TECHNICAL FIELD

The present disclosure relates to wireless communications, and in particular, to resource allocation for sidelink retransmissions in unlicensed spectrum.

BACKGROUND

The Third Generation Partnership Project (3GPP) has developed and is developing standards for Fourth Generation (4G) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (5G) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile wireless devices (WD), as well as communication between network nodes and between WDs. Sixth Generation (6G) wireless communication systems are also under development.

Sidelink communications

Sidelink (SL) is the name in 3GPP specifications for the interface used for direct communication between wireless devices (WDs), also referred to as device-to- device (D2D) communications. This is in comparison to typical cellular communications in which two devices communicate by means of uplink (UL) transmissions (from WD to network node) and downlink (DL) transmissions (from network node to WD). The sidelink interface is sometimes referred to as the PC5 interface. The UL/DL interface is sometimes referred to as the Uu interface.

3GPP specified the sidelink (SL) as part of 3GPP Technical Release 12 (3GPP Rel-12). The target use case (UC) includes Proximity Services (communication and discovery). Support was enhanced during 3GPP Rel-13. In 3GPP Rel-14, the LTE sidelink was extensively redesigned to support vehicular communications (commonly referred to as V2X (between a vehicle and anything) or V2V (between vehicles)). Support was again enhanced during 3 GPP Rel-15. From the point of view of the lowest radio layers, the LTE SL uses broadcast communication. That is, transmission from a WD targets any receiver that is in range. In 3GPP Rel-16, the 3GPP introduced the sidelink for 5G (NR). The driving UC was vehicular communications with more stringent requirements than those typically served using the LTE SL. To meet these requirements, the NR SL is capable of broadcast, groupcast, and unicast communications. In groupcast communication, the intended receivers of a message are typically a subset of the vehicles near the transmitter, whereas in unicast communication, there is a single intended receiver.

Both the LTE SL and the NR SL can operate with and without network coverage and with varying degrees of interaction between the WDs (wireless devices) and the NW (network), including support for standalone, network-less operation.

SL resource pool

Radio resources for SL communication are organized into a SL resource pool. An NR SL resource pool consists of radio resources spanning both the time and frequency domain. In time domain, the SL resource pool consists of NR slots indexed in an ascending order, starting from index 0 up to a maximum index value. Once this maximum index is reached, the slot indexing is started again from index 0, and so on.

Resource allocation for sidelink transmissions

The 3GPP specification defines two resource allocation modes for NR sidelink:

• Network-based resource allocation, in which the network selects the resources and other transmit parameters used by sidelink WDs. In some cases, the network may control every single transmission parameter. In other cases, the network may select the resources used for transmission but may give the transmitter the freedom to select some of the transmission parameters, possibly with some restrictions. In the context of NR SL, 3GPP refers to this resource allocation mode as Mode 1; and • Autonomous resource allocation, in which the WDs autonomously select the resources and other transmit parameters. In this mode, there may be no intervention by the network (e.g., out of coverage, unlicensed carriers without a network deployment, etc.) or very minimal intervention by the network (e.g., configuration of pools of resources, etc.). In the context of NR SL, 3GPP refers to this resource allocation mode as Mode 2.

Note that Mode 1 and Mode 2 only describe the behavior of a WD when acting as a transmitter. From a receiver point of view, there is only one behavior. Moreover, the signals used by Mode 1 transmitters and by Mode 2 transmitters are identical.

Sidelink transmissions and resource reservation

A typical sidelink transmission includes:

• A Physical Sidelink Control Channel transmission (PSCCH) carrying control information including: o One or more reservations of sidelink resources, that may be used by the TX WD in the future for additional SL transmissions; and

• A Physical Sidelink Shared Channel (PSSCH) carrying the data payload as well as some additional control information.

Every PSSCH transmission can reserve up to two retransmissions for the same transport block (TB). In addition, the same first stage SCI can reserve the same (1, 2, or 3) radio resources (i.e., RBs) for transmission of a (single) different TB. This is illustrated in the example of FIG. 1.

Note that although the WD may select resources for transmission of multiple TBs, only a small subset of them are reserved at a time. That is, the WD reserves its selected resources in steps.

Whether the resources reserved for retransmission of a TB are used or not typically depends on SL hybrid automatic repeat request (HARQ) feedback (FB). This is described in the following section. HARO feedback in NR sidelink

For NR SL unicast and groupcast, Hybrid Automatic Repeat reQuest (HARQ) can be used to improve the reliability of communication. Specifically, the receiver WD (Rx WD) of a data packet sends back to the transmitter WD (Tx WD) a positive acknowledgement (ACK) if the Rx WD has decoded the packet correctly. Otherwise, the Rx WD sends a negative acknowledgement (NACK), which acts as a request for the Tx WD to resend the packet. As a result, the Tx WD will transmit a new packet in case of receiving an ACK and retransmit either the same version or a different version of the initial packet in case of receiving a NACK. Sometimes, only ACKs or only NACKs are allowed in the system, but that is not in focus of the present disclosure.

NR SL specifies a new physical channel, termed Physical Sidelink Feedback Channel (PSFCH), to convey the HARQ feedback (i.e., the ACK and/or the NACK) from the Rx WD to the Tx WD. Some features of the PSFCH design in NR SL are described below:

• A SL resource pool has dedicated slots in which the PSFCH can be transmitted, often referred to as PSFCH occasions or PSFCH slots. A PSFCH consists of two identical orthogonal frequency division multiplex (OFDM) symbols transmitted near the end of a PSFCH slot (i.e., the preceding OFDM symbols in the same slot can be used for data transmission). The PSFCH occasion can be (pre-)configured to be located at every N-th slot of the SL resource pool, where N = 1, 2, or 4. In some cases, no PSFCH is allowed in a resource pool, but that is not in the scope of the present disclosure.

• For a Physical Sidelink Shared Channel (PSSCH) transmission (i.e., a transmission of data packet) in slot n, the corresponding HARQ feedback is transmitted in the first PSFCH occasion occurring at or after slot n+M, where M = 2 or 3 to take into account processing delay at the WDs.

• Each PSFCH transmission uses one physical resource block (PRB) and uses a certain code (namely, a certain cyclic shift to be applied on a base sequence). PSFCH for different PSSCH are multiplexed in a PSFCH slot in both the PRB domain and the code domain. There is a rule for mapping between the slot and the subchannels in which a PSSCH is transmitted (besides some identifications of the Tx WD and the Rx WD) and the resource (namely the PRB and the code) to be used by the corresponding PSFCH. Based on this mapping, the Tx WD and the Rx WD know which resource to send and to receive a PSFCH.

• Each PSFCH carries only 1 bit of HARQ FB. Sometimes a WD needs to send more than one PSFCH in the same PSFCH slot, and therefore the WD may need to drop some of the PSFCH. The rule for prioritizing which PSFCH to transmit is typically based on a priority value associated with the corresponding PSSCH.

FIG. 2 illustrates an example segment of a SL resource pool containing PSFCH occasions for the case N = 4 and M = 2.

Note that initial transmission (PSCCH/PSSCH), the corresponding SL HARQ FB, and any subsequent retransmission must be separated in time, as illustrated in the example of FIG. 3. Consequently, reservations for consecutive transmissions must be separated in time, so that:

• there is enough time for the RX WD to (attempt to) decode the initial transmission and prepare the FB. This gap is defined in the specification; and that

• there is enough time for the TX WD to process the FB and prepare the retransmission. This gap is up to WD implementation.

