Patent Description:
To these ends, NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation (CA).

3GPP DRAFT, R1-<NUM> discusses physical layer procedures for sidelink, especially, options for HARQ feedback for groupcast. 3GPP DRAFT, R1-<NUM> discusses an HARQ feedback mechanism for NR sidelink.

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for transmitting sidelink feedback using a multiple bit physical sidelink feedback channel (PSFCH).

Certain wireless communication systems may allow user equipments (UEs) to communicate with each other using sidelink communication links (or sidelink communication channels). For example, a first UE may receive one or more physical sidelink shared channels (PSSCHs) from one or more second UEs. In scenarios where the first UE receives multiple PSSCHs (e.g., a continuous stream of PSSCHs), the first UE may have to transmit multiple physical sidelink feedback channels (PSFCHs) in order to acknowledge the multiple PSSCHs. In some cases, sending multiple PSFCHs in this manner can impact the performance of the communication network, e.g., by reducing network throughput.

To address this, aspects described herein provide techniques for acknowledging multiple PSSCHs using a multiple bit PSFCH (e.g., a single PSFCH with multiple bits). As described below, a receiving UE may receive multiple sidelink transmissions from a transmitting UE on multiple sidelink subchannels. The receiving UE may determine at least one resource set for transmitting feedback corresponding to the multiple sidelink transmissions, based on at least one of the multiple sidelink transmissions. The receiving UE may then transmit the feedback corresponding to the multiple sidelink transmissions using the at least one resource set. By allowing a receiving UE to acknowledge multiple sidelink transmisions using a single, multi-bit sidelink feedback channel , aspects described herein can significantly increase the efficiency and performance of the communication network.

The following description provides examples of transmitting feedback for sidelink transmissions in communication systems, and is not limiting of the scope, applicability, or examples set forth in the claims.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with <NUM>, <NUM>, and/or new radio (e.g., <NUM> NR) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

NR access may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth, millimeter wave mmW, massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC). In addition, these services may coexist in the same subframe.

The electromagnetic spectrum is often subdivided, based on frequency/wavelength, into various classes, bands, channels, etc. In <NUM> NR two initial operating bands have been identified as frequency range designations FR1 (<NUM> - <NUM>) and FR2 (<NUM> - <NUM>). Although a portion of FR1 is greater than <NUM>, FR1 is often referred to (interchangeably) as a "Sub-<NUM>" band in various documents and articles.

NR supports beamforming and beam direction may be dynamically configured.

As shown in <FIG>, the wireless communication network <NUM> includes one or more base station (BSs) 110a-z (each also individually referred to herein as BS <NUM> or collectively as BSs <NUM>) and/or user equipment (UE) 120a-y (each also individually referred to herein as UE <NUM> or collectively as UEs <NUM>).

According to certain aspects, the UEs <NUM> may be configured for sidelink communications. As shown in <FIG>, the UE 120a includes a sidelink resource manager 122a and the UE 120b includes a sidelink resource manager 122b. In some aspects, UEs 120a and/or 120b may be receiving sidelink communications and may use their respective sidelink resource managers to transmit feedback acknowledging the sidelink communications. For example, using sidelink resource manager 122a (or sidelink resource manager 122b), UE 120a (or UE 120b) may receive a plurality of transmissions from another UE on a plurality of sidelink subchannels; determine at least one resource set for transmitting feedback corresponding to the plurality of transmissions, based on at least one of the plurality of transmissions; and transmit to the other UE the feedback corresponding to the plurality of transmissions using the at least one resource set.

Additionally or alternatively, using sidelink resource manager 122a (or sidelink resource manager 122b), UE 120a (or UE 120b) may send a plurality of transmissions to another UE on a plurality of sidelink subchannels; and monitor for feedback corresponding to the plurality of transmissions, from the other UE, based on a codebook size associated with the feedback.

The BSs <NUM> communicate with UEs <NUM> in the wireless communication network <NUM>.

A network controller <NUM> may be in communication with a set of BSs <NUM> and provide coordination and control for these BSs <NUM> (e.g., via a backhaul). In aspects, the network controller <NUM> may be in communication with a core network (not shown) (e.g., a <NUM> Core Network (5GC)), which provides various network functions such as Access and Mobility Management, Session Management, User Plane Function, Policy Control Function, Authentication Server Function, Unified Data Management, Application Function, Network Exposure Function, Network Repository Function, Network Slice Selection Function, etc..

<FIG> illustrates example components of BS 110a and UE 120a (e.g., the wireless communication network <NUM> of <FIG>), which may be used to implement aspects of the present disclosure.

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

The processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), PBCH demodulation reference signal (DMRS), and channel state information reference signal (CSI-RS). A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) in transceivers 232a-232t. Each modulator in transceivers 232a-232t may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Downlink signals from the modulators in transceivers 232a-232t may be transmitted via the antennas 234a-234t, respectively.

At the UE 120a, the antennas 252a-252r may receive the downlink signals from the BS 110a and may provide received signals to the demodulators (DEMODs) in transceivers 254a-254r, respectively. Each demodulator in transceivers 254a-254r may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. A MIMO detector <NUM> may obtain received symbols from all the demodulators in transceivers 254a-254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor <NUM> may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120a to a data sink <NUM>, and provide decoded control information to a controller/processor <NUM>.

On the uplink, at UE 120a, a transmit processor <NUM> may receive and process data (e.g., for the physical uplink shared channel (PUSCH)) from a data source <NUM> and control information (e.g., for the physical uplink control channel (PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators in transceivers 254a-254r (e.g., for SC-FDM, etc.), and transmitted to the BS 110a. At the BS 110a, the uplink signals from the UE 120a may be received by the antennas <NUM>, processed by the demodulators in transceivers 232a-232t, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE 120a.

Antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the UE 120a and/or antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the BS 110a may be used to perform the various techniques and methods described herein. For example, as shown in <FIG>, the controller/processor <NUM> of the UE <NUM> (e.g., UE 120a) has a sidelink resource manager <NUM>, which is configured to implement one or more techniques described herein for supporting sidelink feedback via a multiple bit PSFCH. Although shown at the controller/processor, other components of the UE 120a and BS 110a may be used to perform the operations described herein.

Each subframe may include a variable number of slots (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>,. slots) depending on the SCS. Each slot may include a variable number of symbol periods (e.g., <NUM>, <NUM>, or <NUM> symbols) depending on the SCS. A sub-slot structure may refer to a transmit time interval having a duration less than a slot (e.g., <NUM>, <NUM>, or <NUM> symbols). Each symbol in a slot may be configured for a link direction (e.g., DL, UL, or flexible) for data transmission and the link direction for each subframe may be dynamically switched.

In NR, a synchronization signal block (SSB) is transmitted. In certain aspects, SSBs may be transmitted in a burst where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and/or beam refinement). The SSB includes a PSS, a SSS, and a two symbol PBCH. The SSB can be transmitted in a fixed slot location, such as the symbols <NUM>-<NUM> as shown in <FIG>. The PSS may provide half-frame timing, the SSS may provide the CP length and frame timing. The PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frame, synchronization signal (SS) burst set periodicity, system frame number, etc. The SSBs may be organized into SS bursts to support beam sweeping. The SSB can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmWave. The multiple transmissions of the SSB are referred to as a SS burst set. SSBs in an SS burst set may be transmitted in the same frequency region, while SSBs in different SS bursts sets can be transmitted at different frequency regions.

In some examples, the communication between the UEs <NUM> and BSs <NUM> is referred to as the access link. The access link may be provided via a Uu interface. Communication between devices may be referred as the sidelink.

In some examples, two or more subordinate entities (e.g., UEs <NUM>) may communicate with each other using sidelink signals. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE 120a) to another subordinate entity (e.g., another UE <NUM>) without relaying that communication through the scheduling entity (e.g., UE <NUM> or BS <NUM>), even though the scheduling entity may be utilized for scheduling and/or control purposes. One example of sidelink communication is PC5, for example, as used in V2V, LTE, and/or NR.

Various sidelink channels may be used for sidelink communications, including a physical sidelink discovery channel (PSDCH), a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH may carry discovery expressions that enable proximal devices to discover each other. The PSCCH may carry control signaling such as sidelink resource configurations, resource reservations, and other parameters used for data transmissions, and the PSSCH may carry the data transmissions. The PSFCH may carry feedback, such as channel state information (CSI) related to a sidelink channel quality, acknowledgment information (e.g., acknowledgement (ACK), negative acknowledgment (NACK), etc.) for a PSSCH transmission, etc. In some systems (e.g., NR Release <NUM>), a two stage sidelink control information (SCI) may be supported. Two stage SCI may include a first stage SCI (SCI-<NUM>) and a second stage SCI (e.g., SCI-<NUM>). SCI-<NUM> may include resource reservation and allocation information, information that can be used to decode SCI-<NUM>, etc. SCI-<NUM> may include information that can be used to decode data and to determine whether the UE is an intended recipient of the transmission. SCI-<NUM> and/or SCI-<NUM> may be transmitted over PSCCH.

<FIG> show diagrammatic representations of example V2X systems, in accordance with some aspects of the present disclosure. For example, the vehicles shown in <FIG> may communicate via sidelink channels and may manage resource reservations and/or release of resource reservations as described herein.

The V2X systems, provided in <FIG> provide two complementary transmission modes. A first transmission mode, shown by way of example in <FIG>, involves direct communications (for example, also referred to as side link communications) between participants in proximity to one another in a local area. A second transmission mode, shown by way of example in <FIG>, involves network communications through a network, which may be implemented over a Uu interface (for example, a wireless communication interface between a radio access network (RAN) and a UE).

Referring to <FIG>, a V2X system 400A (for example, including vehicle to vehicle (V2V) communications) is illustrated with two vehicles <NUM>, <NUM>. The first transmission mode allows for direct communication between different participants in a given geographic location. As illustrated, a vehicle can have a wireless communication link <NUM> with an individual (V2P) (for example, via a UE) through a PC5 interface. Communications between the vehicles <NUM> and <NUM> may also occur through a PC5 interface <NUM>. In a like manner, communication may occur from a vehicle <NUM> to other highway components (for example, highway component <NUM>), such as a traffic signal or sign (V2I) through a PC5 interface <NUM>. With respect to each communication link illustrated in <FIG>, two-way communication may take place between elements, therefore each element may be a transmitter and a receiver of information. The V2X system 400A may be a self-managed system implemented without assistance from a network entity. A self-managed system may enable improved spectral efficiency, reduced cost, and increased reliability as network service interruptions do not occur during handover operations for moving vehicles. The V2X system 400A may be configured to operate in a licensed or unlicensed spectrum, thus any vehicle with an equipped system may access a common frequency and share information. Such harmonized/common spectrum operations allow for safe and reliable operation.

