CHANNEL ACCESS WITH RESERVATION FOR SIDELINK COMMUNICATION IN UNLICENSED SPECTRUM

Methods, systems, and devices for wireless communications are described in which a user equipment (UE) may reserve one or more time frequency resources in an unlicensed frequency spectrum band for one or more sidelink transmissions. The UE may reserve the time frequency resources through a sidelink message transmitted in a first slot of a shared channel occupancy (CO). The UE may monitor a subset of slots before the reserved time frequency resources for sidelink transmissions from other UEs sharing the CO. The monitoring of the subset of slots may include decoding control messages or control information in each of the subset of slots, a reference signal received power (RSRP) measurement of sidelink transmissions in the subset of slots, channel sensing with energy detection in a sensing window, or a combination thereof. The UE may communicate in the reserved slot based on the monitoring.

FIELD OF TECHNOLOGY

The following relates generally to wireless communications and more specifically to channel access with reservation for sidelink communication in unlicensed spectrum.

BACKGROUND

Some wireless communications systems may support sidelink access communications, such as communications between multiple UEs (e.g., in a vehicle-to-everything (V2X) system, a vehicle-to-vehicle (V2V) system, a device-to-device (D2D) system, among other examples). Sidelink communications may be deployed in licensed frequency spectrum, or dedicated spectrum for intelligent transportation systems (ITS). Sidelink communications may also be deployed in unlicensed or shared radio frequency spectrum band, which may be shared with other technologies and users. However, sidelink communications in unlicensed spectrum may introduce challenges to channel access due to sharing the frequency spectrum with other technologies (e.g., Wi-Fi) as well as other channel sensing regulations of the spectrum.

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support channel access with reservation for sidelink communication in unlicensed spectrum. Generally, the described techniques provide for efficient channel access for sidelink communications in unlicensed spectrum. A user equipment (UE) may gain access to a sidelink channel of an unlicensed or shared spectrum for an interval of time, which may be referred to as a channel occupancy time (COT) or channel occupancy (CO). The UE may transmit or receive sidelink messages over the sidelink channel during the COT. A wireless communications system using unlicensed spectrum may implement sidelink COT sharing, which may enable multiple UEs to perform sidelink communications during the same COT.

In some cases, a UE may reserve one or more time frequency resources (e.g., symbols, slots, mini slots) within the shared COT for one or more sidelink transmissions. In some examples, the UE may reserve the time frequency resources through a sidelink message transmitted in a slot (e.g., a reserving sidelink transmission). The message may include resource reservation information, which may be included in sidelink control information (SCI) corresponding to the sidelink message. The UE may monitor a subset of time-frequency resources before a reserved resource for sidelink transmissions from other UEs sharing the COT. If the UE monitors continuous sidelink transmission or discontinuous sidelink transmission with each gap value less than a threshold (e.g., 16 μs or 25 μs) over the subset of time-frequency resources, the UE may transmit a sidelink transmission in the reserved resource. If the UE monitors discontinuous sidelink transmission(s) with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs), the UE may assume that the reserved resource may be no longer accessible, and in some cases, the UE may give up transmission in the reserved resource. Additionally or alternatively, the UE may perform channel sensing (e.g., Category 2 listen-before-talk (LBT)) prior to using the reserved resource. For example, the UE may transmit the sidelink transmission in the reserved resource if the UE determines that the channel is accessible after performing channel sensing (e.g., the measured energy level is below an energy threshold in a sensing duration).

In some examples, the UE may reserve time frequency resources in a slot consecutive to the reserving sidelink transmission slot of the UE. The UE may transmit a sidelink transmission in the consecutive reserved slot without performing channel sensing (e.g., Category 2 LBT or Category 4 LBT). In some cases, the UE may reserve the consecutive slot if the reserving sidelink transmission does not request hybrid automatic repeat request (HARQ) feedback.

A method of wireless communications at a UE is described. The method may include determining that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission, transmitting a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE, and communicating in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more reference signal received power (RSRP) measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

An apparatus for wireless communications at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission, transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE, and communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

Another apparatus for wireless communications at a UE is described. The apparatus may include means for determining that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission, transmitting a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE, and communicating in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

A non-transitory computer-readable medium storing code for wireless communications at a UE is described. The code may include instructions executable by a processor to determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission, transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE, and communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for detecting one or more sidelink control messages from at least one other UE indicating a set of reserved slots reserved by the at least one other UE for subsequent communications within the CO, and selecting the reserved slot based on the set of reserved slots such that each slot between the first slot and the reserved slot may be reserved by the UE or the at least one other UE.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for selecting the reserved slot to be consecutive to the first slot, and refraining from performing the channel sensing procedure before the reserved slot based on the reserved slot and the first slot being consecutive.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for selecting the reserved slot to be consecutive to the first slot based on transmissions in the first slot by the UE being independent of feedback in response to the transmissions.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, communicating the reserved slot may include operations, features, means, or instructions for transmitting a feedback request for transmissions in the reserved slot.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the feedback request specifies one or more slots within the CO reserved for feedback.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for detecting, as part of the channel sensing procedure, one or more sidelink control messages from at least one other UE in a second slot preceding the reserved slot, where the second slot and the reserved slot may be consecutive, and communicating in the reserved slot based on detecting the one or more sidelink control messages.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for detecting, as part of the channel sensing procedure, one or more sidelink control messages from at least one other UE in each slot between the first slot and the reserved slot, and communicating in the reserved slot based on detecting the one or more sidelink control messages in each slot between the first slot and the reserved slot.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for communicating in the reserved slot based on an RSRP measurement of sidelink transmissions in all slots between the first slot and the reserved slot exceeding an RSRP threshold.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for communicating in the reserved slot based on an RSRP measurement of sidelink transmissions in a second slot consecutive to the reserved slot exceeding an RSRP threshold.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for communicating in the reserved slot based on the energy detection in the sensing window between the first slot and the reserved slot being below an energy detection threshold.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for performing energy detection in one or more symbols of a second slot preceding the reserved slot, where the second slot and the reserved slot may be consecutive.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining the one or more symbols based on a sensing window size, a reception mode to transmission mode transition time, a fixed gap value, or a combination thereof.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a feedback request for transmissions in the first slot, the feedback request indicating that the reserved slot may be for feedback for the transmissions.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting a feedback request for transmissions in the first slot, the feedback request indicating that the reserved slot and one or more other slots within the CO may be for feedback for the transmissions.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, in the reserved slot, feedback for the transmissions in the first slot, and releasing the one or more other slots based on receiving feedback for the transmissions in the first slot.

DETAILED DESCRIPTION

A wireless communications system may support sidelink communications between wireless devices, such as a user equipment (UE) or other sidelink devices, and such sidelink techniques may support one or more of device-to-device (D2D) communications, vehicle-to-everything (V2X), or vehicle-to-vehicle (V2V) communications, message relaying, discovery signaling, beacon signaling, or other signals transmitted over-the-air from one wireless device to at least one other wireless device. In some cases, sidelink communications may support unicast messaging, groupcast messaging, multicast messaging, broadcast messaging, or combinations thereof. Sidelink communications may deploy in licensed frequency spectrum (e.g., licensed cellular spectrum, intelligent transportation systems (ITS) dedicated spectrum) or in unlicensed (e.g., shared) frequency spectrum.

