRP.

[0162] Aspect 32 is an apparatus for wireless communication including at least one processor coupled to a memory and configured to implement a method as in any of aspects 17-31.

[0163] Aspect 33 is an apparatus for wireless communication including means for implementing a method as in any of aspects 17-31.

[0164] Aspect 34 is a non-transitory computer-readable medium storing computer- executable code, where the code, when executed by a processor, causes the processor to implement a method as in any of aspects 17-31.

[0165] It should be understood that the particular order or hierarchy of blocks in the disclosed process / flow diagrams does not inherently impose a limitation on the scope of the corresponding method. Based upon design choices and other factors, it is within the scope of the corresponding method to reposition the steps / blocks. Also, some of the blocks can be optional. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

[0166] The preceding description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." Terms such as "if," "when," and "while" should be interpreted to mean "under the condition that" rather than imply a temporal or chronological relationship. That is, these phrases are not intended to mean that the action only happens or is performed in a response to or in the timeframe of, the stated condition, but rather only that the stated condition needs to be satisfied or met before the specified action happens or is performed. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term "some" refers to one or more. Combinations such as "at least one of A, B, or C," "one or more of A, B, or C," "at least one of the group consisting of A, B, and C," "one or more of the group consisting of A, B, and C," and "A, B, and / or C" include in combinations A, B, and / or C, and can include multiple A's, B's, or C's. In other words, "at least one of A, B, and C" and "A and / or B and / or C" mean that the group consisting of A, B, and C, for example, can be used, where A is distinct from B and B is distinct from C or where A is the same as B and B is the same as C or where A is the same as B and B is the same as C. Throughout this disclosure the term "group" is used to describe one or more members of a group. The elements of the various aspects described throughout this disclosure are intended to be combinable with each other, unless otherwise indicated. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words "module," "mechanism," "element," "device," and the like can not be exclusive of the word "means." Therefore, any claim that is dependent on another claim should not be construed to be limited to the combination of elements in the dependent claim as opposed to being able to be practiced with any of the combinations of elements set forth in the dependent claim.

Claims

1. An apparatus for wireless communication at a wireless device, comprising: a memory; and at least one processor coupled to the memory and configured to: reserve a set of periodic resources for sidelink transmissions, wherein the reserved set of periodic resources includes reserved resources for sidelink control information, SCI, and reserved resources for data; and transmit the SCI without a data transmission in the periodic resources of a period, wherein the SCI includes an indication of no data transmission associated with the SCI, wherein the indication is included in a first portion of the SCI transmitted on a physical sidelink control channel, PSCCH.

2. The apparatus of claim 1, wherein the wireless device transmits the SCI without the data transmission in the period based on no data for transmission at the wireless device in the period.

3. The apparatus of claim 1, wherein the indication is included in a second portion of the SCI transmitted on a physical sidelink shared channel, PSSCH.

4. The apparatus of claim 1, wherein the SCI reserves no resources within the period and indicates a periodic reservation in a next period.

5. The apparatus of claim 1, wherein the at least one processor is further configured to: receive a hybrid automatic repeat request, HARQ, feedback in response to the SCI.

6. The apparatus of claim 5, wherein the HARQ feedback is received in a physical sidelink feedback channel, PSFCH, based on one or more of: a starting subchannel of the PSCCH in which the SCI is transmitted, a slot that includes the PSCCH in which the SCI is transmitted, a source identifier, or a destination identifier.

7. The apparatus of claim 5, wherein the HARQ feedback is unicast based on the SCI.

8. The apparatus of claim 5, wherein the HARQ feedback is based on a second portion of the SCI transmitted in a physical sidelink shared channel, PSSCH.

9. The apparatus of claim 1, wherein the at least one processor is further configured to: release remaining periodic resources of the set of periodic resources in response to the wireless device having no data to transmit in a threshold number of consecutive periods.

10. The apparatus of claim 9, wherein the wireless device releases the remaining periodic resources based on a codepoint corresponding to a release of a periodic reservation transmitted in the SCI.

11. A method of wireless communication at a wireless device, comprising: reserving a set of periodic resources for sidelink transmissions, wherein the reserved set of periodic resources includes reserved resources for sidelink control information, SCI, and reserved resources for data; and transmitting the SCI without a data transmission in the periodic resources of a period, wherein the SCI includes an indication of no data transmission associated with the SCI, wherein the indication is included in a first portion of the SCI transmitted on a physical sidelink control channel, PSCCH.