NR operation in unlicensed spectrum

3GPP 5G NR supports performing uplink and downlink transmissions in unlicensed spectrum since 3GPP Rel-16. The unlicensed spectrum can be used by any device as long as certain rules for using the channel is met. These rules are often set by regulatory bodies in different parts of the world. In the following, some technical components for operation in unlicensed spectrum are described.

Channel access and Channel Occupancy Time (COT) sharing

In the unlicensed spectrum, the transmission medium (i.e., the channel) is shared by multiple users. To avoid conflicts and collisions of transmissions, channel access procedures are defined. The channel access procedures typically involve the following steps: • Sensing the channel for a certain period to detect whether other equipment (e.g., device, network node, etc.) are transmitting. This is sometimes referred to as performing clear channel assessment (CCA);

• If the channel is sensed as busy (i.e., CCA was unsuccessful or failed), the transmitter does not transmit; and

• If the channel is sensed as idle (i.e., CCA was successful), the transmitter makes use of the channel (e.g., transmits the information or signals, etc.).

The channel is utilized for a certain time, referred to as the channel occupancy time (COT). In some cases, different equipment may share a COT.

There are multiple alternative procedures for performing CCA:

• In some cases (e.g., listen-before-talk (LBT) Type 1), the WD accessing the channel must perform sensing of the channel utilization during a relatively long period (from tens of microseconds to several milliseconds). The period, known as the contention window, is non- deterministic and depends on randomly generated numbers as well as the activity by other devices; and

• In some cases (e.g., LBT Type 2/2A/2B/2C), the WD accessing the channel must perform sensing of the channel utilization during a relatively short period (e.g., up to 25 us) or can avoid performing sensing altogether. In any case, the duration of the sensing period is known beforehand.

Sidelink in unlicensed spectrum

In 3GPP Rel-18, mechanisms may be developed that enable the operation of SL communications in unlicensed spectrum, sometimes referred to as SL-U. It is expected that SL-U design will take NR SL and NR-U designs as a baseline.

Configuration and pre-configuration

In cellular systems, the network typically configures some parameters used by the WDs. This configuration is typically signaled by a network node (e.g., a gNB) to the WD (e.g., using radio resource control (RRC) signaling, broadcast signaling such as master information block (MIB) or system information block (SIB), or some other type of signaling). This is applicable to WDs performing sidelink transmissions if they are in coverage of a network. UEs that are out of network coverage but participate in sidelink communications, may be provided the corresponding parameters by means of a preconfiguration (e.g., stored in the subscriber identity module (SIM)).

Unless explicitly stated, the terms “configuration” and “pre-configuration”, are used to denote both ways of providing the corresponding configuration/parameters to a WD.

With the existing procedures, performing a SL transmission, with its corresponding SL HARQ FB, and a subsequent retransmission, requires assessing that the channel is available 3 times (e.g., by means of clear channel assessment), as illustrated in the example of FIG. 4

SUMMARY

This disclosure relates to operations and methods using resource allocation Mode 2 or any other mode in which the WD(s) perform sensing and resource allocation.

Some embodiments advantageously provide methods, systems, and apparatuses for resource allocation for sidelink retransmissions in unlicensed spectrum.

Some embodiments include methods for accessing the channel in shared spectrum to perform SL (re)transmissions.

A first method includes having a single SL HARQ FB transmission opportunity associated with a reservation. The method may include one or more of the following steps:

• In a first transmission, the TX WD reserves future radio resources to perform a retransmission. The reservation is indicated using control signaling;

• The RX WD gains access to the channel to send SL HARQ FB to the TX WD;

• The RX WD shares a COT with the TX WD; and/or

• The TX WD uses the shared COT to perform a further transmission (e.g., a retransmission). A second method includes having multiple SL HARQ FB transmission opportunities associated with a reservation. The method may include one or more of the following steps:

• In a first transmission, the TX WD reserves future radio resources to perform a retransmission. The reservation is indicated using control signaling. The reservation also allows for determining multiple opportunities for transmitting the corresponding SL HARQ FB;

• The RX WD gains access to the channel to send SL HARQ FB to the TX WD in one of the multiple SL HARQ FB transmission opportunities; and/or

• The TX WD gains access to the channel and performs a further transmission (e.g., a retransmission).

A third method of having multiple SL HARQ FB transmission opportunities associated with a reservation. The method may include one or more of the following steps:

• In a first transmission, the TX WD reserves future radio resources to perform a retransmission. The reservation is indicated using control signaling. The reservation also allows for determining multiple opportunities for transmitting the corresponding SL HARQ FB;

• The RX WD gains access to the channel to send SL HARQ FB to the TX WD in one of the multiple SL HARQ FB transmission opportunities;

• The RX WD shares a COT with the TX WD; and/or

• The TX WD uses the shared COT to perform a further transmission (e.g., a retransmission).

Some embodiments includes methods for accessing the channel in shared spectrum to perform SL (re)transmissions. Some methods make use of one or more of the following principles:

• Associating one or more SL HARQ FB transmission opportunities with a resource reservation; and/or

• Sharing a COT (from RX WD to TX WD) when transmitting the SL HARQ FB.

Some embodiments may provide one or more of the following advantages: • Reduction of the number of times that clear channel assessment must be performed before accessing the channel;

• Enablement of retransmissions on a channel for which the TX-RX pair has gained access (as opposed to requiring the channel access to be gained); and/or

• Reduction of the probability that other devices occupy the channel between SL HARQ FB transmission and a further (re)transmission. According to a first aspect of the present disclosure, a method in a first wireless device, WD, for sidelink, SL, communication with a second WD (e.g., using unlicensed spectrum) is provided. A resource selection for the sidelink, SL, communication with the second WD is determined, where the resource selection includes a first time resource for a first signaling and a second time resource for a second signaling, and the second time resource is subsequent to the first time resource. The first signaling is transmitted to the second WD using the first time resource, where the first signaling indicates the second time resource for the second signaling and enables the second WD to determine at least one additional time resource for SL hybrid automatic repeat request, HARQ, feedback. At least one HARQ feedback signaling is received from the second WD providing feedback for the first signaling using the at least one additional time resource prior to the second time resource. The second signaling is transmitted to the second WD using the second time resource.

According to one or more embodiments of this aspect, the first signaling includes at least one of a scheduling assignment indicating a payload included in the first signaling, and a reservation of the second time resource indicating an intention of the first WD to transmit signaling during the second time resource. According to one or more embodiments of this aspect, the first signaling indicates a last possible time resource on which the first WD expects to receive the at least one HARQ feedback signaling from the second WD. The first WD may also/alternatively receive the at least one HARQ feedback signaling in an earlier time resource than the last possible time resource. According to one or more embodiments of this aspect, the first signaling indicates a plurality of available time resources between the first time resource and the second time resource for the second WD to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first signaling enables the second WD to determine a plurality of available time resources between the first time resource and the second time resource for transmitting the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first signaling indicates a limited number of the plurality of available time resources on which the second WD is permitted to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the method further includes determining a first processing time associated with the first WD, where the plurality of available time resources is determined based on the first processing time, and a final available time resource of the plurality of available time resources is scheduled prior to the second time resource by a first margin that is at least as long as the first processing time. According to one or more embodiments of this aspect, the method further includes determining a second processing time associated with the second WD, where the plurality of available time resources is determined based on the second processing time, and an initial available time resource of the plurality of available time resources is scheduled subsequent to the first time resource by a second margin that is at least as long as the second processing time. According to one or more embodiments of this aspect, the at least one HARQ feedback signaling using the at least one additional time resource is performed during a shared channel occupancy time, COT, shared by the first WD and second WD. According to one or more embodiments of this aspect, the first signaling is transmitted using a clear channel assessment, CCA, procedure, and the second signaling is transmitted using one of a shortened clear channel assessment, CCA, procedure, no CCA procedure, and a listen before talk, LBT, procedure. According to one or more embodiments of this aspect, the first signaling indicates the sharing of the COT to the second WD.