<FIG> shows a V2X system 400B for communication between a vehicle <NUM> and a vehicle <NUM> through a network entity <NUM>. These network communications may occur through discrete nodes, such as a base station (for example, an eNB or gNB), that sends and receives information to and from (for example, relays information between) vehicles <NUM>, <NUM>. The network communications through vehicle to network (V2N) links <NUM> and <NUM> may be used, for example, for long range communications between vehicles, such as for communicating the presence of a car accident a distance ahead along a road or highway. Other types of communications may be sent by the node to vehicles, such as traffic flow conditions, road hazard warnings, environmental/weather reports, and service station availability, among other examples. Such data can be obtained from cloud-based sharing services.

In communication systems that support sidelink communications (e.g., Release <NUM> Sidelink), a UE can send one or more sidelink transmissions (e.g., PSCCH/PSSCH transmission(s)) to one or more other UEs. In some scenarios, for PSCCH/PSSCH transmission, feedback (e.g., ACK/NACK) for PSSCH can be requested to be transmitted in PSFCH. A PSFCH resource can be selected from a resource pool, which may not be a dedicated PSFCH resource pool. For example, a UE can receive an indication (via an SCI format scheduling a PSSCH reception in one or more sub-channels from a number of <MAT> sub-channels) to transmit a PSFCH with hybrid automatic repeat request (HARQ)-ACK information in response to the PSSCH reception. The UE can provide within the PSFCH HARQ-ACK information that includes ACK or NACK.

Given a PSSCH location, the UE can identify resource(s) for the PSFCH transmission. For example, the UE can be provided, by sl-PSFCH-Period-r16 (also referred to as periodPSFCHresource), a number of slots in a resource pool for a period of PSFCH transmission occasion resources. The number of supported slots can be <NUM>, <NUM>, <NUM>, or <NUM>. If the number is zero, PSFCH transmissions from the UE in the resource pool may be disabled. The PSFCH transmission timing is generally based on the first slot with a PSFCH resource after PSSCH and after a "MinTimeGapPSFCH" after the PSSCH. For example, if a UE receives a PSSCH in a resource pool and the HARQ feedback enabled/disabled indicator field in an associated SCI format <NUM>-A or a SCI format <NUM>-B has value <NUM>, the UE may provide the HARQ-ACK information in a PSFCH transmission in the resource pool. The UE can transmit the PSFCH in a first slot that includes PSFCH resources and is at least a number of slots, provided by sl-MinTimeGapPSFCH-r16, of the resource pool after a last slot of the PSSCH reception.

The parameter <MAT>: rbSetPSFCH defines a set of physical resource blocks (PRBs) for PSFCH in a slot. <MAT> may be split between <MAT> (Number of PSSCH slots corresponds to the PSFCH slot) and Nsubch of PSSCH in a slot. There may be a time-first mapping from a PSSCH resource to PSFCH PRBs.

A UE can be provided by sl-PSFCH-RB-Set-r16 a set of <MAT> PRBs in a resource pool for PSFCH transmission in a PRB of the resource pool. For a number of Nsubch subchannels for the resource pool, provided by sl-NumSubchannel, and a number of PSSCH slots associated with a PSFCH slot that is less than or equal to <MAT>, the UE may allocate the <MAT> PRBs from the <MAT> PRBs to slot i among the PSSCH slots associated with the PSFCH slot and sub-channel j, where <MAT>, <NUM> ≤ i < <MAT>, <NUM> ≤ j < Nsubch, and the allocation starts in an ascending order of i and continues in an ascending order of j. <MAT> may be a multiple of <MAT>.

The PSFCH resource pool may have a size <MAT> <MAT>. For example, the UE may determine a number of PSFCH resources available for multiplexing HARQ-ACK information in a PSFCH transmission as <MAT> <MAT> where <MAT> is a number of cyclic shift (CS) pairs for the resource pool (the pair is for ACK/NACK, <NUM> bit), and (<NUM>) <MAT> and the <MAT> PRBs are associated with the starting sub-channel of the corresponding PSSCH or (<NUM>) <MAT> and the <MAT> PRBs are associated with one or more sub-channels from the <MAT> sub-channels of the corresponding PSSCH. The PSFCH resources may be first indexed according to an ascending order of the PRB index, from the <MAT> PRBs, and then according to an ascending order of the cyclic shift pair index from the <MAT> cyclic shift pairs.

The UE can determine an index of a PSFCH resource for a PSFCH transmission in response to a PSSCH reception as <MAT> where PID is a physical layer source ID provided by SCI format <NUM>-A or <NUM>-B scheduling the PSSCH reception, and MID is the identity of the UE receiving the PSSCH as indicated by higher layers if the UE detects a SCI format <NUM>-A with Cast type indicator field value of "<NUM>"; otherwise, MID is zero. In one example, for a unicast or NACK based transmission, MID is zero and the UE may send ACK/NACK or NACK only at a source ID dependent resource in the pool. In another example, for a groupcast based transmission, each destination ID can pick a single resource in the pool and transmit ACK/NACK.

<FIG> illustrates a reference example design for transmitting sidelink feedback using a PSFCH. Here, the UE is configured with a PSFCH resource pool <NUM> for PSCCH/PSSCH slots <NUM>, <NUM>. That is, periodPSFCHresource = <NUM>, such that every two slots maps to one occasion of the PSFCH resource pool <NUM>. The occasion of the PSFCH resource pool <NUM> may be during one or more symbols of slot <NUM>.

