Patent Description:
Aspects of wireless communication may comprise direct communication between devices, such as based on sidelink. There exists a need for further improvements in sidelink communication technology.

R1-<NUM> (<NPL>) discloses physical layer structures for sidelink and DMRS patterns for a physical sidelink control channel (PSCCH) and a physical sidelink shared channel (PSSCH).

R1/<NUM> (<NPL>) also discloses physical layer structures for sidelink and DMRS patterns for PSCCH and PSSCH.

Apparatuses and methods are provided as set out in the independent claims.

By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer.

While aspects and implementations are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, and packaging arrangements. For example, implementations and/or uses may come about via integrated chip implementations and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, artificial intelligence (AI)-enabled devices, etc.). While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or original equipment manufacturer (OEM) devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also include additional components and features for implementation and practice of claimed and described aspect. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processor(s), interleaver, adders/summers, etc.). It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, end-user devices, etc. of varying sizes, shapes, and constitution.

Aspects presented herein may provide a periodic resource allocation mechanism that enables periodically reserved resources to be used for aperiodic traffic. The aspects presented herein may enable a UE to reserve periodic resources based on a sensing or partial sensing technique while also providing support for aperiodic traffic. When a UE elects not to use a reserved resource in a transmission period, the UE may be configured to refrain from transmitting any data in that transmission period, thereby enabling the UE to adapt the resource reservation based on an instantaneous traffic load. Thus, a sidelink resource may be reserved by UEs in a periodic fashion while still providing flexibility for aperiodic traffic.

In certain aspects, the UE <NUM> may include a resource reservation component <NUM> configured to reserve resources on a sidelink. The resource reservation component <NUM> may enable a UE to make resource reservation on a sidelink and to refrain transmitting any data in the reserved resources when the UE determines there is no data to be transmitted in a transmission window. The resource reservation component <NUM> may optionally enable the UE to release the reserved resources after the UE stops to transmit data for a consecutive period. In one configuration, the resource reservation component <NUM> may be configured to reserve a set of periodic resources for sidelink transmission, where the reserved set of periodic resources include reserved resources for SCI and reserved resources for data. In such configuration, the resource reservation component <NUM> may transmit the SCI without a data transmission in a periodic resource for a period. In another configuration, the resource reservation component <NUM> may be configured to receive a reservation from a second wireless device for a set of periodic resources for sidelink transmission. In such configuration, the resource reservation component <NUM> may receive, from the second wireless device, SCI in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission.

Some examples of sidelink communication may include vehicle-based communication such as vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) (e.g., from the vehicle-based communication device to road infrastructure nodes such as a Road Side Unit (RSU)), vehicle-to-network (V2N) (e.g., from the vehicle-based communication device to one or more network nodes, such as a base station), vehicle-to-pedestrian (V2P), cellular vehicle-to-everything (C-V2X), and/or a combination thereof and/or with other devices, which can be collectively referred to as V2X communications. As an example, in <FIG>, a UE <NUM>, e.g., a transmitting Vehicle User Equipment (VUE) or other UE <NUM>, may be configured to transmit messages directly to another UE <NUM>. The communication may be based on V2X or other D2D communication, such as Proximity Services (ProSe), etc. Communication based on V2X and/or D2D may also be transmitted and received by other transmitting and receiving devices, such as Road Side Unit (RSU) <NUM>, etc. Aspects of the communication may be based on PC5 or sidelink communication e.g., as described in connection with the example in <FIG>. Although the following description may provide examples for V2X/D2D communication in connection with <NUM> NR, the concepts described herein may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

<FIG> illustrates example diagrams <NUM> and <NUM> illustrating non-limiting aspects of slot structures that may be used for sidelink communication. The slot structure may be within a <NUM>/NR frame structure in some examples. In other examples, the slot structure may be within an LTE frame structure or a frame structure. Aspects may also be applied within a slot structure of a different radio access technology. The example slot structure in <FIG> is merely one example, and other sidelink communication may have a different frame structure and/or different channels for sidelink communication. Diagram <NUM> illustrates a single resource block of a single slot transmission, e.g., which may correspond to a <NUM> transmission time interval (TTI). A physical sidelink control channel may be configured to occupy multiple physical resource blocks (PRBs), e.g., <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> PRBs. The PSCCH may be limited to a single sub-channel. A PSCCH duration may be configured to be <NUM> symbols or <NUM> symbols, for example. A sub-channel may comprise <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> PRBs, for example. The resources for a sidelink transmission may be selected from a resource pool including one or more subchannels. As a non-limiting example, the resource pool may include between <NUM>-<NUM> subchannels. A PSCCH size may be established for a resource pool, e.g., as between <NUM>-<NUM> % of one subchannel for a duration of <NUM> symbols or <NUM> symbols. The diagram <NUM> in <FIG> illustrates an example in which the PSCCH occupies about <NUM>% of a subchannel, as one example to illustrate the concept of PSCCH occupying a portion of a subchannel. The physical sidelink shared channel (PSSCH) occupies at least one subchannel. The PSCCH may include a first portion of sidelink control information (SCI), and the PSSCH may include a second portion of SCI in some examples.

Each time slot may include a resource block (RB) (also referred to as physical RBs (PRBs)) that extends <NUM> consecutive subcarriers. As illustrated in <FIG>, some of the REs may include control information in PSCCH and some REs may include demodulation RS (DMRS). At least one symbol may be used for feedback. <FIG> illustrates examples with two symbols for a physical sidelink feedback channel (PSFCH) with adjacent gap symbols. A symbol prior to and/or after the feedback may be used for turnaround between reception of data and transmission of the feedback. The gap enables a device to switch from operating as a transmitting device to prepare to operate as a receiving device, e.g., in the following slot. Data may be transmitted in the remaining REs, as illustrated. The data may comprise the data message described herein. The position of any of the data, DMRS, SCI, feedback gap symbols, and/or LBT symbols may be different than the example illustrated in <FIG>. Multiple slots may be aggregated together in some aspects.

<FIG> is a block diagram <NUM> of a first wireless communication device <NUM> in communication with a second wireless communication device <NUM>. The communication may be based on sidelink, e.g., using a PC5 interface. In some examples, the devices <NUM> and <NUM> may communicate based on V2X or other D2D communication. The devices <NUM> and the <NUM> may comprise a UE, an RSU, a base station, etc. In some examples, the device <NUM> may be a UE and the device <NUM> may be a UE. Packets may be provided to a controller/processor <NUM> that implements layer <NUM> and layer <NUM> functionality.

At least one of the TX processor <NUM>, the RX processor <NUM>, or the controller/processor <NUM> of device <NUM> or the TX <NUM>, the RX processor <NUM>, or the controller/processor <NUM> may be configured to perform aspects described in connection with resource reservation component <NUM> of <FIG>.