According to another aspect of the present disclosure, a first wireless device, WD, configured for sidelink, SL, communication with a second WD (e.g., using unlicensed spectrum) is provided. The first WD is configured to determine a resource selection for the sidelink, SL, communication with the second WD, where the resource selection includes a first time resource for a first signaling and a second time resource for a second signaling, and the second time resource is subsequent to the first time resource. The first WD is configured to transmit the first signaling to the second WD using the first time resource, where the first signaling indicates the second time resource for the second signaling and enables the second WD to determine at least one additional time resource for SL hybrid automatic repeat request, HARQ, feedback. The first WD is configured to receive at least one HARQ feedback signaling from the second WD providing feedback for the first signaling using the at least one additional time resource prior to the second time resource. The first WD is configured to transmit the second signaling to the second WD using the second time resource.

According to one or more embodiments of this aspect, the first signaling includes at least one of a scheduling assignment indicating a payload included in the first signaling, and a reservation of the second time resource indicating an intention of the first WD to transmit signaling during the second time resource. According to one or more embodiments of this aspect, the first signaling indicates a last possible time resource on which the first WD expects to receive the at least one HARQ feedback signaling from the second WD. The first WD may also/alternatively receive the at least one HARQ feedback signaling in an earlier time resource than the last possible time resource. According to one or more embodiments of this aspect, the first signaling indicates a plurality of available time resources between the first time resource and the second time resource for the second WD to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first signaling enables the second WD to determine a plurality of available time resources between the first time resource and the second time resource for transmitting the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first signaling indicates a limited number of the plurality of available time resources on which the second WD is permitted to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first WD is further configured to determine a first processing time associated with the first WD, where the plurality of available time resources is determined based on the first processing time, and a final available time resource of the plurality of available time resources is scheduled prior to the second time resource by a first margin that is at least as long as the first processing time. According to one or more embodiments of this aspect, the first WD is further configured to determine a second processing time associated with the second WD, where the plurality of available time resources is determined based on the second processing time, and an initial available time resource of the plurality of available time resources is scheduled subsequent to the first time resource by a second margin that is at least as long as the second processing time. According to one or more embodiments of this aspect, the at least one HARQ feedback signaling using the at least one additional time resource is performed during a shared channel occupancy time, COT, shared by the first WD and second WD. According to one or more embodiments of this aspect, the first signaling is transmitted using a clear channel assessment, CCA, procedure, and the second signaling is transmitted using one of a shortened clear channel assessment, CCA, procedure, no CCA procedure, and a listen before talk, LBT, procedure. According to one or more embodiments of this aspect, the first signaling indicates the sharing of the COT to the second WD.

According to another aspect of the present disclosure, a method in a first WD for sidelink, SL, communication with a second WD (e.g., over unlicensed spectrum) is provided. The method includes receiving a first signaling from the second WD on a first time resource, where the first signaling indicates a second time resource for a second transmission from the second WD, and where the second time resource is subsequent to the first time resource. The method includes determining at least one additional time resource for SL hybrid automatic repeat request, HARQ, feedback based on the first signaling, where the at least one additional time resource is prior to the second time resource. The method includes transmitting, to the second WD, at least one HARQ feedback signaling providing feedback for the first signaling using the at least one additional time resource. The method includes receiving the second signaling from the second WD using the second time resource.

According to one or more embodiments of this aspect, the first signaling includes at least one of a scheduling assignment indicating a payload included in the first signaling, and a reservation of the second time resource indicating an intention of the second WD to transmit signaling during the second time resource. According to one or more embodiments of this aspect, the first signaling indicates a last possible time resource on which the second WD expects to receive the at least one HARQ feedback signaling from the first WD. According to one or more embodiments of this aspect, the first signaling indicates a plurality of available time resources between the first time resource and the second time resource for the first WD to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first WD is further configured to determine, based on the first signaling, a plurality of available time resources between the first time resource and the second time resource for transmitting the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first signaling indicates a limited number of the plurality of available time resources on which the first WD is permitted to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the method further includes determining a first processing time associated with the second WD, where the plurality of available time resources is determined based on the first processing time, and a final available time resource of the plurality of available time resources is scheduled prior to the second time resource by a first margin that is at least as long as the first processing time. According to one or more embodiments of this aspect, the method further includes determining a second processing time associated with the first WD, where the plurality of available time resources is determined based on the second processing time, and an initial available time resource of the plurality of available time resources is scheduled subsequent to the first time resource by a second margin that is at least as long as the second processing time. According to one or more embodiments of this aspect, the at least one HARQ feedback signaling using the at least one additional time resource is performed during a shared channel occupancy time, COT, shared by the first WD and second WD. According to one or more embodiments of this aspect, the at least one HARQ feedback signaling is transmitted using one of a shortened clear channel assessment, CCA, procedure, no CCA procedure, and a listen before talk, LBT, procedure. According to one or more embodiments of this aspect, the first signaling indicates the sharing of the COT by the second WD.

According to another aspect of the present disclosure, a first WD configured for sidelink, SL, communication with a second WD (e.g., over unlicensed spectrum) is provided. The first WD is configured to receive a first signaling from the second WD on a first time resource, where the first signaling indicates a second time resource for a second transmission from the second WD, and where the second time resource is subsequent to the first time resource. The first WD is configured to determine at least one additional time resource for SL hybrid automatic repeat request, HARQ, feedback based on the first signaling, where the at least one additional time resource is prior to the second time resource. The first WD is configured to transmit, to the second WD, at least one HARQ feedback signaling providing feedback for the first signaling using the at least one additional time resource. The first WD is configured to receive the second signaling from the second WD using the second time resource.