Each slot <NUM>, <NUM> includes four subchannels <NUM>. In particular, slot <NUM> includes subchannels <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, and slot <NUM> includes subchannels <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>. Each subchannel <NUM> is associated with a different sub-resourcepool <NUM> (also referred to as a subset of PSFCH resources) of the PSFCH resource pool <NUM> (also referred to as a set of PSFCH resources). For example, subchannel <NUM>-<NUM> is associated with sub-resourcepool <NUM>-<NUM>, subchannel <NUM>-<NUM> is associated with sub-resourcepool <NUM>-<NUM>, subchannel <NUM>-<NUM> is associated with sub-resource pool <NUM>-<NUM>, subchannel <NUM>-<NUM> is associated with sub-resource pool <NUM>-<NUM>, subchannel <NUM>-<NUM> is associated with sub-resource pool <NUM>-<NUM>, subchannel <NUM>-<NUM> is associated with sub-resource pool <NUM>-<NUM>, subchannel <NUM>-<NUM> is associated with sub-resource pool <NUM>-<NUM>, and subchannel <NUM>-<NUM> is associated with sub-resource pool <NUM>-<NUM>.

The number of PSFCH resources (e.g., PRBs) in the PSFCH resource pool <NUM> may be <MAT> and each sub-resource pool <NUM> may include <MAT> PRBs (e.g., from <MAT> PRBs). For a given subchannel <NUM>, the UE may determine a PRB <NUM> within the respective sub-resource pool <NUM> (associated with the subchannel <NUM>) to use for transmitting sidelink feedback (e.g., HARQ-ACK information), based on <MAT>.

As shown in <FIG>, for example, the UE may select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>, and select PRB <NUM>-<NUM> (within sub-resource pool <NUM>-<NUM>) for transmitting sidelink feedback for a sidelink transmission associated with subchannel <NUM>-<NUM>.

One issue with the sidelink feedback design illustrated in <FIG> is that it may not support transmitting a PSFCH with multiple bits. For example, each PSFCH (e.g., PRB <NUM>) may be a single RB single symbol and may have a format similar to (or same as) PUCCH format <NUM>. Thus, each PSFCH can carry a single bit, but may not be used for transmitting multiple bits. In cases where a UE has to send multiple bits of HARQ-ACK information, the UE may have to frequency division multiplex (FDM) multiple PSFCH in order to acknowledge multiple sidelink data (PSSCH) transmissions. This scenario can occur, for example, when the UE has received multiple PSSCHs from the same source UE, where the PSSCHs have PSFCH hashed to the same PSFCH location. In another example, transmitting FDM multiple PSFCH can occur when the PSFCH occasion period is <NUM> or <NUM>. In yet another example, transmitting FDM multiple PSFCH can occur when the UE has received multiple PSSCH from different source UEs and is requested to send PSFCH to each of the different source UEs. The number of PSFCH that a UE can multiplex in the same symbol may be based on a UE capability.

As the number of communication services (e.g., eMBB, CA, unlicensed spectrum, etc.) that support sidelink communication increases, there may a greater number of occurrences where the UE has to transmit FDM multiple PSFCH in order to acknowledge multiple sidelink data transmissions. In the case of eMBB, for example, the same destination node (e.g., UE) may receive a continuous stream of PSSCHs from one or more source nodes. As another example, certain CA scenarios may lead to a large number of ACK/NACK bits being fed back to the source node(s). In yet another example, as sidelink communications moves to the unlicensed band, it may not be possible to configure a sufficient number of PSFCH opportunities to allow for acknowledging a continuous stream of sidelink data transmissions (e.g., the possible PSFCH transmission(s) may have to be more sparse than the specified number PSFCH period).

Accordingly, it may be desirable to provide techniques and apparatus that enable transmission of multiple bits of HARQ-ACK information within a single PSFCH in order to acknowledge multiple sidelink data (e.g., PSSCH) transmissions.

Aspects described herein provide techniques that enable transmission of a PSFCH with multiple bits, e.g., for acknowledging multiple sidelink data transmissions. As described below, using the techniques presented herein, a destination (or receiving) UE can send multiple bits of HARQ-ACK information to a source (or transmitting) UE. The multiple bits of HARQ-ACK information may correspond to multiple PSSCHs from the source UE (e.g., each bit of the multiple bits may correspond to (acknowledge) a different PSSCH of the multiple PSSCHs). Additionally, in cases where one or more previous HARQ-ACK transmissions fail (e.g., due to listen-before-talk (LBT) failure for NR-U), one or more of the multiple bits of the HARQ-ACK information can be used for re-transmission of the HARQ-ACK information.

In some aspects, a single-bit PSFCH design (e.g., in Release <NUM>) may be extended to support multiple bits. For example, a single-bit PSFCH design may be based on NR PUCCH format <NUM> with <NUM> symbol. In some aspects, the multi-bit PSFCH design described herein can support multiple bits by extending PUCCH format <NUM> from NR to sidelink PSFCH. In one aspect, the PUCCH format <NUM> includes a single symbol (similar to PUCCH format <NUM>) (with one additional symbol for automatic gain control (AGC), but the single symbol in PUCCH format <NUM> can support multiple RBs and can handle a large payload, relative to PUCCH format <NUM>.

In some aspects, a multi-bit PSFCH can be supported for unicast transmission, but may not be supported for group cast transmissions or zone based transmissions. Additionally, in some aspects, the UE may not provide HARQ feedback for a broadcast transmission. The UE may receive SCI that indicates whether the transmission is unicast, groupcast, or broadcast. For example, in Release <NUM> sidelink (SL), SCI2-A includes a cast type indicator that explicitly indicates whether the transmission is unicast, groupcast, or broadcast. In another example, SCI2-B can indicate whether the transmission is zone based.