<FIG> is a diagram <NUM> illustrating an example of sidelink communication between wireless devices. The communication may be based on a slot structure including aspects described in connection with <FIG> or another sidelink structure. Although the example in <FIG> is described for the UEs <NUM>, <NUM>, <NUM>, <NUM>, aspects may be applied to other wireless devices configured for communication based on sidelink, such as an RSU, an IAB node, etc. As illustrated in <FIG>, a transmitting UE <NUM> may transmit a transmission <NUM> including a control information (e.g., sidelink control information (SCI)) and/or a corresponding data channel, that may be received by receiving UEs <NUM>, <NUM>, <NUM>. The SCI may include information for decoding the corresponding data and may also be used by receiving device to avoid interference by refraining from transmitting on the occupied resources during a data transmission. For example, the SCI may reserve resources for sidelink communication. The number of TTIs, as well as the RBs that will be occupied by the data transmission, may be indicated in SCI from the transmitting device. The UEs <NUM>, <NUM>, <NUM>, <NUM> may each be capable of operating as a transmitting device in addition to operating as a receiving device. Thus, the UEs <NUM>, <NUM> are illustrated as transmitting transmissions <NUM> and <NUM>. The transmissions <NUM>, <NUM> or <NUM> may be broadcast or multicast to nearby devices. For example, the UE <NUM> may transmit communication intended for receipt by other UEs within a range <NUM> of the UE <NUM>. In other examples, the transmissions <NUM>, <NUM>, or <NUM> may be groupcast to nearby devices that are a member of a group. In other examples, the transmissions <NUM>, <NUM>, or <NUM> may be unicast from one UE to another UE. Additionally, or alternatively, the RSU <NUM> may receive communication from and/or transmit communication <NUM> to the UEs <NUM>, <NUM>, <NUM>, <NUM>.

Resource allocation may refer to how a resource (e.g., time and/or frequency resource) is allocated to a transmitting device for transmitting a packet. In sidelink communication, resource allocation may be performed in a centralized manner (which may be referred to herein as "Mode <NUM>") or in a distributed manner (which may be referred to herein as "Mode <NUM>"). When operating using Mode <NUM>, resource allocations for sidelink communication may be determined by a network entity, such as a base station. For example, the base station may transmit an indication to a UE that indicates the resources that are allocated to the UE to use to transmit sidelink communication, e.g., for transmitting sidelink data packets to other UEs. When operating using Mode <NUM>, the resource allocations for sidelink communication are determined by the communicating UE, e.g., with each UE autonomously determine resources to use for sidelink transmission. For example, a transmitting UE may autonomously determine resource allocations for transmitting sidelink control and data to one or more receiving UE. In order to coordinate the selection of sidelink resources by individual UEs, each UE may use a sensing technique to monitor for resource reservations by other sidelink UEs and may select resources for sidelink transmissions from unreserved resources. Devices communicating based on sidelink, may determine one or more radio resources in the time and frequency domain that are used by other devices in order to select transmission resources that avoid collisions with other devices.

For example, as part of a sensing mechanism for resource allocation mode <NUM>, the UE may determine (e.g., sense) whether the selected sidelink resource has been reserved by other UE(s) before selecting a sidelink resource for a data transmission. If the UE determines that the sidelink resource has not been reserved by other UEs, the UE may use the selected sidelink resource for transmitting the data, e.g., in a PSSCH transmission. The UE may estimate or determine which radio resources (e.g., sidelink resources) may be in-use and/or reserved by others by detecting and decoding sidelink control information (SCI) transmitted by other UEs. The UE may use a sensing-based resource selection algorithm to estimate or determine which radio resources are in-use and/or reserved by others. The UE may receive SCI from another UE that includes reservation information based on a resource reservation field comprised in the SCI. The UE may continuously monitor for (e.g., sense) and decode SCI from peer UEs. The SCI may include reservation information, e.g., indicating slots and RBs that a particular UE has selected for a future transmission. The UE may exclude resources that are used and/or reserved by other UEs from a set of candidate resources for sidelink transmission by the UE, and the UE may select/reserve resources for a sidelink transmission from the resources that are unused and therefore form the set of candidate resources. The UE may continuously perform sensing for SCI with resource reservations in order to maintain a set of candidate resources from which the UE may select one or more resources for a sidelink transmission. Once the UE selects a candidate resource, the UE may transmit SCI indicating its own reservation of the resource for a sidelink transmission. The number of resources (e.g., sub-channels per subframe) reserved by the UE may depend on the size of data to be transmitted by the UE. Although the example is described for a UE receiving reservations from another UE, the reservations may also be received from an RSU or other device communicating based on sidelink.

When operating using Mode <NUM> (e.g., in a distributed manner), the transmitting UE may determine the resources to use for communicating from a resource pool. A resource pool may refer to a collection of time and/or frequency resources on which sidelink communication may occur. <FIG> illustrates an example of time and frequency resources that may be available for sidelink communication. A resource pool may be either preconfigured (e.g., preloaded on a UE), configured by a base station, or otherwise determined by the UE. In some examples, a transmitting UE may randomly select resources from a resource pool for a transmission. In such examples, receiving UEs may continuously monitor candidate resources to receive a communication, e.g., SCI indicating a resource reservation. In some examples, if a nearby UE randomly selects the same resource, a collision or interference may occur.

In some examples, a UE may use historical resource utilization of other UEs to predict future activity. For example, by identifying that a first UE transmits periodically and what resources the first UE uses when transmitting, a second UE may determine on which resources future transmissions by the first UE may occur and also when they may occur. <FIG> illustrates an example of period resources <NUM> that may be reserved by a UE for sidelink communication. Thus, by "listening" to other UE activity in the past (e.g., historical resource utilization), the second UE may predict future activity of the other UEs and can select a resource to use for a transmission that is less likely to result in a collision and/or interference.

However, it may be appreciated that for the second UE to identify historical resource utilization, the second UE may operate in an "always-on" mode to facilitate sensing or receiving of transmission by the other UEs. The continual monitoring by the second UE increases power consumption or processing resources in order to identify historical resource utilization and to predict future activity.

In some examples, a UE may perform partial sensing for determining historical resource utilization of other UEs. When performing partial sensing, the UE may selectively sense a subset of resources and, thus, may reduce power consumption in comparison to monitoring the set of resources. However, partial sensing may not be effective when transmissions by other UEs are not periodic. For example, a UE employing partial sensing may miss information about aperiodic transmissions and, thus, may be unable to accurately predict future activity of the other UEs based on a determined historical resource utilization.

The radio resource allocation for a sidelink communication may be based on resource reservations. For instance, when a UE is preparing to transmit data on a sidelink, the UE may first determine whether resources are reserved by other UEs. Then, the UE may reserve resources from the remaining unreserved resources that are available. <FIG> is a diagram <NUM> illustrating an example of resources reservations for sidelink transmissions. The resource allocation for each UE may be in units of one or more sub-channels in the frequency domain (e.g., sub-channels SC <NUM> to SC <NUM>), and may be based on one slot in the time domain. The UE may also use resources in the current slot to perform an initial transmission, and may reserve resources in future slots for retransmissions. In this example, up to two different future slots may be reserved by the UEs (e.g., UE1 and UE2) for retransmissions. The resource reservation may be limited to a window of pre-defined slots and sub-channels. For example, as shown by diagram <NUM> in <FIG>, the resource reservation may include an eight (<NUM>) time slots by four (<NUM>) sub-channels window, which may provide a total number of thirty-two (<NUM>) available resource blocks. This window for resource reservation may also be referred to as a resource selection window. Each resource block in the resource selection window may be used by a transmitting device for transmitting both data and control information.