According to one or more embodiments of this aspect, the first signaling includes at least one of a scheduling assignment indicating a payload included in the first signaling, and a reservation of the second time resource indicating an intention of the second WD to transmit signaling during the second time resource. According to one or more embodiments of this aspect, the first signaling indicates a last possible time resource on which the second WD expects to receive the at least one HARQ feedback signaling from the first WD. According to one or more embodiments of this aspect, the first signaling indicates a plurality of available time resources between the first time resource and the second time resource for the first WD to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first WD is further configured to determine, based on the first signaling, a plurality of available time resources between the first time resource and the second time resource for transmitting the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first signaling indicates a limited number of the plurality of available time resources on which the first WD is permitted to transmit the at least one HARQ feedback signaling. According to one or more embodiments of this aspect, the first WD is further configured to determine a first processing time associated with the second WD, where the plurality of available time resources is determined based on the first processing time, and a final available time resource of the plurality of available time resources is scheduled prior to the second time resource by a first margin that is at least as long as the first processing time. According to one or more embodiments of this aspect, the first WD is further configured to determine a second processing time associated with the first WD, where the plurality of available time resources is determined based on the second processing time, and an initial available time resource of the plurality of available time resources is scheduled subsequent to the first time resource by a second margin that is at least as long as the second processing time. According to one or more embodiments of this aspect, the at least one HARQ feedback signaling using the at least one additional time resource is performed during a shared channel occupancy time, COT, shared by the first WD and second WD. According to one or more embodiments of this aspect, the at least one HARQ feedback signaling is transmitted using one of a shortened clear channel assessment, CCA, procedure, no CCA procedure, and a listen before talk, LBT, procedure. According to one or more embodiments of this aspect, the first signaling indicates the sharing of the COT by the second WD.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 shows resource reservation for non-periodic transmissions;

FIG. 2 shows an example of a sidelink resource pool;

FIG. 3 shows initial transmission and the corresponding feedback in sidelink communications;

FIG. 4 shows initial sidelink transmission and corresponding clear channel assessment (CCA);

FIG. 5 is a schematic diagram of an example network architecture illustrating a communication system connected via an intermediate network to a host computer according to the principles in the present disclosure;

FIG. 6 is a block diagram of a host computer communicating via a network node with a wireless device over an at least partially wireless connection according to some embodiments of the present disclosure;

FIG. 7 is a flowchart of an example process in a wireless device for resource allocation for sidelink retransmissions in unlicensed spectrum, according to one or more embodiments of the present disclosure;

FIG. 8 is a flowchart of another example process in a wireless device for resource allocation for sidelink retransmissions in unlicensed spectrum, according to one or more embodiments of the present disclosure;

FIG. 9 is a flowchart of another example process in a wireless device for resource allocation for sidelink retransmissions, according to one or more embodiments of the present disclosure;

FIG. 10 is a flowchart of another example process in a wireless device for resource allocation for sidelink retransmissions, according to one or more embodiments of the present disclosure;

FIG. 11 is an illustration of a first SL transmission and reserving a second resource for SL transmission, according to one or more embodiments of the present disclosure;

FIG. 12 is a diagram illustrating an example configuration in which SL HARQ FB and a second resource are in adjacent slots, according to one or more embodiments of the present disclosure; FIG. 13 is a diagram illustrating an example configuration in which a gap corresponds to one slot, according to one or more embodiments of the present disclosure;

FIG. 14 is a diagram illustrating an example configuration for performing a SL transmission, according to one or more embodiments of the present disclosure;

FIG. 15 is a diagram illustrating another example configuration for performing a SL transmission, according to one or more embodiments of the present disclosure; and

FIG. 16 is a diagram illustrating another example configuration for performing a SL transmission, according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

Before describing in detail example embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to resource allocation for sidelink retransmissions in unlicensed spectrum. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Like numbers refer to like elements throughout the description.

As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication.

In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and/or wireless connections.

The term “network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi -standard radio (MSR) radio node such as MSR BS, multi-cell/multicast coordination entity (MCE), integrated access and backhaul (IAB) node, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), self-organizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rd party node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.

In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The WD herein can be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD). The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and/or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (loT) device, or a Narrowband loT (NB-IOT) device, etc.

Also, in some embodiments the generic term “radio network node” is used. It can be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell/multicast Coordination Entity (MCE), IAB node, relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH).

Note that although terminology from one particular wireless system, such as, for example, 3 GPP LTE and/or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure.

Note further, that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Some embodiments provide resource allocation for sidelink retransmissions in unlicensed spectrum.

Returning now to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in FIG. 5 a schematic diagram of a communication system 10, according to an embodiment, such as a 3 GPP -type cellular network that may support standards such as LTE and/or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14. The access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18). Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b (collectively referred to as wireless devices 22) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node 16. Note that although only two WDs 22 and three network nodes 16 are shown for convenience, the communication system may include many more WDs 22 and network nodes 16.

Also, it is contemplated that a WD 22 can be in simultaneous communication and/or configured to separately communicate with more than one network node 16 and more than one type of network node 16. For example, a WD 22 can have dual connectivity with a network node 16 that supports LTE and the same or a different network node 16 that supports NR. As an example, WD 22 can be in communication with an eNB for LTE/E-UTRAN and a gNB for NR/NG-RAN.

The communication system 10 may itself be connected to a host computer 24, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 24 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 26, 28 between the communication system 10 and the host computer 24 may extend directly from the core network 14 to the host computer 24 or may extend via an optional intermediate network 30. The intermediate network 30 may be one of, or a combination of more than one of, a public, private or hosted network. The intermediate network 30, if any, may be a backbone network or the Internet. In some embodiments, the intermediate network 30 may comprise two or more sub-networks (not shown). A wireless device 22 is configured to include a HARQ unit 34 which is configured to perform a first sidelink, SL, transmission indicating to the second WD a reservation of radio resources, the reservation of radio resources enabling the second WD to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback. The HARQ unit 34 is further configured to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback based at least in part on reserved resources indicated by a second WD 22.

Example implementations, in accordance with an embodiment, of the WD 22, network node 16 and host computer 24 discussed in the preceding paragraphs will now be described with reference to FIG. 6. In a communication system 10, a host computer 24 comprises hardware (HW) 38 including a communication interface 40 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 10. The host computer 24 further comprises processing circuitry 42, which may have storage and/or processing capabilities. The processing circuitry 42 may include a processor 44 and memory 46. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 42 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 44 may be configured to access (e.g., write to and/or read from) memory 46, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read- Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Processing circuitry 42 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by host computer 24. Processor 44 corresponds to one or more processors 44 for performing host computer 24 functions described herein. The host computer 24 includes memory 46 that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 48 and/or the host application 50 may include instructions that, when executed by the processor 44 and/or processing circuitry 42, causes the processor 44 and/or processing circuitry 42 to perform the processes described herein with respect to host computer 24. The instructions may be software associated with the host computer 24.

The software 48 may be executable by the processing circuitry 42. The software 48 includes a host application 50.

The communication system 10 further includes a network node 16 provided in a communication system 10 and including hardware 58 enabling it to communicate with the host computer 24 and with the WD 22. The hardware 58 may include a communication interface 60 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 10, as well as a radio interface 62 for setting up and maintaining at least a wireless connection 64 with a WD 22 located in a coverage area 18 served by the network node 16. The radio interface 62 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers. The communication interface 60 may be configured to facilitate a connection 66 to the host computer 24. The connection 66 may be direct or it may pass through a core network 14 of the communication system 10 and/or through one or more intermediate networks 30 outside the communication system 10.

In the embodiment shown, the hardware 58 of the network node 16 further includes processing circuitry 68. The processing circuitry 68 may include a processor 70 and a memory 72. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 68 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 70 may be configured to access (e.g., write to and/or read from) the memory 72, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the network node 16 further has software 74 stored internally in, for example, memory 72, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node 16 via an external connection. The software 74 may be executable by the processing circuitry 68. The processing circuitry 68 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by network node 16. Processor 70 corresponds to one or more processors 70 for performing network node 16 functions described herein. The memory 72 is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 74 may include instructions that, when executed by the processor 70 and/or processing circuitry 68, causes the processor 70 and/or processing circuitry 68 to perform the processes described herein with respect to network node 16.

The communication system 10 further includes the WD 22 already referred to. The WD 22 may have hardware 80 that may include a radio interface 82 configured to set up and maintain a wireless connection 64 with a network node 16 serving a coverage area 18 in which the WD 22 is currently located. The radio interface 82 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and/or one or more RF transceivers.