12. The method of claim 11, wherein the wireless device transmits the SCI without the data transmission in the period based on there being no data for transmission at the wireless device in the period.

13. The method of claim 11, wherein the indication is included in a second portion of the SCI transmitted on a physical sidelink shared channel (PSSCH).

14. The method of claim 11, wherein the SCI does not reserve resources within the period and indicates a periodic reservation in a next period.

15. The method of claim 11, further comprising: receiving hybrid automatic repeat request (HARQ) feedback in response to the SCI.

16. The method of claim 15, wherein the HARQ feedback is received in a physical sidelink feedback channel (PSFCH) based on one or more of: a starting subchannel of the PSCCH in which the SCI is transmitted, a slot comprising the PSCCH in which the SCI is transmitted, a source identifier, or a destination identifier.

17. The method of claim 15, wherein the HARQ feedback is received based on the SCI being unicast.

18. The method of claim 15, wherein the HARQ feedback is received based on a second portion of the SCI being transmitted in a physical sidelink shared channel (PSSCH).

19. The method of claim 11, further comprising: releasing remaining periodic resources of the set of periodic resources based on determining that the wireless device has no data to transmit in a threshold number of consecutive periods.

20. An apparatus for wireless communication at a first wireless device, comprising: a memory; and at least one processor coupled to the memory and configured to: receive, from a second wireless device, a reservation of a set of periodic resources for sidelink transmissions; and receive, from the second wireless device, a sidelink control information (SCI) in a period of the set of periodic resources, the SCI including an indication that the SCI is not associated with a data transmission, wherein the indication is included in a first portion of the SCI in a physical sidelink control channel (PSCCH); and in response to receiving the indication in the first portion of the SCI, refrain from attempting to decode a second portion of the SCI and the data transmission.

21. The apparatus of claim 20, wherein the at least one processor is further configured to: measure a reference signal received power (RSRP) of the PSCCH carrying the SCI; and determine whether resources associated with the SCI are reserved based on the indication and the measured RSRP.

22. The apparatus of claim 20, wherein the SCI does not reserve resources within the period and indicates a periodic reservation in a next period.

23. The apparatus of claim 20, wherein the at least one processor is further configured to: receiving a release of remaining periodic resources of the set of periodic resources, the release based on a codepoint in the SCI corresponding to a periodic reservation release.

24. The apparatus of claim 20, wherein the at least one processor is further configured to: transmit, to the second wireless device, hybrid automatic repeat request (HARQ) feedback in response to the SCI.

25. A method of wireless communication at a first wireless device, comprising: receiving, from a second wireless device, a reservation of a set of periodic resources for a sidelink transmission; and receiving, from the second wireless device, sidelink control information (SCI) in a period of the set of periodic resources, the SCI including an indication that the SCI is not associated with a data transmission, wherein the indication is included in a first portion of the SCI in a physical sidelink control channel (PSCCH); and avoiding attempting to decode a second portion of the SCI and the data transmission in response to receiving the indication in the first portion of the SCI.

26. The method of claim 25, further comprising: measuring a reference signal received power (RSRP) of the PSCCH carrying the SCI; and determining whether resources associated with the SCI are reserved based on the indication and the measured RSRP.

27. The method of claim 25, wherein the SCI does not reserve resources within the period and indicates a periodic reservation in a next period.

28. The method of claim 25, further comprising: receiving a release of remaining periodic resources of the set of periodic resources, the release based on a codepoint in the SCI corresponding to a periodic reservation release.

29. The method of claim 25, further comprising: transmitting, to the second wireless device, hybrid automatic repeat request (HARQ) feedback in response to the SCI.

30. An apparatus for wireless communication at a wireless device, the apparatus comprising means for implementing a method of any of claims 11-19.

31. An apparatus for wireless communication at a first wireless device, the apparatus comprising means for implementing a method of any of claims 25-29.

32. A non-transitory computer-readable medium storing computer-executable code, where the computer-executable code, when executed by a processor of a wireless device, causes the processor to implement a method of any of claims 11-19.

33. A non-transitory computer-readable medium storing computer-executable code, where the computer-executable code, when executed by a processor of a first wireless device, causes the processor to implement a method of any of claims 25-29.

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