Contention window size adjustment for sidelink unlicensed bands

Abstract

Systems, methods, and circuitry are provided for a UE to perform sidelink (SL) communications in unlicensed spectrum to update contention window size (CWS). In one example, a method includes transmitting, during a sidelink (SL) channel occupancy time (COT), one or more physical sidelink shared channel (PSSCH) transmissions to one or more respective receiving (RX) UEs. Each PSSCH includes one or more transport blocks (TBs) and is associated with a channel access priority level (CAPC). The UE updates the CWS for the CAPC based on feedback regarding the reception of the one or more PSSCHs associated with the CAPC, and transmits a subsequent PSSCH associated with the CAPC based on the updated CWS.

Description

[0001] Citation of Related Applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 396,664, filed on August 10, 2022, the contents of which are hereby incorporated by reference in their entirety. Background Art

[0003] Sidelink communications are performed between UEs with limited assistance from the network and form the basis for vehicle-to-everything (V2X) communications systems. Sidelink communications are distinct from downlink communications (network access point (AP) to user equipment (UE)) and uplink communications (UE to AP).

[0004] One limiting factor for wireless innovation is the availability of spectrum. To alleviate this, unlicensed spectrum has been an area of ​​interest to extend the availability of Long Term Evolution (LTE) and New Radio (NR). In this context, recent versions of 3GPP specifications support LTE and NR uplink / downlink operations in unlicensed spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Some examples of circuits, devices and / or methods will be described below by way of example only.In this context, reference will be made to the accompanying drawings.

[0006] Figure 1A , Figure 1B and Figure 1C Various modes of sidelink communication according to various aspects disclosed are schematically illustrated.

[0007] Figure 2 Example sidelink channel occupancy times in accordance with various aspects disclosed are illustrated.

[0008] Figure 3 A series of example side link channel occupancy times in accordance with various aspects disclosed are illustrated.

[0009] Figure 4 is a flow chart illustrating an example method of updating a contention window size during unicast sidelink communications in accordance with various aspects disclosed.

[0010] Figure 5 is a flow chart illustrating an example method of updating a contention window size during unicast sidelink communications in accordance with various aspects disclosed.

[0011] Fig. 6A , Figure 6B , Figure 6C and Figure 6C Various example reference durations in accordance with various aspects disclosed are illustrated.

[0012] Figure 7 is a flow chart illustrating an example method for updating a contention window size during multicast mode 2 sidelink communications in accordance with various aspects disclosed.

[0013] Figure 8 Examples of infrastructure equipment (eg, base stations) in accordance with various aspects disclosed are illustrated.

[0014] Fig. 9 An example of a UE according to various aspects disclosed is illustrated. DETAILED DESCRIPTION

[0015] The present disclosure is described with reference to the accompanying drawings. The accompanying drawings are not drawn to scale, and these drawings are provided only for illustrating the present disclosure. Several aspects of the present disclosure are described below with reference to example applications for illustration. Many specific details, relationships and methods are set forth to provide an understanding of the present disclosure. The present disclosure is not limited by the order of the actions or events illustrated, because some actions can occur in different orders and / or simultaneously with other actions or events. In addition, not all illustrated actions or events are necessary to implement the method according to the selected present disclosure.

[0016] Development of sidelink (SL) communications, distinct from uplink (UL) or downlink (DL) communications, continues, with many additional features provided in Release 17 of the 3GPP specification. As currently configured, sidelink communications do not include several features supported in UL / DL communications. Several of these unsupported features will be outlined here to provide context for some of the proposed solutions.

[0017] Code Block Group (CBG) based Physical Downlink Shared Channel (PDSCH) transmission and Hybrid Automatic Repeat Request (HARQ) divides the transport block (TB) into smaller code blocks, and the smaller code blocks are grouped into code block groups. The receiving device provides separate HARQ feedback for each CBG instead of providing feedback for the entire TB. This allows only those CBGs that are negatively acknowledged (NACKed) to be retransmitted instead of retransmitting the entire TB. The 3GPP specifications for sidelink communications currently do not support CBG based transmission and HARQ.

[0018] Transmission Time Interval (TTI) bundling or slot aggregation is the time the same TB is sent in the PDSCH in a "burst" spanning multiple TTIs. This may be done for redundancy and to provide a higher chance of successful transmission. The 3GPP specifications for sidelink communications do not currently support this type of transmission.

[0019] In NR, PDSCH transmission can start in any symbol of a slot unlike the slots in Long Term Evolution (LTE) where PDSCH is always allocated a full subframe. When PDSCH does not use all symbols in a slot, it is called a partial slot allocation. The 3GPP specifications for sidelink communications do not currently support this type of transmission.

[0020] Figures 1A to 1C is a block diagram of a wireless communication network in which wireless communication devices (e.g., user equipment (UE), or more generally, "devices") communicate using unicast, groupcast, and broadcast sidelinks, respectively. Each UE in the network includes baseband circuitry that includes one or more processors configured to perform various types of sidelink communications. For purposes of this specification, when a "UE" or "device" is described as performing a certain function, it is understood that the processor in the baseband circuitry, in some instances in conjunction with a memory and / or a transceiver, is performing that function. Fig. 9 An example wireless communication device (including baseband circuitry) is illustrated in more detail in FIG.

[0021] Sidelink communication may be performed according to one of two modes. In mode 1, the network controls resource allocation and receives feedback for transport blocks (TBs) sent between UEs (e.g., via signals sent or received by a base station or network node 100). In one example, the resources used for sidelink transmission are signaled to the transmitting UE as a transmission grant. When the network determines that the TB is not decoded by the receiving (RX) UE, the network sends a retransmission grant to the transmitting (TX) UE indicating the resources to be used for retransmitting the TB. Therefore, in general, a transmission grant for the next set of TBs may imply a positive feedback result for the previously transmitted TBs, while a retransmission grant for the previously transmitted TBs may imply a negative feedback result for the previously transmitted TBs.

[0022] In Mode 2, the network pre-configures a sidelink resource pool from which the TX UE selects resources to send a TB to another UE without specific allocation from the network. In Mode 2, feedback for the TB is provided to the TX UE via a hybrid automatic repeat request (HARQ) acknowledgement / negative acknowledgement (ACK / NACK) signal sent on a physical sidelink feedback channel (PSFCH).

[0023] Depending on whether the TX device is to perform unicast, multicast, or broadcast transmission of data, the TX device determines (e.g., via higher layer signaling) a layer 1 destination identifier (L1 destination ID) that uniquely identifies one or more channels between the TX device 101 and a specific RX device (unicast identifier), a group of RX devices (multicast identifier), or all RX devices (broadcast identifier) ​​in the wireless communication network. In one example, the channel identified by the L1 destination ID is a physical sidelink control channel (PSCCH).

[0024] exist Figure 1A In the unicast example of , the TX device 101 attempts to send data (e.g., one or more TBs) to the RX device 102 and not send it to other devices. In mode 1, the TX device 101 requests resources from the network for sending data and receives a send authorization in response. In mode 2, the TX device selects resources from a pre-allocated sidelink resource pool. The TX device 101 initiates communication with the RX device 102 using a unicast L1 destination ID for the device 102. The TX device 101 sends sidelink control information (SCI) using PSCCH resources associated with the L1 destination ID for the RX device 102. The SCI indicates how the RX device 102 subsequently receives a transport block (TB) of data from the TX device 101. For example, the SCI includes a unicast L1 destination ID for the RX device 102 and identifies the frequency and time resources of the physical sidelink shared channel (PSSCH) that is specified to be used to transmit (and in some cases retransmit) the TB.

[0025] The SCI may also indicate whether the RX device provides feedback, such as an acknowledgement / negative acknowledgement (ACK / NACK) indication to confirm the receipt of the TB or to communicate that the TB was not received. To this end, the SCI may include a hybrid automatic repeat request (HARQ) process identifier that uniquely identifies the TB for the RX device to use to provide feedback. In mode 1, the RX device will (e.g., via the base station 100) send feedback to the network. When the network receives a NACK (or does not receive feedback), the network will send a retransmission grant to the TX device 101 to retransmit the TB that was not decoded by the RX device 102. In mode 2, the RX device 102 will send feedback to the TX device 101.

[0026] exist Figure 1A , the TX device 101 is performing unicast sidelink communications with the additional RX device 109. As described above, the unicast communications between different pairs of devices are managed individually by the TX device 101 for each RX device.

[0027] The TX device can communicate with the RX device using multiple data radio bearers (DRBs) associated with different channel access priority levels. The channel access priority levels are subject to different quality of service (QoS) requirements. For example, the TX device can use a DRB with a channel access priority level (CAPC) 1 to send data-encoded voice or V2X messages, while data-encoded buffered streaming video or TCP-based communications such as email or chat can be carried by a DRB with a lower priority access (CAPC 3).