The hardware 80 of the WD 22 further includes processing circuitry 84. The processing circuitry 84 may include a processor 86 and memory 88. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 84 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 86 may be configured to access (e.g., write to and/or read from) memory 88, which may comprise any kind of volatile and/or nonvolatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the WD 22 may further comprise software 90, which is stored in, for example, memory 88 at the WD 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD 22. The software 90 may be executable by the processing circuitry 84. The software 90 may include a client application 92. The client application 92 may be operable to provide a service to a human or non-human user via the WD 22.

The processing circuitry 84 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, and/or processes to be performed, e.g., by WD 22. The processor 86 corresponds to one or more processors 86 for performing WD 22 functions described herein. The WD 22 includes memory 88 that is configured to store data, programmatic software code and/or other information described herein. In some embodiments, the software 90 and/or the client application 92 may include instructions that, when executed by the processor 86 and/or processing circuitry 84, causes the processor 86 and/or processing circuitry 84 to perform the processes described herein with respect to WD 22. For example, the processing circuitry 84 of the wireless device 22 may include a HARQ unit 34 which is configured to perform a first sidelink, SL, transmission indicating to the second WD a reservation of radio resources, the reservation of radio resources enabling the second WD to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback. The HARQ unit 34 is further configured to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback based at least in part on reserved resources indicated by a second WD 22.

In some embodiments, the inner workings of the network node 16, WD 22, and host computer 24 may be as shown in FIG. 6 and independently, the surrounding network topology may be that of FIG. 5.

FIG. 7 is a flowchart of an example process in a first WD 22 for resource allocation for sidelink retransmissions in unlicensed spectrum. One or more blocks described herein may be performed by one or more elements of WD 22 such as by one or more of processing circuitry 84 (including the HARQ unit 34), processor 86, and/or a radio interface 82. WD 22 such as via processing circuitry 84 and/or processor 86 and/or radio interface 62, is configured to perform a first sidelink, SL, transmission indicating to the second WD a reservation of radio resources, the reservation of radio resources enabling the second WD to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback (Block SI 00). The process also includes performing a second transmission to the second WD during a time related to the reserved radio resources (Block SI 02).

In some embodiments, the second transmission is performed during a shared channel occupancy time, COT, shared by the first WD and second WD. In some embodiments, the first transmission further indicates to the second WD an intent to perform the second transmission on the reserved radio resources. In some embodiments, the second transmission is preceded by SL HARQ feedback during the COT. In some embodiments, the second transmission is preceded by SL HARQ feedback transmitted after a clear channel assessment, CCA. In some embodiments, the first transmission indicates a last occasion for which the first WD expects SL HARQ feedback from the second WD.

FIG. 8 is a flowchart of an example process in a wireless device 22 according to some embodiments of the present disclosure. One or more blocks described herein may be performed by one or more elements of wireless device 22 such as by one or more of processing circuitry 84 (including the HARQ unit 34), processor 86, and or radio interface 82. Wireless device 22 such as via processing circuitry 84 and/or processor 86 and/or radio interface 82 is configured to receive from the second WD an indication of a reservation of radio resources (Block SI 04). The process also includes determining (Block SI 06) at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback based at least in part on the reserved resources.

In some embodiments, the determined at least one opportunity is determined to occur during a shared channel occupancy time, COT, shared between the first WD and the second WD. In some embodiments, the determined at least one opportunity is determined to occur after a clear channel assessment, CCA by the first WD. In some embodiments, the at least one opportunity is determined to occur before the reserved resources. In some embodiments, the at least one opportunity and the reserved resources are adjacent in time.

FIG. 9 is a flowchart of another example process in a first WD 22 (e.g., a Tx WD) for resource allocation for sidelink retransmissions, e.g., in unlicensed spectrum. One or more blocks described herein may be performed by one or more elements of the first WD 22 such as by one or more of processing circuitry 84 (including the HARQ unit 34), processor 86, and/or a radio interface 82. The first WD 22 is configured to determine (Block SI 08) a resource selection for the sidelink, SL, communication with the second WD 22, and where the resource selection includes a first time resource for a first signaling and a second time resource for a second signaling, and the second time resource is subsequent to the first time resource. The first WD 22 is configured to transmit (Block SI 10) the first signaling to the second WD 22 using the first time resource, where the first signaling indicates the second time resource for the second signaling and enables the second WD 22 to determine at least one additional time resource for SL hybrid automatic repeat request, HARQ, feedback. The first WD 22 is configured to receive (Block SI 12), from the second WD 22, at least one HARQ feedback signaling providing feedback for the first signaling using the at least one additional time resource prior to the second time resource. The first WD 22 is configured to transmit (Block SI 14) the second signaling to the second WD 22 using the second time resource.

In some embodiments, the first signaling includes at least one of a scheduling assignment indicating a payload included in the first signaling, and a reservation of the second time resource indicating an intention of the first WD 22 to transmit signaling during the second time resource. In some embodiments, the first signaling indicates a last possible time resource on which the first WD 22 expects to receive the at least one HARQ feedback signaling from the second WD 22. The first WD 22 may also/alternatively receive the at least one HARQ feedback signaling in an earlier time resource than the last possible time resource. In some embodiments, the first signaling indicates a plurality of available time resources between the first time resource and the second time resource for the second WD 22 to transmit the at least one HARQ feedback signaling. In some embodiments, the first signaling enables the second WD 22 to determine a plurality of available time resources between the first time resource and the second time resource for transmitting the at least one HARQ feedback signaling. In some embodiments, the first signaling indicates a limited number of the plurality of available time resources on which the second WD 22 is permitted to transmit the at least one HARQ feedback signaling. In some embodiments, the first WD 22 is further configured to determine a first processing time associated with the first WD 22, where the plurality of available time resources is determined based on the first processing time, and a final available time resource of the plurality of available time resources is scheduled prior to the second time resource by a first margin that is at least as long as the first processing time. In some embodiments, the first WD 22 is further configured to determine a second processing time associated with the second WD 22, where the plurality of available time resources is determined based on the second processing time, and an initial available time resource of the plurality of available time resources is scheduled subsequent to the first time resource by a second margin that is at least as long as the second processing time. In some embodiments, the at least one HARQ feedback signaling using the at least one additional time resource is performed during a shared channel occupancy time, COT, shared by the first WD 22 and second WD 22. In some embodiments, the first signaling is transmitted using a clear channel assessment, CCA, procedure, and the second signaling is transmitted using one of a shortened clear channel assessment, CCA, procedure, no CCA procedure, and a listen before talk, LBT, procedure. In some embodiments, the first signaling indicates the sharing of the COT to the second WD 22.

FIG. 10 is a flowchart of another example process in a first WD 22 (e.g., an Rx WD) for resource allocation for sidelink retransmissions, e.g., in unlicensed spectrum. One or more blocks described herein may be performed by one or more elements of the first WD 22 such as by one or more of processing circuitry 84 (including the HARQ unit 34), processor 86, and/or a radio interface 82. The first WD 22 is configured to receive (Block SI 16) a first signaling from the second WD 22 on a first time resource, where the first signaling indicates a second time resource for a second transmission from the second WD 22, where the second time resource is subsequent to the first time resource. The first WD 22 is configured to determine (Block SI 18) at least one additional time resource for SL hybrid automatic repeat request, HARQ, feedback based on the first signaling, where the at least one additional time resource is prior to the second time resource. The first WD 22 is configured to transmit (Block S120), to the second WD 22, at least one HARQ feedback signaling providing feedback for the first signaling using the at least one additional time resource. The first WD 22 is configured to receive (Block S122) the second signaling from the second WD 22 using the second time resource.