In some examples, sidelink communications may support resource (e.g., symbol, slot, mini slot) reservation in autonomous resource allocation for licensed radio frequency spectrum. For example, a UE may identify future time frequency resources (e.g., candidate resources) of a channel available for future sidelink transmission within a selection window. In some cases, to identify candidate resources, the UE may identify time frequency resources reserved by other UEs that communicate using the channel. The UE may monitor each sidelink transmission of the channel within a sensing window, which may include one or more time frequency resources, prior to a reserving sidelink transmission for the UE. In some cases, the UE may monitor the sidelink transmissions within the sensing window by decoding sidelink control information (SCI) for each sidelink transmission within the sensing window. The SCI may provide resource reservation information of time frequency resources reserved for a sidelink transmission by the corresponding UE transmitting the sidelink transmission. In some cases, the UE may identify reserved resources by performing a reference signal received power (RSRP) measurement for each sidelink transmission decoded within the sensing window. The UE may project the RSRP measurement to corresponding reserved resources in the SCI, and compare the RSRP measurement to an RSRP metric (e.g., threshold value) to identify the corresponding resources as reserved (e.g., busy). If the RSRP measurement is above the RSRP threshold for a given transmission, the UE may determine that the corresponding reserved resources are busy. If the RSRP measurement is below the RSRP threshold for a given transmission, the UE may determine that the corresponding reserved resources are available as candidate resources. The UE may then select one or more resources from the candidate resources in the selection window, the candidate resources including one or more resources which may be identified as available in the selection window. The UE may select the one or more resources from the candidate resources upon a triggering for resource selection or an arrival of a packet for transmission. In some cases, the UE may identify the candidate resources in the selection window based on the SCI decoding, the RSRP measurement, or a combination thereof and may then select to reserve candidate resources. In some examples, the UE may select a resource for its current transmission, and the UE may also select a number of resources for future use. In some cases. the UE may reserve the selected resources by indicating reservations via sidelink control signaling in a sidelink transmission performed by the UE. In some examples, the UE may schedule its reserved resources in future slots to transmit a retransmission of information (e.g., packet) from a sidelink transmission.

In some examples, sidelink communications may support resource reservation in unlicensed radio frequency spectrum, which may introduce challenges to channel access. For instance, if a set of wireless devices share a channel occupancy time (COT) (also referred to channel occupancy (CO)) of an unlicensed channel, access to the unlicensed channel during the COT may be lost if transmissions such as V2X transmissions are discontinuous such that one or more gaps between subsequent transmissions exceed a gap threshold (e.g., 16 μs or 25 μs). As such, a wireless device may not be guaranteed that a resource reserved by the wireless device will be available within a COT of an unlicensed channel. Additionally or alternatively, some wireless devices utilizing the shared channel may operate according to a different radio access technology (e.g., Wi-Fi) and may be unable to properly decode sidelink transmission such as V2X sidelink transmissions which may result in the wireless devices not identifying the reserved resources. Further, channel sensing regulations (e.g., listen-before-talk (LBT), COT) may include additional procedures for the UE to reserve time frequency resources and transmit sidelink transmission using the reserved time frequency resources in unlicensed spectrum, which may limit the ability of a UE to access and utilize the reserved resources of the unlicensed channel.

In some cases using channel sensing (e.g., LBT), a wireless device may sense energy and may send a transmission if the energy is below a threshold. In some examples, a wireless device may use Category 1 LBT, which includes using LBT without energy sensing (e.g., the device may transmit immediately, similar to Type 2c channel access in NR unlicensed (NR-U)). In some cases, the wireless device may use Category 2 LBT, which includes using LBT without random back-off (e.g., the device may transmit if the device senses energy in some period below a threshold, similar to Type 2a and Type 2b channel access in NR-U). In some examples, the wireless device may use Category 4 LBT, which includes using LBT with random back-off with a contention window of variable size (e.g., the device may transmit if the device senses energy in a contention window below a threshold, similar to Type 1 channel access in NR-U).

Techniques are described herein for channel access for sidelink communications in unlicensed spectrum. A UE may gain access to a sidelink channel and initiate a CO having a given COT. The UE may transmit one or more sidelink transmissions over the sidelink channel during the COT. A wireless communications system in unlicensed radio frequency spectrum may implement sidelink COT sharing, which may enable multiple UEs to transmit one or more sidelink transmissions over the sidelink channel during a COT. In some cases, a wireless node (base station, core network node, road side unit (RSU), etc.) may initiate and enable COT sharing for sidelink transmissions. In some cases, the COT may be limited to a given time interval (e.g., 2 ms, 5 ms, 10 ms).

In some implementations, the UE may reserve one or more time frequency resources (e.g., one or multiple resource blocks (RBs) or subchannels in one or multiple slots) within the shared COT for one or more sidelink transmissions. The UE may reserve resources in slots which may be consecutive, non-consecutive, or both. In some cases, the UE may reserve time frequency resources through a message transmitted in a slot (e.g., a reserving sidelink transmission). The message may include resource reservation information, which may be included in SCI corresponding to the message. In some examples, other UEs (a second UE, a third UE, etc.) sharing the COT may decode the message. After decoding the message, the other UEs may designate the reserved resources indicated by the UE as busy, and may exclude those resources from being candidate resources of their own reservations.

In some cases, the UE may monitor a subset of slots before a reserved resource for sidelink transmissions from other UEs sharing the COT. In some cases, the UE may monitor for sidelink transmission in the subset of slots by decoding each sidelink transmission in the subset. In some examples, the subset of slots may be selected from a set of unreserved slots between each sidelink transmission of the UE within the COT. For instance, a first UE, sharing a COT with a second UE, may monitor a subset of slots (e.g., each slot between the first UE's reserving sidelink message transmission slot and the first UE's first future reserved slot) for sidelink transmission from the second UE. Alternatively, the subset of slots may be the preceding slot of a reserved resource. In some examples, if the UE monitors continuous sidelink transmission (e.g., each slot in the subset slots has sidelink transmission from other UE(s) been decoded) or discontinuous sidelink transmission with each gap value less than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, the UE may determine that the reserved resource is accessible and communicate in the reserved resource. In some cases, if the UE monitors one or more sidelink transmissions in each slot in the subset of slots, the UE may utilize the reserved resource without performing channel sensing (e.g., Category 2 or Category 4 LBT).

In some cases, the UE may perform a channel sensing procedure preceding the transmission of the reserved resource (e.g., Category 2 LBT). For example, the UE may perform energy detection in a sensing window preceding the reserved resource. The UE may then transmit in the reserved resource if an energy detection level measured in the sensing window is below an energy detection threshold.

In some examples, if the UE monitors discontinuous sidelink transmission with any gap value greater than a threshold (e.g., 16 μs or 25 μs), the UE may perform channel sensing (e.g., LBT). In some cases, the channel sensing may include LBT Category 2 procedures (e.g., without back off, such as Type 2 channel access as defined in a standard such as the 3GPP standard), or LBT Category 4 procedures (e.g., with back off, such as Type 1 channel access as defined in a standard such as the 3GPP standard). The UE may transmit the sidelink transmission in the reserved resource if the UE confirms the channel is free for transmission in the resource after performing channel sensing (e.g., LBT). In some cases, the UE may use Category 1 LBT (e.g., LBT without energy sensing), Category 2 LBT (e.g., LBT without random back-off), or Category 4 LBT (e.g., LBT with random back-off with a contention window of variable size).

In some examples, if the UE monitors discontinuous sidelink transmission having a gap value greater than a threshold (e.g., 16 μs or 25 μs), the UE may give up or refrain from using or transmitting in the reserved resource. For example, the UE may assume the channel may be no longer accessible if the UE detects sidelink transmission discontinuity during a gap that exceed the threshold. Alternatively, the UE may perform channel sensing (e.g., LBT with random back-off) if the UE intends to resume sidelink transmission in the reserved resource or in the future.