If the UE receives SCI that indicates group cast (SCI2-A) or zone based (SCI2-B), the UE may use the legacy single bit PSFCH to acknowledge the group cast or zone based transmission. On the other hand, if the receiving UE receives an indication (e.g., in SCI) of a unicast transmission, the receiving UE can collect HARQ feedback (e.g., ACK(s)/NACK(s)) for multiple PSSCH and can multiplex the HARQ feedback together to transmit in a multi-bit PSFCH. In some aspects, if the UE receives one or more groupcast PSSCH and one or more unicast PSSCH, the UE can group the unicast PSSCH HARQ feedback together into one multi-bit PSFCH transmission, and FDM the multi-bit PSFCH transmission with separate single bit PSFCHs for other groupcast PSSCH. In some aspects, the receiving UE may send different multi-bit PSFCH to different source UEs (e.g., the UE may not multiplex PSFCHs between different source UEs).

Aspects presented herein provide techniques for selecting a PSFCH resource (within a resource set) to use for a multi-bit PSFCH transmission. <FIG> depicts a reference example of selecting a PSFCH resource for a multi-bit PSFCH transmission, according to certain aspects of the present disclosure. As shown, the UE is configured with a PSFCH resource pool <NUM> (also referred to a set of PSFCH resources) for PSCCH/PSSCH slots <NUM>, <NUM> (e.g., periodPSFCHresource = <NUM>). The PSFCH resource pool <NUM> may be similar to PSFCH resource pool <NUM>, except that the PSFCH resources in PSFCH resource pool <NUM> may be based on PUCCH format <NUM>. Each slot <NUM>, <NUM> includes four subchannels <NUM> (e.g., similar to slots <NUM>, <NUM> in <FIG>), and each subchannel <NUM> is associated with a sub-resource pool <NUM> (also referred to a subset of PSFCH resources) (e.g., similar to the association of subchannels <NUM> to sub-resource pools <NUM> in <FIG>).

In certain aspects, the receiving UE can select a PSFCH resource from the sub-resource pool <NUM>, which corresponds to the subchannel <NUM> in which the SCI (e.g., SCI-<NUM>) is received in. With reference to <FIG> for example, assuming the SCI is received in subchannel <NUM>-<NUM> (of slot <NUM>), the receiving UE may select a PSFCH resource from sub-resource pool <NUM>-<NUM>. In another example, assuming the SCI is received in subchannel <NUM>-<NUM> (of slot <NUM>), the receiving UE may select a PSFCH resource from sub-resource pool <NUM>-<NUM>.

One challenge with the example PSFCH resource selection depicted in <FIG> is that, in scenarios where multiple PSSCHs are transmitted to the same receiving UE, it may be unclear to the UE which PSFCH resource to use for the multi-bit PSFCH transmission. In some cases, for example, the receiving UE may not receive all of the PSSCHs transmitted from a transmitting UE. In some instances, the receiving UE may miss a PSSCH due to a SCI miss detection event (e.g., the UE may not detect SCI-<NUM>/SCI-<NUM> corresponding to the PSSCH). In some instances, the receiving UE may miss a PSSCH due to half duplex operation (e.g., if the receiving UE is half duplex, it may not be able to receive PSCCH/PSSCH in a slot if it is also transmitting during that slot). Note that, in some aspects described herein, the UE may be able to assume that, within a given sot, there will not be a FDM PSCCH/PSSCH to the same receiving UE for unicast.

To address this ambiguity, aspects provide techniques that enable the receiving UE to determine a PSFCH resource set (e.g., PSFCH sub-resource pool <NUM>) in scenarios where multiple PSSCH transmissions are transmitted to the receiving UE.

In some aspects, the receiving UE may use the PSFCH sub-resource pool <NUM> corresponding to the latest received SCI when selecting a PSFCH resource for the multi-bit PSFCH. <FIG> depicts a reference example of selecting a PSFCH resource for a multi-bit PSFCH transmission, according to certain aspects of the present disclosure. Here, the UE may receive a first SCI in subchannel <NUM>-<NUM> (of slot <NUM>), corresponding to PSFCH sub-resource pool <NUM>-<NUM>. At a subsequent point in time, the UE may receive a second SCI in subchannel <NUM>-<NUM> (of slot <NUM>), corresponding to PSFCH sub-resource pool <NUM>-<NUM>. In this example, the receiving UE may select a PSFCH resource from PSFCH sub-resource pool <NUM>-<NUM> for the multi-bit PSFCH transmission (e.g., acknowledging the PSSCH transmission in subchannel <NUM>-<NUM> of slot <NUM> and the PSSCH transmission in subchannel <NUM>-<NUM> of slot <NUM>), since PSFCH sub-resource pool <NUM>-<NUM> corresponds to the latest received SCI in subchannel <NUM>-<NUM> (of slot <NUM>).

In aspects where the receiving UE uses the PSFCH sub-resource pool <NUM> corresponding to the latest received SCI for the multi-bit PSFCH, the transmitting UE may perform hypothesis decoding, e.g., in cases the receiving UE misses the later sidelink transmission. In some aspects, the hypothesis may be associated with the codebook size of the PSFCH transmission.

For example, in one aspect, a semi-static codebook can be supported for sidelink communications. With a semi-static codebook, the receiving UE may generate one HARQ-ACK (e.g., ACK/NACK) bit for each of the slots associated with the current PSFCH reporting occasion. The semi-static codebook for sidelink may be similar to the Uu interface semi-static codebook, except that the set of K1 may be based on the PSSCH to PSFCH timing association instead of K1 being indicated in downlink control information (DCI)/SCI.