In some embodiments, the first signaling includes at least one of a scheduling assignment indicating a payload included in the first signaling, and a reservation of the second time resource indicating an intention of the second WD 22 to transmit signaling during the second time resource. In some embodiments, the first signaling indicates a last possible time resource on which the second WD 22 expects to receive the at least one HARQ feedback signaling from the first WD 22. In some embodiments, the first signaling indicates a plurality of available time resources between the first time resource and the second time resource for the first WD 22 to transmit the at least one HARQ feedback signaling. In some embodiments, the first WD 22 is further configured to determine, based on the first signaling, a plurality of available time resources between the first time resource and the second time resource for transmitting the at least one HARQ feedback signaling. In some embodiments, the first signaling indicates a limited number of the plurality of available time resources on which the first WD 22 is permitted to transmit the at least one HARQ feedback signaling. In some embodiments, the first WD 22 is further configured to determine a first processing time associated with the second WD 22, where the plurality of available time resources is determined based on the first processing time, and a final available time resource of the plurality of available time resources is scheduled prior to the second time resource by a first margin that is at least as long as the first processing time. In some embodiments, the first WD 22 is further configured to determine a second processing time associated with the first WD 22, where the plurality of available time resources is determined based on the second processing time, and an initial available time resource of the plurality of available time resources is scheduled subsequent to the first time resource by a second margin that is at least as long as the second processing time. In some embodiments, the at least one HARQ feedback signaling using the at least one additional time resource is performed during a shared channel occupancy time, COT, shared by the first WD 22 and second WD 22. In some embodiments, the at least one HARQ feedback signaling is transmitted using one of a shortened clear channel assessment, CCA, procedure, no CCA procedure, and a listen before talk, LBT, procedure. In some embodiments, the first signaling indicates the sharing of the COT by the second WD 22.

Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for resource allocation for sidelink retransmissions in unlicensed spectrum.

Some embodiments include methods for selecting resources for sidelink transmission. Methods are disclosed for selecting resources for retransmissions, but the resources may be used for other purposes too (e.g., for starting a transmission of a new TB, for transmitting a different TB, etc.).

The following terminology may be used herein:

• TX WD 22: this is the WD 22 that selects the resources for SL transmission (according to methods disclosed herein). The TX WD 22 is also the WD 22 that transmits one or more TBs to a RX WD 22 (or multiple RX WDs) along with control signaling. These messages may be carried by a PSSCH and/or a PSCCH; • RX WD 22: this is the WD 22 that receives the transmission from the TX WD 22. Based on this reception, the RX WD 22 provides SL HARQ FB to the TX WD 22. The SL HARQ FB may be carried by a PSFCH: o The SL HARQ FB may be HARQ- ACK or HARQ-NACK or some other indication; o The extension to multiple RX WDs is straightforward.

The multiple RX WDs may provide the feedback using independent resources or using a common resource. In the latter case, the TX WD 22 observes a superposition of the transmissions by the multiple RX WDs.

In the following, some main example embodiments are disclosed.

• In a first example embodiment: o For every reserved resource there is (only) one associated SL HARQ FB opportunity; and o The RX WD 22 shares the COT with the TX WD 22;

• In a second example embodiment: o For every reserved resource there may be multiple associated SL HARQ FB opportunities;

• Characteristics of the second embodiment may include: o For every reserved resource there may be multiple associated SL HARQ FB opportunities; and o The RX WD 22 shares the COT with the TX WD 22.

• The third main example embodiment combines the first and second main embodiments.

Each of these example embodiments is followed by multiple other example embodiments. The embodiments presented here may be combined in different ways than the ones presented here.

First main example embodiment

In the first main embodiment, the TX WD 22 selects two resources for SL transmission. The two resources are separated in time. The TX WD 22 performs a first SL transmission using the first selected resource. This transmission includes: • Control information: for example, sidelink control information (SCI), carried in a PSCCH and/or a PSSCH. The control information includes an indication of the presence of the payload data (i.e., a scheduling assignment); and/or

• Payload data: for example a TB carried in a PSSCH.

The control information indicates a reservation of the second selected resources. That is, any WD 22 (including the RX WD 22) that receives the control information is aware of the intention of the TX WD 22 to perform a further SL transmission using the second selected resource.

The RX WD 22 receives the SL transmission in the first selected resource and attempts to decode the control information and the payload data:

• If the WD 22 fails to decode the control information, then it misses the scheduling assignment. In this case, the WD 22 is typically unaware that the data has be sent by the TX WD 22 and does not perform further action; and

• If the WD 22 decodes the control information, then it sends SL HARQ FB to the RX WD 22. The SL HARQ FB may indicate ACK or NACK, depending on whether the corresponding PSSCH was decoded or not.

To be able to transmit the SL HARQ FB, the RX WD 22 must gain access to the channel by means of a channel access procedure (e.g., CCA performing LBT, receiving the permission to access the channel from another node or WD 22, etc.). How the RX WD 22 gains access to the channel is outside the scope of this disclosure. It suffices to state that the following may occur:

• the RX WD 22 gains access to the channel; and

• the RX WD 22 is allowed to share the COT with another

WD 22. Transmission of the SL HARQ FB happens on radio resources (e.g., for a PSFCH) that are located before the second selected resource. This allows the RX WD 22 to share the COT with the TX WD 22, which simplifies channel access for the TX WD 22 for transmitting using the reserved resource. For example, the SL HARQ FB transmission by the RX WD 22 and the second reserved resource may be adjacent in time (e.g., in adjacent time slots) or separated by a very short time gap (e.g., separated by a silent or guard period).

When performing the SL HARQ FB transmission, the RX WD 22 shares the COT with the TX WD 22. This means that the TX WD 22 can directly access the channel without performing an additional CCA or that the TX WD 22 can access the channel after performing a simplified CCA (e.g., a shorter such as LBT Type 2/2A/2B/2C).

A principle of the method is illustrated in the example diagram of FIG. 11.

Note that the SL HARQ FB transmission and the second selected resource may be separated in time (e.g., by a guard period or by several slots). The principle of operation, including the COT, sharing between RX WD 22 and TX WD 22, remains the same regardless of the separation (see the examples of FIG. 12 and FIG. 13 and compare to FIG. 11). That is, the COT is shared between RX WD 22 and TX WD 22. However, in practice the TX WD 22 may be required to perform a different CCA procedure in each case. For example, for adjacent transmissions it may be allowed to skip CCA altogether or be required to perform a short CCA. For transmissions separated by a small gap (e.g., less than 25 us), the TX WD 22 may be required to perform a short CCA. For longer gaps, it may be required to perform the same or a longer CCA.

In the following, the CCA between SL HARQ FB transmission and PSCCH/PSSCH transmission is omitted for simplicity, but the descriptions apply as well if the CCA is included.