In one example, a first UE ("UE1) may reserve a sub-channel (e.g., SC <NUM>) in a current slot (e.g., slot <NUM>) for its initial data transmission, and may reserve additional future slots within the window for data retransmissions (e.g., <NUM> and <NUM>). For example, UE1 may reserve sub-channels SC <NUM> at slots <NUM> and SC <NUM> at slot <NUM> for future retransmissions as shown by <FIG>. UE1 may then transmit information regarding which resources are being used and/or reserved by it to other UE(s), such as by including the reservation information in the reservation resource field of the SCI, e.g., a first stage SCI. The UE may be configured to use the SCI to reserve one, two or three transmissions. A maximum number of reservation allowed for a UE may be pre-configured for the UE. For example, a UE may be reserve up to three transmissions within a resource selection window.

As illustrated by <FIG>, a second UE ("UE2") may also reserve resources in sub-channels SC <NUM> and SC <NUM> at time slot <NUM> for its current data transmission, and may reserve a first data retransmission at time slot <NUM> using sub-channels SC <NUM> and SC <NUM>, and reserve a second data retransmission at time slot <NUM> using sub-channels SC <NUM> and SC <NUM> as shown by <FIG>. Similarly, UE2 may then transmit the resource usage and reservation information to other UE(s), such as using the reservation resource field in SCI. The UE may also be configured to make all the reservations with same number of sub-channels (e.g., bandwidth). For example, resources <NUM>, <NUM> and <NUM> reserved by UE1 may have same number of sub-channels (e.g., <NUM>), and resources <NUM>, <NUM> and <NUM> reserved by UE2 may have same number of sub-channels (e.g., <NUM>) as well. However, the starting sub-channel for each reserved resource may be different. For example, resource <NUM> may start at SC <NUM>, resource <NUM> may start at SC <NUM>, and resource <NUM> may start at SC3, etc..

<FIG> is a diagram <NUM> illustrating an example of a resource reservation. If a UE (e.g., a sidelink transmitting UE) is using a first resource <NUM> for transmission at slot i in a period (such as period <NUM> illustrated in <FIG>), the UE may reserve two more resources within the same period, such as a second resource <NUM> at slot i + x and a third resource <NUM> at slot i + y. Each of the reserved resources <NUM>, <NUM> and <NUM> may have a number of z sub-channels. For example, if the period has thirty-two (<NUM>) slots (e.g., with slot index from #<NUM> to #<NUM>), the UE may transmit the first resource <NUM> at slot <NUM> with z sub-channels, and the UE may reserve the second resource <NUM> with z sub-channels at slot i + x where x may be greater than zero (<NUM>), and smaller or equal to thirty-one (<NUM>) (e.g., <NUM> < x ≤ <NUM>), and the UE may further reserve the third resource <NUM> with z sub-channels at slot i + y where y may be greater than x, and smaller or equal to thirty-one (<NUM>) (e.g., x < y ≤ <NUM>). Table <NUM> below is an example reservations signaled by the SCI of the UE in slot i corresponding to <FIG>.

The UE may use the second resource <NUM> and/or the third resource <NUM> for retransmission of the first resource <NUM>, such as when the transmission of the first resource <NUM> fails. The UE may also use the second resource <NUM> and/or the third resource <NUM> for other purposes other than retransmission.

A transmitting UE using a reserved resource for transmission may request a feedback from one or more receiving UEs or a base station for the transmission. Based on the feedback from the one or more receiving UEs or the base station, the transmitting UE may elect not to use a reserved resource. For example, referring back to <FIG>, a transmitting UE may use the first resource <NUM> for a data transmission, and may request a receiving UE or a base station receiving the data transmission to provide a feedback to the transmitting UE. If the transmitting receives a feedback from the receiving UE or the base station confirming the reception/decoding of the data transmission, the transmitting UE may elect not to use the second resources <NUM> and/or the third resource <NUM>, which may originally be configured or reserved for retransmissions of the data transmission.

A sidelink resource reservation may be periodic or aperiodic. For example, a UE may periodically reserve one or more sidelink resources, such as by indicating a reservation period in a SCI or in one part of the SCI (e.g., in SCI-<NUM> of a two-stage SCI as discussed in details in <FIG>). Thus, when the periodic resource reservation is enabled for a UE, the reservations in the SCI may be repeated with the signaled period. In some examples, a reservation period for the periodic resource reservation may be configured to values between <NUM> and <NUM> by signaling in the SCI, and the periodic resource reservation may also be disabled by a (pre-) configuration. In other examples, each resource reservation may be associated with a priority level indicated in the SCI. A resource reservation associated with a higher priority level may pre-empt a resource reservation associated with a lower priority level.

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

<FIG> is a diagram <NUM> illustrating an example of a two-stage SCI. To reduce control overhead and to improve the processing timeline, SCI used for sidelink grant(s) may split into two parts or more. For example, a first SCI part <NUM> may be transmitted within the control region (e.g., the PSCCH region <NUM>) and a second SCI part <NUM> may be transmitted within the downlink traffic region (e.g., the PSSCH region <NUM>). The PSCCH region <NUM> and the PSSCH region <NUM> may together form one slot. The first SCI part <NUM> may include initial control information regarding a sidelink transmission, such as the resource assignment (RA) in SCH <NUM> or other resource reservation information, rank and modulation order of the sidelink assignment, etc. In addition, the first SCI part <NUM> may also include control information about the second SCI part <NUM>. In some examples, the control information may indicate the number of resource elements (size) and code rate of the second SCI part <NUM>. The control information may further indicate the location (e.g., starting resource element) and code rate of the second SCI part <NUM>. The second SCI part <NUM> may include the remaining control information regarding the sidelink assignment. For example, the remaining control information may include non-time critical control information or other resource allocation for data transmission in SCH <NUM>, such as the source and destination ID for the data transmission. In one aspect, a the first SCI part <NUM> (e.g., SCI-<NUM>) format may include one or more of followings: a priority (QoS value), a PSSCH resource assignment (e.g., frequency/time resource for PSSCH), a resource reservation period (e.g., if enabled), a PSSCH DMRS pattern (e.g., if more than one patterns are configured), a second SCI format (e.g. information on the size of the second SCI), a <NUM>-bit beta offset for second stage control resource allocation, number of PSSCH DMRS port(s) (e.g., <NUM> or <NUM>), a <NUM>-bit MCS and/or reserved bits, etc..

As discussed in connection with <FIG> and <FIG>, a resource allocation mechanism based on sensing and/or partial sensing may be configured to be periodic as periodic resource reservation may enable sidelink transmitting UE(s) to identify and predict the activity of other transmitting UE(s) based on their past activities (e.g., their use of reserved resources, etc.). Thus, the resource allocation mechanism may reduce resource collisions between different transmitting UEs. However, the sensing or partial sensing mechanism may be less effective for aperiodic traffic or aperiodic resource allocation as the activity of other transmitting UEs may be less predictable. In addition, the periodic resource allocation may not be flexible enough to accommodate the aperiodic traffic. For example, as the periodic resource allocation may have a fixed resource allocation in every period, the resource allocation within a resource selection window may be fully reserved by multiple UEs for retransmissions, giving aperiodic traffic less options of available resources within the resource selection window. Further, a transmitting UE may reserve a resource and elect not to use the reserved resource, which may result in a waste of the resource and reduce flexibility for other UEs to reuse the resource.