With a semi-static codebook design, the hypothesis of the transmitting UE may be of the same codebook size as the semi-static codebook. Consider a reference example in which the transmitting UE sends two PSCCH/PSSCH transmissions to the receiving UE. Assuming the semi-static codebook size is <NUM> (and <NUM> slots map to one PSFCH), the transmitting UE may first try the <NUM>nd resource set for PSFCH (e.g., the PSFCH resource set associated with the <NUM>nd transmitted PSSCH in slot <NUM>), assuming <NUM> bits of feedback. If the transmitting UE is not able to decode with the <NUM>nd resource set, the transmitting UE may then try the <NUM>st resource set for PSFCH (e.g., the PSFCH resource set associated with the <NUM>nd transmitted PSSCH in slot <NUM>), assuming <NUM> bits of feedback. In some aspects, the hypothesis decoding can be performed in parallel.

In one aspect, a dynamic codebook can be supported for sidelink communications. With a dynamic codebook, a downlink assignment index (DAI) counter and DAI total can be added to SCI for the receiving UE, where the DAI field indicates the size of the dynamic codebook. With a dynamic codebook design, the hypothesis of the transmitting UE may be based on codebook size determined from the DAI field in SCI. Consider a reference example in which the transmitting UE sends two PSCCH/PSSCH transmissions to the receiving UE. In this example, the transmitting UE may first try the <NUM>nd resource set (e.g., sub-resource pool <NUM>-<NUM>) for PSFCH, assuming <NUM> bits feedback. If the transmitting UE is not able to decode with the <NUM>nd resource set, the transmitting UE can then try the <NUM>st resource set (e.g., sub-resource pool <NUM>-<NUM>) for PSFCH, assuming <NUM> bit feedback. In some aspects, the hypothesis decoding can be performed in parallel.

In some aspects, the receiving UE may determine a PSFCH sub-resource pool <NUM> for the multi-bit PSFCH, based on a resource indication (or resource indicator) (e.g., similar to primary resource indicator (PRI) in Uu interface). The resource indication may be included in SCI (e.g., SCI-<NUM>, SCI-<NUM>), and may indicate the sub-resource pool to be used for the PSFCH transmission. The resource indication may indicate and/or include information on which subset of PSFCH resources (e.g., PSFCH sub-resource pool <NUM>) is being used, as opposed to indicating which PSFCH resource within the subset of PSFCH resources is being used (e.g., as in the current Uu interface). By indicating the subset of PSFCH resources (e.g., PSFCH sub-resource pool <NUM>), aspects can reduce the number of bits within the signaling.

In some aspects, the same resource indicator can be indicated from multiple PSSCH. As shown in the example PSFCH resource selection of <FIG>, the resource indicator of SCI received in subchannel <NUM>-<NUM> and the resource indicator of SCI received in subchannel <NUM>-<NUM> indicate the same sub-resource pool <NUM>-<NUM>.

Alternatively, in some aspects, the resource indicator can indicate different PSFCH sub-resource pools <NUM>, and the receiving UE can use the latest received resource indicator to determine the PSFCH sub-resource pool <NUM> for the multi-bit PSFCH. This aspect may be similar to determining the resource based on the current DL grant.

In some aspects, the UE may be configured with a number of PSFCH resources, and the UE may perform resource selection based on the resource indication (e.g., three bits) and hashing (remaining degrees of freedom). In scenarios where there are more sub-resource pools than can be indicated by the resource indication, the UE can be configured to select a subset of the sub-resource pools. In one aspect, this sub-selection can be pre-configured for the UE (based on the PRI), hardcoded, or determined from a hash of the source ID. To support backward compatibility, the transmitting UE can restrict the PSSCH resource usage, so that the selected resource set from the available resource sets corresponds to an occupied subchannel. In some aspects, the available resource sets (e.g., available sub-resource pools) can be source ID and/or destination ID dependent. Additionally, the available resource sets can be function of time, e.g., to avoid persistent collision across UEs.

Aspects also provide techniques that enable the receiving UE to determine a PSFCH resource (within a PSFCH sub-resource pool <NUM>) to use for a multi-bit PSFCH transmission, according to certain aspects of the present disclosure. In some aspects, the receiving UE may select a PSFCH resource (e.g., a set of RBs) within a given PSFCH sub-resource pool <NUM>, based on the size of the payload and coding rate. For example, in cases where the multi-bit PSFCH design is based on PUCCH format <NUM>, the UE can select the number of RBs that is large enough to carry the payload to satisfy a predefined coding rate criteria.

<FIG> illustrates one reference example of PSFCH resource selection within a PSFCH sub-resource pool <NUM>, according to certain aspects of the present disclosure. In this example, assuming the sub-resource pool <NUM> includes a number of RBs (e.g., <NUM> RBs), the sub-resource pool may be divided by the radio resource control (RRC) configured size of the PSFCH (e.g., <NUM> RBs), into RB subsets <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM>, each including <NUM> RBs. The UE may then select one of the RB subsets (e.g., RB subset <NUM>-<NUM>) to use as the PSFCH resource. In one aspect, the UE may select one of the RB subsets (e.g., RB subset <NUM>-<NUM>), based on transmitter ID. In one aspect, the UE may also use a subset of the RBs in the selected RB subset <NUM>, based on the size of the feedback. For example, the receiving UE can use the starting RBs in the selected resource (e.g., RB subset <NUM>-<NUM>) if the number of bits to transmit is less than the RRC configured size of the PSFCH.

