Acknowledgement feedback transmission for sidelink communications in unlicensed spectrum

Abstract

Certain aspects of the present disclosure provide a method for wireless communication by a transmitting UE. The method generally includes transmitting a data transmission to at least one receiving UE in an unlicensed spectrum for sidelink communication, determining whether resources in a time slot are available for the at least one receiving UE to provide acknowledgment feedback for the data transmission, and transmitting a reservation signal in the time slot if the resources are determined to be available.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application hereby claims priority to Greek Provisional Application No. 20200100363, filed on June 24, 2020, which is assigned to the assignee of the present application and is hereby expressly incorporated herein by reference in its entirety as if fully set forth below and for all applicable purposes.

[0003] Public domain

[0004] Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for transmitting acknowledgment feedback in sidelink communications.

[0005] Related technical description

[0006] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcast, etc. These wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of such multiple-access systems include Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, 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, to name just a few.

[0007] These multiple access technologies have been adopted in various telecommunication standards to provide common protocols that enable different wireless devices to communicate at city, country, region, and even global levels. New radio (e.g., 5G NR) is an example of an emerging telecommunication standard. NR is an enhancement set of the LTE mobile standard promulgated by 3GPP. NR is designed to better support mobile broadband Internet access by using OFDMA with cyclic prefix (CP) on downlink (DL) and uplink (UL) to improve spectrum efficiency, reduce costs, improve services, utilize new spectrum, and better integrate with other open standards. To this end, NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

[0008] However, as the demand for mobile broadband access continues to grow, there is a need for further improvements to NR and LTE technologies. Preferably, these improvements should be applicable to other multiple access technologies and the telecommunication standards that employ these technologies.

[0009] Overview

[0010] The systems, methods, and devices of the present disclosure each have several aspects, no single aspect of which is solely responsible for its desirable attributes. Without limiting the scope of the present disclosure as expressed in the appended claims, some features will now be briefly discussed. After considering this discussion, and especially after reading the section entitled "Detailed Description," it will be understood how the features of the present disclosure provide advantages including improved acknowledgment feedback transmission for sidelink communications.

[0011] Certain aspects of the subject matter described in the present disclosure may be implemented in a method for wireless communication by a transmitting user equipment (UE). The method generally includes transmitting a data transmission to at least one receiving UE in an unlicensed spectrum for sidelink communication, determining whether resources in a time slot are available for the at least one receiving UE to provide acknowledgment feedback for the data transmission, and transmitting a reservation signal in the time slot if the resources are determined to be available.

[0012] Certain aspects of the subject matter described in the present disclosure may be implemented in a method for wireless communication by a receiving user equipment (UE). The method generally includes: receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; monitoring a reservation signal from the transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide acknowledgment feedback for the data transmission; and transmitting the acknowledgment feedback for the data transmission if the reservation signal is detected.

[0013] Certain aspects of the subject matter described in the present disclosure may be implemented in a transmitting user equipment (UE). The transmitting UE generally includes means for transmitting a data transmission to at least one receiving UE in an unlicensed spectrum for sidelink communication, means for determining whether resources in a time slot are available for the at least one receiving UE to provide acknowledgement feedback for the data transmission, and means for transmitting a reservation signal in the time slot if the resources are determined to be available.

[0014] Certain aspects of the subject matter described in the present disclosure may be implemented in a receiving user equipment (UE). The receiving UE generally includes: means for receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; means for monitoring a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide acknowledgment feedback for the data transmission; and means for transmitting the acknowledgment feedback for the data transmission if the reservation signal is detected.

[0015] Certain aspects of the subject matter described in the present disclosure may be implemented in a transmitting user equipment (UE). The transmitting UE generally includes: a transmitter configured to transmit data to at least one receiving UE in an unlicensed spectrum for sidelink communication; and a processing system configured to determine whether resources in a time slot are available for the at least one receiving UE to provide acknowledgement feedback for the data transmission, wherein the transmitter is further configured to transmit a reservation signal in the time slot if the resources are determined to be available.

[0016] Certain aspects of the subject matter described in the present disclosure may be implemented in a receiving user equipment (UE). The receiving UE generally includes: a receiver configured to receive a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; a processing system configured to monitor a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide an acknowledgment feedback for the data transmission; and a transmitter configured to transmit the acknowledgment feedback for the data transmission if the reservation signal is detected.

[0017] Certain aspects of the subject matter described in the present disclosure may be implemented in an apparatus for wireless communication. The apparatus generally includes: an interface configured to output data for transmission to at least one user equipment (UE) in an unlicensed spectrum for sidelink communication; and a processing system configured to determine whether resources in a time slot are available for the at least one UE to provide acknowledgement feedback for the data transmission, wherein the interface is further configured to output a reservation signal for transmission in the time slot if the resources are determined to be available.

[0018] Certain aspects of the subject matter described in the present disclosure may be implemented in an apparatus for wireless communication by a receiving user equipment (UE). The apparatus generally includes: an interface configured to obtain a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; and a processing system configured to monitor a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide acknowledgment feedback for the data transmission, wherein the interface is further configured to provide the acknowledgment feedback for the data transmission in the event of detecting the reservation signal.

[0019] Certain aspects of the subject matter described in the present disclosure can be implemented in a computer-readable medium for wireless communication. The computer-readable medium generally includes code executable to perform the following operations: perform a data transmission to at least one receiving UE in an unlicensed spectrum for sidelink communication, determine whether resources in a time slot are available for the at least one receiving UE to provide acknowledgment feedback for the data transmission, and transmit a reservation signal in the time slot if the resources are determined to be available.

[0020] Certain aspects of the subject matter described in the present disclosure may be implemented in a computer-readable medium for wireless communication by a receiving user equipment (UE). The computer-readable medium generally includes code executable to perform the following operations: receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; monitoring a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide acknowledgment feedback for the data transmission; and transmitting the acknowledgment feedback for the data transmission in the event of detecting the reservation signal.

[0021] Aspects of the present disclosure provide apparatuses, devices, processors, and computer-readable media for performing the methods described herein.

[0022] To achieve the foregoing and related ends, one or more aspects include features fully described below and particularly pointed out in the claims. The following description and the accompanying drawings set forth in detail certain illustrative features of one or more aspects. However, these features are only indicative of several of the various ways in which the principles of the various aspects can be employed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to understand in detail the manner in which the above-stated features of the present disclosure are used, a more particular description of the content briefly summarized above may be made with reference to various aspects, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only certain typical aspects of the present disclosure and are not to be considered limiting of its scope, as the description may admit to other equally effective aspects.

[0025] Figure 1 is a block diagram conceptually illustrating an example telecommunications system in accordance with certain aspects of the present disclosure.

[0026] Figure 2 is a block diagram conceptually illustrating designs of example base stations (BSs) and user equipment (UEs) in accordance with certain aspects of the present disclosure.

[0027] Figure 3 is an example frame format for certain wireless communication systems (e.g., New Radio (NR)) in accordance with certain aspects of the present disclosure.

[0028] Figure 4A and Figure 4B A pictorial representation of an example vehicle-to-everything (V2X) system is illustrated in accordance with certain aspects of the present disclosure.

[0029] Figure 5 Illustrated are example resources for sidelink communications.

[0030] Figure 6

[0013] Example operations for wireless communications by a transmitting user equipment (UE) are illustrated in accordance with certain aspects of the present disclosure.

[0031] Figure 7

[0013] Example operations for wireless communications by a recipient UE are illustrated in accordance with certain aspects of the present disclosure.

[0032] Figure 8 Illustrated is an example timeline for acknowledgment feedback for sidelink communications in accordance with certain aspects of the present disclosure.

[0033] Fig. 9 Illustrated is an example timeline for acknowledgment feedback for sidelink communications in accordance with certain aspects of the present disclosure.

[0034] Fig.10 Illustrated are communications devices that may include various components configured to perform operations for the techniques disclosed herein in accordance with aspects of the present disclosure.

[0035] Fig.11 Illustrated are communications devices that may include various components configured to perform operations for the techniques disclosed herein in accordance with aspects of the present disclosure.

[0036] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized in other aspects without specific recitation.

[0037] Detailed Description

[0038] Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for transmitting acknowledgment feedback in sidelink communications using unlicensed spectrum.

[0039] In New Radio (NR), user equipment (UE) can exchange sidelink data (e.g., user data and control signaling) directly with other UEs without the assistance (e.g., relay) of a base station. This type of sidelink communication is often referred to as peer-to-peer (also referred to as device-to-device or D2D) communication. Examples of peer-to-peer communication include vehicle-to-everything (V2X) communication, where a vehicle can communicate with another vehicle (V2V) or a different device (such as a base station, a traffic control system, etc.).

[0040] One challenge in a V2X system is to confirm safe reception of sidelink data by a receiving UE (also referred to as an Rx UE). That is, in order to improve sidelink communication, the Rx UE may need to send positive (or negative) feedback (e.g., hybrid automatic repeat request (HARQ) feedback) to a transmitting UE (also referred to as a Tx UE) to confirm successful (or unsuccessful) reception of the data. For example, when the Rx UE does not successfully decode the data received from the Tx UE, the Rx UE may need to send a negative acknowledgement (NACK) to the Tx UE to indicate to the Tx UE that the data transmission was unsuccessful.

[0041] The following description provides an example of HARQ feedback transmission in sidelink communication, but does not limit the scope, applicability or examples set forth in the claims. Changes may be made to the functions and arrangements of the elements discussed without departing from the scope of the present disclosure. Various examples may appropriately omit, replace, or add various procedures or components. For example, the described method may be performed in an order different from the order described, and various steps may be added, omitted, or combined. Moreover, the features described with reference to some examples may be combined in some other examples. For example, any number of aspects set forth herein may be used to implement a device or practice method. In addition, the scope of the present disclosure is intended to cover such devices or methods practiced using other structures, functionalities, or structures and functionalities as supplements to the various aspects of the present disclosure set forth herein or in addition. It should be understood that any aspect of the present disclosure disclosed herein may be implemented by one or more elements of the claims. The wording "exemplary" is used herein to mean "used as an example, instance, or explanation". Any aspect described as "exemplary" herein is not necessarily to be interpreted as being superior to or superior to other aspects.

