WO2024026819A1

WO2024026819A1 - Assisted feedback configuration decision

Info

Publication number: WO2024026819A1
Application number: PCT/CN2022/110496
Authority: WO
Inventors: Laura Luque SANCHEZ; Renato Barbosa ABREU; Nuno Manuel KIILERICH PRATAS; Ling Yu; Timo Erkki Lunttila; Vinh Van Phan; Yong Liu; Jianguo Liu; Torsten WILDSCHEK
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Priority date: 2022-08-05
Filing date: 2022-08-05
Publication date: 2024-02-08
Anticipated expiration: 2025-02-05
Also published as: CN119654947A

Abstract

Example embodiments of the present disclosure relate to assisted feedback configuration decision. In an example method, a first terminal device performs, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; performs a second LBT procedure based on a second detection threshold lower than the first detection threshold; and determines a feedback configuration of the sidelink transmission based on a result of the second LBT procedure. In this way, the first terminal device can try to avoid failure in receiving feedback from the second terminal device.

Description

ASSISTED FEEDBACK CONFIGURATION DECISION

FIELD

Example embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to a first terminal device, a second terminal device, apparatuses and a computer readable storage medium for assisted feedback configuration decision.

BACKGROUND

In the communication technology, there is a constant evolution ongoing in order to provide efficient and reliable solutions for utilizing wireless communication networks. Each new generation has its own technical challenges for handling different situations and processes that are needed to connect and serve devices connected to wireless networks. To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. The new communication systems can support various types of service applications for terminal devices.

In 3GPP Rel-18 work item, it is agreed to enhance sidelink transmission, in which the sidelink in unlicensed spectrum (SL-U) is one important part. For data transmitting in an unlicensed spectrum channel in SL, a terminal device can be required to perform a listen before talk (LBT) channel access procedure. On the other hand, providing a feedback (for example, a HARQ feedback) for a transmission is a kind of technique to achieve efficient and reliable transmissions. However, in SL-U there may be no guarantee that the terminal device can perform the transmissions of data or a feedback (for example, a HARQ feedback) due to possibility of LBT failure.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for assisted feedback configuration decision.

In a first aspect, there is provided a first terminal device. The first terminal device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the first terminal device at least to: perform, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; perform a second LBT procedure based on a second detection threshold lower than the first detection threshold; and determine a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In a second aspect, there is provided a second terminal device. The second terminal device second terminal device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the second terminal device at least to: determine whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device; based on determining that the request is received, perform an LBT procedure; based on success of the LBT procedure, transmit feedback to the first terminal device, and based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.

In a third aspect, there is provided a method. The method comprises: performing, at a first terminal device, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; performing a second LBT procedure based on a second detection threshold lower than the first detection threshold; and determining a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In a fourth aspect, there is provided a method. The method comprises: determining, at a second terminal device, whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device; based on determining that the request is received, performing an LBT procedure; based on success of the LBT procedure, transmitting the feedback to the first terminal device, and based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.

In a fifth aspect, there is provided an apparatus. The apparatus comprising: means for performing, at a first terminal device, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; means for performing a second LBT procedure based on a second detection threshold lower than the first detection threshold; and means for determining a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In an sixth aspect, there is provided an apparatus. The apparatus comprising: means for determining, at a second terminal device, whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device; means for based on determining that the request is received, performing an LBT procedure; based on success of the LBT procedure, transmitting feedback to the first terminal device, and means for based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.

In a seventh aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method in the third, fourth aspects.

In an eighth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: perform, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; perform a second LBT procedure based on a second detection threshold lower than the first detection threshold; and determine a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In a ninth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: determine whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device; based on determining that the request is received, performing an LBT procedure; based on success of the LBT procedure, transmitting feedback to the first terminal device, and based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.

In a tenth aspect, there is provided a device, comprising: performing circuitry configured to perform, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; performing circuitry configured to perform a second LBT procedure based on a second detection threshold lower than the first detection threshold; and determining circuitry configured to determine a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In a eleventh aspect, there is provided a device, comprising: determining circuitry configured to determine whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device; performing circuitry configured to based on determining that the request is received, performing an LBT procedure; transmitting circuitry configured to based on success of the LBT procedure, transmitting the feedback to the first terminal device; , and based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1A illustrates an example of sidelink resource allocation mode 1 in which some example embodiments of the present disclosure may be implemented;

FIG. 1B illustrates an example of sidelink resource allocation mode 2 in which some example embodiments of the present disclosure may be implemented;

FIG. 2A illustrates an example of acquisition of the COT by an the first terminal device via LBT Type 1 in which some example embodiments of the present disclosure may be implemented;

FIG. 2B illustrates an example of an allowed gap for LBT Type 2A in which some example embodiments of the present disclosure may be implemented;

FIG. 2C illustrates another example of an allowed gap for LBT Type 2A in which some example embodiments of the present disclosure may be implemented;

FIG. 2D illustrates an example of an allowed gap for LBT Type 2B in which some example embodiments of the present disclosure may be implemented;

FIG. 2E illustrates another example of an allowed gap for LBT Type 2B in which some example embodiments of the present disclosure may be implemented;

FIG. 2F illustrates an example of an allowed gap for LBT Type 2C in which some example embodiments of the present disclosure may be implemented;

FIG. 2G illustrates another example of an allowed gap for LBT Type 2C in which some example embodiments of the present disclosure may be implemented;

FIG. 2H illustrates an example of a COT acquisition by the first terminal device and the second terminal device with some example embodiments of the present disclosure;

FIG. 2I illustrates an example of SL slot in which some example embodiments of the present disclosure may be implemented;

FIG. 2J illustrates another example of SL slot in which some example embodiments of the present disclosure may be implemented;

FIG. 2K illustrates an example of channel mapping in which some example embodiments of the present disclosure may be implemented;

FIG. 3 illustrates an example of a process flow for LBT procedure with more than one Energy Detection Threshold (EDT) in accordance with some example embodiments of the present disclosure;

FIG. 4 illustrates an example of an LBT procedure with more than one EDT in accordance with some example embodiments of the present disclosure;

FIG. 5A illustrates an example of a method implemented at a first terminal device with some example embodiments of the present disclosure;

FIG. 5B illustrates another example of a method implemented at a first terminal device with some example embodiments of the present disclosure;

FIG. 6 illustrates an example of a method implemented at a second terminal device with some example embodiments of the present disclosure;

FIG. 7 illustrates a simplified block diagram of a device that is suitable for implementing some example embodiments of the present disclosure; and

FIG. 8 illustrates a block diagram of an example of a computer readable medium in accordance with some example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar elements.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (s) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the fourth generation (4G) , 4.5G, the future fifth generation (5G) communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to as a gNB) , a Remote Radio Unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a relay, an Integrated and Access Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , or an Access Terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (for example, remote surgery) , an industrial device and applications (for example, a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “terminal device” , “communication device” , “terminal” may be used interchangeably.

As mentioned above, in SL-U there may be no guarantee that a UE can perform the transmissions of data or a feedback (for example, a HARQ feedback) due to possibility of LBT failure. More specifically, for positive and negative feedback, such as ACK/NACK of HARQ, if the second terminal device intends to provide positive feedback to the first terminal device and the LBT procedure fails, it would not be able to transmit the feedback. This would lead to unnecessary retransmissions from the first terminal device since it will assume that the second terminal device has not received the message. For negative feedback only, if the second terminal device intends to transmit the negative feedback to the first terminal device, and it is prevented due to LBT failure, the first terminal device would not send any needed retransmissions, because the first terminal device would assume that the second terminal device has successfully received and decoded the message. It would be beneficial for the first terminal device to have the flexibility to decide when to enable or request for the feedback. The decision can be made using available information, such as the environment, channel, previous feedback success rate, etc.

In example embodiments of the present disclosure, the application provides a mechanism to solve the above discussed issues. The inventor proposes a new set of methods for assisted feedback configuration decision, to solve the feedback reliable issue. For a sidelink transmission to be transmitted from the first terminal device to a second terminal device, the first terminal device performs a first listen before talk (LBT) procedure based on a first detection threshold. The first terminal device performs a second LBT procedure based on a second detection threshold lower than the first detection threshold, and determines a feedback configuration of the sidelink transmission based on a result of the second LBT procedure. This way, the first terminal device can try to avoid failure in receiving feedback from the second terminal device, and keep reliable and efficient SL transmission.

In example embodiments of the present disclosure, with the feedback configuration, the first terminal device can determine whether to make the second terminal device to transmit the feedback, such as HARQ feedback, or make the SL transmission with link adaptation. Additionally or alternatively, the SL transmission can be made with at least one blind repetition.

FIG. 1A illustrates an example of sidelink resource allocation mode 1 in which some example embodiments of the present disclosure may be implemented. In network environment 100, there are a network device 105, the first terminal device 101, and the second terminal device 103. The first terminal device 101 and the second terminal device 103 may be vehicles, mobile phones, or other terminal devices.

In some example embodiments, SL may be designed to facilitate the first terminal device 101 to communicate with other nearby at least one terminal device via direct/SL communication, such as with the second terminal device 103. Two resource allocation modes can be specified, and the first terminal device is configured with one of them to perform its NR SL transmissions. These modes are denoted as NR SL mode 1 and NR SL mode 2. In mode 1, a sidelink transmission resource is assigned or scheduled by the network device 105 to the second terminal device 103, while the first terminal device 101 in NR SL mode 2 autonomously selects its SL transmission resources.

In mode 1, when the network device 105 is responsible for the SL resource allocation, the configuration and operation is similar to the one over the Uu interface. The first terminal device 101 transmits a SL service request 110 to the network device 105, and receives resource allocation 120 from the network device 105. The first terminal device 101 makes SL transmission 130 to the second terminal device 103, and receives SL feedback 140 from the second terminal device 103.

In mode 2, as in FIG. 1B, the first terminal devices 101 perform autonomously the resource selection with the aid of a sensing procedure in a sensing window. More specifically, the first terminal device 101 in NR SL mode 2 first performs a sensing procedure over at least one configured SL transmission resource pool, in order to obtain the knowledge of at least one reserved resource by other nearby at least one SL TX terminal device. Based on the knowledge obtained from sensing, the first terminal device 101 may select at least one resource from the available SL resources accordingly in a selection window. In order for the first terminal device 101 to perform sensing and obtain the necessary information to receive SL transmission, it needs to decode sidelink control information (SCI) . The SCI associated with a data transmission can include a 1st-stage SCI and 2nd-stage SCI

In some example embodiments, the SCI follows a 2-stage SCI structure, whose main motivation is to support the size difference between the SCIs for various NR-V2X SL service types, such as broadcast, groupcast and unicast. The 1st-stage SCI, or in SCI format 1-A, is carried by PSCCH and contains: information to enable sensing operations, information needed to determine resource allocation of the PSSCH and to decode 2nd-stage SCI. The 2nd-stage SCI, or SCI format 2-A and 2-B, is carried by PSSCH, which is multiplexed with SL-SCH, and contains: source and destination identities, information to identify and decode the associated SL-SCH Transmission Block (TB) , control of HARQ feedback in unicast /groupcast, and trigger for CSI feedback in unicast.

ETSI EN 301 893 V2.1.1 (2017-05) , or RLAN Harmonized Standard covering the essential requirements of article 3.2 of Directive 2014/53/EU is considered as the main reference. In sub-7GHz unlicensed bands, the new radio (NR) coexistence with other systems, such as IEEE 802.11, is ensured via a Listen Before Talking (LBT) channel access mechanism. Where, a terminal device intending to perform a sideline (SL) transmission needs first to successfully complete an LBT check, before being able to initiate transmission.

For a terminal device to pass an LBT check then it must observe the channel as available for a number of consecutive Clear Channel Assessment (CCA) slots. In sub-7GHz the duration of these slots is 9 μs. The UE deems the channel as available in a CCA slot if the measured power, or the collected energy during the CCA slot, is below a regulatory specified threshold, which can depend on the operating band and geographical region.

In some example embodiments, when a first terminal device 101 initiates the sidelink communication, or the first TD 101 takes the role of an initiating device, then the first TD 101 has to acquire the “right” to access the channel for a certain period of time, which is denoted in the regulations as Channel Occupancy Time (COT) , by applying an “extended” LBT procedure where the channel must be deemed as free for the entire duration of a Contention Window (CW) . This “extended” LBT procedure, is named as LBT Type 1. Acquisition of the COT by the first terminal device via LBT Type 1 is illustrated in FIG. 2A.

The duration of both the COT and CW depends on the Channel Access Priority Class (CAPC) associated with the first TD 101’s traffic, as shown in In some example embodiments, the Table 1. Control plane traffic, such as Physical Channel Control Channel (PSCCH) is transmitted with Channel Access Priority Class p=1, while user plane traffic has p>1, as in Table 1.

In some example embodiments, the LBT Type 1 details for the Uu uplink (UL) case depicted in In some example embodiments, the Table 1 can be adopted in SL, but is noted that the downlink (DL) case LBT Type 1 parameters or a different set of channel access parameters could also in principle be adopted in SL.

Table 1 Channel Access Priority Class (CAPC) for UL

In some example embodiments, the Table 1 can be from the 3GPP specification TS 37.213, table 4.2.1-1: Channel Access Priority Class (CAPC) for UL. The contention window length in CCA slots associated with each CAPC has a minimum value CW _min, p and a maximum value CW _max, p. The duration of the COT is given by T _ulm cot, p.

In some example embodiments, for p=3, 4, T _ulm cot, p=10ms if the higher layer parameter absenceOfAnyOtherTechnology-r14 or absenceOfAnyOtherTechnology-r16 is provided, otherwise, T _ulm cot, p=6ms. In some example embodiments, when T _ulm cot, p=6ms it may be increased to 8ms by inserting one or more gaps. The minimum duration of a gap shall be 100us. The maximum duration before including any such gap shall be 6ms.