Additional example embodiments

In one embodiment, the TX WD 22 reserves more than one resource (see FIG. 14). Each reserved resource is associated with a transmission opportunity for SL HARQ FB (e.g., a PSFCH resource) to acknowledge reception of the first SL transmission from the TX WD 22: • In one dependent embodiment, the RX WD 22 acknowledges the reception of the first SL transmission from the TX WD 22 only once; and/or

• In one dependent embodiment, the RX WD 22 may acknowledge the reception of the first SL transmission from the TX WD 22 multiple times. For example, if the RX WD 22 does not receive a retransmission from the TX WD 22 in the reserved resource associated with the SL HARQ FB occasion in which it transmitted the SL HARQ FB, then it uses the SL HARQ FB occasion associated with the next reserved resource. Recall that the reserved resource and the corresponding SL HARQ FB occasion may or may not be adjacent in time.

• In one embodiment, each of the multiple reserved resources follows a SL HARQ FB transmission opportunity (as illustrated in FIG. 14) for acknowledging the first transmission by the TX WD 22. For example, each SL HARQ FB transmission opportunity and the subsequent reserved resource (resources reserved for subsequent PSCCH/PSSCH transmission in FIG. 14) are on adjacent slots for SL transmission (e.g., adjacent slots in a pool of resources for SL transmission); and/or

• In another embodiment, there may be a gap (e.g., of one or multiple slots) between SL HARQ FB transmission and the subsequent reserved resource.

In one embodiment, the SL HARQ feedback transmission explicitly indicates that the COT is shared by the RX WD 22 to the TX WD 22. For example, a code (e.g., a cyclic shift) is applied on top of a sequence carrying HARQ FB without COT sharing to indicate the COT sharing. In one alternative, COT sharing is indicated explicitly. However, the type of channel access used by the TX WD 22 is determined implicitly based on the time gap between SL HARQ feedback transmission and the reserved resource. In another alternative, the type of channel access used by the TX WD 22 is also indicated explicitly by the RX WD 22. In another embodiment, the COT sharing is always used between RX WD 22 and TX WD 22 when retransmission is performed (e.g., defined in the specification) and type of channel access used by the TX WD 22 is determined based on the time gap between SL HARQ feedback transmission and the reserved resource. In one embodiment, the RX WD 22 may be provided with alternative means to know that it is expected to send SL HARQ FB to the TX WD 22. That is, the RX WD 22 need not decode the control information accompanying the payload data transmission that it has to acknowledge. For example, the RX WD 22 may have been provided with the corresponding control information in an earlier transmission or by means of a configuration (from the TX WD 22, from another WD 22, from a network node 16, etc.). For example a SL grant may be provided to the RX WD 22, by which the RX WD 22 knows that a transmission may take place on a certain resource and that SL HARQ FB must be conveyed.

In another embodiment, the TX WD 22 uses the second resource (i.e., the reserved resource) for retransmission of the same TB (i.e., the TB transmitted in the first resource). In another embodiment, the TX uses the second resource for transmission of a different TB.

Note that in the first main embodiment, the time of the resource used for transmitting the SL HARQ FB is determined based on the reservation indication in the SCI. In one embodiment, other aspects of the resource used for transmitting the SL HARQ FB (e.g., the frequency location) are determined based on the reservation indication in the SCI (e.g., the reserved sub -channel (s) determine(s) the frequency resource used for transmitting the SL HARQ FB). In another embodiment, other aspects of the resource used for transmitting the SL HARQ FB (e.g., the frequency location) are determined based on the resource used for the SL transmission (i.e., the first resource). For example, the sub-channel(s) of the first resource determine the frequency resource used for transmitting the SL HARQ FB).

Second example main embodiment

In the second example main embodiment, the TX WD 22 selects two resources for SL transmission. The two resources are separated in time. The TX WD 22 performs a first SL transmission using the first selected resource. This transmission may include:

• Control information, for example, an SCI carried in a PSCCH and/or a PSSCH. The control information may include an indication of the presence of the payload data (i.e., a scheduling assignment); and/or

• Payload data, for example, a TB carried in a PSSCH. The control information indicates a reservation of the second selected resources. That is, any WD 22 (e.g., the RX WD 22) that receives the control information is aware of the intention of the TX WD 22 to perform a further SL transmission using the second selected resource.

The RX WD 22 receives the SL transmission in the first selected resource and attempts to decode the control information and the payload data:

• If the WD 22 fails to decode the control information, then it misses the scheduling assignment. In this case, the WD 22 is typically unaware that the data has be sent by the TX WD 22 and does not perform further action; and

• If the WD 22 decodes the control, then it sends SL HARQ FB to the RX WD 22. The SL HARQ FB may indicate ACK or NACK.

To be able to transmit the SL HARQ FB, the RX WD 22 may gain access to the channel by means of a channel access procedure (e.g., CCA performing LBT), including receiving the permission to access the channel from another node or WD 22, etc. How the RX WD 22 gains access to the channel is outside the scope of this disclosure. Note that whether the RX WD 22 can access the channel for transmitting the SL HARQ FB cannot be known beforehand. In fact, the RX WD 22 may not be able to access the channel within a short time window.

Transmission of the SL HARQ FB may happen on one of multiple resources, which may include suitable radio resources (e.g., for a PSFCH) between the first selected resource and the second selected resource. For example:

• The control information in the first SL transmission indicates the last occasion on which the TX WD 22 expects the SL HARQ FB transmissions; and/or

• The RX WD 22 may use any suitable radio resource before the last occasion.

A principle of the method is illustrated in FIG. 15.

Note that there is an absence of COT sharing in this second main embodiment. The use of COT sharing is discussed in the third main embodiment.

Additional embodiments In one embodiment, the reservation information in the control information is used to determine the last occasion on which the TX WD 22 expects the SL HARQ FB transmissions.

In another embodiment, an additional field in the control information is used to determine the last occasion on which the TX WD 22 expects the SL HARQ FB transmissions.

In one embodiment, the SL HARQ FB may come on a limited number K of PSFCH transmission occasions (as opposed to any transmission occasion between first and second resource). In one dependent embodiment, the value of K may depend on the interval between the first and the second resources.

In one embodiment, the SL HARQ FB can only come within an interval between the first transmission and the reserved resource (i.e., the second resource selected by the TX WD 22 selected). This allows for corresponding processing gaps at the RX WD 22 (to decode the SL transmission from the TX WD 22 and prepare the corresponding feedback) and at the TX WD 22 (to decode the SL HARQ FB transmission from the RX WD 22 and prepare the subsequent SL transmission, e.g., a retransmission). This is illustrated in FIG. 16.

In one embodiment, the TX WD 22 reserves more than one resource. That is, the control information indicates a reservation of the multiple resources:

• In one embodiment, the method described here refers to one of the reservations (e.g., the first one, the last one) or to a reservation that is specifically indicated for this purpose (e.g., by further control signaling); and/or

• In one embodiment, the method described here refers to any of the reservations.

In one embodiment, the RX WD 22 transmits SL HARQ FB on every occasion that it can get access to the channel, until the last occasion on which the TX WD 22 expects the SL HARQ FB transmissions.

Third main embodiment The third main embodiment combines the first and second main embodiments. In this embodiment, the TX WD 22 selects two resources for SL transmission. The two resources are separated in time. The TX WD 22 performs a first SL transmission using the first selected resource. This transmission may include:

• Control information, for example an SCI carried, in a PSCCH and/or a PSSCH. The control information may carry an indication of the presence of the payload data (i.e., a scheduling assignment); and/or

• Payload data (e.g., a TB), carried e.g., in a PSSCH.