In some examples, the UE may reserve a future slot consecutive to the UE's reserving sidelink transmission slot. The UE may transmit a sidelink transmission in the consecutive future reserved slot without performing channel sensing (e.g., LBT). In some cases, the UE may reserve the consecutive future slot if the reserving sidelink transmission does not request feedback (e.g., hybrid automatic repeat request (HARQ) feedback). In some cases, a reserved resource may be released (e.g., unreserved) based on HARQ feedback to a previous sidelink transmission transmitted by the UE.

Aspects of the disclosure are initially described in the context of wireless communications systems. Aspects are then described with respect to time-frequency plots and a process flow. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to channel access with reservation for sidelink communication in unlicensed spectrum.

In some cases, a UE115may gain access to a sidelink channel for a COT. In some cases, the COT may be configured as a given time interval (e.g., 2 ms, 5 ms, 10 ms). The UE115may transmit or receive one or more sidelink messages over the sidelink channel during the COT. For example, the UE115may transmit a message in a first slot of the COT using a channel of the shared radio frequency spectrum band. In some cases, the message may indicate future time frequency resources reserved within the COT. The UE115may monitor a subset of slots from a set of slots between each reserved time frequency resource within the COT. The UE115may communicate over the reserved time frequency resources without performing channel sensing (e.g., LBT) if the UE115monitors continuous sidelink transmission or discontinuous sidelink transmission with each gap of transmission less than a threshold (e.g., 16 μs or 25 μs) in the subset of slots. If the UE115monitors discontinuous sidelink transmission with any gap of transmission greater than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, the UE115assumes the reserved resource may be no longer accessible and, in some cases, may drop the transmission via the reserved resource. Additionally or alternatively, the UE115may perform channel sensing (e.g., LBT) before determining whether the reserved resource is accessible by the UE115.

FIG.2illustrates an example of a wireless communications system200that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. In some examples, wireless communications system200may implement aspects of wireless communications system100. Wireless communications system200may include base station105-a, which may be an example of a base station105as described herein, and wireless device115-a, wireless device115-b, and wireless device115-c, which may each be an example of a wireless device115described herein. While some examples of techniques for channel reservation for sidelink communications with COT sharing described herein are described as wireless device-to-wireless device COT sharing in a wireless device group205, other devices may implement these techniques. For example, base stations105, access points, relay nodes, or other types of wireless devices, may implement techniques similar to the wireless device group205.

A wireless communications system200in unlicensed radio frequency spectrum may implement sidelink COT sharing, which may enable one or more wireless devices115to transmit one or more sidelink messages over a channel210during a COT. For example, a wireless device115-amay determine that a channel210of a shared radio frequency spectrum band may be available for use for a COT. wireless device115-a(or base station105-a) may gain access to the channel210for the COT and may initiate COT sharing with a wireless device115-b. In some cases, the channel210may be a physical shared channel (e.g., physical sidelink shared channel (PSSCH). wireless device115-amay initiate COT sharing by transmitting a COT sharing configuration215-ato wireless device115-b. The COT sharing configuration215-amay include SCI as well as sharing information for the COT. Based on the sharing information, wireless device115-bmay determine whether the COT supports sharing with wireless device115-b. For instance, if wireless device115-bdetermines that sharing is supported for the COT, wireless device115-bmay gain a capability time frequency resources in the channel210within the same COT as wireless device115-a. In some examples, wireless device115-bmay transmit a sidelink feedback transmission to wireless device115-a, or may transmit some combination thereof within the shared COT. In some examples, wireless device group205may include wireless device115-aand wireless device115-bsharing a COT. In some cases, wireless device group205may share the COT with wireless device115-c.

In some cases, a wireless node (e.g., base station, RSU, etc.) may provide the sharing information to configure COT sharing for sidelink transmissions. For example, a base station105-amay transmit COT sharing configuration215-bto wireless device115-a. The COT sharing configuration215-bmay include sharing information of a COT for one or more wireless devices115(e.g., wireless device group205) over a geographic coverage area110-a.

According to some aspects, wireless device group205may support resource reservation for sidelink communications in shared radio frequency spectrum over the shared COT. For example, wireless device115-amay reserve one or more time frequency resources225(e.g., slots) within the shared COT for one or more sidelink transmissions in the channel. wireless device115-amay reserve time frequency resources225which may be consecutive, non-consecutive, or both. In some cases, wireless device115-amay reserve time frequency resources225through a reserving sidelink transmission220. The reserving sidelink transmission220may include a message which may indicate resource reservation information. In some cases, the message may be included in SCI of the reserving sidelink transmission220. In some examples, wireless device115-bmay detect the message. After detecting the message, wireless device115-bmay decode the message to designate reserved time frequency resources225indicated by wireless device115-aas busy, and may exclude reserved time frequency resources225from being resources utilized in wireless device115-breservations.

Additionally or alternatively, wireless device115-bmay refrain from using the reserved time frequency resources225indicated by wireless device115-aby performing an RSRP measurement on reserving sidelink transmission220. In some cases, wireless device115-bmay project the RSRP measurement onto the reserved time frequency resources225, and may compare the RSRP measurement to an RSRP metric (e.g., threshold value) to identify the time frequency resources225as reserved (e.g., busy). For instance, if wireless device115-bmeasures an RSRP measurement over the reserving sidelink transmission220greater than an RSRP metric, wireless device115-bmay identify the time frequency resources225as reserved. In some cases, wireless device115-amay implement similar processes of refraining from utilizing reserved resources of wireless device115-b(e.g., SCI of the messages, RSRP measurement, or a combination thereof). In some examples, wireless device115-amay identify reserved resources of wireless device115-bby detecting and decoding messages transmitted in the channel210during or prior to COT sharing.

In some cases, while wireless device115-amay reserve the time frequency resources225, wireless device115-amay not guarantee that reserved time frequency resources225may be available to access in the channel210when time to utilize reserved time frequency resources225. While wireless device115-bmay identify those reserved time frequency resources225as busy, other wireless devices such as wireless device115-cmay not identify reserved time frequency resources225as busy and therefore may utilize reserved time frequency resources225due to wireless device115-coperating in accordance with a different radio access technology (e.g., Wi-Fi). For example, wireless device115-cmay attempt to communicate over the channel210in the shared spectrum, and may transmit Wi-Fi signaling230if there may be any gap of transmission greater than a threshold (e.g., 16 μs or 25 μs) between reserving sidelink transmission220and reserved time frequency resources225. As such, if there may be any gap of transmission greater than a threshold (e.g., 16 μs or 25 μs) between reserving sidelink transmission220and reserved time frequency resources225, wireless devices115may lose access to the channel as a sidelink transmission transmitted by wireless device115-ain reserved time frequency resources225may collide with transmissions from other technologies. For example, if wireless device115-caccesses the channel during a gap, a transmission from wireless device115-ain reserved time frequency resources225may collide with a transmission from wireless device115-cin reserved time frequency resources225.

To help mitigate transmission collisions, wireless device115-amay monitor a subset of slots before reserved time frequency resources225for sidelink transmissions from other wireless devices (e.g., wireless device115-band wireless device115-c) in the channel210. In some examples, if wireless device115-amonitors continuous sidelink transmission or discontinuous sidelink transmission with each gap of transmission less than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, wireless device115-amay transmit a sidelink transmission in reserved time frequency resource225. For example, if wireless device115-adetects continuous sidelink transmission or discontinuous sidelink transmission with each gap of transmission less than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, the wireless device115-amay determine that V2X wireless device may retain the COT and the wireless device115-amay be able to transmit in the reserved time frequency resource225. In some examples, if wireless device115-amonitors discontinuous sidelink transmission with any gap of transmission greater than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, wireless device115-amay assume reserved time frequency resources225no longer accessible. In some examples, wireless device115-amay give up transmission in reserved time frequency resources225and may perform channel sensing (e.g., Type 1 channel access procedure as specified in 3GPP, which may be referred to as Category 4 LBT (i.e., LBT with random back-off), or sidelink decoding based channel access as described previously) to access the channel210if wireless device115-astill has a packet to transmit. In other examples, wireless device115-amay perform channel sensing (e.g., Type 2 channel access procedure as specified in 3GPP, which may be referred to as Category 2 LBT (i.e., LBT without random back-off)) prior to utilizing the reserved time frequency resource225. Wireless device115-amay then utilize the time frequency resource225based on the channel availability after performing the channel sensing (e.g., Type 2 channel access).