<FIG> illustrates another reference example of PSFCH resource selection within a PSFCH sub-resource pool, according to certain aspects of the present disclosure. In this example, the UE may determine the number of RBs that are needed for the PSFCH transmissions. The UE may then divide the sub-resource pool <NUM> into a number of RB subsets <NUM><NUM>-<NUM>, where the number of RB subsets <NUM> is based on the determined number of RBs needed for the PSFCH transmission. In <FIG>, for example, assuming the UE needs <NUM> RBs for the PSFCH transmission, the UE can divide the sub-resource pool <NUM> (including <NUM> RBs) into <NUM> RB subsets <NUM><NUM>-<NUM>, each including <NUM> RBs, and select one of the RB subsets (e.g., RB subset <NUM>-<NUM>) to use for the PSFCH transmission. In one aspect, the UE may select one of the RB subsets (e.g., RB subset <NUM>-<NUM>), based on transmitter ID.

<FIG> is a flow diagram illustrating example operations <NUM> for wireless communication, in accordance with certain aspects of the present disclosure. The operations <NUM> may be performed, for example, by a (receiving) (first) UE (e.g., such as the UE 120a in the wireless communication network <NUM>). The operations <NUM> may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor <NUM> of <FIG>). Further, the transmission and reception of signals by the UE in operations <NUM> may be enabled, for example, by one or more antennas (e.g., antennas <NUM> of <FIG>). In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor <NUM>) obtaining and/or outputting signals.

The operations <NUM> may begin, at <NUM>, where the (first) UE receives a plurality of transmissions from another (second) UE on a plurality of sidelink subchannels (e.g., subchannels <NUM>). Referring to <FIG>, for example, the UE may receive a first PSSCH on subchannel <NUM>-<NUM> during slot <NUM> and a second PSSCH on subchannel <NUM>-<NUM> during slot <NUM>.

At <NUM>, the UE determines at least one resource set (e.g., sub-resource pool <NUM>) for transmitting feedback corresponding to the plurality of transmissions, based on at least one of the plurality of transmissions. Referring to <FIG>, for example, the UE may select one of the sub-resource pools <NUM> within PSFCH resource pool <NUM> to use for selecting a PSFCH resource for the multi-bit HARQ-ACK transmission to acknowledge the PSSCH transmissions in slots <NUM> and <NUM>.

At <NUM>, the UE transmits (to the other UE) the feedback corresponding to the plurality of transmissions using the at least one resource set. For example, the UE can transmit the multi-bit HARQ-ACK using a single PSFCH resource (e.g., RB subset <NUM>) from within the determined sub-resource pool <NUM>. The feedback may include multiple bits, where each bit indicates an ACK or NACK for a different one of the transmissions.

In some aspects, the transmission of the feedback (at <NUM>) may be based on a transmission mode associated with the plurality of transmissions. For example, the operations <NUM> may further include receiving SCI from the (second) UE, where the SCI indicates a transmission mode associated with the plurality of transmissions. In one aspect, the (first) UE may transmit (at <NUM>) a single PSFCH comprising the multiple bits when the transmission mode is unicast. The single PSFCH may be based on PUCCH format <NUM> with one symbol (e.g., one symbol PUCCH format <NUM>). In one aspect, the (first) UE may transmit (at <NUM>) multiple PSFCHs, each corresponding to one of the multiple bits, when the transmission mode is groupcast or zone based.

In some aspects, the operations <NUM> may further include receiving multiple SCI (e.g., from the second UE), where each SCI corresponds to (i) one of the plurality of transmissions and (ii) one of multiple resource sets to use for transmitting feedback for the respective transmission corresponding to the SCI. With reference to <FIG>, for example, the (first) UE can receive a first SCI for a first PSSCH in subchannel <NUM>-<NUM> of slot <NUM> and a second SCI for a second PSSCH in subchannel <NUM>-<NUM> of slot <NUM>. The first SCI may correspond to sub-resource pool <NUM>-<NUM> (for the transmission of feedback to acknowledge the first PSSCH) and the second SCI may correspond to sub-resource pool <NUM>-<NUM> (for the transmission of feedback to acknowledge the second PSSCH).

In some aspects, the (first) UE, at <NUM>, can determine the at least one resource set by (i) determining which of the multiple SCI is a latest received SCI (e.g., SCI received in subchannel <NUM>-<NUM> of slot <NUM> in <FIG>) and (ii) setting the resource set (e.g., sub-resource pool <NUM>-<NUM> in <FIG>) associated with the latest received SCI as the at least one resource set for transmitting the feedback corresponding to the plurality of transmissions.

In some aspects, the (first) UE, at <NUM>, can determine the at least one resource set, based on a resource indicator in each of the multiple SCI. For example, the operations <NUM> may further include receiving a resource indicator in each of the multiple SCI (e.g., PRI in SCI received in subchannel <NUM>-<NUM> of slot <NUM> in <FIG>, and PRI in SCI received in subchannel <NUM>-<NUM> of slot <NUM> in <FIG>). Each resource indicator can indicate the resource set (e.g., sub-resource pool <NUM>-<NUM> of <FIG>) to use for transmitting the feedback corresponding to the plurality of transmissions.

In some aspects, the operations <NUM> can further include determining the feedback for the plurality of transmissions, based on a DAI field included in one or more of the multiple SCI. For example, the DAI field can be associated with a dynamic codebook, where the DAI field indicates a DAI counter and DAI total. In some aspects, the operations <NUM> can further include determining the feedback for the plurality of transmission, based on a semi-static codebook.