The control information indicates a reservation of the second selected resources. Then a WD 22 (e.g., the RX WD 22) that receives the control information is aware of the intention of the TX WD 22 to perform a further SL transmission using the second selected resource.

The RX WD 22 receives the SL transmission in the first selected resource and attempts to decode the control information and the payload data:

• If the WD 22 fails to decode the control information, then it misses the scheduling assignment. In this case, the WD 22 is typically unaware that the data has be sent by the TX WD 22 and does not perform further action; and/or

• If the WD 22 decodes the control, then it sends SL HARQ FB to the RX WD 22. The SL HARQ FB may indicate ACK or NACK.

To be able to transmit the SL HARQ FB, the RX WD 22 must gain access to the channel by means of a channel access procedure (e.g., CCA performing LBT, receiving the permission to access the channel from another node or WD 22, etc.). Note that whether the RX WD 22 can access the channel for transmitting the SL HARQ FB cannot be known beforehand. In fact, the RX WD 22 may not be able to access the channel at within a short time window. How the RX WD 22 gains access to the channel is outside the scope of this disclosure, but the RX WD 22 may be allowed to share the COT with another WD 22.

Transmission of the SL HARQ FB may happen on any suitable radio resource (e.g., for a PSFCH) between the first selected resource and the second selected resource: • The control information indicates the last occasion on which the TX WD 22 expects the SL HARQ FB transmissions; and/or

• The RX WD 22 may use any suitable radio resource before the last occasion.

When performing the SL HARQ FB transmission, the RX WD 22 may share the COT with the TX WD 22. This means that the TX WD 22 can directly access the channel without performing an additional CCA or that the TX WD 22 can access the channel after performing a simplified CCA (e.g., a shorter such as LBT Type 2/2A/2B/2C).

Note that in some cases, there may be a gap between the SL HARQ FB transmission and the subsequent reserved resource.

Additional embodiments

The additional embodiments for the other two main embodiments are applicable here. In particular, multiple resources may be reserved by the TX WD 22. Multiple SL HARQ FB occasions are associated with each reserved resource. The RX WD 22 shares the COT with the TX WD 22 when conveying the SL HARQ FB.

An example of operation is the following:

• A first SL transmission using a first resource may convey a reservation for a second and a third resource;

• SL HARQ FB for the first transmissions may be sent on one of multiple occasions prior to the second resource. The RX WD 22 shares the COT with the TX WD 22 when conveying the SL HARQ FB; and/or

• The TX WD 22 may access the channel using the second resource without CCA or using a short CCA. This transmission may be acknowledged using one of the SL HARQ FB occasions associated with the next reservation.

Some Examples:

Example Al . A first wireless device, WD, configured to communicate with a second WD, the first WD configured to, and/or comprising a radio interface and/or comprising processing circuitry configured to: perform a first sidelink, SL, transmission indicating to the second WD a reservation of radio resources, the reservation of radio resources enabling the second WD to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback; and perform a second transmission to the second WD during a time related to the reserved radio resources.

Example A2. The first WD of Example Al, wherein the second transmission is performed during a shared channel occupancy time, COT, shared by the first WD and second WD.

Example A3. The first WD of any of Example Al and A2, wherein the first transmission further indicates to the second WD an intent to perform the second transmission on the reserved radio resources.

Example A4. The first WD of any of Examples A1-A3, wherein the second transmission is preceded by SL HARQ feedback during the COT.

Example A5. The first WD of any of Examples A1-A3, wherein the second transmission is preceded by SL HARQ feedback transmitted after a clear channel assessment, CCA.

Example A6. The first WD of any of Examples A1-A5, wherein the first transmission indicates a last occasion for which the first WD expects SL HARQ feedback from the second WD.

Example BL A method implemented in a first wireless device, WD, configured to communicate with a second WD, the method comprising: performing a first sidelink, SL, transmission indicating to the second WD a reservation of radio resources, the reservation of radio resources enabling the second WD to determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback; and performing a second transmission to the second WD during a time related to the reserved radio resources.

Example B2. The method of Example Bl, wherein the second transmission is performed during a shared channel occupancy time, COT, shared by the first WD and second WD.

Example B3. The method of any of Example Bl and B2, wherein the first transmission further indicates to the second WD an intent to perform the second transmission on the reserved radio resources.

Example B4. The method of any of Examples Bl -B3, wherein the second transmission is preceded by SL HARQ feedback during the COT. Example B5. The method of any of Examples Bl -B3, wherein the second transmission is preceded by SL HARQ feedback transmitted after a clear channel assessment, CCA.

Example B6. The method of any of Examples Bl -B5, wherein the first transmission indicates a last occasion for which the first WD expects SL HARQ feedback from the second WD.

Example Cl . A first wireless device, WD, configured to communicate with a second wireless device, the first WD configured to, and/or comprising a radio interface and/or processing circuitry configured to: receive from the second WD an indication of a reservation of radio resources; and determine at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback based at least in part on the reserved resources.

Example C2. The first WD of Example Cl, wherein the determined at least one opportunity is determined to occur during a shared channel occupancy time, COT, shared between the first WD and the second WD.

Example C3. The first WD of Example Cl, wherein the determined at least one opportunity is determined to occur after a clear channel assessment, CCA, by the first WD.

Example C4. The first WD of any of Examples C1-C3, wherein the at least one opportunity is determined to occur before the reserved resources.

Example C5. The first WD of Example C4, wherein the at least one opportunity and the reserved resources are adjacent in time.

Example DI . A method implemented in a first wireless device, WD, configured to communicate with a second WD, the method comprising: receiving from the second WD an indication of a reservation of radio resources; and determining at least one opportunity for SL hybrid automatic repeat request, HARQ, feedback based at least in part on the reserved resources.

Example D2. The method of Example DI, wherein the determined at least one opportunity is determined to occur during a shared channel occupancy time, COT, shared between the first WD and the second WD. Example D3. The method of Example DI, wherein the determined at least one opportunity is determined to occur after a clear channel assessment, CCA by the first WD.

Example D4. The method of any of Examples D1-D3, wherein the at least one opportunity is determined to occur before the reserved resources.

Example D5. The method of Example C4, wherein the at least one opportunity and the reserved resources are adjacent in time.

As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and/or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and/or functionality described herein may be performed by, and/or associated to, a corresponding module, which may be implemented in software and/or firmware and/or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.

Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Python, Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.

Abbreviations that may be used in the preceding description include: Abbreviation Explanation

ACK Acknowledgement

CCA Clear channel assessment

COT Channel occupancy time

CW Contention window

D2D Device-to-device communication

FB Feedback

HARQ Hybrid automatic repeat request

LBT Listen before talk

MIB Master information block

NACK Negative acknowledgement

NR New radio

NW Network

PSCCH Physical sidelink control channel

PSFCH Physical sidelink feedback channel

PSSCH Physical sidelink shared channel

PDB Packet delay budget

PRB Physical resource blocks

RB Resource block

RRC Radio Resource Control

SL Sidelink

SCI Sidelink control information

SIB System information block

SL Sidelink

SL-U Sidelink in unlicensed spectrum

TB Transport block

UC Use Case

UE User equipment

V2I Vehicle-to-infrastructure

V2P Vehicle-to-pedestrian V2V Vehicle-to-vehicle

V2X Vehicle-to-anything communication

It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims