Method and apparatus for determining sidelink HARQ-ACK feedback transmission opportunity via unlicensed spectrum

Abstract

The embodiment of the invention relates to a method and equipment for determining a transmission opportunity fed back through a side link HARQ-ACK of an unlicensed spectrum. In accordance with some embodiments of the present disclosure, a UE may: perform a first channel access procedure to initiate a first COT; determining a first PSFCH opportunity within the first COT; determining whether a HARQ-ACK feedback to be transmitted in the first PSFCH occasion exists or not; and in response to determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH occasion, null a gap symbol of the first PSFCH occasion within the first COT, or in response to determining that HARQ-ACK feedback is not to be transmitted in the first PSFCH occasion, performing continuous transmission in the first PSFCH occasion.

Description

Technical Field

[0001] Embodiments of the present disclosure relate generally to wireless communication techniques, and more particularly, to link hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback transmit opportunity determination via unlicensed spectrum. Background Art

[0002] Wireless communication systems are widely deployed to provide various telecommunication services, such as telephony, video, data, messaging, broadcast, etc. Wireless communication systems may employ multiple access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of wireless communication systems may include fourth generation (4G) systems (e.g., long term evolution (LTE) systems, advanced LTE (LTE-A) systems, or LTE-A Pro systems) and fifth generation (5G) systems, which may also be referred to as new radio (NR) systems.

[0003] In the wireless communication system described above, a user equipment (UE) can communicate with another UE via a data path supported by an operator's network (eg, a cellular or Wi-Fi network infrastructure). The data path supported by the operator's network may include a base station (BS) and multiple gateways.

[0004] Some wireless communication systems may support sidelink communications, where devices (e.g., UEs) that are relatively close to each other may communicate directly with each other via a sidelink, rather than being linked through a BS. The term "sidelink" may refer to a radio link established for communication between devices (e.g., UEs) rather than through a cellular infrastructure (e.g., uplink and downlink). Sidelink transmissions may be performed on both licensed and unlicensed spectrum.

[0005] There is a need to deal with sidelink transmissions on unlicensed spectrum. Summary of the invention

[0006] Some embodiments of the present disclosure provide a first user equipment (UE). The first UE may include a transceiver, and a processor coupled to the transceiver. The processor may be configured to: perform a first channel access procedure to start a first channel occupancy time (COT); determine a first physical sidelink feedback channel (PSFCH) opportunity within the first COT; determine whether there is a hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback to be transmitted in the first PSFCH opportunity; and leave the gap symbol for the first PSFCH opportunity blank within the first COT in response to determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, or perform continuous transmission in the first PSFCH opportunity in response to determining that HARQ-ACK feedback will not be transmitted in the first PSFCH opportunity.

[0007] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the PSFCH resource pool.

[0008] In some embodiments of the present disclosure, determining the presence of HARQ-ACK feedback to be transmitted in a first PSFCH opportunity may include: determining a first HARQ-ACK feedback to be transmitted for a first PSSCH in a first PSFCH opportunity, wherein the first PSSCH is transmitted by a first UE; determining a second HARQ-ACK feedback to be transmitted for a second PSSCH in the first PSFCH opportunity, wherein the second PSSCH is received by the first UE; and determining a third HARQ-ACK feedback to be transmitted for a third PSSCH in the first PSFCH opportunity, wherein the third PSSCH is not transmitted or received by the first UE.

[0009] In some embodiments of the present disclosure, the processor may be further configured to: perform energy detection or a second channel access process in the first PSFCH opportunity in response to an inability to determine whether there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, and perform continuous transmission in the remaining duration of the first PSFCH opportunity in response to the detected energy being lower than a threshold or the second channel access process being successful.

[0010] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the first COT.

[0011] In some embodiments of the present disclosure, the processor may be further configured to: transmit a first PSSCH to a second UE in the first COT; and determine whether a first HARQ-ACK feedback of the first PSSCH will be transmitted in a first PSFCH opportunity or outside the first COT.

[0012] In some embodiments of the present disclosure, the processor may be further configured to: in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT, perform a third channel access process to start a second COT after the first COT, and transmit a second SCI to request the second UE to transmit the first HARQ-ACK feedback in a second PSFCH opportunity. The second PSFCH opportunity is within the second COT and is determined based on the PSFCH periodicity with reference to the second COT. In some embodiments of the present disclosure, the processor may be further configured to: in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT, determine to cancel the first PSFCH opportunity.

[0013] In some embodiments of the present disclosure, the processor may be further configured to perform continuous transmission in the first PSFCH opportunity in response to determining to cancel the first PSFCH opportunity.

[0014] In some embodiments of the present disclosure, the PSFCH periodicity is based on the CAPC used to perform the first channel access procedure. In some embodiments of the present disclosure, the PSFCH periodicity is based on the maximum duration of the first COT. In some embodiments of the present disclosure, the PSFCH periodicity is predefined or configured by RRC signaling.

[0015] In some embodiments of the present disclosure, the processor may be further configured to transmit a first SCI for scheduling a first PSSCH in a first COT to a second UE. The first SCI includes a HARQ-ACK feedback timing indicator for the second UE to determine a PSFCH opportunity for transmitting a first HARQ-ACK feedback for the first PSSCH. The processor may be further configured to determine whether the first HARQ-ACK feedback will be transmitted in the first PSFCH opportunity or outside the first COT.

[0016] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset between a first time slot in which a first PSSCH is transmitted and a second time slot in which a first HARQ-ACK feedback for the first PSSCH is transmitted.

[0017] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset from a set of HARQ-ACK feedback timing values.

[0018] In some embodiments of the present disclosure, the first SCI indicates a channel access type for the second UE to transmit the first HARQ-ACK feedback.

[0019] In some embodiments of the present disclosure, the processor may be further configured to: in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT, set the HARQ-ACK feedback timing indicator in the first SCI to indicate an inapplicable HARQ-ACK feedback timing value (e.g., -1) or a reserved code point, perform a third channel access procedure to start a second COT after the first COT, and transmit a second SCI in the second COT to request the second UE to transmit the first HARQ-ACK feedback in the second PSFCH opportunity. The second PSFCH opportunity is within the second COT and is determined based on the HARQ-ACK feedback timing value indicated by the HARQ-ACK feedback timing indicator in the second SCI.

[0020] In some embodiments of the present disclosure, the processor may be further configured to: in response to determining that the first HARQ-ACK feedback for the first PSSCH is to be transmitted outside the first COT, set the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value indicating a third PSFCH opportunity for transmitting the first HARQ-ACK feedback. The third PSFCH opportunity is outside the first COT.

[0021] In some embodiments of the present disclosure, the processor may be further configured to: in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted in the first PSFCH opportunity, set the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value indicating the first PSFCH opportunity for transmitting the first HARQ-ACK feedback.

[0022] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a HARQ-ACK feedback request indicator requesting transmission of the first HARQ-ACK feedback in the second COT.

[0023] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a first HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests transmission of HARQ-ACK feedback associated with the (several) HARQ process numbers indicated by the first HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the first HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0024] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a second HARQ process number field for requesting to transmit HARQ-ACK feedback of (several) previous PSSCHs associated with (several) HARQ process numbers indicated by the second HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the second HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0025] In some embodiments of the present disclosure, the second SCI is specifically used to request HARQ-ACK feedback, and the second SCI includes a third HARQ process number field indicating a HARQ process number associated with the first HARQ-ACK feedback.

[0026] In some embodiments of the present disclosure, the first HARQ process number field, the second HARQ process number field or the third HARQ process number field further indicates at least one of the following: a HARQ process number associated with HARQ-ACK feedback that cannot be transmitted in the first COT due to a channel access process failure, or a HARQ process number associated with HARQ-ACK feedback that the first UE did not correctly receive in the first COT.

[0027] In some embodiments of the present disclosure, when the second HARQ process number field indicates the same HARQ process number as the fourth HARQ process number field in the second SCI associated with the PSSCH scheduled by the second SCI, the second HARQ process number field does not request to transmit any HARQ-ACK feedback.

[0028] In some embodiments of the present disclosure, the processor may be further configured to: receive the first HARQ-ACK feedback in the third PSFCH opportunity; and in response to not receiving the first HARQ-ACK feedback in the third PSFCH opportunity, perform a fourth channel access process to start a third COT after the third PSFCH opportunity, and transmit a third SCI in the third COT to request the second UE to transmit the first HARQ-ACK feedback in the third COT.

[0029] In some embodiments of the present disclosure, the processor may be further configured to: determine whether to disable the first HARQ-ACK feedback of the first PSSCH; and perform at least one of the following in response to determining to disable the first HARQ-ACK feedback of the first PSSCH: setting the HARQ-ACK feedback timing indicator in the first SCI to indicate an inapplicable HARQ-ACK feedback timing value (e.g., -2) or a reserved code point; or setting a HARQ enable / disable indicator in the first SCI to disable the HARQ-ACK feedback of the first PSSCH.

[0030] Some embodiments of the present disclosure provide a second UE. The second UE may include a transceiver, and a processor coupled to the transceiver. The processor may be configured to: receive from a first UE a first sidelink control information (SCI) for scheduling a first physical sidelink shared channel (PSSCH) within a first channel occupancy time (COT) initiated by the first UE; determine a first physical sidelink feedback channel (PSFCH) opportunity within the first COT; determine whether a first hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback of the first PSSCH will be transmitted in the first PSFCH opportunity; and perform a first channel access process in a gap symbol of the first PSFCH opportunity within the first COT in response to determining that the first HARQ-ACK feedback will be transmitted in the first PSFCH opportunity, and transmit a first HARQ-ACK feedback to the first UE in the first PSFCH opportunity in response to the first channel access process being successful.

[0031] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the PSFCH resource pool.

[0032] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the first COT.

[0033] In some embodiments of the present disclosure, the processor may be further configured to: in response to determining that the first HARQ-ACK feedback for the first PSSCH will be transmitted outside the first COT, postpone transmitting the first HARQ-ACK feedback until a second SCI for requesting transmission of the first HARQ-ACK feedback in a second PSFCH opportunity is received from the first UE in a second COT initiated by the first UE. The second PSFCH opportunity is within the second COT and is determined based on the PSFCH periodicity with reference to the second COT.

[0034] In some embodiments of the present disclosure, the PSFCH periodicity is based on the CAPC used to perform the channel access procedure to start the first COT. In some embodiments of the present disclosure, the PSFCH periodicity is based on the maximum duration of the first COT. In some embodiments of the present disclosure, the PSFCH periodicity is predefined or configured by RRC signaling.

[0035] In some embodiments of the present disclosure, the first SCI includes a HARQ-ACK feedback timing indicator for the second UE to determine a PSFCH timing for transmitting a first HARQ-ACK feedback for a first PSSCH.

[0036] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset between a first time slot in which a first PSSCH is transmitted and a second time slot in which a first HARQ-ACK feedback for the first PSSCH is transmitted.

[0037] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset from a set of HARQ-ACK feedback timing values.

[0038] In some embodiments of the present disclosure, the first SCI indicates a channel access type for the second UE to transmit the first HARQ-ACK feedback.

[0039] In some embodiments of the present disclosure, the processor may be further configured to: defer transmitting the first HARQ-ACK feedback until a second SCI for requesting transmission of the first HARQ-ACK feedback in a second PSFCH opportunity is received from the first UE in a second COT initiated by the first UE, if the HARQ-ACK feedback timing indicator in the first SCI indicates an inapplicable HARQ-ACK feedback timing value (e.g., -1) or a reserved code point. The second PSFCH opportunity is within the second COT and is determined based on the HARQ-ACK feedback timing value indicated by the HARQ-ACK feedback timing indicator in the second SCI.

[0040] In some embodiments of the present disclosure, the processor may be further configured to: transmit the first HARQ-ACK feedback in the third PSFCH opportunity when the HARQ-ACK feedback timing indicator in the first SCI indicates an applicable HARQ-ACK feedback timing value for a third PSFCH opportunity outside the first COT for transmitting the first HARQ-ACK feedback.

[0041] In some embodiments of the present disclosure, the processor may be further configured to: transmit the first HARQ-ACK feedback in the first PSFCH opportunity when the HARQ-ACK feedback timing indicator in the first SCI indicates an applicable HARQ-ACK feedback timing value for the first PSFCH opportunity for transmitting the first HARQ-ACK feedback.

[0042] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a HARQ-ACK feedback request indicator requesting transmission of the first HARQ-ACK feedback in the second COT.

[0043] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a first HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests transmission of HARQ-ACK feedback associated with the (several) HARQ process numbers indicated by the first HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the first HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0044] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a second HARQ process number field for requesting to transmit HARQ-ACK feedback of (several) previous PSSCHs associated with (several) HARQ process numbers indicated by the second HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the second HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0045] In some embodiments of the present disclosure, the second SCI is specifically used to request HARQ-ACK feedback, and the second SCI includes a third HARQ process number field indicating a HARQ process number associated with the first HARQ-ACK feedback.

[0046] In some embodiments of the present disclosure, the first HARQ process number field, the second HARQ process number field or the third HARQ process number field further indicates at least one of the following: a HARQ process number associated with HARQ-ACK feedback that cannot be transmitted in the first COT due to a channel access process failure, or a HARQ process number associated with HARQ-ACK feedback that the first UE did not correctly receive in the first COT.

[0047] In some embodiments of the present disclosure, when the second HARQ process number field indicates the same HARQ process number as the fourth HARQ process number field in the second SCI associated with the PSSCH scheduled by the second SCI, the second HARQ process number field does not request to transmit any HARQ-ACK feedback.

[0048] In some embodiments of the present disclosure, the processor may be further configured to: perform a second channel access process for transmitting the first HARQ-ACK feedback in the third PSFCH opportunity; transmit the first HARQ-ACK feedback in the third PSFCH opportunity in response to the success of the second channel access process; and discard the third PSFCH opportunity in response to the unsuccessful second channel access process.

[0049] In some embodiments of the present disclosure, the processor may be further configured to: receive a third SCI from the first UE in a third COT initiated by the first UE for requesting transmission of the first HARQ-ACK feedback in a third COT in response to the second channel access process being unsuccessful.

[0050] In some embodiments of the present disclosure, in the case where the first HARQ-ACK feedback of the first PSSCH is deactivated, the HARQ-ACK feedback timing indicator in the first SCI indicates an inapplicable HARQ-ACK feedback timing value (e.g., -2) or a reserved code point. In some embodiments of the present disclosure, in the case where the first HARQ-ACK feedback of the first PSSCH is deactivated, the HARQ enable / disable indicator in the first SCI indicates that the HARQ-ACK feedback of the first PSSCH is deactivated.