[0028] Figure 1B A multicast sidelink communication is illustrated in which a TX device 101 attempts to send data to a group G that includes several devices 102, 103, 104, and 105 (although there are only four devices in the illustrated group, there may be a different number of devices in the group). The groupcast L1 destination ID identifies the PSCCH channel for SCI monitored by the devices in group G. To enable multicast communication, the TX device 101 determines the L1 destination ID for group G. The TX device 101 sends the SCI using the PSCCH resources associated with the L1 destination ID for group G. The SCI indicates how the devices in group G subsequently receive TBs from device 101. For example, the SCI includes the multicast L1 destination ID for group G and identifies the frequency and time resources of the physical sidelink shared channel (PSSCH) that will be used to transmit and retransmit (in some cases) TBs. As described above, the selection of resources for sidelink communication and the channel used by the RX device for feedback is controlled by whether the sidelink communication is mode 1 or mode 2.

[0029] The SCI may indicate multicast option 1 or 2, which indicates whether and how the RX devices in group G provide feedback. In multicast option 1, when feedback is enabled, the only type of feedback provided by the RX device is NACK, and in some examples, when a particular RX device is out of communication range as specified in the SCI, the RX device does not provide any feedback. In multicast option 2, when feedback is enabled, the RX device provides both ACK / NACK feedback. The SCI may include a hybrid automatic repeat request (HARQ) process identifier that uniquely identifies the TB for the RX device to use to provide feedback.

[0030] Figure 1CBroadcast sidelink communication is illustrated, in which the TX device 101 attempts to send data to all devices in the network or all devices in the network that can receive the sent data. The broadcast L1 destination ID identifies the PSCCH channel for SCI monitored by all devices in the network. In order to enable broadcast communication, the device 101 determines the broadcast L1 destination ID for the network. The TX device 101 uses the PSCCH resources associated with the broadcast L1 destination ID for the network to send SCI. The SCI indicates how the devices in the network subsequently receive data from the device 101. For example, the SCI includes the broadcast L1 destination ID and identifies the frequency and time resources of the physical sidelink shared channel (PSSCH) that will be used to transmit and retransmit (in some cases) TBs. As described above, the selection of resources for sidelink communication is controlled by whether the sidelink communication is mode 1 or mode 2. There is no feedback in broadcast communication.

[0031] Previous 3GPP releases supported UL / DL communications in unlicensed spectrum (NR-U). 3GPP Release 18 will support sidelink communications in unlicensed spectrum. Figure 2 , defines a channel access mechanism for sidelink communications in NR-U. As with UL / DL, devices can compete for access to the unlicensed band by performing a clear channel assessment (CCA) and a listen-before-talk (LBT) process during a contention window (CW) 210. The CW has a length or size (CWS) that varies depending on the sensed channel conditions and other factors. Any device (e.g., TX UE, base station, network node, access point (AP), etc.) that intends to transmit in an unlicensed spectrum first performs a channel sensing operation before initiating any transmission. Once a device has sensed an idle channel (e.g., by sensing less than a threshold amount of energy in the channel during a CW or detecting a specific sequence), the device acquires a SL channel occupancy time (COT) 215, during which the device can send its data payload and receive feedback signals from the receiving UE and / or base station. The maximum SL COT has a predetermined length, which is set by the channel access priority level associated with the particular transmission.

[0032] For example, in Figure 2, once CCA succeeds, during SLCOT 215, the TX UE may send PSSCH 220 including TBs with CAPC 1 to UE A, PSSCH 223 including TBs with CAPC 1 to UE B, and PSSCH 225 including TBs with CAPC 2 to UE A. The TX UE may receive HARQ-ACK / NACK feedback on the PSFCH and / or receive transmit and retransmit grants on the Uu link from the base station at any time (not just during SLCOT 215).

[0033] Depending on the LBT class, additional back-off mechanisms are employed to avoid conflicts when interference occurred during a previous transmission in the unlicensed spectrum. The back-off mechanisms consist of increasing the CWS to the next value when interference is detected, and decreasing or resetting the CWS when no interference is detected. The manner in which the CWS is increased, the conditions under which the CWS can be reset to its minimum value and / or the maximum value of the CWS can be controlled by local adjustments. For example, ETSI EN 301 893 requires an exponential expansion of the CWS during each adjustment (e.g., (((CW+1)×m)–1, where m≥2), which means that the “next value” of the CWS is the result of a prescribed formula unless the calculated value would violate the maximum CWS. In other examples, a range of CWS values ​​can be preconfigured, in which case the next higher value is selected to increase the CWS.

[0034] In both LTE and NR, the CW update procedures are defined separately for UL and DL based on the HARQ design and scheduling differences between UL and DL. In both LTE and NR, the DL / US COT and CWS are managed on a per-CAPC basis.

[0035] A CWS update process should be established for sidelink communications based on the sidelink HARQ design and scheduling.Described herein are systems, methods, and circuits for updating a CWS for sidelink communications in an unlicensed spectrum (SL-U) and / or determining an appropriate reference duration for sensing feedback when determining whether to update the CWS.

[0036] Figure 3A series of SLCOTs 350, 360, 370 obtained by a TX UE are illustrated. Each SLCOT is illustrated as including four full time slots. The length of the SL COT may include any number of partial time slots or full time slots and may vary over time. In the latest SLCOT 370, the TX UE sends PSSCH 320 and PSSCH 323, which may be sent to different RX UEs and / or for different CAPCs. It can be seen that PSSCH 320 starts at the beginning of a full time slot in the SL COT, while PSSCH 323 starts at a partial time slot. Although each SLCOT is illustrated as starting at a time slot boundary, in some examples, the SLCOT may start at a partial time slot.

[0037] Unicast SL CWS update on a per-CAPC basis

[0038] Figure 4 4 is a flow chart outlining an example method 400 for updating a CWS on a per-CAPC basis. The method 400 may be performed by a TX UE for each CAPC with which it is performing unicast SL communications. In this technique, the CWS is updated based on feedback received regarding all TBs with the CAPC, including feedback from any of a plurality of UEs with which the TX UE is performing unicast communications. At 410, the CWS has a current value for the CAPC. The value may have been previously updated using the method 400 or be a default or preconfigured value for the CAPC. At 420, the TX UE determines whether it has received any HARQ feedback (e.g., via the PSFCH). As previously described, depending on the mode of unicast operation, HARQ feedback may not be configured, and instead a transmit / retransmit grant may be received from the base station to control retransmissions of the TB when necessary. If the TX UE has received HARQ feedback, then at 430, the TX UE analyzes the HARQ feedback received for the TB in the most recent SL COT (e.g., Figure 3 HARQ feedback received by the TB sent during the reference duration of the SL COT 370).

[0039] At 440, one or more CWS reset criteria are applied to HARQ feedback for TBs sent during the reference duration. For example, if at least one HARQ-ACK is received for a TB sent for CAPC during the reference duration, the CWS may be reset to a minimum value. If more than a predetermined proportion (X%) of TBs sent for CAPC during the reference duration are HARQ-ACK confirmed, the CWS may be reset to a minimum value. In one example, X is 20%. If more than a predetermined proportion (Y%) of CBGs for TBs sent for CAPC during the reference duration are HARQ-ACK confirmed, the CWS may be reset to a minimum value. In one example, Y is less than X (e.g., 10%). If the CWS reset criteria are not met, the CWS may be increased to its next value.

[0040] Returning to 420, if HARQ feedback has not been received, the method proceeds to 450 and the TX UE determines whether any transmit grant or retransmit grant has been received during a window of predetermined length after the reference duration in the earliest SL COT since the last CWS update. Figure 3 In SLCOTs 350, 360, and 370, the TX UE transmits PSSCH 320 to the first UE. In SLCOT 370, the TX UE also transmits PSSCH 323 to the second UE. Figure 3 , for the illustrated CAPC, SL COT 350 is the earliest SL COT since the most recent CWS update for the CAPC.

[0041] exist Figure 3 In the example Figure 4 The predetermined length T of 450 is applied W The window starts when the reference duration 355 of the earliest SL COT 350 expires. Note that the reference duration 355 may be different from the reference duration 375 of the SL COT 370, as will be described in more detail below. The predetermined length may be preconfigured or determined by the UE based on the characteristics of the SL transmission. In one example, the predetermined length is calculated based on max(TA, TB+1) milliseconds, where TA is a constant, such as 5ms, and TB is the duration of the transmission burst starting from the reference duration in milliseconds.

[0042] At 450, the CWS may be increased to the next value when a retransmission grant is received during the window (meaning that a previously transmitted TB was not decoded), or a Mode 1 transmission grant is not received during the window, or a Mode 2 transmission does not occur during the window. At 450, the CWS may be maintained when a retransmission grant is not received during the window, or a Mode 1 transmission grant is received during the window, or a Mode 2 transmission occurs during the window (meaning that a previously transmitted TB was decoded).

[0043] Unicast SL CWS update per unicast pair per CAPC

[0044] Figure 5 5 is a flowchart outlining an example method 500 for updating a CWS for each unicast pair based on each CAPC. For the purposes of this description, a unicast pair refers to a specific TX UE and RX UE participating in a unicast SL communication. The method 500 may be performed by a TX UE for each RX UE with which it is performing unicast SL communication for a CAPC. In this technique, the CWS for each unicast pair is updated individually based on feedback from the RX UE of the unicast pair regarding TBs with a CAPC. At 510, the CWS has a current value for the unicast pair and the CAPC. The value may have been previously updated using the method 500 or may be a default value or preconfigured value for the CAPC. At 520, the TX UE determines whether it has received any HARQ feedback from the RX UE in the unicast pair (e.g., via the PSFCH). As previously described, depending on the mode of unicast operation, HARQ feedback may not be configured, but a transmit / retransmit grant may be received from the base station to control the retransmission of the TB when necessary. If the TX UE has received HARQ feedback from the RX UE, then at 530, the TX UE analyzes the HARQ feedback for the latest SL COT (eg, Figure 3 HARQ feedback of TB reception sent to the RX UE during a reference duration of the SL COT 370).

[0045] At 540, one or more CWS reset criteria are applied to the HARQ feedback for the TBs sent to the RX UE during the reference duration. For example, if at least one HARQ-ACK is received for the TBs sent to the RX UE for the CAPC during the reference duration, the CWS may be reset to a minimum value. In some instances, a higher threshold number of HARQ-ACKs received (e.g., greater than or equal to two ACKs) may be used as a criterion for a CWS reset. If more than a predetermined proportion (Y%) of CBGs for the TBs sent to the RX UE for the CAPC during the reference duration are HARQ-ACK acknowledged, the CWS may be reset to a minimum value. In one example, Y is 10%. If the CWS reset criteria are not met, the CWS for the CAPC / unicast pair may be increased to its next value.

[0046] Returning to 520, if HARQ feedback has not been received from the RX UE, the method proceeds to 550, and the TX UE determines whether any transmission grant or retransmission grant has been received with respect to the RX UE during a window of a predetermined length after the reference duration in the earliest SL COT since the last CWS update. Figure 3 , assuming that a CWS update occurs with respect to the first RX UE, in SLCOTs 350, 360, and 370, the TX UE sends PSSCH 320 to the first UE. In SLCOT 370, the TX UE also sends PSSCH 323 to the second RX UE. Figure 3 , with respect to the first RX UE and the illustrated CAPC, SL COT 350 is the earliest SL COT since the most recent CWS update for the CAPC. The CWS for the second RX UE is managed separately.

[0047] exist Figure 3 In the example Figure 5 The predetermined length T of 550 is applied W The window starts when the reference duration 355 of the earliest SL COT 350 expires. Note that the reference duration 355 may be different from the reference duration 375 of the SL COT 370, as will be described in more detail below. The predetermined length may be preconfigured or determined by the UE based on the characteristics of the SL transmission. In one example, the predetermined length is calculated based on max(TA, TB+1) milliseconds, where TA is a constant, such as 5ms, and TB is the duration of the transmission burst starting from the reference duration in milliseconds.

[0048] At 550, when a retransmission grant is received during the window or a transmission grant is not received during the window for a TB for the RX UE (meaning that a previously transmitted TB was not decoded), the CWS may be increased to a next value. At 550, when a retransmission grant is not received during the window or a transmission grant is received during the window for a TB for the RX UE (meaning that a previously transmitted TB to the RX UE was decoded), the CWS may be maintained.

[0049] Reference duration

[0050] As already discussed, when HARQ feedback is configured, the CWS is updated based on the HARQ feedback received for those TBs transmitted in the PSSCH during the reference duration of the latest SLT COT. The reference duration for a particular SL COT may be determined based on the type of SL transmission that occurred during the SL COT (for a CAPC or CAPC / UE pair). FIG. 6A to FIG. 6D Different SL transmission schemes and example reference durations within the latest SL COT are illustrated. PSSCH is illustrated as FIG. 6A to FIG. 6D The shaded area in .

[0051] exist Fig. 6A In one example, each SL transmission is configured to occur in a single time slot and start at a time slot boundary of the SL COT 610. In this case, the reference duration 615 is the first time slot of the latest SL COT 610. Figure 6B In the embodiment, each SL transmission is configured to be repeated k times (e.g., k=3 is illustrated) in k time slots (e.g., PSSCH bursts), and each transmission starts at a time slot boundary of the SL COT 620. In this case, the reference duration 625 is the consecutive x time slots of the latest SL COT 620. Alternatively, the reference duration (reference duration 627) may start at the starting point of the latest SLCOT 620 and end at the end of the PSSCH burst.

[0052] exist Figure 6C In , each SL transmission is configured to occur in a single time slot with multiple starting positions (e.g., partial time slots) enabled. In this case, in one example, the reference duration 635 is from the starting point of the SL COT 630 until the first full time slot of the latest SL COT 630. Fig.6DIn the example, each SL transmission is configured to be repeated k times (for example, k=3 is illustrated) in k time slots with multiple starting positions (for example, partial time slots) enabled. In this case, the reference duration may be the consecutive x time slots (reference duration 645) after the starting point of the latest SL COT 640. Alternatively, the reference duration (reference duration 655) may start at the starting point of the latest SL COT 640 and end at the end of the PSSCH burst.

[0053] Where partial slots are enabled and the beginning partial slot includes a PSSCH associated with a first CAPC and the second full slot includes a PSSCH associated with a different CAPC, the CWS for the CAPC for CCA is maintained regardless of whether the PSSCH associated with the CAPC for CCA is in the beginning partial slot or in the second full slot. The CWS for the CAPC for CCA may be updated based on subsequent feedback for the PSSCH sent in a later SL COT.

[0054] Multicast Mode 1CWS Update

[0055] In groupcast mode 1, the RX UE is configured to provide HARQ-NACK feedback without providing HARQ-ACK feedback. HARQ-NACKs from the RX UEs in the group are communicated on the shared PFSCH resources. In groupcast mode 1, the CWS may not be adjusted but may be set to a fixed size. The size may be the preconfigured minimum CWS for the CAPC or some other relevant value. For example, the CWS for transmissions associated with a particular CAPC may be fixed at the average of the preconfigured minimum CWS and the preconfigured maximum CWS, or at the middle of multiple CWS values ​​preconfigured for the CAPC.

[0056] In another example, in multicast mode 1, in response to receiving HARQ-NACK feedback for one or more TBs sent to the group during the reference duration, the CWS may be increased to the next value. The CWS may be increased for each SL COT in which a HARQ-NACK is received until a preconfigured maximum CWS is reached. When the CWS reaches the maximum value, the CWS may be reset to the preconfigured minimum CWS value immediately, or after a defined period of time or a defined number of subsequent SL COTs.

[0057] Multicast Mode 2CWS Update

[0058] In multicast mode 2, each RX UE uses its own PSFCH resource to provide HARQ ACK / NACK feedback. Figure 77 is a flow chart outlining an example method 700 for updating a CWS on a per-CAPC basis when performing multicast mode 2 communications. The method 700 may be performed by a TX UE for each CAPC for which it is performing multicast mode 2 SL communications. In the technique, the CWS is updated based on feedback received regarding all TBs with the CAPC, including feedback from any RX UE in the group. At 710, the CWS has a current value for the CAPC. The value may have been previously updated using the method 700 or be a default or preconfigured value for the CAPC. At 720, the TX UE determines whether it has received any HARQ feedback (e.g., via a dedicated PSFCH). As previously described, depending on the mode of unicast operation, HARQ feedback may not be configured, but instead a transmit / retransmit grant may be received from the base station to control retransmission of the TB when necessary. If the TX UE has received HARQ feedback, then at 730, the TX UE analyzes the HARQ feedback for the TB received in the latest SL COT (e.g., Figure 3 HARQ feedback received by the TB sent during the reference duration of the SL COT 370).

[0059] At 740, one or more CWS reset criteria are applied to HARQ feedback for TBs sent during the reference duration. For example, if at least one HARQ-ACK is received for a TB sent for a CAPC during the reference duration, the CWS may be reset to a minimum value. In some instances, a higher threshold number of HARQ-ACKs received (e.g., greater than or equal to two ACKs) may be used as a criterion for a CWS reset. If more than a predetermined proportion (X%) of TBs sent for a CAPC during the reference duration are HARQ-ACK confirmed, the CWS may be reset to a minimum value. In one example, X is 20%. If more than a predetermined proportion (Y%) of CBGs for TBs sent for a CAPC during the reference duration are HARQ-ACK confirmed, the CWS may be reset to a minimum value. In one example, Y is less than X (e.g., 10%). If the CWS reset criteria are not met, the CWS may be increased to its next value.

[0060] Returning to 720, if HARQ feedback has not been received, the method proceeds to 750 and the TX UE determines whether any transmit grant or retransmit grant has been received during a window of predetermined length after the reference duration in the earliest SL COT since the last CWS update. Figure 3 , it is assumed that in SLCOTs 350, 360, and 370, the TX UE sends PSSCH 320 to the first group of RX UEs. In SLCOT 370, the TX UE also sends PSSCH 323 to the unicast UEs. Figure 3, with respect to groups and CAPCs, SL COT 350 is the earliest SL COT since the most recent CWS update for CAPCs.

[0061] exist Figure 3 In the example Figure 7 The predetermined length T of 750 is applied W The window starts when the reference duration 355 of the earliest SL COT 350 expires. The predetermined length may be preconfigured or determined by the UE based on the characteristics of the SL transmission. In one example, the predetermined length is calculated according to max(TA, TB+1) milliseconds, where TA is a constant, such as 5ms, and TB is the duration of the transmission burst starting from the reference duration in milliseconds.

[0062] At 750, when a retransmission grant is received during the window (meaning that a previously transmitted TB was not decoded), or a Mode 1 transmission grant is not received during the window, or a Mode 2 transmission does not occur during the window, the CWS may be increased to the next value. At 750, when a retransmission grant is not received during the window, or a Mode 1 transmission grant is received during the window, or a Mode 2 transmission occurs during the window (meaning that a previously transmitted TB was decoded), the CWS may be maintained.

[0063] CWS Update for Broadcast SL

[0064] There is no feedback mechanism for broadcast SL communication, so the CWS for the CAPC may not be determined based on feedback for TBs sent via broadcast. In one example, when the TX UE is also performing unicast or multicast SL communication, the TX UE may use the same CWS as the CAPC currently used for unicast or multicast communication. In another example, the CWS is fixed at a preconfigured minimum CWS or a preconfigured minimum CWS for the CAPC. Alternatively, the CWS may be fixed at a preconfigured broadcast CWS, which may be configured on a per-CAPC basis and may be longer than the minimum CWS value configured for unicast or multicast. In yet another example, the TX UE may randomly select a CWS before each CCA process, or periodically select a CWS before two or more CCA processes.

[0065] Several flow charts outlining example methods have been provided. In this specification and the appended claims, the use of the term "determine" with reference to some entity (e.g., parameter, variable, etc.) when describing method steps or functions is to be interpreted broadly. For example, "determine" is interpreted to cover communications such as receiving and parsing an encoded entity or value of an entity. "Determine" should be interpreted to cover accessing and reading a memory (e.g., a lookup table, register, device memory, remote memory, etc.) storing an entity or value for an entity. "Determine" should be interpreted to cover calculating or deriving an entity or value of an entity based on other quantities or entities. "Determine" should be interpreted to cover any way of inferring or identifying an entity or value of an entity.

[0066] As used herein, the term identify, when used with reference to an entity or a value of an entity, is to be broadly interpreted to encompass any manner of determining an entity or a value of an entity. For example, the term identify is to be interpreted to encompass communications such as receiving and parsing an encoded entity or a value of an entity. The term identify should be interpreted to encompass accessing and reading a memory storing an entity or a value for an entity (e.g., a device queue, a lookup table, a register, a device memory, a remote memory, etc.).

[0067] As used herein, the term "encoding" when used with reference to some entity or value of an entity is to be broadly interpreted to encompass any manner or technique for generating a data sequence or signal that communicates the entity to another component.

[0068] As used herein, the term "select" when used with reference to an entity or value of an entity is to be interpreted broadly to encompass any manner of determining an entity or value of an entity from a plurality or a series of possible choices. For example, the term "select" is to be interpreted as encompassing accessing and reading a memory (e.g., a lookup table, register, device memory, remote memory, etc.) storing an entity or value for an entity and returning an entity or entity value from those stored. The term "select" is to be interpreted as applying one or more constraints or rules to a set of input parameters to determine an appropriate entity or entity value. The term "select" is to be interpreted broadly to encompass any manner of selecting an entity based on one or more parameters or conditions.

[0069] Figure 8 An example of infrastructure equipment 800 according to various aspects is illustrated. The infrastructure equipment 800 (or "system 800") can be implemented as a base station, a radio head, a RAN node (such as Figures 1A to 1C BS100) and / or any other elements / devices discussed herein. System 800 may support Figures 1A to 1C The described sidelink communications, such as, for example, conveying an indication of an allocated sidelink resource pool to the UE (Mode 2) or sending a transmit grant or a retransmit grant (Mode 1).

[0070] System 800 includes application circuit 805, baseband circuit 810, one or more radio front end modules (RFEM) 815, memory circuit 820, power management integrated circuit (PMIC) 825, power tee circuit 830, network controller circuit 835, network interface connector 840, satellite positioning circuit 845 and user interface circuit 850. In some aspects, device 800 may include additional elements such as, for example, memory / storage, display, camera, sensor or input / output (I / O) interface. In other aspects, the components described below may be included in more than one device. For example, the circuit may be included separately in more than one device for CRAN, vBBU or other similar implementations.

[0071] The application circuit 805 may include circuits such as, but not limited to, one or more processors (or processor cores), cache memory, and one or more of the following: a low dropout regulator (LDO), an interrupt controller, a serial interface such as SPI, I2C or a general programmable serial interface module, a real-time clock (RTC), a timer-counter including an interval timer and a watchdog timer, a general input / output (I / O or IO), a memory card controller such as a secure digital (SD) multimedia card (MMC) or similar product, a universal serial bus (USB) interface, a mobile industry processor interface (MIPI) interface, and a joint test access group (JTAG) test access port. The processor (or core) of the application circuit 805 may be coupled to or may include a memory / storage element, and may be configured to execute instructions stored in the memory / storage element to enable various applications or operating systems to run on the system 800. In some implementations, the memory / storage element can be an on-chip memory circuit that can include any suitable volatile and / or non-volatile memory, such as DRAM, SRAM, EPROM, EEPROM, flash memory, solid-state memory, and / or any other type of memory device technology, such as those discussed herein.

[0072] The processor of the application circuit 805 may include, for example, one or more processor cores (CPUs), one or more application processors, one or more graphics processing units (GPUs), one or more reduced instruction set computing (RISC) processors, one or more Acorn RISC Machine (ARM) processors, one or more complex instruction set computing (CISC) processors, one or more digital signal processors (DSPs), one or more FPGAs, one or more PLDs, one or more ASICs, one or more microprocessors or controllers, or any suitable combination thereof. In some aspects, the application circuit 805 may include or may be a dedicated processor / controller for operating in accordance with various aspects of the present invention. As an example, the processor of the application circuit 805 may include one or more processor, Processor: Advanced Micro Devices (AMD) Processor, Accelerated Processing Unit (APU) or processors; ARM-based processors licensed by ARM Holdings, Ltd., such as the ARM Cortex-A series processors provided by Cavium(TM), Inc. and MIPS-based designs from MIPS Technologies, Inc., such as the MIPS Warrior P-class processor; etc. In some aspects, system 800 may not utilize application circuit 805, and instead may include a dedicated processor / controller to process IP data received, for example, from an EPC or 5GC.

[0073] The user interface circuit 850 may include one or more user interfaces designed to enable a user to interact with the system 800 or a peripheral component interface designed to enable a peripheral component to interact with the system 800. The user interface may include, but is not limited to, one or more physical or virtual buttons (e.g., a reset button), one or more indicators (e.g., light emitting diodes (LEDs)), a physical keyboard or keypad, a mouse, a touch pad, a touch screen, a speaker or other audio emitting device, a microphone, a printer, a scanner, a headset, a display screen or display device, etc. The peripheral component interface may include, but is not limited to, a non-volatile memory port, a universal serial bus (USB) port, an audio jack, a power interface, etc.

[0074] Figure 8The components shown can communicate with each other using interface circuits that can include any number of bus and / or interconnect (IX) technologies, such as industry standard architecture (ISA), extended ISA (EISA), peripheral component interconnect (PCI), peripheral component interconnect extended (PCIx), PCI express (PCIe), or any number of other technologies. The bus / IX can be a proprietary bus, for example, used in a SoC-based system. Other bus / IX systems can be included, such as an I2C interface, an SPI interface, a point-to-point interface, and a power bus, etc.

[0075] Fig. 9 An example of a UE platform 900 (or "device 900") according to various aspects is illustrated. In various aspects, the UE platform 900 may be suitable for use as Figures 1A to 1C UE 101-109 and / or any other element / device discussed herein. Platform 900 may include any combination of components shown in the example. The components of platform 900 may be implemented as integrated circuits (ICs), parts of ICs, discrete electronic devices, or other modules, logic, hardware, software, firmware, or combinations thereof adapted in computer platform 900, or as components otherwise incorporated within a chassis of a larger system. Fig. 9 The block diagram is intended to show a high-level view of the components of computer platform 900. However, some of the components shown may be omitted, additional components may be present, and different arrangements of the components shown may occur in other implementations.

[0076] The application circuit 905 includes circuits such as, but not limited to, one or more processors (or processor cores), cache memory, and one or more of an LDO, an interrupt controller, a serial interface (such as SPI), I2C or a general programmable serial interface module, an RTC, a timer-counter (including an interval timer and a watchdog timer), a general I / O, a memory card controller (such as an SDMMC or similar controller), a USB interface, a MIPI interface, and a JTAG test access port. The processor (or core) of the application circuit 905 may be coupled to or may include a memory / storage element and may be configured to execute instructions stored in the memory / storage element to enable various applications or operating systems to run on the system 900. In some specific implementations, the memory / storage element may be an on-chip memory circuit that may include any suitable volatile and / or non-volatile memory, such as DRAM, SRAM, EPROM, EEPROM, flash memory, solid-state memory, and / or any other type of memory device technology, such as those discussed herein.

[0077] For example, the processor of application circuit 905 may include a general purpose or special purpose processor, such as a processor available from Inc., Cupertino, CA's A-series processor (e.g., A13 Bionic) or any other such processor. The processor of the application circuit 905 may also be one or more of the following: Advanced Micro Devices (AMD) Processor or Accelerated Processing Unit (APU); from Inc.'s core processors, Snapdragon by Technologies, Inc. TM Processor, Texas Instruments, Open Multimedia ApplicationsPlatform(OMAP) TM processors; MIPS-based designs from MIPS Technologies, Inc., such as the MIPS Warrior M-class, Warrior I-class, and Warrior P-class processors; ARM-based designs licensed from ARM Holdings, Ltd., such as the ARM Cortex-A, Cortex-R, and Cortex-M series processors; etc. In some implementations, the application circuit 905 can be part of a system on a chip (SoC), in which the application circuit 905 and other components are formed as a single integrated circuit or a single package.

[0078] The baseband circuit or processor 910 may be implemented as, for example, a solder-in substrate including one or more integrated circuits, a single packaged integrated circuit soldered to a main circuit board, or a multi-chip module including two or more integrated circuits. The baseband circuit or processor 910 may include hardware or stored executable instructions that enable the UE to send data to one or more other UEs using a SL communication protocol (e.g., unicast, multicast, broadcast), receive a transmission grant and a retransmission grant (mode 1) from a base station, receive HARQ-ACK or HARQ-NACK feedback, and / or adjust the CWS for operation in an unlicensed spectrum based on feedback / transmission grant, retransmission grant.

[0079] The platform 900 may further include an interface circuit (not shown) for connecting external devices to the platform 900. External devices connected to the platform 900 via the interface circuit include a sensor circuit 921 and an electromechanical component (EMC) 922, and a removable memory device coupled to a removable memory circuit 923.

[0080] The battery 930 can power the platform 900, but in some examples, the platform 900 can be mounted in a fixed location and can have a power source coupled to a power grid. The battery 930 can be a lithium-ion battery, a metal-air battery such as a zinc-air battery, an aluminum-air battery, a lithium-air battery, etc. In some implementations, such as in V2X applications, the battery 930 can be a typical lead-acid car battery.

[0081] Embodiment 1 is a device for a user equipment (UE) to operate in an unlicensed spectrum, the device comprising one or more processors, the one or more processors being configured to cause the UE to: during a sidelink (SL) channel occupancy time (COT), send one or more physical sidelink shared channel (PSSCH) transmissions to one or more corresponding receiving (RX) UEs according to a SL communication protocol, wherein each PSSCH comprises one or more transport blocks (TBs), wherein each PSSCH transmission is associated with a channel access priority class (CAPC); update a contention window size for the CAPC based on feedback regarding the one or more PSSCH receptions associated with the CAPC; and send subsequent PSSCHs associated with the CAPC based on the updated CWS.

[0082] Embodiment 2 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: update the CWS in response to receiving a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK) feedback regarding a TB sent with the CAPC during a reference duration within the SL COT.

[0083] Embodiment 3 includes the subject matter of embodiment 2, including or omitting optional elements, wherein the one or more processors are configured to: when no HARQ-ACK or HARQ-NACK feedback is received, update the CWS based on whether a mode 1 transmission grant or a retransmission grant is received during a time window of a predetermined length after the reference duration of the earliest SL COT since the last CWS update or whether a mode 2 transmission occurs for a TB associated with the CAPC.

[0084] Embodiment 4 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least one of the TBs sent for the CAPC during the reference duration within the SL COT, and increase the CWS to a next level in response to receiving at least one HARQ-NACK and no HARQ-ACK for the TBs sent for the CAPC during the reference duration within the SL COT.

[0085] Embodiment 5 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving HARQ-ACKs for at least a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT.

[0086] Embodiment 6 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

[0087] Embodiment 7 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to receiving a HARQ-ACK for less than a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT.

[0088] Embodiment 8 includes the subject matter of embodiment 7, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0089] Embodiment 9 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to not receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

[0090] Embodiment 10 includes the subject matter of embodiment 9, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0091] Embodiment 11 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent for the CAPC during the reference duration within the SLCOT; and not receiving a mode 1 transmission authorization, or receiving a retransmission authorization, or no mode 2 transmission occurs for the TB with the CAPC within a time window of a predetermined length after expiration of the reference duration of the earliest SLCOT since the last update of the CWS.

[0092] Embodiment 12 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0093] Embodiment 13 comprises the subject matter of embodiment 11, including or omitting optional elements, wherein the predetermined length is determined based on max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0094] Embodiment 14 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: maintain the CWS at a current value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent for the CAPC during the reference duration within the SLCOT; and not receiving a retransmission authorization, or receiving a mode 1 transmission authorization, or causing a mode 2 transmission for the TB with the CAPC during a time window of a predetermined length after expiration of the reference duration of the earliest SLCOT since the last update of the CWS.

[0095] Embodiment 15 comprises the subject matter of embodiment 14, including or omitting optional elements, wherein the predetermined length is determined based on max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0096] Embodiment 16 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: adjust the CWS for CAPC on a per receive (RX) UE basis such that the CWS for CAPC and the RX UE are updated based on feedback regarding reception of TBs sent to the RX UE during the reference duration.

[0097] Embodiment 17 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: for each CAPC, increase a contention window size (CWS) to a next value in response to receiving a HARQ-NACK for a TB sent to the RX UE group for the CAPC during a reference duration.

[0098] Embodiment 18 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to reset the CWS to a minimum CWS value when the increased CWS value exceeds a preconfigured maximum CWS value.

[0099] Embodiment 19 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum CWS value after the UE has sent a PSSCH according to the maximum CWS for a preconfigured period of time.

[0100] Embodiment 20 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the reference duration includes a duration of a first time slot of the SL COT.

[0101] Embodiment 21 includes the subject matter of embodiment 1, including or omitting optional elements, wherein when the UE sends x PSSCHs in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

[0102] Embodiment 22 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the reference time duration starts at a partial time slot starting point of the SL COT and ends at a first full time slot after the partial time slot starting point of the SL COT.

[0103] Embodiment 23 includes the subject matter of embodiment 1, including or omitting optional elements, wherein the reference time duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH in the SL COT.

[0104] Embodiment 24 includes the subject matter of embodiment 1, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs for the CAPC in the SL COT, the reference duration starts at the partial time slot starting point of the SL COT and ends k consecutive full time slots after the partial time slot starting point of the SL COT.

[0105] Embodiment 25 includes the subject matter of embodiment 1, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs for the CAPC in the SL COT, the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH burst in the SL COT.

[0106] Embodiment 26 is a device for a user equipment (UE) to perform sidelink communication in an unlicensed spectrum, the device comprising one or more processors, wherein the one or more processors are configured to cause the UE to: perform a clear channel estimation (CCA) during a contention window for a channel access priority level (CPAC) having a fixed contention window size (CWS) to obtain a sidelink occupancy time (SL COT); and during the SL COT, send a signal encoding corresponding one or more transport blocks (TBs) in corresponding one or more physical sidelink shared channels (PSSCHs) to a group of one or more RX UEs, wherein each PSSCH is associated with the CAPC.

[0107] Embodiment 27 comprises the subject matter of embodiment 26, including or omitting optional elements, wherein the CWS comprises a preconfigured minimum CWS value.

[0108] Embodiment 28 comprises the subject matter of embodiment 26, including or omitting optional elements, wherein the CWS comprises a preconfigured maximum CWS value.

[0109] Embodiment 29 includes the subject matter of Embodiment 26, including or omitting optional elements, wherein the CWS includes a midpoint value of a preconfigured minimum CWS value and a preconfigured maximum CWS value.

[0110] Embodiment 30 includes the subject matter of Embodiment 26, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS value for the CAPC.

[0111] Embodiment 31 includes the subject matter of Embodiment 26, including or omitting optional elements, wherein the CWS includes a preconfigured maximum CWS value for the CAPC.

[0112] Embodiment 32 includes the subject matter of Embodiment 26, including or omitting optional elements, wherein the CWS comprises a midpoint value of a preconfigured minimum CWS value and a preconfigured maximum CWS value for the CAPC.

[0113] Embodiment 33 includes the subject matter of Embodiment 26, including or omitting optional elements, wherein the one or more processors are configured to randomly select a value for the CWS.

[0114] Embodiment 34 includes the subject matter of Embodiment 26, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS for broadcast communications.

[0115] Embodiment 27 includes the subject matter of embodiment 26, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS for broadcast communications for the CAPC.

[0116] Embodiment 36 is an apparatus for a user equipment (UE) operating in an unlicensed spectrum, the apparatus comprising one or more processors configured to cause the UE to: transmit one or more physical sidelink shared channel (PSSCH) transmissions to one or more corresponding receiving (RX) UEs according to a SL unicast communication protocol during a sidelink (SL) channel occupancy time (COT), wherein each PSSCH comprises one or more transport blocks (TBs), wherein each PSSCH transmission is associated with a channel access priority class (CAPC). The one or more processors are configured to: for each CAPC, in response to receiving a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK) feedback, update a contention window size (CWS) for the CAPC based on feedback about TB reception for the CAPC transmission during a reference duration within the SL COT. The one or more processors are configured to: in response to not receiving HARQ-ACK or HARQ-NACK feedback, update the CWS for the CAPC based on whether a mode 1 transmission grant or a retransmission grant is received during a time window of a predetermined length after the reference duration of the earliest SL COT since the last CWS update or whether a mode 2 transmission occurs for a TB with the CAPC; and based on the updated CWS, send a subsequent PSSCH for the CAPC according to the unicast communication protocol.

[0117] Embodiment 37 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least one of the TBs sent for the CAPC during the reference duration within the SL COT, and increase the CWS to a next level in response to receiving at least one HARQ-NACK and no HARQ-ACK for the TBs sent for the CAPC during the reference duration within the SL COT.

[0118] Embodiment 38 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving HARQ-ACKs for at least a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT.

[0119] Embodiment 39 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

[0120] Embodiment 40 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to receiving a HARQ-ACK for less than a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT.

[0121] Embodiment 41 includes the subject matter of Embodiment 40, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0122] Embodiment 42 includes the subject matter of embodiment 40, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to not receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

[0123] Embodiment 43 includes the subject matter of Embodiment 42, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0124] Embodiment 44 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; and not receiving a mode 1 transmission authorization, or receiving a retransmission authorization, or no mode 2 transmission occurs for the TB with the CAPC within a time window of a predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS.

[0125] Embodiment 45 includes the subject matter of Embodiment 44, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0126] Embodiment 46 includes the subject matter of embodiment 44, including or omitting optional elements, wherein the predetermined length is determined based on max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0127] Embodiment 47 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the one or more processors are configured to: maintain the CWS at a current value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; and not receiving a retransmission authorization, or receiving a mode 1 transmission authorization, or causing a mode 2 transmission for the TB with the CAPC during a time window of a predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS.

[0128] Embodiment 48 comprises the subject matter of embodiment 47, including or omitting optional elements, wherein the predetermined length is determined based on max(TA,TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0129] Embodiment 49 includes the subject matter of Embodiment 36, including or omitting optional elements, wherein the reference duration includes a duration of a first time slot of the SL COT.

[0130] Embodiment 50 includes the subject matter of embodiment 36, including or omitting optional elements, wherein when the UE transmits x PSSCHs in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

[0131] Embodiment 51 includes the subject matter of Embodiment 36, including or omitting optional elements, wherein the reference duration starts at a partial time slot starting point of the SL COT and ends at a first full time slot after the partial time slot starting point of the SL COT.

[0132] Embodiment 52 includes the subject matter of embodiment 36, including or omitting optional elements, wherein the reference time duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH in the SL COT.

[0133] Embodiment 53 includes the subject matter of embodiment 36, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs for the CAPC in the SL COT, the reference duration starts at the partial time slot starting point of the SL COT and ends k consecutive full time slots after the partial time slot starting point of the SL COT.

[0134] Embodiment 54 includes the subject matter of embodiment 36, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs for the CAPC in the SL COT, the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH burst in the SL COT.

[0135] Embodiment 55 is an apparatus for a user equipment (UE) operating in an unlicensed spectrum, the apparatus comprising one or more processors configured to cause the UE to update a contention window size (CWS). The one or more processors are configured to cause the UE to send a corresponding signal encoding a corresponding transport block (TB) on a physical sidelink shared channel (PSSCH) to one or more corresponding receiving (RX) UEs according to a SL unicast communication protocol during a sidelink (SL) channel occupancy time (COT), wherein each PSSCH is associated with a channel access priority level (CAPC). The one or more processors are configured to: for each RX UE and each CAPC, in response to receiving a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK) feedback from the RX UE, update a contention window size (CWS) for the RX UE and the CAPC based on feedback regarding reception of TBs sent to the RX UE for the CAPC during a reference duration within the SL COT, and in response to not receiving HARQ-ACK or HARQ-NACK feedback from the RX UE, update the CWS for the CAPC / RX UE based on whether a mode 1 transmission grant or a retransmission grant is received during a time window of a predetermined length after the reference duration of the earliest SL COT since the last CWS update for the CAPC / RX UE or whether a mode 2 transmission occurs for a TB with the CAPC and the RX UE; and based on the updated CWS, send a subsequent PSSCH to the RX UE for the CAPC according to the unicast communication protocol.

[0136] Embodiment 56 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least one TB sent by the CAPC to the RXUE during the reference duration.

[0137] Embodiment 57 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of TBs sent by the CAPC to the RX UE.

[0138] Embodiment 58 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to receiving a HARQ-ACK for less than a predetermined proportion of the TBs sent to the RX UE for the CAPC during the reference duration within the SL COT.

[0139] Embodiment 59 includes the subject matter of Embodiment 58, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0140] Embodiment 60 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to not receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent to the RX UE for the CAPC during the reference duration within the SL COT.

[0141] Embodiment 61 includes the subject matter of Embodiment 60, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0142] Embodiment 62 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent to the RX for the CAPC during the reference duration within the SL COT; and not receiving a mode 1 transmission authorization for subsequent TBs for the RX UE, or receiving a retransmission authorization, or no mode 2 transmission occurs for the TB sent to the RX UE for the CAPC within a time window of a predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS.

[0143] Embodiment 63 includes the subject matter of Embodiment 62, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0144] Embodiment 64 includes the subject matter of embodiment 62, including or omitting optional elements, wherein the predetermined length is determined based on max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0145] Embodiment 65 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the one or more processors are configured to: maintain the CWS at a current value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent to the RX UE for the CAPC during the reference duration within the SL COT; and not receiving a retransmission authorization, or receiving a mode 1 transmission authorization, or a mode 2 transmission occurs for the TB for the RX UE and the CAPC during a time window of a predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS.

[0146] Embodiment 66 includes the subject matter of embodiment 65, including or omitting optional elements, wherein the predetermined length is determined based on max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0147] Embodiment 67 includes the subject matter of Embodiment 55, including or omitting optional elements, wherein the reference duration includes a duration of a first time slot of the SL COT.

[0148] Embodiment 68 includes the subject matter of embodiment 55, including or omitting optional elements, wherein when the UE sends x PSSCHs to the RX UE in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

[0149] Embodiment 69 includes the subject matter of Embodiment 55, including or omitting optional elements, wherein the reference duration starts at a partial time slot starting point of the SL COT and ends at a first full time slot after the partial time slot starting point of the SL COT.

[0150] Embodiment 70 includes the subject matter of embodiment 55, including or omitting optional elements, wherein the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH for the RX UE in the SL COT.

[0151] Embodiment 71 includes the subject matter of embodiment 55, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs to the RX UE for the CAPC in the SL COT, the reference duration starts at the partial time slot starting point of the SL COT and ends k consecutive full time slots after the partial time slot starting point of the SL COT.

[0152] Embodiment 72 includes the subject matter of embodiment 55, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs to the RX UE for the CAPC in the SL COT, the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH burst in the SL COT.

[0153] Embodiment 73 is a device for a user equipment (UE) to perform multicast mode 1 communication in an unlicensed spectrum, the device comprising one or more processors, the one or more processors being configured to enable the UE to: perform a clear channel estimation (CCA) during a contention window for a channel access priority level (CPAC) having a fixed contention window size (CWS) to obtain a side link occupancy time (SL COT); and during the SL COT, send a corresponding signal encoding corresponding one or more transport blocks (TBs) in corresponding one or more physical sidelink shared channels (PSSCHs) to a group of one or more RX UEs according to a multicast mode 1 communication protocol, wherein each PSSCH is associated with the CAPC.

[0154] Embodiment 74 comprises the subject matter of embodiment 73, including or omitting optional elements, wherein the CWS comprises a preconfigured minimum CWS value.

[0155] Embodiment 75 comprises the subject matter of embodiment 73, including or omitting optional elements, wherein the CWS comprises a preconfigured maximum CWS value.

[0156] Embodiment 76 comprises the subject matter of Embodiment 73, including or omitting optional elements, wherein the CWS comprises a midpoint value of a preconfigured minimum CWS value and a preconfigured maximum CWS value.

[0157] Embodiment 77 includes the subject matter of Embodiment 73, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS value for the CAPC.

[0158] Embodiment 78 includes the subject matter of Embodiment 73, including or omitting optional elements, wherein the CWS includes a preconfigured maximum CWS value for the CAPC.

[0159] Embodiment 79 includes the subject matter of Embodiment 73, including or omitting optional elements, wherein the CWS includes a midpoint value of a preconfigured minimum CWS value and a preconfigured maximum CWS value for the CAPC.

[0160] Embodiment 80 is an apparatus for a user equipment (UE) to perform multicast mode 1 communication in an unlicensed spectrum, the apparatus comprising one or more processors configured to cause the UE to: during a side link occupancy time (SL COT), send a signal encoding one or more transport blocks (TBs) in one or more physical sidelink shared channels (PSSCHs) to a group of one or more corresponding RX UEs according to a multicast mode 1 communication protocol, wherein each PSSCH is associated with a channel access priority class (CAPC); and for each CAPC, increase a contention window size (CWS) to a next value in response to receiving a HARQ-NACK for a TB sent to the group of RX UEs for the CAPC during a reference duration.

[0161] Embodiment 81 comprises the subject matter of embodiment 80, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum CWS value when the increased CWS value exceeds a preconfigured maximum CWS value.

[0162] Embodiment 82 includes the subject matter of embodiment 80, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum CWS value after the UE has sent a PSSCH according to a maximum CWS for a preconfigured time period.

[0163] Embodiment 83 includes the subject matter of Embodiment 80, including or omitting optional elements, wherein the reference duration includes a duration of a first time slot of the SL COT.

[0164] Embodiment 84 includes the subject matter of embodiment 80, including or omitting optional elements, wherein when the UE sends x PSSCHs to the RX UE in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

[0165] Embodiment 85 includes the subject matter of Embodiment 80, including or omitting optional elements, wherein the reference duration starts at a partial time slot starting point of the SL COT and ends at a first full time slot after the partial time slot starting point of the SL COT.

[0166] Embodiment 86 includes the subject matter of embodiment 80, including or omitting optional elements, wherein the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH for the RX UE in the SL COT.

[0167] Embodiment 87 includes the subject matter of embodiment 80, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs to the RX UE for the CAPC in the SL COT, the reference duration starts at the partial time slot starting point of the SL COT and ends k consecutive full time slots after the partial time slot starting point of the SL COT.

[0168] Embodiment 88 includes the subject matter of embodiment 80, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs to the RX UE for the CAPC in the SL COT, the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH burst in the SL COT.

[0169] Embodiment 89 is a device for a user equipment (UE) to perform multicast mode 2 communication in an unlicensed spectrum, the device comprising one or more processors, the one or more processors being configured to enable the UE to: during a sidelink (SL) channel occupancy time (COT), send one or more physical sidelink shared channel (PSSCH) transmissions to a group of one or more corresponding receiving (RX) UEs according to a SL multicast mode 2 communication protocol, wherein each PSSCH comprises one or more transport blocks (TBs), wherein each PSSCH transmission is associated with a channel access priority level (CAPC). The one or more processors are configured to: for each CAPC, in response to receiving a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK) feedback, update a contention window size (CWS) for the CAPC based on feedback regarding reception of TBs sent for the CAPC during a reference duration within the SL COT, and in response to not receiving HARQ-ACK or HARQ-NACK feedback, update the CWS for the CAPC based on whether a mode 1 transmission grant or a retransmission grant is received during a time window of a predetermined length after the reference duration of the earliest SL COT since the last CWS update or whether a mode 2 transmission occurs for a TB with the CAPC; and based on the updated CWS, send a subsequent PSSCH for the CAPC according to the multicast mode 2 communication protocol.

[0170] Embodiment 90 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least one of the TBs sent for the CAPC during the reference duration within the SL COT, and increase the CWS to a next level in response to receiving at least one HARQ-NACK and no HARQ-ACK for the TBs sent for the CAPC during the reference duration within the SL COT.

[0171] Embodiment 91 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving HARQ-ACKs for at least a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT.

[0172] Embodiment 92 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

[0173] Embodiment 93 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to receiving a HARQ-ACK for less than a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT.

[0174] Embodiment 94 includes the subject matter of Embodiment 94, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS according to (2*CWS+1).

[0175] Embodiment 95 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to not receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

[0176] Embodiment 96 includes the subject matter of Embodiment 95, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0177] Embodiment 97 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: increase the CWS to a next value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; and not receiving a mode 1 transmission authorization, or receiving a retransmission authorization, or no mode 2 transmission occurs for the TB with the CAPC within a time window of a predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS.

[0178] Embodiment 98 includes the subject matter of Embodiment 97, including or omitting optional elements, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

[0179] Embodiment 99 comprises the subject matter of embodiment 97, including or omitting optional elements, wherein the predetermined length is determined based on max(TA,TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0180] Embodiment 100 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the one or more processors are configured to: maintain the CWS at a current value in response to: not receiving a HARQ-ACK or HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; and not receiving a retransmission authorization, or receiving a mode 1 transmission authorization, or causing a mode 2 transmission for the TB with the CAPC during a time window of a predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS.

[0181] Embodiment 101 comprises the subject matter of embodiment 100, including or omitting optional elements, wherein the predetermined length is determined based on max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

[0182] Embodiment 102 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the reference duration includes a duration of a first time slot of the SL COT.

[0183] Embodiment 103 includes the subject matter of embodiment 89, including or omitting optional elements, wherein when the UE transmits x PSSCHs in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

[0184] Embodiment 104 includes the subject matter of Embodiment 89, including or omitting optional elements, wherein the reference duration starts at a partial time slot starting point of the SL COT and ends at a first full time slot after the partial time slot starting point of the SL COT.

[0185] Embodiment 105 includes the subject matter of embodiment 89, including or omitting optional elements, wherein the reference time duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH in the SL COT.

[0186] Embodiment 106 includes the subject matter of embodiment 89, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs for the CAPC in the SL COT, the reference duration starts at the partial time slot starting point of the SL COT and ends k consecutive full time slots after the partial time slot starting point of the SL COT.

[0187] Embodiment 107 includes the subject matter of embodiment 89, including or omitting optional elements, wherein when the UE sends x multiple PSSCHs for the CAPC in the SL COT, the reference duration starts at a partial time slot start point of the SL COT and ends at a partial time slot end point of the PSSCH burst in the SL COT.

[0188] Embodiment 108 is a device for a user equipment (UE) to perform a broadcast side link (SL) in an unlicensed spectrum, the device comprising one or more processors, the one or more processors being configured to cause the UE to: perform a clear channel assessment (CCA) during a contention window having a contention window size (CWS) to obtain a SL channel occupancy time (COT); and during the SL channel occupancy time (COT), send a corresponding signal encoding a corresponding transport block (TB) in one or more physical side link shared channels (PSSCHs) to one or more corresponding other UEs according to a broadcast protocol, wherein the one or more PSSCHs are associated with a channel access priority level (CAPC).

[0189] Embodiment 109 includes the subject matter of embodiment 108, including or omitting optional elements, wherein the CWS comprises a CWS for performing unicast or multicast SL communication by the UE for the CAPC.

[0190] Embodiment 110 includes the subject matter of Embodiment 108, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS.

[0191] Embodiment 111 includes the subject matter of embodiment 108, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS for the CAPC.

[0192] Embodiment 112 includes the subject matter of Embodiment 108, including or omitting optional elements, wherein the one or more processors are configured to randomly select a value for the CWS.

[0193] Embodiment 113 includes the subject matter of Embodiment 108, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS for broadcast communications.

[0194] Embodiment 114 includes the subject matter of embodiment 108, including or omitting optional elements, wherein the CWS includes a preconfigured minimum CWS for broadcast communications for the CAPC.

[0195] Embodiment 115 is a method comprising any action or combination of actions as substantially described herein in the detailed description.

[0196] Embodiment 116 is a method as substantially described herein with reference to each or any combination of the figures included herein or with reference to each or any combination of the paragraphs in the detailed description.

[0197] Embodiment 117 is a user equipment configured to perform any action or combination of actions included in the user equipment as substantially described herein in the detailed description.

[0198] Embodiment 118 is a network node configured to perform any action or combination of actions included in the network node as substantially described herein in the detailed description.

[0199] Embodiment 119 is a non-transitory computer-readable medium storing instructions that, when executed, cause performance of any action or combination of actions as substantially described herein in the detailed description.

[0200] Although the method is illustrated above and described as a series of actions or events, it should be understood that the order of such actions or events illustrated should not be interpreted as having a limiting meaning. For example, some actions can occur simultaneously with other actions or events other than those illustrated and / or described herein in different orders. In addition, all the actions shown may not be required to realize one or more aspects or embodiments disclosed herein. In addition, one or more actions in the actions shown herein can be carried out in one or more separate actions and / or stages. In some embodiments, the method shown above can be implemented in a computer-readable medium using instructions stored in a memory. Many other embodiments and variations are possible within the scope of the present disclosure protected by the claims.

[0201] The term "coupled" is used throughout the specification. The term can cover connections, communications, or signal paths that enable a functional relationship consistent with the description of the present disclosure. For example, if device A generates a signal to control device B to perform an action, then in the first example, device A is coupled to device B, or in the second example, if the intermediate component C does not substantially change the functional relationship between device A and device B so that device B is controlled by device A via the control signal generated by the device, then device A is coupled to device B through the intermediate component C.

[0202] It is understood that the use of personally identifiable information should be subject to privacy policies and practices that are generally recognized to meet or exceed industry or government requirements for maintaining user privacy. Specifically, personally identifiable information data should be managed and processed to minimize the risk of unintentional or unauthorized access or use, and the nature of the authorized use should be clearly stated to users.

Claims

1. An apparatus for a user equipment (UE) operating in an unlicensed spectrum, the apparatus comprising one or more processors configured to cause the UE to: transmitting, during a sidelink (SL) channel occupancy time (COT), one or more physical sidelink shared channel (PSSCH) transmissions to one or more corresponding receiving (RX) UEs according to a SL communication protocol, wherein each PSSCH comprises one or more transport blocks (TBs), wherein each PSSCH transmission is associated with a channel access priority level (CAPC); updating a contention window size (CWS) for the CAPC based on feedback regarding reception of the one or more PSSCHs associated with the CAPC; and A subsequent PSSCH associated with the CAPC is sent based on the updated CWS.

2. The apparatus of claim 1 , wherein the one or more processors are configured to update the CWS in response to receiving a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK) feedback regarding a TB sent with the CAPC during a reference duration within the SL COT.

3. The apparatus of claim 2, wherein the one or more processors are configured to, when no HARQ-ACK or HARQ-NACK feedback is received, update the CWS based on whether a Mode 1 transmission grant or a retransmission grant is received during a time window of a predetermined length after the reference duration of the earliest SL COT since the last CWS update or whether a Mode 2 transmission occurs for a TB associated with the CAPC.

4. The apparatus of claim 2, wherein the one or more processors are configured to: reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least one of the TBs sent for the CAPC during the reference duration within the SL COT, and increase the CWS to a next level in response to receiving at least one HARQ-NACK and no HARQ-ACK for the TBs sent for the CAPC during the reference duration within the SL COT.

5. The apparatus of claim 2, wherein the one or more processors are configured to reset the CWS to a minimum value in response to receiving a HARQ-ACK for at least a predetermined proportion of the TBs or at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

6. The apparatus of claim 2, wherein the one or more processors are configured to, in response to receiving a HARQ-ACK for less than a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT, or in response to not receiving a HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT, increase the CWS to a next value.

7. The apparatus of claim 2, wherein the one or more processors are configured to: The CWS is increased to a next value in response to: not receiving a HARQ-ACK or a HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; and Within a time window of predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS, no Mode 1 transmission grant is received, or a retransmission grant is received, or no Mode 2 transmission occurs for the TB with the CAPC.

8. The apparatus according to any one of claims 1 to 7, wherein the one or more processors are configured to increase the CWS according to (2*CWS+1).

9. The apparatus of claim 2, wherein the one or more processors are configured to: The CWS is maintained at a current value in response to: not receiving a HARQ-ACK or a HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; and During a time window of predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS, no retransmission grant is received, or a Mode 1 transmission grant is received, or a Mode 2 transmission occurs for the TB with the CAPC.

10. The apparatus according to any one of claims 7 or 9, wherein the predetermined length is determined according to max(TA, TB+1) milliseconds, where TA is 5 milliseconds and TB is the duration of the PSSCH starting from the reference duration.

11. The apparatus of claim 2, wherein the one or more processors are configured to adjust the CWS for the CAPC on a per receive (RX) UE basis such that the CWS for the CAPC and the RX UE are updated based on feedback regarding reception of TBs sent to the RX UE during the reference duration.

12. The apparatus of claim 2, wherein the reference duration comprises a duration of a first time slot of the SLCOT. 13 . The apparatus of claim 2 , wherein when the UE transmits x PSSCHs in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

14. The apparatus according to claim 2, wherein the reference duration starts at a partial time slot start point of the SL COT and ends at the first full time slot after the partial time slot start point of the SL COT, ends at a partial time slot end point of the PSSCH in the SL COT, ends k consecutive full time slots after the partial time slot start point of the SL COT when the UE sends x multiple PSSCHs for the CAPC in the SL COT, or ends at a partial time slot end point of a PSSCH burst in the SL COT when the UE sends x multiple PSSCHs for the CAPC in the SL COT.

15. The apparatus of claim 1, wherein the one or more processors are configured to, for each CAPC, increase a contention window size (CWS) to a next value in response to receiving a HARQ-NACK for a TB transmitted during a reference duration to a RX UE group for the CAPC.

16. The apparatus of claim 1, wherein the one or more processors are configured to reset the CWS to a minimum CWS value when an updated CWS exceeds a preconfigured maximum CWS value or after the UE has transmitted a PSSCH according to the maximum CWS for a preconfigured period of time.

17. An apparatus for a user equipment (UE) to perform sidelink communication in an unlicensed spectrum, the apparatus comprising one or more processors configured to cause the UE to: performing a clear channel estimation (CCA) during a contention window for a channel access priority class (CPAC) with a fixed contention window size (CWS) to obtain a side link occupation time (SL COT); and During the SLCOT, a signal encoding corresponding one or more transport blocks (TBs) in corresponding one or more physical sidelink shared channels (PSSCHs) is transmitted to a group of one or more RX UEs, wherein each PSSCH is associated with the CAPC. The apparatus of claim 17 , wherein the CWS comprises a preconfigured minimum or maximum CWS value.

19. The apparatus of claim 17, wherein the CWS comprises a midpoint value of a preconfigured minimum CWS value and a preconfigured maximum CWS value.

20. The apparatus of claim 17, wherein the CWS comprises a preconfigured minimum or maximum CWS value for the CAPC.

21. The apparatus of claim 17, wherein the CWS comprises a midpoint value of a preconfigured minimum CWS value and a preconfigured maximum CWS value for the CAPC.

22. The apparatus of claim 17, wherein the one or more processors are configured to randomly select a value for the CWS.

23. The apparatus of claim 17, wherein the CWS comprises a preconfigured minimum or maximum CWS for broadcast communications.

24. A method for a user equipment (UE) to operate in an unlicensed spectrum, the method comprising: transmitting, during a sidelink (SL) channel occupancy time (COT), one or more physical sidelink shared channel (PSSCH) transmissions to one or more corresponding receiving (RX) UEs according to a SL communication protocol, wherein each PSSCH comprises one or more transport blocks (TBs), wherein each PSSCH transmission is associated with a channel access priority level (CAPC); updating a contention window size (CWS) for the CAPC based on feedback regarding reception of the one or more PSSCHs associated with the CAPC; and A subsequent PSSCH associated with the CAPC is sent based on the updated CWS.

25. The method according to claim 24, comprising: The CWS is updated in response to receiving a hybrid automatic repeat request (HARQ) acknowledgement (ACK) or negative acknowledgement (NACK) feedback regarding a TB sent with the CAPC during a reference duration within the SL COT.

26. The method according to claim 25, comprising: When no HARQ-ACK or HARQ-NACK feedback is received, the CWS is updated based on whether a Mode 1 transmission grant or a retransmission grant is received during a time window of a predetermined length after the reference duration of the earliest SL COT since the last CWS update, or whether a Mode 2 transmission occurs for a TB associated with the CAPC.

27. The method according to claim 25, comprising: The CWS is reset to a minimum value in response to receiving a HARQ-ACK for at least one of the TBs sent for the CAPC during the reference duration within the SL COT, and the CWS is increased to a next level in response to receiving at least one HARQ-NACK and no HARQ-ACK for the TBs sent for the CAPC during the reference duration within the SL COT.

28. The method according to claim 25, comprising: The CWS is reset to a minimum value in response to receiving a HARQ-ACK for at least a predetermined proportion of the TBs or at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT.

29. The method according to claim 25, comprising: In response to receiving HARQ-ACK for less than a predetermined proportion of the TBs sent for the CAPC during the reference duration within the SL COT, or in response to not receiving HARQ-ACK for at least a predetermined proportion of code block groups (CBGs) of the TBs sent for the CAPC during the reference duration within the SL COT, increasing the CWS to a next value.

30. The method of claim 25, comprising: The CWS is increased to a next value in response to: not receiving a HARQ-ACK or a HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; as well as Within a time window of predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS, no Mode 1 transmission grant is received, or a retransmission grant is received, or no Mode 2 transmission occurs for the TB with the CAPC.

31. The method of claim 25, comprising: The CWS is maintained at a current value in response to: not receiving a HARQ-ACK or a HARQ-NACK for the TB sent for the CAPC during the reference duration within the SL COT; as well as During a time window of predetermined length after expiration of the reference duration of the earliest SL COT since the last update of the CWS, no retransmission grant is received, or a Mode 1 transmission grant is received, or a Mode 2 transmission occurs for the TB with the CAPC.

32. The method of claim 25, comprising: The CWS for CAPC is adjusted on a per receive (RX) UE basis such that the CWS for CAPC and the RX UE is updated based on feedback regarding reception of TBs sent to the RX UE during the reference duration.

33. The method of claim 25, wherein the reference duration comprises a duration of a first time slot of the SLCOT.

34. The method of claim 25, wherein when the UE transmits x PSSCHs in the SL COT, the reference duration includes k consecutive first complete time slots in the SL COT.

35. The method of claim 25, wherein the reference duration starts at a partial time slot start point of the SL COT and ends at the first full time slot after the partial time slot start point of the SL COT, ends at a partial time slot end point of the PSSCH in the SL COT, ends k consecutive full time slots after the partial time slot start point of the SL COT when the UE sends x multiple PSSCHs for the CAPC in the SL COT, or ends at a partial time slot end point of a PSSCH burst in the SL COT when the UE sends x multiple PSSCHs for the CAPC in the SL COT.

36. The method of claim 24, comprising: For each CAPC, a contention window size (CWS) is increased to a next value in response to receiving a HARQ-NACK for a TB sent during a reference duration to the RX UE group for that CAPC.

37. The method of claim 24, comprising: The CWS is reset to the minimum CWS value when the updated CWS exceeds a preconfigured maximum CWS value or after the UE has sent PSSCH according to the maximum CWS for a preconfigured period of time.

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