Aspects presented herein may provide a periodic resource allocation mechanism that enables periodically reserved resources to be used for aperiodic sidelink traffic, which may enable UEs to reserve resources periodically based on sensing or partial sensing technique while providing support for aperiodic traffic. In one aspect, the resource reservation among one or more transmitting UEs may be periodic to enable or facilitate the sensing activity by other transmitting UE(s), such as described in connection with <FIG>. If a UE elects not to use a reserved resource in a transmission period, the UE may be configured to refrain from transmitting any data (e.g., padding data) in the reserved resources within the transmission period, thereby enabling the UE to adapt the resource reservation based on an instantaneous traffic load. Thus, a sidelink resource may be reserved by UEs in a periodic fashion while still providing flexibility for aperiodic traffic.

In a given period, when a UE does not have any data transmission, the UE may remain idle and not transmit SCI and/or data. For example, the UE may skip transmissions for the given period. While this may enable power saving for the UE, the UE may lose its periodically reserved resources for the sidelink channel (e.g., periodic time and frequency resources) if the UE does not transmit for a certain period. For example, as described in connection with <FIG> and <FIG>, when a transmitting UE reserves a resource for transmission, the UE may reserve additional resources for future transmission. However, when the UE does not transmit (e.g., in a currently reserved slot), the UE may not reserve the additional future slot(s). For example, each periodic resource may indicate the next periodic resource. If the UE does not transmit within a periodic resource, the next periodic resource may not be indicated. Thus, resources within the sidelink channel may be reserved and occupied by other UE(s) and/or base station, and the UE may not be able to reserve any resource in the future if the sidelink channel becomes fully occupied. On the other hand, to maintain periodic resource reservations, the UE may continue to transmit both data (e.g., SCH <NUM>) and control information (e.g., SCI) using the reserved resources, where the data may be padding data (i.e., data with bit paddings). While this may enable the UE to maintain the resource reservation within the channel, it may be a waste of power for the UE and a waste of resources that could potentially be used by other UEs.

<FIG> are diagrams 800A and 800B illustrating examples of a UE making and using reserved resources according to aspects of the present disclosure. In one aspect, a transmitting UE may reserve a set of periodic resources within a transmission period, such as described in connection with <FIG> and <FIG>. The transmission period may be based on a periodic resource reservation, such as the period between periodic resources. In some examples, the transmission period may be based on a resource selection window. When sidelink data is ready for transmission by the transmitting UE, e.g., prior to the start of the transmission period, the transmitting UE may use the periodic reserved resources to transmit the data. For example, as shown by <FIG>, a transmitting UE may reserve resources <NUM>, <NUM> and <NUM> within a transmission period <NUM> (e.g., resource window). If a data <NUM> arrives at the transmitting UE before the start of the transmission period <NUM>, the transmitting UE may use the reserved resources <NUM>, <NUM> and/or <NUM> to transmit and/or retransmit the data <NUM> and its corresponding SCI <NUM>. On the other hand, as shown by <FIG>, if the transmitting UE determines that there is no data to be transmitted in transmission period <NUM>, the transmitting UE may be configured to transmit SCI <NUM> in the reserved resources <NUM>, <NUM> and/or <NUM> without transmitting data (e.g., without transmitting padding data). The transmission of the SCI without the data may enable the transmitting UE to maintain the resource reservation for future transmissions without occupying the data region (e.g., the PSSCH region <NUM> in <FIG>) when there is no data to be transmitted. As the data region (or PSSCH resources) within the reserved resources <NUM>, <NUM> and <NUM> is not used by the transmitting UE, the unused resources may be used by other devices, e.g., to serve aperiodic traffic, emergency traffic, etc. The transmission of the SCI without the data may also effectively reduce resource collision between aperiodic traffic and the periodic reserved resource.

While the transmitting UE may choose not to transmit any data in the PSSCH, the transmitting UE may still indicate its PSSCH resource allocation (e.g., via the SCI), such that the transmitting UE may continue to reserve time-domain and/or frequency-domain resources associated with the PSSCH (i.e., data) transmission. In other words, the transmitting may continue to perform PSSCH resource reservation or assignment (e.g., frequency or time resource for PSSCH) as if there is data to be transmitted, but may choose not to transmit any data in the reserved or assigned resource(s). Thus, the transmitting UE may continue to reserve the resources by indicating reserved resources in the SCI on the data channel. As such, other UEs that decodes the SCI (i.e., SCI-<NUM>) may still be able to know what time/frequency domain resources are to be reserved/used by the transmitting UE.

In one aspect of the present disclosure, for a transmitting UE to inform other UEs, or other devices such as a base station, that the transmitting UE is not going to transmit any data in one or more reserved resources within a transmission period, such as described in connection with <FIG>, the transmitting UE may indicate in SCI whether there is an associated data transmission from the transmitting UE. For example, the transmitting UE may use one or more bits of the SCI or may add or more bits to the SCI (e.g., to the SL_SCH field) to indicate whether there is data associated with its transmission. In another example, the UE may include a single bit in the SCI that indicates whether there is a data transmission associated with the SCI. In such an example, the transmitting UE may indicate zero (<NUM>) in the bit indication field of the SCI when there is no associated data transmission. Then, the UE may use the reserved resources to transmit SCI and skip transmission of data. In response, a receiving UE may receive the SCI, determine that there is no accompanying data transmission and skip monitoring for the data or attempting to receive the data, which may conserve the power of the receiving UE. In such an example, the transmitting UE may indicate one (<NUM>) in the bit field of the SCI when there is data transmission. Then, the UE may use the reserve resources to transmit both the SCI and the data. A UE receiving the SCI may determine that there is an accompanying data transmission and may determine information for the data transmission and attempt to receive the data transmission.

As described in connection with <FIG>, the SCI used for sidelink grant(s) may include two parts, where a first SCI part (e.g., SCI-<NUM>) may be transmitted within the control region (e.g., PSCCH) and a second SCI part (e.g., SCI-<NUM>) may be transmitted within the downlink traffic region (e.g., PSSCH). In one aspect (e.g., Option <NUM>), the indication of whether the transmitting UE is going to send data in the reserved resources of the period may be contained in the SCI-<NUM>. The transmitting UE may transmit the SCI-<NUM> in the reserved resources without transmitting data or SCI-<NUM> when there is no data transmission. In another aspect (e.g., Option <NUM>), the indication about whether the transmitting UE is sending any data in the reserved resources may be contained in the SCI-<NUM>, and the transmitting UE may transmit both the SCI-<NUM> and the SCI-<NUM> in the reserved resources without transmitting data when there is no data transmission. If a receiving device receives the indication that the transmitting UE is not transmitting data associated with the SCI, such as through the indication in either the SCI-<NUM> or the SCI-<NUM>, then the receiving device may skip attempting to decode or monitor the data.

In some examples, transmitting the indication in SCI-<NUM> (e.g., Option <NUM>) may be more suitable for a unicast-service, where the SCI-<NUM> may be directed to one receiving device. As the SCI-<NUM> may contain the source and destination ID, the receiving device may be able to determine whether the SCI-<NUM> is targeted to the receiving device. For example, the transmitting UE may include the indication about whether there is accompanying data along with the source and destination ID in the SCI-<NUM>, and the receiving device may look at the destination ID as well as the indication in the SCI-<NUM> to determine whether there is a data transmission intended for the receiving device. If the SCI-<NUM> indicates that there is no data transmission, the receiving device may skip decoding the data or the receiving device does not expect there is any data to be decoded. On the other hand, transmitting the indication about whether there is accompanying data in SCI-<NUM> (e.g., Option <NUM>) may be more suitable or useful for group-cast/broadcast where there is a group of receiving devices that may receive the SCI.

As discussed in connection with <FIG> and <FIG>, a transmitting UE may use one SCI to reserve up to two more resources in the current transmission period (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) in addition to the reservation(s) in the next transmission period (e.g., <NUM>, <NUM>, <NUM> in the next transmission for periodic resource reservation). In one aspect of the present disclosure, if the transmitting UE indicates that there is no data transmission associated with the current SCI, the transmitting UE may not reserve other resources in the current transmission period, such as described in connection with <FIG>. For example, the UE may avoid reserving resources in a current transmission period. However, the transmitting UE may still indicate the reservation in the next transmission period, such as by indicating the period in the SCI-<NUM>. For example, as shown by diagram <NUM> in <FIG>, when a transmitting UE indicates in a current SCI <NUM> (e.g., SCI-<NUM>) for which the UE is not going to transmit any associated data in a current transmission period <NUM>, the transmitting UE may use a resource <NUM> within the current transmission period <NUM> to send the SCI <NUM>, but the transmitting UE may not reserve, or may skip reserving, other resources within the current transmission period <NUM>, such as resources <NUM> and <NUM>, etc. However, the transmitting UE may still make resource reservation for the next transmission period <NUM>, such as a resource <NUM>. As other resources in the same period (e.g., <NUM>, <NUM>) may be used for retransmissions, if there is no data transmission in the current transmission period, the transmitting UE may not have data to retransmit.

In another aspect of the present disclosure, a transmitting UE may be configured to release periodic reservations. For example, if a transmitting UE does not have data to transmit in K consecutive periods, then the transmitting UE may determine to release its reserved resource. The value K may be an integer defined at the transmitting UE or indicated to/configured for the transmitting UE, such as by a base station. If the transmitting UE has data to transmit after releasing its reserved resource, the transmitting UE may select or reserve new resources. For example, if the transmitting UE does not transmit data for a certain period of time, it may be likely that the transmitting UE has finished the transmission and may have no data to transmit. Thus, the transmitting UE may be configured to release its reserved resources. The releasing of periodic resources may enable more resources to be used by other devices.

In one example, after reaching K consecutive periods without data transmission, a transmitting UE may explicitly release the reservation (e.g., the periodic resource reservation). For example, the transmitting UE may indicate the release by setting the reservation period indicated in the SCI-<NUM> to a particular codepoint that is associated with a resource reservation release. For example, there may be an indication field for resource reservation period in SCI-<NUM> which may be used by the transmitting UE to indicate a time in which its next reservation may take place (e.g., <NUM>, <NUM> etc.). If this resource reservation period field in the SCI-<NUM> is enabled, other UE(s) or base station may determine that the transmitting UE has another transmission after the current transmission. The time or period in which the next reserved transmission arrives may be based on the periodicity of the resource reservation. Thus, the transmitting UE may explicitly release its reserved resources by setting resource reservation period field in the SCI-<NUM> to a certain codepoint, such as all zeros, etc. Other UE(s) that receives the SCI-<NUM> from the transmitting UE may determine that the transmitting UE has explicitly released its reserved resources, and may choose to use the released resources.

<FIG> is a diagram <NUM> illustrating an example of a resource allocation mechanism according to some aspects of the present disclosure. A transmitting UE may periodically reserve a plurality of resources <NUM> in multiple transmission periods (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> etc.). When a data packet <NUM> arrives before the transmission period <NUM> or the transmission occasion, the transmitting UE may use the resource <NUM> at transmission period <NUM> to transmit both the SCI <NUM> and the data packet <NUM>, and the transmitting UE may also use the SCI <NUM> transmitted in the transmission period to make resource reservation for next transmission period <NUM>. At transmission period <NUM>, if the transmitting UE has no data for transmission, then the transmitting UE may transmit SCI <NUM> in transmission period <NUM> without transmitting the data. However, the UE may still indicate the resource reservation for the next transmission period <NUM> by indicating the periodic resource in the SCI <NUM>. For example, the transmitting UE may still indicate the reserved resources (i.e., the dashed resources <NUM> in <FIG>) in the SCI (i.e., SCI-<NUM>) on the data channel (e.g., PSSCH), but the transmitting UE may not transmit any transmissions on the indicated resources as the transmitting UE's goal of indicating the resources of data transmission is to reserve the resources and may not be for actual data transmission. Thus, other UEs that decodes the SCI (i.e., SCI-<NUM>) may still be able to know what time/frequency domain resources are to be reserved by the transmitting UE.

The UE may perform/apply the same action at transmission periods, <NUM>, <NUM>, <NUM>, etc. However, if there is no data transmission after a consecutive number of periods (e.g., <NUM>), the transmitting UE may be configured to release the resource reservation, such as after transmission period <NUM>. Thus, at transmission period <NUM>, the UE may still transmit the SCI <NUM> which was reserved at the transmission period <NUM>, but the SCI <NUM> in transmission period <NUM> may contain an indication (e.g., by setting the period to a particular codepoint) indicating that the transmitting UE has released its reserved resources. The transmitting UE may stop using later instances of the periodic resource reservation, such as at reservation period <NUM>. If the UE has data to transmit after releasing the periodic resources, the UE may perform a new resource determination and reservation. Based on the codepoint in the SCI, other UEs or a base station may determine that the transmitting UE has released its reserved resources in transmission period <NUM>, and they may use this resource instead.

As described in connection with <FIG>, a transmitting UE using a reserved resource for transmission may request feedback from the receiving device. In response, the receiving device may transmit a hybrid automatic repeat request (HARQ)-ACK feedback if the transmission is successfully received and/or may transmit a HARQ-NACK feedback if the transmission fails (e.g., the transmission is not received after a certain period or if the received transmission is unable to be decoded, etc.). In one aspect, when a transmitting UE indicates that there is no data transmission associated with a transmission, the receiving device may still transmit HARQ-ACK feedback to the transmitting UE. For example, in the case of unicast, when an intended receiving UE decodes the transmitting UE's SCI and determines that there is no data transmission associated with the SCI, the receiving UE may still transmit HARQ-ACK feedback, and the HARQ-ACK feedback may indicate whether the SCI is received correctly. This feedback information may be used by the transmitting UE for link adaptation and measurement.

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

The transmitting UE may determine the HARQ-ACK resource using the mapping between the PSCCH and the physical sidelink feedback channel (PSFCH). As shown by diagram <NUM> in <FIG>, the starting sub-channel of a PSSCH (i.e., the data channel) may be used to determine the HARQ-ACK resource (i.e., the PSFCH). Thus, the transmitting UE may receive the HARQ feedback in the PSFCH based on one or more of: a starting sub-channel of a PSCCH in which the SCI is transmitted (e.g., either SCI-<NUM> or SCI if present), a slot including the PSCCH (e.g., either SCI-<NUM> or SCI if present), a source identifier, and/or a destination identifier of the transmission, etc. For example, when there is SCI transmitted without a data transmission is associated with the SCI, the UE may change its dependence on the data channel to the control channel. Thus, the UE may determine the HARQ-ACK feedback resource based on the sub-channel of the PSCCH and the slot index of the PSCCH. In other words, the sub-channel and the slot of the data transmission may be changed to the sub-channel and the slot of the control transmission in order to determine the feedback resource.

Additionally, or optionally, when a receiving UE receives an SCI indicating there is no data transmission from a transmitting UE, the receiving UE may determine whether to send the HARQ-ACK/NACK feedback based on whether the receiving UE receives an associated SCI-<NUM>. For example, if the receiving UE does not receive an SCI-<NUM>, such as if the SL_SCH field is contained in the SCI-<NUM>, the receiving UE may elect not to transmit a HARQ-ACK feedback. On the other hand, if the SL_SCH field is contained in the SCI-<NUM> and received by the receiving UE, the receiving UE may transmit a HARQ-ACK feedback to the transmitting UE.

<FIG> is a communication flow <NUM> between a first UE and a second UE according to aspects of the present disclosure. Aspects presented herein may enable a UE to reserve periodic resources based on a sensing or partial sensing, and when the UE elects not to use a reserved resource in a transmission period, the UE may be configured to refrain from transmitting any data in that transmission period, thereby enabling the UE to adapt the resource reservation based on an instantaneous traffic load.

At <NUM>, a first UE <NUM> may reserve a set of periodic resources for sidelink transmission, where the reserved set of periodic resources may include reserved resources for SCI and reserved resources for data, such as described in connection with <FIG> and <FIG>.

At <NUM>, after the first UE <NUM> reserves the set of periodic resources, the first UE <NUM> may indicate its reserve resource(s) in SCI, and may transmit the SCI to other UEs, such as a second UE <NUM>. As such, the second UE <NUM> may receive the resource reservation information from the first UE <NUM> for the set of periodic resources for sidelink transmission.

At <NUM>, the first UE <NUM> may determine not to transmit data in a period. For example, the first UE <NUM> may have completed a data transmission in a previous transmission occasion, and may have no additional data for transmission in the current transmission occasion. As such, the first UE <NUM> may determine not to transmit the data in the period based on there being no data for transmission at the first UE <NUM> in the period.

At <NUM>, after determining not to transmit data in a period, the first UE <NUM> may transmit, to the second UE <NUM>, SCI without transmitting data in a periodic resource for the period, such as described in connection with <FIG>, <FIG> and <FIG>.

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

At <NUM>, if the second UE <NUM> is configured to transmit a HARQ feedback for the SCI without data, the first UE <NUM> may receive a HARQ feedback for the SCI that is transmitted without data (e.g., for the SCI transmitted at <NUM>). For example, the first UE <NUM> may receive (or the second UE <NUM> may transmit) the HARQ feedback in a physical sidelink feedback channel (PSFCH) based on a starting sub-channel of a PSCCH in which the SCI is transmitted, a slot including the PSCCH in which the SCI is transmitted, a source identifier, and/or a destination identifier, etc. In another example, the first UE <NUM> may receive (or the second UE <NUM> may transmit) the HARQ feedback based on the SCI being unicast. In another example, the first UE <NUM> may receive (or the second UE <NUM> may transmit) the HARQ feedback based on a second part of the SCI being transmitted in a PSSCH.

At <NUM>, as described in connection with <FIG>, if the first UE <NUM> determines that it does not have data to transmit in a threshold number of consecutive periods, the first UE <NUM> may release one or more remaining periodic resources in the set of periodic resources.

At <NUM>, the first UE <NUM> may indicate to the second UE <NUM> regarding the releasing of the periodic resource reservation(s). For example, the first UE <NUM> may transmit the indication to the second UE <NUM> based on a codepoint transmitted in the SCI that corresponds to a release of a periodic reservation. For example, there may be an indication field for resource reservation period in SCI-<NUM> which may be used by the first UE <NUM> to indicate a time in which its next reservation may take place (e.g., <NUM>, <NUM> etc.). If this resource reservation period field in the SCI-<NUM> is enabled, the second UE <NUM> may determine that the first UE <NUM> has another transmission after the current transmission. Thus, the first UE <NUM> may explicitly release its reserved resources by setting resource reservation period field in the SCI-<NUM> to a certain codepoint, such as all zeros, etc. In response, the second UE <NUM> that receives the SCI-<NUM> from the first UE <NUM> may determine that the first UE <NUM> has explicitly released its reserved resources, and the second UE <NUM> may choose to use the released resources.

In some examples, as shown at <NUM>, the second UE <NUM> may measure RSRP for PSCCH that carries the SCI (e.g., the SCI received at <NUM>) (e.g., measure the DMRS of the PSCCH that contains the SCI), and the second UE <NUM> may determine whether a resource associated with the SCI is reserved based on the indication and the measured RSRP. For example, the second UE <NUM> (which may not be communicating with the first UE <NUM>) may monitor one or more SCIs transmitted by one or more UEs in its proximity (e.g., its reception range), and the second UE <NUM> may determine a resource in a next period may be reserved by at least one other UE if the second UE <NUM> detects that an SCI contains an indication that the SCI is not associated with a data transmission, and if the measured RSRP for the PSCCH that carries the SCI is above a threshold. For example, when a sensing UE (e.g., a transmitting UE that is transmitting a transmission to a receiving UE) detects an SCI from another (reserving) UE indicating resource reservation, the sensing UE may measure how strong the signal from the reserving UE is, such as based on measuring the RSRP of the channel. This may enable the sensing UE to determine how strong the interference may be experienced by the receiver of the sensing UE (e.g., the receiving UE) if the sensing UE is to transmit a packet in the corresponding resource. Thus, if the measured RSRP is large (e.g., above a threshold), this may indicate that the interference experienced by the receiver of the sensing UE is likely to be large, and hence the sensing UE may determine that this resource may not be used for transmission, and may skip using this resource. On the other hand, if the measured RSRP is small (e.g., below the threshold), this may indicate that the interference experienced by the receiver of the sensing UE is likely to be small, and therefore the sensing UE may determine to transmit using this resource. In other words, in both cases, the resource may be reserved by another UE(s) based on sending SCI. However, if the measured interference is small, the sensing UE may still use that resource for communication (e.g., as if the resource is not reserved). As such, in some examples, the sensing UE may determine whether a resource is available based on measured RSRP (instead of determining whether the resource is reserved or not).

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a wireless device or a component of a wireless device (e.g., a UE <NUM>, <NUM>; an RSU <NUM>; the device <NUM> or <NUM>; the apparatus <NUM>; a processing system, which may include the memory <NUM> and which may be the device <NUM> or a component of the device <NUM>, such as the TX processor <NUM>, the RX processor <NUM>, and/or the controller/processor <NUM>). The method may enable the UE to use periodic reserved resources to serve aperiodic traffic. The method may improve the use of wireless resources in sidelink communication.

At <NUM>, the wireless device may reserve a set of periodic resources for sidelink transmission, where the reserved set of periodic resources may include reserved resources for SCI and reserved resources for data, such as described in connection with <FIG>, <FIG>, <FIG>, and <FIG>. For example, at <NUM>, the first UE <NUM> may reserve a set of periodic resources for sidelink transmission that includes reserved resources for SCI and data. The reservation of the set of periodic resources for sidelink transmission may be performed, e.g., by the resource reservation component <NUM> of the apparatus <NUM> in <FIG>.

At <NUM>, the wireless device may determine not to transmit data in a period, such as described in connection with <FIG>, <FIG>, <FIG>, and <FIG>. For example, at <NUM>, the first UE <NUM> may determine not to transmit data in a period. The determination of not to transmit data may be performed, e.g., by the data transmission determination component <NUM> of the apparatus <NUM> in <FIG>. As such, the wireless device may determine not to transmit the data in the period based on there being no data for transmission at the wireless device in the period.