[0051] Some embodiments of the present disclosure provide a method for wireless communication performed by a first UE. The method may include: performing a first channel access procedure to start a first channel occupation time (COT); determining a first physical sidelink feedback channel (PSFCH) opportunity within the first COT; determining whether there is a hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback to be transmitted in the first PSFCH opportunity; and leaving a gap symbol for the first PSFCH opportunity blank within the first COT in response to determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, or performing continuous transmission in the first PSFCH opportunity in response to determining that HARQ-ACK feedback will not be transmitted in the first PSFCH opportunity.

[0052] Some embodiments of the present disclosure provide a method for wireless communication performed by a second UE. The method may include: receiving first sidelink control information (SCI) from a first UE that schedules a first physical sidelink shared channel (PSSCH) within a first channel occupancy time (COT) initiated by the first UE; determining a first physical sidelink feedback channel (PSFCH) opportunity within the first COT; determining whether a first hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback of the first PSSCH will be transmitted in the first PSFCH opportunity; and performing a first channel access process in a gap symbol of the first PSFCH opportunity within the first COT in response to determining that the first HARQ-ACK feedback will be transmitted in the first PSFCH opportunity, and transmitting a first HARQ-ACK feedback to the first UE in the first PSFCH opportunity in response to the first channel access process being successful.

[0053] Some embodiments of the present disclosure provide a device. According to some embodiments of the present disclosure, the device may include: at least one non-transitory computer-readable medium having computer-executable instructions stored thereon; at least one receiving circuit system; at least one transmitting circuit system; and at least one processor coupled to the at least one non-transitory computer-readable medium, the at least one receiving circuit system, and the at least one transmitting circuit system, wherein the at least one non-transitory computer-readable medium and the computer-executable instructions may be configured to cause the device to perform the method according to some embodiments of the present disclosure with the at least one processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to describe the manner in which the advantages and features of the present disclosure can be obtained, the description of the present disclosure is presented by reference to specific embodiments thereof which are illustrated in the accompanying drawings. These drawings depict only exemplary embodiments of the present disclosure and therefore should not be considered limiting of its scope.

[0055] Figure 1 A schematic diagram illustrating a wireless communication system according to some embodiments of the present disclosure;

[0056] Figures 2 to 4 Describing exemplary configurations of PSFCH opportunities according to some embodiments of the present disclosure;

[0057] Figure 5 and 6 A flowchart illustrating an exemplary process for sidelink communications according to some embodiments of the present disclosure; and

[0058] Figure 7 A block diagram illustrating an exemplary apparatus according to some embodiments of the present disclosure. DETAILED DESCRIPTION

[0059] The detailed description of the drawings is intended as a description of the preferred embodiments of the present disclosure and is not intended to represent the only form in which the present disclosure can be practiced. It should be understood that the same or equivalent functions can be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present disclosure.

[0060] Reference will now be made in detail to some embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided under specific network architectures and new service scenarios (e.g., 3rd Generation Partnership Project (3GPP) 5G, 3GPP Long Term Evolution (LTE) Release 8, etc.). It is considered that, with the development of network architectures and new service scenarios, all embodiments in the present disclosure are also applicable to similar technical issues; and in addition, the terms described in the present disclosure may change, which should not affect the principles of the present disclosure.

[0061] Figure 1 A schematic diagram illustrating a wireless communication system 100 according to some embodiments of the present disclosure.

[0062] like Figure 1 , wireless communication system 100 may include a base station (e.g., BS 120) and some UEs 110 (e.g., UE 110a, UE 110b, and UE 110c). Figure 1 A specific number of UEs 110 and one BS 120 are depicted in FIG. 1 , but it is contemplated that any number of BSs and UEs in and out of coverage of the BSs may be included in the wireless communication system 100 .

[0063] In some embodiments of the present disclosure, BS 120 may be referred to as an access point, access terminal, base, base unit, macro cell, Node B, evolved Node B (eNB), gNB, home Node B, relay node, or device, or described using other terms used in the art. BS 120 is typically part of a radio access network that may include one or more controllers communicatively coupled to one or more corresponding BSs. BS 120 may communicate with (several) UEs 110 via downlink (DL) communication signals.

[0064] UE(s) 110 (e.g., UE 110a, UE 110b, or UE 110c) may include a computing device, such as a desktop computer, a laptop computer, a personal digital assistant (PDA), a tablet computer, a smart TV (e.g., a TV connected to the Internet), a set-top box, a game console, a security system (including a security camera), a vehicle-mounted computer, a network device (e.g., a router, a switch, and a modem), or the like. According to some embodiments of the present disclosure, UE(s) 110 may include a portable wireless communication device, a smart phone, a cellular phone, a flip phone, a device with a subscriber identity module, a personal computer, a selective call receiver, or any other device capable of sending and receiving communication signals on a wireless network. In some embodiments of the present disclosure, UE(s) 110 include a wearable device, such as a smart watch, a fitness band, an optical head-mounted display, or the like. In addition, (several) UEs 110 may be referred to as subscriber units, mobile devices, mobile stations, users, terminals, mobile terminals, wireless terminals, fixed terminals, subscriber stations, user terminals, IoT devices, vehicles or devices, or described using other terms used in the art. (Several) UEs 110 may communicate with BS 120 via uplink (UL) communication signals.

[0065] The wireless communication system 100 may be compatible with any type of network capable of sending and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a network based on time division multiple access (TDMA), a network based on code division multiple access (CDMA), a network based on orthogonal frequency division multiple access (OFDMA), an LTE network, a network based on 3GPP, a 3GPP 5G network, a satellite communication network, a high altitude platform network, and / or other communication networks.

[0066] In some embodiments of the present disclosure, the wireless communication system 100 is compatible with the 5G NR of the 3GPP protocol. For example, the BS 120 may transmit data on the DL using an orthogonal frequency division multiplexing (OFDM) modulation scheme and the (several) UEs 110 may transmit data on the UL using a discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) or cyclic prefix OFDM (CP-OFDM) scheme. However, more generally, the wireless communication system 100 may implement some other open or proprietary communication protocols, such as WiMAX, as well as other protocols.

[0067] In some embodiments of the present disclosure, BS 120 and (several) UE 110 may communicate using other communication protocols (e.g., wireless communication protocols of the IEEE 802.11 series). In addition, in some embodiments of the present disclosure, BS 120 and (several) UE 110 may communicate via a licensed spectrum, while in some other embodiments, BS 120 and (several) UE 110 may communicate via an unlicensed spectrum. The present disclosure is not intended to be limited to implementations of any particular wireless communication system architecture or protocol.

[0068] BS 120 may define one or more cells, and each cell may have a coverage area 130. In exemplary wireless communication system 100, some UEs (eg, UE 110a and UE 110b) are within the coverage of BS 120, but BS 120 may not be as Figure 1 120, and may be any one of the BSs 120 in the wireless communication system, and some UEs (e.g., UE 110c) are outside the coverage of the BS 120. For example, in the case where the wireless communication system includes two BSs 120, UE 110a being within the coverage of either of the two BSs means that UE 110a is within the coverage of the BSs 120 in the wireless communication system (i.e., in coverage); and UE 110a being outside the coverage of the two BSs 120 means that UE 110a is outside the coverage of the BSs 120 in the wireless communication system (i.e., out of coverage).

[0069] Still reference Figure 1UE 110a and UE 110b may communicate with each other via, for example, a Uu link (by Figure 1 ) and BS 120. UE 110a, UE 110b, and UE 110c may communicate via a side link (indicated by a dashed arrow in FIG. Figure 1 In some embodiments, UE 110a, UE 110b, and UE 110c may form a UE group.

[0070] The sidelink transmission may involve a physical sidelink control channel (PSCCH) and an associated physical sidelink shared channel (PSSCH), which are scheduled by sidelink control information (SCI) carried on the PSCCH. The SCI and the associated PSSCH may be transmitted from a transmitting UE (hereinafter referred to as "Tx UE") to a receiving UE (hereinafter referred to as "Rx UE") in a unicast manner, transmitted to a group of Rx UEs in a multicast manner, or transmitted to Rx UEs within range in a broadcast manner. For example, referring to Figure 1 , UE 110a (acting as a Tx UE) may transmit data to UE 110b or UE 110c (acting as a Rx UE).

[0071] The PSSCH may carry data that may require corresponding HARQ-ACK feedback from (several) Rx UEs to Tx UEs. For example, broadcast transmissions may not require HARQ-ACK feedback, and unicast or multicast transmissions may enable HARQ-ACK feedback under some preconditions. HARQ-ACK feedback for the PSSCH may be carried on a physical sidelink feedback channel (PSFCH). In the context of the present disclosure, PSFCH and HARQ-ACK feedback may be used interchangeably.

[0072] In some embodiments of the present disclosure, a PSFCH may be transmitted within a PSFCH resource pool, which may be periodically configured for a sidelink. For example, a UE may be instructed by an SCI format for scheduling PSSCH reception to transmit a PSFCH with HARQ-ACK information in response to PSSCH reception. The UE may provide HARQ-ACK information, which may include an acknowledgment (ACK) or a negative ACK (NACK) or only a NACK, depending on the HARQ-ACK feedback option adopted. For example, a certain number of time slots in a resource pool for a period of PSFCH transmission opportunity resources may be provided to the UE (e.g., via sl-PSFCH-Period specified in the 3GPP specification). If the number is zero, PSFCH transmissions from the UE in the resource pool are disabled.

[0073] When the UE receives a PSSCH in a resource pool and the SCI associated with the PSSCH (e.g., a HARQ feedback enable / disable indicator field in the SCI) indicates that HARQ feedback is enabled (e.g., the HARQ feedback enable / disable indicator has a value of 1 in SCI format 2-A or SCI format 2-B), the UE may provide HARQ-ACK information in a PSFCH transmission in the resource pool. For example, the UE may transmit the PSFCH in the first (e.g., earliest) time slot that contains PSFCH resources (e.g., a PSFCH opportunity) and is at least a certain number of time slots away from the last time slot of the PSSCH reception in the resource pool (e.g., provided by sl-MinTimeGapPSFCH specified in the 3GPP specification).

[0074] In some embodiments of the present disclosure, sidelink transmissions may be performed on an unlicensed spectrum. This is advantageous because sidelink transmissions via an unlicensed spectrum may achieve, for example, an increased data rate. In order to achieve fair coexistence between various systems (e.g., NR systems (e.g., NR-U systems) and other wireless systems), a channel access procedure, also known as a listen-before-talk (LBT) test, may be performed prior to communicating on an unlicensed spectrum.

[0075] Various types of channel access procedures may be supported, including but not limited to channel access type 1 and channel access type 2. In some examples, channel access type 2 may further include channel access type 2A, channel access type 2B, and channel access type 2C. Detailed definitions of channel access type 1 and channel access type 2 may be found in the 3GPP specifications.

[0076] In some embodiments, by performing a channel access type 1 procedure (also known as LBT Cat. 4), the UE may obtain channel occupancy (CO) and occupy the channel until the maximum channel occupancy time (MCOT). In some embodiments, the duration of the MCOT may be related to the channel access priority class (CAPC) value of the service priority and may be 2ms, 4ms, 6ms, 8ms, or 10ms, which is equivalent to 2, 4, 6, 8, or 10 time slots in the case of a 15kHz subcarrier spacing (SCS), 4, 8, 12, 16, or 20 time slots in the case of a 30kHz SCS, 8, 16, 24, 32, or 40 time slots in the case of a 60kHz SCS, or 16, 32, 48, 64, or 80 time slots in the case of a 120kHz SCS. Therefore, after the UE performs a successful channel access type 1 procedure, the UE may occupy the channel for a maximum of several or tens of time slots, depending on the corresponding CAPC value and SCS.

[0077] In some embodiments of the present disclosure, when performing sidelink transmissions on unlicensed spectrum, a periodic PSFCH configuration may also be employed. However, this configuration may have disadvantages. For example, when a UE initiates COT by performing a channel access type 1 procedure, COT may often be interrupted by periodic PFSCH opportunities. This is especially true because the PSFCH period is relatively small (i.e., 1, 2, or 4 slots).

[0078] Figure 2 An exemplary periodic PFSCH configuration 200 is shown according to some embodiments of the present disclosure. Figure 2 , the PSFCH periodicity is 4 time slots. For example, time slots n+3, n+7, n+11, and n+15 may include PFSCH opportunities 221, 222, 223, and 224, respectively. (Several) UEs may activate COT 251, COT 252, and COT 253. COT 251 may be interrupted by PFSCH opportunity 221. COT 252 may be interrupted by PFSCH opportunity 222. COT 253 may be interrupted by PFSCH opportunities 223 and 224. It should be noted that COTs 251 to 253 may be activated by the same or different UEs.

[0079] In some examples, a UE that activates COT 251 may transmit SCI 211 and 212 in slot n and slot n+1, which schedule PSSCH with corresponding HARQ-ACK feedback to be transmitted in PSFCH opportunity 221. The UE may also transmit SCI 213 and 214 in slot n+2 and slot n+3, which schedule PSSCH with corresponding HARQ-ACK feedback to be transmitted in PSFCH opportunity 222. Similarly, SCI 215 to 218 transmitted in slot n+6 to slot n+9 in COT 252 may schedule PSSCH with corresponding HARQ-ACK feedback to be transmitted in PSFCH opportunity 223. SCI 219 transmitted in slot n+12 in COT 253 may schedule PSSCH with corresponding HARQ-ACK feedback to be transmitted in PSFCH opportunity 224.

[0080] like Figure 2 As shown in Figure 2, even with a relatively large PSFCH periodicity, COT may be frequently interrupted. When the duration of COT exceeds 4 time slots, e.g. Figure 2 In COT 253, it will be interrupted twice. For example, this interruption brings the following disadvantages:

[0081] (1) The Tx UE cannot continuously transmit the sidelink transmission in the time domain because the Tx UE needs to continuously monitor the channel and perform a channel access procedure (eg, channel access type 2) before it resumes its sidelink transmission.

[0082] (2) The Tx UE is likely to lose the channel. When the gap is larger than the minimum sensing interval (e.g., 16us or 25us), there is a risk of losing the channel. When the COT is interrupted by a PSFCH opportunity and no PSFCH is transmitted during the opportunity due to, for example, feedback based only on NACK or disabled HARQ-ACK feedback, the probability of losing the channel is quite high, for example, considering that one PSFCH opportunity of the gap symbol containing the PSFCH opportunity may occupy 4 consecutive symbols of about 280us.

[0083] (3) For a PSFCH opportunity within the COT of a UE, when a PSFCH transmission in the PSFCH opportunity is not targeted at the COT initiator UE, the PSFCH transmission may not be consistent with regulatory requirements.

[0084] (4) If the PSFCH is not within any COT, a channel access procedure (eg, channel access type 1) for transmitting the PSFCH in the PSFCH opportunity may have to be performed by the Rx UE. The Rx UE may initiate a COT only for transmitting the PSFCH. The channel access procedure may fail.

[0085] (5) When the PSFCH periodicity is relatively small (e.g., 1 or 2 time slots), the current COT mechanism does not work properly.

[0086] Embodiments of the present disclosure provide a solution for HARQ-ACK feedback transmission via unlicensed spectrum on a side link. The proposed solution can at least solve the above problems. More details about the embodiments of the present disclosure will be described below in conjunction with the accompanying drawings.

[0087] In some embodiments of the present disclosure, for sidelink transmissions via unlicensed spectrum, PSFCH transmission timing is determined based on PSFCH periodicity with reference to a PSFCH resource pool.PSFCH periodicity may be configured by radio resource control (RRC) signaling or predefined in (several) standards.

[0088] For a UE that wishes to transmit a PSFCH, a channel access procedure (e.g., channel access type 2) is performed before transmitting the PSFCH in a PSFCH transmission opportunity. The PSFCH transmission opportunity is defined with reference to the initial time slot of the PSFCH resource pool. For example, if Then the time slot may have a PSFCH transmission opportunity resource, where k represents the time slot index referring to the initial time slot of the PSFCH resource pool (eg, k=0 refers to the initial time slot of the PSFCH resource pool), and Indicates PSFCH periodicity. Based on this configuration, the PSFCH transmission opportunity will not change dynamically in the time domain. In the context of the present disclosure, PSFCH transmission opportunity and PSFCH opportunity can be used interchangeably.

[0089] The Tx UE (denoted as UE#1 for simplicity) may start the COT by performing a channel access procedure (e.g., channel access type 1). In order to solve the above-mentioned problem caused by the periodic PSFCH transmission opportunity, UE#1 may determine whether there is a PSFCH transmission opportunity within the COT and whether there is a HARQ-ACK feedback (or at least one PSFCH) to be transmitted in the PSFCH transmission opportunity within the COT, and then act accordingly based on the determination.

[0090] For example, in some embodiments, when UE#1 determines that the PSFCH transmission opportunity is within the COT and further determines that there is HARQ-ACK feedback to be transmitted in the PSFCH transmission opportunity (represented as scenario #1), UE#1 may leave the gap symbols of the PSFCH transmission opportunity within the COT blank. For example, the symbol (e.g., one symbol) before the PSFCH transmission opportunity may be left blank so that the UE may perform a channel access procedure (e.g., channel access type 2) before transmitting the PSFCH in the PSFCH transmission opportunity. For example, the symbol (e.g., one symbol) after the PSFCH transmission opportunity may be left blank so that UE#1 may perform a channel access procedure (e.g., channel access type 2) before resuming transmission in the COT (e.g., in the next time slot). In some instances, when the PSFCH transmission opportunity is located at the end of the COT, there may be no gap symbols after the PSFCH transmission opportunity.

[0091] In some embodiments, when UE#1 determines that the PSFCH transmission opportunity is within the COT and further determines that there is no HARQ-ACK feedback (or no PSFCH) to be transmitted in the PSFCH transmission opportunity (represented as scenario #2), UE#1 may perform continuous transmission in the PSFCH transmission opportunity. For example, UE#1 may perform continuous transmission in the PSFCH transmission opportunity within the COT and in the gap symbol for the PSFCH transmission opportunity. The gap symbol of the PSFCH transmission opportunity may include a symbol before the PSFCH transmission opportunity (e.g., one symbol), a symbol after the PSFCH transmission opportunity (e.g., one symbol), or both, as described above. In this way, the risk of losing the channel can be avoided.

[0092] In some embodiments, when UE#1 determines that the PSFCH transmission opportunity is within the COT, but cannot determine whether there is HARQ-ACK feedback to be transmitted in the PSFCH transmission opportunity (for example, whether a UE other than UE#1 can transmit PSFCH in the PSFCH transmission opportunity) (represented as scenario #3), UE#1 may perform energy detection or a channel access procedure in the PSFCH transmission opportunity (for example, in the initial or first symbol of the PSFCH transmission opportunity). In response to the detected energy being lower than a threshold or the channel access procedure being successful, indicating that the channel is empty, UE#1 may perform continuous transmission in the remaining duration of the PSFCH transmission opportunity (for example, in the second symbol of the PSFCH transmission opportunity) to avoid the risk of losing the channel. UE#1 may also perform continuous transmission in symbols after the PSFCH transmission opportunity.

[0093] In this way, due to the required channel access process (e.g., channel access type 2), the PSFCH transmission opportunity can ensure a high LBT success probability. In some cases, including, for example, when UE#1 determines that PSFCH will not be transmitted in the PSFCH transmission opportunity, UE#1 may perform continuous transmission to reserve the channel in the PSFCH transmission opportunity (for simplicity, this transmission may also be referred to as a reservation signal or reservation transmission in the present disclosure). Details about the reservation signal (or reservation transmission) will be described in detail below. On the other hand, in some cases, including, for example, when UE#1 determines that PSFCH will be transmitted in the PSFCH transmission opportunity, UE#1 may not transmit the reservation signal.

[0094] In some embodiments of the present disclosure, when UE#1 determines whether there is HARQ-ACK feedback or PSFCH to be transmitted in the PSFCH transmission opportunity within the COT initiated by UE#1, the following situation may be involved: UE#1 may further determine whether to transmit a reservation signal in the PSFCH transmission opportunity based on the following situation.

[0095] Case 1: UE#1 may determine whether it will transmit HARQ-ACK feedback or PSFCH for a PSSCH received by UE#1 in a PSFCH transmission opportunity in the COT. For example, UE#1 may receive a PSSCH in a time slot and may determine whether UE#1 will transmit HARQ-ACK feedback for a received PSSCH in a PSFCH transmission opportunity in the COT. For example, this determination may be made based on an associated HARQ-ACK enable / disable indicator and a projection type indicator in the SCI or PSCCH that schedules the PSSCH. The projection type indicator may indicate a HARQ-ACK feedback option for the PSSCH.

[0096] When UE#1 determines to transmit one or more PSFCHs in the PSFCH transmission opportunity, UE#1 may transmit the one or more PSFCHs in the PSFCH transmission opportunity. UE#1 may not transmit a reservation signal in the PSFCH transmission opportunity.

[0097] For example, refer again to Figure 2 , where the PSFCH transmission opportunity can be configured by RRC signaling with a PSFCH periodicity of 4 slots, assuming that UE#1 starts COT 252. Assuming that UE#1 receives PSSCH in slots n+2 and n+3 and wishes to transmit the corresponding PSFCH (e.g., HARQ-ACK feedback of PSSCH) in slot n+7, UE#1 can transmit PSFCH in slot n+7 and not transmit a reserved signal on the channel.

[0098] Case 2: UE#1 may determine whether it will receive HARQ-ACK feedback or PSFCH for a PSSCH transmitted by UE#1 in a PSFCH transmission opportunity in the COT. For example, UE#1 may transmit a PSSCH to another UE in a time slot, and may determine whether UE#1 will receive HARQ-ACK feedback for a PSSCH transmitted in a PSFCH transmission opportunity in the COT (i.e., to be transmitted by another UE that is the RxUE of UE#1). For example, this determination may be made based on an associated HARQ-ACK enable / disable indicator and a projection type indicator in the SCI or PSCCH that schedules the PSSCH.

[0099] When UE#1 determines that it will receive one or more PSFCHs of the PSSCH transmitted by UE#1 in the PSFCH transmission opportunity, UE#1 may receive the one or more PSFCHs in the PSFCH transmission opportunity. UE#1 may not transmit a reservation signal in the PSFCH transmission opportunity.

[0100] For example, refer again to Figure 2 , where the PSFCH transmission timing can be configured by RRC signaling with a PSFCH periodicity of 4 slots, assuming that UE#1 activates COT 251 and 252. Assuming that UE#1 transmits PSSCH in slots n+2 and n+3 and instructs (several) corresponding Rx UEs to transmit corresponding PSFCH in slot n+7 (e.g., HARQ-ACK feedback of PSSCH), UE#1 can receive PSFCH in slot n+7 and does not transmit a reservation signal on the channel.

[0101] Case 3: UE#1 may determine whether HARQ-ACK feedback for PSSCH or PSFCH, which is not transmitted or received by UE#1, will be transmitted in the PSFCH transmission opportunity in the COT. For example, a Tx UE (e.g., UE#A) different from UE#1 may transmit PSSCH to an Rx UE (e.g., UE#B) different from UE#1 in a time slot. UE#1 may determine whether HARQ-ACK feedback for PSSCH will be transmitted by UE#B or received by UE#A in the PSFCH transmission opportunity in the COT. For example, this determination may be made based on an associated HARQ-ACK enable / disable indicator and a projection type indicator in an SCI or PSCCH that schedules PSSCH. For example, UE#1 may make a determination by decoding an SCI or PSCCH that schedules a PSSCH transmitted by UE#A in a time slot, where the corresponding HARQ-ACK feedback will be transmitted in the PSFCH transmission opportunity.

[0102] When UE#1 determines that UE#B will transmit one or more PSFCHs in the PSFCH transmission opportunity, UE#1 may not transmit the reservation signal in the PSFCH transmission opportunity.

[0103] For example, refer again to Figure 2 , where the PSFCH transmission opportunity can be configured by RRC signaling with a PSFCH periodicity of 4 time slots, assuming that UE#A starts COT 251 and UE#1 starts COT 252. Assuming that UE#A transmits PSSCH to UE#B in time slots n+2 and n+3, according to the PSCCH received in time slots n+2 and n+3, which instructs UE#B to transmit the corresponding PSFCH in time slot n+7, UE#1 may not transmit a reserved signal on the channel.

[0104] As mentioned above, in scenario #2, UE #1 may perform continuous transmission in the PSFCH transmission opportunities within the COT initiated by UE #1. Continuous transmission may be implemented in various ways.

[0105] For example, in some embodiments of the present disclosure, UE#1 may continuously transmit the ongoing PSSCH in the PSFCH transmission opportunity. For example, UE#1 may continuously transmit the ongoing PSSCH until the end of the time slot in which the PSFCH transmission opportunity occurs, so as to fully occupy the time slot. For example, the PSFCH transmission opportunity and the gap symbol for the PSFCH transmission opportunity (if any) may be used by the ongoing PSSCH for sidelink transmission. The gap symbol of the PSFCH transmission opportunity may include the symbol before the PSFCH transmission opportunity (e.g., one symbol), the symbol after the PSFCH transmission opportunity (e.g., one symbol), or both, as described above. In these embodiments, no symbols are wasted.

[0106] For example, refer again to Figure 2 , assuming that UE#1 starts COT 252 and determines that scenario #2 occurs, UE#1 may transmit PSSCH using PSFCH opportunity 222 and the gap symbols before and after PSFCH opportunity 222. For example, PSSCH may be transmitted from its scheduled position in slot n+7 until the end of slot n+7.

[0107] In some embodiments of the present disclosure, UE#1 may continuously transmit a signal (e.g., signal #A) after the ongoing PSSCH in the PSFCH transmission opportunity and the gap symbol of the PSFCH transmission opportunity (if any), without a gap greater than the minimum sensing interval (e.g., 16us or 25us). For example, UE#1 may transmit a signal after the ongoing PSSCH until the end of the time slot in which the PSFCH transmission opportunity occurs, so as to fully occupy the time slot. For example, the PSFCH transmission opportunity and the gap symbol of the PSFCH transmission opportunity are used to transmit signal #A. For example, the gap between the PSSCH and signal #A in the time slot may be less than or equal to the minimum sensing interval.

[0108] Signal #A can be implemented in various ways. For example, signal #A can be a repetition of one or more last symbols of the ongoing PSSCH. For example, signal #A can be a repetition of one or more first symbols of the next time slot. For example, signal #A can be any other signal that a person skilled in the art can imagine.

[0109] For example, refer again to Figure 2 Assuming that UE#1 starts COT 252 and determines that scenario #2 occurs, UE#1 can use PSFCH opportunity 222 and the gap symbols before and after PSFCH opportunity 222 to transmit signal #A.

[0110] In some embodiments of the present disclosure, UE#1 may transmit a signal only for a reserved channel in a PSFCH transmission opportunity.

[0111] For example, UE#1 may transmit an interleaving-based channel (e.g., an interleaving-based PSFCH) in a PSFCH transmission opportunity (e.g., two symbols reserved for PSFCH transmission). The channel may be transmitted on an interleaving randomly selected from the available interleavings or on a default interleaving (e.g., the lowest or highest interleaving) predefined or (pre)configured in (several) standards.

[0112] For the gap symbol (if any) before or after the PSFCH transmission opportunity, UE#1 may also transmit (several) signals on (several) gap symbols so that there is no gap greater than the minimum sensing interval (e.g., 16us or 25us). For example, UE#1 may extend the cyclic prefix (CP) of the first symbol of the interleaved channel or the last symbol of the ongoing PSSCH in the gap symbol before the PSFCH transmission opportunity. UE#1 may extend the CP of the first symbol of the next slot or the last symbol of the interleaved channel in the gap symbol after the PSFCH transmission opportunity.

[0113] As mentioned above, in some cases, scenario #3 may occur. For example, UE#1 may determine that it itself will not transmit (several) PSFCHs in the PSFCH transmission opportunity. UE#1 may also determine that its Rx UE will not transmit (several) PSFCHs in the PSFCH transmission opportunity based on, for example, the Rx UE adopts ACK / NACK-based feedback. However, in the case where the Rx UE adopts feedback based only on NACK, UE#1 cannot determine whether its Rx UE will transmit PSFCH in the PSFCH transmission opportunity. In the case where, for example, another UE adopts feedback based only on NACK or UE#1 does not receive or correctly decode the PSCCH of another UE, UE#1 cannot determine whether there is another UE (e.g., UE#B) that will transmit (several) PSFCHs in the PSFCH transmission opportunity.

[0114] In this scenario, as described above, UE#1 can determine whether the channel is empty in the PSFCH transmission opportunity by, for example, performing energy detection or a channel access procedure. Based on the result, UE#1 can perform continuous transmission in the PSFCH transmission opportunity.

[0115] For example, in some embodiments of the present disclosure, UE#1 may detect energy on the initial or first symbol of a PSFCH transmission opportunity. If the detected energy is below an energy detection threshold (which may be predefined or (pre) configured), UE#1 may assume that there are no other UEs transmitting PSFCH in the current PSFCH transmission opportunity. UE#1 may transmit a reservation signal starting from the second symbol of the current PSFCH transmission opportunity until the end of the current timeslot. The reservation signal described with respect to scenario #2 may also be applicable here.

[0116] In some embodiments of the present disclosure, UE#1 may perform a channel access procedure (e.g., a type 2 channel access procedure) within the first symbol of a PSFCH transmission opportunity. For example, UE#1 may perform a type 2 channel access procedure within the first 16us or 25us of the first symbol of a PSFCH transmission opportunity, the last 16us or 25us of the first symbol of a PSFCH transmission opportunity, or any 16us or 25us sensing interval within the first symbol of a PSFCH transmission opportunity. If the channel access procedure is successful, UE#1 may assume that there are no other UEs transmitting PSFCH in the current PSFCH transmission opportunity. In some instances, UE#1 may transmit a reservation signal starting from the second symbol of the current PSFCH transmission opportunity until the end of the current timeslot. In some instances, UE#1 may transmit a reservation signal after performing the channel access procedure until the end of the current timeslot. The reservation signal described with respect to scenario #2 may also be applicable here.