In some aspects, the operations <NUM> further include determining a set of RBs within the at least one resource set for transmitting the feedback corresponding to the plurality of transmissions. In one aspect, for example, the (first) UE can determine an amount of the RBs within the at least one resource set, based on a size of the PSFCH (e.g., the RRC configured PSFCH size), and select a subset of the amount of RBs as the set of RBs (e.g., RB subset <NUM>-<NUM> in <FIG>), based on a size of the feedback.

In another aspect, the (first) UE can determine an amount of RBs within the at least one resource set, based on a size of the feedback (e.g., <NUM> RBs). The number of the subset of RBs (e.g., four RB subsets <NUM><NUM>-<NUM> in <FIG>) can be based on the determined amount of RBs. The amount of RBs in each subset of RBs may be equal to the size of the feedback.

<FIG> is a flow diagram illustrating example operations <NUM> for wireless communication, in accordance with certain aspects of the present disclosure. The operations <NUM> may be performed, for example, by a (transmitting) UE (e.g., such as the UE 120b in the wireless communication network <NUM>). The operations <NUM> may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor <NUM> of <FIG>). Further, the transmission and reception of signals by the UE in operations <NUM> may be enabled, for example, by one or more antennas (e.g., antennas <NUM> of <FIG>). In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor <NUM>) obtaining and/or outputting signals.

The operations <NUM> may begin, at <NUM>, where the (transmitting) UE sends a plurality of transmissions to another (receiving) UE on a plurality of sidelink subchannels. At <NUM>, the UE monitors for feedback corresponding to the plurality of transmissions, from the other (receiving) UE, based on a codebook size associated with the feedback. The feedback, for example, can include a PSFCH with multiple bits, where each of the multiple bits indicates an ACK or NACK for a different one of the plurality of transmissions.

In some aspects, a semi-static codebook can be configured for the feedback. In these aspects, monitoring for the feedback (at <NUM>) may include (i) setting the codebook size associated with the feedback to a codebook size of the semi-static codebook and (ii) performing a hypothesis decoding operation, based on the codebook size associated with the feedback.

In some aspects, a dynamic codebook can be configured for the feedback. In these aspects, monitoring for the feedback (at <NUM>) may include (i) determining the codebook size based on an indication in SCI for each of the plurality of transmissions and (ii) performing a hypothesis decoding operation, based on the codebook size.

<FIG> illustrates a communications device <NUM> that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated in <FIG> and <FIG>. The communications device <NUM> includes a processing system <NUM> coupled to a transceiver <NUM> (e.g., a transmitter and/or a receiver).

The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium/memory <NUM> via a bus <NUM>. In certain aspects, the computer-readable medium/memory <NUM> is configured to store instructions (e.g., computer-executable code) that when executed by the processor <NUM>, cause the processor <NUM> to perform the operations illustrated in <FIG> and <FIG>, or other operations for performing the various techniques discussed herein for supporting multi-bit PSFCH. In certain aspects, computer-readable medium/memory <NUM> stores code <NUM> for receiving a plurality of transmissions from a second UE on a plurality of sidelink subchannels; code <NUM> for determining at least one resource set for transmitting feedback corresponding to the plurality of transmissions, based on at least one of the plurality of transmissions; code <NUM> for transmitting the feedback corresponding to the plurality of transmissions using the at least one resource set; code <NUM> for sending a plurality of transmissions to a second UE on a plurality of sidelink subchannels; and code <NUM> for monitoring for feedback corresponding to the plurality of transmissions, based on a codebook size associated with the feedback, etc..

In certain aspects, the processor <NUM> has circuitry configured to implement the code stored in the computer-readable medium/memory <NUM>. The processor <NUM> includes circuitry <NUM> for receiving a plurality of transmissions from a second UE on a plurality of sidelink subchannels; circuitry <NUM> for determining at least one resource set for transmitting feedback corresponding to the plurality of transmissions, based on at least one of the plurality of transmissions; circuitry <NUM> for transmitting the feedback corresponding to the plurality of transmissions using the at least one resource set; circuitry <NUM> for sending a plurality of transmissions to a second UE on a plurality of sidelink subchannels; and circuitry <NUM> for monitoring for feedback corresponding to the plurality of transmissions, based on a codebook size associated with the feedback, etc..

The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, a digital signal processor (DSP), an application specific integrated circuit (ASIC), or a processor (e.g., a general purpose or specifically programmed processor).

The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a DSP, an ASIC, a field programmable gate array (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein.

For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein, for example, instructions for performing the operations described herein and illustrated in <FIG> and/or <FIG>.

Claim 1:
A method for wireless communications by a first user equipment, UE, comprising:
receiving sidelink control information, SCI, from a second UE, the SCI indicating a transmission mode associated with a plurality of transmissions;
receiving (<NUM>) the plurality of transmissions from the second UE on one or more sidelink shared channels, PSSCHs;
determining (<NUM>) at least one resource set for transmitting feedback corresponding to the plurality of transmissions;
transmitting (<NUM>) the feedback corresponding to the plurality of transmissions using the at least one resource set; and
wherein transmitting the feedback is based on the transmission mode,
wherein transmitting the feedback comprises transmitting a single physical sidelink feedback channel, PSFCH, comprising the plurality of bits, when the transmission mode is unicast, each of the plurality of bits indicating an acknowledgement, ACK, or negative acknowledgement, NACK, for a different one of the plurality of transmissions, and
wherein transmitting the feedback comprises transmitting a plurality of physical sidelink feedback channels, PSFCHs, each comprising one of the plurality of bits, when the transmission mode is groupcast or zone based.