FIG.3illustrates an example of a time frequency diagram300that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. In some examples, time frequency diagram300may implement aspects of the wireless communications systems100or200. In some examples, the time frequency diagram300may correspond to a COT315and may be a function of a frequency domain as well as a time domain. For example, time frequency diagram300may span a number of slots320(e.g., slot n, slot n+1, slot n+2, etc.) in a time domain of the COT315, and may span a number of subchannels (e.g., subchannels310-athrough310-d) of a channel305in the frequency domain. In some examples, resources of the time frequency diagram300may span one symbol by one subcarrier, or one symbol by multiple subcarriers.

The time frequency diagram300may include a first wireless device reserving a time frequency resource330in slot320-fwithin a COT315shared with one or more other wireless devices (e.g., a second wireless device, a third wireless device, etc.). In some examples, the first wireless device may select a time frequency resource to reserve (e.g., time frequency resource330). In some cases, selecting resources to reserve may include the first wireless device identifying resources335already reserved by either the first wireless device or other wireless devices. In some cases, the first wireless device may detect one or more sidelink transmissions transmitted from other wireless devices prior to the reserving slot320-a. In some cases, the first wireless device may detect the one or more sidelink transmissions transmitted from other wireless devices in the prior slot to the reserving slot. Each sidelink transmission may include a sidelink control message or SCI which may indicate set of resources335reserved by the other wireless devices. For instance, the first wireless device may decode the sidelink control message or SCI of one or more sidelink transmissions transmitted prior to reserving slot and may designate the resources335reserved by the other wireless devices as reserved (e.g., busy). In some examples, the first wireless device may select to reserve a resource in the next unreserved slot (e.g., time frequency resource330) of the COT subsequent to the reserving slot320-a. In other examples, the first wireless device may select to reserve a resource in a random unreserved slot of the COT subsequent to the reserving slot320-a. In other examples, the first wireless device may select to reserve a resource randomly from resources that are identified as available.

Additionally or alternatively, selecting resources to reserve may include the first wireless device identifying resources335already reserved by other wireless devices by performing an RSRP measurement on a control message or sidelink transmission(s) from the other wireless devices. The first wireless device may project the RSRP measurement onto the resources335indicated by the other wireless devices, and may compare the RSRP measurement to an RSRP metric (e.g., threshold value) to identify resources335as reserved (e.g., busy). For example, the first wireless device may measure an RSRP measurement for a sidelink transmission of a second wireless device. The sidelink transmission may be reserving the resources335for future sidelink transmission by the second wireless device. If the RSRP measurement is greater than an RSRP metric, the first wireless device may identify the resources335of the second wireless device as busy and may exclude it from candidate resources. If the RSRP measurement is less than the RSRP metric, the first wireless device may identify resources335as available and may identify resources335as candidate resources for the first wireless device.

In some cases, after selecting to reserve time frequency resource330, the first wireless device may monitor a subset of slots before reserved time frequency resource330for sidelink transmissions from other wireless devices sharing the COT. The first wireless device may determine whether the reserved time frequency resource330may be accessible based on the monitoring of sidelink transmissions from the other wireless devices in each slot of the subset of slots. In some examples, the subset of slots may be selected from a set of slots between each sidelink transmission of the first wireless device within the COT. In some cases, the subset of slots may be each slot between the first wireless device's reserving sidelink message transmission slot and the first wireless device's future reserved slot. For example, the first wireless device may monitor a subset of slots which may include each slot between reserving resource325and reserved time frequency resource330for sidelink transmission from other wireless devices (e.g., slots320-b,320-c,320-d, and320-e). In some examples, the subset of slots may be the slot that preceding the slot having the reserved resource. For example, the first wireless device may monitor slot320-e, the slot that is preceding the slot320-f.

In some examples, the first wireless device may detect sidelink transmission from one or more other wireless devices the subset of slots (e.g., slots320-bthrough320-e) based on decoding control messages or SCI in each slot of the subset of slots. For instance, the first wireless device may detect sidelink transmission from a second wireless device in resource335-abased on decoding the control message or SCI of sidelink transmission transmitted by the second wireless device. Additionally or alternatively, decoding the control message or SCI of other wireless devices may indicate future resources reserved by other wireless devices. For instance, a second wireless device in the shared COT may utilize resource335-ato reserve resource335-b. The first wireless device may decode the reserving sidelink transmission in resource335-a, and may designate resource335-bas reserved (e.g., busy).

In some examples, the first wireless device may detect sidelink transmission from one or more other wireless devices in the subset of slots (e.g., slots320-bthrough320-e) based on an RSRP measurement in each slot in the subset of slots. For example, the first wireless device may detect sidelink transmission from a second wireless device in resource335-abased on performing an RSRP measurement on slot320-bin the subset of slots (e.g., slots320-bthrough320-e). In some cases, the first wireless device may detect sidelink transmissions from other wireless devices for each slot in the subset of slots by either decoding control messages or SCI, performing an RSRP measurement, or a combination thereof. If in each of the subset of slots, the first wireless device detects sidelink transmission(s), the first wireless device determines that sidelink transmissions from V2X UEs are continuous, the first wireless device determines that V2X UEs including the first wireless device still retain the COT and can transmit in the reserved time frequency resource330. Otherwise, the first wireless device may assume that the reserved time frequency resource330is no longer accessible (the UE may either give up its transmission or perform CAT2 LBT before transmitting in the reserved time frequency resource330).

In some cases, the subset of slots may include the preceding slot of a reserved resource. For example, the subset of slots may include slot320-ewhen the first wireless device reserves time frequency resource330. The first wireless device may monitor slot320-e. The first wireless device may then determine whether the reserved time frequency resource330may be accessible based on the monitoring of sidelink transmissions from the other wireless devices in slot320-e. In some examples, the first wireless device may detect sidelink transmission from one or more other wireless devices in slot320-ebased on decoding a control message or SCI of sidelink transmission transmitted by one or more other wireless devices. For instance, the first wireless device may detect sidelink transmission from a second wireless device based on decoding a control message or SCI of sidelink transmission transmitted by the second wireless device in slot320-e. In some examples, the first wireless device may detect sidelink transmission from one or more other wireless devices in slot320-ebased on an RSRP measurement in slot320-e. For instance, the first wireless device may detect sidelink transmission from a second wireless device in slot320-eover resource335-dbased on an RSRP measurement in slot320-e. In some cases, the first wireless device may detect sidelink transmissions from other wireless devices for slot320-eby either decoding control messages or SCI, performing an RSRP measurement, or a combination thereof.

In some cases, the first wireless device may monitor the subset of slots (e.g., slots320-bthrough320-eor slot320-e) before reserved time frequency resources330for sidelink transmissions from other wireless devices in the channel305to identify accessibility of reserved time frequency resource330. In some examples, if the first wireless device monitors continuous sidelink transmission or discontinuous sidelink transmission with each gap of transmission less than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, the first wireless device may transmit a sidelink transmission in reserved time frequency resource330. The first wireless device monitoring continuous sidelink transmission or discontinuous sidelink transmission with each gap of transmission less than a threshold (e.g., 16 μs or 25 μs) in the subset of slots may indicate that the first wireless device and other wireless devices retain the COT. In some examples, if the first wireless device monitors discontinuous sidelink transmission with any gap of transmission greater than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, the first wireless device may assume reserved time frequency resources330may be no longer accessible. In some examples, the first wireless device may give up transmission in reserved time frequency resources330and may perform channel sensing (e.g., Type 1 channel access procedure as specified in 3GPP; or sidelink decoding based channel access as described previously) to access the channel305if the first wireless device still has a packet to transmit. In other examples, the first wireless device may perform channel sensing (e.g., Type 2 channel access procedure as specified in 3GPP in a sensing window) prior to utilizing the reserved time frequency resource330. The first wireless device may then utilize the time frequency resource330based on the channel availability after performing the channel sensing (e.g., Type 2 channel access).

In some cases, the first wireless device may utilize time frequency resource330while refraining from performing channel sensing (e.g., LBT) prior to the time frequency resource330if the first wireless device monitors continuous sidelink transmission (e.g., no stop in transmission) or discontinuous sidelink transmission with each gap value less than a threshold (e.g., 16 μs or 25 μs) over the subset of slots. For instance, the first wireless device may monitor a subset of slots (e.g., slots320-bthrough320-eor slot320-e) for sidelink transmission from other wireless devices. If the first wireless device monitors for sidelink transmission from one or more other wireless devices with no gaps or gap values less than a threshold (e.g., 16 μs or 25 μs) across the subset of slots in sidelink transmission over the channel305, then the first wireless device may utilize the reserved time frequency resource330without performing channel sensing (e.g., LBT) prior to the time frequency resource330. In some cases, the first wireless device may perform channel sensing (e.g., LBT without random back-off) between reserving slot320-aand reserved slot320-f. The first wireless device may then transmit in reserved time frequency resource330if the channel sensing procedure indicates channel305is available. For example, the first wireless device may perform energy detection in a sensing window preceding reserved time frequency resource330. The first wireless device may then transmit a sidelink transmission in reserved time frequency resource330if the measured energy level in the sensing window is below an energy threshold in a sensing duration.

In some examples, the first wireless device may perform channel sensing (e.g., LBT) prior to the reserved time frequency resource330if the first wireless device monitors discontinuous sidelink transmission with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs) in the subset of slots. For instance, the first wireless device may monitor a subset of slots (e.g., slots320-bthrough320-eor slot320-e) for sidelink transmission from other wireless devices In some cases, a sidelink transmission from a second wireless device in resource335-dmay stop transmitting for at least a time threshold (e.g., 16 μs or 25 μs) within the slot320-e. The first wireless device may then perform channel sensing (e.g., LBT) prior to the reserved time frequency resource330. The first wireless device may utilize reserved time frequency resource330if the first wireless device confirms the channel305is free for transmission in the time frequency resource330after performing channel sensing (e.g., LBT).

FIG.4illustrates an example of a time frequency diagram400that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. In some examples, time frequency diagram400may implement aspects of wireless communications systems100or200. In some examples, the time frequency diagram400may correspond to a COT and may be a function of a frequency domain as well as a time domain. For example, time frequency diagram400may span over slots420-aand420-bin a time domain of the COT, and may span a number of subchannels (e.g., subchannels410-athrough410-d) of a channel405in the frequency domain. In some examples, resources of the time frequency diagram400may span one symbol by one subcarrier, or one symbol by multiple subcarriers. In some examples, time frequency diagram400may describe the channel sensing (e.g., LBT) procedure of the present disclosure.

A first wireless device may transmit a message in a reserving resource, the message indicating a non-consecutive reserved time frequency resource430in slot420-b. In some cases, the first wireless device may perform channel sensing (e.g., LBT) over a channel405(e.g., a sidelink channel) in a shared COT if the first wireless device monitors discontinuous sidelink transmission with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs) in a subset of slots prior to the reserved time frequency resource430. In some cases, the first wireless device may detect sidelink transmission from other wireless devices for the subset of slots by either decoding control messages or SCI, performing an RSRP measurement, or a combination thereof. In some cases, the channel sensing (e.g., LBT) may be performed in a sensing window435. In some examples, the channel sensing (e.g., LBT) may be performed over the subchannel410-bfor the reserved time frequency resource430. In other examples, the channel sensing (e.g., LBT) may be performed over the channel405.

In some cases, the subset of slots may be each slot subsequent to the reserving resource and prior to the reserved time frequency resource430(e.g., slot420-a). If the first wireless device detects discontinuous sidelink transmission with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs) in the subset of slots, the first wireless device may perform channel sensing (e.g., LBT) in the sensing window435. In other cases, the subset of slots may be the preceding slot420-aof the reserved time frequency resource430. Similarly, if the first wireless device detects discontinuous sidelink transmission with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs) in slot420-a, the first wireless device may perform channel sensing (e.g., LBT) in the sensing window435. For instance, the first wireless device may not detect any sidelink control messages425from other wireless devices within slot420-awhich may indicate a gap value greater than a threshold (e.g., 16 μs or 25 μs) and may activate the first wireless device to perform channel sensing (e.g., LBT) in the sensing window435. In some cases, the first wireless device may determine to perform channel sensing (e.g., LBT) before ending slot420-adue to few OFDM symbols for the sidelink control messages425.

In some cases, channel sensing may include LBT procedures. An LBT procedure may include different Categories for attempting to access an unlicensed frequency band. In some examples, channel sensing may implement a Category 2 LBT. The Category 2 LBT may include an LBT without a random back-off, and a sensing duration for the sensing window435which may be determined by an energy detection window size, a reception mode to transmission mode transition time, a fixed gap value, or a combination thereof. The sensing duration may begin within slot420-aand end when slot420-bbegins. In other examples, channel sensing may implement a Category 4 LBT. The Category 4 LBT may include an LBT with a random back-off and may start sensing when the first wireless device determines discontinuous sidelink transmission with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs) in a slot (e.g., slot420-a) in the subset of slots.

In some examples, the first wireless device may detect discontinuous sidelink transmission with at least one gap value greater than a threshold (e.g., 16 μs or 25 μs) in slot420-bprior to the reserved time frequency resource430. In some aspects, the sensing window435may begin at the start of slot420-band end at the start of reserved time frequency resource430.

FIG.5illustrates an example of a time frequency diagram500that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. In some examples, time frequency diagram500may implement aspects of wireless communications systems100and200. In some examples, the time frequency diagram500may correspond to a shared COT and may be a function of a frequency domain as well as a time domain. For example, time frequency diagram500may span over slots520-aand520-iin a time domain of the COT, and may span a number of subchannels (e.g., subchannels510-athrough510-d) of a channel505in the frequency domain. In some examples, resources of the time frequency diagram500may span one symbol by one subcarrier, or one symbol by multiple subcarriers. In some examples, time frequency diagram500may describe multiple or consecutive channel access reservations with feedback transmission for sidelink communication in unlicensed spectrum.

Time frequency diagram500may include a first wireless device and a second wireless device sharing COT515. In some examples, the first wireless device may reserve time frequency resource530-ain slot520-bconsecutive to a time frequency resource525-a. In some cases, the first wireless device may refrain from performing channel sensing (e.g., LBT) for consecutive slot reservation. Additionally or alternatively, the first wireless device may reserve in consecutive time frequency resource530-aif the sidelink transmission in time frequency resource525-amay not request feedback (e.g., HARQ feedback). In some examples, the first wireless device may transmit a feedback request in time frequency resource530-afor a sidelink transmission transmitted in time frequency resource530-a.

In some examples, the first wireless device may reserve a single resource within a sidelink transmission. For instance, a sidelink transmission in time frequency resource525-amay reserve time frequency resource530-afor use by the first wireless device. A sidelink transmission in time frequency resource530-amay then reserve time frequency resource535-afor use by the first wireless device, and a sidelink transmission in time frequency resource535-amay then reserve time frequency resource540-afor use by the first wireless device. In other examples, the first wireless device may reserve multiple resources with a sidelink transmission. For instance, a sidelink transmission in time frequency resource525-amay reserve time frequency resource530-a, time frequency resource535-a, and time frequency resource540-afor use by the first wireless device.

In some cases, the first wireless device may transmit a feedback request along with the reservation message transmitted in the COT. The feedback request may indicate that one or more reserved resources may be for feedback of one or more sidelink messages. Further, reserved resources may be released based on the feedback received from other wireless devices sharing the COT (e.g., the second wireless device). For example, the first wireless device may reserve time frequency resource530-a, time frequency resource535-aand time frequency resource540-athrough a sidelink transmission transmitted in time frequency resource525-a. The sidelink transmission may include a feedback request which may indicate that time frequency resource530-amay receive feedback from the second wireless device regarding the transmission sent by the first wireless device in time frequency resource525-a. If the first wireless device receives a negative acknowledgment (NACK) feedback in time frequency resource530-a, the first wireless device may utilize the reserved time frequency resource535-a. If the wireless device receives an acknowledgment (ACK) feedback, then the first wireless device may release time frequency resource535-aand time frequency resource540-a.

In some cases, the second wireless device may employ similar techniques as the first wireless device for reservation of one or more resources (e.g., time frequency resource530-b. time frequency resource535-b, and time frequency resource540-b) through a reserving sidelink transmission transmitted in the time frequency resource525-bby the second wireless device. The first wireless device and the second wireless device may identify the reserved resources of the other by decoding control messages or SCI in sidelink transmissions, performing an RSRP measurement, or a combination thereof. For example, the second wireless device may decode the sidelink transmissions transmitted by the first wireless device in time frequency resource525-aand time frequency resource530-ato identify future resources (e.g., time frequency resource535-a) reserved by the first wireless device.

FIG.6illustrates an example of a process flow600that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. In some examples, process flow600may implement aspects of wireless communications system100,200, or300. Process flow600may include sidelink transmissions between a wireless device115-dand a wireless device115-e, which may be examples of corresponding devices as described herein. Alternative examples of the following may be implemented, where some steps are performed in a different order than described or are not performed at all. In some cases, steps may include additional features not mentioned below, or further steps may be added.

At605, wireless device115-dand wireless device115-emay each determine that a channel on an shared radio frequency spectrum band is available for use by the wireless device for a COT. wireless device115-dand wireless device115-emay share a COT sharing configuration. The COT sharing configuration may include SCI as well as sharing information for the COT. Based on the sharing information, wireless device115-dand wireless device115-emay determine to share the COT.

At610, wireless device115-emay transmit one or more sidelink control messages indicating a set of reserved slots reserved by wireless device115-efor subsequent communications within the COT. wireless device115-dmay detect the one or more sidelink control messages transmitted by wireless device115-eprior to a first slot. At615, wireless device115-dmay decode the sidelink control message and may identify the resources reserved by wireless device115-eas reserved (e.g., busy). In some cases, wireless device115-dmay identify the resources indicated by wireless device115-eby performing an RSRP measurement on a control message or sidelink transmission from wireless device115-e. wireless device115-dmay project the RSRP measurement onto the reserved resources indicated by wireless device115-e, and may compare the RSRP measurement to an RSRP metric (e.g., threshold value) to identify the resources as reserved (e.g., busy).

At620, wireless device115-dmay select a reserved slot within the COT for a subsequent communication by wireless device115-d. In some examples, wireless device115-dmay select the reserved slot based on the set of identified reserved slots of wireless device115-dor wireless device115-e. In some cases, wireless device115-dmay select the reserved slot to be consecutive to the first slot. In some examples, wireless device115-dmay select the reserved slot to be consecutive to the first slot based on sidelink transmissions in the first slot by wireless device115-dbeing independent of feedback. At625, wireless device115-dmay transmit a message (e.g., reservation message) in the first slot of the COT over the channel. The message may indicate the reserved slot within the COT for subsequent communication by wireless device115-d.

At630, wireless device115-dmay transmit a feedback request for transmissions in the first slot. In some examples, the feedback request may indicate that the reserved slot may be for feedback for the transmissions. In other examples, the feedback request may indicate that the reserved slot and one or more other slots within the COT may be for feedback for the transmissions.

At635, wireless device115-dmay monitor a subset of slots between the first slot and the reserved slot for sidelink transmissions from wireless device115-e. In some cases, the subset of slots may be the preceding slot of the reserved resource. The monitoring of the subset of slots may include decoding control messages or SCI in each slot. For instance, if wireless device115-ddecodes control messages or SCI in a slot of the subset of slots, then wireless device115-dmay acknowledge the sidelink transmission. In some cases, the monitoring of the subset of slots may include an RSRP measurement of sidelink transmissions of each slot. For instance, wireless device115-dmay perform an RSRP measurement over a slot in the subset of slots. If the RSRP measurement exceeds a threshold, wireless device115-dmay acknowledge the sidelink transmission. At640, wireless device115-emay transmit sidelink messages in the subset of slots.

At645, the wireless device115-dmay determine whether to refrain from or perform channel sensing (e.g., LBT). If wireless device115-dmonitored continuous sidelink transmission or discontinuous sidelink transmission with each gap value less than a threshold (e.g., 16 μs or 25 μs) over the subset of slots, wireless device115-dmay transmit a sidelink transmission in the reserved resource while refraining from performing channel sensing (e.g., (LBT)). In some examples, if wireless device115-dmonitored discontinuous sidelink transmission with any gap value greater than a threshold (e.g., 16 μs) or 25 μs, wireless device115-dmay perform channel sensing (e.g., LBT). In some cases, wireless device115-dmay refrain from channel sensing (e.g., (LBT)) if the reserved slot may be consecutive to the first slot.

At650, wireless device115-dmay perform channel sensing (e.g., LBT) based on the monitoring. In some cases, channel sensing may include a Category 2 LBT procedure or a Category 4 LBT procedure. In some cases, the LBT procedure may listen over one or more symbols in the preceding slot of the reserved slot. At655, wireless device115-dmay utilize the reserved resource by transmitting a sidelink message in the resource. In some examples, wireless device115-dmay confirm the channel is free for transmission in the resource after performing channel sensing (e.g., LBT) before utilizing the reserved resource.

At660, wireless device115-dmay transmit a feedback request for transmissions in the reserved slot. In some cases, the feedback request may be independent of feedback for transmissions in the first slot. In some cases, the feedback request may specify one or more slots within the COT reserved for feedback. At665, wireless device115-dmay receive feedback for transmissions in the first slot from wireless device115-e. At670, wireless device115-dmay release one or more other slots based on receiving feedback for the transmissions in the first slot.

FIG.7shows a block diagram700of a device705that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The device705may be an example of aspects of a UE115or a wireless device115as described herein. The device705may include a receiver710, a communications manager715, and a transmitter720. The device705may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses).

The receiver710may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to channel access with reservation for sidelink communication in unlicensed spectrum, etc.). Information may be passed on to other components of the device705. The receiver710may be an example of aspects of the transceiver1020described with reference toFIG.10. The receiver710may utilize a single antenna or a set of antennas.

The communications manager715may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission, transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE, and communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof. The communications manager715may be an example of aspects of the communications manager1010described herein.

The transmitter720may transmit signals generated by other components of the device705. In some examples, the transmitter720may be collocated with a receiver710in a transceiver module. For example, the transmitter720may be an example of aspects of the transceiver1020described with reference toFIG.10. The transmitter720may utilize a single antenna or a set of antennas.

In some examples, the communications manager715may be implemented as an integrated circuit or chipset for a mobile device modem, and the receiver710and transmitter720may be implemented as analog components (e.g., amplifiers, filters, antennas) coupled with the mobile device modem to enable wireless transmission and reception over one or more bands.

The communications manager715as described herein may be implemented to realize one or more potential advantages. One implementation may enable the device705to provide assistance for efficient channel access for sidelink communications between the device705and one or more other devices in unlicensed spectrum. Based on the techniques for efficient channel access for sidelink communications between the device705and one or more other devices in unlicensed spectrum, the device705may support channel reservation and, therefore, may refrain from additional channel sensing procedures to utilize time frequency resources in the channel. As such, the device705may increase the likelihood of efficient occupancy of the channel and, accordingly, may more efficiently power a processor or one or more processing units associated with transmitting and receiving communications over the channel, which may enable the device to save power and increase battery life.

The receiver810may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to channel access with reservation for sidelink communication in unlicensed spectrum, etc.). Information may be passed on to other components of the device805. The receiver810may be an example of aspects of the transceiver1020described with reference toFIG.10. The receiver810may utilize a single antenna or a set of antennas.

The communications manager815may be an example of aspects of the communications manager715as described herein. The communications manager815may include a channel availability component820, a message transmitter825, and a communications component830. The communications manager815may be an example of aspects of the communications manager1010described herein.

The channel availability component820may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission.

The message transmitter825may transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE.

The communications component830may communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

The transmitter835may transmit signals generated by other components of the device805. In some examples, the transmitter835may be collocated with a receiver810in a transceiver module. For example, the transmitter835may be an example of aspects of the transceiver1020described with reference toFIG.10. The transmitter835may utilize a single antenna or a set of antennas.

FIG.9shows a block diagram900of a communications manager905that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The communications manager905may be an example of aspects of a communications manager715, a communications manager815, or a communications manager1010described herein. The communications manager905may include a channel availability component910, a message transmitter915, a communications component920, a detection manager925, a slot reservation component930, a LBT manager935, a feedback request transmitter940, a symbol component945, a feedback receiver950, and a release component955. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses).

The channel availability component910may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission.

The message transmitter915may transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE.

The communications component920may communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

In some examples, the communications component920may communicate in the reserved slot based on detecting one or more sidelink control messages from at least one other UE in a second slot preceding the reserved slot, where the second slot and the reserved slot are consecutive.

In some examples, the communications component920may communicate in the reserved slot based on detecting one or more sidelink control messages from at least one other UE in each slot between the first slot and the reserved slot.

In some examples, the communications component920may communicate in the reserved slot based on the RSRP measurement of sidelink transmissions of all slots between the first slot and the reserved slot exceeding the RSRP threshold.

In some examples, the communications component920may communicate in the reserved slot based on the RSRP measurement of sidelink transmissions in a second slot consecutive to the reserved slot exceeding the RSRP threshold.

In some examples, the communications component920may communicate in the reserved slot based on the energy detection in a sensing window preceding the reserved slot being below the energy detection threshold.

The detection manager925may detect one or more sidelink control messages from at least one other UE indicating a set of reserved slots reserved by the at least one other UE for subsequent communications within the CO.

In some examples, the detection manager925may detect one or more sidelink control messages from at least one other UE in a second slot preceding the reserved slot, where the second slot and the reserved slot are consecutive.

In some examples, the detection manager925may detect one or more sidelink control messages from at least one other UE in each slot between the first slot and the reserved slot.

The slot reservation component930may select the reserved slot based on the set of reserved slots such that each slot between the first slot and the reserved slot is reserved by the UE or the at least one other UE.

In some examples, the slot reservation component930may select the reserved slot to be consecutive to the first slot.

In some examples, the slot reservation component930may select the reserved slot to be consecutive to the first slot based on transmissions in the first slot by the UE being independent of feedback in response to the transmissions.

The LBT manager935may refrain from performing the channel sensing procedure before the reserved slot based on the reserved slot and the first slot being consecutive.

In some examples, the LBT manager935may perform the channel sensing procedure in one or more symbols of a second slot preceding the reserved slot, where the second slot and the reserved slot are consecutive.

The feedback request transmitter940may transmit a feedback request for transmissions in the reserved slot independent of feedback for transmissions in the first slot.

In some examples, the feedback request transmitter940may transmit a feedback request for transmissions in the first slot, the feedback request indicating that the reserved slot is for feedback for the transmissions.

In some examples, the feedback request transmitter940may transmit a feedback request for transmissions in the first slot, the feedback request indicating that the reserved slot and one or more other slots within the COT interval are for feedback for the transmissions.

In some cases, the feedback request specifies one or more slots within the COT interval reserved for feedback.

The symbol component945may determine the one or more symbols based on a sensing window size, a reception mode to transmission mode transition time, a fixed gap value, or a combination thereof.

The feedback receiver950may receive, in the reserved slot, feedback for the transmissions in the first slot.

The release component955may release the one or more other slots based on receiving feedback for the transmissions in the first slot.

FIG.10shows a diagram of a system1000including a device1005that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The device1005may be an example of or include the components of device705, device805, a UE115, or a wireless device115as described herein. The device1005may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager1010, an I/O controller1015, a transceiver1020, an antenna1025, memory1030, and a processor1040. These components may be in electronic communication via one or more buses (e.g., bus1045).

The communications manager1010may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission, transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE, and communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

The I/O controller1015may manage input and output signals for the device1005. The I/O controller1015may also manage peripherals not integrated into the device1005. In some cases, the I/O controller1015may represent a physical connection or port to an external peripheral. In some cases, the I/O controller1015may utilize an operating system such as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, or another known operating system. In other cases, the I/O controller1015may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller1015may be implemented as part of a processor. In some cases, a user may interact with the device1005via the I/O controller1015or via hardware components controlled by the I/O controller1015.

In some cases, the wireless device may include a single antenna1025. However, in some cases the device may have more than one antenna1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The code1035may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code1035may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code1035may not be directly executable by the processor1040but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG.11shows a flowchart illustrating a method1100that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The operations of method1100may be implemented by a UE115or its components or a wireless device115or its components as described herein. For example, the operations of method1100may be performed by a communications manager as described with reference toFIGS.7through10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At1105, the UE may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission. The operations of1105may be performed according to the methods described herein. In some examples, aspects of the operations of1105may be performed by a channel availability component as described with reference toFIGS.7through10.

At1110, the UE may transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE. The operations of1110may be performed according to the methods described herein. In some examples, aspects of the operations of1110may be performed by a message transmitter as described with reference toFIGS.7through10.

At1115, the UE may communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof. The operations of1115may be performed according to the methods described herein. In some examples, aspects of the operations of1115may be performed by a communications component as described with reference toFIGS.7through10.

FIG.12shows a flowchart illustrating a method1200that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The operations of method1200may be implemented by a UE115or its components or a wireless device115or its components as described herein. For example, the operations of method1200may be performed by a communications manager as described with reference toFIGS.7through10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At1205, the UE may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission. The operations of1205may be performed according to the methods described herein. In some examples, aspects of the operations of1205may be performed by a channel availability component as described with reference toFIGS.7through10.

At1210, the UE may detect one or more sidelink control messages from at least one other UE indicating a set of reserved slots reserved by the other UEs for subsequent communications within the COT interval. The operations of1210may be performed according to the methods described herein. In some examples, aspects of the operations of1210may be performed by a detection manager as described with reference toFIGS.7through10.

At1215, the UE may select the reserved slot based on the set of reserved slots such that each slot between the first slot and the reserved slot is reserved by the UE or the at least one other UE. The operations of1215may be performed according to the methods described herein. In some examples, aspects of the operations of1215may be performed by a slot reservation component as described with reference toFIGS.7through10.

At1220, the UE may transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE. The operations of1220may be performed according to the methods described herein. In some examples, aspects of the operations of1220may be performed by a message transmitter as described with reference toFIGS.7through10.

At1225, the UE may communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof. The operations of1225may be performed according to the methods described herein. In some examples, aspects of the operations of1225may be performed by a communications component as described with reference toFIGS.7through10.

FIG.13shows a flowchart illustrating a method1300that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The operations of method1300may be implemented by a UE115or its components or a wireless device115or its components as described herein. For example, the operations of method1300may be performed by a communications manager as described with reference toFIGS.7through10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At1305, the UE may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission. The operations of1305may be performed according to the methods described herein. In some examples, aspects of the operations of1305may be performed by a channel availability component as described with reference toFIGS.7through10.

At1310, the UE may select the reserved slot to be consecutive to the first slot. The operations of1310may be performed according to the methods described herein. In some examples, aspects of the operations of1310may be performed by a slot reservation component as described with reference toFIGS.7through10.

At1315, the UE may transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE. The operations of1315may be performed according to the methods described herein. In some examples, aspects of the operations of1315may be performed by a message transmitter as described with reference toFIGS.7through10.

At1320, the UE may refrain from performing the channel sensing procedure before the reserved slot based on the reserved slot and the first slot being consecutive. The operations of1320may be performed according to the methods described herein. In some examples, aspects of the operations of1320may be performed by a LBT manager as described with reference toFIGS.7through10.

At1325, the UE may communicate in the reserved slot based on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof. The operations of1325may be performed according to the methods described herein. In some examples, aspects of the operations of1325may be performed by a communications component as described with reference toFIGS.7through10.

FIG.14shows a flowchart illustrating a method1400that supports channel access with reservation for sidelink communication in unlicensed spectrum in accordance with aspects of the present disclosure. The operations of method1400may be implemented by a UE115or its components or a wireless device115or its components as described herein. For example, the operations of method1400may be performed by a communications manager as described with reference toFIGS.7through10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described herein. Additionally or alternatively, a UE may perform aspects of the functions described herein using special-purpose hardware.

At1405, the UE may determine that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission. The operations of1405may be performed according to the methods described herein. In some examples, aspects of the operations of1405may be performed by a channel availability component as described with reference toFIGS.7through10.

At1410, the UE may transmit a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE. The operations of1410may be performed according to the methods described herein. In some examples, aspects of the operations of1410may be performed by a message transmitter as described with reference toFIGS.7through10.

At1415, the UE may detect one or more sidelink control messages from at least one other UE in a second slot preceding the reserved slot, where the second slot and the reserved slot are consecutive. The operations of1415may be performed according to the methods described herein. In some examples, aspects of the operations of1415may be performed by a detection manager as described with reference toFIGS.7through10.

At1420, the UE communicate in the reserved slot based one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof or based on detecting the one or more sidelink control messages in the second slot preceding the reserved slot. The operations of1420may be performed according to the methods described herein. In some examples, aspects of the operations of1420may be performed by a communications component as described with reference toFIGS.7through10.

Aspect 1: A method for wireless communications at a UE, including: determining that a CO in a shared radio frequency spectrum band is available for use by the UE for sidelink transmission; transmitting a message in a first slot of the CO using a channel of the shared radio frequency spectrum band, the message indicating a reserved slot within the CO for a subsequent communication by the UE; and communicating in the reserved slot based at least in part on one or more control messages between the first slot and the reserved slot, one or more RSRP measurements between the first slot and the reserved slot, a channel sensing procedure with energy detection within a sensing window, or a combination thereof.

Aspect 2: The method of aspect 1, further including: detecting one or more sidelink control messages from at least one other UE indicating a set of reserved slots reserved by the at least one other UE for subsequent communications within the CO; and selecting the reserved slot based at least in part on the set of reserved slots such that each slot between the first slot and the reserved slot is reserved by the UE or the at least one other UE.

Aspect 3: The method of any of aspects 1 through 2, further including: selecting the reserved slot to be consecutive to the first slot; and refraining from performing the channel sensing procedure before the reserved slot based at least in part on the reserved slot and the first slot being consecutive.

Aspect 4: The method of aspect 3, further including: selecting the reserved slot to be consecutive to the first slot based at least in part on transmissions in the first slot by the UE being independent of feedback in response to the transmissions.

Aspect 5: The method of any of aspects 3 through 4, where communicating the reserved slot includes: transmitting a feedback request for transmissions in the reserved slot.

Aspect 6: The method of aspect 5, where the feedback request specifies one or more slots within the CO reserved for feedback.

Aspect 7: The method of any of aspects 1 through 6, further including: detecting, as part of the channel sensing procedure, one or more sidelink control messages from at least one other UE in a second slot preceding the reserved slot, where the second slot and the reserved slot are consecutive; and communicating in the reserved slot based at least in part on detecting the one or more sidelink control messages.

Aspect 8: The method of any of aspects 1 through 7, further including: detecting, as part of the channel sensing procedure, one or more sidelink control messages from at least one other UE in each slot between the first slot and the reserved slot; and communicating in the reserved slot based at least in part on detecting the one or more sidelink control messages in each slot between the first slot and the reserved slot.

Aspect 9: The method of any of aspects 1 through 8, further including: communicating in the reserved slot based at least in part on an RSRP measurement of sidelink transmissions in all slots between the first slot and the reserved slot exceeding an RSRP threshold.

Aspect 10: The method of any of aspects 1 through 9, further including: communicating in the reserved slot based at least in part on an RSRP measurement of sidelink transmissions in a second slot consecutive to the reserved slot exceeding an RSRP threshold.

Aspect 11: The method of any of aspects 1 through 10, further including: communicating in the reserved slot based at least in part on the energy detection in the sensing window between the first slot and the reserved slot being below an energy detection threshold.

Aspect 12: The method of aspect 11, further including: performing energy detection in one or more symbols of a second slot preceding the reserved slot, where the second slot and the reserved slot are consecutive.

Aspect 13: The method of aspect 12, further including: determining the one or more symbols based at least in part on a sensing window size, a reception mode to transmission mode transition time, a fixed gap value, or a combination thereof.

Aspect 14: The method of any of aspects 1 through 13, further including: transmitting a feedback request for transmissions in the first slot, the feedback request indicating that the reserved slot is for feedback for the transmissions.

Aspect 15: The method of any of aspects 1 through 14, further including: transmitting a feedback request for transmissions in the first slot, the feedback request indicating that the reserved slot and one or more other slots within the CO are for feedback for the transmissions.

Aspect 16: The method of aspect 15, further including: receiving, in the reserved slot, feedback for the transmissions in the first slot; and releasing the one or more other slots based at least in part on receiving feedback for the transmissions in the first slot.

Aspect 17: An apparatus for wireless communications at a UE, including a processor; memory coupled with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to perform a method of any of aspects 1 through 16.

Aspect 18: An apparatus for wireless communications at a UE, including at least one means for performing a method of any of aspects 1 through 16.