WO2023137755A1

WO2023137755A1 - Method and apparatus for sidelink harq-ack feedback transmission over unlicensed spectrum

Info

Publication number: WO2023137755A1
Application number: PCT/CN2022/073523
Authority: WO
Inventors: Haipeng Lei; Xiaodong Yu; Zhennian SUN; Xin Guo; Yu Zhang
Original assignee: Lenovo (Beijing) Limited
Priority date: 2022-01-24
Filing date: 2022-01-24
Publication date: 2023-07-27

Abstract

Embodiments of the present disclosure relate to methods and apparatuses for HARQ-ACK feedback on a sidelink over an unlicensed spectrum. According to some embodiments of the disclosure, a UE may: receive a physical sidelink shared channel (PSSCH); determine a plurality of transmission opportunities (TOs) for transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH; perform a channel access procedure for transmitting the HARQ-ACK feedback on a first TO of the plurality of TOs; and in response to the channel access procedure for the first TO being successful, transmit the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in the first TO.

Description

METHOD AND APPARATUS FOR SIDELINK HARQ-ACK FEEDBACK TRANSMISSION OVER UNLICENSED SPECTRUM

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to wireless communication technology, and more particularly to a hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback transmission (s) on a sidelink over an unlicensed spectrum.

BACKGROUND

Wireless communication systems are widely deployed to provide various telecommunication services, such as telephony, video, data, messaging, broadcasts, and so on. 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, such as long term evolution (LTE) systems, LTE-advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may also be referred to as new radio (NR) systems.

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

Some wireless communication systems may support sidelink communications, in which devices (e.g., UEs) that are relatively close to each other may communicate with one another directly via a sidelink, rather than being linked through the BS. The term "sidelink" may refer to a radio link established for communicating among devices (e.g., UEs) , as opposed to communicating via the cellular infrastructure (e.g., uplink and downlink) . Sidelink transmission may be performed on a licensed spectrum and an unlicensed spectrum.

There is a need for handling sidelink transmissions on an unlicensed spectrum.

SUMMARY

Some embodiments of the present disclosure provide a user equipment (UE) . The UE may include: a transceiver; and a processor coupled to the transceiver. The processor may be configured to: receive a physical sidelink shared channel (PSSCH) ; determine a plurality of transmission opportunities (TOs) for transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH; perform a channel access procedure for transmitting the HARQ-ACK feedback on a first TO of the plurality of TOs; and in response to the channel access procedure for the first TO being successful, transmit the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in the first TO.

Some embodiments of the present disclosure provide a user equipment (UE) . The UE may include: a transceiver; and a processor coupled to the transceiver. The processor may be configured to: transmit a physical sidelink shared channel (PSSCH) ; determine a plurality of transmission opportunities (TOs) for receiving hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH; and receive the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in a first TO of the plurality of TOs.

Some embodiments of the present disclosure provide a method for wireless communication performed by a user equipment (UE) . The method may include: receiving a physical sidelink shared channel (PSSCH) ; determining a plurality of transmission opportunities (TOs) for transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH; performing a channel access procedure for transmitting the HARQ-ACK feedback on a first TO of the plurality of TOs; and in response to the channel access procedure for the first TO being successful, transmitting the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in the first TO.

Some embodiments of the present disclosure provide a method for wireless communication performed by a user equipment (UE) . The method may include: transmitting a physical sidelink shared channel (PSSCH) ; determining a plurality of transmission opportunities (TOs) for receiving hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH; and receiving the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in a first TO of the plurality of TOs.

Some embodiments of the present disclosure provide an apparatus. According to some embodiments of the present disclosure, the apparatus may include: at least one non-transitory computer-readable medium having stored thereon computer-executable instructions; at least one receiving circuitry; at least one transmitting circuitry; and at least one processor coupled to the at least one non-transitory computer-readable medium, the at least one receiving circuitry and the at least one transmitting circuitry, wherein the at least one non-transitory computer-readable medium and the computer executable instructions may be configured to, with the at least one processor, cause the apparatus to perform a method according to some embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the advantages and features of the disclosure can be obtained, a description of the disclosure is rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. These drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered limiting of its scope.

FIG. 1 illustrates a schematic diagram of a wireless communication system in accordance with some embodiments of the present disclosure;

FIG. 2 illustrates an exemplary sidelink transmission in accordance with some embodiments of the present disclosure;

FIG. 3 illustrates an exemplary sidelink transmission in accordance with some embodiments of the present disclosure;

FIG. 4 illustrates a flow chart of an exemplary procedure of wireless communications in accordance with some embodiments of the present disclosure;

FIG. 5 illustrates a flow chart of an exemplary procedure of wireless communications in accordance with some embodiments of the present disclosure; and

FIG. 6 illustrates a block diagram of an exemplary apparatus in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

The detailed description of the appended 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 may be practiced. It should be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present disclosure.

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 architecture and new service scenarios, such as the 3rd generation partnership project (3GPP) 5G (NR) , 3GPP long-term evolution (LTE) Release 8, and so on. It is contemplated that along with the developments of network architectures and new service scenarios, all embodiments in the present disclosure are also applicable to similar technical problems; and moreover, the terminologies recited in the present disclosure may change, which should not affect the principles of the present disclosure.

FIG. 1 illustrates a schematic diagram of a wireless communication system 100 in accordance with some embodiments of the present disclosure.

As shown in FIG. 1, a 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) . Although a specific number of UEs 110 and one BS 120 are depicted in FIG. 1, it is contemplated that any number of BSs and UEs in and outside of the coverage of the BSs may be included in the wireless communication system 100.

In some embodiments of the present disclosure, BS 120 may be referred to as an access point, an access terminal, a base, a base unit, a macro cell, a Node-B, an evolved Node B (eNB) , a gNB, a Home Node-B, a relay node, or a device, or described using other terminology used in the art. BS 120 is generally a part of a radio access network that may include one or more controllers communicably coupled to one or more corresponding BSs. BS 120 may communicate with UE (s) 110 via downlink (DL) communication signals.

UE (s) 110 (e.g., UE 110a, UE 110b, or UE 110c) may include computing devices, such as desktop computers, laptop computers, personal digital assistants (PDAs) , tablet computers, smart televisions (e.g., televisions connected to the Internet) , set-top boxes, game consoles, security systems (including security cameras) , vehicle on-board computers, network devices (e.g., routers, switches, and modems) , 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 telephone, a flip phone, a device having a subscriber identity module, a personal computer, a selective call receiver, or any other device that is capable of sending and receiving communication signals on a wireless network. In some embodiments of the present disclosure, UE (s) 110 includes wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like. Moreover, UE (s) 110 may be referred to as a subscriber unit, a mobile, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, an IoT device, a vehicle, or a device, or described using other terminology used in the art. UE (s) 110 may communicate with BS 120 via uplink (UL) communication signals.

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

In some embodiments of the present disclosure, wireless communication system 100 is compatible with 5G NR of the 3GPP protocol. For example, BS 120 may transmit data using an orthogonal frequency division multiple (OFDM) modulation scheme on the DL and UE (s) 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. More generally, however, the wireless communication system 100 may implement some other open or proprietary communication protocols, for example, WiMAX, among other protocols.

In some embodiments of the present disclosure, BS 120 and UE (s) 110 may communicate using other communication protocols, such as the IEEE 802.11 family of wireless communication protocols. Further, in some embodiments of the present disclosure, BS 120 and UE (s) 110 may communicate over licensed spectrums, whereas in some other embodiments, BS 120 and UE (s) 110 may communicate over unlicensed spectrums. The present disclosure is not intended to be limited to the implementation of any particular wireless communication system architecture or protocol.

BS 120 may define one or more cells, and each cell may have a coverage area 130. In the exemplary wireless communication system 100, some UEs (e.g., UE 110a and UE 110b) are within the coverage of BS 120, which may not be the specific BS 120 as shown in FIG. 1 and can be any one of the BSs 120 in a wireless communication system, and some UEs (e.g., UE 110c) are outside of the coverage of BS 120. For example, in the case that the wireless communication system includes two BSs 120 with UE 110a being within the coverage of any one of the two BSs means that UE 110a is within the coverage of a BS 120 (i.e., in-coverage) in the wireless communication system; and UE 110a being outside of the coverage of both BSs 120 means that UE 110a is outside the coverage of a BS 120 (i.e., out-of-coverage) in the wireless communication system.

Still referring to FIG. 1, UE 110a and UE 110b may communicate with BS 120 via, for example, a Uu link (denoted by dotted arrow in FIG. 1) . UE 110a, UE 110b, and UE 110c may communicate with each other via a sidelink (denoted by solid arrow in FIG. 1) .

Sidelink transmission may involve a physical sidelink control channel (PSCCH) and an associated physical sidelink shared channel (PSSCH) , which is scheduled by the sidelink control information (SCI) carried on the PSCCH. The SCI and 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, to a group of Rx UEs in a groupcast manner, or to Rx UEs within a range in a broadcast manner. For example, referring to FIG. 1, UE 110a (acting as a Tx UE) may transmit data to UE 110b or UE 110c (acting as an Rx UE) .

The PSSCH may carry data which may require corresponding HARQ-ACK feedback from the Rx UE (s) to the Tx UE. In some examples, the broadcast transmission may not need HARQ-ACK feedback. In some examples, unicast and groupcast transmissions may enable HARQ-ACK feedback under certain preconditions. The HARQ-ACK feedback for a PSSCH may be carried on a physical sidelink feedback channel (PSFCH) . In some embodiments of the present disclosure, one PSFCH can carry only a single HARQ-ACK information bit.

In some embodiments of the present disclosure, sidelink transmission may be performed on an unlicensed spectrum. This is advantageous because a sidelink transmission over an unlicensed spectrum can achieve, for example, increased data rate.

For a sidelink transmission on an unlicensed spectrum, in response to channel an access procedure (also known as a listen-before-talk (LBT) test or LBT procedure) being successful, a Tx UE may transmit a PSSCH to an Rx UE and wait for the reception of a PSFCH from the Rx UE. In some examples, due to the unpredicted result before the Rx UE performs an LBT, the sidelink HARQ-ACK feedback (i.e., PSFCH) may not be transmitted when the LBT at the Rx UE side fails. Without the HARQ-ACK feedback, the Tx UE may have to retransmit the PSSCH even when the Rx UE has correctly decoded the PSSCH.

In some examples, when the LBT at the Rx UE side is successful, the Rx UE may transmit the PSFCH to the Tx UE. However, due to hidden node interference on the shared unlicensed spectrum, the Tx UE may not correctly decode the PSFCH. In this scenario, the Tx UE may still have to retransmit the PSSCH even when the Rx UE has correctly decoded the PSSCH.

Embodiments of the present disclosure provide solutions to improve the reliability of PSFCH or sidelink HARQ-ACK feedback transmissions over an unlicensed spectrum. For example, a plurality of transmission opportunities (TOs) may be provided for a sidelink HARQ-ACK feedback transmission. The disclosed solutions can avoid the aforementioned drawbacks. More details on the embodiments of the present disclosure will be illustrated in the following text in combination with the appended drawings.

In some embodiments of the present disclosure, for a sidelink HARQ-ACK feedback to be transmitted on an unlicensed carrier, the sidelink HARQ-ACK feedback can have a plurality of transmission opportunities (TOs) .

In some embodiments of the present disclosure, the number of TOs of the HARQ-ACK feedback corresponding to a PSSCH can be configured by a signaling message or predefined, for example, in a standard (s) . In some examples, the number of TOs may be greater than or equal to a maximum number of TOs, which may be predefined, for example, in a standard (s) . In some examples, each TO may be determined based on a UE processing time and a PSFCH periodicity configuration. For example, an initial transmission (e.g., the first TO of the plurality of TOs) of the PSFCH carrying the HARQ-ACK feedback may be based on the UE processing time according to one of the known methods in the art. The subsequent retransmission (s) (e.g., the second to the last TOs of the plurality of TOs) may be determined according to the PSFCH periodicity (denoted as “P” ) .

The PSFCH periodicity P may mean that every P sidelink slots (also named as “logic slots” for sidelink communication) have a single transmission occasion for transmitting a PSFCH. For example, a sidelink resource pool including resources for sidelink communication or sidelink resources may be assigned to a UE for sidelink operations. The sidelink resource pool may be scheduled or configured by a BS or may be pre-configured at a UE, for example, during the manufacture of the UE according to an industrial standard (s) (e.g., predefined in a standard (s) ) . A PSFCH resource pool may be configured (or pre-configured) for every P contiguous slots. For example, “P = 4” may mean that a PSFCH resource pool may be configured in a fourth slot of every 4 slots. Here, the P contiguous slots may mean P contiguous logic slots for sidelink and not repeated in the following paragraphs.

For example, it is assumed that a UE may receive radio resource control (RRC) signaling configured the number of TOs of sidelink HARQ-ACK feedback as N. Assuming that the UE receives a PSSCH in slot #n, the UE may determine that the first PSFCH (e.g., a first TO) carrying the HARQ-ACK feedback corresponding to the PSSCH is to be transmitted in slot #n+x, wherein x is the slot level offset subject to the UE processing time and PSFCH periodicity configuration. The UE may further determine the remaining N-1 TOs for the HARQ-ACK feedback corresponding to the PSSCH as slot #n+x+P, slot #n+x+2P, …, slot #n+x+ (N-1) *P, where P is the PSFCH periodicity in a resource pool.

In this way, a PSFCH (or HARQ-ACK feedback) corresponding to each PSSCH can have N TOs, and each TO can be determined as long as the PSSCH is received.

In some embodiments of the present disclosure, the number of TOs of the HARQ-ACK feedback corresponding to a PSSCH may be dynamically scheduled. For example, the maximum number of TOs of the sidelink HARQ-ACK feedback may be configured by a signaling message or predefined, for example, in a standard (s) . A SCI may dynamically indicate the actually number of TOs (which is less than or equal to the maximum number of TOs) for the HARQ-ACK feedback corresponding to the PSSCH scheduled by the SCI.

For example, it is assumed that the maximum number of TOs of the sidelink HARQ-ACK feedback is configured as M. A SCI format may include

bits (hereinafter, “TO number indicator” ) to indicate the actual number of TOs for the HARQ-ACK feedback corresponding to the PSSCH scheduled by the SCI format. In some examples, a code point (e.g., corresponding to the value of 1) of the TO number indicator may indicate a single TO. In some examples, a code point (e.g., corresponding to the value of 0) of the TO number indicator may indicate disabling the sidelink HARQ-ACK feedback.

Assuming that a UE receives a PSSCH in slot #n’, the UE may determine that the first PSFCH (e.g., a first TO) carrying the HARQ-ACK feedback corresponding to the PSSCH is to be transmitted in slot #n’+x, wherein x is the slot level offset subject to the UE processing time and PSFCH periodicity configuration. Assuming that the SCI format scheduling the PSSCH indicates the actual number of TOs of the HARQ-ACK feedback as m, the m TOs for the HARQ-ACK feedback corresponding to the PSSCH may include slot #n’+x, slot #n’+x+P, slot #n’+x+2P, …, slot #n’+x+ (m-1) *P, where P is the PSFCH periodicity in a resource pool. In some examples, the value of m equal to 1 may suggest a single TO for the HARQ-ACK feedback. In some examples, the value of m equal to 0 may suggest disabled HARQ-ACK feedback.

In this way, the Tx UE can flexibly adjust the TOs of a PSFCH according to the channel condition.

For example, from the perspective of a Tx UE, it may perform an LBT test and occupy the channel for a channel occupancy time (COT) in response to a successful LBT test. This COT may be referred to as “Tx UE initiated COT. ” The Tx UE may transmit an SCI format to schedule a PSSCH to an Rx UE. When the corresponding PSFCH is to be transmitted within the Tx UE initiated COT, the Rx UE may perform a first type of LBT test (also known as “LBT Category 2, ” “LBT Cat 2” or “one-shot LBT” or “channel access Type 2” in 3GPP specification TS 37.213) before transmitting the PSFCH. In this case, the Tx UE can indicate a single transmission opportunity for the Rx UE to transmit the PSFCH. When the PSFCH is to be transmitted within the Tx UE initiated COT and there are at least one (e.g., s) PSFCH slots within the remaining COT, the Tx UE can indicate s transmission opportunities for the Rx UE to transmit the PSFCH within the remaining COT. When the PSFCH is to be transmitted outside the Tx UE initiated COT, the Rx UE may perform a second type of LBT test (also known as “LBT Category 4” or “LBT Cat 4” or “channel access Type 1” in 3GPP specification TS 37.213) before transmitting the PSFCH. In this case, the Tx UE can indicate a plurality of transmission opportunity for the Rx UE to transmit the PSFCH.

There are multiple categories of LBT, including for example LBT Cat 1, LBT Cat 2, LBT Cat 3 and LBT Cat 4. LBT Cat 1 may mean that no LBT procedure is performed by a transmitter. LBT Cat 2 may mean that a LBT procedure is performed without random back-off, and the duration of time that the channel is sensed to be idle before the transmitter transmits is deterministic, e.g., at least 25us sensing interval. LBT Cat 3 may mean that a LBT procedure is performed with random back-off with a fixed contention window size. A transmitter may draw a random number N within a contention window, the size of which is specified by a minimum and maximum value of N. The size of the content window may be fixed. The random number N is used in the LBT procedure to determine the duration of time that the channel is sensed to be idle before the transmitter transmits on the channel. LBT Cat 4 may mean that a LBT procedure is performed with random back-off with a variable contention window size. Similarly, a transmitter may draw a random number M within a contention window, the size of which is specified by a minimum and maximum value of M. The transmitter can vary the size of the contention window when drawing the random number M. The random number M is used in the LBT procedure to determine the duration of time that the channel is sensed to be idle before the transmitter transmits on the channel. The sensing slot duration may be 9us for each LBT category.

FIG. 2 illustrates an exemplary sidelink transmission in accordance with some embodiments of the present disclosure. Details described in all of the foregoing embodiments of the present disclosure are applicable for the embodiments shown in FIG. 2.

Referring to FIG. 2, it is assumed that a UE is configured with a PSFCH periodicity of 4. The UE may receive a PSSCH 211 in slot n. In some example, the UE may need at least two slots for decoding the received PSSCH and generate a PSFCH carrying the corresponding sidelink HARQ-ACK feedback. In some example, the SCI format scheduling PSSCH 211 may indicate four TOs for the sidelink HARQ-ACK feedback corresponding to PSSCH 211. The UE may determine the four TOs for the sidelink HARQ-ACK feedback in slot n+3, slot n+7, slot n+11 and slot n+15, respectively. For example, the UE can transmit PSFCHs 221-224 carrying the HARQ-ACK feedback corresponding to PSSCH 211 in slot n+3, slot n+7, slot n+11 and slot n+15, respectively. PSFCH 221 may be referred to as an initial PSFCH transmission, and PSFCHs 222-224 may be referred to as a PSFCH retransmission. It should be noted that whether the actual transmission occurs or not may subject to the outcome of an LBT test. In addition, whether the actual transmission occurs or not may also subject to the PSFCH transmission scheme, as will be described in the following text.

An LBT test is performed before a TO. For example, referring again to FIG. 2, the UE may perform an LBT test (e.g., LBT Cat 2 or LBT Cat 4) for transmitting the HARQ-ACK feedback on a TO (e.g., in slot n+3 in FIG. 2) of the four TOs. In response to the LBT test for the TO being successful, the UE may transmit the HARQ-ACK feedback on a PSFCH resource (e.g., PSFCH 221) in the TO.

In some embodiments, the HARQ-ACK feedback corresponding to a PSSCH may only be transmitted once in the plurality of TOs. For example, in response to a successful transmission of the HARQ-ACK feedback on a PSFCH resource in one of the plurality of TOs, the UE may release the remaining TO (s) of the plurality of TOs are released. That is, the HARQ-ACK feedback or the corresponding PSFCH is not repeatedly transmitted in the remaining TOs.

For example, referring again to FIG. 2, when an LBT test on slot n+3 in FIG. 2 is successful, the UE may transmit PSFCH 221 in slot n+3 and may release the remaining TOs (e.g., TOs in slot n+7, slot n+11 and slot n+15) . That is, PSFCHs 222-224 will not be transmitted. However, if the LBT test on slot n+3 in FIG. 2 fails, the UE may perform an LBT test on each of the remaining TOs until a successful LBT test. For example, assuming that the LBT tests on slot n+3, slot n+7, slot n+11 in FIG. 2 fail and the LBT test on slot n+15 in FIG. 2 is successful, the UE may transmit PSFCH 224 in slot n+15.

In some embodiments, the HARQ-ACK feedback corresponding to a PSSCH can be repeatedly transmitted in the plurality of TOs. For example, after the UE successful transmits the HARQ-ACK feedback or the corresponding PSFCH on a PSFCH resource in one of the plurality of TOs, the UE may still try to transmit the HARQ-ACK feedback or the corresponding PSFCH on the remaining TOs. For example, in response to a successful LBT test on another TO of the plurality of TOs, the UE may transmit the HARQ-ACK feedback or the corresponding PSFCH on another PSFCH resource in the another TO. However, if the LBT test on the another TO fails, the UE may not transmit the corresponding PSFCH (s) in the another TO. The UE may repeatedly perform the above operations till the last TO of the plurality of TOs.

For example, referring again to FIG. 2, when an LBT test on slot n+3 in FIG. 2 is successful, the UE may transmit PSFCH 221 in slot n+3. When an LBT test on slot n+7 in FIG. 2 fails, the UE may not transmit PSFCH 222 in slot n+7. When an LBT test on slot n+11 in FIG. 2 is successful, the UE may transmit PSFCH 223 in slot n+11. When an LBT test on slot n+15 in FIG. 2 is successful, the UE may transmit PSFCH 224 in slot n+15.

In some embodiments, an LBT test may fail on each of the plurality TOs, the UE may not transmit the HARQ-ACK feedback corresponding to the scheduled PSSCH. In other words, the UE may drop the sidelink HARQ-ACK feedback transmission.

In some embodiments, PSFCH resource collision may occur. For example, an initiation transmission or a retransmission of a PSFCH of a UE may collide with a retransmission of another PSFCH of the UE. For example, an initiation transmission of a PSFCH of a UE may collide with a retransmission of a PSFCH of another UE.

For example, referring to FIG. 3, for PSSCH 311 in slot n, a UE may determine an initial PSFCH transmission 331 in slot n+3 and PSFCH retransmissions 332-334 in slot n+7, slot n+11 and slot n+15, respectively. Taking PSFCH retransmission 332 as an example, the UE may determine a PSFCH resource from a PSFCH resource pool for PSFCH retransmission 332. For a PSSCH in slot n+1, the UE may determine an initial PSFCH transmission 341 in slot n+7. The UE may determine the same PSFCH resource from the PSFCH resource pool for initial PSFCH transmission 341. Therefore, PSFCH resource collision occurs.

Embodiments of the present disclosure further provide solutions to avoid the PSFCH resource collision.

In some embodiments of the present disclosure, separate resource pools may be configured for an initial PSFCH transmission and each PSFCH retransmission. In other words, each PSFCH transmission may be in a dedicated resource pool. Each resource pool is within the PSFCH slot according to the PSFCH period. The resource pool can be a set of physical resource blocks (PRBs) , orthogonal sequences, or any combination thereof dedicated for a certain (re) transmission.

In some embodiments, a PSFCH resource pool may be configured to associate with a specific PSFCH transmission. For example, when configuring a PSFCH resource pool, the index of a transmission time or transmission opportunity is provided. Assuming that a maximum of K TOs for a PSFCH is supported, a maximum of K PSFCH resource pools may be configured with each PSFCH resource pool corresponding to a corresponding TO.

For example, a first transmission of a given HARQ-ACK feedback (e.g., PSFCH 221 in FIG. 2) may be transmitted in a resource pool for initial PSFCH transmission; a second transmission of the given HARQ-ACK feedback (e.g., PSFCH 222 in FIG. 2) may be transmitted in another resource pool for second PSFCH transmission; a third transmission of the given HARQ-ACK feedback (e.g., PSFCH 223 in FIG. 2) may be transmitted in yet another resource pool for third PSFCH transmission, and so on till the last PSFCH transmission among the plurality of TOs. Each resource pool is within the PSFCH slot according to the PSFCH period.

In some embodiments of the present disclosure, the same resource pool may be configured for an initial PSFCH transmission of PSFCH and a PSFCH retransmission (s) . The index of a transmission time or transmission opportunity may be used to determine a PSFCH resource in the resource pool. For example, referring to FIG. 2, the four TOs (e.g., corresponding to PSFCHs 221-224) may be indexed as 0-3, respectively. The UE may determine respective PSFCH resources in a configured resource pool for transmitting PSFCHs 221-224 based on the indexes the four TOs.

In some examples, a UE may determine the PSFCH resource for an initial PSFCH transmission or a PSFCH retransmission in a resource pool according to

In the formula, P _ID denotes a physical layer source ID provided by the SCI format scheduling the PSSCH. M _ID denotes the identity of the UE receiving the PSSCH when the UE detects a SCI format indicating a groupcast with ACK or NACK based HARQ-ACK feedback (e.g., the value of a cast type indicator field of the SCI format being "01" ) ; or otherwise, M _ID is zero.

denotes a total number of PSFCH resources available for multiplexing HARQ-ACK information in a PSFCH transmission. In the formula, i denotes the transmission time or the index of the TO. For example, i=0 for an initial transmission (e.g., PSFCH 221 in FIG. 2) , i=1 for the second transmission (e.g., PSFCH 222 in FIG. 2) , …, i=M-1 for the M ^th transmission.

FIG. 4 illustrates a flow chart of an exemplary procedure 400 for wireless communications in accordance with some embodiments of the present disclosure. Details described in all of the foregoing embodiments of the present disclosure are applicable for the embodiments shown in FIG. 4. In some examples, the procedure may be performed by a UE, for example, UE 110 in FIG. 1.

Referring to FIG. 4, in operation 411, a UE may receive a PSSCH. The PSSCH may be scheduled by an SCI format. In operation 413, the UE may determine a plurality of TOs for transmitting HARQ-ACK feedback corresponding to the PSSCH.

In some embodiments, the number of the plurality of TOs may be smaller than or equal to a maximum number of TOs, which may be configured by a signaling message or predefined. In some embodiments, the number of the plurality of TOs may be configured by a signaling message or predefined. In some embodiments, the number of the plurality of TOs may be indicated by the SCI format scheduling the PSSCH.

In some embodiments, the UE may determine the plurality of TOs based on the number of the plurality of TOs and a PSFCH transmission period.

In operation 415, the UE may perform a channel access procedure for transmitting the HARQ-ACK feedback on one (denoted as “first TO” for clarity) of the plurality of TOs. The channel access procedure may be an LBT Cat 2 or an LBT Cat 4. In response to the channel access procedure for the first TO being successful, the UE may transmit the HARQ-ACK feedback on a PSFCH resource (denoted as “first PSFCH resource” for clarity) in the first TO in operation 417.

In some embodiments, in response to a successful transmission of the HARQ-ACK feedback on the first PSFCH resource in the first TO, the UE may release the remaining TO of the plurality of TOs. In other words, the HARQ-ACK feedback for the PSSCH may be transmitted at most once among the plurality of TOs.

In some embodiments, in response to the channel access procedure for the first TO being successful, the UE may perform another channel access procedure (LBT Cat 2 or LBT Cat 4) for transmitting the HARQ-ACK feedback on another TO (denoted as “second TO” for clarity) of the plurality of TOs. In response to the channel access procedure for the second TO being successful, the UE may transmit the HARQ-ACK feedback on another PSFCH resource (denoted as “second PSFCH resource” for clarity) in the second TO. In other words, the HARQ-ACK feedback for the PSSCH may be repeatedly transmitted among the plurality of TOs.

In some embodiments, in response to the channel access procedure for the first TO being failed, the UE may perform a channel access procedure for transmitting the HARQ-ACK feedback on another TO (e.g., second TO or other TOs) of the plurality of TOs. In response to the channel access procedure for the second TO being successful, the UE may transmit the HARQ-ACK feedback on the second PSFCH resource in the second TO.

In some embodiments, in response to the channel access procedure for transmitting the HARQ-ACK feedback failed on each of the plurality of TOs, the UE may drop the transmission of the HARQ-ACK feedback.

In some embodiments, the first PSFCH resource and the second PSFCH resource may be located in separate PSFCH resource pools. For example, the UE may be configured with a corresponding resource pool dedicated to each of the plurality of TOs.

In some embodiments, the first PSFCH resource and the second PSFCH resource may be located in the same PSFCH resource pool. The UE may respectively determine the first PSFCH resource and the second PSFCH resource based on the indexes of the first TO and the second TO among the plurality of TOs.

It should be appreciated by persons skilled in the art that the sequence of the operations in exemplary procedure 400 may be changed and some of the operations in exemplary procedure 400 may be eliminated or modified, without departing from the spirit and scope of the disclosure.

FIG. 5 illustrates a flow chart of an exemplary procedure 500 for wireless communications in accordance with some embodiments of the present disclosure. Details described in all of the foregoing embodiments of the present disclosure are applicable for the embodiments shown in FIG. 5. In some examples, the procedure may be performed by a UE, for example, UE 110 in FIG. 1.

Referring to FIG. 5, in operation 511, a UE may transmit a PSSCH. The PSSCH may be scheduled by an SCI format. In operation 513, the UE may determine a plurality of TOs for receiving HARQ-ACK feedback corresponding to the PSSCH.

In some embodiments, the number of the plurality of TOs may be smaller than or equal to a maximum number of TOs, which may be configured by a signaling message or predefined. In some embodiments, the number of the plurality of TOs may be configured by a signaling message or predefined. In some embodiments, the number of the plurality of TOs may be dynamically indicated by the SCI format scheduling the PSSCH.

In operation 515, the UE may receive the HARQ-ACK feedback on a PSFCH resource (denoted as “a first PSFCH resource” for clarity) in a TO (denoted as “a first TO” for clarity) of the plurality of TOs.

In some embodiments, the HARQ-ACK feedback for the PSSCH may be transmitted at most once among the plurality of TOs. For example, in response to receiving the HARQ-ACK feedback corresponding to the PSSCH on the first PSFCH resource in the first TO, the UE may not receive the HARQ-ACK feedback corresponding to the same PSSCH in another TO (e.g., the remaining TO (s) ) of the plurality of TOs.

In some embodiments, the HARQ-ACK feedback for the PSSCH can be repeatedly transmitted among the plurality of TOs. For example, in addition to receiving the HARQ-ACK feedback on the first PSFCH resource in the first TO, the UE may further receive the HARQ-ACK feedback on another PSFCH resource (denoted as “second PSFCH resource” for clarity) in another TO (denoted as “second TO”for clarity) of the plurality of TOs.

In some embodiments, in response to not receiving the HARQ-ACK feedback on the first PSFCH resource in the first TO, the UE may receive the HARQ-ACK feedback on another PSFCH resource (e.g., the second PSFCH resource) in another TO (e.g., the second TO) of the plurality of TOs. In some embodiments, the UE may not receive any HARQ-ACK feedback corresponding to the PSSCH among the plurality of TOs.

In some embodiments, the first PSFCH resource and the second PSFCH resource may be located in the same PSFCH resource pool. The first PSFCH resource and the second PSFCH resource may be based on the indexes of the first TO and the second TO among the plurality of TOs.

It should be appreciated by persons skilled in the art that the sequence of the operations in exemplary procedure 500 may be changed and some of the operations in exemplary procedure 500 may be eliminated or modified, without departing from the spirit and scope of the disclosure.

FIG. 6 illustrates a block diagram of an exemplary apparatus 600 according to some embodiments of the present disclosure. As shown in FIG. 6, the apparatus 600 may include at least one processor 606 and at least one transceiver 602 coupled to the processor 606. The apparatus 600 may be a UE or a BS.

Although in this figure, elements such as the at least one transceiver 602 and processor 606 are described in the singular, the plural is contemplated unless a limitation to the singular is explicitly stated. In some embodiments of the present application, the transceiver 602 may be divided into two devices, such as a receiving circuitry and a transmitting circuitry. In some embodiments of the present application, the apparatus 600 may further include an input device, a memory, and/or other components.

In some embodiments of the present application, the apparatus 600 may be a UE. The transceiver 602 and the processor 606 may interact with each other so as to perform the operations with respect to the UEs described above, for example, in FIGS. 1-5.

In some embodiments of the present application, the apparatus 600 may be a BS. The transceiver 602 and the processor 606 may interact with each other so as to perform the operations with respect to the BSs described above, for example, in FIGS. 1-5.

In some embodiments of the present application, the apparatus 600 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 have stored thereon computer-executable instructions to cause the processor 606 to implement the method with respect to the UEs as described above. For example, the computer-executable instructions, when executed, cause the processor 606 interacting with transceiver 602 to perform the operations with respect to the UEs described in FIGS. 1-5.

For example, in some embodiments of the present disclosure, the non-transitory computer-readable medium may have stored thereon computer-executable instructions to cause the processor 606 to implement the method with respect to the BSs as described above. For example, the computer-executable instructions, when executed, cause the processor 606 interacting with transceiver 602 to perform the operations with respect to the BSs described in FIGS. 1-5.

Those having ordinary skill in the art would understand that the operations or steps of a method described in connection 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. A 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. Additionally, in some aspects, the operations or steps of a method may reside as one or any combination or set of codes and/or instructions on a non-transitory computer-readable medium, which may be incorporated into a computer program product.

While this disclosure has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations may be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in other embodiments. Also, all of the elements of each figure are not necessary for the operation of the disclosed embodiments. For example, one of ordinary skill in the art of the disclosed embodiments would be enabled to make and use the teachings of the disclosure by simply employing the elements of the independent claims. Accordingly, embodiments of the disclosure as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the disclosure.

In this document, the terms "includes, " "including, " or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "a, " "an, " or the like does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element. Also, the term "another" is defined as at least a second or more. The term "having" and the like, as used herein, are defined as "including. " Expressions such as "A and/or B" or "at least one of A and B" may include any and all combinations of words enumerated along with the expression. For instance, the expression "A and/or B" or "at least one of A and B" may include A, B, or both A and B. The wording "the first, " "the second" or the like is only used to clearly illustrate the embodiments of the present application, but is not used to limit the substance of the present application.

Claims

A user equipment (UE) , comprising:

a transceiver; and

a processor coupled to the transceiver, wherein the processor is configured to:

receive a physical sidelink shared channel (PSSCH) ;

determine a plurality of transmission opportunities (TOs) for transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH;

perform a channel access procedure for transmitting the HARQ-ACK feedback on a first TO of the plurality of TOs; and

in response to the channel access procedure for the first TO being successful, transmit the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in the first TO.
The UE of claim 1, wherein the processor is further configured to perform at least one of:

receiving a signaling message indicating the number of the plurality of TOs; or

receiving sidelink control information (SCI) scheduling the PSSCH, wherein the SCI indicates the number of the plurality of TOs.
The UE of claim 2, wherein the number of the plurality of TOs is smaller than or equal to a maximum number of TOs, and wherein the maximum number of TOs is configured by a signaling message or is predefined.
The UE of claim 2, wherein determining the plurality of TOs comprises determining the plurality of TOs based on the number of the plurality of TOs and a PSFCH transmission period.
The UE of claim 1, wherein the processor is further configured to perform at least one of the following:

in response to a successful transmission of the HARQ-ACK feedback on the first PSFCH resource in the first TO, releasing the remaining TO of the plurality of TOs;

in response to the channel access procedure for the first TO being successful, performing a channel access procedure for transmitting the HARQ-ACK feedback on a second TO of the plurality of TOs, and in response to the channel access procedure for the second TO being successful, transmitting the HARQ-ACK feedback on a second PSFCH resource in the second TO;

in response to the channel access procedure for the first TO being failed, performing a channel access procedure for transmitting the HARQ-ACK feedback on a second TO of the plurality of TOs, and in response to the channel access procedure for the second TO being successful, transmitting the HARQ-ACK feedback on a second PSFCH resource in the second TO; or

in response to the channel access procedure for transmitting the HARQ-ACK feedback failed on each of the plurality of TOs, dropping the transmission of the HARQ-ACK feedback.
The UE of claim 5, wherein the first PSFCH resource and the second PSFCH resource are located in separate PSFCH resource pools.
The UE of claim 5, wherein the first PSFCH resource and the second PSFCH resource are located in the same PSFCH resource pool, and are respectively determined based on the indexes of the first TO and the second TO among the plurality of TOs.
A user equipment (UE) , comprising:

a transceiver; and

a processor coupled to the transceiver, wherein the processor is configured to:

transmit a physical sidelink shared channel (PSSCH) ;

determine a plurality of transmission opportunities (TOs) for receiving hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH; and

receive the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in a first TO of the plurality of TOs.
The UE of claim 8, wherein the processor is further configured to transmit sidelink control information (SCI) scheduling the PSSCH, wherein the SCI indicates the number of the plurality of TOs.
The UE of claim 9, wherein the number of the plurality of TOs is smaller than or equal to a maximum number of TOs, and wherein the maximum number of TOs is configured by a signaling message or is predefined.
The UE of claim 9, wherein determining the plurality of TOs comprises determining the plurality of TOs based on the number of the plurality of TOs and a PSFCH transmission period.
The UE of claim 8, wherein the processor is further configured to receive the HARQ-ACK feedback on a second PSFCH resource in a second TO of the plurality of TOs.
The UE of claim 12, wherein the first PSFCH resource and the second PSFCH resource are located in separate PSFCH resource pools; or

wherein the first PSFCH resource and the second PSFCH resource are located in the same PSFCH resource pool, and are respectively determined based on the indexes of the first TO and the second TO among the plurality of TOs.
The UE of claim 8, wherein the processor is further configured to perform at least one of the following:

in response to receiving the HARQ-ACK feedback on the first PSFCH resource in the first TO, not receiving the HARQ-ACK feedback on the remaining TO of the plurality of TOs;

in response to receiving the HARQ-ACK feedback on the first PSFCH resource in the first TO, continuing to receive the HARQ-ACK feedback on a second PSFCH resource in a second TO of the plurality of TOs; or

in response to not receiving the HARQ-ACK feedback on the first PSFCH resource in the first TO, receiving the HARQ-ACK feedback on a second PSFCH resource in a second TO of the plurality of TOs.
A method performed by a user equipment (UE) , comprising:

receiving a physical sidelink shared channel (PSSCH) ;

determining a plurality of transmission opportunities (TOs) for transmitting hybrid automatic repeat request acknowledgement (HARQ-ACK) feedback corresponding to the PSSCH;

performing a channel access procedure for transmitting the HARQ-ACK feedback on a first TO of the plurality of TOs; and

in response to the channel access procedure for the first TO being successful, transmitting the HARQ-ACK feedback on a first physical sidelink feedback channel (PSFCH) resource in the first TO.