[0117] In some instances, from the perspective of the Rx UE of UE#1 (denoted as UE#2 for simplicity), UE#2 may receive from UE#1 an SCI scheduling a PSSCH within a COT initiated by UE#1. UE#2 may determine whether to transmit HARQ-ACK feedback of the received PSSCH in a PSFCH transmission opportunity within the COT. The PSFCH transmission timing may be determined based on the PSFCH periodicity with reference to the PSFCH resource pool. In response to determining that the HARQ-ACK feedback will be transmitted in a PSFCH transmission opportunity within the COT, UE#2 may perform a channel access procedure (e.g., channel access type 2) in a gap symbol (e.g., one symbol before the PSFCH transmission opportunity) for the PSFCH transmission opportunity within the COT. UE#2 may transmit HARQ-ACK feedback to UE#1 in a PSFCH transmission opportunity in response to the channel access procedure being successful. UE#1 may perform a channel access procedure (eg, channel access type 2) after the PSFCH transmission opportunity (eg, in the gap symbol of the PSFCH transmission opportunity) before it resumes its sidelink transmission in the COT.

[0118] In some embodiments of the present disclosure, for sidelink transmission via unlicensed spectrum, the PSFCH transmission timing is determined based on the PSFCH periodicity with reference to the COT. For example, the PSFCH transmission timing is limited within the COT and is determined based on the PSFCH periodicity and the initial time slot of the COT.

[0119] In some embodiments, the PSFCH periodicity may be configured by RRC signaling or predefined in (several) standards. For example, when the SCS is 15kHz, the PSFCH periodicity may be equal to 2 or 4 time slots; when the SCS is 30kHz, the PSFCH periodicity may be equal to 2, 4 or 8 time slots; when the SCS is 60kHz, the PSFCH periodicity may be equal to 2, 4, 6, 8, 10, 12 or 16 time slots.

[0120] In some embodiments, the PSFCH periodicity may be based on the CAPC used to perform the channel access procedure that initiates the COT. For example, when the SCS is 15kHz, for a CAPC value of 1 or 2, the PSFCH periodicity may be equal to 2 slots; and for a CAPC value of 3 or 4, the PSFCH periodicity may be equal to 4 slots. For example, when the SCS is 30kHz, for a CAPC value of 1 or 2, the PSFCH periodicity may be equal to 2 or 4 slots; and for a CAPC value of 3 or 4, the PSFCH periodicity may be equal to 4 or 8 slots. For example, when the SCS is 60kHz, for a CAPC value of 1 or 2, the PSFCH periodicity may be equal to 2 or 4 or 8 slots; and for a CAPC value of 3 or 4, the PSFCH periodicity may be equal to 4 or 8 or 10 or 12 or 16 slots. The detailed PSFCH periodicity may be configured by RRC signaling or predefined in (several) standards.

[0121] In some embodiments, the PSFCH periodicity may be based on the maximum duration of the COT. For example, when the SCS is 15kHz, the PSFCH periodicity may be equal to 2 slots for a maximum duration of 2ms, 3ms, or 4ms; and for a maximum duration of 6ms, 8ms, or 10ms, the PSFCH periodicity may be equal to 4 slots. For example, when the SCS is 30kHz, the PSFCH periodicity may be equal to 2 or 4 slots for a maximum duration of 2ms, 3ms, or 4ms; and for a maximum duration of 6ms, 8ms, or 10ms, the PSFCH periodicity may be equal to 4 or 8 slots. For example, when the SCS is 60kHz, the PSFCH periodicity may be equal to 2 or 4 or 8 slots for a maximum duration of 2ms, 3ms, or 4ms; and for a maximum duration of 6ms, 8ms, or 10ms, the PSFCH periodicity may be equal to 4 or 8 or 10 or 12 or 16 slots. The detailed PSFCH periodicity may be configured by RRC signaling or predefined in (several) standards.

[0122] For a UE that wishes to transmit HARQ-ACK feedback or PSFCH, a channel access procedure (e.g., channel access type 2) is performed before transmitting HARQ-ACK feedback or PSFCH in the PSFCH transmission opportunity. The Tx UE (denoted as UE#1A for simplicity) may start the COT by performing a channel access procedure (e.g., channel access type 1). UE#1A may determine the PSFCH transmission opportunity with reference to the initial time slot of the COT. For example, if Then the time slot may have a PSFCH transmission opportunity resource, where k1 represents the time slot index of the initial time slot of the reference COT (e.g., k=0 refers to the initial time slot of the COT), and Indicates the PSFCH periodicity. The PSFCH transmission timing will change dynamically in the time domain according to the CAPC or MCOT of the COT or be configured by RRC signaling.

[0123] For the PSSCH transmitted by UE#1A in the COT, the corresponding PSFCH (or HARQ-ACK feedback) may be transmitted by (several) Rx UEs in the first (e.g., earliest) time slot that contains PSFCH resources (e.g., PSFCH transmission opportunity) and satisfies the Rx UE's processing delay requirement from PSSCH to the corresponding PSFCH (or HARQ-ACK feedback). The PSFCH transmission opportunity within the COT may be reserved by UE#1A for (several) Rx UEs to transmit PSFCH (or HARQ-ACK feedback). Before transmitting PSFCH (or HARQ-ACK feedback) within the COT, the Rx UE may require a channel access procedure (e.g., channel access type 2).

[0124] In some instances, due to the processing delay requirement of the Rx UE from the PSSCH to the corresponding PSFCH, if the PSFCH (or HARQ-ACK feedback) cannot be transmitted within the current COT, it can be automatically postponed by the Rx UE. UE#1A can start a new COT and trigger the Rx UE to transmit the postponed PSFCH (or HARQ-ACK feedback) in the PSFCH transmission opportunity (e.g., the earliest PSFCH transmission opportunity) within the new COT according to the PSFCH periodicity. As will be described in detail later, various embodiments are provided to implement the triggering mechanism of the PSFCH transmission opportunity.

[0125] In some instances, when, for example, UE#1A decides to disable HARQ-ACK feedback for PSSCH transmitted in a time slot, the PSFCH transmission opportunity may be canceled, where the corresponding HARQ-ACK feedback will be transmitted in the PSFCH transmission opportunity within the COT. For the canceled PSFCH transmission opportunity, UE#1A may perform continuous transmission in the PSFCH transmission opportunity to fully utilize the channel and avoid the risk of losing the channel. As will be described in detail later, various embodiments are provided to implement the cancellation mechanism of the PSFCH transmission opportunity. In another example, UE#1A may decide to disable HARQ-ACK feedback for PSSCH transmitted in the COT with corresponding HARQ-ACK feedback to be transmitted in the PSFCH transmission opportunity outside the COT.

[0126] In this way, the PSFCH transmission opportunity is always within the COT initiated by the Tx UE, which ensures a high LBT success probability due to the required channel access procedure (e.g., channel access type 2). The ongoing sidelink transmission from UE#1A is not interrupted by the PSFCH transmission opportunity, especially when the PSFCH transmission opportunity is located at the end of the COT. If UE#1A determines to disable the corresponding HARQ-ACK feedback transmission in the PSFCH transmission opportunity, then UE#1A can easily transmit a signal for reserving the channel in the PSFCH transmission opportunity. In some cases, including, for example, when UE#1A determines to disable the corresponding HARQ-ACK feedback transmission in the PSFCH transmission opportunity, UE#1A may perform continuous transmission to reserve the channel in the PSFCH transmission opportunity (e.g., transmit a reservation signal or a reservation transmission).

[0127] The triggering mechanism for requesting sidelink HARQ-ACK feedback (eg, for PSSCH in a previous COT) may be implemented in various ways.

[0128] For example, UE#1A may start a COT (denoted as COT#1A) and transmit a PSSCH to an Rx UE (denoted as UE#2A) in COT#1A. In some instances, UE#1A may determine that HARQ-ACK feedback (or PSFCH) of PSSCH cannot be transmitted within COT#1A. UE#1A may perform a channel access procedure (e.g., channel access type 1) to start another COT (denoted as COT#2A), and may trigger UE#2A to transmit a deferred HARQ-ACK feedback in a PSFCH transmission opportunity within COT#2A. COT#2A is outside COT#1A.

[0129] In some embodiments of the present disclosure, UE#1A may transmit SCI (denoted as SCI#A) in COT#2A to request UE#2A to transmit deferred HARQ-ACK feedback in a PSFCH transmission opportunity within COT#2A. For example, the PSFCH transmission opportunity may be indicated by SCI#A. For example, the PSFCH transmission opportunity may be a specific one (e.g., the earliest) of at least one PSFCH transmission opportunity within COT#2A. At least one PSFCH transmission opportunity may be determined based on PSFCH periodicity with reference to COT#2A.

[0130] For example, in some embodiments of the present disclosure, SCI#A may schedule PSSCH in COT#2A. SCI#A may include a HARQ-ACK feedback request indicator requesting transmission of deferred HARQ-ACK feedback within COT#2A. The size of the HARQ-ACK feedback request indicator may be at least one bit.

[0131] For example, when a UE (e.g., UE#1A) starts a new COT, it may transmit an SCI with a HARQ-ACK feedback request indicator requesting (several) Rx UEs (e.g., UE#2A) to transmit deferred HARQ-ACK feedback in the new COT. For the Rx UE, since it knows the deferred HARQ-ACK feedback (e.g., by determining that the HARQ-ACK feedback cannot be transmitted in the (several) previous COTs), it may transmit the deferred HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ-ACK feedback request indicator.

[0132] In some embodiments of the present disclosure, SCI#A may schedule PSSCH in COT#2A. SCI#A may include a HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests that HARQ-ACK feedback associated with (several) HARQ process numbers indicated by the HARQ process number field be transmitted in COT#2A. One or more HARQ process numbers may be indicated by the HARQ process number field in SCI#A and are requested to be used to transmit corresponding HARQ-ACK feedback in the same PSFCH transmission opportunity. That is, HARQ-ACK feedback associated with (several) HARQ process numbers indicated by the HARQ process number field is requested to be transmitted in COT#2A. In other words, the HARQ-ACK feedback to be transmitted in COT#2A corresponds to (several) previous PSSCHs associated with the HARQ process number indicated by the HARQ process number field in SCI#A.

[0133] The HARQ-ACK feedback to be transmitted in COT#2A may include deferred HARQ-ACK feedback that could not be responded to in (several) previous COTs due to, for example, UE processing delay, HARQ-ACK feedback that could not be transmitted in (several) previous COTs due to channel access process failure, HARQ-ACK feedback that could not be correctly received in (several) previous COTs due to, for example, hidden node interference, or any combination thereof. In other words, the (several) HARQ process numbers indicated by the HARQ process number field may include a HARQ process number associated with deferred HARQ-ACK feedback, a HARQ process number associated with HARQ-ACK feedback that could not be transmitted in the previous COT due to channel access process failure, a HARQ process number associated with HARQ-ACK feedback that UE#1A did not correctly receive in the previous COT, or any combination thereof.

[0134] For example, when a UE (e.g., UE#1A) starts a new COT, it may transmit an SCI having a HARQ-ACK feedback request indicator and an associated HARQ process number indication (e.g., a HARQ process number field) requesting (several) Rx UEs (e.g., UE#2A) to transmit corresponding HARQ-ACK feedback in the new COT. For the Rx UE, since it may know the requested HARQ-ACK feedback based on the associated HARQ process number indication, it may transmit the requested HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ-ACK feedback request indicator and the associated HARQ process number indication.

[0135] SCI#A may further include another HARQ process number field, which indicates a HARQ process number associated with a PSSCH scheduled by SCI#A or a HARQ-ACK feedback of a scheduled PSSCH.

[0136] In some embodiments of the present disclosure, SCI#A may schedule PSSCH in COT#2A. Compared with the previous embodiment, SCI#A may not include a HARQ-ACK feedback request indicator. SCI#A may include a HARQ process number field (denoted as field #1), which requests to transmit HARQ-ACK feedback associated with (several) HARQ process numbers indicated by field #1 in COT#2A. One or more HARQ process numbers may be indicated by field #1 in SCI#A and are requested to transmit corresponding HARQ-ACK feedback in the same PSFCH transmission opportunity. That is, it is requested to transmit HARQ-ACK feedback associated with (several) HARQ process numbers indicated by field #1 in COT#2A. In other words, the HARQ-ACK feedback to be transmitted in COT#2A corresponds to (several) previous PSSCHs associated with (several) HARQ process numbers indicated by field #1 in SCI#A.

[0137] The HARQ-ACK feedback to be transmitted in COT#2A may include deferred HARQ-ACK feedback that could not be responded to in (several) previous COTs due to, for example, UE processing delay, HARQ-ACK feedback that could not be transmitted in (several) previous COTs due to channel access process failure, HARQ-ACK feedback that could not be correctly received in (several) previous COTs due to, for example, hidden node interference, or any combination thereof. In other words, the (several) HARQ process numbers indicated by field #1 may include HARQ process numbers associated with deferred HARQ-ACK feedback, HARQ process numbers associated with HARQ-ACK feedback that could not be transmitted in the previous COT due to channel access process failure, HARQ process numbers associated with HARQ-ACK feedback that UE#1A did not correctly receive in the previous COT, or any combination thereof.

[0138] SCI#A may further include another HARQ process number field (denoted as field #2) indicating a HARQ process number associated with a PSSCH scheduled by SCI#A or a HARQ-ACK feedback for a scheduled PSSCH. In some embodiments, in the case where field #1 indicates the same HARQ process number as field #2, it may be suggested that field #1 does not request the transmission of any HARQ-ACK feedback corresponding to the previous PSSCH. That is, the same HARQ process number indicated by two HARQ process number fields in the SCI may indicate an invalid situation.

[0139] For example, when a UE (e.g., UE#1A) starts a new COT, it may transmit an SCI with a HARQ process number indication (e.g., a HARQ process number field) requesting (several) Rx UEs (e.g., UE#2A) to transmit corresponding HARQ-ACK feedback of (several) previous PSSCHs in the new COT. For the Rx UE, since it can know the requested HARQ-ACK feedback based on the HARQ process number indication, it can transmit the requested HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ process number indication.

[0140] In some embodiments of the present disclosure, SCI#A may be an SCI specifically used to request HARQ-ACK feedback. That is, a new SCI format may be introduced to request HARQ-ACK feedback for (several) previous PSSCHs. SCI#A may not schedule any PSSCH.

[0141] For example, SCI#A may include a HARQ process number field indicating the HARQ process number (several) associated with the HARQ-ACK feedback to be transmitted in COT#2A. One or more HARQ process numbers may be indicated by the HARQ process number field in SCI#A and are requested to be used to transmit corresponding HARQ-ACK feedback in the same PSFCH transmission opportunity. In other words, the HARQ-ACK feedback to be transmitted in COT#2A corresponds to the (several) previous PSSCHs associated with the HARQ process number indicated by the HARQ process number field in SCI#A.

[0142] The HARQ-ACK feedback to be transmitted in COT#2A may include deferred HARQ-ACK feedback that could not be responded to in (several) previous COTs due to, for example, UE processing delay, HARQ-ACK feedback that could not be transmitted in (several) previous COTs due to channel access process failure, HARQ-ACK feedback that could not be correctly received in (several) previous COTs due to, for example, hidden node interference, or any combination thereof. In other words, the (several) HARQ process numbers indicated by the HARQ process number field may include a HARQ process number associated with deferred HARQ-ACK feedback, a HARQ process number associated with HARQ-ACK feedback that could not be transmitted in the previous COT due to channel access process failure, a HARQ process number associated with HARQ-ACK feedback that UE#1A did not correctly receive in the previous COT, or any combination thereof.

[0143] For example, when a UE (e.g., UE#1A) starts a new COT, it may transmit an SCI with a HARQ process number indication (e.g., a HARQ process number field) requesting (several) Rx UEs (e.g., UE#2A) to transmit corresponding HARQ-ACK feedback in the new COT. For the Rx UE, since it can know the requested HARQ-ACK feedback (and the corresponding (several) PSSCHs) based on the HARQ process number indication, it may transmit the requested HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ process number indication.

[0144] The cancellation mechanism of PSFCH transmission opportunity can be implemented in various ways.

[0145] For example, UE#1A may start a COT (denoted as COT#1B) and transmit a PSSCH to an Rx UE (e.g., UE#2A) in COT#1B. UE#1A may determine the PSFCH transmission timing within COT#1B. However, in some cases, UE#1A may determine to cancel the PSFCH transmission timing within COT#1B. The following are some examples of such situations. For example, the HARQ-ACK feedback of the PSSCH transmitted in the time slot is disabled, wherein the corresponding HARQ-ACK feedback will be transmitted in the PSFCH transmission timing. For example, the HARQ-ACK feedback will not be transmitted in the PSFCH transmission timing. For example, UE#1A may determine that the HARQ-ACK feedback of (several) PSSCHs transmitted in the time slot within COT#1B will be transmitted outside COT#1B. In response to the above situation, UE#1A may determine to cancel the PSFCH transmission timing. In response to determining to cancel the PSFCH transmission timing, UE#1A may perform continuous transmission in the canceled PSFCH transmission timing. Continuous transmission can be implemented in various ways.

[0146] For example, in some embodiments of the present disclosure, UE#1A may continuously transmit the ongoing PSSCH in the PSFCH transmission opportunity. For example, UE#1A may continuously transmit the ongoing PSSCH until the end of the time slot in which the PSFCH transmission opportunity is canceled, so as to fully occupy the time slot. For example, the PSFCH transmission opportunity and the gap symbol for the PSFCH transmission opportunity (if any) may be used by the ongoing PSSCH for sidelink transmission. The gap symbol of the PSFCH transmission opportunity may include a symbol before the PSFCH transmission opportunity (e.g., one symbol), a symbol after the PSFCH transmission opportunity (e.g., one symbol), or both, as described above. In these embodiments, symbols are not wasted for the canceled PSFCH transmission opportunity.

[0147] In some embodiments of the present disclosure, UE#1A may continuously transmit a signal (e.g., signal #B) after the ongoing PSSCH in the canceled PSFCH transmission opportunity and the gap symbol of the PSFCH transmission opportunity (if any) without a gap greater than the minimum sensing interval (e.g., 16us or 25us). For example, UE#1A may transmit a signal after the ongoing PSSCH until the end of the time slot in which the PSFCH transmission opportunity is canceled so as to fully occupy the time slot. For example, the PSFCH transmission opportunity and the gap symbol of the PSFCH transmission opportunity are used to transmit signal #B. For example, the gap between the PSSCH and signal #B in the time slot may be less than or equal to the minimum sensing interval.

[0148] Signal #B can be implemented in various ways. For example, signal #B can be a repetition of one or more last symbols of the ongoing PSSCH. For example, signal #B can be a repetition of one or more first symbols of the next time slot. For example, signal #B can be any other signal that a person skilled in the art can imagine.

[0149] In some embodiments of the present disclosure, UE#1A may transmit a signal only for a reserved channel in a cancelled PSFCH transmission opportunity.

[0150] For example, UE#1A may transmit an interleaving-based channel (e.g., an interleaving-based PSFCH) in a cancelled PSFCH transmission opportunity (e.g., two symbols reserved for PSFCH transmission). The channel may be transmitted on an interleaving randomly selected from the available interleavings or on a default interleaving (e.g., the lowest or highest interleaving) predefined or (pre)configured in (several) standards.

[0151] For the gap symbol (if any) before or after the canceled PSFCH transmission opportunity, UE#1A may also transmit (several) signals on (several) gap symbols so that there is no gap greater than the minimum sensing interval (e.g., 16us or 25us). For example, UE#1A may extend the cyclic prefix (CP) of the first symbol of the interleaved channel or the last symbol of the ongoing PSSCH in the gap symbol before the PSFCH transmission opportunity. UE#1A may extend the CP of the first symbol of the next time slot or the last symbol of the interleaved channel in the gap symbol after the PSFCH transmission opportunity.

[0152] In some examples, from the perspective of a Tx UE (e.g., UE#1A), UE#1A may transmit an SCI scheduling a PSSCH within a COT initiated by UE#1A to an Rx UE (e.g., UE#2A). UE#1A may determine a PSFCH transmission opportunity within the COT based on the PSFCH periodicity with reference to the COT. UE#1A may determine whether HARQ-ACK feedback of a scheduled PSSCH will be transmitted in a PSFCH transmission opportunity within the COT or will be transmitted outside the COT, or whether to cancel the PSFCH transmission opportunity.

[0153] In some instances, UE#1A may determine whether to transmit HARQ-ACK feedback for the scheduled PSSCH in a PSFCH transmission opportunity within the COT. In response to determining that HARQ-ACK feedback will be transmitted in a PSFCH transmission opportunity within the COT, UE#1A may leave the gap symbol of the first PSFCH opportunity within the COT blank. In some instances, UE#1A may determine to cancel the PSFCH transmission opportunity within the COT, and may perform continuous transmission in the canceled PSFCH opportunity. In some instances, UE#1A may determine that HARQ-ACK feedback will be transmitted outside the COT, so a new COT may be started after the previous COT, and UE#2A may be triggered to transmit HARQ-ACK feedback in the new COT.

[0154] In some embodiments, from the perspective of the Rx UE of UE#1A (e.g., UE#2A), UE#2A may receive SCI from UE#1A that schedules the PSSCH within the COT initiated by UE#1A. UE#2A may determine whether to transmit HARQ-ACK feedback of the received PSSCH in the PSFCH transmission opportunity within the COT. The PSFCH transmission timing may be determined based on the PSFCH periodicity with reference to the COT. In response to determining that the HARQ-ACK feedback will be transmitted in the PSFCH transmission opportunity within the COT, UE#2A may perform a channel access procedure (e.g., channel access type 2) in the gap symbol (e.g., one symbol before the PSFCH transmission opportunity) for the PSFCH transmission opportunity within the COT. UE#2A may transmit HARQ-ACK feedback to UE#1A in the PSFCH transmission opportunity in response to the channel access procedure being successful. UE#1A may perform a channel access procedure (eg, channel access type 2) after the PSFCH transmission opportunity (eg, in the gap symbol of the PSFCH transmission opportunity) before it resumes its sidelink transmission in the COT.

[0155] In some instances, UE#2A may determine to disable HARQ-ACK feedback received via PSSCH, and therefore may not transmit in the PSFCH transmission opportunity. In some instances, in response to determining that HARQ-ACK feedback will be transmitted outside the COT, UE#2A may postpone transmitting the HARQ-ACK feedback until a trigger signal requesting the transmission of HARQ-ACK feedback is received. For example, UE#2A may receive SCI from UE#1A in a new COT initiated by UE#1A, requesting the transmission of HARQ-ACK feedback in the PSFCH opportunity within the new COT. The PSFCH opportunity within the new COT is determined based on the PSFCH periodicity with reference to the new COT. Then, UE#2A may transmit the requested HARQ-ACK feedback in the PSFCH opportunity within the new COT.

[0156] Figure 3 An exemplary periodic PFSCH configuration 300 is shown according to some embodiments of the present disclosure. Figure 3 , the PSFCH periodicity is 4 time slots. The PSFCH transmission opportunity is determined based on the PSFCH periodicity and the initial time slot of the COT. For example, (several) UEs may start COT 351 and COT 352. Based on the PSFCH periodicity and the initial time slot of COT 351, time slot n+4 may include PFSCH opportunity 321. Based on the PSFCH periodicity and the initial time slot of COT 352, time slot n+10 and time slot n+14 may include PFSCH opportunities 322 and 323, respectively.

[0157] In some examples, a Tx UE that activates COT 351 may transmit PSSCH 311 and 312 in slot n+1 and slot n+2. HARQ-ACK feedback for PSSCH 311 and 312 may be transmitted in PSFCH opportunity 321. The Tx UE may leave the gap symbol before PSFCH opportunity 321 blank so that (several) Rx UEs that receive PSSCH 311 and 312 may perform a channel access procedure in the gap symbol.

[0158] The Tx UE may also transmit PSSCH 313 and 314 in slot n+3 and slot n+4. HARQ-ACK feedback for PSSCH 313 and 314 may be transmitted outside COT 351. Therefore, HARQ-ACK feedback for PSSCH 313 and 314 may be postponed. The Rx UE receiving PSSCH 313 and 314 may wait for a trigger signal requesting transmission of HARQ-ACK feedback for PSSCH 313 and 314. In some examples, the Tx UE may activate COT 352 and may transmit SCI in PFSCH opportunity 322 to trigger transmission of HARQ-ACK feedback for PSSCH 313 and 314. The Tx UE may also transmit PSSCH 315 to 319 and 331 to 333 in slots n+7 to n+14, respectively. The HARQ-ACK feedback for PSSCH 315 to 319 and 331 may be transmitted within the COT 352. For example, the HARQ-ACK feedback for PSSCH 315 and 316 may be transmitted in the PFSCH opportunity 322, as well as the deferred HARQ-ACK feedback for PSSCH 313 and 314. The HARQ-ACK feedback for PSSCH 317 to 319 and 331 may be transmitted in the PFSCH opportunity 323. The HARQ-ACK feedback for PSSCH 332 and 333 may be transmitted outside the COT 352 and thus deferred. The HARQ-ACK feedback for PSSCH 332 and 333 may be triggered for transmission in a similar manner as the HARQ-ACK feedback for PSSCH 313 and 314.

[0159] In some embodiments of the present disclosure, for sidelink transmissions via unlicensed spectrum, the PSFCH transmission timing may be dynamically determined based on the HARQ-ACK feedback timing from the PSSCH to the corresponding PSFCH.

[0160] For a UE that wishes to transmit a PSFCH, a channel access procedure (e.g., channel access type 1 or channel access type 2) is performed before transmitting the PSFCH in the PSFCH transmission opportunity. The PSFCH transmission opportunity may be defined with reference to the time slot in which the corresponding PSSCH is transmitted and the dynamically indicated time slot level offset. For example, time slot k may have a PSFCH transmission opportunity resource if k=n+x, where x is the dynamically indicated time slot level offset and n is the time slot in which the corresponding PSSCH is transmitted. In this way, the PSFCH transmission opportunity is fully dynamically changed in the time domain.

[0161] The Tx UE (denoted as UE#1B for simplicity) may start the COT by performing a channel access procedure (e.g., channel access type 1). UE#1B may transmit at least one SCI scheduling at least one PSSCH in the COT. UE#1B may dynamically determine a PSFCH transmission timing corresponding to at least one PSSCH transmitted in a set of time slots in the COT. In some embodiments, the SCI may include a HARQ-ACK feedback timing indicator of UE#1B to determine a PSFCH transmission timing for transmitting HARQ-ACK feedback of a scheduled PSSCH.

[0162] For example, the HARQ-ACK feedback timing indicator included in the SCI may indicate a slot level offset between a time slot in which a PSSCH scheduled by the SCI is transmitted and a time slot in which a corresponding PSFCH transmission opportunity is determined (e.g., a time slot in which HARQ-ACK feedback for a scheduled PSSCH is transmitted). For example, UE#1B may determine a PSFCH transmission opportunity in time slot k corresponding to a PSSCH transmitted in time slot n, and then UE#1B may indicate a slot level offset x=kn via the HARQ-ACK feedback timing indicator.

[0163] In some embodiments, the slot level offset may be indicated from a set of HARQ-ACK feedback timing values, which may include {0, +1, +2, +3, +4, +5, +6, +7} or other larger or smaller values. In some embodiments, the set of HARQ-ACK feedback timing values ​​may be configured by RRC signaling or predefined in (several) standards. Assuming that the set of HARQ-ACK feedback timing values ​​includes N values, then at least N may be required in the SCI. The ones digit indicates a value in the set of values.

[0164] In this way, the PSFCH transmission timing may be changed according to the transmission strategy of UE#1B and may vary depending on the COT.

[0165] In some embodiments, UE#1B may determine that HARQ-ACK feedback corresponding to PSSCH will be transmitted in the current COT. In some embodiments, if HARQ-ACK feedback corresponding to PSSCH will be transmitted outside the current COT, UE#1B may postpone the HARQ-ACK feedback. In some embodiments, UE#1B may trigger the corresponding Rx UE to transmit the postponed HARQ-ACK feedback after UE#1B starts a new COT. In some embodiments, UE#1B may instruct the corresponding Rx UE to transmit HARQ-ACK feedback, even if the HARQ-ACK feedback may be transmitted outside the current COT. In some embodiments, UE#1B may instruct the corresponding Rx UE to deactivate HARQ-ACK feedback. Correspondingly, the PSFCH transmission timing is dynamically indicated by UE#1B to enable the Rx UE to transmit the HARQ-ACK feedback corresponding to the PSSCH. Details on the relationship between the transmission strategy, PSFCH transmission timing, and HARQ-ACK feedback timing indicator will be described below.

[0166] In some embodiments, the channel access type (or LBT type) may also be indicated in the SCI so that the Rx UE transmits the corresponding HARQ-ACK feedback or PSFCH. For example, in the case where the HARQ-ACK feedback or PSFCH of the PSSCH will be transmitted within the COT initiated by UE#1B, UE#1B may indicate channel access type 2 (e.g., channel access type 2A, 2B, or 2C) to the Rx UE receiving the PSSCH. For example, in the case where the HARQ-ACK feedback or PSFCH of the PSSCH will be transmitted outside the COT initiated by UE#1B, UE#1B may indicate channel access type 1 to the Rx UE receiving the PSSCH. In some embodiments, the channel access type may be indicated using the CAPC or CP extension in the SCI. In some embodiments, the channel access type may be indicated separately in the SCI (e.g., without the CAPC or CP extension).