At <NUM>, the wireless device may transmit the SCI without a data transmission in a periodic resource for a period, such as described in connection with <FIG>, <FIG>, <FIG>, and <FIG>. For example, at <NUM>, the first UE <NUM> may transmit SCI without transmitting data to the second UE <NUM>. The transmission of the SCI without data may be performed, e.g., by the SCI processing component <NUM> and/or the transmission component <NUM> of the apparatus <NUM> in <FIG>. In one example, the SCI may include an indication that there is no data transmission associated with the SCI. In such an example, a two-stage SCI may be used, such that the indication may be included in a first portion of the SCI (e.g., SCI-<NUM>) that is transmitted on a PSCCH. In another example, the indication may be included in a second portion of the SCI (e.g., SCI-<NUM>) that is transmitted on a PSSCH, such as described in connection with <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>. In another example, when there is no data to transmit within the period, the SCI may not reserve resources within the period and may indicate a periodic reservation in a next period. As such, the wireless device may transmit the SCI without the data transmission in the period based on there being no data for transmission at the wireless device in the period.

At <NUM>, the wireless device may receive HARQ feedback in response to the SCI, such as described in connection with <FIG>, <FIG>, and <FIG>. For example, at <NUM>, the first UE <NUM> may receive a HARQ feedback from the second UE <NUM> for the SCI transmitted without data. The reception of the HARQ feedback may be performed, e.g., by the HARQ feedback process component <NUM> and/or reception component <NUM> of the apparatus <NUM> in <FIG>. In one example, the wireless device may receive the HARQ feedback in a PSFCH based on one or more of: a starting sub-channel of a PSCCH in which the SCI is transmitted, a slot including the PSCCH in which the SCI is transmitted, a source identifier, or a destination identifier. In another example, the wireless device may receive the HARQ feedback based on the SCI being unicast. In another example, the HARQ feedback may be received based on a second part of the SCI being transmitted in a PSSCH, such as described in connection with <FIG> and <FIG>.

At <NUM>, the wireless device may release remaining periodic resources in the set of periodic resources based on determining that the wireless device does not have the data to transmit in a threshold number of consecutive periods, such as described in connection with <FIG> and <FIG>. For example, at <NUM>, the first UE <NUM> may release remaining periodic resources in the set of periodic resources if the first UE <NUM> does not have data to transmit in a threshold number of consecutive periods. The release of the remaining periodic resources may be performed, e.g., by the reserved resource release component <NUM> of the apparatus <NUM> in <FIG>. For example, the wireless device may release the remaining periodic resources based on a codepoint transmitted in the SCI that corresponds to a release of a periodic reservation.

The apparatus <NUM> is a wireless device that supports sidelink communication. In some aspects, the apparatus <NUM> may be a transmitting UE or a component of a transmitting UE. The apparatus may include a baseband processor <NUM> (also referred to as a modem) coupled to an RF transceiver <NUM>. In some aspects, the baseband processor <NUM> may be a cellular baseband processor, and the RF transceiver may be a cellular RF transceiver. In some aspects, the apparatus <NUM> may further include one or more subscriber identity modules (SIM) cards <NUM>, an application processor <NUM> coupled to a secure digital (SD) card <NUM> and a screen <NUM>, a Bluetooth module <NUM>, a wireless local area network (WLAN) module <NUM>, a Global Positioning System (GPS) module <NUM>, and/or a power supply <NUM>. The baseband processor <NUM> communicates through the RF transceiver <NUM> with the wireless device <NUM> and/or BS <NUM>/<NUM>. The baseband processor <NUM> may include a computer-readable medium / memory. The baseband processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory. The software, when executed by the baseband processor <NUM>, causes the baseband processor <NUM> to perform the various functions described supra. The computer-readable medium / memory may also be used for storing data that is manipulated by the baseband processor <NUM> when executing software. The baseband processor <NUM> further includes a reception component <NUM>, a communication manager <NUM>, and a transmission component <NUM>. The components within the communication manager <NUM> may be stored in the computer-readable medium / memory and/or configured as hardware within the baseband processor <NUM>. The baseband processor <NUM> may be a component of the wireless device <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>. In one configuration, the apparatus <NUM> may be a modem chip and include just the baseband processor <NUM>, and in another configuration, the apparatus <NUM> may be the entire wireless device (e.g., see <NUM> of <FIG>) and include the additional modules of the apparatus <NUM>.

The communication manager <NUM> includes a resource reservation component <NUM> that is configured to reserve a set of periodic resources for sidelink transmission, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes a data transmission determination component <NUM> that is configured to determine not to transmit data in a period, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes an SCI processing component <NUM> that is configured to transmit the SCI without a data transmission in a periodic resource for a period, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes a HARQ feedback process component <NUM> that is configured to receive HARQ feedback in response to the SCI, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes a reserved resource release component <NUM> that is configured to release remaining periodic resources in the set of periodic resources based on determining that the wireless device does not have the data to transmit in a threshold number of consecutive periods, e.g., as described in connection with <NUM> of <FIG>.

The apparatus may include additional components that perform each of the blocks of the algorithm in the flowcharts of <FIG>. As such, each block in the flowcharts of <FIG> may be performed by a component and the apparatus may include one or more of those components.

In one configuration, the apparatus <NUM>, and in particular the baseband processor <NUM>, includes means for reserving a set of periodic resources for sidelink transmission (e.g., the resource reservation component <NUM>). The apparatus <NUM> includes means for determining not to transmit data in a period (e.g., the data transmission determination component <NUM>). The apparatus <NUM> includes means for transmitting the SCI without a data transmission in a periodic resource for a period (e.g., the SCI processing component <NUM> and/or the transmission component <NUM>). The apparatus <NUM> includes means for receiving HARQ feedback in response to the SCI (e.g., the HARQ feedback process component <NUM> and/or reception component <NUM>). The apparatus <NUM> includes means for releasing remaining periodic resources in the set of periodic resources based on determining that the wireless device does not have the data to transmit in a threshold number of consecutive periods (e.g., the reserved resource release component <NUM>).

The means may be one or more of the components of the apparatus <NUM> configured to perform the functions recited by the means. As described supra, the apparatus <NUM> may include the TX Processor <NUM>, the RX Processor <NUM>, and the controller/processor <NUM>. As such, in one configuration, the means may be the TX Processor <NUM>, the RX Processor <NUM>, and the controller/processor <NUM> configured to perform the functions recited by the means.

<FIG> is a flowchart <NUM> of a method of wireless communication. The method may be performed by a first wireless device or a component of a first wireless device (e.g., the UE <NUM>, <NUM>; an RSU <NUM>; the device <NUM> or <NUM>; the apparatus <NUM>; a processing system, which may include the memory <NUM> and which may be the device <NUM> or a component of the device <NUM>, such as the TX processor <NUM>, the RX processor <NUM>, and/or the controller/processor <NUM>). The method may enable the first wireless device to monitor receive CSI without data, such that the first wireless device may skip monitoring for data in a sidelink transmission to conserve power. The method may improve the use of wireless resources in sidelink communication.

At <NUM>, the first wireless device may receive a reservation from a second wireless device for a set of periodic resources for sidelink transmission, such as described in connection with <FIG>, <FIG>, and <FIG>. For example, at <NUM>, the second UE <NUM> may receive a reservation from the first UE <NUM> for a set of periodic resources for sidelink transmission. The reception of the reservation may be performed, e.g., by the sidelink reservation process component <NUM> and/or the reception component <NUM> of the apparatus <NUM> in <FIG>.

At <NUM>, the first wireless device may receive, from the second wireless device, SCI in a period of the periodic resources, the SCI may include an indication that the SCI is not associated with a data transmission, such as described in connection with <FIG>, <FIG> and <FIG>. For example, at <NUM>, the second UE <NUM> may receive SCI in a period from the first UE <NUM>, where the SCI may include an indication that the SCI is not associated with a data transmission. The reception of the SCI may be performed, e.g., by the sidelink transmission process component <NUM> and/or the reception component <NUM> of the apparatus <NUM> in <FIG>.

In one example, the indication may be included in a first part of the SCI (e.g., SCI-<NUM>) that is received in a PSCCH. In such an example, the first wireless device may refrain from attempting to decode a second part of the SCI and the data transmission in response to receiving the indication in the first part of the SCI. In another example, the indication may be included in a second part of the SCI (e.g., SCI-<NUM>) that is received in a PSSCH, such as described in connection with <FIG>, <FIG>, <FIG>, and <FIG>. In such an example, the first wireless device may refrain from attempting to decode the data transmission in response to receiving the indication in the second part of the SCI. In another example, when the SCI indicates it is not associated with the data, the SCI may not reserve resources within the period but may indicate a periodic reservation in a next period.

At <NUM>, the first wireless device may receive a release of remaining periodic resources in the set of periodic resources, the release being based on a codepoint in the SCI that corresponds to a release of a periodic reservation, such as described in connection with <FIG>. For example, at <NUM>, the second UE <NUM> may receive a release of remaining periodic resources in the set of periodic resources from the first UE <NUM>. The reception of the release may be performed, e.g., by the reservation release process component <NUM> and/or the reception component <NUM> of the apparatus <NUM> in <FIG>.

At <NUM>, the first wireless device may transmit HARQ feedback to the second wireless device in response to the SCI, such as described in connection with <FIG> and <FIG>. For example, at <NUM>, the second UE <NUM> may transmit HARQ feedback to the first UE <NUM> in response to the SCI. The transmission of the HARQ feedback may be performed, e.g., by the HARQ feedback component <NUM> and/or the transmission component <NUM> of the apparatus <NUM> in <FIG>.

In one example, the HARQ feedback may be transmitted in a PSFCH based on one or more of: a starting sub-channel of the PSCCH in which the SCI is transmitted, a slot including the PSCCH in which the SCI is transmitted, a source identifier, or a destination identifier. In another example, the HARQ feedback may be transmitted based on the SCI being unicast. In another example, the HARQ feedback may be transmitted based on a second part of the SCI being transmitted in a PSSCH.

In other examples, the first wireless device may refrain from transmitting HARQ feedback to the second wireless device in response to the SCI. In one example, the first wireless device may refrain from transmitting the HARQ feedback based on the SCI being groupcasted or broadcasted. In another example, the first wireless device may refrain from transmitting the HARQ feedback based on the indication being received in a first part of the SCI received in a PSCCH, such as described in connection with <FIG> and <FIG>.

In another example, as shown at <NUM>, the first wireless device may measure RSRP for PSCCH that carries the SCI (e.g., measure the DMRS of the PSCCH that contains the SCI), and the first wireless device may determine whether a resource associated with the SCI is reserved based on the indication and the measured RSRP. For example, the first wireless device (which may not be communicating with the second UE) may monitor one or more SCIs transmitted by one or more UEs in its proximity (e.g., reception range), and the first wireless device may determine a resource in a next period may be reserved by at least one UE if the first wireless device detects that an SCI contains an indication that the SCI is not associated with a data transmission, and if the measured RSRP for the PSCCH that carries the SCI is above a threshold.

The apparatus <NUM> may be a wireless device that supports sidelink communication. In some aspects, the apparatus <NUM> may be a UE or a component of a UE. The apparatus may include a baseband processor <NUM> (also referred to as a modem) coupled to a RF transceiver <NUM>. In some aspects, the baseband processor <NUM> and the RF transceiver <NUM> may be a cellular baseband processor and a cellular RF transceiver. In some aspects, the apparatus <NUM> may further include one or more subscriber identity modules (SIM) cards <NUM>, an application processor <NUM> coupled to a secure digital (SD) card <NUM> and a screen <NUM>, a Bluetooth module <NUM>, a wireless local area network (WLAN) module <NUM>, a Global Positioning System (GPS) module <NUM>, and/or a power supply <NUM>. The baseband processor <NUM> communicates through the RF transceiver <NUM> with the UE <NUM> and/or BS <NUM>/<NUM>. The baseband processor <NUM> may include a computer-readable medium / memory. The baseband processor <NUM> is responsible for general processing, including the execution of software stored on the computer-readable medium / memory. The software, when executed by the baseband processor <NUM>, causes the baseband processor <NUM> to perform the various functions described supra. The computer-readable medium / memory may also be used for storing data that is manipulated by the baseband processor <NUM> when executing software. The baseband processor <NUM> further includes a reception component <NUM>, a communication manager <NUM>, and a transmission component <NUM>. The components within the communication manager <NUM> may be stored in the computer-readable medium / memory and/or configured as hardware within the baseband processor <NUM>. The baseband processor <NUM> may be a component of the device <NUM> and may include the memory <NUM> and/or at least one of the TX processor <NUM>, the RX processor <NUM>, and the controller/processor <NUM>. In one configuration, the apparatus <NUM> may be a modem chip and include just the baseband processor <NUM>, and in another configuration, the apparatus <NUM> may be the entire UE (e.g., see <NUM> of <FIG>) and include the additional modules of the apparatus <NUM>.

The communication manager <NUM> includes a sidelink reservation process component <NUM> that is configured to receive a reservation from a second wireless device for a set of periodic resources for sidelink transmission, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes a sidelink transmission process component <NUM> that is configured to receive, from the second wireless device, SCI in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes a reservation release process component <NUM> that is configured to receive a release of remaining periodic resources in the set of periodic resources, the release being based on a codepoint in the SCI that corresponds to a release of a periodic reservation, e.g., as described in connection with <NUM> of <FIG>. The communication manager <NUM> further includes a HARQ feedback component <NUM> that is configured to transmit HARQ feedback to the second wireless device in response to the SCI, e.g., as described in connection with <NUM> of <FIG>.

In one configuration, the apparatus <NUM>, and in particular the baseband processor <NUM>, includes means for receiving a reservation from a second wireless device for a set of periodic resources for sidelink transmission (e.g., the sidelink reservation process component <NUM> and/or the reception component <NUM>). The apparatus <NUM> includes means for receiving, from the second wireless device, SCI in a period of the periodic resources, the SCI including an indication that the SCI is not associated with a data transmission (e.g., the sidelink transmission process component <NUM> and/or the reception component <NUM>). The apparatus <NUM> includes means for receiving a release of remaining periodic resources in the set of periodic resources, the release being based on a codepoint in the SCI that corresponds to a release of a periodic reservation (e.g., the reservation release process component <NUM> and/or the reception component <NUM>). The apparatus <NUM> includes means for transmitting HARQ feedback to the second wireless device in response to the SCI (e.g., the HARQ feedback component <NUM> and/or the transmission component <NUM>).

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