In some example embodiments, the first terminal device 101 initiating the transmission (the initiating terminal device) upon successfully completing the LBT Type 1 110 and performing a SL transmission to the second terminal device 103, in Physical Sidelink Control Channel (PSCCH) and Physical Sidelink Share Channel (PSSCH) 120, acquires the COT1 with duration associated with the corresponding CAPC. The acquired COT1 is valid even in the case where the first terminal device 101 pauses its transmission, although if the first terminal device 101 wants to perform a new transmission (within the COT) . It is still required to perform a “reduced” LBT procedure. This “reduced” LBT procedure can be named as LBT Type 2, as in 3GPP specification TS 37.213, with the following variants:

Type 2A (25 μs LBT) is for SL transmissions within the initiating terminal device acquired COT, in case the gap between two SL transmissions is ≥ 25 μs, as well for SL transmissions following another SL transmission, as shown in FIG. 2B and FIG. 2C. In FIG. 2B and 2C, the LBT Type 1 and transmission with gray background is taken by the first terminal device 101, and transmission with white background is taken by the second terminal device 103.

Type 2B (16 μs LBT) is for SL transmission within the initiating terminal device acquired COT, which can only be used for SL transmissions following another SL with gap exactly equal to 16 μs, as shown in FIG. 2D and FIG. 2E. In FIG. 2D and 2E, the LBT Type 1 and transmission with gray background is taken by the first terminal device 101, and transmission with white background is taken by the second terminal device 103.

Type 2C (no LBT) can only be used for SL transmission following another SL, with a gap < 16 μs and the allowed duration of the SL transmission of ≤ 584 μs) , as shown in FIG. 2F and FIG. 2G. In FIG. 2F and 2G, the LBT Type 1 and transmission with gray background is taken by the first terminal device 101, and transmission with white background is taken by the second terminal device 103. The ordinary in the skill arts can understand that the gap can also be other value.

FIG. 2H illustrates an example of a COT acquisition by the first terminal device and the second terminal device with some example embodiments of the present disclosure. The first terminal device 101 and the second terminal device 103 in FIG. 2H may be the same with those in FIG. 1A. In some example embodiments, when a first terminal device 101 initiates the sidelink communication, or the first TD 101 takes the role of an initiating device. After LBT Type 1 210, the first TD 101 has to acquire the “right” to access the channel for a certain period of time, which is denoted in the regulations as Channel Occupancy Time1 (COT1) . The first terminal device 101 may take sidelink transmission in PSCCH/PSSCH 220 to the second terminal device 103. The second terminal device 103 can make LBT type 2 230, then send feedback to the first terminal device 101 in Physical Sidelink Feedback Channel (PSFCH) 240.

In some example embodiments, the first terminal device 101 can share its acquired COT1 with the second terminal device 103. For this purpose, the first terminal device 101 may inform the second terminal device 103 about the duration of COT1, such as via control signaling. The second terminal device 103 may use this information to decide which type of LBT it should apply upon performing a transmission for which the second terminal device 103 is the initiating device. In case the second terminal device 103 transmission falls outside the COT1, then the second terminal device 103 will have to acquire a new COT2 using the LBT Type 1 250 with the appropriate CAPC. After that, the second terminal device 103 may take sidelink transmission in PSCCH/PSSCH 260 to the third terminal device 201. After LBT type 2 270, the third terminal device 201 may transmit feedback in PSFCH 280.

In some example embodiments, the configuration of the resources in the sidelink resource pool defines the minimum information required for a RX terminal device to be able to decode a transmission, which includes the number of sub-channels, the number of Physical Resource Block (PRB) sper sub-channels, the number of symbols in the PSCCH, where slots have a PSFCH and other configuration aspects not relevant to this invention.

In some example embodiments, the details of the actual sidelink transmission, or the payload is provided in the PSCCH (1st-stage SCI) for each individual transmission, which includes: the time and frequency resources, the Demodulation Reference Signal (DMRS) configuration of the PSSCH, the MCS, PSFCH, and others. In one example embodiment, a SL slot comprises PSCCH and PSSCH, as in FIG. 2I. In another example embodiment, the SL slot comprises PSCCH, PSSCH and PSFCH, as in FIG. 2J.

In one example embodiment, the configuration of the PSCCH, such as DMRS, MCS, the number of symbols used, is part of the resource pool configuration. Furthermore, the indication of which slots have PSFCH symbols is also part of the resource pool configuration. However, the configuration of the PSSCH, such as the number of symbols being used, the DMRS pattern and the MCS, is provided by the 1st-stage SCI, which is the payload sent within the PSCCH.

The PSFCH was introduced during Rel-16 to enable HARQ feedback over the sidelink from the second terminal device 103 that is the intended recipient of a PSSCH transmission or the second terminal device 103, to the terminal device that performed the transmission, such as the first terminal device 101. Within a PSFCH, a Zadoff-Chu sequence in one PRB is repeated over two OFDM symbols, the first of which can be used for AGC, near the end of the SL resource in a slot. The Zadoff-Chu sequence as base sequence can be pre-configured per sidelink resource pool.

The time resources for PSFCH are pre-configured to occur once every 0, 1, 2, or 4 slots according to 3GPP TS 38.331. The HARQ feedback resource in PSFCH is derived from the resource location of PSCCH/PSSCH. For PSSCH-to-HARQ timing, there is a configuration parameter K with the unit of slot. The time occasion for PSFCH is determined from K. For a PSSCH transmission with its last symbol in slot n, HARQ feedback is in slot n+a where a is the smallest integer larger than or equal to K with the condition that slot n+a contains PSFCH resources. The time gap of at least K slots allows considering the second terminal device 103’s processing delay in decoding the PSCCH and generating the HARQ feedback. K can be equal to 2 or 3, and a single value of K can be pre-configured per resource pool. This allows several RX terminal devices using the same resource pool to utilize the same mapping of PSFCH resource for the HARQ feedback. With the parameter K, the N PSSCH slots associated with a slot with PSFCH can be determined.

FIG. 2K illustrates an example of channel mapping in which some example embodiments of the present disclosure may be implemented. The period of PSFCH resources is configured as N=4, where there are 4 PSSCH slots associated with the PSFCH, and K, or sl-MinTimeGapPSFCH is configured as 2. With L sub-channels in a resource pool and N PSSCH slots associated with a slot containing PSFCH, there are N*L sub-channels associated with a PSFCH symbol. With M PRBs available for PSFCH in a PSFCH symbol, there are M PRBs available for the HARQ feedback of transmissions over N *L sub-channels.

With M configured to be a multiple of N*L, then a distinct set of Mset = M/ (N *L) PRBs can be associated with the HARQ feedback for each sub-channel within a PSFCH period. The first set of Mset PRBs among the M PRBs available for PSFCH are associated with the HARQ feedback of a transmission in the first sub-channel in the first slot. The second set of Mset PRBs are associated with the HARQ feedback of a transmission in the first sub-channel in the second slot and so on.

In some example embodiments, it is illustrated in FIG. 2b with N=4, L=3 and with all PRBs in a PSFCH symbol available for PSFCH. In this example, the HARQ feedback for a transmission at PSSCH x is sent on the set x of Mset PRBs in the corresponding PSFCH symbol, with x=1, …, 12.

In some example embodiments, the set of Mset PRBs associated with a sub-channel can be shared among multiple RX terminal devices in case of ACK/NACK feedback for groupcast communications or in the case of different PSSCH transmissions in the same sub-channel. For each PRB available for PSFCH, there are Q cyclic shift pairs available to support the ACK or NACK feedback of Q RX terminal devices within the PRB. For a resource pool, the number of cyclic shift pairs Q is pre-configured and can be equal to 1, 2, 3 or 6.

In some example embodiments, it can be computed the number F of PSFCH resources available for supporting the HARQ feedback of a given transmission. In 3GPP TS 38.213, F is denoted as

With each PSFCH resource used by one RX terminal device, F available PSFCH resources can be used for the ACK/NACK feedback of up to F RX terminal devices.

In some example embodiments, the F PSFCH resources available for multiplexing the HARQ feedback for the PSSCH can be determined based on two options:

Option 1: F is based on the L PSSCH sub-channels used by a PSSCH, where the F can be computed as: F=L PSSCH*Mset*Q PSFCHs, which is associated with the L PSSCH sub-channels of a PSSCH. There are L PSSCH sub-channels of a PSSCH, Mset PRBs for PSFCH associated with each sub-channel, and Q cyclic shift pairs available in each PRB.

Option 2: F is based only on the starting sub-channel used by a PSSCH, or based only on one sub-channel for the case when L PSSCH>1) . F = Mset *Q PSFCHs, which is associated with the starting sub-channel of a PSSCH. There are Mset PRBs for PSFCH associated with each sub-channel; and Q cyclic shift pairs available in each PRB.

In some example embodiments, the available F PSFCH resources are indexed based on a PRB index in frequency domain, and a cyclic shift pair index in code domain. The mapping of the PSFCH index i (i=1, 2, …, F) to the PRBs and to the Q cyclic shift pairs is such that the PSFCH index i first increases with the PRB index until reaching the number of available PRBs for PSFCH. Then, it increases with the cyclic shift pair index, again with the PRB index and so on.

Among the F PSFCHs available for the HARQ feedback of a given transmission, the RX terminal device selects for its HARQ feedback PSFCH with index i given by:

i= (T _ID+R _ID) mod F,

where T _ID is the Layer 1 identity of the RX terminal device, which is indicated in the 2nd-stage SCI. R _ID=0 for unicast ACK/NACK feedback and groupcast NACK-only feedback. The groupcast NACK-only feedback is groupcast option 1.

For groupcast ACK/NACK feedback, or groupcast option 2, R _ID is equal to the RX terminal device identifier within the group, which is indicated by higher layers. For a number X of RX terminal devices within a group, the RX terminal device identifier is an integer between 0 and X-1. A RX terminal device determines which PRB and cyclic shift pair should be used for sending its HARQ feedback based on the PSFCH index i. The RX terminal device uses the first or second cyclic shift from the cyclic shift pair associated with the selected PSFCH index i in order to send NACK or ACK, respectively.

By RX terminal devices selecting PSFCHs with index i, a TX terminal device can distinguish the HARQ feedback of different RX terminal devices via the RX terminal device identifier, such as for groupcast option 2, and the HARQ feedback intended for the TX terminal device via the Layer 1 ID of the TX terminal device, such as for unicast. As R _ID=0 for groupcast option 1, the RX terminal devices select the same PSFCH index i for their NACK-only feedback based solely on the Layer 1 ID FIRST TERMINAL DEVICE 101 identifier T _ID.

For a PSFCH transmission or reception with HARQ-ACK information, a priority value for the PSFCH is equal to the priority value indicated by an SCI format 1-A associated with the PSFCH. For PSFCH transmission with conflict information, a priority value for the PSFCH is equal to the smallest priority value determined by the corresponding SCI formats 1-A for the conflicting resources. For PSFCH reception with conflict information, a priority value for the PSFCH is equal to the priority value determined by the corresponding SCI format 1-A for the conflicting resource.

In some example embodiments, for HARQ with ACK/NACK feedback, if the second terminal device 103 intends to transmit positive HARQ ACK to the first terminal device 101 and the LBT procedure fails, it would not be able to transmit the feedback in the expected PSFCH symbol. This would lead to unnecessary retransmissions from the first terminal device 101 since it will assume that the second terminal device 103 has not received the message.

In some example embodiments, for HARQ with NACK only feedback, on the other hand, in the cases in which only NACK HARQ feedback is configured, if the intention of the second terminal device 103 to transmit NACK to the first terminal device 101 is prevented due to LBT failure, the first terminal device 101 would not transmit any (needed) retransmissions because it would assume that the second terminal device 103 has successfully received and decoded the message.

In some example embodiments, in SL-U, it would be beneficial for the first terminal device 101 to have the flexibility to decide when to enable or request for HARQ feedback from the second terminal device 103, and to make such decision in the smart possible manner using the information that is already available about the environment, channel, previous feedback success rate, etc.

FIG. 3 illustrates an example of a process flow for LBT procedure with more than one Energy Detection Threshold (EDT) in accordance with some example embodiments of the present disclosure. In the process 300, for a sidelink transmission to be transmitted from the first terminal device 101 to a second terminal device 103, the first terminal device 101 performs (310) a first LBT procedure based on a first detection threshold. In addition, the first terminal device 101 performs (315) a second LBT procedure based on a second detection threshold, the second threshold is lower than the first threshold. Then, the first terminal device 101 determines (320) a feedback configuration of the sidelink transmission based on a result of the second LBT procedure. If the first terminal device 101 determines that the second LBT procedure is successful, the first terminal device 101 determines to enable a feedback from the second terminal device 103 for the sidelink transmission.

Then, the first terminal device 101 transmits (325) the request for feedback 330 to the second terminal device 103. If the first terminal device 101 determines that the second LBT procedure is unsuccessful, first terminal device 101 determines to disable a feedback from the second terminal device 103. This way, the first terminal device 101 can try to avoid failure in receiving feedback from the second terminal device 103, and keep reliable and efficient SL transmission. In some example embodiments, the feedback can be HARQ feedback. The feedback can also be other feedback for the sidelink transmission, such as without error correction channel coding, and with a CRC check alternatively.

In some example embodiments, the first detection threshold can be the first Energy Detection Threshold (EDT1) , and the second detection threshold can be the second Energy Detection Threshold (EDT2) . The first detection threshold and the second detection threshold can be in energy power, voltage or electricity, and so on.

In some example embodiments, the first LBT procedure and the second LBT procedure can be performed simultaneously using the same channel access Type. When applying LBT Type 1, the first terminal device 101 applies both EDT1 and EDT2 when applying LBT in all CCA slots. If the first LBT with EDT1 is successful, then the contention window counter can be decreased until it reaches zero and the first terminal device 101 can attempt channel access.

If during the contention window countdown the amount of CCA slots where the second LBT with EDT2 was unsuccessful, or the received signal power is above the second detection threshold, then this is indication that there are transmissions taking place in the vicinity of the second terminal device 103, and therefore the first terminal device 101 should not transmit HARQ feedback request to the second terminal device 103. Otherwise, the first terminal device 101 can request HARQ feedback. When applying LBT Type 2, the first terminal device 101 applies both EDT1 and EDT2 when applying LBT in CCA slot. In case the first LBT with EDT1 is successful, then the first terminal device 101 can proceed with the sidelink transmission, but it will only request HARQ feedback if the second LBT with EDT2 is also successful. This way, the total LBT procedure time can be reduced.

In some example embodiments, the second LBT with EDT2 may be performed at the end of the first LBT with EDT1, such as in the case of LBT Type 1, using a single energy detection. Alternatively, the second LBT with EDT2 can be performed after the first LBT with EDT1, such as at the time when the second terminal device 103 is expected to perform its own LBT prior to HARQ feedback with PSFCH transmission. This way, more flexibility is introduced to the first LBT with EDT 1 and the second LBT with EDT2.

In some example embodiments, based on determining that the second LBT procedure is unsuccessful, the first terminal device 101 implements link adaption. In link adaption, the first terminal device 101 may reduce the constellation in modulation. Additionally or alternatively, the first terminal device 101 may reduce channel coding rate in the sidelink transmission. Additionally or alternatively, the first terminal device 101 may implement at least one blind repetition. Additionally or alternatively, the first terminal device 101 may increase transmitting power. Additionally or alternatively, the first terminal device 101 may increase transmission diversity, such frequency diversity, time diversity, or special diversity. Additionally or alternatively, the first terminal device 101 may increase beamforming gain. The ordinary in the art can understand that other schemes can be adopted in the link adaption. This way, the first terminal device 101 can transmit the sidelink to the second terminal device 103 more reliable, without the HARQ feedback.

In some example embodiments, the second detection threshold can be determined based on a fraction of the first detection threshold. Additionally or alternatively, the second detection threshold can be determined based on a size of a group of terminal devices to which the sidelink transmission is groupcast, the second terminal device being one in the group of terminal devices. Additionally or alternatively, the second detection threshold can be determined based on a channel busy ratio (CBR) associated with the sidelink transmission. Additionally or alternatively, the second detection threshold can be determined based on a physical sidelink feedback channel (PSFCH) load associated with the sidelink transmission. Additionally or alternatively, the second detection threshold can be determined based on a traffic priority of the sidelink transmission. Additionally or alternatively, the second detection threshold can be determined based on a traffic type of the sidelink transmission. This way, the second detection threshold may be determined more accurately.

In some example embodiments, the first terminal device 101 is can determine the feedback configuration of the sidelink transmission based on the number of terminal devices to which the sidelink transmission is groupcast. Additionally or alternatively, the first terminal device 101 is can determine the feedback configuration of the sidelink transmission based on a PSFCH load associated with the sidelink transmission. Additionally or alternatively, the first terminal device 101 is can determine the feedback configuration of the sidelink transmission based on a determination that the second terminal device has a coverage issue. This way, more factors can be considered in the determination of the feedback configuration of the sidelink transmission, and the determination can be made more accurately.

In some example embodiments, the first terminal device 101 can receive the first detection threshold from the network device 105. Additionally or alternatively, the first terminal device 101 can receive the second detection threshold from the network device 105. The network device 105 can have more information about the network than terminal devices, so can calculate the first detection threshold and the second detection threshold more accurately.

In some example embodiments, the first terminal device 101 can receives (360) an indication for LBT procedure 355. The indication for LBT procedure 355 can be indication that an LBT procedure performed by the second terminal device 103 for transmitting the feedback to the first terminal device 101 is successful. The first terminal device 101 can adjust the second detection threshold based on the indication 355. This way, the feedback transmission from the second terminal device 103 can be more reliable.

In some example embodiments, the first terminal device 101 can determine that the feedback is not received from the second terminal device. In this case, the second terminal device 103 may be far away from the first terminal device 101. The first terminal device may adjust the second detection threshold to a lower value, in order to get feedback from the second terminal device in a longer distance.

In some example embodiments, the first terminal device 101 can determine that the feedback is received from the second terminal device. In this case, the second terminal device 103 may be near from the first terminal device 101. The first terminal device may adjust the second detection threshold to a higher value, in order to avoid interference from other terminal devices.

In some example embodiments, with on the LBT2 successful, the first terminal device 101 can determine that the feedback is not received from the second terminal device 103. Based on the second LBT procedure success, it can be determined by the first terminal device 101 that second terminal device 103 does not receive the sidelink transmission from the first terminal device 101. The first terminal device can know that it is caused by bad channel quality, such as the second terminal device 103 is outside of the range of the first terminal device 101.

In some example embodiments, with on the LBT2 procedure failure, the first terminal device 101 can determine that an LBT failure happens at the second terminal device 103 for transmitting the feedback. This way, the first terminal device 101 can determine the reason of the feedback failure from the second terminal device 103 more accurately.

Continuing with reference to FIG. 3, on the other side, the second terminal device 103 receives (340) the request for feedback from the first terminal device 101. The second terminal device 103 determines (335) whether a request for feedback is received from the first terminal device 101. With determination of reception of the request from the first terminal device 101, the second terminal device 103 may transmit the feedback, such as the HARQ feedback to the first terminal device 101. The second terminal device 103 performs (345) an LBT procedure for transmitting the feedback to the first terminal device. Based on success of the LBT procedure, the second terminal device 103 transmits the feedback to the first terminal device 101. The second terminal device 103 transmits (350) an indication 355 that the LBT procedure is successful to the first terminal device 101. Based on determining that the request for feedback is not received, the second terminal device 103 avoids transmitting the feedback to the first terminal device 101. This way, the feedback, such as the HARQ feedback can be transmitted from the second terminal device 103 to the first terminal device 101 more reliable.

FIG. 4 illustrates an example of an LBT procedure with more than one EDT in accordance with some example embodiments of the present disclosure. In some example embodiments, the first terminal device 101 may perform LBT using two different EDTs where the first EDT, or EDT1 can be given by regulations, and the second EDT or EDT2 is lower than the first EDT and therefore is able to detect transmissions from terminal devices which are located at a further distance.

In some example embodiments, EDT2 can be a general value or given as function of EDT1. Additionally or alternatively, EDT2 can be given as a function of other parameters such as group size, CBR, PSFCH load, traffic priority, or traffic type. If the LBT with EDT1 410 is successful, then the first terminal device 101 can proceed with its transmission. The LBT with EDT2 420 is used to decide if the first terminal device 101 should use blind repetitions or should instead ask for HARQ feedback. If the LBT with EDT2 420 is successful, the first terminal device 101 assumes no interference close to the second terminal device 103, and therefore asks for HARQ feedback, without link adaptation.

If the LBT with EDT2 420 is unsuccessful, the first terminal device 101 assumes there could be problems with interferers close to the second terminal device 103, and this cause the failure of LBT with EDT2 420. Therefore, the first terminal device 101 can determine to take link adaptation or blind repetitions. In link adaption, the first terminal device 101 can reduce the constellation in modulation. Additionally or alternatively, the first terminal device 101 can reduce the channel coding rate. Additionally or alternatively, the first terminal device 101 can use at least one blind repetition. This can be illustrated in Table 3. The second terminal device 103 can also use LBT with ETD2 430 before transmitting HARQ feedback, to avoid interference from other terminal devices.

Table 3. Decision on HARQ feedback based on LBT outcome using two different EDTs.

In some example embodiments, the first terminal device 101 may use the information of the EDT2, to enable the distinction between interference related failure (LBT failure) and channel quality related failure to make adaptively determination on handling of HARQ retransmissions triggered by missing of HARQ feedback as well as SL radio link failure detection.

In some example embodiments, if HARQ with NACK only is configured and feedback is not received, the first terminal device 101 can determine whether the cause may be bad channel quality with LBT success, such as due to the second terminal device 103 being outside of the range of the first terminal device 101. Or the reason may be the second terminal device 103 LBT failure, if the second terminal device 103 LBT with EDT2 is not successful. In case of the former, the first terminal device 101 may not be triggered to make HARQ retransmission. In case of latter and the targeted reliability requirement of SL groupcast is high, First terminal device 101 may be triggered to make HARQ retransmission due to missing of HARQ NACK feedback caused by the second terminal device 103 LBT failure.

In some example embodiments, if HARQ with ACK/NACK is configured for either SL groupcast or SL unicast, the first terminal device 101 can also use the result of LBT with EDT2 to determine whether missing of HARQ ACK/NACK feedback is due to bad channel quality or due to the second terminal device 103 LBT failure. If missing of HARQ ACK/NACK feedback is determined to be caused by the second terminal device 103 LBT failure, the first terminal device 101 may not take the missing of HARQ ACK/NACK into account in SL RLF determination. Additionally or alternatively, the first terminal device 101 may determine whether to make HARQ retransmission or not depending on such as reliability requirement of SL groupcast or unicast transmission, the latest SL Channel State Information (CSI) report from the second terminal device 103, or other information in the following.

In some example embodiments, the LBT procedure with EDT1 and the LBT procedure with EDT2 may be performed simultaneously using the same channel access Type. For example, when applying LBT Type 1, the First terminal device 101 applies both EDT1 and EDT2 when applying LBT in all CCA slots. If the LBT with EDT1 is successful, then the contention window counter can be decreased until it reaches zero and the first terminal device 101 can attempt channel access. If during the contention window countdown the amount of CCA slots where the LBT with EDT2 was unsuccessful, or is above the second detection threshold, then this is indication that there are transmissions taking place in the vicinity of the first terminal device 101 intended receiver, and therefore the first terminal device 101 should not request HARQ feedback. Otherwise, the first terminal device 101 can request HARQ feedback. When applying LBT Type 2, the first terminal device 101 applies both EDT1 and EDT2 when applying LBT in CCA slot. In case the LBT with EDT1 is successful, then the first terminal device 101 can proceed with its transmission, but it will only request HARQ feedback if the LBT with EDT2 is also successful.

In some example embodiments, EDT2 may be performed at the end of EDT1, such as in the case of LBT Type 1, using a single energy detection. Alternatively, LBT procedure with EDT2 is performed after LBT procedure with EDT1, such as at the time when the second terminal device 101 is expected to perform its own LBT prior to PSFCH transmission.

In some example embodiments, the knowledge provided by the LBT with two or more different detection thresholds, such as EDT1 and EDT2, may be combined with other type of information or knowledge to trigger the HARQ feedback request when initiating a transmission. Some examples of other useful information can be given as following.

The useful information can be the number of terminal devices being served. In case of groupcast, if the number of terminal devices is very large, the probability that at least one of the Rx terminal devices is not able to successfully receive and decode the message is higher. This would lead to the Tx terminal device to retransmit the missing data in most cases anyway. Therefore, the Tx terminal device may take a proactive approach and use link adaptation or even blind retransmissions to avoid the overhead and interference caused by a large number of users accessing the channel for providing feedback.

Additionally or alternatively, the useful information can be PSFCH load or number of PSFCH resource blocks being normally used, in combination with the number of terminal devices being served. A high usage of PSFCH resource blocks may lead to PSFCH capacity issues that will prevent some of the Rx terminal devices to provide the HARQ feedback. This is even more relevant in unlicensed spectrum, especially if the resource pool is constrained to 20MHz, and also if interlaced PSFCH is adopted for meeting OCB and PSD requirements.

Additionally or alternatively, the useful information can be existence of coverage issues. If the Tx terminal device knows in advance that the Rx terminal devices are having coverage problems due to being in the edge of the range or due to any other path loss, obstacle or fading, it may operate for applying link adaptation to maximize the success probability for those terminal devices to receive the data. Otherwise, if there are no coverage problems and the expected probability to successfully perform the transmission and reception is high, it may enable HARQ feedback.

In some example embodiments, the second terminal device 103 may provide feedback to the first terminal device 101 which allows the adaptation of the EDT2. LBT success by the second terminal device 103 can make the EDT2 tend towards EDT1 in case that first terminal device 101 was detecting LBT failure with the original EDT2. Alternatively, the absence of PSFCH feedback can be used to make EDT2 stricter.

FIG. 5A illustrates an example of a method 500 implemented at a first terminal device 101 with some example embodiments of the present disclosure. At block 510, the first terminal device performs for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold. At block 520, the first terminal device 101 performs a second LBT procedure based on a second detection threshold lower than the first detection threshold. At block 530, the first terminal device 101 determines a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In some embodiments, in determining the feedback configuration of the sidelink transmission, the first terminal device 101 can determine that the second LBT procedure is successful. Then, based on determining that the second LBT procedure is successful, the first terminal device 101 may determine to enable a feedback from the second terminal device for the sidelink transmission.

In some embodiments, the first terminal device 101 further transmits, to the second terminal device, a request for the feedback. In some embodiments, the first terminal device 101 further receives, from the second terminal device, a feedback for adjusting the second detection threshold, then adjusts the second detection threshold based on the indication. The feedback for for adjusting the second detection threshold comprises: an indication of whether an LBT procedure performed by the second terminal device for transmitting the feedback to the first terminal device is successful or is unsuccessful. Then, the first terminal device 101 adjusts the second detection threshold based on the feedback for adjusting the second detection threshold.

In some embodiments, the first terminal device 101 further determines that the feedback is not received from the second terminal device. Then, based on determining that the feedback is not received, the first terminal device 101 may adjust the second detection threshold to a lower value. In some embodiments, the first terminal device 101 further determines that the feedback is received from the second terminal device. Then, based on determining that the feedback is received, the first terminal device 101 may adjust the second detection threshold to a higher value.

FIG. 5B illustrates another example of a method implemented at a first terminal device with some example embodiments of the present disclosure.

In block 560, the first terminal device 101 determines that the feedback is not received from the second terminal device. In block 570, the first terminal device determines whether the second LBT procedure is successful. Then, based on the second LBT procedure successful, in block 580, the first terminal device 101 determines the second terminal device 102 not receiving the sidelink transmission from the first terminal device. Or based on the second LBT procedure failure, in block 590, the first terminal device 101 determines an LBT failure at the second terminal device for transmitting the feedback.

In some embodiments, in determining the feedback configuration of the sidelink transmission, the first terminal device 101 determines that the second LBT procedure is unsuccessful. Then, based on determining that the second LBT procedure is unsuccessful, the first terminal device 101 determines to disable a feedback from the second terminal device on the sidelink transmission. In some embodiments, the first terminal device 101 further transmits the sidelink transmission to the second terminal device with at least one of a link adaptation or at least one blind repetition. In some embodiments, the first LBT procedure and the second LBT procedure are performed simultaneously, or the second LBT procedure is performed at an end of the first LBT procedure, or the second LBT procedure is performed after the first LBT procedure.

In some embodiments, the second detection threshold is determined based on a fraction of the first detection threshold. Additionally or alternatively, the second detection threshold is determined based on a size of a group of terminal devices to which the sidelink transmission is groupcast, the second terminal device being one in the group of terminal devices. Additionally or alternatively, the second detection threshold is determined based on a channel busy ratio (CBR) associated with the sidelink transmission. Additionally or alternatively, the second detection threshold is determined based on a physical sidelink feedback channel (PSFCH) load associated with the sidelink transmission. Additionally or alternatively, the second detection threshold is determined based on a traffic priority of the sidelink transmission. Additionally or alternatively, the second detection threshold is determined based on a traffic type of the sidelink transmission.

In some embodiments, in determining the feedback configuration of the sidelink transmission, the first terminal device 101 further determines based on at least one of: the number of terminal devices to which the sidelink transmission is groupcast, a PSFCH load associated with the sidelink transmission, or a determination that the second terminal device has a coverage issue. In some embodiments, the first terminal device further receives, from a network device, at least one of the first detection threshold or the second detection threshold. In some embodiments, the first terminal device is configured to determine whether to request a HARQ feedback per transport block (TB) .

FIG. 6 illustrates an example of a method 600 implemented at the second terminal device 103 with some example embodiments of the present disclosure. At block 610, the second terminal device 103 determines whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device. At block 620, based on determining that the request is received, the second terminal device 103 performs an LBT procedure. At block 630, based on success of the LBT procedure, the second terminal device 103 transmit feedback to the first terminal device. Further more, the second terminal device 103 transmits, to the first terminal device, an indication that the LBT procedure is successful. At block 640, based on determining that the request is not received, the second terminal device 103 avoids transmitting the feedback to the first terminal device.

In some embodiments, an apparatus capable of performing the method 500 (for example, the first terminal device 101) may comprise means for performing the respective steps of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus comprises means for performing, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold; means for performing a second LBT procedure based on a second detection threshold lower than the first detection threshold; and means for determining a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.

In some embodiments, the means for determining the feedback configuration of the sidelink transmission comprises: means for determining that the second LBT procedure is successful; and means for based on determining that the second LBT procedure is successful, determining to enable a feedback from the second terminal device for the sidelink transmission. In some embodiments, the apparatus further comprises: means for transmitting, to the second terminal device, a request for the feedback.

In some embodiments, the apparatus further comprises: means for receiving, from the second terminal device, a feedback for adjusting the second detection threshold, the feedback for adjusting the second detection threshold comprises: an indication of whether an LBT procedure performed by the second terminal device for transmitting the feedback to the first terminal device is successful or is unsuccessful; and means for adjusting the second detection threshold based on the feedback for adjusting the second detection threshold. In some embodiments, the apparatus further comprises: means for determining that the feedback is not received from the second terminal device; and means for based on determining that the feedback is not received, adjusting the second detection threshold to a lower value.

In some embodiments, the apparatus further comprises: means for determining that the feedback is received from the second terminal device; and means for based on determining that the feedback is received, adjusting the second detection threshold to a higher value. In some embodiments, the apparatus further comprises: means for determining that the feedback is not received from the second terminal device; and means for determining, based on the second LBT procedure success, the second terminal device not receiving the sidelink transmission from the first terminal device, or means for determining, based on the second LBT procedure failure, an LBT failure at the second terminal device for transmitting the feedback.

In some embodiments, the means for determining the feedback configuration of the sidelink transmission comprises: means for determining that the second LBT procedure is unsuccessful; and means for based on determining that the second LBT procedure is unsuccessful, determining to disable a feedback from the second terminal device on the sidelink transmission. In some embodiments, the apparatus further comprises: means for transmitting the sidelink transmission to the second terminal device with at least one of a link adaptation or at least one blind repetition.

In some embodiments, the first LBT procedure and the second LBT procedure are performed simultaneously, the second LBT procedure is performed at an end of the first LBT procedure, or the second LBT procedure is performed after the first LBT procedure. In some embodiments, the second detection threshold is determined based on at least one of: a fraction of the first detection threshold, a size of a group of terminal devices to which the sidelink transmission is groupcast, the second terminal device being one in the group of terminal devices, a channel busy ratio (CBR) associated with the sidelink transmission, a physical sidelink feedback channel (PSFCH) load associated with the sidelink transmission, a traffic priority of the sidelink transmission, or a traffic type of the sidelink transmission.

In some embodiments, means for determining the feedback configuration of the sidelink transmission is further based on at least one of: the number of terminal devices to which the sidelink transmission is groupcast, a PSFCH load associated with the sidelink transmission, or a determination that the second terminal device has a coverage issue. In some embodiments, the apparatus further comprises: means for receiving, from a network device, at least one of the first detection threshold or the second detection threshold.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 500. In some embodiments, the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some embodiments, an apparatus capable of performing the method 600 (for example, the second terminal device 103) may comprise means for performing the respective steps of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some embodiments, the apparatus comprises means for determining, at a second terminal device, whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device; means for based on determining that the request is received, performing an LBT procedure; means for based on success of the LBT procedure, transmitting the feedback to the first terminal device, and means for based on determining that the request is not received, avoid transmitting the feedback to the first terminal device. In some embodiments, the apparatus further comprises means for transmitting to the first terminal device, a feedback for adjusting a threshold in LBT procedure in the first terminal device, the feedback for adjusting the threshold in LBT procedure in the first terminal device comprises: an indication of the LBT procedure successful in the second terminal device.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 600. In some embodiments, the means comprises at least one processor; and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

FIG. 7 illustrates a simplified block diagram of a device 700 that is suitable for implementing some example embodiments of the present disclosure. The device 700 may be provided to implement a communication device, for example, the first terminal device 101, the second terminal device 103, or the network device 105 as shown in FIG. 1 or FIG. 2. As shown, the device 700 includes one or more processors 710, one or more memories 720 coupled to the processor 710, and one or more communication modules 740 coupled to the processor 710.

The communication module 740 is for bidirectional communications. The communication module 740 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 710 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 720 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 724, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 722 and other volatile memories that will not last in the power-down duration.

A computer program 830 includes computer executable instructions that are executed by the associated processor 710. The program 830 may be stored in the ROM 724. The processor 710 may perform any suitable actions and processing by loading the program 730 into the RAM 722.

The embodiments of the present disclosure may be implemented by means of the program 730 so that the device 700 may perform any process of the disclosure as discussed with reference to FIGS. 1 to 6. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the program 730 may be tangibly contained in a computer readable medium which may be included in the device 700 (such as in the memory 720) or other storage devices that are accessible by the device 700. The device 700 may load the program 730 from the computer readable medium to the RAM 722 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

FIG. 8 illustrates a block diagram of an example of a computer readable medium 800 in accordance with some example embodiments of the present disclosure. The computer readable medium 800 has the program 730 stored thereon. It is noted that although the computer readable medium 800 is depicted in form of CD or DVD in FIG. 8, the computer readable medium 800 may be in any other form suitable for carry or hold the program 730.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the

method

500, or 600 as described above with reference to FIG. 5 or 6. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A first terminal device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the first terminal device at least to:

perform, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold;

perform a second LBT procedure based on a second detection threshold lower than the first detection threshold; and

determine a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.
The first terminal device of claim 1, wherein the first terminal device is caused to determine the feedback configuration of the sidelink transmission by:

determining that the second LBT procedure is successful; and

based on determining that the second LBT procedure is successful, determining to enable a feedback from the second terminal device for the sidelink transmission.
The first terminal device of claim 2, wherein the first terminal device is further caused to:

transmit, to the second terminal device, a request for the feedback.
The first terminal device of claim 3, wherein the first terminal device is further caused to:

receive, from the second terminal device, information for adjusting the second detection threshold,

adjust the second detection threshold based on the information for adjusting the second detection threshold,

the information for adjusting the second detection threshold comprises: an indication of whether an LBT procedure performed by the second terminal device for transmitting the feedback to the first terminal device is successful or is unsuccessful.
The first terminal device of any of claims 3-4, wherein the first terminal device is further caused to:

determine that the feedback is not received from the second terminal device; and

based on determining that the feedback is not received, adjust the second detection threshold to a lower value.
The first terminal device of any of claims 3-5, wherein the first terminal device is further caused to:

determine that the feedback is received from the second terminal device; and

based on determining that the feedback is received, adjust the second detection threshold to a higher value.
The first terminal device of any of claims 1-6, wherein the first terminal device is further caused to:

determine that the feedback is not received from the second terminal device; and

determine, based on the second LBT procedure success, the second terminal device not receiving the sidelink transmission from the first terminal device, or

determine, based on the second LBT procedure failure, an LBT failure at the second terminal device for transmitting the feedback.
The first terminal device of claim 1, wherein the first terminal device is caused to determine the feedback configuration of the sidelink transmission by:

determining that the second LBT procedure is unsuccessful; and

based on determining that the second LBT procedure is unsuccessful, determining to disable a feedback from the second terminal device on the sidelink transmission.
The first terminal device of claim 8, wherein the first terminal device is further caused to:

transmit the sidelink transmission to the second terminal device with at least one of a link adaptation or at least one blind repetition.
The first terminal device of any of claims 1-9, wherein:

the first LBT procedure and the second LBT procedure are performed simultaneously,

the second LBT procedure is performed at an end of the first LBT procedure, or

the second LBT procedure is performed after the first LBT procedure, when the second terminal device is supposed to perform its own LBT procedure.
The first terminal device of any of claims 1-10, wherein the second detection threshold is determined based on at least one of:

a fraction of the first detection threshold,

a size of a group of terminal devices to which the sidelink transmission is groupcast, the second terminal device being one in the group of terminal devices,

a channel busy ratio (CBR) associated with the sidelink transmission,

a physical sidelink feedback channel (PSFCH) load associated with the sidelink transmission,

a traffic priority of the sidelink transmission, or

a traffic type of the sidelink transmission.
The first terminal device of any of claims 1-11, wherein the first terminal device is caused to determine the feedback configuration of the sidelink transmission further based on at least one of:

the number of terminal devices to which the sidelink transmission is groupcast,

a PSFCH load associated with the sidelink transmission, or

a determination that the second terminal device has a coverage issue.
The first terminal device of any of claims 1-12, wherein the first terminal device is further caused to:

receive, from a network device, at least one of the first detection threshold or the second detection threshold.
The first terminal device of any of claims 1-13, wherein the first terminal device is configured to determine whether to request a HARQ feedback per transport block (TB) .
A second terminal device comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the second terminal device at least to:

determine whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device;

based on determining that the request is received, performing an LBT procedure;

based on success of the LBT procedure, transmitting feedback to the first terminal device;

and

based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.
The second terminal device of claim 15, wherein the second terminal device is further caused to:

transmitting to the first terminal device, information for adjusting a threshold in LBT procedure in the first terminal device,

the information for adjusting the threshold in LBT procedure in the first terminal device comprises: an indication of the LBT procedure successful in the second terminal device.
A method comprising:

performing, at a first terminal device, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold;

performing a second LBT procedure based on a second detection threshold lower than the first detection threshold; and

determining a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.
A method comprising:

determining, at a second terminal device, whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device;

based on determining that the request is received, performing an LBT procedure;

based on success of the LBT procedure, transmitting feedback to the first terminal device; and

based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.
An apparatus comprising:

means for performing, at a first terminal device, for a sidelink transmission to be transmitted from the first terminal device to a second terminal device, a first listen before talk (LBT) procedure based on a first detection threshold;

means for performing a second LBT procedure based on a second detection threshold lower than the first detection threshold; and

means for determining a feedback configuration of the sidelink transmission based on a result of the second LBT procedure.
An apparatus comprising:

means for determining, at a second terminal device, whether a request is received from a first terminal device, the request being for a feedback on a sidelink transmission from the first terminal device to the second terminal device;

means for based on determining that the request is received, performing an LBT procedure;

based on success of the LBT procedure, transmitting feedback to the first terminal device; and

means for based on determining that the request is not received, avoid transmitting the feedback to the first terminal device.
A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the method of claim 17 or 18.