[0167] In some embodiments, the SCI may also include an indicator for indicating whether the HARQ-ACK feedback or PSFCH corresponding to the PSSCH scheduled by the SCI will be transmitted within the COT or outside the COT. For example, in the case where the HARQ-ACK feedback or PSFCH of the PSSCH will be transmitted within the COT initiated by UE#1B, UE#1B may indicate that the HARQ-ACK feedback or PSFCH is within the COT, so that the Rx UE can perform channel access type 2 (e.g., channel access type 2A, 2B, or 2C) before transmitting the HARQ-ACK feedback or PSFCH. For example, in the case where the HARQ-ACK feedback or PSFCH of the PSSCH will be transmitted outside the COT initiated by UE#1B, UE#1B may indicate that the HARQ-ACK feedback or PSFCH is outside the COT, so that the Rx UE can perform channel access type 1 before transmitting the HARQ-ACK feedback or PSFCH. This indicator may include at least one bit. For example, a value of '0' for the indicator indicates that HARQ-ACK feedback or PSFCH of PSSCH will be transmitted within the COT, and a value of '1' for the indicator indicates that HARQ-ACK feedback or PSFCH of PSSCH will be transmitted outside the COT; or vice versa.

[0168] In this way, the PSFCH transmission opportunity can be within the COT initiated by the Tx UE, which ensures a high LBT success probability due to the required channel access procedure (e.g., channel access type 2, such as channel access type 2A, 2B or 2C). The ongoing sidelink transmission from UE#1B will not be interrupted by the PSFCH transmission opportunity, especially when the PSFCH transmission opportunity is located at the end of the current COT or outside the current COT. If the sidelink HARQ-ACK feedback is outside the current COT or is not successfully received, UE#1B can easily trigger the Rx UE to (re)transmit the sidelink HARQ-ACK feedback. There is no need to define PSFCH periodicity in these embodiments.

[0169] As described above, the PSFCH transmission timing may be dynamically changed according to the transmission strategy of the Tx UE. For example, UE#1B may start COT (denoted as COT#1C). UE#1B may transmit SCI to the Rx UE (denoted as UE#2B) in COT#1C to schedule PSSCH in COT#1C. UE#1B may set the HARQ-ACK feedback timing indicator in SCI based on the transmission strategy.

[0170] For example, UE#1B may determine whether to transmit HARQ-ACK feedback for the scheduled PSSCH in COT#1C (eg, in a PSFCH transmission opportunity in COT#1C).

[0171] In some embodiments, in response to determining (e.g., based on UE processing delay) that HARQ-ACK feedback for PSSCH will be transmitted within COT #1C, UE #1B may set the HARQ-ACK feedback timing indicator in the SCI to a HARQ-ACK feedback timing value (i.e., an applicable value) indicating a PSFCH transmission opportunity for transmitting HARQ-ACK feedback. The PSFCH transmission opportunity is within COT #1C. UE #2B may perform a channel access procedure (e.g., channel access type 2, such as channel access type 2A, 2B, or 2C) before transmitting HARQ-ACK feedback or PSFCH in a PSFCH transmission opportunity within the COT.

[0172] For example, UE#1B may leave the (several) interstitial symbols of the PSFCH transmission opportunity blank. UE#2B may perform a channel access procedure in the interstitial symbols before the PSFCH transmission opportunity. For example, UE#1B may perform a channel access procedure (e.g., channel access type 2) in the interstitial symbols after the PSFCH transmission opportunity before UE#1B resumes transmission in COT#1C (e.g., in the next time slot).

[0173] In some embodiments, in response to determining (e.g., based on UE processing delay) that HARQ-ACK feedback for PSSCH will be transmitted outside COT#1C, UE#1B may set the HARQ-ACK feedback timing indicator in the SCI to indicate an inapplicable HARQ-ACK feedback timing value or a reserved code point. In this way, the HARQ-ACK feedback is postponed. The inapplicable HARQ-ACK feedback timing value may be from a set of HARQ-ACK feedback timing values ​​and may be a negative value (e.g., -1). UE#1B may start a new COT after COT#1C, and then trigger UE#2B to transmit the postponed HARQ-ACK feedback in the PSFCH transmission opportunity within the new COT. For example, UE#1B may perform a channel access procedure (e.g., channel access type 1) to start a new COT, and may transmit SCI in the new COT to request UE#2B to transmit HARQ-ACK feedback in the PSFCH transmission opportunity within the new COT. The PSFCH transmission timing within the new COT may be determined based on the HARQ-ACK feedback timing value (eg, an applicable value) indicated by the HARQ-ACK feedback timing indicator in the SCI transmitted in the new COT.

[0174] In some embodiments, in response to determining (e.g., based on UE processing delay) that HARQ-ACK feedback for PSSCH will be transmitted outside COT#1C, UE#1B may set the HARQ-ACK feedback timing indicator in the SCI to a HARQ-ACK feedback timing value indicating a PSFCH transmission opportunity for transmitting HARQ-ACK feedback. The PSFCH transmission opportunity is outside COT#1C. That is, the indicated HARQ-ACK feedback timing value is an applicable value and points to a time slot outside COT#1C.

[0175] In response to receiving the SCI, UE#2B may perform a channel access procedure for transmitting HARQ-ACK feedback in the indicated PSFCH transmission opportunity. For example, the channel access procedure may be a channel access type 1 procedure for starting a new COT. The indicated PSFCH transmission opportunity is within the new COT. The channel access procedure may be associated with the lowest CAPC value. For example, the channel access procedure may be a channel access type 2 procedure.

[0176] In some examples, in response to a successful channel access procedure, UE#2B may transmit HARQ-ACK feedback in the indicated PSFCH transmission opportunity. In response to an unsuccessful channel access procedure, UE#2B may discard the indicated PSFCH transmission opportunity (or the PSFCH or HARQ-ACK feedback that was intended to be transmitted in the PSFCH opportunity).

[0177] After UE#1B indicates the applicable HARQ-ACK feedback timing value to UE#2B, UE#1B may attempt to receive HARQ-ACK feedback (or PSFCH) in the indicated PSFCH transmission opportunity. In some embodiments, when UE#1B fails to detect or receive HARQ-ACK feedback (or PSFCH) from UE#2B in the indicated PSFCH transmission opportunity, UE#1B may trigger UE#2B to (re)transmit HARQ-ACK feedback (or PSFCH) in a new COT initiated by UE#1B. For example, UE#1B may transmit SCI to UE#2B in the new COT initiated by UE#1B for requesting to transmit HARQ-ACK feedback in the new COT.

[0178] In some embodiments, UE#1B may determine whether to disable HARQ-ACK feedback for the PSSCH scheduled in COT#1C. In response to determining to disable HARQ-ACK feedback for the PSSCH, UE#1B may perform at least one of the following: setting the HARQ-ACK feedback timing indicator in the SCI for scheduling the PSSCH to indicate a specific HARQ-ACK feedback timing value or a reserved code point; or setting the HARQ enable / disable indicator in the SCI for scheduling the PSSCH to disable HARQ-ACK feedback for the first PSSCH. The specific HARQ-ACK feedback timing value may be an inapplicable value (e.g., -2). The specific HARQ-ACK feedback timing value may be a predefined value. The specific HARQ-ACK feedback timing value may be from a set of HARQ-ACK feedback timing values. The HARQ enable / disable indicator may include at least one bit indicating whether the corresponding HARQ-ACK feedback is disabled or enabled.

[0179] The triggering mechanism for requesting sidelink HARQ-ACK feedback (eg, for PSSCH in a previous COT) may be implemented in various ways.

[0180] For example, UE#1B may start a COT (denoted as COT#1D) and transmit a PSSCH to an Rx UE (e.g., UE#2B) in COT#1D. In some instances, UE#1B may determine that HARQ-ACK feedback (or PSFCH) for PSSCH cannot be transmitted within COT#1D. UE#1B may perform a channel access procedure (e.g., channel access type 1) to start another COT (denoted as COT#2D), and may trigger UE#2B to transmit a deferred HARQ-ACK feedback in a PSFCH transmission opportunity within COT#2D. COT#2D is outside COT#1D.

[0181] In some embodiments of the present disclosure, UE#1B may transmit SCI (denoted as SCI#B) in COT#2D to request UE#2B to transmit deferred HARQ-ACK feedback in a PSFCH transmission opportunity within COT#2D. The PSFCH transmission opportunity may be indicated by a HARQ-ACK feedback timing indicator in SCI#B and may be within COT#2D. For example, the HARQ-ACK feedback timing indicator in SCI#B may indicate an applicable HARQ-ACK feedback timing value from a set of HARQ-ACK feedback timing values.

[0182] For example, in some embodiments of the present disclosure, SCI#B may schedule PSSCH in COT#2D. SCI#B may include a HARQ-ACK feedback request indicator requesting transmission of deferred HARQ-ACK feedback within COT#2D. The size of the HARQ-ACK feedback request indicator may be at least one bit.

[0183] For example, when a UE (e.g., UE#1B) starts a new COT, it may transmit an SCI with a HARQ-ACK feedback request indicator requesting (several) Rx UEs (e.g., UE#2B) to transmit deferred HARQ-ACK feedback in the new COT. For the Rx UE, since it knows the deferred HARQ-ACK feedback (e.g., by determining that the HARQ-ACK feedback cannot be transmitted in the (several) previous COTs), it may transmit the deferred HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ-ACK feedback request indicator.

[0184] In some embodiments of the present disclosure, SCI#B may schedule PSSCH in COT#2D. SCI#B may include a HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests the transmission of HARQ-ACK feedback associated with (several) HARQ process numbers indicated by the HARQ process number field in COT#2D. One or more HARQ process numbers may be indicated by the HARQ process number field in SCI#B and are requested to transmit corresponding HARQ-ACK feedback in the same PSFCH transmission opportunity. That is, the HARQ-ACK feedback associated with (several) HARQ process numbers indicated by the HARQ process number field is requested to be transmitted in COT#2D. In other words, the HARQ-ACK feedback to be transmitted in COT#2D corresponds to (several) previous PSSCHs associated with the HARQ process number indicated by the HARQ process number field in SCI#B.

[0185] The HARQ-ACK feedback to be transmitted in COT#2D may include deferred HARQ-ACK feedback that could not be responded to in (several) previous COTs due to, for example, UE processing delay, HARQ-ACK feedback that could not be transmitted in (several) previous COTs due to channel access process failure, HARQ-ACK feedback that could not be correctly received in (several) previous COTs due to, for example, hidden node interference, or any combination thereof. In other words, the (several) HARQ process numbers indicated by the HARQ process number field may include a HARQ process number associated with deferred HARQ-ACK feedback, a HARQ process number associated with HARQ-ACK feedback that could not be transmitted in the previous COT due to channel access process failure, a HARQ process number associated with HARQ-ACK feedback that UE#1B did not correctly receive in the previous COT, or any combination thereof.

[0186] For example, when a UE (e.g., UE#1B) starts a new COT, it may transmit an SCI having a HARQ-ACK feedback request indicator and an associated HARQ process number indication (e.g., a HARQ process number field) requesting (several) Rx UEs (e.g., UE#2B) to transmit corresponding HARQ-ACK feedback in the new COT. For the Rx UE, since it can know the requested HARQ-ACK feedback based on the associated HARQ process number indication, it can transmit the requested HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ-ACK feedback request indicator and the associated HARQ process number indication.

[0187] SCI#B may further include another HARQ process number field, which indicates a HARQ process number associated with a PSSCH scheduled by SCI#B or a HARQ-ACK feedback of a scheduled PSSCH.

[0188] In some embodiments of the present disclosure, SCI#B may schedule PSSCH in COT#2D. Compared with the previous embodiment, SCI#B may not include a HARQ-ACK feedback request indicator. SCI#B may include a HARQ process number field (denoted as field #1'), which requests the transmission of HARQ-ACK feedback associated with (several) HARQ process numbers indicated by field #1' in COT#2D. One or more HARQ process numbers may be indicated by field #1' in SCI#B and are requested to transmit corresponding HARQ-ACK feedback in the same PSFCH transmission opportunity. That is, it is requested to transmit HARQ-ACK feedback associated with (several) HARQ process numbers indicated by field #1' in COT#2D. In other words, the HARQ-ACK feedback to be transmitted in COT#2D corresponds to (several) previous PSSCHs associated with (several) HARQ process numbers indicated by field #1' in SCI#B.

[0189] The HARQ-ACK feedback to be transmitted in COT#2D may include deferred HARQ-ACK feedback that could not be responded to in (several) previous COTs due to, for example, UE processing delay, HARQ-ACK feedback that could not be transmitted in (several) previous COTs due to channel access process failure, HARQ-ACK feedback that could not be correctly received in (several) previous COTs due to, for example, hidden node interference, or any combination thereof. In other words, the (several) HARQ process numbers indicated by field #1' may include HARQ process numbers associated with deferred HARQ-ACK feedback, HARQ process numbers associated with HARQ-ACK feedback that could not be transmitted in the previous COT due to channel access process failure, HARQ process numbers associated with HARQ-ACK feedback that UE#1B did not correctly receive in the previous COT, or any combination thereof.

[0190] SCI#B may further include another HARQ process number field (denoted as field #2') indicating a HARQ process number associated with a PSSCH scheduled by SCI#B or a HARQ-ACK feedback of a scheduled PSSCH. In some embodiments, in the case where field #1' indicates the same HARQ process number as field #2', it may be suggested that field #1' does not request the transmission of any HARQ-ACK feedback corresponding to the previous PSSCH. That is, the same HARQ process number indicated by two HARQ process number fields in the SCI may indicate an invalid situation.

[0191] For example, when a UE (e.g., UE#1B) starts a new COT, it may transmit an SCI with a HARQ process number indication (e.g., a HARQ process number field) requesting (several) Rx UEs (e.g., UE#2B) to transmit corresponding HARQ-ACK feedback of (several) previous PSSCHs in the new COT. For the Rx UE, since it can know the requested HARQ-ACK feedback based on the HARQ process number indication, it can transmit the requested HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ process number indication.

[0192] In some embodiments of the present disclosure, SCI#B may be an SCI specifically used to request HARQ-ACK feedback. That is, a new SCI format may be introduced for requesting HARQ-ACK feedback for (several) previous PSSCHs. SCI#B may not schedule any PSSCH, and the HARQ-ACK feedback timing indicator included in the SCI may indicate the HARQ-ACK feedback timing from the time slot in which the SCI is transmitted and the time slot in which the HARQ-ACK feedback is to be transmitted.