[0042] In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a specific radio access technology (RAT) and may operate on one or more frequencies. RAT may also be referred to as a radio technology, air interface, etc. Frequency may also be referred to as a carrier, subcarrier, frequency channel, frequency tone, subband, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs.

[0043] The techniques described herein can be used for various wireless networks and radio technologies. Although various aspects may be described herein using terms typically associated with 3G, 4G, and / or new radio (e.g., 5G NR) wireless technologies, various aspects of the present disclosure may be applied in communication systems based on other generations.

[0044] NR access can support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHz or more), millimeter wave (mmW) targeting high carrier frequency (e.g., 24 GHz to 53 GHz or more), massive machine type communication MTC (mMTC) targeting non-backward compatible MTC technology, and / or mission critical services targeting ultra-reliable low latency communication (URLLC). These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTIs) to meet corresponding quality of service (QoS) requirements. In addition, these services can coexist in the same subframe. NR supports beamforming and the beam direction can be dynamically configured. MIMO transmission with precoding can also be supported. MIMO configuration in DL can support up to 8 transmit antennas (with multi-layer DL transmission of up to 8 streams) and up to 2 streams per UE. Multi-layer transmission of up to 2 streams per UE can be supported. Aggregation of multiple cells can be supported using up to 8 serving cells.

[0045] Figure 1 1 is a block diagram conceptually illustrating an example wireless communication network 100 in which certain aspects of the present disclosure may be practiced. For example, UEs 120a and 120b may include, among other modules / managers, sidelink (SL) feedback managers 122a and 122b, respectively, which are configured to perform the following described Figure 6 Operation 600 and Figure 7 Operation 700.

[0046] The wireless communication network 100 may be, for example, a NR system (eg, a 5G NR network). Figure 1 As shown in , the wireless communication network 100 may be in communication with a core network 132. The core network 132 may be in communication with one or more base stations (BSs) 110 and / or user equipments (UEs) 120 in the wireless communication network 100 via one or more interfaces.

[0047] like Figure 1 As illustrated in , the wireless communication network 100 may include several BSs 110a-z (each also individually referred to herein as BS 110, or collectively referred to as BS 110) and other network entities. BS 110 may provide communication coverage for a particular geographic area (sometimes referred to as a "cell"), which may be stationary or mobile depending on the location of the mobile BS 110. In some examples, BS 110 may be interconnected to each other and / or to one or more other BSs or network nodes (not shown) in the wireless communication network 100 via various types of backhaul interfaces (e.g., direct physical connections, wireless connections, virtual networks, etc.) using any suitable transport network. Figure 1In the example shown in FIG. 1 , BSs 110a, 110b, and 110c may be macro BSs for macro cells 102a, 102b, and 102c, respectively. BS 110x may be a pico BS for pico cell 102x. BSs 110y and 110z may be femto BSs for femto cells 102y and 102z, respectively. A BS may support one or more cells.

[0048] BS 110 communicates with UEs 120a-y (each also individually referred to herein as UE 120, or collectively referred to as UE 120) in the wireless communication network 100. UEs 120 (e.g., 120x, 120y, etc.) may be dispersed throughout the wireless communication network 100, and each UE 120 may be stationary or mobile. The wireless communication network 100 may also include a relay station (e.g., relay station 110r) (also referred to as a relay, etc.) that receives transmissions of data and / or other information from an upstream station (e.g., BS 110a or UE 120r) and sends transmissions of the data and / or other information to a downstream station (e.g., UE 120 or BS 110), or that relays transmissions between UEs 120 to facilitate communication between the devices.

[0049] Figure 2 1 and 120a (eg, Figure 1 Example components of a wireless communication network 100).

[0050] At BS 110a, transmit processor 220 may receive data from data source 212 and control information from controller / processor 240. The control information may be for a physical broadcast channel (PBCH), a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH), a physical downlink control channel (PDCCH), a group common PDCCH (GC PDCCH), etc. The data may be for a physical downlink shared channel (PDSCH), etc. A medium access control (MAC)-control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. The MAC-CE may be carried in a shared channel, such as a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

[0051] The processor 220 may process (e.g., encode and symbol map) data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols (such as for a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a PBCH demodulation reference signal (DMRS), and a channel state information reference signal (CSI-RS)). The transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on ​​data symbols, control symbols, and / or reference symbols, where applicable, and may provide an output symbol stream to a modulator (MOD) 232a-232t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator may further process (e.g., convert to analog, amplify, filter, and up-convert) the output sample stream to obtain a downlink signal. The downlink signals from the modulators 232a-232t may be transmitted via antennas 234a-234t, respectively.

[0052] At UE 120a, antennas 252a-252r may receive downlink signals from BS 110a and may provide received signals to demodulators (DEMODs) 254a-254r in the transceiver, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all demodulators 254a-254r, perform MIMO detection on the received symbols where applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for UE 120a to a data sink 260, and provide decoded control information to a controller / processor 280.

[0053] On the uplink, at the UE 120a, a transmit processor 264 may receive and process data from a data source 262 (e.g., for a physical uplink shared channel (PUSCH)) and control information from a controller / processor 280 (e.g., for a physical uplink control channel (PUCCH)). The transmit processor 264 may also generate reference symbols for reference signals (e.g., a sounding reference signal (SRS)). The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266, if applicable, further processed by modulators 254a-254r in the transceiver (e.g., for SC-FDM, etc.), and transmitted to the BS 110a. At the BS 110a, the uplink signal from the UE 120a may be received by the antenna 234, processed by the modulator 232, detected by the MIMO detector 236, if applicable, and further processed by the receive processor 238 to obtain decoded data and control information sent by the UE 120a. Receive processor 238 may provide decoded data to data sink 239 and decoded control information to controller / processor 240 .

[0054] Memories 242 and 282 may store data and program codes for BS 110a and UE 120a, respectively.A scheduler 244 may schedule UEs for data transmission on the downlink and / or uplink.

[0055] The antennas 252, processors 266, 258, 264 and / or controller / processor 280 of the UE 120a, and / or the antennas 234, processors 220, 230, 238 and / or controller / processor 240 of the BS 110a may be used to perform the various techniques and methods described herein. Figure 2 As shown in FIG. 1 , the controller / processor 280 of the UE 120a may have a SL feedback manager 281 configured for (HARQ) feedback transmission according to various aspects described herein. Although shown at the controller / processor, other components of the UE 120a and the BS 110a may also be used to perform the operations described herein.

[0056] NR can utilize orthogonal frequency division multiplexing (OFDM) with cyclic prefix (CP) on uplink and downlink. NR can support half-duplex operation using time division duplex (TDD). OFDM and single carrier frequency division multiplexing (SC-FDM) divide the system bandwidth into multiple orthogonal subcarriers, which are also often called frequency modulation, frequency slot, etc. Each subcarrier can be modulated with data. Modulation codewords can be sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers can be fixed, and the total number of subcarriers can depend on the system bandwidth. The minimum resource allocation (so-called resource block (RB)) can be 12 consecutive subcarriers. The system bandwidth can also be divided into subbands. For example, one subband can cover multiple RBs. NR can support a base subcarrier spacing (SCS) of 15KHz, and other SCSs (e.g., 30kHz, 60kHz, 120kHz, 240kHz, etc.) can be defined relative to the base SCS.

[0057] Figure 3 300 is a diagram showing an example of a frame format for NR. The transmission timeline of each of the downlink and uplink may be divided into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 ms) and may be divided into 10 subframes with indices 0 to 9, each subframe being 1 ms. Each subframe may include a variable number of slots (e.g., 1, 2, 4, 8, 16, ... slots), depending on the SCS. Each slot may include a variable number of symbol periods (e.g., 7, 12, or 14 symbols), depending on the SCS. An index may be assigned to the symbol period in each slot. A mini slot (which may be referred to as a subslot structure) refers to a transmission time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols). Each symbol in a slot may indicate a link direction (e.g., DL, UL, or flexible) for data transmission, and the link direction for each subframe may be dynamically switched. The link direction may be based on the slot format. Each time slot may include DL / UL data and DL / UL control information.

[0058] In NR, synchronization signal blocks (SSBs) are transmitted. In certain aspects, each SSB may be transmitted in a burst, where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and / or beam refinement). The SSBs include the PSS, SSS, and a two-symbol PBCH. The SSBs may be transmitted at fixed timeslot locations (such as Figure 3PBCH is transmitted in the symbols 0-3 shown in . PSS and SSS can be used by UE for cell search and acquisition. PSS can provide half-frame timing, while SS can provide CP length and frame timing. PSS and SSS can provide cell identity. PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frames, SS burst set periodicity, system frame number, etc.

[0059] SSBs may be organized into SS bursts to support beam sweeping. Further system information, such as Remaining Minimum System Information (RMSI), System Information Block (SIB), Other System Information (OSI), may be transmitted on the Physical Downlink Shared Channel (PDSCH) in certain subframes. SSBs may be transmitted up to 64 times, for example, up to 64 different beam directions for millimeter wave (mmWave). Multiple transmissions of SSBs are referred to as SS burst sets. SSBs in an SS burst set may be transmitted in the same frequency region, while SSBs in different SS burst sets may be transmitted in different frequency regions.

[0060] In some examples, the communication between UE 120 and BS 110 is referred to as an access link. The access link may be provided via a Uu interface. The communication between devices may be referred to as a side link.

[0061] In some examples, two or more subordinate entities (e.g., UE 120) can use sidelink signals to communicate with each other. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relay, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh networks, and / or various other suitable applications. In general, a sidelink signal may refer to a communication from a subordinate entity (e.g., UE 120a, e.g., Figure 1 )) to another subordinate entity (e.g., UE 122a UE 120) without relaying the signal of the communication through a scheduling entity (e.g., UE 120 or BS 110), even though the scheduling entity may be used for scheduling and / or control purposes. In some examples, the sidelink signal may be communicated using a licensed spectrum (unlike wireless local area networks, which typically use unlicensed spectrum). An example of a sidelink communication is PC5, for example, as used in V2V, LTE, and / or NR.

[0062] Various sidelink channels may be used for sidelink communications, including a physical sidelink discovery channel (PSDCH), a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH may carry discovery expressions that enable neighboring devices to discover each other. The PSCCH may carry control signaling (such as sidelink resource configuration and other parameters for data transmission), while the PSSCH may carry data transmission. The PSFCH may carry sidelink feedback, such as distance-based and / or non-distance-based HARQ feedback related to data transmission between two or more UEs communicating directly with each other.

[0063] Figure 4A and Figure 4B A diagrammatic representation of an example V2X system according to some aspects of the present disclosure is shown. For example, as described herein, Figure 4A and Figure 4B The vehicle shown in can perform data transmissions via a sidelink channel and can receive sidelink feedback regarding those data transmissions.

[0064] Figure 4A and Figure 4B The V2X system shown in Figure 1 provides two complementary transmission modes. Figure 4A The first transmission mode shown as an example in FIG. 4 may involve direct communication (also referred to as sidelink communication) between parties that are adjacent to each other in a local area. Sidelink transmission of UEs (e.g., vehicles 402 and 404, or traffic lights 410) may be implemented via a PC5 interface (e.g., a wireless communication interface between a first UE and a second UE). Figure 4B The second transmission mode shown as an example in may involve network communication through the network, which may be achieved through a Uu interface (eg, a wireless communication interface between a radio access network (RAN) and a UE).

[0065] Reference Figure 4A , a V2X system 400 (e.g., vehicle-to-vehicle (V2V) communications) is illustrated with two vehicles 402, 404. A first transmission mode allows direct communication between different parties in a given geographic location. As illustrated, the vehicles may have a wireless communication link 406 (V2P) with an individual (e.g., with the individual's mobile phone) through a PC5 interface. Communications between vehicles 402 and 404 may also occur through a PC5 interface 408. Communications (V2I) from vehicle 402 to other highway components (e.g., highway components 410 (such as traffic signals or signs)) may occur in a similar manner through a PC5 interface 412. For Figure 4AFor each communication explained in , two-way communication is possible between elements, so each element can be both a sender and a receiver of information.

[0066] The V2X system 400 may be a self-managed system implemented without assistance from a network entity. A self-managed system may achieve improved spectrum efficiency, reduced costs, and increased reliability because no network service interruption occurs during handover operations for moving vehicles. The V2X system may be configured to operate in licensed and / or unlicensed spectrum, whereby any vehicle with an equipped system may access a common frequency and share information. Such coordinated / shared spectrum operations allow for safe and reliable operation.

[0067] Figure 4B A V2X system 450 is shown for communicating between a vehicle 452 and a vehicle 454 via a network entity 456. These network communications may be accomplished via discrete nodes (such as a BS (e.g., a BS)) that send information to and receive information from the vehicles 452, 454 (e.g., relay information between the vehicles 452, 454). Figure 1 10a)) occurs. Network communications via vehicle-to-network (V2N) links 458 and 410 can be used, for example, for long-range communications between vehicles, such as for communicating that there is a traffic accident at a distance ahead along a road or highway. Other types of communications, such as traffic flow conditions, road hazard warnings, environmental / weather reports, and service station availability, etc., can be sent by wireless nodes to vehicles. Such data can be obtained from cloud-based sharing services.

[0068] Example HARQ feedback transmission for sidelink communications in unlicensed spectrum

[0069] Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for transmitting acknowledgment feedback in sidelink communications using unlicensed spectrum.

[0070] Current cellular V2X communication designs are targeted for deployment in licensed spectrum. Such designs typically share spectrum in licensed cellular bands or dedicated ITS (Intelligent Transport System) spectrum. In licensed cellular spectrum, V2X systems share uplink spectrum in cellular networks. In dedicated ITS spectrum, spectrum around 5.9 GHz is allocated for V2X in some areas.

[0071] Due to spectrum scarcity, dedicated spectrum is not guaranteed in some areas. For example, in some regions / countries, dedicated spectrum is allocated for LTE V2X (specified in LTE Release 14 and Release 15), but no spectrum is available for NR V2X (specified in NR Release 16 for advanced V2X use cases such as autonomous driving).

[0072] As a result, cellular V2X communications will most likely be deployed in unlicensed spectrum, as this may be the only option in some areas. However, unlicensed spectrum may be shared by other technologies such as Wi-Fi. Currently, 3GPP does not have provisions for such unlicensed operations for cellular V2X, which may be due to various factors (e.g., considering regulatory requirements for unlicensed spectrum such as listen before talk (LBT), channel occupancy restrictions, etc.).

[0073] For V2X (or sidelink / D2D in general) communications in unlicensed spectrum, it may be desirable to enable HARQ feedback as a mechanism to help ensure quality of service. In such scenarios, the data transmitting UE may retransmit a packet if a previous transmission failed (e.g., as indicated by receiving NACK feedback).

[0074] The implementation of sidelink HARQ feedback transmission may depend on the specific transmission mode. For example, for unicast transmission mode, a single receiving UE transmits HARQ feedback. For groupcast (broadcast / multicast) transmission, multiple receiving UEs may transmit HARQ feedback for the same data transmitter.

[0075] The use of unlicensed spectrum is typically subject to various regulatory requirements, depending on the region. One of the requirements is Listen Before Talk (LBT): it forces a device to transmit in an unlicensed channel only if the channel is sensed to be idle (by listening). LBT may mean that the device performs a Clear Channel Assessment (CCA), which involves measuring the energy or power in the channel over a certain duration of time. The exact time at which the device transmits may depend on the specific category of LBT. For Category 2 (CAT 2) LBT, the device transmits if the CCA indicates that the channel is idle; for example, as specified in the Type 2 channel access procedure in 3GPP. For Category 4 (CAT 4) LBT, the device performs a random backoff (extended CCA) within the contention window if the CCA indicates that the channel is idle, and transmits only if the channel remains idle during the backoff period; for example, as specified in the Type 1 channel access procedure in 3GPP.

[0076] Sidelink HARQ feedback transmission in unlicensed spectrum is also subject to channel availability. This constraint may be even more challenging considering feedback transmission in multicast communications.

[0077] Figure 5An example sidelink HARQ feedback timeline is illustrated. In the illustrated example, UE1 transmits a data packet (e.g., in PSSCH) in time slot n and expects HARQ feedback from one (unicast) or multiple (multicast) receiving UEs in time slot n+k. The scheduling parameter k allows the receiving UE a certain amount of time to decode the data transmission. In other words, the receiving UE may not be able to transmit HARQ feedback immediately after data channel reception.

[0078] exist Figure 5 In the example of , if a receiving UE receives data transmission in time slot n and the HARQ feedback processing (data channel decoding and HARQ signal generation) time requires k time slots, the receiving UE will not be able to transmit HARQ feedback earlier than time slot n+k.

[0079] However, as mentioned above, HARQ feedback transmission may also be subject to LBT. For example, when data transmission ends at time slot n, but HARQ feedback transmission does not occur until time slot n+k, there will be a gap between data transmission and HARQ feedback transmission. If the gap is larger than a threshold time (e.g., 16us), LBT channel sensing may be required to ensure that the channel is (still) available for HARQ feedback transmission (in many scenarios the processing time is likely to be much larger than 16us).

[0080] Various aspects of the present disclosure provide a HARQ feedback transmission mechanism for V2X communications in unlicensed / shared spectrum. As will be described in more detail below, after data transmission, a transmitting UE (Tx UE) may perform channel sensing to determine whether sidelink resources are available for HARQ feedback, and may send a reservation signal to reserve the resources and indicate the availability to one or more receiving (Rx) UEs.

[0081] Figure 6 and 7 Operations 600 and 700 for HARQ feedback from a Tx UE and an Rx UE are illustrated, respectively. Figure 8 These operations can be understood by referring to the example sidelink HARQ timeline shown in FIG.

[0082] Figure 6 6 illustrates example operations 600 for wireless communications by a transmitting UE in accordance with certain aspects of the present disclosure. Operations 600 may be performed, for example, by a Tx UE (e.g., such as UE 120a (e.g., in wireless communication network 100) Figure 1 )) is performed to transmit sidelink data and signal a receiving UE whether resources are available for acknowledging the data.

[0083] Operations 600 begin, at 602, with transmitting data to at least one receiving UE in an unlicensed spectrum for sidelink communication. Figure 8 As shown in , data may be transmitted in the PSSCH. One or more Rx UEs may receive data transmission from a Tx UE.

[0084] At 604, the transmitting UE determines whether resources in the time slot are available for the at least one receiving UE to provide acknowledgement feedback for the data transmission. At 606, the transmitting UE transmits a reservation signal in the time slot if the resources are determined to be available.

[0085] like Figure 8 As shown in , after data transmission, the Tx UE senses the channel to determine whether resources are available for HARQ feedback transmission. If the channel (e.g., in a PSFCH slot) is determined to be idle based on the sensing, the Tx UE transmits a reservation signal in the PSFCH slot (to reserve the resource and indicate availability to one or more Rx UEs).

[0086] Figure 7 Example operations 700 for wireless communications by a receiving UE are illustrated and may be considered similar to Figure 6 For example, operation 700 may be performed by an Rx UE (eg, such as UE 120b (eg, in wireless communication network 100)). Figure 1 )) to execute from (execute Figure 6 ) of operations 600 of the Tx UE receives sidelink data, monitors for indications that resources are available to acknowledge the data, and transmits an acknowledgement if such resources are available.

[0087] Operations 700 begin at 702, receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication. At 704, the receiving UE monitors a reservation signal from the transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide an acknowledgment feedback for the data transmission; alternatively, the receiving UE monitors a reservation signal from the transmitting UE, the reservation signal triggering the receiving UE to provide an acknowledgment feedback for the data transmission. At 706, the receiving UE transmits an acknowledgment feedback for the data transmission if the reservation signal is detected.

[0088] There are various alternatives for determining the time slot for sidelink HARQ feedback. For example, according to a first alternative, the time slot may be configured for HARQ feedback transmission (e.g., via RRC signaling), or may be preconfigured. In this case, the Tx UE senses in one of the configured HARQ feedback time slots to determine whether it is idle. According to a second alternative, there may be no dedicated time slot for HARQ feedback transmission. In this case, the Tx UE senses in a time slot determined based on a (pre)configured / predefined HARQ timeline. For example, the parameter k when determining the HARQ timeline has a configured or preconfigured value; the Tx UE or Rx UE determines the time slot to be used for HARQ feedback transmission based on the k value.

[0089] In either case, if the Tx UE determines based on sensing that the channel is idle, the Tx UE transmits a reservation signal in the time slot. As mentioned above, the reservation signal serves two general purposes. First, the transmission of the reservation signal reserves resources because other devices that sense the reservation signal will postpone their transmissions. For example, when a Wi-Fi device senses the channel, it will see a busy channel (due to the reservation signal), and thus later HARQ feedback will not be interfered with.

[0090] Secondly, the reservation signal will trigger the Rx UE(s) to transmit its HARQ feedback. The Rx UE will detect the reservation signal in the HARQ feedback slot based on one of the alternatives discussed above: the HARQ feedback slot may be determined based on the HARQ timeline or the HARQ slot (pre) configuration (and the HARQ timeline). The Rx UE may transmit the HARQ feedback (e.g. Figure 8 (explained in ).

[0091] For Tx UE, channel sensing may be CCA (Clear Channel Assessment) based on energy detection. In such a case, if the energy (or power) measured during the sensing period is less than a threshold, the channel may be considered to be idle.

[0092] If the Tx UE senses that the channel is idle, it may transmit a reservation signal according to various options. According to a first option, the Tx UE may sense the channel only during a (pre)determined time period and immediately transmit a reservation signal if the energy / power measured during the time period is below a threshold. Channel sensing may be performed in a sensing window (e.g., a 16us window) having a predetermined position and size. In one example, the sensing window is a time window in a HARQ feedback slot (e.g., Figure 8In another example, the sensing window may be located at the end of the time slot before the HARQ feedback. According to the second option, the Tx UE performs a backoff (e.g., a random backoff within the contention window, similar to the CAT 4 LBT mentioned above), and the Tx UE transmits a reservation signal when the channel is idle during the contention window.

[0093] like Fig. 9 As explained in , in some cases, energy sensing by the Tx UE may not be required. For example, the HARQ feedback slot may fall within the COT (channel occupancy time) initiated by the Tx UE (or another UE). In such a case, the Tx UE may determine that the previous slot (the slot before the PSFCH / HARQ feedback slot) or the previous symbol (the symbol before the symbol configured for PSFCH / HARQ feedback transmission in the HARQ feedback slot) has been occupied by a sidelink transmission (the sidelink transmission of the Tx UE or the sidelink transmission from other UEs), and the Tx UE may transmit the reserved signal only in the HARQ feedback slot. For the case where the Tx UE determines that the previous slot or symbol has a transmission from (or from) other UEs, the Tx UE may have decoded a sidelink control signal or data transmission from another UE. As explained, the Rx UE may transmit the HARQ feedback (in the PSFCH) over a gap after the reserved signal.

[0094] In some cases, the HARQ feedback transmission time slots may be (pre)configured in a periodic manner. For example, one time slot out of every N time slots (e.g., N=2, 4, etc.) may be (pre)configured for HARQ feedback transmission. In such cases, the sensing and reservation signal transmissions occur within the (pre)configured HARQ feedback time slots. The HARQ timeline may be such that the Tx UE transmits the signal no earlier than time slot n+k (e.g., Figure 5 ), where n is a data transmission time slot and k is a scheduling parameter value (pre-)defined / (pre-)configured for the HARQ timeline.

[0095] In some cases, there may not be a dedicated time slot for HARQ feedback transmission.In such cases, there are various alternatives for determining the HARQ feedback time slot.

[0096] According to a first alternative, the Tx UE and the Rx UE determine the time slot for HARQ feedback transmission based on a (pre)defined / (pre)configured HARQ timeline (e.g., the (pre)defined HARQ timeline is n+k, where k has a (pre)defined value). In other words, for data transmission ending in time slot n, the first time slot that may have HARQ feedback transmission for the corresponding data is time slot n+k, and the Tx UE will sense and transmit a reservation signal in time slot n+k.

[0097] According to a second alternative, the Tx UE indicates the HARQ feedback timeline when transmitting data.For example, the Tx UE may indicate the k value in the Sidelink Control Information (SCI) that schedules the data transmission or some other SCI transmission.

[0098] When the feedback slot is sensed as busy, the Tx UE has various options. In some cases, the reservation signal may be common to all UEs. In such cases, as long as the reservation signal is detected by the Rx UE (from any UE), the Rx UE knows that the channel has been reserved for sidelink transmission, and the Rx UE can transmit its HARQ feedback. This may mean that although a particular Tx UE may see a busy channel, another Tx UE may not see it, and the other Tx UE transmits its reservation signal in the HARQ feedback slot. This may assume that data transmission / HARQ feedback transmission can be multiplexed in the same slot in a frequency division multiplexing (FDM) manner (e.g., this means that multiple UEs can transmit concurrently in the same slot).

[0099] In one case (case 1), if the Rx UE has detected a reservation signal (from the Tx UE or a different Tx UE), the Rx UE will transmit HARQ feedback in the feedback resources within the feedback slot. In such a case, the Tx UE will always detect HARQ feedback transmission in the feedback resources within the feedback slot, regardless of whether it successfully transmitted the reservation signal.

[0100] In another case (case 2), the channel may be really busy so that the Rx UE cannot detect any reserved signal in the feedback slot. In this case, the Rx UE may not transmit HARQ feedback in this feedback slot (because the Tx UE will not be able to decode the HARQ feedback in this feedback slot). In such a case, the Rx UE may simply discard the HARQ feedback, or a HARQ feedback transmission window may be defined to accommodate such a scenario.

[0101] For example, such a HARQ feedback transmission window may include one or more HARQ feedback slots. For data transmission, its HARQ feedback will be mapped to the HARQ feedback window. If the HARQ feedback window has multiple HARQ feedback slots, the Tx UE may sense the next slot in the window without detecting its HARQ feedback in the current slot in the feedback window.

[0102] There are various options for transmitting the reservation signal. For example, the reservation signal can be a subband signal transmitted as part of the frequency resource (RB / subchannel). In some cases, the reservation signal can be transmitted in the same frequency position where the HARQ feedback will be transmitted. In some cases, multiple Tx UEs can transmit the reservation signal in one HARQ feedback slot (e.g., via FDM). Similarly, for HARQ feedback transmission, HARQ feedback transmissions for different data transmissions can be FDMed in the same HARQ feedback slot.

[0103] Channel sensing (performed by the Tx UE) as proposed herein can help ensure that there is no interference between sidelink HARQ feedback transmissions and transmissions from other technologies (e.g., Wi-Fi) sharing the same unlicensed spectrum. Channel sensing performed by the Tx UE and a reservation signal sent by the Tx UE to trigger HARQ feedback transmissions as described herein can help ensure that HARQ feedback from multiple recipient UEs are transmitted in the same HARQ feedback resources (time or time / frequency resources) in a multicast communication.

[0104] Fig.10 The description may include operations configured to perform the techniques disclosed herein (such as, Figure 6 1000 may include a processing system 1002 coupled to a transceiver 1008 (e.g., a transmitter and / or a receiver). The transceiver 1008 may be configured to transmit and receive signals for the communication device 1000 (such as various signals as described herein) via an antenna 1010. The processing system 1002 may be configured to perform processing functions for the communication device 1000, including processing signals received and / or to be transmitted by the communication device 1000.

[0105] The processing system 1002 may include a processor 1004 coupled to a computer readable medium / memory 1012 via a bus 1006. In some aspects, the computer readable medium / memory 1012 may be configured to store data that, when executed by the processor 1004, causes the processor 1004 to execute Figure 6In some aspects, the computer-readable medium / memory 1012 may store code 1014 for outputting data for transmission to at least one receiving UE in an unlicensed spectrum for sidelink communication; code 1016 for determining whether resources in a time slot are available for the at least one UE to provide acknowledgment feedback for the data transmission; and / or code 1018 for outputting a reservation signal for transmission in the time slot if the resources are determined to be available.

[0106] In certain aspects, processor 1004 may have circuitry configured to implement code stored in computer-readable medium / memory 1012. Processor 1004 may include circuitry 1020 for outputting data for transmission to at least one receiving UE in an unlicensed spectrum for sidelink communication; circuitry 1022 for determining whether resources in a time slot are available for the at least one UE to provide acknowledgment feedback for the data transmission; and / or circuitry 1024 for outputting a reservation signal for transmission in the time slot if the resources are determined to be available.

[0107] Fig.11 The description may include operations configured to perform the techniques disclosed herein (such as, Figure 7 1100 includes various components (e.g., corresponding to means-plus-function components) of the communication device 1100 and the operations explained in the description. The communication device 1100 may include a processing system 1102 coupled to a transceiver 1108 (e.g., a transmitter and / or a receiver). The transceiver 1108 may be configured to transmit and receive signals (such as various signals as described herein) for the communication device 1110 via the antenna 1100. The processing system 1102 may be configured to perform processing functions for the communication device 1100, including processing signals received and / or to be transmitted by the communication device 1100.

[0108] The processing system 1102 may include a processor 1104 coupled to a computer readable medium / memory 1112 via a bus 1106. In certain aspects, the computer readable medium / memory 1112 may be configured to store instructions that, when executed by the processor 1104, cause the processor 1104 to execute instructions. Figure 7In some aspects, the computer-readable medium / memory 1112 may store code 1114 for obtaining a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; code 1116 for monitoring a reservation signal from the transmitting UE indicating that resources in a time slot are available for the receiving UE to provide acknowledgment feedback for the data transmission; and / or code 1118 for outputting the acknowledgment feedback for the data transmission for transmission if the reservation signal is detected.

[0109] In certain aspects, processor 1104 may have circuitry configured to implement code stored in computer-readable medium / memory 1112. Processor 1104 may include circuitry 1120 for obtaining a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; circuitry 1122 for monitoring a reservation signal from the transmitting UE indicating that resources in a time slot are available for the receiving UE to provide acknowledgment feedback for the data transmission; and / or circuitry 1124 for outputting the acknowledgment feedback for the data transmission for transmission if the reservation signal is detected.

[0110] In addition to the above aspects, many aspects of specific combinations are also within the scope of the present disclosure, some of which are described in detail below:

[0111] Aspect 1: A method for wireless communication by a transmitting user equipment (UE), comprising: transmitting data to at least one receiving UE in an unlicensed spectrum for sidelink communication; determining whether resources in a time slot are available for the at least one receiving UE to provide confirmation feedback for the data transmission; and transmitting a reservation signal in the time slot if the resources are determined to be available.

[0112] Aspect 2: The method as described in Aspect 1, wherein the reservation signal reserves the resource for the confirmation feedback and triggers the at least one receiving UE to send the confirmation feedback.

[0113] Aspect 3: A method as described in any of Aspects 1-2, wherein: the determination involves a clear channel assessment (CCA) based on at least one of the energy or power measured during the sensing period; and the resource is determined to be available when the detected energy or power is equal to or less than a threshold.

[0114] Aspect 4: The method as described in Aspect 3, wherein the transmitting UE transmits the reservation signal when the detected energy or power is equal to or less than the threshold.

[0115] Aspect 5: The method as described in Aspect 3 further includes: performing a backoff procedure when the CCA indicates that the channel is idle based on the detected energy or power being equal to or less than the threshold, wherein the transmitting UE transmits the reservation signal when the channel remains idle during the backoff procedure.

[0116] Aspect 6: A method as described in any one of Aspects 1-5, wherein the resource is determined to be available in the following circumstances: the time slot is within a channel occupation time (COT) initiated by the transmitting UE or the other UE; and the previous time slot has been occupied by a sidelink transmission performed by the transmitting UE or the other UE.

[0117] Aspect 7: The method as described in Aspect 6 further includes: determining that the previous time slot has been occupied by the other UE by decoding at least one of sidelink control signaling or data transmission from the other UE.

[0118] Aspect 8: The method as described in any one of aspects 1-7, wherein the time slot comprises a time slot in a set of time slots configured for the acknowledgment feedback.

[0119] Aspect 9: The method according to aspect 8, wherein the transmitting UE determines resource availability and transmits the reservation signal in the earliest time slot that satisfies the acknowledgment feedback timeline condition among the configured time slots.

[0120] Aspect 10: The method according to any one of aspects 1-9, wherein the time slot is determined based on an acknowledgment feedback timeline condition.

[0121] Aspect 11: The method of aspect 10, wherein the data transmission includes an indication of the acknowledgement feedback timeline condition.

[0122] Aspect 12: The method according to any one of aspects 1-11, further comprising: monitoring the confirmation feedback regardless of whether the reservation signal is transmitted.

[0123] Aspect 13: The method as described in any one of Aspects 1-12 further includes: performing the following operations when it is determined that the resource is unavailable: deciding not to monitor the confirmation feedback from the at least one receiving UE; or monitoring the confirmation feedback from the at least one receiving UE according to the confirmation feedback transmission window.

[0124] Aspect 14: A method as described in any one of Aspects 1-13, wherein the time slot is one of multiple confirmation feedback time slots within a confirmation feedback window; and in the case of determining that the resource is not available in the time slot, the method further includes: determining whether resources in a subsequent time slot in the confirmation feedback window are available for the at least one receiving UE to provide the confirmation feedback for the data transmission.

[0125] Aspect 15: The method as described in any one of aspects 1-14, wherein the reservation signal is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0126] Aspect 16: The method of aspect 15 further comprises: receiving the confirmation feedback via the same portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0127] Aspect 17: The method according to any one of aspects 1-16, wherein the reservation signal is transmitted in the same portion of frequency resources used to transmit the acknowledgment feedback.

[0128] Aspect 18: The method according to any one of aspects 1-17, wherein reservation signals from a plurality of transmitting UEs including the transmitting UE are frequency division multiplexed (FDM) in the same time slot.

[0129] Aspect 19: The method as described in any one of Aspects 1-18 further comprises: receiving the confirmation feedback via a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0130] Aspect 20: The method as described in any one of Aspects 1-19 further comprises: receiving the confirmation feedback via a set of frequency resources that at least partially overlap with frequency resources in the unlicensed spectrum used for sidelink communication.

[0131] Aspect 21: A method as described in any one of Aspects 1-20, wherein at least one of the following is satisfied: confirmation feedback for different data transmissions is frequency division multiplexed (FDM) in the same time slot; or confirmation feedback from different receiving UEs among the at least one receiving UE is frequency division multiplexed (FDM) in the same time slot.

[0132] Aspect 22: A method for wireless communication by a receiving user equipment (UE), comprising: receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; monitoring a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide confirmation feedback for the data transmission; and transmitting the confirmation feedback for the data transmission when the reservation signal is detected.

[0133] Aspect 23: The method of aspect 22, wherein the time slot comprises a time slot in a set of time slots configured for acknowledgment feedback.

[0134] Aspect 24: The method according to any one of aspects 22-23, wherein the data transmission includes an acknowledgment feedback timeline condition when transmitting data, and the receiving UE transmits the acknowledgment feedback according to the acknowledgment feedback timeline condition.

[0135] Aspect 25: The method according to any one of Aspects 22-24, further comprising: transmitting the confirmation feedback even if the reservation signal is not detected.

[0136] Aspect 26: The method according to any one of Aspects 22-25, wherein the acknowledgment feedback is transmitted according to an acknowledgment feedback transmission window.

[0137] Aspect 27: The method as described in any one of Aspects 22-26, wherein the reserved signal is monitored in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0138] Aspect 28: The method according to any one of aspects 22-27, wherein the reservation signal is monitored in the same portion of frequency resources used to transmit the acknowledgment feedback.

[0139] Aspect 29: The method according to any one of aspects 22-28, wherein the at least one transmitting UE comprises a plurality of transmitting UEs, and the reserved signals from the plurality of transmitting UEs are frequency division multiplexed (FDM) in the same time slot.

[0140] Aspect 30: The method as described in any one of Aspects 22-29, wherein the acknowledgment feedback is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0141] Aspect 31: A method as described in any one of Aspects 22-30, wherein at least one of the following is satisfied: confirmation feedback for different data transmissions is frequency division multiplexed (FDM) in the same time slot; or confirmation feedback from different receiving UEs including the receiving UE is frequency division multiplexed (FDM) in the same time slot.

[0142] Aspect 32: A transmitting user equipment (UE), comprising: a device for transmitting data to at least one receiving UE in an unlicensed spectrum for sidelink communication; a device for determining whether resources in a time slot are available for the at least one receiving UE to provide confirmation feedback for the data transmission; and a device for transmitting a reservation signal in the time slot if the resources are determined to be available.

[0143] Aspect 33: The transmitting UE according to Aspect 32, wherein the reservation signal reserves the resource for the confirmation feedback and triggers the at least one receiving UE to send the confirmation feedback.

[0144] Aspect 34: A transmitting UE as described in any of Aspects 32-33, wherein the determination involves a clear channel assessment (CCA) based on at least one of energy or power measured during a sensing period; and the resource is determined to be available if the detected energy or power is equal to or less than a threshold.

[0145] Aspect 35: The transmitting UE according to Aspect 34, wherein the transmitting UE transmits the reservation signal if the detected energy or power is equal to or less than the threshold.

[0146] Aspect 36: The transmitting UE as described in Aspect 34 further includes: a device for performing a backoff procedure when the CCA indicates that the channel is idle based on the detected energy or power being equal to or less than the threshold, wherein the transmitting party transmits the reservation signal when the channel remains idle during the backoff procedure.

[0147] Aspect 37: A transmitting UE as described in any of Aspects 32-36, wherein the resource is determined to be available under the following circumstances: the time slot is within a channel occupation time (COT) initiated by the transmitting UE or another UE; and the previous time slot has been occupied by a sidelink transmission performed by the transmitting UE or the other UE.

[0148] Aspect 38: The transmitting UE as described in Aspect 37 further includes: a device for determining that the previous time slot has been occupied by the other UE by decoding at least one of sidelink control signaling or data transmission from the other UE.

[0149] Aspect 39: The transmitting UE according to any one of Aspects 32-38, wherein the time slot comprises a time slot in a set of time slots configured for the acknowledgment feedback.

[0150] Aspect 40: The transmitting UE according to aspect 39, wherein the transmitting UE determines resource availability and transmits the reservation signal in an earliest time slot that satisfies an acknowledgment feedback timeline condition among the configured time slots.

[0151] Aspect 41: The transmitting UE according to any one of Aspects 32-40, wherein the time slot is determined based on an acknowledgment feedback timeline condition.

[0152] Aspect 42: The transmitting UE according to Aspect 41, wherein the data transmission includes an indication of the acknowledgment feedback timeline condition.

[0153] Aspect 43: The transmitting UE according to any one of Aspects 32-42, further comprising: means for monitoring the confirmation feedback regardless of whether the reservation signal is transmitted.

[0154] Aspect 44: The transmitting UE as described in any one of Aspects 32-43, when determining that the resource is unavailable, further includes: a device for deciding not to monitor the confirmation feedback from the at least one receiving UE; or a device for monitoring the confirmation feedback from the at least one receiving UE according to the confirmation feedback transmission window.

[0155] Aspect 45: A transmitting UE as described in any one of Aspects 32-44, wherein the time slot is one of multiple confirmation feedback time slots within a confirmation feedback window; and in the case of determining that the resource is not available in the time slot, the transmitting UE further includes: a device for determining whether resources in a subsequent time slot in the confirmation feedback window are available for the at least one receiving UE to provide the confirmation feedback for the data transmission.

[0156] Aspect 46: The transmitting UE according to any one of Aspects 32-45, wherein the reservation signal is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0157] Aspect 47: The transmitting UE as described in Aspect 46 further includes: a device for receiving the confirmation feedback via the same part of frequency resources in the unlicensed spectrum used for sidelink communication.

[0158] Aspect 48: The transmitting UE according to any one of Aspects 32-47, wherein the reservation signal is transmitted in the same portion of frequency resources used to transmit the acknowledgment feedback.

[0159] Aspect 49: The transmitting UE according to any one of aspects 32-48, wherein reserved signals from a plurality of transmitting UEs including the transmitting UE are frequency division multiplexed (FDM) in the same time slot.

[0160] Aspect 50: The transmitting UE as described in any one of Aspects 32-49 further includes: a device for receiving the confirmation feedback via a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0161] Aspect 51: The transmitting UE as described in any one of Aspects 32-50 further includes: a device for receiving the confirmation feedback via a set of frequency resources that at least partially overlaps with the frequency resources in the unlicensed spectrum used for sidelink communication.

[0162] Aspect 52: A transmitting UE as described in any one of Aspects 32-51, wherein at least one of the following is satisfied: confirmation feedback for different data transmissions is frequency division multiplexed (FDM) in the same time slot; or confirmation feedback from different receiving UEs among the at least one receiving UE is frequency division multiplexed (FDM) in the same time slot.

[0163] Aspect 53: A receiving user equipment (UE), comprising: a device for receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; a device for monitoring a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide confirmation feedback for the data transmission; and a device for transmitting the confirmation feedback for the data transmission when the reservation signal is detected.

[0164] Aspect 54: The receiving UE according to Aspect 53, wherein the time slot comprises a time slot in a set of time slots configured for acknowledgment feedback.

[0165] Aspect 55: The receiving UE as described in any one of Aspects 53-54, wherein the data transmission includes an acknowledgment feedback timeline condition when transmitting data; and the receiving UE transmits the acknowledgment feedback according to the acknowledgment feedback timeline condition.

[0166] Aspect 56: The receiving UE as described in any one of Aspects 53-55 further includes: a device for transmitting the confirmation feedback even if the reservation signal is not detected.

[0167] Aspect 57: The receiving UE according to any one of Aspects 53-56, wherein the acknowledgment feedback is transmitted according to an acknowledgment feedback transmission window.

[0168] Aspect 58: The receiving UE as described in any of Aspects 53-57, wherein the reserved signal is monitored in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0169] Aspect 59: The receiving UE according to any one of Aspects 53-58, wherein the reserved signal is monitored in the same portion of frequency resources used to transmit the acknowledgment feedback.

[0170] Aspect 60: The receiving UE according to any one of aspects 53-59, wherein the at least one transmitting UE comprises a plurality of transmitting UEs, and the reserved signals from the plurality of transmitting UEs are frequency division multiplexed (FDM) in the same time slot.

[0171] Aspect 61: The receiving UE as described in any of Aspects 53-60, wherein the confirmation feedback is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0172] Aspect 62: A receiving UE as described in any one of Aspects 53-61, wherein at least one of the following is satisfied: confirmation feedback for different data transmissions is frequency division multiplexed (FDM) in the same time slot; or confirmation feedback from different receiving UEs including the receiving UE is frequency division multiplexed (FDM) in the same time slot.

[0173] Aspect 63: A transmitting user equipment (UE), comprising: a transmitter configured to transmit data to at least one receiving UE in an unlicensed spectrum for sidelink communication; and a processing system configured to determine whether resources in a time slot are available for the at least one receiving UE to provide confirmation feedback for the data transmission, wherein the transmitter is further configured to transmit a reservation signal in the time slot if the resources are determined to be available.

[0174] Aspect 64: The transmitting UE according to Aspect 63, wherein the reservation signal reserves the resource for the confirmation feedback and triggers the at least one receiving UE to send the confirmation feedback.

[0175] Aspect 65: A transmitting UE as described in any of Aspects 63-64, wherein the determination involves a clear channel assessment (CCA) based on at least one of energy or power measured during a sensing period; and the resource is determined to be available if the detected energy or power is equal to or less than a threshold.

[0176] Aspect 66: The transmitting UE according to Aspect 65, wherein the transmitting UE transmits the reservation signal if the detected energy or power is equal to or less than the threshold.

[0177] Aspect 67: A transmitting UE as described in Aspect 65, wherein the processing system is further configured to perform a backoff procedure when the CCA indicates that the channel is idle based on the detected energy or power being equal to or less than the threshold, and the transmitting party transmits the reservation signal when the channel remains idle during the backoff procedure.

[0178] Aspect 68: A transmitting UE as described in any of Aspects 63-67, wherein the resource is determined to be available under the following circumstances: the time slot is within a channel occupation time (COT) initiated by the transmitting UE or another UE; and the previous time slot has been occupied by a sidelink transmission performed by the transmitting UE or the other UE.

[0179] Aspect 69: The transmitting UE according to Aspect 68, wherein the processing system is further configured to determine that the previous time slot has been occupied by the other UE by decoding at least one of sidelink control signaling or data transmission from the other UE.

[0180] Aspect 70: The transmitting UE according to any one of Aspects 63-69, wherein the time slot comprises a time slot in a set of time slots configured for the acknowledgment feedback.

[0181] Aspect 71: The transmitting UE according to aspect 70, wherein the transmitting UE determines resource availability and transmits the reservation signal in an earliest time slot that satisfies an acknowledgment feedback timeline condition among the configured time slots.

[0182] Aspect 72: The transmitting UE according to any one of Aspects 63-71, wherein the time slot is determined based on an acknowledgment feedback timeline condition.

[0183] Aspect 73: The transmitting UE as described in Aspect 72, wherein the data transmission includes an indication of the acknowledgment feedback timeline condition.

[0184] Aspect 74: The transmitting UE according to any one of Aspects 63-73, wherein the processing system is further configured to monitor the acknowledgment feedback regardless of whether the reservation signal is transmitted.

[0185] Aspect 75: A transmitting UE as described in any one of Aspects 63-74, wherein the processing system is further configured to perform the following operations when it is determined that the resource is not available: decide not to monitor the confirmation feedback from the at least one receiving UE; or monitor the confirmation feedback from the at least one receiving UE according to the confirmation feedback transmission window.

[0186] Aspect 76: A transmitting UE as described in any of Aspects 63-75, wherein the time slot is one of multiple confirmation feedback time slots within a confirmation feedback window; and in the event that it is determined that the resource is not available in the time slot, the processing system is further configured to: determine whether resources in a subsequent time slot in the confirmation feedback window are available for the at least one receiving UE to provide the confirmation feedback for the data transmission.

[0187] Aspect 77: The transmitting UE according to any one of Aspects 63-76, wherein the reservation signal is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0188] Aspect 78: The transmitting UE as described in Aspect 77 further comprises: a receiver configured to receive the confirmation feedback via the same part of frequency resources in the unlicensed spectrum used for sidelink communication.

[0189] Aspect 79: The transmitting UE according to any one of Aspects 63-78, wherein the reservation signal is transmitted in the same portion of frequency resources used to transmit the acknowledgment feedback.

[0190] Aspect 80: The transmitting UE according to any one of aspects 63-79, wherein reserved signals from a plurality of transmitting UEs including the transmitting UE are frequency division multiplexed (FDM) in the same time slot.

[0191] Aspect 81: The transmitting UE as described in any one of Aspects 63-80 further includes: a receiver configured to receive the confirmation feedback via a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0192] Aspect 82: The transmitting UE as described in any of Aspects 63-81 further includes: a receiver configured to receive the confirmation feedback via a set of frequency resources that at least partially overlap with the frequency resources in the unlicensed spectrum used for sidelink communication.

[0193] Aspect 83: A transmitting UE as described in any one of Aspects 63-82, wherein at least one of the following is satisfied: confirmation feedback for different data transmissions is frequency division multiplexed (FDM) in the same time slot; or confirmation feedback from different receiving UEs among the at least one receiving UE is frequency division multiplexed (FDM) in the same time slot.

[0194] Aspect 84: A receiving user equipment (UE), comprising: a receiver configured to receive data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; a processing system configured to monitor a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide confirmation feedback for the data transmission; and a transmitter configured to transmit the confirmation feedback for the data transmission when the reservation signal is detected.

[0195] Aspect 85: The receiving UE according to aspect 84, wherein the time slot comprises a time slot in a set of time slots configured for acknowledgment feedback.

[0196] Aspect 86: The receiving UE according to any one of aspects 84-85, wherein the data transmission includes an acknowledgment feedback timeline condition when transmitting data, and the transmitter transmits the acknowledgment feedback according to the acknowledgment feedback timeline condition.

[0197] Aspect 87: The receiving UE as described in any of Aspects 84-86, wherein the transmitter is further configured to: transmit the confirmation feedback even if the reservation signal is not detected.

[0198] Aspect 88: The receiving UE as described in any one of Aspects 84-87, wherein the acknowledgment feedback is transmitted according to an acknowledgment feedback transmission window.

[0199] Aspect 89: The receiving UE as described in any of Aspects 84-88, wherein the reserved signal is monitored in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0200] Aspect 90: The receiving UE according to any one of aspects 84-89, wherein the reserved signal is monitored in the same portion of frequency resources used to transmit the acknowledgment feedback.

[0201] Aspect 91: A receiving UE as in any one of aspects 84-90, wherein: the at least one transmitting UE comprises a plurality of transmitting UEs; and the reserved signals from the plurality of transmitting UEs are frequency division multiplexed (FDM) in the same time slot.

[0202] Aspect 92: The receiving UE as described in any of Aspects 84-91, wherein the confirmation feedback is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communication.

[0203] Aspect 93: A receiving UE as described in any one of Aspects 84-92, wherein at least one of the following conditions is satisfied: confirmation feedback for different data transmissions is frequency division multiplexed (FDM) in the same time slot; or confirmation feedback from different receiving UEs including the receiving UE is frequency division multiplexed (FDM) in the same time slot.

[0204] Aspect 94: An apparatus for wireless communication, comprising: an interface configured to output data for transmission to at least one user equipment (UE) in an unlicensed spectrum for sidelink communication; and a processing system configured to determine whether resources in a time slot are available for the at least one UE to provide confirmation feedback for the data transmission, wherein the interface is further configured to output a reservation signal for transmission in the time slot if the resources are determined to be available.

[0205] Aspect 95: An apparatus for wireless communication by a receiving user equipment (UE), comprising: an interface configured to obtain data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; and a processing system configured to monitor a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide confirmation feedback for the data transmission, wherein the interface is further configured to output the confirmation feedback for the data transmission for transmission when the reservation signal is detected.

[0206] Aspect 96: A computer-readable medium for wireless communications, comprising code executable to: output data for transmission to at least one user equipment (UE) in an unlicensed spectrum for sidelink communication; determine whether resources in a time slot are available for the at least one UE to provide acknowledgment feedback for the data transmission; and output a reservation signal for transmission in the time slot if the resources are determined to be available.

[0207] Aspect 97: A computer-readable medium for wireless communication by a receiving user equipment (UE), comprising code executable to: obtain a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; monitor a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide confirmation feedback for the data transmission; and output the confirmation feedback for the data transmission for transmission if the reservation signal is detected.

[0208] The techniques described herein may be used for various wireless communication technologies, such as NR (e.g., 5G NR), 3GPP Long Term Evolution (LTE), Advanced LTE (LTE-A), Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), Time Division Synchronous Code Division Multiple Access (TD-SCDMA), and other networks. The terms "network" and "system" are often used interchangeably. A CDMA network may implement radio technologies such as Universal Terrestrial Radio Access (UTRA), cdma2000, and the like. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95, and IS-856 standards. A TDMA network may implement radio technologies such as Global System for Mobile Communications (GSM). OFDMA networks can implement radio technologies such as NR (e.g., 5G RA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDMA, etc. UTRA and E-UTRA are parts of Universal Mobile Telecommunications System (UMTS). LTE and LTE-A are versions of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). cdma2000 and UMB are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). NR is an emerging wireless communication technology under development.

[0209] In 3GPP, the term "cell" may refer to the coverage area of ​​a B node (NB) and / or a NB subsystem serving the coverage area, depending on the context in which the term is used. In NR systems, the terms "cell" and BS, next-generation B node (gNB or g B node), access point (AP), distributed unit (DU), carrier, or transmission reception point (TRP) may be used interchangeably. The BS may provide communication coverage for macro cells, pico cells, femto cells, and / or other types of cells. A macro cell may cover a relatively large geographic area (e.g., a radius of several thousand meters) and may allow unrestricted access by UEs with service subscriptions. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscriptions. A femto cell may cover a relatively small geographic area (e.g., a residence) and may allow restricted access by UEs associated with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs of users in a residence, etc.). A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS.

[0210] UE may also be referred to as a mobile station, terminal, access terminal, subscriber unit, station, customer premises equipment (CPE), cellular phone, smart phone, personal digital assistant (PDA), wireless modem, wireless communication device, handheld device, laptop computer, cordless phone, wireless local loop (WLL) station, tablet computer, camera, gaming device, netbook, smartbook, ultrabook, appliance, medical device or medical equipment, biometric sensor / device, wearable device (such as smart watch, smart clothing, smart glasses, smart wristband, smart jewelry (e.g., smart ring, smart bracelet, etc.)), entertainment device (e.g., music device, video device, satellite radio, etc.), transportation component or sensor, smart meter / sensor, industrial manufacturing equipment, global positioning system device, or any other suitable device configured to communicate via wireless or wired medium. Some UEs may be considered machine type communication (MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, etc., which can communicate with a BS, another device (e.g., a remote device), or some other entity. A wireless node can provide connectivity for or to a network (e.g., a wide area network (such as the Internet) or a cellular network), for example, via a wired or wireless communication link. Some UEs may be considered Internet of Things (IoT) devices, which may be narrowband IoT (NB-IoT) devices.

[0211] In some examples, access to the air interface may be scheduled. A scheduling entity (e.g., BS) allocates resources for communication between some or all devices and equipment within its service area or cell. A scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communications, subordinate entities utilize resources allocated by the scheduling entity. A base station is not the only entity that can be used as a scheduling entity. In some examples, a UE may act as a scheduling entity, and may schedule resources for one or more subordinate entities (e.g., one or more other UEs), and other UEs may utilize resources scheduled by the UE for wireless communication. In some examples, a UE may act as a scheduling entity in a peer-to-peer (P2P) network and / or in a mesh network. In a mesh network example, UEs may communicate directly with each other in addition to communicating with a scheduling entity.

[0212] Each method disclosed herein includes one or more steps or actions for implementing the method. These method steps and / or actions can be interchangeable with each other without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions can be changed without departing from the scope of the claims.

[0213] As used herein, a phrase referring to "at least one of" a list of items refers to any combination of those items, including single members. As an example, "at least one of a, b, or c" is intended to cover: a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other ordering of a, b, and c).

[0214] As used herein, the term "determining" encompasses a wide variety of actions. For example, "determining" may include calculating, computing, processing, deriving, investigating, searching (e.g., searching in a table, a database, or another data structure), ascertaining, and the like. Also, "determining" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, "determining" may include resolving, selecting, choosing, establishing, and the like.

[0215] The previous 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 easily understood by those skilled in the art, and the universal principles defined herein can be applied to other aspects. Thus, the claims are not intended to be limited to the various aspects shown herein, but should be granted the full scope consistent with the language of the claims, wherein the singular reference to the element is not intended to mean "there is and only one" (unless specifically stated) but "one or more". Unless otherwise specifically stated, the term "some / some" refers to one or more. The elements of the various aspects described throughout this disclosure are all structural and functional equivalents currently or hereafter known to ordinary technicians in the art and are explicitly incorporated herein by reference, and are intended to be covered by the claims. In addition, nothing disclosed herein is intended to be donated to the public, regardless of whether such disclosure is explicitly recorded in the claims. Any element of the claim should not be interpreted under the provisions of 35 U.S.C. § 112 (f), unless the element is explicitly stated using the phrase "device for..." or in the case of a method claim, the element is stated using the phrase "step for...".

[0216] The various operations of the methods described above may be performed by any suitable device capable of performing the corresponding functions. These devices may include various hardware and / or software components and / or modules, including but not limited to circuits, application specific integrated circuits (ASICs), or processors. Generally, where there are operations illustrated in the figures, these operations may have corresponding paired device-plus-function components with similar numbers. For example, Figure 2 The processors 258, 264, and 266 of the UE 120a and / or the controller / processor 280, and / or the processors 220, 230, 238, and / or the controller / processor 240 of the BS 110a shown in FIG. 1 may be configured to perform Figure 6 Operation 600 and / or Figure 7 Operation 700.

[0217] The means for receiving may include Figure 2 The transceiver, receiver or at least one antenna and at least one receiving processor described in the embodiment. The device for transmitting, the device for sending or the device for outputting may include Figure 2 The transceiver, transmitter or at least one antenna and at least one transmit processor illustrated in the embodiment. The means for determining, the means for executing, the means for deciding and the means for monitoring may include a processing system, which may include one or more processors, such as Figure 21 and 12. Processors 258, 264, and 266 of UE 120a and / or controller / processor 280 and / or processors 220, 230, 238 and / or controller / processor 240 of BS 110a are shown in FIG.

[0218] In some cases, a device may not actually transmit a frame, but may have an interface (means for outputting) for outputting a frame for transmission. For example, a processor may output a frame to a radio frequency (RF) front end via a bus interface for transmission. Similarly, a device may not actually receive a frame, but may have an interface (means for obtaining) for obtaining a frame received from another device. For example, a processor may obtain (or receive) a frame from an RF front end via a bus interface for reception.

[0219] The various illustrative logical blocks, modules, and circuits described in conjunction with the present disclosure may be implemented or executed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0220] If implemented in hardware, an example hardware configuration may include a processing system in a wireless node. The processing system may be implemented using a bus architecture. Depending on the specific application and overall design constraints of the processing system, the bus may include any number of interconnecting buses and bridges. The bus may link together various circuits including a processor, a machine-readable medium, and a bus interface. The bus interface may be used to connect a network adapter, etc., to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In a user terminal (see Figure 1 ), a user interface (e.g., a keypad, display, mouse, joystick, etc.) may also be connected to the bus. The bus may also link various other circuits, such as timing sources, peripherals, voltage regulators, power management circuits, and the like, which are well known in the art and will not be described further. The processor may be implemented with one or more general and / or special purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuit systems capable of executing software. Those skilled in the art will recognize how to best implement the functionality described with respect to the processing system, depending on the specific application and the overall design constraints imposed on the overall network or system.

[0221] If implemented in software, each function may be stored on or transmitted by a computer-readable medium as one or more instructions or codes. Software should be broadly interpreted to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or other. Computer-readable media include both computer storage media and communication media, which include any media that facilitate the transfer of computer programs from one place to another. The processor may be responsible for managing the bus and general processing, including executing software modules stored on a machine-readable storage medium. A computer-readable storage medium may be coupled to a processor so that the processor can read and write information from / to the storage medium. In an alternative, a storage medium may be integrated into a processor. As an example, a machine-readable medium may include a transmission line, a carrier modulated by data, and / or a computer-readable storage medium having instructions stored thereon that is separated from a wireless node, all of which may be accessed by a processor through a bus interface. Alternatively or additionally, a machine-readable medium or any part thereof may be integrated into a processor, such as a cache and / or a general register file, which may be the case. As an example, examples of machine-readable storage media may include RAM (random access memory), flash memory, ROM (read only memory), PROM (programmable read only memory), EPROM (erasable programmable read only memory), EEPROM (electrically erasable programmable read only memory), registers, magnetic disks, optical disks, hard drives, or any other suitable storage media, or any combination thereof. Machine-readable media may be implemented in a computer program product.

[0222] A software module may include a single instruction, or many instructions, and may be distributed over several different code segments, between different programs, and across multiple storage media. A computer-readable medium may include multiple software modules. These software modules include instructions that cause a processing system to perform various functions when executed by an apparatus such as a processor. These software modules may include a transmission module and a reception module. Each software module may reside in a single storage device or may be distributed across multiple storage devices. As an example, when a triggering event occurs, a software module may be loaded into a RAM from a hard drive. During the execution of a software module, a processor may load some instructions into a cache to increase access speed. One or more cache lines may then be loaded into a general register file for execution by the processor. When describing the functionality of a software module as described below, it will be understood that such functionality is implemented by the processor when the processor executes instructions from the software module.

[0223] Likewise, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technology (such as infrared (IR), radio, and microwave), then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technology (such as infrared, radio, and microwave) is included in the definition of medium. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Disks, where disks often reproduce data magnetically, and discs reproduce data optically with lasers. Thus, in some aspects, computer-readable media may include non-transitory computer-readable media (e.g., tangible media). Additionally, for other aspects, computer-readable media may include transient computer-readable media (e.g., signals). Combinations of the above should also be included within the scope of computer-readable media.

[0224] Thus, certain aspects may include a computer program product for performing the operations presented herein. For example, such a computer program product may include a computer-readable medium having stored (and / or encoded) thereon instructions that can be executed by one or more processors to perform the operations described herein, such as for performing the operations described herein and in Figure 6-7 Instructions for the operations explained in .

[0225] In addition, it should be appreciated that modules and / or other appropriate means for performing the methods and techniques described herein may be downloaded and / or otherwise obtained by a user terminal and / or base station where applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage device (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or a floppy disk, etc.) so that once the storage device is coupled to or provided to a user terminal and / or base station, the device can obtain the various methods. In addition, any other suitable technology suitable for providing the methods and techniques described herein to a device may be utilized.

[0226] It will be understood that the claims are not limited to the precise configuration and components illustrated above. Various changes, substitutions and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

1. A method for wireless communication by a transmitting user equipment (UE), comprising: transmitting data to at least one receiving UE in an unlicensed spectrum for sidelink communication; determining whether resources in a time slot are available for the at least one receiving UE to provide acknowledgement feedback for the data transmission; as well as A reservation signal is transmitted in the time slot if the resource is determined to be available.

2. The method of claim 1, wherein the reservation signal reserves the resource for the acknowledgment feedback and triggers the at least one receiving UE to send the acknowledgment feedback.

3. The method of claim 1, wherein: The determining involves a clear channel assessment (CCA) based on at least one of energy or power detected during a sensing period; and The resource is determined to be available if the detected energy or power is equal to or less than a threshold value.

4. The method of claim 3, wherein: The transmitting UE transmits the reservation signal if the detected energy or power is equal to or less than the threshold.

5. The method of claim 3, further comprising performing a backoff procedure if the CCA indicates that the channel is idle based on the detected energy or power being equal to or less than the threshold, wherein: The transmitting UE transmits the reservation signal if the channel remains idle during the backoff procedure.

6. The method of claim 1, wherein the resource is determined to be available when: The time slot is within a channel occupation time (COT) initiated by the transmitting UE or another UE; and The previous time slot has been occupied by a sidelink transmission by the transmitting UE or the other UE.

7. The method of claim 6, further comprising: Determining that the previous time slot has been occupied by the other UE by decoding at least one of sidelink control signaling or data transmission from the other UE.

8. The method of claim 1, wherein the time slot comprises one of a set of time slots configured for the acknowledgment feedback.

9. The method of claim 8, wherein the transmitting UE determines resource availability and transmits the reservation signal in an earliest time slot that satisfies an acknowledgment feedback timeline condition among the configured time slots.

10. The method of claim 1, wherein the time slot is determined based on an acknowledgment feedback timeline condition.

11. The method of claim 10, wherein the data transmission includes an indication of the acknowledgment feedback timeline condition.

12. The method of claim 1, further comprising: The acknowledgement feedback is monitored regardless of whether the reservation signal is transmitted.

13. The method according to claim 1, wherein the following operations are performed when it is determined that the resource is unavailable: Deciding not to monitor the acknowledgement feedback from the at least one receiving UE; or The acknowledgment feedback from the at least one receiving UE is monitored according to an acknowledgment feedback transmission window.

14. The method of claim 1, wherein: The time slot is one of a plurality of acknowledgment feedback time slots within an acknowledgment feedback window; and In case it is determined that the resource is not available in the time slot, the method further includes determining whether resources in a subsequent time slot in the acknowledgment feedback window are available for the at least one receiving UE to provide the acknowledgment feedback for the data transmission.

15. The method of claim 1, wherein the reservation signal is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communications.

16. The method of claim 15, further comprising: The acknowledgment feedback is received via a same portion of frequency resources in the unlicensed spectrum used for sidelink communications.

17. The method of claim 1, wherein the reservation signal is transmitted in the same portion of frequency resources used to transmit the acknowledgment feedback.

18. The method of claim 1 or 15, wherein reservation signals from a plurality of transmitting UEs including the transmitting UE are frequency division multiplexed (FDM) in the same time slot.

19. The method of claim 1, further comprising: The acknowledgment feedback is received via a portion of frequency resources in the unlicensed spectrum used for sidelink communications.

20. The method of claim 1, further comprising: The acknowledgment feedback is received via a set of frequency resources that at least partially overlap with frequency resources in the unlicensed spectrum used for sidelink communications.

21. A method for wireless communication by a receiving user equipment (UE), comprising: receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; monitoring a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide an acknowledgment feedback for the data transmission; as well as The acknowledgment feedback for the data transmission is transmitted if the reservation signal is detected.

22. The method of claim 21, wherein the time slot comprises a time slot in a set of time slots configured for acknowledgment feedback.

23. The method of claim 21, wherein: The data transmission includes a timeline condition for receiving feedback when transmitting the data; and The receiving UE transmits the acknowledgment feedback according to the acknowledgment feedback timeline condition.

24. The method of claim 21, further comprising: The acknowledgment feedback is transmitted even if the reservation signal is not detected.

25. The method of claim 21, wherein the acknowledgment feedback is transmitted according to an acknowledgment feedback transmission window.

26. The method of claim 21, wherein the reservation signal is monitored in a portion of frequency resources in the unlicensed spectrum used for sidelink communications.

27. The method of claim 21, wherein the reservation signal is monitored in the same portion of frequency resources used to transmit the acknowledgment feedback.

28. The method of claim 21, wherein: The at least one transmitting UE includes a plurality of transmitting UEs; and The reserved signals from the multiple transmitting UEs are frequency division multiplexed (FDM) in the same time slot.

29. The method of claim 21, wherein the acknowledgment feedback is transmitted in a portion of frequency resources in the unlicensed spectrum used for sidelink communications.

30. The method of claim 21, wherein at least one of the following is satisfied: Frequency division multiplexing (FDM) of acknowledgement feedback for different data transmissions in the same time slot; or Acknowledgement feedbacks from different receiving UEs including the receiving UE are frequency division multiplexed (FDM) in the same time slot.

31. A transmitting user equipment (UE), comprising: means for transmitting data to at least one receiving UE in an unlicensed spectrum for sidelink communication; means for determining whether resources in a time slot are available for the at least one receiving UE to provide acknowledgment feedback for the data transmission; as well as Means for transmitting a reservation signal in the time slot if the resource is determined to be available.

32. A receiving user equipment (UE), comprising: means for receiving a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communication; means for monitoring a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide acknowledgement feedback for the data transmission; as well as means for transmitting the acknowledgment feedback for the data transmission if the reservation signal is detected.

33. A transmitting user equipment (UE), comprising: a transmitter configured to transmit data to at least one receiving UE in an unlicensed spectrum for sidelink communication; as well as a processing system configured to determine whether resources in a time slot are available for the at least one receiving UE to provide an acknowledgement feedback for the data transmission, Wherein the transmitter is further configured to transmit a reservation signal in the time slot if the resource is determined to be available.

34. A receiving user equipment (UE), comprising: a receiver configured to receive a data transmission from at least one transmitting UE in an unlicensed spectrum for sidelink communications; a processing system configured to monitor a reservation signal from the at least one transmitting UE, the reservation signal indicating that resources in a time slot are available for the receiving UE to provide an acknowledgment feedback for the data transmission; as well as A transmitter is configured to transmit the acknowledgment feedback for the data transmission if the reservation signal is detected.

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