[0193] For example, SCI#B may include a HARQ process number field indicating the HARQ process number (several) associated with the HARQ-ACK feedback to be transmitted in COT#2D. One or more HARQ process numbers may be indicated by the HARQ process number field in SCI#B and are requested to be used to transmit corresponding HARQ-ACK feedback in the same PSFCH transmission opportunity. In other words, the HARQ-ACK feedback to be transmitted in COT#2D corresponds to the (several) previous PSSCHs associated with the HARQ process number indicated by the HARQ process number field in SCI#B.

[0194] The HARQ-ACK feedback to be transmitted in COT#2D may include deferred HARQ-ACK feedback that could not be responded to in (several) previous COTs due to, for example, UE processing delay, HARQ-ACK feedback that could not be transmitted in (several) previous COTs due to channel access process failure, HARQ-ACK feedback that could not be correctly received in (several) previous COTs due to, for example, hidden node interference, or any combination thereof. In other words, the (several) HARQ process numbers indicated by the HARQ process number field may include a HARQ process number associated with deferred HARQ-ACK feedback, a HARQ process number associated with HARQ-ACK feedback that could not be transmitted in the previous COT due to channel access process failure, a HARQ process number associated with HARQ-ACK feedback that UE#1B did not correctly receive in the previous COT, or any combination thereof.

[0195] For example, when a UE (e.g., UE#1B) starts a new COT, it may transmit an SCI with a HARQ process number indication (e.g., a HARQ process number field) requesting (several) Rx UEs (e.g., UE#2B) to transmit corresponding HARQ-ACK feedback in the new COT. For the Rx UE, since it can know the requested HARQ-ACK feedback (and the corresponding (several) PSSCHs) based on the HARQ process number indication, it may transmit the requested HARQ-ACK feedback in the new COT in response to receiving the SCI, wherein the SCI includes the HARQ process number indication.

[0196] Figure 4 An exemplary dynamic PFSCH transmission timing according to some embodiments of the present disclosure is shown. Figure 4 In the process, the PSFCH transmission timing is dynamically determined.

[0197] For example, a Tx UE that starts COT 451 may transmit SCI to schedule PSSCH 411 to 414 in slots n+1 to n+4. The Tx UE may determine that HARQ-ACK feedback for PSSCH 411 and 412 may be transmitted within COT 451, and then the HARQ-ACK feedback timing indicator in the SCI that schedules PSSCH 411 and 412 may be set to indicate PSFCH opportunity 421 or slot n+4 where PSFCH opportunity 421 is located. The Tx UE may leave the gap symbol before PSFCH opportunity 421 blank so that (several) Rx UEs that receive PSSCH 411 and 412 may perform a channel access procedure in the gap symbol. (Several) Rx UEs that receive PSSCH 411 and 412 may determine PSFCH opportunity 421 in response to receiving the corresponding SCI. Before transmitting HARQ-ACK feedback of PSSCH 411 and 412 in PSFCH opportunity 421 , Rx UE(s) may perform a channel access procedure in the gap symbol before PSFCH opportunity 421 .

[0198] In some examples, for example, when the Tx UE determines that the HARQ-ACK feedback of the PSSCHs 413 and 414 cannot be transmitted within the COT 451, the Tx UE may determine to postpone the HARQ-ACK feedback of the PSSCHs 413 and 414. The Tx UE may set the HARQ-ACK feedback timing indicator in the SCI that schedules the PSSCHs 413 and 414 to indicate an inapplicable value (e.g., a predefined inapplicable HARQ-ACK feedback timing value). In response to receiving the SCI that schedules the PSSCHs 413 and 414, the (several) Rx UEs will know that the HARQ-ACK feedback of the PSSCHs 413 and 414 is postponed based on the indicated inapplicable value, and may wait for a trigger signal requesting the transmission of the HARQ-ACK feedback of the PSSCHs 413 and 414. In some examples, the Tx UE may start the COT 452 and may transmit an SCI in a PFSCH opportunity 422 to trigger the transmission of HARQ-ACK feedback for PSSCH 413 and 414. The Tx UE may also transmit PSSCH 415 to 418 in time slots n+7 to n+10, respectively. HARQ-ACK feedback for PSSCH 415 and 416 may be transmitted within the COT 452. The Tx UE may set the HARQ-ACK feedback timing indicator in the SCI that schedules PSSCH 415 and 416 to indicate the PFSCH opportunity 422. The Tx UE may leave the gap symbol before the PSFCH opportunity 422 blank so that (several) Rx UEs receiving PSSCH 413 to 416 may perform a channel access procedure in the gap symbol before the HARQ-ACK feedback is transmitted in the PFSCH opportunity 422.

[0199] In some examples, the Tx UE may determine that the HARQ-ACK feedback for PSSCH 417 and 418 cannot be transmitted within COT 452, and may indicate that the HARQ-ACK feedback for PSSCH 417 and 418 will be transmitted outside COT 452. For example, the Tx UE may set the HARQ-ACK feedback timing indicator in the SCI that schedules PSSCH 417 and 418 to indicate time slot n+12 (e.g., PFSCH opportunity 423). In response to receiving the SCI that schedules PSSCH 417 and 418, the Rx UE(s) will know that the HARQ-ACK feedback for PSSCH 417 and 418 should be transmitted in time slot n+12 (e.g., PFSCH opportunity 423). In some examples, the Rx UE(s) may perform a channel access procedure in the gap symbol prior to the PFSCH opportunity 423 and may transmit HARQ-ACK feedback for the PSSCH 417 and 418 in the PFSCH opportunity 423 in response to the channel access procedure being successful.

[0200] Figure 5 A flowchart illustrating an exemplary process 500 of wireless communication according to some embodiments of the present disclosure. The details described in all the above embodiments of the present disclosure apply to Figure 5 In some examples, the process may be performed by a UE (e.g., Figure 1 UE 110 in the system executes.

[0201] refer to Figure 5 In operation 511, the first UE may perform a first channel access procedure to start a first COT. For example, the first UE may be UE#1, UE#1A, or UE#1B as described above. In operation 513, the first UE may determine a first PSFCH opportunity within the first COT. In operation 515, the first UE may determine whether there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity.

[0202] In operation 517, the first UE may leave the gap symbol of the first PSFCH opportunity within the first COT blank in response to determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity; or the first UE may perform continuous transmission in the first PSFCH opportunity in response to determining that HARQ-ACK feedback will not be transmitted in the first PSFCH opportunity.

[0203] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the PSFCH resource pool.

[0204] In some embodiments of the present disclosure, determining the presence of HARQ-ACK feedback to be transmitted in a first PSFCH opportunity may include: determining a first HARQ-ACK feedback to be transmitted for a first PSSCH in a first PSFCH opportunity, wherein the first PSSCH is transmitted by a first UE; determining a second HARQ-ACK feedback to be transmitted for a second PSSCH in the first PSFCH opportunity, wherein the second PSSCH is received by the first UE; and determining a third HARQ-ACK feedback to be transmitted for a third PSSCH in the first PSFCH opportunity, wherein the third PSSCH is not transmitted or received by the first UE.

[0205] In some embodiments of the present disclosure, the first UE may perform energy detection or a second channel access process in the first PSFCH opportunity in response to being unable to determine whether there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, and perform continuous transmission in the remaining duration of the first PSFCH opportunity in response to the detected energy being lower than a threshold or the second channel access process being successful.

[0206] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the first COT.

[0207] In some embodiments of the present disclosure, the first UE may transmit the first PSSCH to the second UE in the first COT.The first UE may determine whether to transmit the first HARQ-ACK feedback of the first PSSCH in the first PSFCH opportunity or outside the first COT.

[0208] In some embodiments of the present disclosure, the first UE may perform a third channel access procedure to start a second COT after the first COT in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT, and transmit a second SCI to request the second UE to transmit the first HARQ-ACK feedback in a second PSFCH opportunity. The second PSFCH opportunity is within the second COT and is determined based on the PSFCH periodicity with reference to the second COT. In some embodiments of the present disclosure, the first UE may determine to cancel the first PSFCH opportunity in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT.

[0209] In some embodiments of the present disclosure, the first UE may perform continuous transmission in the first PSFCH opportunity in response to determining to cancel the first PSFCH opportunity.

[0210] In some embodiments of the present disclosure, the PSFCH periodicity is based on the CAPC used to perform the first channel access procedure. In some embodiments of the present disclosure, the PSFCH periodicity is based on the maximum duration of the first COT. In some embodiments of the present disclosure, the PSFCH periodicity is predefined or configured by RRC signaling.

[0211] In some embodiments of the present disclosure, the first UE may transmit a first SCI for scheduling a first PSSCH in a first COT to a second UE. The first SCI includes a HARQ-ACK feedback timing indicator for enabling the second UE to determine a PSFCH opportunity for transmitting a first HARQ-ACK feedback for the first PSSCH. The first UE may determine whether the first HARQ-ACK feedback will be transmitted in the first PSFCH opportunity or outside the first COT.

[0212] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset between a first time slot in which a first PSSCH is transmitted and a second time slot in which a first HARQ-ACK feedback for the first PSSCH is transmitted.

[0213] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset from a set of HARQ-ACK feedback timing values.

[0214] In some embodiments of the present disclosure, the first SCI indicates a channel access type for the second UE to transmit the first HARQ-ACK feedback.

[0215] In some embodiments of the present disclosure, the first UE may, in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT, set the HARQ-ACK feedback timing indicator in the first SCI to indicate an inapplicable HARQ-ACK feedback timing value (e.g., -1) or a reserved code point, perform a third channel access procedure to start a second COT after the first COT, and transmit a second SCI in the second COT to request the second UE to transmit the first HARQ-ACK feedback in the second PSFCH opportunity. The second PSFCH opportunity is within the second COT and is determined based on the HARQ-ACK feedback timing value indicated by the HARQ-ACK feedback timing indicator in the second SCI.

[0216] In some embodiments of the present disclosure, the first UE may, in response to determining that the first HARQ-ACK feedback for the first PSSCH will be transmitted outside the first COT, set the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value indicating a third PSFCH opportunity for transmitting the first HARQ-ACK feedback. The third PSFCH opportunity is outside the first COT.

[0217] In some embodiments of the present disclosure, the first UE may, in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted in the first PSFCH opportunity, set the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value indicating the first PSFCH opportunity for transmitting the first HARQ-ACK feedback.

[0218] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a HARQ-ACK feedback request indicator requesting transmission of the first HARQ-ACK feedback in the second COT.

[0219] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a first HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests transmission of HARQ-ACK feedback associated with the (several) HARQ process numbers indicated by the first HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the first HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0220] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a second HARQ process number field for requesting to transmit HARQ-ACK feedback of (several) previous PSSCHs associated with (several) HARQ process numbers indicated by the second HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the second HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0221] In some embodiments of the present disclosure, the second SCI is specifically used to request HARQ-ACK feedback, and the second SCI includes a third HARQ process number field indicating a HARQ process number associated with the first HARQ-ACK feedback.

[0222] In some embodiments of the present disclosure, the first HARQ process number field, the second HARQ process number field or the third HARQ process number field further indicates at least one of the following: a HARQ process number associated with HARQ-ACK feedback that cannot be transmitted in the first COT due to a channel access process failure, or a HARQ process number associated with HARQ-ACK feedback that the first UE did not correctly receive in the first COT.

[0223] In some embodiments of the present disclosure, when the second HARQ process number field indicates the same HARQ process number as the fourth HARQ process number field in the second SCI associated with the PSSCH scheduled by the second SCI, the second HARQ process number field does not request to transmit any HARQ-ACK feedback.

[0224] In some embodiments of the present disclosure, the first UE may receive the first HARQ-ACK feedback in a third PSFCH opportunity. In some embodiments of the present disclosure, in response to not receiving the first HARQ-ACK feedback in the third PSFCH opportunity, the first UE may perform a fourth channel access procedure to start a third COT after the third PSFCH opportunity, and transmit a third SCI in the third COT to request the second UE to transmit the first HARQ-ACK feedback in the third COT.

[0225] In some embodiments of the present disclosure, the first UE may determine whether to disable the first HARQ-ACK feedback of the first PSSCH. The first UE may perform at least one of the following in response to determining to disable the first HARQ-ACK feedback of the first PSSCH: setting the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value (e.g., -2) indicating inapplicability or a reserved code point; or setting a HARQ enable / disable indicator in the first SCI to disable the HARQ-ACK feedback of the first PSSCH.

[0226] Those skilled in the art will appreciate that the order of operations in exemplary process 500 may be changed, and some operations in exemplary process 500 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0227] Figure 6 A flowchart illustrating an exemplary process 600 of wireless communication according to some embodiments of the present disclosure. The details described in all the above embodiments of the present disclosure apply to Figure 6 In some examples, the process may be performed by a UE (e.g., Figure 1 UE 110 in the system executes.

[0228] refer to Figure 6 In operation 611, the second UE may receive from the first UE a first SCI for scheduling a first PSSCH within a first COT initiated by the first UE. For example, the first UE may be UE#1, UE#1A, or UE#1B as described above. The second UE may be UE#2, UE#2A, or UE#2B as described above.

[0229] In operation 613, the second UE may determine a first PSFCH opportunity within the first COT. In operation 615, the second UE may determine whether a first HARQ-ACK feedback of a first PSSCH will be transmitted in the first PSFCH opportunity.

[0230] In operation 617, in response to determining that a first HARQ-ACK feedback will be transmitted in a first PSFCH opportunity, the second UE may perform a first channel access process in a gap symbol of the first PSFCH opportunity within the first COT, and transmit a first HARQ-ACK feedback to the first UE in the first PSFCH opportunity in response to the first channel access process being successful.

[0231] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the PSFCH resource pool.

[0232] In some embodiments of the present disclosure, the first PSFCH opportunity is determined based on the PSFCH periodicity with reference to the first COT.

[0233] In some embodiments of the present disclosure, in response to determining that the first HARQ-ACK feedback of the first PSSCH will be transmitted outside the first COT, the second UE may postpone transmitting the first HARQ-ACK feedback until receiving a second SCI for requesting transmission of the first HARQ-ACK feedback in a second PSFCH opportunity from the first UE in a second COT initiated by the first UE. The second PSFCH opportunity is within the second COT and is determined based on the PSFCH periodicity with reference to the second COT.

[0234] In some embodiments of the present disclosure, the PSFCH periodicity is based on the CAPC used to perform the channel access procedure to start the first COT. In some embodiments of the present disclosure, the PSFCH periodicity is based on the maximum duration of the first COT. In some embodiments of the present disclosure, the PSFCH periodicity is predefined or configured by RRC signaling.

[0235] In some embodiments of the present disclosure, the first SCI includes a HARQ-ACK feedback timing indicator for the second UE to determine a PSFCH timing for transmitting a first HARQ-ACK feedback for a first PSSCH.

[0236] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset between a first time slot in which a first PSSCH is transmitted and a second time slot in which a first HARQ-ACK feedback for the first PSSCH is transmitted.

[0237] In some embodiments of the present disclosure, the HARQ-ACK feedback timing indicator indicates an offset from a set of HARQ-ACK feedback timing values.

[0238] In some embodiments of the present disclosure, the first SCI indicates a channel access type for the second UE to transmit the first HARQ-ACK feedback.

[0239] In some embodiments of the present disclosure, in a case where the HARQ-ACK feedback timing indicator in the first SCI indicates an inapplicable HARQ-ACK feedback timing value (e.g., -1) or a reserved code point, the second UE may postpone transmitting the first HARQ-ACK feedback until a second SCI for requesting transmission of the first HARQ-ACK feedback in a second PSFCH opportunity is received from the first UE in a second COT initiated by the first UE. The second PSFCH opportunity is within the second COT and is determined based on the HARQ-ACK feedback timing value indicated by the HARQ-ACK feedback timing indicator in the second SCI.

[0240] In some embodiments of the present disclosure, when the HARQ-ACK feedback timing indicator in the first SCI indicates an applicable HARQ-ACK feedback timing value for a third PSFCH opportunity outside the first COT for transmitting the first HARQ-ACK feedback, the second UE may transmit the first HARQ-ACK feedback in the third PSFCH opportunity.

[0241] In some embodiments of the present disclosure, when the HARQ-ACK feedback timing indicator in the first SCI indicates an applicable HARQ-ACK feedback timing value for the first PSFCH opportunity for transmitting the first HARQ-ACK feedback, the second UE may transmit the first HARQ-ACK feedback in the first PSFCH opportunity.

[0242] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a HARQ-ACK feedback request indicator requesting transmission of the first HARQ-ACK feedback in the second COT.

[0243] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a first HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests transmission of HARQ-ACK feedback associated with the (several) HARQ process numbers indicated by the first HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the first HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0244] In some embodiments of the present disclosure, the second SCI schedules the PSSCH in the second COT and includes a second HARQ process number field for requesting to transmit HARQ-ACK feedback of (several) previous PSSCHs associated with (several) HARQ process numbers indicated by the second HARQ process number field in the second COT. The (several) HARQ process numbers indicated by the second HARQ process number field include the HARQ process number associated with the first HARQ-ACK feedback.

[0245] In some embodiments of the present disclosure, the second SCI is specifically used to request HARQ-ACK feedback, and the second SCI includes a third HARQ process number field indicating a HARQ process number associated with the first HARQ-ACK feedback.

[0246] In some embodiments of the present disclosure, the first HARQ process number field, the second HARQ process number field or the third HARQ process number field further indicates at least one of the following: a HARQ process number associated with HARQ-ACK feedback that cannot be transmitted in the first COT due to a channel access process failure, or a HARQ process number associated with HARQ-ACK feedback that the first UE did not correctly receive in the first COT.

[0247] In some embodiments of the present disclosure, when the second HARQ process number field indicates the same HARQ process number as the fourth HARQ process number field in the second SCI associated with the PSSCH scheduled by the second SCI, the second HARQ process number field does not request to transmit any HARQ-ACK feedback.

[0248] In some embodiments of the present disclosure, the second UE may perform a second channel access procedure for transmitting the first HARQ-ACK feedback in the third PSFCH opportunity. In response to the second channel access procedure being successful, the second UE may transmit the first HARQ-ACK feedback in the third PSFCH opportunity. In response to the second channel access procedure being unsuccessful, the second UE may discard the third PSFCH opportunity.

[0249] In some embodiments of the present disclosure, in response to the second channel access procedure being unsuccessful, the second UE may receive, from the first UE in a third COT initiated by the first UE, a third SCI for requesting transmission of the first HARQ-ACK feedback in the third COT.

[0250] In some embodiments of the present disclosure, in the case where the first HARQ-ACK feedback of the first PSSCH is deactivated, the HARQ-ACK feedback timing indicator in the first SCI indicates an inapplicable HARQ-ACK feedback timing value (e.g., -2) or a reserved code point. In some embodiments of the present disclosure, in the case where the first HARQ-ACK feedback of the first PSSCH is deactivated, the HARQ enable / disable indicator in the first SCI indicates that the HARQ-ACK feedback of the first PSSCH is deactivated.

[0251] Those skilled in the art will appreciate that the order of operations in exemplary process 600 may be changed, and some operations in exemplary process 600 may be eliminated or modified without departing from the spirit and scope of the present disclosure.

[0252] Figure 7 700 according to some embodiments of the present disclosure. Figure 7 , the apparatus 700 may include at least one processor 706 and at least one transceiver 702 coupled to the processor 706. The apparatus 700 may be a UE.

[0253] Although elements such as at least one transceiver 702 and processor 706 are described in the singular in this figure, the plural form is contemplated unless explicitly stated to be limited to the singular form. In some embodiments of the present application, the transceiver 702 can be divided into two devices, such as a receiving circuit system and a transmitting circuit system. In some embodiments of the present application, the device 700 can further include an input device, a memory and / or other components.

[0254] According to some embodiments of the present application, the device 700 may be a UE. The transceiver 702 and the processor 706 may interact with each other to perform Figures 1 to 6 The operations of the UE are described in .

[0255] In some embodiments of the present application, the device 700 may further include at least one non-transitory computer-readable medium. For example, in some embodiments of the present disclosure, the non-transitory computer-readable medium may store thereon computer-executable instructions for causing the processor 706 to implement the method described above with respect to the UE. For example, when the computer-executable instructions are executed, the processor 706 interacts with the transceiver 702 to perform Figures 1 to 6 The operations of the UE are described in .

[0256] It should be understood by those of ordinary skill in the art that the operations or steps of the methods described in conjunction with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. In addition, in some aspects, the operations or steps of the methods may reside as one or any combination or set of codes and / or instructions on a non-transitory computer-readable medium that can be incorporated into a computer program product.

[0257] Although the present disclosure has been described with respect to specific embodiments of the present disclosure, it is apparent that many substitutions, modifications, and variations may be apparent to those skilled in the art. For example, the various components of the embodiments may be interchanged, added, or substituted in other embodiments. Moreover, all elements of each figure are not necessary for the operation of the disclosed embodiments. For example, a person of ordinary skill in the field of the disclosed embodiments will be able to make and use the teachings of the present disclosure by simply adopting the elements of the independent claims. Therefore, the embodiments of the present disclosure set forth herein are intended to be illustrative rather than restrictive. Various changes may be made without departing from the spirit and scope of the present disclosure.

[0258] In this archive, the term "includes / including" or any other changes thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment containing the element list not only includes those elements but also may include other elements that are not explicitly listed or inherent to this process, method, article or equipment. The element starting with "a / an" or the like does not exclude the existence of additional identical elements in the process, method, article or equipment containing the element without more constraints. Moreover, the term "another" is defined as at least the second or more. As used herein, the term "having" and the like are defined as "including". For example, the expression of "A and / or B" or "at least one of A and B" may include any and all combinations of words listed together with the expression. For example, the expression "A and / or B" or "at least one of A and B" may include A, B or both A and B. The words of "first", "second" or the like are only used to clearly illustrate the embodiments of the present application, and are not used to limit the essence of the present application.

Claims

1. A first user equipment UE, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to: performing a first channel access procedure to start a first channel occupation time COT; Determining a first physical sidelink feedback channel PSFCH timing within the first COT; determining whether there is a hybrid automatic repeat request acknowledgement HARQ-ACK feedback to be transmitted in the first PSFCH opportunity; and leaving gap symbols of the first PSFCH opportunity within the first COT blank in response to determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, or Continuous transmission is performed in the first PSFCH opportunity in response to determining that HARQ-ACK feedback is not to be transmitted in the first PSFCH opportunity.

2. The first UE of claim 1 , wherein determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity comprises: Determining to transmit a first HARQ-ACK feedback of a first physical sidelink shared channel (PSSCH) in the first PSFCH opportunity, wherein the first PSSCH is transmitted by the first UE; determining that a second HARQ-ACK feedback for a second PSSCH is to be transmitted in the first PSFCH opportunity, wherein the second PSSCH is received by the first UE; and Determining that a third HARQ-ACK feedback for a third PSSCH is to be transmitted in the first PSFCH opportunity, wherein the third PSSCH is not transmitted or received by the first UE.

3. The first UE of claim 1, wherein the processor is further configured to: In response to being unable to determine whether there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, performing energy detection or a second channel access procedure in the first PSFCH opportunity, and Continuous transmission is performed for a remaining duration of the first PSFCH opportunity in response to the detected energy being below a threshold or the second channel access procedure being successful. 4 . The first UE according to claim 1 , wherein the first PSFCH timing is determined based on PSFCH periodicity with reference to the first COT.

5. The first UE of claim 4, wherein the processor is further configured to: transmitting a first physical sidelink shared channel PSSCH to a second UE in the first COT; and A determination is made whether a first HARQ-ACK feedback for the first PSSCH is to be transmitted in the first PSFCH opportunity or outside of the first COT.

6. The first UE of claim 5, wherein the processor is further configured to: in response to determining that the first HARQ-ACK feedback for the first PSSCH is to be transmitted outside the first COT, performing a third channel access procedure to start a second COT after the first COT, and transmitting second sidelink control information SCI to request the second UE to transmit the first HARQ-ACK feedback in a second PSFCH opportunity, wherein the second PSFCH opportunity is within the second COT and is determined based on the PSFCH periodicity with reference to the second COT; or Determine to cancel the first PSFCH opportunity.

7. The first UE of claim 1, wherein the processor is configured to: Transmitting first sidelink control information SCI for scheduling a first physical sidelink shared channel PSSCH in the first COT to a second UE, wherein the first SCI includes a HARQ-ACK feedback timing indicator for enabling the second UE to determine a PSFCH timing for transmitting a first HARQ-ACK feedback for the first PSSCH; and A determination is made as to whether the first HARQ-ACK feedback is to be transmitted in the first PSFCH opportunity or outside of the first COT.

8. The first UE according to claim 7, wherein the first SCI indicates a channel access type for the second UE to transmit the first HARQ-ACK feedback.

9. The first UE of claim 7, wherein the processor is configured to: in response to determining that the first HARQ-ACK feedback for the first PSSCH is to be transmitted outside the first COT, setting the HARQ-ACK feedback timing indicator in the first SCI to indicate an inapplicable HARQ-ACK feedback timing value or a reserved code point, performing a third channel access procedure to start a second COT after the first COT, and transmitting a second SCI in the second COT to request the second UE to transmit the first HARQ-ACK feedback in a second PSFCH opportunity, wherein the second PSFCH opportunity is within the second COT and is determined based on a HARQ-ACK feedback timing value indicated by a HARQ-ACK feedback timing indicator in the second SCI; or setting the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value indicating a third PSFCH opportunity for transmitting the first HARQ-ACK feedback, wherein the third PSFCH opportunity is outside the first COT; or The processor is configured to, in response to determining that the first HARQ-ACK feedback of the first PSSCH is to be transmitted in the first PSFCH opportunity, set the HARQ-ACK feedback timing indicator in the first SCI to a HARQ-ACK feedback timing value indicating the first PSFCH opportunity for transmitting the first HARQ-ACK feedback.

10. The first UE according to claim 6 or 9, wherein the second SCI schedules a PSSCH in the second COT and comprises a HARQ-ACK feedback request indicator requesting transmission of the first HARQ-ACK feedback in the second COT; wherein the second SCI schedules a PSSCH in the second COT and comprises a first HARQ process number field and a HARQ-ACK feedback request indicator, wherein the HARQ-ACK feedback request indicator requests transmission of a HARQ-ACK feedback associated with a HARQ process number indicated by the first HARQ process number field in the second COT, and wherein the HARQ process number indicated by the first HARQ process number field comprises a HARQ process number associated with the first HARQ-ACK feedback; wherein the second SCI schedules a PSSCH in the second COT and comprises a second HARQ process number field for requesting transmission of HARQ-ACK feedback of a previous PSSCH associated with a HARQ process number indicated by the second HARQ process number field in the second COT, and wherein the HARQ process number indicated by the second HARQ process number field comprises a HARQ process number associated with the first HARQ-ACK feedback; or The second SCI is specifically used to request HARQ-ACK feedback, and the second SCI includes a third HARQ process number field indicating a HARQ process number associated with the first HARQ-ACK feedback.

11. The first UE according to claim 10, wherein the first HARQ process number field, the second HARQ process number field or the third HARQ process number field further indicates at least one of the following: a HARQ process number associated with HARQ-ACK feedback that cannot be transmitted in the first COT due to a channel access process failure, or a HARQ process number associated with HARQ-ACK feedback that the first UE did not correctly receive in the first COT.

12. The first UE of claim 9, wherein the processor is configured to: receiving the first HARQ-ACK feedback in the third PSFCH opportunity; or In response to not receiving the first HARQ-ACK feedback in the third PSFCH opportunity, performing a fourth channel access process to start a third COT after the third PSFCH opportunity, and transmitting a third SCI in the third COT to request the second UE to transmit the first HARQ-ACK feedback in the third COT.

13. The first UE of claim 7, wherein the processor is configured to: determining whether to disable the first HARQ-ACK feedback of the first PSSCH; and In response to determining to deactivate the first HARQ-ACK feedback for the first PSSCH, performing at least one of the following: Setting the HARQ-ACK feedback timing indicator in the first SCI to indicate an inapplicable HARQ-ACK feedback timing value or a reserved code point; or The HARQ enable / disable indicator in the first SCI is set to disable HARQ-ACK feedback of the first PSSCH.

14. A second user equipment UE, comprising: Transceiver; and a processor coupled to the transceiver, wherein the processor is configured to: receiving, from a first UE, first side link control information SCI for scheduling a first physical side link shared channel PSSCH within a first channel occupation time COT initiated by the first UE; Determining a first physical side link feedback channel PSFCH timing within the first COT; determining whether to transmit a first hybrid automatic repeat request acknowledgement HARQ-ACK feedback of the first PSSCH in the first PSFCH opportunity; and In response to determining that the first HARQ-ACK feedback is to be transmitted in the first PSFCH opportunity, performing a first channel access procedure in a gap symbol of the first PSFCH opportunity within the first COT, and The first HARQ-ACK feedback is transmitted to the first UE in the first PSFCH opportunity in response to the first channel access procedure being successful.

15. A method performed by a first user equipment UE, comprising: performing a first channel access procedure to start a first channel occupation time COT; Determining a first physical sidelink feedback channel PSFCH timing within the first COT; determining whether there is a hybrid automatic repeat request acknowledgement HARQ-ACK feedback to be transmitted in the first PSFCH opportunity; and leaving gap symbols of the first PSFCH opportunity within the first COT blank in response to determining that there is HARQ-ACK feedback to be transmitted in the first PSFCH opportunity, or Continuous transmission is performed in the first PSFCH opportunity in response to determining that HARQ-ACK feedback is not to be transmitted in the first PSFCH opportunity.

Images